Patrick Loughran - Failed Stone-Birkhäuser Architecture (2002) - Inglês (2024)

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Oscar Eustachio 11/10/2024

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<p>Failed Stone</p><p>p_001_005_bp 17.10.2006 18:08 Uhr Seite 1</p><p>To my children: Galvin, Carly and Liam</p><p>May the buildings that house you in</p><p>the future benefit from the experience</p><p>gained from buildings in the past.</p><p>p_001_005_bp 17.10.2006 18:08 Uhr Seite 2</p><p>Failed Stone</p><p>Problems and Solutions with Concrete and Masonry</p><p>Birkhäuser – Publishers for Architecture</p><p>Basel · Berlin · Boston</p><p>Patrick Loughran</p><p>p_001_005_bp 17.10.2006 18:08 Uhr Seite 3</p><p>We would like to thank the Graham Foundation for</p><p>Advanced Studies in the Fine Arts for their generous</p><p>support of this publication.</p><p>“When I was a little boy…..</p><p>I used to walk by the beach and move stones</p><p>Just so there would be some residue of my existence,</p><p>Some change in the world</p><p>that resulted from my having been there.”</p><p>Richard Solomon, 2002 speech</p><p>Director of the Graham Foundation from 1993–2005</p><p>p_001_005_bp 17.10.2006 18:08 Uhr Seite 4</p><p>Table of Contents</p><p>Preface</p><p>Thermal Hysteresis</p><p>Impact</p><p>Efflorescence</p><p>Surface Defects</p><p>Discoloration</p><p>Corrosion</p><p>Structure</p><p>Leakage</p><p>Acknowledgments</p><p>About the Author</p><p>Selected Bibliography</p><p>Index</p><p>Illustration Credits</p><p>6</p><p>10</p><p>22</p><p>34</p><p>48</p><p>70</p><p>92</p><p>108</p><p>130</p><p>152</p><p>153</p><p>154</p><p>156</p><p>159</p><p>p_001_005_bp 17.10.2006 18:08 Uhr Seite 5</p><p>In the spring of 2002, I wrote a book entitled</p><p>Falling Glass: Problems and Solutions in</p><p>Contemporary Architecture. The research for</p><p>Falling Glass helped me understand how</p><p>glass failures could be avoided and enlight-</p><p>ened me as to which innovations were being</p><p>explored within the glass industry. Originally,</p><p>the book was to include the investigation of</p><p>a variety of building materials. Ria Stein, the</p><p>book’s editor, encouraged me to concentrate</p><p>on glass with an offer to investigate other</p><p>materials in future publications. Failed Stone</p><p>represents a continuation of my research</p><p>on building materials, specifically concrete,</p><p>masonry, and stone.</p><p>To the untrained eye, the cover photo of this</p><p>book appears to be a wonderfully textured</p><p>material creating a basket weave appearance.</p><p>To people familiar with façade design, the</p><p>image shows the stone cladding of a world-</p><p>renowned project, Finlandia Hall in Helsinki,</p><p>designed by architect Alvar Aalto. The bowed</p><p>panels were not part of the original design,</p><p>but the effect of thermal hysteresis on flat</p><p>white marble from Carrara, Italy. The panels</p><p>deformed to an un-repairable state just</p><p>10 years after completion of the project,</p><p>requiring the complete re-cladding of the</p><p>entire building at a cost of more than 3 million</p><p>euros. As I initially researched this project,</p><p>I had an understanding that the façade prob-</p><p>lem had been repaired in a similar fashion</p><p>to many other buildings throughout the world.</p><p>White marble buildings had become notorious</p><p>failures that were being re-clad with metal</p><p>and granite façades. I was shocked to find</p><p>out that Finlandia Hall was re-clad with the</p><p>same material that originally failed: thin white</p><p>marble panels from Carrara. Incredibly, the</p><p>photo on the cover is not of the original build-</p><p>ing, but of the replacement panels just a few</p><p>years after installation. This architectural</p><p>tragedy reminds me of a quote from George</p><p>Santayana, an American philosopher and</p><p>poet, “Those who cannot learn from history</p><p>are doomed to repeat it.”</p><p>The mission of Failed Stone is to present</p><p>knowledge from past projects in an effort to</p><p>prevent the occurrence of future problems.</p><p>As Falling Glass described the limitations of</p><p>glass in façade design, Failed Stone provides</p><p>a guide to better understanding concrete,</p><p>masonry, and stone. By sharing the lessons</p><p>learned from great works like Finlandia Hall,</p><p>my hope is to enhance the art of building.</p><p>I am fortunate to practice architecture in</p><p>Chicago, a city rich in architectural history.</p><p>Chicago’s great architectural past can come</p><p>at a price. Turn-of-the-century buildings con-</p><p>structed with corroding carbon steel connec-</p><p>tions represent a hazard to pedestrians at the</p><p>street level. Loose terra-cotta fragments have</p><p>fallen to the street requiring many of our walk-</p><p>ways to be sheltered with protective scaffold-</p><p>ing. These older terra-cotta buildings are not</p><p>the only masonry element with problems.</p><p>More recent developments in masonry, such</p><p>as the mortar additive “Sarabond”, have</p><p>brought about catastrophic building corrosion</p><p>failures throughout the world. What at the</p><p>time seemed like an innovative new product</p><p>turned out to be an admixture which has been</p><p>blamed for brick walls falling off of the face</p><p>of new buildings. Although I believe there are</p><p>lessons to be learned regarding the use of new</p><p>products on large-scale projects, my intention</p><p>is not to discourage the pursuit of innovation.</p><p>On the contrary, I hope to encourage it through</p><p>shared information.</p><p>As the subtitle suggests, this book is not all</p><p>about the problems, but also the solutions.</p><p>The architectural community is on the cusp of</p><p>breaking tradition with materials that have</p><p>Preface</p><p>6 7</p><p>Terra-cotta blocks netted</p><p>over to prevent from falling to</p><p>the streets, Mather Tower,</p><p>Chicago, 1928.</p><p>page 7 Concrete structure</p><p>of Rhône-Alpes TGV Station</p><p>at the Lyon Airport, 1994.</p><p>p_006_009_preface_bp 17.10.2006 18:07 Uhr Seite 6</p><p>p_006_009_preface_bp 26.10.2006 18:31 Uhr Seite 7</p><p>been used for centuries: concrete, stone, and</p><p>masonry. Innovations with concrete in particu-</p><p>lar have pushed it to the forefront of architec-</p><p>tural design solutions. Today architects are</p><p>using concrete in revolutionary new ways.</p><p>Superplasticizers are added to mixtures to</p><p>keep concrete fluid during pours. Fiber rein-</p><p>forcement technology has abandoned the</p><p>limitations of steel rebar structures. The possi-</p><p>bilities of concrete seem endless. We photo-</p><p>engrave our concrete to bring it to life. We add</p><p>copper aggregate to give it a natural green</p><p>patina that changes with time. The industry</p><p>has even developed a concrete mix that is</p><p>translucent to allow light into concrete spaces.</p><p>The use of modern concrete has allowed for</p><p>the creation of amazing structures like the</p><p>Rhône-Alpes TGV station at the Lyon Airport;</p><p>however, the collapsed precast panels at</p><p>the Terminal 2E at the Charles de Gaulle Inter-</p><p>national Airport in Paris are a sober reminder</p><p>that concrete has limitations.</p><p>Stone has traditionally been used in massive</p><p>sections to enclose our churches allowing</p><p>stain glass to bring light inside. Today modern</p><p>cathedrals such as Our Lady of the Angels</p><p>in Los Angeles use exposed colored concrete</p><p>to form its thick walls and 1 1/2 cm (5/8 inch)</p><p>thick alabaster stone to bring light into the</p><p>church. Ironically, these stone panels are</p><p>protected on the outside by glass, reminding</p><p>designers that as stone becomes thin, it</p><p>also becomes weak. The E.N.S.A.D. – Ecole</p><p>Nationale Supérieure des Arts Décoratifs</p><p>façade shows the limitations of thin stone.</p><p>The Paris school is composed of a translucent</p><p>marble curtain wall. A fine layer of marble is</p><p>laminated to the glass of a traditional curtain</p><p>wall system. The fabrication of these glass</p><p>and stone units requires the exterior stone</p><p>surface to be polished down to a very thin</p><p>layer in order to improve light transmittance.</p><p>The building’s stone appearance has been</p><p>challenged by people throwing rocks from</p><p>the street which penetrated the stone façade.</p><p>Other stone façades have followed the</p><p>E.N.S.A.D. project with the hope of resisting</p><p>much more severe attacks. The Israeli Foreign</p><p>Ministry Building provides a beautiful stone</p><p>façade designed to resist bombs. The façade</p><p>8 9</p><p>above The translucent</p><p>marble façade is prone to</p><p>vandalism and breakage.</p><p>E.N.S.A.D. – Ecole Nationale</p><p>Supérieure des Arts Décora-</p><p>tifs, Paris.</p><p>right Translucent stone</p><p>façade allows light into the</p><p>building. E.N.S.A.D., Paris,</p><p>1997</p><p>right Alabaster window.</p><p>Cathedral of Our Lady of the</p><p>Angels, Los Angeles.</p><p>p_006_009_preface_bp 26.10.2006 18:31 Uhr Seite 8</p><p>of the reception hall includes panels so thin</p><p>that the wall lights up like a lantern</p><p>the enclosure. From base-</p><p>balls to bombs, concrete, stone and masonry</p><p>enclosures can resist the forces thrown at</p><p>them when designed for impact.</p><p>1</p><p>The Oklahoma City bombing proved to be a</p><p>painful example of the importance for building</p><p>structures to sustain significant local damage</p><p>and remain standing.</p><p>2</p><p>Two major considerations in blast-resistant</p><p>design: the loss of structural load-carrying</p><p>capacity/stability and the fragmentation and</p><p>propulsion of architectural and other building</p><p>components, which become projectile threats</p><p>to life safety.</p><p>3</p><p>The strength of an enclosure system ist not</p><p>the only property to consider when designing</p><p>to resist an explosion. Ductility of a wall sys-</p><p>tem is critical to absorbing extreme forces.</p><p>4</p><p>Stone is a brittle material that has strength</p><p>limitations when reduced in thickness. The</p><p>finish applied to a material can alter its</p><p>strength. A sandblast or bush-hammered fin-</p><p>ish to stone will reduce the flexural strength of</p><p>the material. This can be critical when design-</p><p>ing for localized loading from impact on thin</p><p>stone material.</p><p>5</p><p>Successful plaza design must anticipate the</p><p>misuse by skateboarders. A variety of tech-</p><p>niques can be used in the design of benches</p><p>and curbs to make them unappealing to this</p><p>group.</p><p>Lessons Learned</p><p>The Lincoln Park Zoo, Regen-</p><p>stein Center for African Apes,</p><p>designed by Goettsch Partners,</p><p>has a sharp corner to the exte-</p><p>rior gorilla habitat.</p><p>Because the corner is exposed</p><p>to the gorillas and keepers at</p><p>grade level, the durable corner</p><p>was fabricated as a solid unit</p><p>and beveled to resist chipping.</p><p>Regenstein Center for African</p><p>Apes, 2004, Chicago.</p><p>How Can Buildings Be Protected</p><p>from Impact?</p><p>p_022_033_chapt_2_bp 17.10.2006 18:05 Uhr Seite 33</p><p>Architects have used masonry materials since</p><p>the beginning of time. The Egyptians built</p><p>monuments to their kings, the Greeks built</p><p>temples for their gods, and the Romans con-</p><p>structed arenas for assembling large groups.</p><p>Today, masonry remains a staple for buildings</p><p>that are intended to last. Although construc-</p><p>tion techniques have evolved, common prob-</p><p>lems in masonry still exist. One problem that</p><p>brick, concrete and stone have in common is</p><p>efflorescence. Efflorescence can be defined</p><p>as the deposit of soluble compounds carried</p><p>by water onto the surface of a building. Some-</p><p>times described as “new building bloom”,</p><p>the chalky powder is a common nuisance for</p><p>many architects, buildings and building own-</p><p>ers. The sporadic blemishes can tarnish the</p><p>rich texture of façades in new construction.</p><p>Efflorescence can disappear after a short</p><p>period of time, as the new building dries out</p><p>and rainwater rinses the façade clean of the</p><p>salt deposits. However, if the source of the</p><p>problem is not stopped, efflorescence can</p><p>riddle a building for years. If left untreated,</p><p>the consolidation of powdery salts can crystal-</p><p>lize and become a serious detriment to a</p><p>building envelope. If trapped behind the</p><p>surface of a wall, the expansive properties of</p><p>efflorescence can cause cracking, spalling,</p><p>and lead to structural problems.</p><p>The causes of efflorescence can vary; howev-</p><p>er, the following factors must be present for</p><p>it to surface on a building. First, there must be</p><p>water movement through the wall to dissolve</p><p>the salt compounds. This is a critical factor,</p><p>and efflorescence can commonly be traced</p><p>to water infiltration in buildings. Leaking walls</p><p>or ineffective roof flashing transitions are a</p><p>precursor to the marks of efflorescence. The</p><p>34 35</p><p>Efflorescence</p><p>above New building bloom.</p><p>right The use of Portland</p><p>cement to replace lime in</p><p>mortar has been found to</p><p>increase the amount of the</p><p>efflorescence on our buildings.</p><p>page 35 Efflorescence can</p><p>be a problem with modern</p><p>buildings with brick façades.</p><p>Auditorium Parco della</p><p>Musica, Rome, 2002.</p><p>p_034_047_chapt_3_bp 17.10.2006 18:28 Uhr Seite 34</p><p>p_034_047_chapt_3_bp 17.10.2006 18:28 Uhr Seite 35</p><p>second factor is that water soluble compo-</p><p>nents must be in or adjacent to the wall sys-</p><p>tem. The source of water soluble compounds</p><p>can be the brick façade of a building, the con-</p><p>crete back-up system of a structure, the mor-</p><p>tar used in a stone façade, or even the ground</p><p>material at the base of an exterior wall. The</p><p>final factor to the problem is that the water</p><p>moving through the system must be able to</p><p>reach an exterior surface of the wall. A new</p><p>richly textured exterior wall can be riddled</p><p>with white blotches that appear like pimples</p><p>on a teenager’s face. When the powdery mate-</p><p>rial reaches the surfaces of a building to the</p><p>dismay of the building owner, everyone scram-</p><p>bles for a solution to this age-old problem.</p><p>Efflorescence can be found in concrete and</p><p>stone enclosures; however, it is most common</p><p>in brick façades. Efflorescence is for the most</p><p>part a visual defect and it rarely causes struc-</p><p>tural problems. There are many products</p><p>available to treat the issue. Many believe efflo-</p><p>rescence is to be expected to a small degree</p><p>for brick buildings and suggest it will eventual-</p><p>ly go away once the salt deposits are depleted.</p><p>What is critical to understand is that if the</p><p>source of water movement is not stopped and</p><p>soluble materials are still present, efflores-</p><p>cence will frustrate building owners for years.</p><p>Most efflorescence is noticed on the exterior</p><p>of a masonry wall, but more damaging efflo-</p><p>rescence can occur below the wall surface.</p><p>It is amazing that a construction defect that</p><p>dates back to Roman times still riddles con-</p><p>temporary architecture today.</p><p>The Auditorium Parco della Musica in Rome</p><p>was designed to serve as a multifunction</p><p>complex dedicated to music. Constructed</p><p>over the remains of a Roman villa dating</p><p>to the 4th century, the site consists of three</p><p>concert halls and one large amphitheater. The</p><p>scale of these “music box” structures is enor-</p><p>mous. Each of the building elements resem-</p><p>bles a large beetle resting on a masonry plinth</p><p>surrounded by luxurious vegetation. The</p><p>goal of these brick and metal enclosures was</p><p>to acoustically separate each of the concert</p><p>halls. All three of the buildings share similar</p><p>details. The roofs are composed of metal-</p><p>standing seam roofing, covering a wood struc-</p><p>ture, with a concrete foundation surrounded</p><p>36 37</p><p>above Common factors of</p><p>efflorescence</p><p>1 Water source</p><p>2 Water soluble components</p><p>in wall</p><p>3 Evaporating water must</p><p>reach the surface leaving salt</p><p>deposits behind.</p><p>right Site plan of theater</p><p>complex.</p><p>Auditorium Parco della</p><p>Musica.</p><p>right Large amounts of</p><p>efflorescence appear on the</p><p>unprotected exterior walls.</p><p>Covered walls show no sign</p><p>of efflorescence.</p><p>Auditorium Parco della</p><p>Musica.</p><p>below Raked mortar joints</p><p>provide poor weatherability</p><p>as compared to concave or</p><p>flush joints.</p><p>Auditorium Parco della</p><p>Musica.</p><p>p_034_047_chapt_3_bp 17.10.2006 18:28 Uhr Seite 36</p><p>by a base of Roman brick masonry walls. Each</p><p>of the masonry walls is capped with a traver-</p><p>tine stone coping. Although the Auditorium</p><p>Parco della Musica was completed in 2002,</p><p>the effects of efflorescence are still visible on</p><p>many of the building’s exterior masonry walls</p><p>in 2005.</p><p>The origin of the water soluble components</p><p>is most likely in the Roman brick and mortar.</p><p>The source of moving water could be attrib-</p><p>uted to the travertine coping at the top of the</p><p>walls. Unsealed travertine has a high absorp-</p><p>tion rating. This porous horizontal surface at</p><p>the top of a wall can wick water down into</p><p>the cavity below. In addition to the absorptive</p><p>properties of the travertine cap material, the</p><p>stone coping mortar joints on a regular interval</p><p>allow for a second path for water to penetrate</p><p>the top horizontal surface. On the face of the</p><p>wall the masonry joints have been raked back</p><p>for aesthetic reasons. Although this helps</p><p>create a richer wall texture, the raked joints</p><p>provide an easy path for water to infiltrate the</p><p>wall. The ability of water to move through the</p><p>wall</p><p>is facilitated by the lack of flashing below</p><p>the coping and the absence of effective weep</p><p>holes at the base of the wall. Thus penetrating</p><p>water can be trapped in the wall cavity and</p><p>will evaporate through the body of the brick</p><p>and mortar joints to the exterior. This moving</p><p>water carries soluble components and eventu-</p><p>ally evaporates on the face of the building,</p><p>leaving patches of white powder in its wake.</p><p>It should be noted that the masonry exterior</p><p>walls of the building that are protected from</p><p>rainwater by large overhangs do not show</p><p>signs of efflorescence. In order to better</p><p>understand efflorescence and the potentially</p><p>serious nature of the defect, one needs to</p><p>examine the chemical composition of the</p><p>problem.</p><p>above Large wood-framed</p><p>structure wrapped in metal</p><p>rests on masonry walls.</p><p>Auditorium Parco della</p><p>Musica.</p><p>below Building section of</p><p>music hall. Auditorium Parco</p><p>della Musica.</p><p>1 Laminated wood structure</p><p>2 Metal standing seam roof-</p><p>ing</p><p>3 Roman brick base</p><p>p_034_047_chapt_3_bp 17.10.2006 18:28 Uhr Seite 37</p><p>Chemical Composition</p><p>Efflorescence is a calcium or alkaline salt</p><p>which forms as a blotchy, powdery or crys-</p><p>talline deposit on the surface of masonry walls</p><p>and concrete products. There are many kinds</p><p>of salt that can be detected in samples of</p><p>efflorescence. The following are a list of the</p><p>most common:</p><p>Sodium sulfate</p><p>Sodium carbonate</p><p>Sodium bicarbonate</p><p>Sodium silicate</p><p>Potassium sulfate</p><p>Calcium sulfate</p><p>Calcium carbonate</p><p>Magnesium sulfate</p><p>If the efflorescence contains sodium sulfate it</p><p>can lead to a problem called “salt hydration</p><p>distress” (SHD) which means that the sodium</p><p>sulfate combines with water, causing the min-</p><p>eral to expand and take up more space.</p><p>Depending on the temperature and humidity</p><p>at the building location, sodium sulfate can</p><p>change between the anhydrous (without</p><p>water) and hydrous (with water) states. As the</p><p>salt converts back and forth between states,</p><p>the forces created by the volume change can</p><p>spall the adjacent brick, concrete or stucco</p><p>material. SHD is also more prevalent when rel-</p><p>ative humidity fluctuates during the course of</p><p>a day, such as in coastal regions of California</p><p>and Australia.</p><p>The more common examples of efflorescence</p><p>take two basic forms. The first is the powdery</p><p>surface spread uniformly over a wall which</p><p>can give a pigmented concrete block or clay</p><p>brick a faded appearance. This efflorescence</p><p>is easily treated with a light application of</p><p>products designed to remove the salts from</p><p>the surface of the wall. The second form is a</p><p>crystallized material that is more difficult to</p><p>remove.</p><p>Crystallization</p><p>If left untreated the powdery efflorescence</p><p>that can blemish a wall will continue through</p><p>many cycles of depositing salts to the surface,</p><p>re-dissolving when new water occurs, drying</p><p>out afterwards. Finally the deposits can form</p><p>crystals on the wall which become tightly</p><p>bonded to the surface material. Crystallized</p><p>efflorescence is more difficult to remove than</p><p>the powdery type and can lead to serious</p><p>structural damage to brick and mortar cavity</p><p>walls.</p><p>Brick and Mortar Joints</p><p>The occurrence and amount of efflorescence</p><p>often has some relationship to the composi-</p><p>tion of the mortar used in a wall assembly. For</p><p>example, a particular type of brick and a cer-</p><p>tain type of mortar could have no occurrence</p><p>of efflorescence; however, the same brick with</p><p>another mortar may produce a wall that has</p><p>extensive salt deposits. The large quantities of</p><p>sodium and potassium salts (usually sulfates)</p><p>in most efflorescence suggest Portland</p><p>cement as their source. The use of Portland</p><p>cement to replace lime in mortar has been</p><p>found to increase the amount of efflorescence</p><p>on our buildings. Efflorescence can be mini-</p><p>mized by reducing the amount of Portland</p><p>cement, sodium and potassium salts present</p><p>in the mortar batch.</p><p>Although mortar is a governing source of the</p><p>salts found in efflorescence, it is not the only</p><p>source. Bricks may contain appreciable</p><p>amounts of salts which are dissolved by mois-</p><p>ture and brought to the surface through time.</p><p>Bricks can be tested to determine the amount</p><p>of salts present. The test consists of placing</p><p>a brick on end in a pan of distilled water for</p><p>seven days. With time the water is drawn</p><p>upwards through the brick and evaporates</p><p>on the surface of the brick. If soluble salts are</p><p>present in the brick, they will be deposited</p><p>on its surface.</p><p>The absorption rate of a brick also influences</p><p>the amount of efflorescence that will develop</p><p>on the wall. A brick with a high rate of water</p><p>absorption combined with a high cement mor-</p><p>3938</p><p>Crystallized efflorescence in a</p><p>masonry wall.</p><p>Testing of brick for efflores-</p><p>cence.</p><p>p_034_047_chapt_3_bp 17.10.2006 18:28 Uhr Seite 38</p><p>tar will produce large deposits of efflorescence.</p><p>The same mortar used with a brick having a</p><p>moderate rate of absorption will produce only</p><p>small amounts of efflorescence. By using a</p><p>brick with a low rate of absorption with the</p><p>same mortar, the masonry wall can be virtually</p><p>unmarked by efflorescence. In materials that</p><p>allow free movement of water, efflorescence</p><p>can prove to be a problem. By restricting the</p><p>amount of water movement through a wall,</p><p>efflorescence can be minimized.</p><p>Concrete</p><p>Most people think of efflorescence as a prob-</p><p>lem for brick buildings. However, because</p><p>Portland cement is one of the contributing fac-</p><p>tors to the issue, concrete walls can also fall</p><p>prey to the chalky white deposits. A concrete</p><p>mix typically has several ingredients including</p><p>sand, aggregate, and Portland cement.</p><p>Cements are typically the greatest source of</p><p>soluble materials contributing to efflores-</p><p>cence. Concrete walls exposed to wetting are</p><p>susceptible to efflorescence. Because the</p><p>natural color of concrete is very close to the</p><p>white powdery residue of efflorescence, it is</p><p>less noticeable and tolerated more frequently.</p><p>The University of Cincinnati School of Archi-</p><p>tecture and Interior Design expansion con-</p><p>tains exterior concrete walls that are exposed</p><p>to rain on all sides. These walls exhibit a mild</p><p>film of efflorescence on the exterior surface</p><p>noticeable as a white powder substance.</p><p>However, because the concrete substrate</p><p>resembles the color and texture of efflores-</p><p>cence, it is not perceived as a problem.</p><p>Exposed concrete wall shows</p><p>evidence of slight efflores-</p><p>cence. Expansion of University</p><p>of Cincinnati School of Archi-</p><p>tecture and Interior Design.</p><p>right Small whites streaks</p><p>on concrete wall could be</p><p>the result of efflorescence or</p><p>latex additive in the concrete.</p><p>Our Lady of the Angels, Los</p><p>Angeles, 2002.</p><p>p_034_047_chapt_3_bp 17.10.2006 18:28 Uhr Seite 39</p><p>The Metropolitan Correctional Center in</p><p>Chicago was constructed with sleek concrete</p><p>walls and narrow windows to prevent the</p><p>escape of inmates. The building is nested in</p><p>the heart of Chicago’s downtown business</p><p>district. Although the walls may prevent the</p><p>escape of inmates, the passage of water has</p><p>not been stopped in all areas of the exterior</p><p>wall. Spalling concrete can be seen as a side</p><p>effect of moving water and of salt deposits.</p><p>The white efflorescence film shown near an</p><p>exterior window provides the smoking gun</p><p>to a problem of water migration through the</p><p>wall.</p><p>Efflorescence can commonly occur in brick-</p><p>work adjoining concrete material. In this situa-</p><p>tion concrete is frequently wetted from rain</p><p>and snow melting on it. The soluble salts of</p><p>the concrete are dissolved and can be carried</p><p>into the brickwork beneath. Salts which cause</p><p>efflorescence may originate in the concrete</p><p>masonry back-up behind the brick facing of</p><p>a wall. Initially, the outer face of the wall may</p><p>be free of salt deposits. However, with pro-</p><p>longed dampness of the interior wall, salts</p><p>can be carried into the brickwork, leading to</p><p>efflorescence on the surface. For this reason,</p><p>masonry walls near defective drains or roof</p><p>flashings are often marked by efflorescence,</p><p>while other</p><p>parts of the building appear to</p><p>be unaffected by the problem. Similarly, walls</p><p>that are splashed by water from sprinklers,</p><p>mechanical equipment, or fountains can be</p><p>prone to marks of efflorescence.</p><p>Acrylic and latex additives are sometimes</p><p>used as admixtures to concrete masonry and</p><p>mortar. These white products will sometimes</p><p>leach out to the surface and appear like efflo-</p><p>rescence. Although similar in appearance,</p><p>the removal process is different. Efflorescence</p><p>is not limited to brick and concrete façades.</p><p>Because efflorescence is related to mortar,</p><p>it can be a problem with stone façades, where</p><p>walls are tied together with mortar joints.</p><p>40 41</p><p>right Small windows prevent</p><p>inmates from escaping.</p><p>Metropolitan Correctional</p><p>Center, Chicago, 1975.</p><p>below Dripping water from an</p><p>air-conditioning unit is the</p><p>cause of efflorescence on this</p><p>masonry wall.</p><p>right Spalled concrete at</p><p>window detail.</p><p>Metropolitan Correctional</p><p>Center.</p><p>page 41 Exterior cast in place</p><p>concrete walls.</p><p>Metropolitan Correctional</p><p>Center.</p><p>p_034_047_chapt_3_korr_bp 27.10.2006 13:37 Uhr Seite 40</p><p>p_034_047_chapt_3_bp 23.10.2006 13:44 Uhr Seite 41</p><p>p_034_047_chapt_3_bp 17.10.2006 18:29 Uhr Seite 42</p><p>Stone</p><p>Located in front of the United States Capitol,</p><p>the National Museum of the American Indian</p><p>was added to the National Mall in 2004. It was</p><p>the last available site on the Mall, just south of</p><p>the East Building of the National Gallery of Art.</p><p>In strong contrast to its classic Greek and</p><p>Roman architectural neighbors, the museum</p><p>resembles a rock formation carved out of a</p><p>sandstone canyon by wind and water. The</p><p>building is clad in more than 2,400 tons of</p><p>Kasota dolomitic limestone and required</p><p>approximately 50,000 pieces of cut stone of</p><p>varying sizes. The five-story-tall museum has a</p><p>cantilevered overhang at the main east</p><p>entrance, sheltering visitors from the sun and</p><p>rain. The base of the building, surrounded by</p><p>pools and fountains, has a band of American-</p><p>mist granite. It is at this location that traces of</p><p>efflorescence can be seen in the limestone</p><p>wall where a fountain splashes water onto the</p><p>base of the building. Splashing water from the</p><p>fountain penetrates the porous limestone wall</p><p>at these locations. As the water evaporates</p><p>from the cool north face of the building, salt</p><p>deposits are left on the surface of the stone.</p><p>The undulating walls of the Museum required</p><p>extensive flashing details and transitions. It is</p><p>at these locations where water has the poten-</p><p>tial to infiltrate the wall. Marks of efflorescence</p><p>can be seen below a northern roof transition.</p><p>It should be noted that all of the efflorescence</p><p>markings visible on the wall were on the north</p><p>side of the building. Because of the newness</p><p>of the building, some of these marks could be</p><p>attributed to “new building bloom.”</p><p>New Building Bloom</p><p>Efflorescence has often been characterized as</p><p>“new building bloom” because it commonly</p><p>occurs shortly after a new wall is constructed.</p><p>The reason for this is that during the construc-</p><p>tion of an exterior wall the system is often left</p><p>unprotected. During this period, incomplete</p><p>cavity walls and materials may experience</p><p>penetration by a large amount of water behind</p><p>the outer face of the wall from rain. After the</p><p>final coping has been installed at the top of</p><p>the wall, the excess water from the construc-</p><p>tion period will work its way out of the building</p><p>skin toward the exterior. As the excess water</p><p>travels through the wall, it brings the soluble</p><p>construction material with it, leaving the salt</p><p>deposits in its wake. Once this water has left</p><p>the wall, the efflorescence should not reap-</p><p>pear because the source of the water was</p><p>solely due to the construction process. New</p><p>building bloom can be minimized by covering</p><p>the cavity wall during construction in order to</p><p>prevent the penetration of rainwater or snow. If</p><p>efflorescence appears on a wall that has been</p><p>property-protected during the assembly of the</p><p>wall, it can be a signal that wall leaks are the</p><p>problem. If a wall is well protected during con-</p><p>struction, efflorescence need not occur.</p><p>left Efflorescence marks near</p><p>the water feature.</p><p>National Museum of the</p><p>American Indian.</p><p>right Efflorescence marks at</p><p>roof transition.</p><p>National Museum of the</p><p>American Indian.</p><p>page 42 Undulating Kasota</p><p>dolomitic limestone walls</p><p>resemble cliffs carved out by</p><p>nature.</p><p>National Museum of the</p><p>American Indian, Washington,</p><p>D.C., 2004.</p><p>right Large overhang protects</p><p>the front entrance to the</p><p>museum.</p><p>National Museum of the</p><p>American Indian.</p><p>p_034_047_chapt_3_bp 17.10.2006 18:29 Uhr Seite 43</p><p>Coping and Flashing Conditions</p><p>Efflorescence is initiated by the flow of water</p><p>through building materials. If the flow of water</p><p>is excessive and uncontrolled, unsightly</p><p>blotches on building elements can result.</p><p>Effective copings at the top of masonry walls</p><p>and parapets are critical to preventing water</p><p>infiltration problems. The Vontz Center for</p><p>Molecular Studies in Cincinnati, Ohio, has iso-</p><p>lated areas where the white powder of efflores-</p><p>cence suggests the infiltration of water. Sig-</p><p>nage at the entrance to the building depicts</p><p>an example of a coping condition that strug-</p><p>gles to keep water out of the wall system.</p><p>Capped with a Rowlock course of brick, the</p><p>top of the sign wall has unprotected horizontal</p><p>masonry joints at approximately 100mm</p><p>(4 inches) on center. These mortar joints allow</p><p>water into the wall cavity. Infiltrating water</p><p>finds its way back to the surface of the wall,</p><p>carrying salt deposits with it. The deposits are</p><p>left behind as a reminder that masonry joints</p><p>on a horizontal surface should be expected to</p><p>crack and let in water. A possible solution to</p><p>the water problem is to cap the top course of</p><p>the wall with a metal coping. Although slightly</p><p>different in appearance, the coping would</p><p>shed water away from the signage and protect</p><p>the wall from water infiltration. Other areas of</p><p>the building show signs of ineffective flashing</p><p>details that have left streaks of white efflores-</p><p>cence. Penetrating rainwater is the source of</p><p>most of the damage; however, water can also</p><p>come from the surrounding earth if masonry is</p><p>not separated from soil.</p><p>Wicking from Soil</p><p>The movement of water from the base of a</p><p>foundation can lead to efflorescence. Soils</p><p>containing soluble salts can be wicked up</p><p>through a masonry wall leaving powdery white</p><p>deposits on the surface of the building skin. In</p><p>order to prevent this problem from occurring,</p><p>masonry walls should not come in contact</p><p>with soils. Soils can typically contain a fair</p><p>amount of salts and organic materials. During</p><p>the design phase of a building, it is important</p><p>to separate masonry products from the sur-</p><p>rounding soil. Improper storage of material on</p><p>the ground prior to using in construction is</p><p>also a common cause of salt contamination.</p><p>One of the most difficult conditions to rectify</p><p>on a building is water that comes from soils in</p><p>contact with masonry at the base of a build-</p><p>ing. At locations where soils do come in con-</p><p>tact with masonry, waterproofing coatings are</p><p>required to prevent the transfer of water and</p><p>staining salts from contacting porous wall sur-</p><p>faces. At planter locations where water is not</p><p>contained or properly weeped through planter</p><p>drains, staining from organic materials can</p><p>form on the face of a wall. These stains are a</p><p>signal that water is not traveling in the intend-</p><p>ed path and that repair of the waterproofing</p><p>will be required. The Canadian Embassy in</p><p>44 45</p><p>Building sign at Vontz Center</p><p>for Molecular Studies at the</p><p>University of Cincinnati, Ohio,</p><p>1999.</p><p>1 Existing brick coping allows</p><p>water to infiltrate the wall</p><p>2 A solution to the water</p><p>problem would be to install a</p><p>metal coping</p><p>right Ineffective flashings can</p><p>result in efflorescent stains.</p><p>Vontz Center for Molecular</p><p>Studies.</p><p>p_034_047_chapt_3_bp 17.10.2006 18:29 Uhr Seite 44</p><p>Washington, D.C., has a series of balconies at</p><p>the</p><p>interior courtyard which show signs of</p><p>migrating water. The green stains that mark</p><p>the outside face of these walls are a signal that</p><p>moisture from the soil is evaporating through</p><p>the wall. Constant moisture present on build-</p><p>ing materials can provide conditions of grow-</p><p>ing algae and mold.</p><p>A base flashing, installed above grade</p><p>between foundation and masonry wall, will</p><p>prevent upward movement of ground water</p><p>which otherwise might carry salts into the wall.</p><p>If the cause of the efflorescence is due to ris-</p><p>ing water table or ground water, the solution</p><p>does not come easily. It is critical to design</p><p>adjacent horizontal surfaces to drain away</p><p>from masonry walls and to provide damp-</p><p>proof course at the level where the water table</p><p>is anticipated.</p><p>A brick cap above the building</p><p>sign allows water to infiltrate</p><p>the wall.</p><p>Vontz Center for Molecular</p><p>Studies.</p><p>right Masonry building sig-</p><p>nage at the entrance to the</p><p>building.</p><p>Vontz Center for Molecular</p><p>Studies.</p><p>Masonry must be separated</p><p>from soil material.</p><p>1 Limestone in contact with</p><p>soils can lead to efflorescence</p><p>and staining of the wall.</p><p>2 Base flashing under elevat-</p><p>ed limestone material can help</p><p>prevent wicking of water from</p><p>soil.</p><p>3 Where limestone is located</p><p>below grade, dampproofing</p><p>must be installed to protect</p><p>the stone.</p><p>p_034_047_chapt_3_bp 17.10.2006 18:29 Uhr Seite 45</p><p>Cold Weather Friend</p><p>Efflorescence is common in the winter</p><p>months in northern climates because lower</p><p>temperatures slow down the evaporation</p><p>process of water. For this reason, it is more</p><p>prevalent on north-facing walls than south-</p><p>facing walls. As evaporation is slowed down,</p><p>salt deposits do not evaporate with the water</p><p>and are left behind on the surface of the wall.</p><p>In the summer months, the rate of evapora-</p><p>tion of moisture from a masonry wall can be</p><p>very high. This allows for moisture to quickly</p><p>move through the wall to the outer surface,</p><p>allowing for less of the salt deposits to be left</p><p>in its path. In contrast, the winter months</p><p>provide the perfect environment for the slow</p><p>evaporation of water from a wall and thus the</p><p>accumulation of efflorescence. Efflorescence</p><p>can be brought on by climatic and environ-</p><p>mental changes. In late fall, winter, and early</p><p>spring efflorescence can appear after a rainy</p><p>period, when evaporation is much slower and</p><p>temperatures are cooler.</p><p>How Can Efflorescence Be Removed?</p><p>Efflorescence can be removed much more</p><p>easily than other types of stains on a wall.</p><p>Typically, the efflorescence salt deposits are</p><p>water soluble and if present on an exterior</p><p>surface may disappear with normal wetting</p><p>of the surface by rain. Powdery efflorescence</p><p>can be removed with a dry brush or water</p><p>and a stiff brush. Light detergents can be</p><p>used to clean the wall of other stains during</p><p>the process. During the removal process, it</p><p>is important not to saturate the wall as this</p><p>will push the salts into the surface. The objec-</p><p>tive is to remove the salt deposits in order to</p><p>prevent their reoccurrence.</p><p>The exterior of a brick façade is typically</p><p>“washed down” soon after completion. This</p><p>process cleans the wall of excess mortar and</p><p>construction stains. While acids are frequently</p><p>used to remove efflorescence, they can con-</p><p>tain chlorides which contribute to efflores-</p><p>cence. This is one reason why many buildings</p><p>show signs of efflorescence shortly after an</p><p>acid washdown of a masonry wall. Another</p><p>reason is that the water used for rinsing the</p><p>wall has gone into the masonry and brought</p><p>out more of the salts.</p><p>Heavy accumulation of efflorescence, in the</p><p>crystallized form, can usually be removed with</p><p>a solution of muriatic or nitric acid and scrub-</p><p>bing (1 part acid to 12 parts water). Caution</p><p>should be taken with the application of acid</p><p>because of its hazardous nature. The wall</p><p>must be saturated with water both before and</p><p>after scrubbing. In addition to harming the</p><p>applicator, muriatic acid can rust metal sur-</p><p>faces.</p><p>Less common efflorescence salts that change</p><p>their chemical structure during their forma-</p><p>tion will require proprietary compounds to be</p><p>removed. For these severe cases, chemical</p><p>products are available to take care of the</p><p>problem. These products are specially</p><p>designed for efflorescence removal and do</p><p>not contain chlorides that contribute to the</p><p>problem.</p><p>Green stains indicate moisture</p><p>from the planters.</p><p>Canadian Embassy, Washing-</p><p>ton, D.C., 1989.</p><p>Some water repellants can</p><p>cause more harm than good.</p><p>1 Silicone sealers penetrate</p><p>the face of the wall.</p><p>2 Water penetrates wall</p><p>through defects, evaporates</p><p>out as vapor, but leaves salts</p><p>at line of sealer.</p><p>3 Crystallization of salts can</p><p>cause spalling of surface</p><p>material from internal pres-</p><p>sures.</p><p>right Efflorescence can scar</p><p>the face of a building.</p><p>46 47</p><p>p_034_047_chapt_3_bp 17.10.2006 18:29 Uhr Seite 46</p><p>Since so many factors may contribute to the</p><p>development of efflorescence, no one pre-</p><p>cautionary measure can be expected to take</p><p>care of all potential conditions. The goal is to</p><p>reduce all of the contributing factors to a</p><p>minimum. Each condition must be explored</p><p>separately, the first being the materials that</p><p>compose the wall. In order for efflorescence</p><p>to form, soluble salts must be present. Some</p><p>control may therefore be taken by the selec-</p><p>tion of materials which are low in salt content.</p><p>Clay bricks, for example, may be tested to</p><p>determine whether they contain salts which</p><p>will contribute to efflorescence. The use of</p><p>lime and of low-alkali Portland cement and</p><p>low-alkali masonry cement will greatly reduce</p><p>the capacity of mortar to contribute to efflores-</p><p>cence. Hydrated limes are relatively pure and</p><p>can have four to 10 times less efflorescing</p><p>potential than cements. Careful storage of</p><p>the materials on the job site is also necessary</p><p>to avoid contamination from salt-carrying</p><p>ground water.</p><p>Water is the vehicle used for the salt deposits.</p><p>Stopping the path of water will stop efflores-</p><p>cence. Failure to repair cracked or broken</p><p>mortar joints can contribute to the problem.</p><p>When efflorescence is linked to abnormal</p><p>wetting of the wall, as from a roof leak or</p><p>sprinkler head, it is critical to correct these</p><p>problems prior to removing the efflorescence.</p><p>In a similar manner, when the cause of efflo-</p><p>rescence is water penetration of a coping,</p><p>the solution is installing a damp-proof course</p><p>or metal coping to interrupt the movement</p><p>of water into the brickwork.</p><p>Water repellents used to suppress efflores-</p><p>cence are available in the construction mar-</p><p>ket. In order for water repellents to work effec-</p><p>tively, water must be able to evaporate through</p><p>them. However, the salt molecules which are</p><p>larger in size are prevented from escaping by</p><p>the coating. Penetrating sealers are designed</p><p>to create a barrier that stops salt migration,</p><p>yet breathes out water vapor. Silicone water</p><p>repellents may appear to control efflorescence</p><p>by stopping water intrusion; however, they can</p><p>cause greater damage if they prevent the</p><p>escape of crystallized efflorescing salts,</p><p>thus forcing the building material to absorb</p><p>the expansive pressure of internal crystalliza-</p><p>tion.</p><p>It can be hazardous to apply seals to walls</p><p>that contain both moisture and salts. The</p><p>moisture may evaporate through the treated</p><p>surface, but salt deposits can accumulate</p><p>behind the sealer near the surface. Localized</p><p>accumulation of salts and their crystallization</p><p>may cause the surface of the material to spall</p><p>or flake off. The use of a silicone treatment</p><p>to suppress efflorescence may be dangerous</p><p>in cases where excessive water migration</p><p>produces hydrostatic pressure buildup from</p><p>entrapped salts below the surface. This is</p><p>particularly true when there are large amounts</p><p>of salts in the masonry and the units are soft</p><p>and porous.</p><p>1</p><p>Efflorescence will continue to reappear as long</p><p>as there is a source of soluble compounds</p><p>present and water continues to move through</p><p>the wall. Stopping the source of water</p><p>is</p><p>imperative to stopping the reappearance of</p><p>efflorescence.</p><p>2</p><p>The potential for efflorescence can be mini-</p><p>mized by choosing bricks rated non-effloresc-</p><p>ing and by using low-alkali cement. Mortars</p><p>with high lime/cement ratio also help reduce</p><p>the risk of efflorescence.</p><p>3</p><p>Copings and parapets are especially suscepti-</p><p>ble to water infiltration. Stopping water intru-</p><p>sion at these locations will aid in stopping</p><p>efflorescence at the masonry wall below.</p><p>4</p><p>Do not put masonry products in contact with</p><p>soil. If masonry is in contact with soil it can</p><p>wick up salts that can lead to staining and</p><p>efflorescence. Elevated base flashing prevents</p><p>the migration of water up a building wall.</p><p>5</p><p>It is important to cover the masonry wall cavity</p><p>and materials during construction in order to</p><p>minimize the amount of water inside the cav-</p><p>ity. Incidental water inside the wall will eventu-</p><p>ally evaporate out of the wall; unfortunately,</p><p>it may leave salt deposit behind. Reducing</p><p>water movement after the completion of con-</p><p>struction through proper design and detailing</p><p>will minimize the risk of efflorescence.</p><p>6</p><p>Some surfaces are more prone to efflores-</p><p>cence because they are more permeable and</p><p>promote water travel. Many bricks have higher</p><p>soluble salts in some batches. The risk of</p><p>efflorescence can be reduced if these two fac-</p><p>tors are considered when selecting building</p><p>materials; however, because these building</p><p>materials come from the earth, the potential</p><p>for some water soluble salts will always be</p><p>present.</p><p>Lessons Learned How Can Efflorescence Be Avoided?</p><p>p_034_047_chapt_3_bp 17.10.2006 18:29 Uhr Seite 47</p><p>Surface defects can be a glaring distraction</p><p>to the design of a building, just as a chipped</p><p>tooth can distract from an otherwise perfect</p><p>smile. Since the building’s exterior often dis-</p><p>plays an image of the owner to the world,</p><p>the builder should have sufficient knowledge</p><p>of potential surface defects to prevent their</p><p>occurrence.</p><p>Stone is a natural material, having inherent</p><p>flaws and variations. The stone fabricator can</p><p>make repairs to the appearance of a stone</p><p>panel much as a dentist can repair cavities in</p><p>teeth. Filling the fissures and cracks with resin</p><p>material can make the stone look uniform and</p><p>presentable. This type of repair has its own</p><p>limitations and cannot mask all flaws in stone.</p><p>Stone inclusions are embedded foreign mate-</p><p>rial that can break up the uniform color and</p><p>texture of a stone panel. Some stones, like</p><p>marble, have veining and grain that can dis-</p><p>tract from the appearance of a façade if not</p><p>properly matched. A single incorrectly orient-</p><p>ed panel can look seriously out of place on</p><p>a stone façade.</p><p>Man-made materials like concrete are more</p><p>prone to irregularities of finish. Cast-in-place</p><p>concrete has a history of being hidden from</p><p>view. New trends in contemporary design</p><p>have put concrete workmanship back in the</p><p>spotlight. These designs are supported by new</p><p>technologies such as self-compacting and</p><p>ultrahigh strength concrete. However, even</p><p>with these advances, concrete is a very unfor-</p><p>giving material with a long memory. Any mis-</p><p>takes in the pour will be cast in stone for all to</p><p>remember. Heightened quality control meas-</p><p>ures are required when concrete is to be left</p><p>exposed. Special techniques have been devel-</p><p>oped to minimize honeycombing, spalling and</p><p>other surface irregularities. In order to gage</p><p>these improvements, it is helpful to review an</p><p>older architectural icon constructed of cast-in-</p><p>place concrete.</p><p>48 49</p><p>Surface Defects</p><p>above Like a chipped tooth,</p><p>surface defects on a façade</p><p>can distract from an otherwise</p><p>perfect smile.</p><p>right Broken stone panel at</p><p>One South La Salle Street,</p><p>Chicago.</p><p>page 49 The Jay Pritzker</p><p>Pavilion at Millenium Park in</p><p>Chicago, 2004. Cracks in</p><p>concrete are virtually unavoid-</p><p>able. A shrinkage crack has</p><p>tauntingly formed adjacent to</p><p>the control joint designed to</p><p>prevent it.</p><p>p_048_069_chapt_4_bp 17.10.2006 18:22 Uhr Seite 48</p><p>p_048_069_chapt_4_bp 17.10.2006 18:22 Uhr Seite 49</p><p>The Salk Institute for Biological Studies in</p><p>La Jolla, California, designed by architect</p><p>Louis Kahn, was completed in 1965. This</p><p>complex was designed in collaboration with</p><p>the Institute’s founder, Jonas Salk, M.D. Dr.</p><p>Salk was the developer of the polio vaccine,</p><p>and the Institute was designed to provide a</p><p>home for future medical studies. The complex</p><p>consists of two mirror-image structures that</p><p>flank a grand courtyard, opening onto land-</p><p>scape to the east and the Pacific Ocean to the</p><p>west. Each of the six-story buildings houses</p><p>offices and laboratories. The careful selection</p><p>of wood, stone, and concrete material was</p><p>aimed at making a maintenance-free building</p><p>enclosure. The window units are framed in</p><p>teak wood. The plaza provides a durable</p><p>“façade to the sky” using travertine marble.</p><p>The sharp edges of the stone gutters, which</p><p>direct water to the famous axial water trough,</p><p>have kept their crisp-sharp edges through</p><p>the years. The most distinctive material in</p><p>the complex is the concrete.</p><p>The cast-in-place concrete walls at the Salk</p><p>Institute were created with a special mix</p><p>designed to create a pinkish “pozzolanic”</p><p>glow. Formwork boards went from floor to floor</p><p>above left The poured-in-</p><p>place concrete walls at the</p><p>Salk Institute were to show</p><p>how the building was con-</p><p>structed.</p><p>right above Honeycombing</p><p>of concrete corners is not</p><p>uncommon at the Salk Insti-</p><p>tute.</p><p>right below Bugholes are</p><p>abundant on many of the walls</p><p>at the Salk Institute.</p><p>p_048_069_chapt_4_bp 17.10.2006 18:22 Uhr Seite 50</p><p>with projecting joint marks between forms</p><p>and exposed wall ties. Each of these elements</p><p>provides a regular pattern on the walls. In the</p><p>architect’s words, “these joints are the begin-</p><p>ning of ornament.” Louis Kahn wanted to</p><p>show in every way exactly how the concrete</p><p>building was constructed. The goal at the time</p><p>was not to make perfect concrete. The discol-</p><p>oration between pours is visible, wall ties were</p><p>left exposed with chips and irregularities, and</p><p>defects like honeycombing were left</p><p>untouched. Once the concrete was set, there</p><p>was no further processing of the finish, neither</p><p>grinding, filling, nor painting.</p><p>In the 1990s, the Salk Institute was cramped</p><p>for space and embarked on a controversial</p><p>expansion to its campus. Many groups resis-</p><p>ted adding to the site of such an architectural-</p><p>ly significant work; but the east buildings</p><p>completed in 1995 with the understanding</p><p>that the finished details of the new buildings</p><p>would match those of the original. In fact, a</p><p>noticeable improvement in the surface details</p><p>of the new buildings can be seen. The finish</p><p>quality and uniformity of color on the new</p><p>buildings is in strong contrast to the existing</p><p>structure. Wall ties are perfectly executed and</p><p>the form lines are flawless. The surface of the</p><p>new walls is smooth with no large voids or</p><p>irregularities. The outside corners are crisp</p><p>with no spalling, chips or cracks. The new</p><p>and old buildings at the Salk Institute serve as</p><p>an excellent case study of how the concrete</p><p>industry has improved finishing techniques</p><p>over the past 40 years. In order to understand</p><p>these improvements, it is important to analyze</p><p>typical surface defects in concrete.</p><p>Surface Defects in Cast-in-Place Concrete</p><p>Because concrete is made of a variety of</p><p>materials, incorrect mixing or placing can lead</p><p>to visual surface imperfections. These are not</p><p>only unsightly; they can seriously reduce the</p><p>concrete durability with consequential finan-</p><p>cial implications. Surface defects in cast-in-</p><p>place concrete can take many forms. The</p><p>following are the classic flaws that can arise</p><p>with cast-in-place concrete.</p><p>Honeycombing</p><p>Honeycombing is a defect resulting in zones</p><p>of concrete that are devoid of cement mortar.</p><p>While these are generally visible at the sur-</p><p>face, they can extend to some depth within</p><p>the concrete. This flaw comes from a failure of</p><p>the cement</p><p>mortar to effectively fill the spaces</p><p>between coarse aggregate particles. Its cause</p><p>is typically linked to an inappropriate concrete</p><p>composition or to inadequate compaction dur-</p><p>ing a pour. The composition of the mix must</p><p>be well graded and take into account the</p><p>water content of sand and aggregate. The</p><p>steel reinforcement must be detailed so as to</p><p>allow the concrete mix to flow around the rein-</p><p>forcing bars, and between the bars and the</p><p>formwork. Hence, concrete cover influences</p><p>above The travertine paved</p><p>plaza provides a beautiful</p><p>“façade to the sky.”</p><p>right The concrete finish of</p><p>the new buildings at the Salk</p><p>Institute have crisp corners</p><p>and smooth surfaces free of</p><p>any honeycombing or large</p><p>bugholes.</p><p>p_048_069_chapt_4_bp 17.10.2006 18:22 Uhr Seite 51</p><p>the size of aggregate in the concrete; the con-</p><p>crete mix must be able to flow into the rein-</p><p>forcement cover zone. Honeycombing can</p><p>also result from formwork that is too flexible or</p><p>poorly fixed; gaps in the formwork allow the</p><p>cement grout to leak out.</p><p>Form Scabbing</p><p>Form scabs are surface defects caused by</p><p>the movement of forms prior to the concrete</p><p>setting. The most common defect comes from</p><p>concrete sticking to the forms during strip-</p><p>ping. This typically results when the forms</p><p>are stripped too early and results in large</p><p>voids in the finished wall. Another example</p><p>of form scabbing can be seen in leakage of</p><p>mortar onto the surface concrete of a lower lift</p><p>because of movement of the formwork above.</p><p>Bugholes</p><p>Bugholes, also known as blowholes, are the</p><p>result of entrapped air bubbles in the surface</p><p>of hardened concrete. Bugholes often occur</p><p>in vertical cast-in-place concrete surfaces</p><p>and should not be considered a defect unless</p><p>they are unusually large, 19mm (3/4 inch)</p><p>or larger in diameter. Bugholes are principally</p><p>caused by improper, often excessive, vibra-</p><p>tion. This problem can be worsened by the</p><p>use of unsuitable concrete mixes; an overly</p><p>stiff mix can cause increased bughole forma-</p><p>tion. Another cause can be impermeable</p><p>formwork; this can prevent the passage of</p><p>air bubbles across the concrete to formwork</p><p>interface. Some formwork release agents,</p><p>improperly applied, can contribute to this</p><p>problem.</p><p>Aggregate Transparency</p><p>Dark areas reveal the locations of coarse</p><p>aggregate particles near the surface. When</p><p>the aggregate is not uniformly distributed, the</p><p>pattern also will not be uniform. Several caus-</p><p>es have been identified: flexible forms, caus-</p><p>ing a pumping action during compaction,</p><p>incorrect mix design, and excessive vibration</p><p>contribute to aggregate transparency.</p><p>Fins and Offsets</p><p>Cast-in-place concrete forms have size limita-</p><p>tions and therefore require joints between</p><p>units. If these joints are not sealed properly,</p><p>a surface defect can result. Fins are narrow</p><p>linear projections on a formed concrete sur-</p><p>face, resulting from mortar flowing into the</p><p>space between the forms. An offset is a step</p><p>in the concrete surface due to an abrupt</p><p>change in alignment of adjacent forms. It can</p><p>occur either horizontally or vertically. Similar to</p><p>a fin, an offset interrupts the smooth appear-</p><p>ance of a surface. For smooth-formed con-</p><p>crete surfaces the maximum allowable offset</p><p>or fin would be 3mm (1/8 inch).</p><p>5352</p><p>Surface defects in cast-in-</p><p>place concrete from form</p><p>joints.</p><p>1 Offset</p><p>2 Fin</p><p>below Small crack in traver-</p><p>tine paving, Salk Institute.</p><p>p_048_069_chapt_4_bp 17.10.2006 18:22 Uhr Seite 52</p><p>above The concrete finish of</p><p>the new buildings at the Salk</p><p>Institute have crisp corners</p><p>and smooth surfaces.</p><p>below left Finish, form lines,</p><p>and tie holes on the Salk Insti-</p><p>tute expansion are virtually</p><p>flawless.</p><p>below right Finish, form lines,</p><p>and tie holes on the original</p><p>Salk Institute were never</p><p>intended to be perfect.</p><p>p_048_069_chapt_4_bp 17.10.2006 18:22 Uhr Seite 53</p><p>Cracks</p><p>Concrete cracks occur for a number of rea-</p><p>sons, including shrinkage, thermal contraction,</p><p>and subgrade settlement. As concrete cures,</p><p>water evaporates and the material shrinks ever</p><p>so slightly. Normal concrete can resist com-</p><p>pression; however, it is weak in resisting tensile</p><p>forces. If the shrinkage forces are greater than</p><p>the concrete’s developing tensile strength,</p><p>early-age plastic shrinkage cracks will occur.</p><p>This form of cracking principally results from</p><p>an excessive rate of evaporation during the all-</p><p>important curing period. It can be avoided by</p><p>keeping the concrete surface damp during the</p><p>curing process. Some shrinkage and thermal</p><p>cracking forces will inevitably arise and are</p><p>typically controlled by the provision of joints to</p><p>define the crack location. Where cracking is</p><p>particularly undesirable (as in the case of</p><p>water-retaining structures), additional second-</p><p>ary reinforcement can be added to limit the</p><p>crack width. Good practice enables us to con-</p><p>trol cracking.</p><p>Curling of Concrete Slabs</p><p>Concrete slabs on grade can curl up at joints</p><p>and around the perimeter of the slab. In top-</p><p>ping slab conditions the top slab can lose con-</p><p>tact with the subbase material, curling up at</p><p>the ends. Curling is most noticeable at con-</p><p>struction control joints, but it can also occur at</p><p>cracks and saw-cut joints. The cause of curl-</p><p>ing is differential shrinkage that occurs in a</p><p>slab as the exposed top surface shrinks and</p><p>54 55</p><p>Retaining walls display layer</p><p>marks in the concrete.</p><p>The Jay Pritzker Pavilion.</p><p>The Jay Pritzker Pavilion,</p><p>Chicago, 2004, provides con-</p><p>crete control joints at ten feet</p><p>on center in order to provide</p><p>a uniform cracking of the con-</p><p>crete retaining walls. In some</p><p>locations the cracks appear</p><p>adjacent to the control joints.</p><p>p_048_069_chapt_4_bp 17.10.2006 18:22 Uhr Seite 54</p><p>the core does not. Although it is possible to</p><p>repair curling in most slabs, prevention by</p><p>controlling shrinkage is preferred. Good mix</p><p>proportioning, proper curing, and placement</p><p>of saw-cut joints can help to reduce the</p><p>effects of curling.</p><p>Layer Marks</p><p>Prominent layer marks can occur as a result</p><p>of inadequate compaction and long-time inter-</p><p>vals between placing the layers. Layer marks</p><p>can also result from a change in the composi-</p><p>tion of the concrete mix.</p><p>Scaling</p><p>Scaling of concrete can occur when water is</p><p>absorbed into the concrete materials and</p><p>freezes with low temperatures. This is particu-</p><p>larly true of flatwork exposed to weather in</p><p>cold climates. Scaling is often caused by the</p><p>expansion and contraction of surface concrete</p><p>due to the freeze/thaw cycling. This type of</p><p>defect will typically appear near joints after a</p><p>year of thermal cycling. The solution to this</p><p>problem is to provide additional air entrain-</p><p>ment to the mix, prior to pouring the concrete.</p><p>Thin scaling can be caused by improper fin-</p><p>ishing and curing operations and is exacerbat-</p><p>ed by the application of snow and ice removal</p><p>products such as salt.</p><p>Spalling and Reinforcement Marks</p><p>Spalling occurs as a result of environmental</p><p>attack where the concrete cover to reinforce-</p><p>ment is inadequate; the steel reinforcement</p><p>close to the surface of the concrete rusts.</p><p>Rusting of the steel causes the volume of the</p><p>steel to expand and break the surface of the</p><p>concrete (See the chapter “Corrosion” for a</p><p>more detailed explanation). As with scaling,</p><p>spalling can also be caused by improper fin-</p><p>ishing and curing operations and is exacerbat-</p><p>ed by the application of snow and ice removal</p><p>products such as salt.</p><p>Reinforcement marks arise when the concrete</p><p>cover is absent, usually due to displacement</p><p>of the reinforcement cage before or during the</p><p>concreting operation. The bars soon rust and</p><p>cause staining of the concrete surface.</p><p>Irregular Tie Holes</p><p>Tie bars connect in the gang form frames and</p><p>prevent the forms from bulging out under the</p><p>hydrostatic pressure of the liquid concrete.</p><p>Tie holes are the void in a concrete surface</p><p>left when a tie end is snapped off, broken</p><p>back, or removed. Ties that are broken back</p><p>or snapped off frequently leave irregular</p><p>holes,</p><p>whereas threaded internal disconnecting ties</p><p>leave more uniform holes. Where spreader</p><p>cones are used on the ties, the holes are uni-</p><p>form. Tie holes are normally filled; however,</p><p>in exposed locations where they are spaced</p><p>in a regular pattern, they have become an</p><p>important architectural detail in contemporary</p><p>design. Tie bar spacing must consider the</p><p>strength of the panels. If the spacing between</p><p>tie bars becomes too great, the formwork will</p><p>bow out and create an uneven finished sur-</p><p>face.</p><p>right Spalling at corroded</p><p>reinforcement. Salk Institute.</p><p>far right Scaling of concrete</p><p>slab exposed to cold weather.</p><p>Cracks in the floor slab around</p><p>an interior column oppose the</p><p>anticipated crack direction.</p><p>Cracking can be caused by</p><p>improper isolation-joint design</p><p>that does not provide relief at</p><p>reentrant corners.</p><p>Curling at a saw-cut joint in</p><p>slab.</p><p>1 Saw-cut joint prior to curl-</p><p>ing of concrete</p><p>2 Saw-cut joint after curling</p><p>of concrete</p><p>p_048_069_chapt_4_bp 17.10.2006 18:22 Uhr Seite 55</p><p>56 57</p><p>Cathedral of Our Lady of the</p><p>Angels, Los Angeles, 2002.</p><p>right Colored concrete poses</p><p>a challenge to repair as seen</p><p>by tie hole fix at Our Lady of</p><p>the Angels.</p><p>below Tie holes in cast-in-</p><p>place concrete can be covered</p><p>with a variety of techniques.</p><p>1 Welded water stop plate</p><p>2 Metal or plastic cone</p><p>3 Wall thickness</p><p>4 Formwork anchor (thread-</p><p>ed rod)</p><p>5 Plastic cone</p><p>6 Formwork</p><p>7 Filled with mortar</p><p>8 Plugged (e.g. with lead)</p><p>9 Filled and shaped with</p><p>mortar</p><p>10 Filled with mortar</p><p>p_048_069_chapt_4_bp 17.10.2006 18:22 Uhr Seite 56</p><p>The Forming of Concrete</p><p>Surface defects in concrete can be linked to</p><p>the method of casting the material. Through</p><p>the years, the techniques of forming concrete</p><p>have improved, requiring architects to rethink</p><p>how they use concrete. New products have</p><p>provided designers with alternative methods</p><p>of molding concrete in exciting new ways that</p><p>reduce the risk of surface defects.</p><p>Cast-in-place Concrete</p><p>Completed in 125 A.D., the Pantheon provides</p><p>one of the oldest surviving buildings con-</p><p>structed with cast-in-place concrete. Remark-</p><p>able for its size, the dome was the largest built</p><p>in ancient times. Without the use of steel rein-</p><p>forcement, the dome spans 43m (142 feet)</p><p>in diameter and rises to a height of 22m</p><p>(71 feet) above its base. Romans developed</p><p>mortar for their concrete from fine volcanic</p><p>ash (known as pozzolana), lime (from burnt</p><p>limestone), and water. Added to this was</p><p>crushed brick and animal blood. The builders</p><p>of the Pantheon were very conscious of their</p><p>materials and reduced the weight of the con-</p><p>crete from the base (heaviest) to the top of</p><p>the dome (lightest) by using aggregate of dif-</p><p>ferent weights, the lightest aggregate used</p><p>being pumice. After nearly 2000 years, we are</p><p>continuing to refine the process of forming</p><p>concrete.</p><p>Formwork</p><p>Today, concrete formwork can be classified</p><p>into two groups: absorbent and non-absorbent.</p><p>Non-absorbent formwork is generally one</p><p>of three different types: wood modified with</p><p>synthetic resin, coated steel, or plastic form-</p><p>work. Absorbent formwork draws water out of</p><p>the surface of concrete by suction during the</p><p>hardening process. Timber formwork is an</p><p>example of absorbent formwork, which can</p><p>leave surface defects from organic material in</p><p>the wood, like wood sugar. By applying a pre-</p><p>treatment of cement wash followed by brush-</p><p>ing, these defects can be avoided. The cement</p><p>wash can also remove fine splinters from</p><p>rough formwork. If not removed, the splinter</p><p>can be left behind in the exposed concrete</p><p>and give the concrete a yellowish appearance</p><p>after the forms are removed. Absorbent form-</p><p>work must be watered within 12 hours before</p><p>pouring so that the formwork does not remove</p><p>too much water from the curing concrete;</p><p>water absorption will reduce the water/cement</p><p>ratio at the surface of the concrete. This</p><p>reduction can result in incomplete hydration</p><p>of cement and seriously compromise the pro-</p><p>tective properties of the concrete cover to rein-</p><p>forcement. Color differences can occur due to</p><p>formwork that sucks more or less water from</p><p>the mix. Leakage of water from joints of forms</p><p>right Spalling concrete is still</p><p>visible on cast-in-place con-</p><p>crete walls of Wright’s 1905</p><p>Unity Temple even after signif-</p><p>icant repairs to the structure</p><p>in 2000.</p><p>right The Pantheon is one of</p><p>the oldest surviving buildings</p><p>constructed with cast-in-place</p><p>concrete.</p><p>p_048_069_chapt_4_bp 17.10.2006 18:22 Uhr Seite 57</p><p>draws cement and other fine particles toward</p><p>joints and causes a slightly darker hydration</p><p>discoloration.</p><p>The swelling of the wood, prior to pouring,</p><p>helps make the formwork joints water tight.</p><p>Fins are created when cement paste oozes out</p><p>between the forms. Form joint construction</p><p>can reduce the likelihood of fins in locations</p><p>where concrete walls are to be left exposed.</p><p>Too much swelling can cause the forms to</p><p>warp and lift.</p><p>Smooth-form concrete used in exposed loca-</p><p>tions is obtained from smooth form-facing</p><p>material arranged in an orderly and symmetri-</p><p>cal manner with a minimum of seams. Tie</p><p>holes and defects are patched, and fins and</p><p>other projections larger than 3mm (1/8 inch)</p><p>are removed. Small bugholes are acceptable;</p><p>however, bugholes larger than 19mm (3/4 inch)</p><p>diameter are to be filled.</p><p>Precast Concrete</p><p>Precast concrete consists of molding concrete</p><p>elements face down in a controlled environ-</p><p>ment prior to incorporating them in a struc-</p><p>ture. In the case of facing material, the finish</p><p>quality is improved using this method; gravita-</p><p>tional force and the short path length enables</p><p>air bubbles to easily rise through the liquid</p><p>concrete, which together with controlled</p><p>preparation compaction and curing produces</p><p>high-quality concrete with crisp edges and a</p><p>58 59</p><p>right and below University</p><p>Library in Utrecht, 2004.</p><p>Fabrication of rubber mold for</p><p>precast concrete panels and</p><p>façade detail.</p><p>p_048_069_chapt_4_bp 17.10.2006 18:22 Uhr Seite 58</p><p>smooth surface. Precast concrete fabrication</p><p>typically occurs in a factory setting followed by</p><p>shipping completed units to the site via trucks.</p><p>There are size limitations with this method of</p><p>construction, based on a truck’s ability to</p><p>transport very large pieces. Larger panels can</p><p>be cast on site and tilted into position.</p><p>Although precast concrete fascia panels have</p><p>been around for many years, they continue to</p><p>improve the quality of fabrication and design</p><p>of this architectural element. The University</p><p>Library in Utrecht, the Netherlands, provides</p><p>an excellent example of the quality that can be</p><p>achieved with contemporary precast concrete</p><p>construction.</p><p>The design of the University Library in</p><p>Utrecht, completed in 2004, has a powerful</p><p>cubic structure of massive appearance as</p><p>viewed from the exterior. Dutch architect Wiel</p><p>Arets’ design tried to avoid any impressions of</p><p>an isolated monolith. The glazing had to be</p><p>printed with a grid of dots to provide an ade-</p><p>quate degree of sunscreening for the interior</p><p>spaces. A regular grid of dots was not accept-</p><p>able to the designers, so a screen pattern was</p><p>developed by artist Kim Zwarts based upon a</p><p>photograph of willow branches. The concrete</p><p>panels achieve the same motif in a relief</p><p>achieved through the use of rubber molds laid</p><p>in the concrete forms.</p><p>By this method, the concrete panels provide a</p><p>three-dimensional surface quality. The con-</p><p>crete has a smooth black-painted surface.</p><p>The panels were stylized using four gray</p><p>tones. The relief for the form was manually cut</p><p>to a maximum depth of 25mm (1 inch) in a</p><p>sheet of polyurethane. Each gray tone was</p><p>allotted its own separate plane.</p><p>The concrete surface was colored. However,</p><p>colored pigments in the concrete mix were not</p><p>used because of cost and potential variations</p><p>in surface tone. The concrete surface was</p><p>painted after it had set. Two coats of paint</p><p>were applied to the interior panels and three</p><p>coats to the exposed panels of</p><p>the building.</p><p>above The Phaeno Science</p><p>Center, Wolfsburg, Germany,</p><p>2005, was constructed with</p><p>cast-in-place concrete (left</p><p>side of photo) as well as</p><p>precast concrete panels. With</p><p>time the color variation is</p><p>expected to go away.</p><p>p_048_069_chapt_4_bp 17.10.2006 18:22 Uhr Seite 59</p><p>p_048_069_chapt_4_bp 17.10.2006 18:22 Uhr Seite 60</p><p>Self-compacting Concrete</p><p>Self-compacting concrete (SCC) was first</p><p>developed in Japan in 1988 to reduce labor</p><p>costs in the placement of concrete. As the</p><p>name suggests, self-compacting concrete</p><p>achieves full compaction due to its self-</p><p>weight. Consolidation is an inherent property</p><p>of the mix and hence no vibration is required</p><p>during concrete pouring. Combining high</p><p>strength with an extremely fluid mix, self-com-</p><p>pacting concrete provides a method of pro-</p><p>ducing concrete shapes that would otherwise</p><p>be impossible to achieve. Like honey on toast,</p><p>the new material in its liquid stage can fill</p><p>complex geometric molds, even with dense</p><p>steel reinforcement. The polycarboxylate</p><p>ether superplasticizer provides the required</p><p>flow characteristics. Once the material has</p><p>hardened it attains high strengths, in the</p><p>range of 60–100 MPa (8.7–14.5 ksi). Ultra-</p><p>high performance self-compacting concrete</p><p>(UHPSCC) has strength characteristics in</p><p>excess of 150 MPa (21.8 ksi).</p><p>The Phaeno Science Center in Wolfsburg,</p><p>Germany, completed in 2005, used this mate-</p><p>rial to achieve amorphic forms cast in the field</p><p>with self-compacting concrete. The asymmet-</p><p>ric voided slab ceiling was intended to merge</p><p>into the cones without any transition zones or</p><p>color differences. The surfaces of the cones</p><p>reveal the wood grain from the formwork and</p><p>the formwork connections. Practice for the</p><p>aboveground cones was possible through</p><p>trial pores in the underground car park,</p><p>using cones that are not highly visible to the</p><p>public. Attention to detail by the design team</p><p>required that the boards be tapered to rein-</p><p>force the cone shape of the form. Although</p><p>not obvious to the eye, the boards were trape-</p><p>zoidal in shape, not rectangular, and the nail</p><p>positions on the boards were arranged in a</p><p>regular pattern. The prefabricated formwork</p><p>elements were artificially aged on-site with</p><p>a cement wash, in order to provide a consis-</p><p>tent appearance to the concrete after the</p><p>forms were removed. The wax-based form-</p><p>work release agent was spray-applied prior</p><p>to pouring.</p><p>Curing is particularly important to the finish</p><p>of self-compacting concrete. The Phaeno</p><p>Science Center battled with trying to provide</p><p>uniform color and texture for an incredibly</p><p>complicated building form. The goal was to</p><p>have everything in the same high-quality sur-</p><p>face finish. The cement mix was closely moni-</p><p>tored to obtain consistency in color and tex-</p><p>ture. The surface finish can resemble an ele-</p><p>phant skin if the concrete mixture is not kept</p><p>in constant motion during pouring. For this</p><p>reason, the mix was pumped into the forms.</p><p>page 60 The self-compacting</p><p>concrete elements at the</p><p>Phaeno Science Center,</p><p>Wolfsburg, which were con-</p><p>structed on site have a fair</p><p>amount of surface defects at</p><p>some difficult transitions.</p><p>right and below The factory</p><p>constructed precast concrete</p><p>panels at the Phaeno Science</p><p>Center are close to perfect.</p><p>Strength and Workability.</p><p>1 In concrete the slump is</p><p>measured as the distance the</p><p>concrete settles.</p><p>2 Too much sand makes the</p><p>mix unworkable and sets up</p><p>too quickly.</p><p>3 The ideal slump for</p><p>traditional concrete is 100</p><p>to 150mm (4 to 6 inches)</p><p>4 In traditional concrete too</p><p>much slump will produce</p><p>weak concrete.</p><p>5 SCC produces maximum</p><p>slope without compromising</p><p>strength.</p><p>p_048_069_chapt_4_bp 17.10.2006 18:22 Uhr Seite 61</p><p>Fiber-reinforced Concrete</p><p>Concrete is a relatively brittle material and will</p><p>crack if exposed to tensile forces. Since the</p><p>mid-1800s, steel reinforcing has been used to</p><p>overcome this problem. Acting as a composite</p><p>system, the properly located reinforcing steel</p><p>provides the tensile strength necessary for</p><p>structural stability. It was discovered that by</p><p>adding fibers to the concrete mix its inherent</p><p>tensile strength can be increased by as much</p><p>as five times. A variety of different fibers can</p><p>be used according to the material properties</p><p>required. As a result, tensile forces due to</p><p>shrinkage or thermal movement can be resist-</p><p>ed by the fiber-reinforced concrete.</p><p>Finishing Treatments in Concrete</p><p>Many surface defects in concrete can be hid-</p><p>den by finishing treatments. Each finishing</p><p>treatment provides a different effect, but with</p><p>certain limitations. Finishing of concrete</p><p>surfaces can take place during the curing</p><p>process or after the concrete has fully cured.</p><p>It is important to consider the impact that</p><p>the choice of finishing treatment has on the</p><p>integrity of the concrete cover. This relatively</p><p>thin layer provides the required surface dura-</p><p>bility, and the designer must select any finish-</p><p>ing technique with this in mind. The following</p><p>is a list of selected surface finishes that can</p><p>be used to minimize the effects of surface</p><p>defects.</p><p>Sandblast Finish</p><p>Sandblasting today is generally carried out</p><p>using abrasive materials other than sand, its</p><p>silica dust being dangerous to health. By</p><p>using an abrasive, fired at the surface by a</p><p>compressed air jet, concrete can be cleared</p><p>of dirt, rust, and small surface defects. A</p><p>sandblast finish is often used to provide a uni-</p><p>form appearance on a surface marked with</p><p>defects. A classic example of this method of</p><p>finishing is the expansion of the Dulles Inter-</p><p>national Airport in Washington, D.C, undertak-</p><p>en in 1999. The terminal expansion consisted</p><p>of extending the 1962 structure at both ends,</p><p>essentially doubling the size of the building.</p><p>The original innovative structural form was re-</p><p>used for the expansion. Although unchanged</p><p>from the initial design, stricter building codes</p><p>mandated a stronger concrete mix and safety</p><p>glazing. At the end of construction, it was</p><p>desirable to have the same finish on both the</p><p>new and the old concrete piers (constructed</p><p>over 30 years previously). The solution was to</p><p>sandblast the concrete surfaces of all the</p><p>piers, thus providing a uniform appearance to</p><p>all elements.</p><p>Bush Hammering</p><p>A bush hammer is a traditional hand tool that</p><p>looks like a hammer with a serrated face con-</p><p>taining many pyramid-shaped points. The tool</p><p>was used to dress concrete or stone surfaces.</p><p>Today, bush hammer surfaces are created</p><p>with power-driven equipment. The Mexican</p><p>Embassy in Berlin, Germany, constructed in</p><p>2001, used bush hammering of the concrete</p><p>surfaces at the main building entrance to</p><p>emulate this traditional Mexican technique for</p><p>finishing concrete. 18m (60 foot) tall columns</p><p>tilted to varying degrees provide a curtain of</p><p>white concrete leading visitors into the build-</p><p>ing. The white concrete uses a formula of</p><p>white cement, marble chips and pulverized</p><p>marble. By exposing the marble aggregate</p><p>through bush hammering, the light-reflecting</p><p>capacity of the concrete is improved and a</p><p>uniform texture achieved. The thin concrete</p><p>blades are actually precast concrete, whereas</p><p>the portal frame was cast in place. The bush</p><p>hammer finishing technique provided a</p><p>method of making two different methods of</p><p>forming concrete look the same.</p><p>Exposed Aggregate Concrete</p><p>To produce an exposed aggregate (washed</p><p>out) concrete finish, the aggregates in the mix</p><p>are exposed by washing out the cement paste</p><p>at the concrete surface. This is achieved by</p><p>applying a retarder to the surface of the con-</p><p>crete. The retarder slows hydration of the sur-</p><p>face layer of cement, making it less hard than</p><p>the cement beneath it. The surface layer can</p><p>then be washed out to reveal the underlying</p><p>course aggregate particles. A muriatic acid</p><p>solution may then be applied to further clean</p><p>and brighten the aggregate particles. The</p><p>Headquarters of Sozialverband Deutschland</p><p>in Berlin, completed in 2003, provides a good</p><p>62 63</p><p>above</p><p>and below Mexican</p><p>Embassy, Berlin, 2001. Like a</p><p>curtain billowing through an</p><p>open window, the warped</p><p>plane implied by the pillars</p><p>directs pedestrians toward</p><p>the entrance.</p><p>page 63 Existing concrete</p><p>columns match finish of new</p><p>concrete columns by sand-</p><p>blasting all columns. Dulles</p><p>International Airport Expan-</p><p>sion, Washington, D.C., 1999.</p><p>p_048_069_chapt_4_bp 17.10.2006 18:22 Uhr Seite 62</p><p>p_048_069_chapt_4_bp 17.10.2006 18:22 Uhr Seite 63</p><p>example of the uniform appearance of an</p><p>exposed aggregate concrete finish. The build-</p><p>ing’s colorful shiny windows stand out in a</p><p>background of textured black concrete. The</p><p>precast concrete panel finish was achieved by</p><p>washing out the paste of the precast panels,</p><p>exposing the crushed fine black basalt aggre-</p><p>gate. The design provides precast corner</p><p>panels that wrap the edges of the building</p><p>with large thick returns. The corner edge is a</p><p>sharp crisp line. The edges of the panels were</p><p>protected during transportation and installa-</p><p>tion. Because the panels are elevated above</p><p>the ground floor of the building, they are not</p><p>vulnerable to chipping.</p><p>Polished Concrete</p><p>A polished concrete finish is completed after</p><p>the concrete has cured. Typically, the cement</p><p>slurry in a concrete mix rises to the surface,</p><p>covering the aggregate. The polishing process</p><p>involves removal of the cement slurry that</p><p>hides the internal composition of the concrete</p><p>and provides a surface that can resemble</p><p>a terrazzo floor. Like terrazzo, the polishing</p><p>process brings out the rich color of the mix</p><p>components. Polished concrete requires an</p><p>intense scrutiny of materials and processes.</p><p>The Kunstmuseum in Vaduz, Liechtenstein,</p><p>completed in 2000, used polished concrete</p><p>to make what appears to be a monolithic</p><p>block at the base of a cliff. The main exhibi-</p><p>tion rooms are on the upper floor, covered</p><p>with skylights, and have no windows to the</p><p>exterior. The form joints were ground down.</p><p>Any surface voids along with the wall ties</p><p>were filled with a matching concrete mix prior</p><p>to grinding the wall. All details are designed</p><p>to achieve flush joints over the entire building.</p><p>In strong contrast to the Salk Institute, this</p><p>museum design tries to hide any clues as to</p><p>how the building was formed. The concrete</p><p>polishing revealed the special stone aggre-</p><p>gate, broken black basalt, fine-grained green,</p><p>red and white Rhine River gravel, against the</p><p>black pigmented cement. The final effect was</p><p>a semi-reflective surface that constantly</p><p>changes with the effects of natural light.</p><p>64 65</p><p>above and right Exposed</p><p>aggregate in precast concrete</p><p>panels, Headquarters of</p><p>Sozialverband Deutschland,</p><p>Léon Wohlhage Wernik</p><p>Architekten, Berlin, 2003.</p><p>p_048_069_chapt_4_korr_bp 27.10.2006 13:48 Uhr Seite 64</p><p>Surface Defects in Stone</p><p>Granite is formed from liquid magma, the</p><p>molten rock found at the core of the earth,</p><p>cooled slowly to form a substance approach-</p><p>ing the hardness and durability of a diamond.</p><p>Granite is an igneous rock, its chemical com-</p><p>positions similar to lava. However, granite</p><p>owes its hardness and density to the fact that</p><p>it has solidified deep within the earth, under</p><p>extreme pressure. Over the eons, seismic</p><p>activity has changed the crust of the planet,</p><p>forcing veins of granite to the surface. Gla-</p><p>ciers scraped off layers of dirt, sand and</p><p>rock to expose granite formations. Typically</p><p>revealed by outcrops, the deposits have been</p><p>discovered on all continents.</p><p>The rocks that form the earth’s crust fall into</p><p>three generic groups: igneous, sedimentary,</p><p>and metamorphic. The beauty and durability</p><p>of these naturally formed rocks bring variation</p><p>to the architectural form. With these variations</p><p>come characteristics that can be seen as</p><p>defects.</p><p>Inclusions</p><p>An inclusion is the term given to foreign mat-</p><p>ter in natural stone. Because stone is quarried</p><p>from the earth, it can have inclusions includ-</p><p>ing metal, carbon, or even shells. Building</p><p>stone is not typically required to have no</p><p>inclusions; however, an excess amount can</p><p>detract from its appearance. The percentage</p><p>and size of acceptable inclusions should be</p><p>compared against an established standard</p><p>so that stone pieces can be accepted or</p><p>rejected.</p><p>above Kunstmuseum Liech-</p><p>tenstein.</p><p>above Section at roof at</p><p>Kunstmuseum Liechtenstein</p><p>in Vaduz, 2000.</p><p>1 Ground and polished sur-</p><p>face</p><p>2 Cast-in-place concrete</p><p>structure, 40cm (15 3/4 inches)</p><p>3 Foamed glass insulation</p><p>14cm (5 1/2 inches)</p><p>4 Air space with plaster walls</p><p>5 Glass skylight</p><p>6 Sunshade lamella</p><p>7 Steel support beam</p><p>8 Passable glass ceiling</p><p>9 Suspended ceiling with</p><p>perforated plastic sheet</p><p>right Kunstmuseum in</p><p>Vaduz.</p><p>p_048_069_chapt_4_bp 17.10.2006 18:22 Uhr Seite 65</p><p>Veining Patterns</p><p>The veining in stone is caused by the pres-</p><p>ence of trace elements at the time of its for-</p><p>mation. Iron oxide makes the pinks, yellows,</p><p>browns and reds. Most gray, blue-gray and</p><p>black lines are from bituminous substances.</p><p>These veins are a distinctive part of a stone’s</p><p>appearance and must be considered in the</p><p>design and installation of the stone. The natu-</p><p>ral folds and veins found in marble and some</p><p>granite create distinctive markings throughout</p><p>the stone. The quarried blocks are cut and</p><p>finished for particular patterns. Uncontrolled</p><p>use of natural stone finishes on a building can</p><p>appear as a visual defect, making it necessary</p><p>to commit to a pattern when installing the</p><p>stone. Understanding the veining patterns</p><p>avoids a break in the overall effect. Traditional</p><p>veining patterns are: blend, slip, book match,</p><p>and diamond match.</p><p>Fissures and Cracks</p><p>Fissures and cracks are natural defects found</p><p>in some stones. Exotic stones desired for their</p><p>playful veining and brilliant color are often the</p><p>materials most affected by these defects. For</p><p>years, the stone industry has sought to remedy</p><p>such defects with the use of resins to fill the</p><p>fissures and cracks; the appearance of a solid</p><p>piece of stone can then be achieved after sur-</p><p>face polishing. Resins are chemical ingredi-</p><p>ents used to infill surface voids in a stone.</p><p>Resins give a smooth surface that is difficult</p><p>to detect in the finished stone; however, they</p><p>should be used with care.</p><p>Resins are not typically stable in an environ-</p><p>ment exposed to ultraviolet radiation. Fading</p><p>of resin material can become visible years</p><p>after an installation has been exposed to</p><p>direct sunlight. Resin-filled materials can be</p><p>difficult to refurbish, because the exact mate-</p><p>rial used in the resin can be unknown and</p><p>therefore difficult to match. Lastly, the chemi-</p><p>cals used in resins are not natural and are not</p><p>always known or tested for surfaces used for</p><p>the preparation and consumption of food. The</p><p>use of resin infill for kitchen counter tops is a</p><p>large controversy in the stone industry.</p><p>Surface Defects in Brick and Terra-</p><p>cotta</p><p>One of the most demanding brick finishes to</p><p>keep defect-free is sculptured brick. Sculp-</p><p>tured brick panels are the most unusual</p><p>example of customized masonry. The forms</p><p>are sculptured pieces handcrafted from the</p><p>green clayware before firing. The unburned</p><p>units are firm enough to allow the artist to</p><p>work freely without damage to the brick body,</p><p>but sufficiently soft for carving, scraping and</p><p>cutting. After firing, the sculptured surface is</p><p>permanently set in the brick face. The brick</p><p>surface can be selected from a variety of tex-</p><p>tures, including: smooth, wire-cut, stippled,</p><p>bark and brushed. Defects like chippage,</p><p>warpage, and cracks in brick are common in</p><p>66 67</p><p>above Traditional veining pat-</p><p>terns in stone.</p><p>1 Blend pattern</p><p>2 Slip pattern</p><p>3 Match pattern (also called</p><p>book-matched)</p><p>4 Diamond-matched pattern</p><p>below One out-of-place stone</p><p>can distract from the uniform</p><p>veining pattern of a stone wall.</p><p>above The Walt Disney</p><p>Concert Hall in Los Angeles,</p><p>completed in 2003, illustrates</p><p>the natural color and texture</p><p>variation natural stone on a</p><p>wall.</p><p>right The Walt Disney Con-</p><p>cert Hall,</p><p>running bond ran-</p><p>dom pattern of stone wall.</p><p>p_048_069_chapt_4_bp 17.10.2006 18:22 Uhr Seite 66</p><p>the industry, but can be eliminated by visual</p><p>inspection and testing.</p><p>Visual Inspection</p><p>After leaving the kiln, bricks and terra-cotta</p><p>panels are cooled and inspected for chips</p><p>and color variation. Rejected material is either</p><p>sold as “seconds” or ground up and mixed</p><p>with clay to be used in another production</p><p>run. Some chipping of masonry can go unde-</p><p>tected through the fabrication process, or</p><p>bricks may be damaged by shipping and han-</p><p>dling. It is up to the mason to make the final</p><p>review of bricks prior to building them into</p><p>the wall. The International Masonry Institute</p><p>allows no chips or cracks that are visible</p><p>when viewed from a distance of not less than</p><p>6m (20 feet) under diffused lighting.</p><p>Brick Testing</p><p>Ancient brickmakers took clay from the</p><p>ground, mixed it with water, shaped it like</p><p>bread dough into oblong units, and let it air-</p><p>dry in the sun. Today, brick construction is far</p><p>more sophisticated and the performance</p><p>requirements for the bricks are much more</p><p>stringent. Compression strength and absorp-</p><p>tion are directly related to the durability of</p><p>masonry. In addition to inspection of the sur-</p><p>face appearance of the bricks, quality testing</p><p>is essential for ensuring material durability</p><p>and avoiding future surface defects. Bricks</p><p>are made with raw materials that possess a</p><p>natural level of variation. Typically, the desired</p><p>higher compression strengths and lower</p><p>absorption rates of brick are linked not only to</p><p>the raw materials used, but also to higher kiln</p><p>firing temperatures. For this reason, bricks are</p><p>laboratory-tested to verify water absorption,</p><p>compression strength, and efflorescence.</p><p>Freeze-thaw testing is required for bricks to</p><p>be used in severe weathering regions. Tests</p><p>are conducted on a yearly basis for each type</p><p>of brick and a certificate of test and authentic-</p><p>ity is then issued. Architects can require that</p><p>testing be completed for the run of brick to</p><p>be used for a specific project; however, this</p><p>is not typical.</p><p>Building Stone Surface Finishes</p><p>GEOLOGICAL CATEGORY COMMON NAME FINISHES</p><p>Sandstone</p><p>Limestone</p><p>Dolomite</p><p>A) Smooth (machine finished by saw,</p><p>finder or planner)</p><p>B) Machine tooled (with uniform grooves)</p><p>C) Chat sawn (non-uniform)</p><p>D) Shot sawn (irregular and uneven</p><p>markings)</p><p>E) Split face (concave-convex)</p><p>F) Rock face (convex)</p><p>1. SEDIMENTARY</p><p>Marble</p><p>Serpentine</p><p>Onyx</p><p>Slate 1</p><p>Quartzite1</p><p>Gneiss2</p><p>Travertine 4</p><p>A) Sanded</p><p>B) Honed</p><p>C) Polished</p><p>D) Wheel abraded</p><p>E) Bush hammered</p><p>F) Split face</p><p>G) Rock face</p><p>2. METAMORPHIC</p><p>Granite</p><p>Syenite</p><p>Diorite3</p><p>Gabbro</p><p>Andesite</p><p>Basalt</p><p>A) Sawn</p><p>B) Honed</p><p>C) Polished</p><p>D) Machine tooled (four-cut, six-cut,</p><p>chiseled, axed, ponted, etc.)</p><p>E) Flammed (also called thermal)</p><p>F) Sand finished</p><p>G) Split face</p><p>H) Rock face</p><p>3. IGNEOUS</p><p>1 Slate and quartzite cannot be polished.</p><p>2 Gneiss will take all of the finishes of marble and may also be flame finished.</p><p>3 Diorite will not take flame finish.</p><p>4 Travertine is actually a limestone but is classified with marbles for surface finishes. Travertine finishes include</p><p>filled, partially filled, and unfilled.</p><p>Sculptured brick free of</p><p>defects, exterior wall of Zoo</p><p>Berlin.</p><p>p_048_069_chapt_4_bp 17.10.2006 18:22 Uhr Seite 67</p><p>In the architectural community, a concrete</p><p>material of the highest quality is typically</p><p>referred to as “Ando Concrete.” Tadao Ando,</p><p>the world-renowned Japanese architect, has</p><p>been a catalyst for perfecting the art of cast-</p><p>in-place concrete in projects around the</p><p>world. Famous for the finished quality of his</p><p>walls, visitors have to use restraint not to</p><p>stroke the surface of the silky smooth walls.</p><p>The Pulitzer Foundation of the Arts in St.Louis,</p><p>Missouri, completed in 2003, is a good exam-</p><p>ple of how Ando has been able to maintain</p><p>very high standards outside of his home</p><p>country. Built as a museum to house the</p><p>Pulitzer family’s art collection, the building</p><p>also acts as a headquarters for the charitable</p><p>foundation. A goal of the foundation is to fos-</p><p>ter an understanding between modern art and</p><p>architecture. The building has a simple form,</p><p>two elongated rectangles, each 7.5m (24 feet)</p><p>wide, are placed parallel to one another, with</p><p>a rectangular pool of equal width between</p><p>them. The interplay of levels and plains works</p><p>well with the monolithic appearance of cast-</p><p>in-place concrete. The sparseness of detailing</p><p>allows for greater attention to the finish of</p><p>the building materials. In order to achieve the</p><p>high level of finish on the concrete, three</p><p>aspects of the project had to be mastered:</p><p>formwork, mix design and pouring proce-</p><p>dures.</p><p>The concrete’s formwork panels were cut and</p><p>fitted together like bespoke furniture. The</p><p>forms were made of plastic-coated plywood</p><p>manufactured in Europe from short grain</p><p>hardwood material. The panels were butted</p><p>together tightly. Then the form panels were</p><p>sealed and polished to a glossy surface. Tie</p><p>bar cones were custom-made using a hybrid</p><p>assembled from traditional cones used in the</p><p>industry. This gave the contractor greater flex-</p><p>ibility to uniformly construct a wall of varying</p><p>thicknesses. The rounding of the tie bar holes</p><p>is exactly conical. They are precisely sealed</p><p>with concrete dowels, which are carefully</p><p>positioned and installed. Nothing is left to</p><p>chance, from the juxtaposition of board sizes</p><p>to the arrangement of tie bar holes. The forms</p><p>were constructed on site in a temporary build-</p><p>ing and lifted into place by crane. The form</p><p>release agent was critical to achieving the</p><p>desired glossy surface finish.</p><p>With the architect’s desire to create the “per-</p><p>fect concrete,” construction crews spent</p><p>years forming the walls of this single building.</p><p>The structure had 150 wall pours, which took</p><p>place over a two-and-a-half-year time period.</p><p>In order to maintain a uniform appearance</p><p>the concrete mix was designed with great</p><p>care. In order to maintain a consistent color</p><p>on all walls, the raw materials were closely</p><p>monitored and water levels controlled to</p><p>obtain a uniform mix for all concrete pours.</p><p>Higher water levels in concrete can darken</p><p>the color of the finished material. Merrimac</p><p>stone was used in the aggregate at the</p><p>Pulitzer Foundation because it has a very low</p><p>absorption rate,and is abundant in the region.</p><p>The mixture went through several trials. The</p><p>maximum aggregate size was reduced to</p><p>19mm (3/4 inch) in order to improve the</p><p>strength of the mix at the top of the tall forms.</p><p>Timing was critical during concrete place-</p><p>ment. The concrete mix used for the project</p><p>was extremely dense and set quickly, taking</p><p>approximately two hours to stiffen after being</p><p>mixed. In order to maintain the quality of color</p><p>and finish, the time from mixing the material</p><p>to removing the last vibrator could take no</p><p>more than two hours. This criterion put enor-</p><p>mous pressure on concrete suppliers because</p><p>the material was mixed off-site at the suppli-</p><p>er’s plant and delivered by truck. Concrete</p><p>skips were positioned using cranes and pro-</p><p>vided just enough material to fill to the top of</p><p>the formwork. Many men were required to</p><p>vibrate the concrete in order to ensure com-</p><p>paction. The architect has said that the shine</p><p>on the surface of the concrete was a reflection</p><p>of the skill of the people that put it there. Even</p><p>with the highest quality control during con-</p><p>struction, defects occurred. At the Pulitzer</p><p>Foundation, a total of three walls were</p><p>replaced after curing because of imperfec-</p><p>tions. This attention to detail produced fin-</p><p>ished monolithic planes that deserve the</p><p>description “Ando concrete.”</p><p>68 69</p><p>Ando Concrete, Pulitzer Foun-</p><p>dation, St. Louis, 2003.</p><p>Fabrication of wood forms at</p><p>Pulitzer Foundation, St. Louis.</p><p>How Can Surface Defects Be Avoided</p><p>and Repaired?</p><p>p_048_069_chapt_4_bp 17.10.2006 18:22 Uhr Seite 68</p><p>Concrete Repairs</p><p>The repair of concrete blemishes is possible,</p><p>but</p><p>at night.</p><p>The onyx panels are more than beautiful. They</p><p>have been designed with spring clip connec-</p><p>tions tested for blast design. Today’s stone</p><p>enclosures can provide both light and protec-</p><p>tion to the inhabitants within.</p><p>Designers are transforming materials of the</p><p>past like masonry into materials of the future.</p><p>A traditional perception of brick is that of a</p><p>building tool used for heavy-looking buildings</p><p>with straight lines. The work of Eladio Dieste</p><p>has challenged that perception with masonry</p><p>structures that are light and fluid. His build-</p><p>ings celebrate the ingenuity of a great design-</p><p>er who was not limited by Uruguay’s construc-</p><p>tion materials or labor force. Similar to brick,</p><p>the use of terra-cotta is experiencing a re-birth</p><p>in modern architecture. Many architects had</p><p>abandoned terra-cotta as an old fashion deco-</p><p>rative element prone to corrosion problems</p><p>in buildings from our past. Architects such as</p><p>Goettsch Partners have given this traditional</p><p>material a dynamic new life in modern archi-</p><p>tecture with terra-cotta panels designed to</p><p>resist weather and corrosion.</p><p>Part of the credit for these advances in con-</p><p>crete, stone, and masonry goes to new tech-</p><p>nologies from the construction industry and</p><p>part goes to the imaginations of the architec-</p><p>tural community. This publication serves not</p><p>only to educate architects, educators, and</p><p>students on the principles of concrete, stone,</p><p>and masonry design, but to foster the pursuit</p><p>of new ideas within the construction industry.</p><p>The projects discussed in this book were</p><p>developed by some of the greatest architects</p><p>of the 20 th and 21st centuries. They are innova-</p><p>tive, creative designs. With any new creative</p><p>endeavor comes the possibility of flaws and</p><p>in some cases the possibility of “failed stone”.</p><p>This book describes many of the problems</p><p>behind today’s contemporary façade designs</p><p>and offers possible measures designers can</p><p>take to prevent problems. Each chapter of the</p><p>book focuses on a particular mode of failure.</p><p>The introduction of the chapter will discuss</p><p>the fundamentals of the problem. Specific</p><p>building examples will follow with explanations</p><p>of how the type of failure can be detected.</p><p>The end of each chapter will conclude with</p><p>recommendations as to what could have been</p><p>done differently to eliminate or minimize the</p><p>risk of failure.</p><p>While this is a book about failures, it is not</p><p>about liabilities, and the issue of whose fault</p><p>these failures were remains deliberately un-</p><p>discussed. The intention was not to determine</p><p>responsibilities for past mistakes but to help</p><p>avoid similar problems in the future.</p><p>Terra-cotta panel façade,</p><p>designed by Goettsch Partners,</p><p>Hessel Museum, CCS Bard</p><p>College, New York, 2006.</p><p>p_006_009_preface_bp 17.10.2006 18:07 Uhr Seite 9</p><p>Approximately 100 kilometers (60 miles) west</p><p>of Florence, Italy, is a city called Carrara in the</p><p>province of Tuscany. Well known around the</p><p>world for its white marble quarries, Carrara</p><p>has provided its stone for such famous historic</p><p>projects as the Trocadarro in Rome and the</p><p>Marble Arch in London. In recent history, the</p><p>white marble became infamous in modern</p><p>architecture for being a failing cladding mate-</p><p>rial for a number of contemporary large-scale</p><p>projects. The stone failures have been attrib-</p><p>uted to a phenomenon known as thermal</p><p>hysteresis.</p><p>Hysteresis is the changed response to an</p><p>object due to a given influence, which leaves</p><p>a permanent record of how the object was</p><p>influenced. For example, if one were to push</p><p>a piece of clay it will assume a new shape,</p><p>and when the hand is removed the clay will</p><p>not return to its original form. The clay pro-</p><p>vides a physical history of the forces that have</p><p>been applied to it.</p><p>Carrara white marble, exposed to large tem-</p><p>perature variation, can suffer from the effects</p><p>of thermal hysteresis. The effect can transform</p><p>a flat piece of thin white marble into a dish-</p><p>like form. The distortion is due to higher tem-</p><p>peratures and differential thermal cycles from</p><p>front to back of the panels, which results in</p><p>different magnitudes of expansion. Simply</p><p>put, as the stone is exposed to temperature</p><p>variation it transforms its shape and never</p><p>returns back to its original form. Like the clay</p><p>example, thermal hysteresis permanently</p><p>deforms the shape of the white marble. In</p><p>addition to a change in the stone’s appear-</p><p>ance, thermal hysteresis includes a significant</p><p>degradation of material strength. Over time</p><p>the thin marble panels not only dish outward</p><p>in a convex manner, they also become signifi-</p><p>cantly weaker in flexural strength. Over years</p><p>of thermal cycling, the stone panels can</p><p>degrade to the point of becoming a block of</p><p>loose granular material. Although the effects</p><p>of thermal hysteresis on white marble have</p><p>been known since the 1920s, the dangers of it</p><p>became painfully evident in the 1970s when</p><p>thin white marble panels installed on various</p><p>towers around the world began to fail.</p><p>10 11</p><p>Thermal Hysteresis</p><p>above Carrara, in the province</p><p>of Tuscany contains some of</p><p>the most famous stone quar-</p><p>ries in the world, known for</p><p>their white marble.</p><p>center Like the imprint of a</p><p>hand pushed in hard clay,</p><p>thermal hysteresis can leave a</p><p>physical history of forces</p><p>applied to a material.</p><p>right Interior Carrara marble</p><p>finishes at Amoco Building</p><p>have not changed.</p><p>page 11 Amoco Building,</p><p>Chicago, completed in 1972,</p><p>had a history of stone prob-</p><p>lems related to thermal hys-</p><p>teresis.</p><p>p_010_021_chapt_1_bp 17.10.2006 18:03 Uhr Seite 10</p><p>p_010_021_chapt_1_bp 17.10.2006 18:03 Uhr Seite 11</p><p>In the late 1960s, the Amoco Company</p><p>embarked on the design of a new corporate</p><p>office building in Chicago. The building design</p><p>was developed as an 80-story tower like no</p><p>other. It was to be one of the tallest buildings</p><p>in the world. The Amoco Building had a</p><p>unique exterior skin design with chevron</p><p>shaped steel columns clad in white stone at</p><p>the perimeter of the building. The triangular</p><p>sections of the columns contained the bulk of</p><p>the mechanical services such as the utilities</p><p>and air-conditioning piping, thus permitting</p><p>flush window walls inside the building. The</p><p>plan allowed for a column-free space between</p><p>the exterior wall and the center core. The</p><p>design provided exceptional views of the city</p><p>and Lake Michigan. Business executives in</p><p>the building could not fight over corner offices,</p><p>because there were none. The tower’s design</p><p>incorporated a reentrant corner that made all</p><p>of the perimeter offices the same.</p><p>During the design phase of the project, the</p><p>selection of the stone to clad the building was</p><p>not made lightly. In 1970, six Italian marbles</p><p>were examined. Three samples of each mar-</p><p>ble were tested. Selection of the stone consid-</p><p>ered appearance, strength, and availability.</p><p>The Carrara Alpha Gray marble was preferred</p><p>based primarily on color. Prior to fabricating</p><p>the stone cladding, extensive testing and</p><p>research on the stone was completed. Repre-</p><p>sentative samples of the selected marble were</p><p>tested for flexural strength before and after</p><p>exposure to thermal cycling. Testing indicated</p><p>that a minimum flexural strength of 9.65 MPa</p><p>(1,400 psi), incorporating the maximum anti-</p><p>cipated strength loss of 40 percent due to</p><p>thermal cycling, should be used for the proj-</p><p>ect. A full-scale mock-up test was conducted</p><p>in Florida at Construction Research Laboratory</p><p>for wind and water intrusion as well as struc-</p><p>tural testing of the glazing and stone suspen-</p><p>sion system. This mock-up was used to test</p><p>the assembly as a whole as well as to provide</p><p>a visual review of the details prior to starting</p><p>construction of the actual building.</p><p>At the conclusion of the design and testing</p><p>phase of the project, 44,000 pieces of Alpha</p><p>Gray marble from Carrara, Italy, were used</p><p>to clad the perimeter columns of the Amoco</p><p>Building. The work was completed in 1972.</p><p>The average stone size was 127 x 107 x 32mm</p><p>(50 inches high by 42 inches wide by 1 1/4</p><p>inches</p><p>can be difficult. Any remedial solution</p><p>should be practiced and reviewed prior to</p><p>carrying out the work. Blowholes and areas</p><p>of honeycombing should be filled using an</p><p>appropriate mortar mix to match the color and</p><p>texture of the finished wall. Surface irregulari-</p><p>ties can be removed by grinding the concrete</p><p>surface. However, this should be done care-</p><p>fully in locations where the concrete is to be</p><p>left exposed. Without considerable skill, the</p><p>cure can look worse than the disease, draw-</p><p>ing more attention to the defective area than</p><p>if it had been left alone. Where the surface</p><p>of a wall has excessive bugholes or areas of</p><p>honeycomb concrete, the entire wall can be</p><p>“bagged” in order to give it a uniform appear-</p><p>ance. Bagging consists of applying a thin</p><p>layer of cement slurry evenly over a surface</p><p>prior to rubbing it down with a crumpled</p><p>cement bag. When using this method of cov-</p><p>ering defects, care should be taken to ensure</p><p>that the durability of the structure is not</p><p>affected. Like plaster work, repairs to concrete</p><p>can be as much an art as a technique and</p><p>success can vary depending on the experi-</p><p>ence of the applicator.</p><p>Mock-up Samples</p><p>Concrete, masonry and stone have surface</p><p>quality limitations that must be understood by</p><p>all parties involved in a project. The best way</p><p>to avoid disappointment with finished compo-</p><p>nents is to specify a representative mock-up</p><p>for the project. The mock-up should exactly</p><p>reproduce all details that will be executed on</p><p>the project, from corner details to wall to ceil-</p><p>ing transitions. Stone panels should show all</p><p>representative veining, color and inclusions</p><p>that are expected from the selected stone. It</p><p>is important for designers to specify a repair</p><p>sample for all finished concrete, together with</p><p>the repair procedure. Damage is inevitable on</p><p>a construction site, and repairs will invariably</p><p>be required. A completed mock-up, accepted</p><p>by all parties as the representative quality</p><p>expected on the project, will prevent argu-</p><p>ments during construction.</p><p>Lessons Learned</p><p>1</p><p>Concrete cracks. Some surface defects are to</p><p>be expected with this man-made material.</p><p>Even the dome of the Pantheon has recorded</p><p>drawings showing the cracks that have devel-</p><p>oped over the years. Properly placed rein-</p><p>forcement and control joints can aid in the</p><p>reduction of cracks; however, some cracking</p><p>is virtually inevitable.</p><p>2</p><p>Improvements in concrete mix design and in</p><p>the quality of formwork has led to the rebirth</p><p>of exposed concrete in architecture. Great</p><p>improvements have been made in reducing</p><p>the amount of surface defects that can occur</p><p>with this poured-in-place material.</p><p>3</p><p>Precast concrete has traditionally been a</p><p>method of achieving a higher-quality concrete</p><p>finish. Rubber forms have provided architects</p><p>with a tool for creating exciting concrete</p><p>details.</p><p>4</p><p>Finishing treatments can provide a method of</p><p>removing minor concrete defects. Surface</p><p>defects can be removed from a finished wall</p><p>through techniques like polishing and sand-</p><p>blasting.</p><p>5</p><p>Stone is a natural material and comes with</p><p>natural imperfections such as inclusions.</p><p>Designers must understand the limitations of</p><p>these materials. When possible, avoid the use</p><p>of stones that have been filled with resin</p><p>materials. Resins can discolor under ultravio-</p><p>let radiation and can present difficulties when</p><p>refurbishing.</p><p>6</p><p>The surface quality of bricks is dependent on</p><p>inspection of the material prior to installation</p><p>when defective bricks should be discarded.</p><p>The strength of bricks is related to the absorp-</p><p>tion rate of the material. Testing is required in</p><p>order to verify low absorption rates.</p><p>Concrete mock-up for Lincoln</p><p>Park Zoo, Regenstein Center</p><p>for African Apes, Chicago,</p><p>2004.</p><p>Extensive vibration is required</p><p>during pours to remove air</p><p>pockets that can lead to sur-</p><p>face defects. Pulitzer Founda-</p><p>tion, St. Louis.</p><p>p_048_069_chapt_4_bp 17.10.2006 18:22 Uhr Seite 69</p><p>Architects may envisage their buildings as</p><p>having the coat of a white stallion and be dis-</p><p>appointed when finished surfaces take on the</p><p>motley appearance of a pinto. With exposed</p><p>construction materials like concrete, maintain-</p><p>ing uniformity of color is extremely important.</p><p>Color differences in concrete have several</p><p>causes, from variation in mix design to curing</p><p>methods. Uniformity can be achieved; how-</p><p>ever, tight quality control of construction mate-</p><p>rials and methods is required.</p><p>Natural stone comes out of the ground with</p><p>a certain color. That color is typically altered</p><p>by the finishing applied to the material. For</p><p>example, a polished finish takes on a different</p><p>color when compared to a thermal finish. The</p><p>color can change even more through unwant-</p><p>ed staining. Some stains are permanent and</p><p>can be remedied only by replacing the stone.</p><p>Natural stone staining can be avoided by</p><p>protecting it from harmful building products</p><p>and construction materials. Ironically, one of</p><p>the most damaging stains comes from water.</p><p>Designers must carefully consider how water</p><p>runs off the face of a building. Rainwater</p><p>can streak buildings with unwanted dirt and</p><p>chemicals in unexpected locations. Although</p><p>building maintenance plays its part, good</p><p>design can make a façade age well.</p><p>Color variation can be desirable. Stains and</p><p>color changes are then planned and welcome.</p><p>These are projects that challenge the ele-</p><p>ments with a clear understanding of the limits</p><p>and attributes of their enclosure. Selecting the</p><p>correct material and finish for a particular</p><p>building is critical to preventing disappoint-</p><p>ment.</p><p>The church Dio Padre Misericordioso in</p><p>Rome, also known as the Jubilee Church, was</p><p>completed in 2003 to celebrate the third mil-</p><p>lennium. It is surrounded by 1970s apartment</p><p>blocks in the suburb of Tor Tre Teste, about</p><p>10km (6 miles) east of the center of Rome.</p><p>The structure houses a main sanctuary, seat-</p><p>ing approximately 250 people, a chapel and a</p><p>baptistery. Three self-supporting concrete</p><p>70 71</p><p>Discoloration</p><p>above Architects may envis-</p><p>age their buildings as having</p><p>the coat of a white stallion and</p><p>be disappointed when finished</p><p>surfaces take on the motley</p><p>appearance of a pinto.</p><p>right Plastic films are often</p><p>used to maintain moisture</p><p>levels when curing concrete.</p><p>The evaporation and conden-</p><p>sation of water at different</p><p>points under a plastic film</p><p>can cause discoloration in the</p><p>curing process. Known as the</p><p>“greenhouse effect,” the use</p><p>of plastic films over curing</p><p>concrete can discolor the fin-</p><p>ish of the concrete.</p><p>page 71 The super white</p><p>exposed concrete finish of</p><p>Jubilee Church, Rome, show-</p><p>ing signs of discoloration on</p><p>the exterior of the building.</p><p>p_070_091_chapt_5_bp 17.10.2006 18:38 Uhr Seite 70</p><p>p_070_091_chapt_5_bp 17.10.2006 18:38 Uhr Seite 71</p><p>shells, symbolizing the Holy Trinity of the</p><p>Roman Catholic Church, are the focal point of</p><p>the exterior façade. Soaring from a travertine</p><p>stone plaza, the concrete walls, formed as</p><p>segments of a sphere, range in height from</p><p>17.4m to 27.4m (57 to 90 feet). The sail-like</p><p>forms were actually constructed as 10.9 tonne</p><p>(US short 12 ton) precast concrete elements</p><p>that were lifted into place. The curved panels</p><p>provide shelter from direct sun shining into</p><p>the church. To prevent the panels from dis-</p><p>coloring, brilliantly white cement incorporating</p><p>photocatalytic particles was used in the con-</p><p>crete mix. This special mixture of concrete</p><p>was intended to neutralize atmospheric pollu-</p><p>tants, keeping the panels brilliantly white.</p><p>Close inspection of the outside surface of the</p><p>panels reveals levels of discoloration. Unlike</p><p>white marble, glass or coated aluminum,</p><p>the concrete has changed in color just two</p><p>years after the building was completed. The</p><p>surfaces that have been exposed to sun,</p><p>rain, pollutants and temperature swings have</p><p>become blotchy. What was once an even</p><p>white concrete shell has turned into a quilt</p><p>pattern of different shades of white. In strong</p><p>contrast, the interior</p><p>side of the shells has</p><p>72 73</p><p>above What was once an</p><p>even white concrete shell has</p><p>turned into a quilt pattern of</p><p>different shades of white.</p><p>right In strong contrast, the</p><p>interior side of the shells has</p><p>maintained its original brilliant</p><p>white color and finish. Jubilee</p><p>Church.</p><p>Three self-supporting concrete</p><p>shells, symbolizing the Holy</p><p>Trinity of the Roman Catholic</p><p>Church, are the focal point of</p><p>the exterior façade. Jubilee</p><p>Church, Rome, 2003.</p><p>p_070_091_chapt_5_bp 17.10.2006 18:38 Uhr Seite 72</p><p>maintained its original brilliant white color and</p><p>finish. Like many contemporary projects, the</p><p>exposed concrete at Jubilee Church is not</p><p>painted, but was designed with the expecta-</p><p>tion that the concrete mix would sustain the</p><p>desired intense white appearance.</p><p>Other buildings have maintained a uniform</p><p>white appearance by using white aluminum</p><p>panels with coatings that have been tested</p><p>and are warranted against fading. The Getty</p><p>Center in Los Angeles provides a good exam-</p><p>ple of curved white aluminum panels that</p><p>have withstood the test of time and remain</p><p>brilliantly white on all elevations. The discol-</p><p>oration of the exterior concrete of the Jubilee</p><p>Church is minor; however, other forms of dis-</p><p>coloration can be much more dramatic.</p><p>Discoloration of Concrete</p><p>When concrete is exposed to view, architects</p><p>typically desire a uniform color and texture.</p><p>Many times they are disappointed when an</p><p>uneven color develops. “Pinto concrete”</p><p>describes the large, irregularly shaped, dark-</p><p>colored blotches on the surface of concrete.</p><p>Typically a problem with flatwork, the Portland</p><p>Cement Association has documented several</p><p>common causes of surface discoloration in</p><p>concrete. Each factor must be considered in</p><p>order to achieve the required finish.</p><p>Water-Cement Ratio</p><p>The change to the water-cement ratio of a</p><p>concrete mix can dramatically affect the color</p><p>of the concrete. A high water-cement ratio will</p><p>produce a lighter-colored concrete as com-</p><p>pared to a darker color of the same mix with a</p><p>low water-cement ratio. Although the mix may</p><p>have the same water-cement ratio in the deliv-</p><p>ery truck, variations can occur after the con-</p><p>crete is poured. For example, if the grade is</p><p>not uniformly moistened prior to pouring a</p><p>concrete slab on grade, localized dry spots</p><p>can reduce the water-cement ratio in the mix</p><p>and cause localized discoloration.</p><p>The Getty Center in Los Ange-</p><p>les, 1997, provides a good</p><p>example of curved white</p><p>aluminum panels that have</p><p>withstood the test of time and</p><p>remain brilliantly white on</p><p>all elevations.</p><p>right Raw materials used in</p><p>concrete can absorb addition-</p><p>al water when uncovered in a</p><p>construction yard. This addi-</p><p>tional water can slightly affect</p><p>the color of raw concrete.</p><p>p_070_091_chapt_5_bp 17.10.2006 18:38 Uhr Seite 73</p><p>Cement</p><p>Individual brands and types of cement may</p><p>differ in color depending on the source of the</p><p>raw material. A change in the type of cement</p><p>used during a project can cause a noticeable</p><p>color change in the concrete. If consistent</p><p>color is desired for a large project, a uniform</p><p>source of cement should be obtained prior to</p><p>starting the work.</p><p>Calcium Chloride</p><p>Calcium chloride is an admixture used to</p><p>accelerate the curing time of concrete. Great</p><p>care should be taken with calcium chloride</p><p>admixtures as relatively little chloride will</p><p>cause corrosion of embedded steel reinforce-</p><p>ment in moist conditions. In addition, calcium</p><p>chloride or admixtures containing calcium</p><p>chloride can darken a concrete surface. A</p><p>mottled appearance of light or dark spots can</p><p>result, depending on how the concrete is</p><p>cured and on the alkali content of the cement.</p><p>Repeated washing or weathering of the con-</p><p>crete can lesson this defect; however, light</p><p>spots can be particularly difficult to remove</p><p>and may require a chemical wash to improve</p><p>uniformity. Light spots on a dark background</p><p>can be caused by a low alkali to calcium chlo-</p><p>ride ratio. Dark spots on light background are</p><p>formed by a high alkali to calcium chloride</p><p>ratio. Spots can also be caused by coarse</p><p>aggregate particles located just below the sur-</p><p>face of the concrete. This type of discoloration</p><p>is known as “aggregate transparency.” The</p><p>coarse aggregate can interfere with the sur-</p><p>face mortar’s chloride content by blocking the</p><p>normal upward migration of chloride salts to</p><p>the drying surface. Water ponding of slabs</p><p>and the use of membrane curing compounds</p><p>can reduce the amount of discoloration</p><p>caused by chlorides in a concrete pour.</p><p>7574</p><p>right Concrete Discoloration.</p><p>A change in cement type or</p><p>the percentage of water in</p><p>a mix can create a shift in the</p><p>color.</p><p>The Pinakothek der Moderne,</p><p>an art museum in Munich,</p><p>completed in 2002, appears to</p><p>have discoloration caused by</p><p>concrete consolidation issues.</p><p>The underside of the roof slab</p><p>is exposed to view at the main</p><p>entrance.</p><p>The Pinakothek der Moderne.</p><p>p_070_091_chapt_5_bp 17.10.2006 18:38 Uhr Seite 74</p><p>Mineral Admixtures</p><p>Similar to the effect of mixing paint, colored</p><p>mineral admixtures will affect the color of the</p><p>final mix. For example, dark gray fly ash will</p><p>give concrete a darker color, whereas tan- or</p><p>beige-colored fly ashes will produce a tan-col-</p><p>ored concrete. Silica fume can give concrete a</p><p>dark gray tint.</p><p>Aggregates</p><p>The choice of aggregates will affect the color</p><p>of the finished concrete. For example, white</p><p>sand can produce uniform white-colored con-</p><p>crete. Dark areas can occur over coarse</p><p>aggregate particles near the surface. Aggre-</p><p>gates containing contaminates such as iron</p><p>oxides and sulfides can cause unsightly rust</p><p>stains if they are located near the surface of</p><p>concrete. The formed concrete ceiling and</p><p>large concrete lintels of the East Wing of the</p><p>National Gallery of Art in Washington, D.C.,</p><p>have a similar color to the Tennessee marble</p><p>used to clad the building.</p><p>The East Wing of the National</p><p>Gallery of Art in Washington,</p><p>D.C., competed 1978. The</p><p>architectural concrete is com-</p><p>posed of white cement, a</p><p>coarse pink aggregate, a fine</p><p>white aggregate and marble</p><p>dust from the same Tennessee</p><p>quarries that provided stone</p><p>for the exterior cladding.</p><p>The East Wing of the National</p><p>Gallery of Art.</p><p>p_070_091_chapt_5_bp 17.10.2006 18:38 Uhr Seite 75</p><p>Finishing</p><p>The finishing of a concrete slab can greatly</p><p>affect its color. Hard-steel troweling reduces</p><p>the water-cement ratio of the surface con-</p><p>crete, resulting in a darker color. Trowel burn</p><p>occurs when hard troweling of a concrete</p><p>surface is executed after the concrete has</p><p>become too stiff to be troweled properly. It can</p><p>cause extreme discoloration by significantly</p><p>reducing the water-cement ratio at the sur-</p><p>face. Metal abrasion on the surface of the</p><p>concrete can be an indication of the effect.</p><p>Trowel burns are extremely difficult to remove;</p><p>therefore, timely finishing of the concrete is</p><p>critical to maintaining uniform color.</p><p>Curing</p><p>Proper curing is essential for concrete. Great</p><p>care should be taken to ensure not only that</p><p>curing produces the optimum concrete quality</p><p>from a mix, but also that unwanted discol-</p><p>oration doesn’t occur. Discoloration of a con-</p><p>crete surface can be the result of procedures</p><p>or compounds used in the curing process.</p><p>Plastic films are often used to maintain mois-</p><p>ture levels when curing concrete. The evapo-</p><p>ration and condensation of water at different</p><p>points under a plastic film can cause discol-</p><p>oration in the curing process. Known as the</p><p>“greenhouse effect,” water condenses under</p><p>folds in the film and runs down to collect in</p><p>low spots where the plastic film is in contact</p><p>with the concrete. Because the concrete sur-</p><p>face is exposed to varying water contents and</p><p>thus non-uniform curing, slight to extreme dis-</p><p>coloration in the finish of the concrete can</p><p>occur. This type of discoloration is typically</p><p>associated with concrete mixtures containing</p><p>calcium chloride. The “greenhouse effect”</p><p>can be avoided by uniformly wetting the con-</p><p>crete as</p><p>it cures. If a plastic film is used dur-</p><p>ing curing, it should be laid as flat as possible</p><p>over the concrete.</p><p>Efflorescence</p><p>Efflorescence is a white crystalline deposit that</p><p>can develop on new concrete. Water in wet</p><p>hardened concrete contains dissolved salts</p><p>(usually a carbonate). As the salt-water solu-</p><p>tion evaporates, salts may be left on the sur-</p><p>face. Efflorescence can typically be removed</p><p>with a dry brushing and will not persist provid-</p><p>ed the salt-water solution and evaporation are</p><p>limited.</p><p>Forms</p><p>In a cast-in-place wall, the forms used to hold</p><p>the concrete during hardening can greatly</p><p>influence the color and texture of the con-</p><p>crete. Forms with different rates of absorption</p><p>produce different shades of color. For exam-</p><p>ple, unsealed wood forms will absorb moisture</p><p>from the concrete, which causes dark-colored</p><p>surfaces due to the reduced water-cement</p><p>ratio. Sealed, non-absorbing forms will lighten</p><p>surfaces of concrete, as water levels remain</p><p>high during the curing process. Discoloration</p><p>caused by varying absorption rates can also</p><p>be triggered by non-uniform application of</p><p>release agents to the forms, as can a change</p><p>in the type or brand of form release agent dur-</p><p>ing a project. Forms that separate or pull away</p><p>from the concrete surface, allowing air to</p><p>come in contact with the surface, can cause a</p><p>drying discoloration of the exposed area.</p><p>If formwork panel joints are not tight and</p><p>sealed, water and cement paste may ooze out</p><p>of the joints, creating defects in the hardened</p><p>concrete (see the “Surface Defects” chapter</p><p>for more details). The loss of water causes a</p><p>reduction in the water-cement ratio near the</p><p>leaking joint, resulting in a darker color. When</p><p>forms are used repeatedly for separate pours,</p><p>it can be difficult to maintain tight well-sealed</p><p>joints.</p><p>76 77</p><p>Trowel burn occurs when hard</p><p>troweling of a concrete surface</p><p>is executed after the concrete</p><p>has become too stiff.</p><p>The San Nicola Stadium in</p><p>Bari in the South of Italy,</p><p>1990, shows color differentia-</p><p>tion across the concrete sur-</p><p>face. Variation in the absorp-</p><p>tion of forms or inconsistent</p><p>application of the form release</p><p>agent can cause this type of</p><p>discoloration.</p><p>p_070_091_chapt_5_bp 17.10.2006 18:38 Uhr Seite 76</p><p>Release agents</p><p>A separating film known as a release agent</p><p>prevents adhesion between formwork and</p><p>concrete. Release agents ease the tasks of</p><p>cleanly stripping formwork from the concrete</p><p>component and of cleaning the formwork</p><p>surface. A highly effective release agent will</p><p>produce a better quality surface. It is impor-</p><p>tant to make sure that particles of loose dirt,</p><p>rust flakes, and construction debris are not</p><p>deposited onto the film as this can lead to</p><p>color changes of the finished concrete sur-</p><p>face. Release agents can be oils, waxes,</p><p>paints and emulsions. Pure mineral oil release</p><p>agents tend to leave residues on the form-</p><p>work. They are typically used in applications</p><p>where higher levels of surface finish quality</p><p>are not required. For the best finish the</p><p>release agent must not accumulate unevenly</p><p>on the formwork. It is also important that the</p><p>products used are waterproof in case bad</p><p>weather delays concrete pouring during the</p><p>construction process.</p><p>A pink color can occur on a formed surface if</p><p>the forming material or release agent contains</p><p>phenolics. The phenolics react with the alkali</p><p>hydroxide solutions in the fresh concrete to</p><p>cause staining. The best way to prevent this is</p><p>to use a non-staining release agent on wood</p><p>forms that have been properly sealed with a</p><p>non-phenolic sealer. The pink stain generally</p><p>disappears after a few weeks of air-drying. Col-</p><p>oration of concrete is not always a problem;</p><p>indeed, in some cases it is the desired effect.</p><p>Colored Concrete</p><p>In many cases concrete is intentionally col-</p><p>ored to provide contrast in a façade. Cincin-</p><p>nati’s Contemporary Arts Center, completed in</p><p>2003, was designed around the concept of an</p><p>“urban carpet” to draw in pedestrian traffic</p><p>Contemporary Arts Center,</p><p>Cincinnati, Ohio, 2003.</p><p>Colored concrete on the build-</p><p>ing façades differentiates the</p><p>shifting volumes.</p><p>right above Contemporary</p><p>Arts Center. Unintentionally,</p><p>the concrete that bears the</p><p>building’s name appears to</p><p>have been cast with a different</p><p>method than the other panels</p><p>adjacent to it.</p><p>right Met Lofts, Los Angeles,</p><p>completed in 2006 by the firm</p><p>Johnson Fain. Surface discol-</p><p>oration on exterior concrete</p><p>walls is intentionally left</p><p>untouched to provide an urban</p><p>feel to the façade. Stains</p><p>resulting from the form release</p><p>agent and efflorescence have</p><p>not been removed.</p><p>p_070_091_chapt_5_bp 17.10.2006 18:38 Uhr Seite 77</p><p>from the downtown streets of Cincinnati. Lay-</p><p>ers of concrete begin outside at the base of</p><p>the building and unfold through the interior</p><p>spaces. Colored concrete on the building</p><p>façades further differentiates the shifting vol-</p><p>umes. Coloring is achieved by including a pig-</p><p>ment in the mix. Uncolored panels bearing the</p><p>name of the museum appear to be uninten-</p><p>tionally darker in color. The origin of this color</p><p>shift may be related to this particular panel</p><p>being constructed at a later date than the rest</p><p>of the adjacent panels on the façade. In an</p><p>effort to avoid issues of non-uniformity of con-</p><p>crete, some projects choose to exaggerate dis-</p><p>coloration.</p><p>The Ruffi Gymnasium, completed in 2001 in</p><p>Marseilles, by Rémy Marciano, provides an</p><p>excellent solution to the natural variation that</p><p>can be experienced between concrete pours.</p><p>Adjacent to the St. Martin’s Church, the semi-</p><p>industrial nature of the gym design is contex-</p><p>tual with the semi-industrial, shed vernacular</p><p>of the region. The concrete panels on the</p><p>exterior of the building provide privacy and</p><p>durability for three interconnecting gyms.</p><p>Instead of trying for a uniform finish, the con-</p><p>crete is treated to accentuate differences</p><p>between different pours. The patchwork of dif-</p><p>78 79</p><p>right and below Ruffi Gymna-</p><p>sium, Marseilles, 2001. The</p><p>patchwork of differently toned</p><p>concrete panels on the façade</p><p>provides a deliberately pat-</p><p>terned effect. The panel colors</p><p>were achieved by applying dif-</p><p>ferent types of varnish to the</p><p>concrete surface.</p><p>below right Ruffi Gymnasium.</p><p>The reflection of St. Martin’s</p><p>Church is appropriately visible</p><p>in the unique window.</p><p>p_070_091_chapt_5_bp 17.10.2006 18:38 Uhr Seite 78</p><p>ferently toned concrete panels on the façade</p><p>provides a deliberately patterned effect. The</p><p>panel colors were achieved by applying differ-</p><p>ent types of varnish to the concrete surface.</p><p>Painting Concrete</p><p>Painting can provide a uniform appearance to</p><p>concrete. It can also be useful for covering</p><p>defects due to construction or vandalism. Fur-</p><p>thermore, a painted surface will provide pro-</p><p>tection for reinforced concrete, depending on</p><p>the paint formulation. The concrete works of</p><p>Santiago Calatrava are many times painted to</p><p>give the structure a uniform appearance.</p><p>Coatings have varied in performance through</p><p>the years and have not always been effective</p><p>in adhering to a concrete substrate. Great his-</p><p>toric works have often struggled with painted</p><p>concrete. The Guggenheim Museum, New</p><p>York, was completed shortly after Frank Lloyd</p><p>Wright died, in 1959. This building has had a</p><p>continual problem with the exterior paint. The</p><p>façade is frequently in disrepair and needs to</p><p>be painted every four years. These problems</p><p>could be related to the surface preparation of</p><p>the concrete or to the coating used to cover it.</p><p>New painting products have been developed</p><p>which provide a longer-lasting elastomeric</p><p>solution for buildings. The painting industry</p><p>today has a variety of products to provide a</p><p>uniform appearance to concrete. Some paint</p><p>products can be classified as stains because</p><p>they penetrate the surface of the material. A</p><p>stain is thus integral to the concrete and does</p><p>not peel off. Light-tinted stains will maintain a</p><p>certain amount of color variation that may be</p><p>desired in the finished</p><p>product.</p><p>Chemical Staining</p><p>Concrete surfaces can be chemically stained</p><p>to give variations in color and texture. The</p><p>Mustakivi School and Community Center in</p><p>Helsinki uses chemically stained precast con-</p><p>crete panels to break up the uniformity of a</p><p>complex of buildings clad with precast con-</p><p>crete sandwich panels. The exterior panels of</p><p>the school block form a load-bearing struc-</p><p>ture, which supports precast floor planks at</p><p>the first floor and roof level. The precast sand-</p><p>wich panels consist of two internally connect-</p><p>ed concrete wythes separated by an insulated</p><p>core. The colors on the external panel surface</p><p>represent a canvas of abstract art, of neutral</p><p>tones and regular shapes arranged in an</p><p>asymmetric design. Not all of the surface col-</p><p>ors are even; some panels are rusty gold in</p><p>appearance, some look green with wood stain,</p><p>and some are yellow in color. The basic earth</p><p>colors of iron oxides and copper sulphides are</p><p>particularly interesting. This project refutes the</p><p>notion that concrete sandwich panels have to</p><p>be boring. The chemical stain is a very thin</p><p>layer on the surface of the concrete panel.</p><p>The stain is durable under exposure to rain or</p><p>snow, but cannot withstand heavy abrasion. A</p><p>surface treatment of commercial sealant was</p><p>used to avoid dirt and unwanted graffiti pene-</p><p>trating the concrete micro-pores of the panel</p><p>surface. The appearance of chemical staining</p><p>Guggenheim Museum, New York,</p><p>was completed shortly after Frank</p><p>Lloyd Wright died, in 1959.</p><p>Guggenheim Museum, New York.</p><p>The façade is frequently in disrepair</p><p>and needs to be painted every four</p><p>years.</p><p>p_070_091_chapt_5_bp 17.10.2006 18:38 Uhr Seite 79</p><p>is largely dependent on the absorbency of the</p><p>concrete surface and its pore structure. Instal-</p><p>lation requires a certain amount of artistry and</p><p>can be much more labor-intensive than stand-</p><p>ard pigmented concrete.</p><p>The staining of concrete can be seen by some</p><p>groups as not only beautiful, but divine. In</p><p>April 2005, the water stains on a concrete wall</p><p>under a Chicago highway became a small pil-</p><p>grimage location for hundreds of kneeling visi-</p><p>tors. Many believe that the stain was not just</p><p>water mixed with salts leaking through the</p><p>underpass wall from the highway above, but</p><p>the apparition of the Virgin Mary created to</p><p>console the world for the loss of Pope John</p><p>Paul II. The stained concrete became a place</p><p>of worship for many Christians in Chicago.</p><p>Although this image was only visible for a few</p><p>months, the coloration of concrete through a</p><p>chemical process can create permanent</p><p>images that will remain on the surface of a</p><p>structure for many years.</p><p>80 81</p><p>The Mustakivi School and</p><p>Community Center in Helsinki,</p><p>1998, designed by ArkHouse,</p><p>uses chemically stained</p><p>precast concrete panels for</p><p>non-uniform earthy tones.</p><p>below Precast concrete sand-</p><p>wich panels, Mustakivi School</p><p>and Community Center.</p><p>1 Exterior wythe panel is</p><p>chemically stained</p><p>2 Interior wythe provides for</p><p>building structure</p><p>The apparition of the Virgin</p><p>Mary was caused by a water</p><p>stain on a concrete wall.</p><p>Chicago, 2005.</p><p>p_070_091_chapt_5_korr_bp 27.10.2006 14:17 Uhr Seite 80</p><p>Photoengraved Concrete</p><p>Concrete can be photoengraved through a</p><p>process similar to silk-screening. A photo is</p><p>screen-printed as a layer of tiny dots onto a</p><p>polystyrene sheet, but instead of using paint</p><p>or ink, the image is printed with a cure</p><p>retarder liquid. A cure retarder is a chemical</p><p>that slows the cure rate of concrete. The pre-</p><p>pared sheet is then placed into the concrete</p><p>mold and the concrete poured on top of it.</p><p>When the concrete has set, it is removed from</p><p>the mold and pressure-washed, revealing a</p><p>half-tone image on the finished concrete sur-</p><p>face. Eberswalde Technical School, designed</p><p>by Herzog and de Meuron, used photoen-</p><p>graved concrete to provide detail to what</p><p>would otherwise be a flat concrete box. The</p><p>photoengraved pattern was also applied to the</p><p>glass using a silkscreen coating technique.</p><p>The concrete impression process has proven</p><p>to be very successful, retaining its color and</p><p>detail many years after completion. Like many</p><p>finished surfaces, a regular pattern of color</p><p>variation can hide any slight discoloration of</p><p>the surface. The discoloration of materials is</p><p>not limited to concrete. Natural stone can also</p><p>have shifts in color that are not anticipated.</p><p>Eberswalde Technical School,</p><p>built in Eberswalde near</p><p>Berlin, in 1999.</p><p>Concrete can be photo-</p><p>engraved through a process</p><p>similar to silk-screening.</p><p>Eberswalde Technical School.</p><p>The concrete impression</p><p>process has proven to be very</p><p>successful, retaining its color</p><p>and detail many years after</p><p>completion.</p><p>p_070_091_chapt_5_bp 17.10.2006 18:38 Uhr Seite 81</p><p>Discoloration of Natural Stone</p><p>Many natural stones exhibit variations in color</p><p>and texture. Stone is after all a natural materi-</p><p>al quarried from the ground. The Washington</p><p>Monument in Washington, D.C., serves as</p><p>a reminder of how the color of stone can vary.</p><p>Construction of the monument started in 1836</p><p>but was halted during the American Civil War.</p><p>After the war, work continued on the monu-</p><p>ment. There is a clear demarcation in the</p><p>sculpture from when the work stopped and</p><p>started again. The color shift could be attrib-</p><p>uted to a change in the location of the quarry</p><p>supplying the stone, or to discoloration that</p><p>occurred between halting the project and the</p><p>completion time. This element of discoloration</p><p>tells an important story about the history</p><p>of the monument and of the United States.</p><p>Other interesting forms of stone discoloration</p><p>can be seen in the city of Washington, D.C.</p><p>Staining of Stone</p><p>The East Wing of the National Gallery of Art,</p><p>in Washington, D.C., designed by architect</p><p>I. M. Pei, has the most famous example of</p><p>stained stone in the history of modern archi-</p><p>tecture. The sleek, angular modernism of the</p><p>museum, completed in 1978, is in strong</p><p>contrast to the neoclassical design of the</p><p>1941 Natural Gallery of Art just to the west.</p><p>Both designs use the same Tennessee pink</p><p>82 83</p><p>marble to enclose their walls; both, however,</p><p>take on completely different forms. In 1986,</p><p>The American Institute of Architects, College</p><p>of Fellows, designated the East Wing for the</p><p>National Gallery of Art as one of the ten most</p><p>successful examples of architectural design in</p><p>the United States. The famous solid corner</p><p>pieces have provided the architectural com-</p><p>munity with an icon. Visitors touch the corner</p><p>both in tradition and genuine curiosity leaving</p><p>one famous stain. A similar stain occurs</p><p>inside the building on a sign carved in stone</p><p>that bears the building architect’s name. The</p><p>East Wing walls consist of exterior blocks of</p><p>stone supported by stainless steel connec-</p><p>tions from concrete and brick core walls aver-</p><p>aging 30cm (12 inches) in thickness. Neo-</p><p>prene strips between blocks allow for expan-</p><p>sion and contraction while eliminating the</p><p>need for sealant or mortar joints. This design</p><p>detail reduces the need for maintenance</p><p>through failed sealant joints or tuckpointing.</p><p>The typical stone joints for this project are not</p><p>in contact with any sealant.</p><p>Contact with certain sealants can often cause</p><p>discoloration of stone. The silicone oil or plas-</p><p>ticizers used to improve the elastic modulus</p><p>The East Wing of the National</p><p>Gallery of Art, in Washington,</p><p>D.C., has the most famous</p><p>example of stained stone in</p><p>the history of modern architec-</p><p>ture.</p><p>below The Washington Mon-</p><p>ument in Washington, D.C.,</p><p>shows a clear demarcation in</p><p>the sculpture from when the</p><p>work stopped and started</p><p>again.</p><p>Woman touching the National</p><p>Gallery of Art sharp corner.</p><p>p_070_091_chapt_5_bp 17.10.2006 18:38 Uhr Seite 82</p><p>(ability to expand and contract) of certain</p><p>sealants and primers can lead to staining of</p><p>the stone. Porous materials exposed to</p><p>sealants with a high plasticizer content will be</p><p>stained. Oil-based caulks are not recom-</p><p>mended for use with limestone. Many butyl</p><p>sealants can</p><p>stain stone, and the most com-</p><p>mon occurrence of this problem is contact</p><p>with high-modulus silicone. Uncured silicone</p><p>oil can leach into the stone, permanently dis-</p><p>coloring the material. The collection of dirt on</p><p>silicone sealant and horizontal projections can</p><p>also lead to staining of stone. As rainwater</p><p>washes over these features, it can deposit</p><p>excessive amounts of dirt on isolated areas of</p><p>the wall. This concentrated streaking can lead</p><p>to unwanted staining. Water runoff can be a</p><p>major source of staining on concrete, stone</p><p>and masonry buildings.</p><p>Natural Discoloration</p><p>Indiana and Indianapolis were named after</p><p>their first human inhabitants. Completed in</p><p>1989, the Eiteljorg Museum of American Indi-</p><p>ans and Western Art, pays tribute to this</p><p>group. The 10,960m2 (118,000 square feet)</p><p>honey-colored museum is composed of nearly</p><p>12,000 pieces of hand-cut Minnesota</p><p>dolomite, a stone creating the feel of the</p><p>Southwestern Pueblo. Plum-colored German</p><p>sandstone serves as the building’s base. It</p><p>was decided to allow algae to decorate the</p><p>museum walls. In 2005, construction of the</p><p>Mel and Joan Perelman Wing doubled the</p><p>size of the institution. The new north end of</p><p>the museum faces the Indianapolis Center</p><p>Canal. The finish of the stone changed</p><p>between completion of the original building</p><p>and the time it was expanded. The difference</p><p>comes partly from the algae growth. If algae</p><p>discoloration is not wanted in heavily planted</p><p>wetted areas, application of a water repellent</p><p>coating should be considered. These coatings</p><p>form a hydrophobic layer that requires renew-</p><p>al every two to three years as its effect</p><p>reduces with time. If an alga is to be allowed</p><p>to build up on concrete surfaces, the cover to</p><p>steel reinforcement must be thicker. Other</p><p>forms of natural discoloration are less desir-</p><p>able than growth of algae on the Eiteljorg</p><p>Museum of American Indians and Western</p><p>Art.</p><p>Completed in 1989, the Eitel-</p><p>jorg Museum of American</p><p>Indians and Western Art pays</p><p>tribute to this group.</p><p>above The finish of the stone</p><p>changed between completion</p><p>of the original building and the</p><p>time it was expanded. The</p><p>difference comes partly from</p><p>the algae growth. Eiteljorg</p><p>Museum of American Indians</p><p>and Western Art, Indianapolis.</p><p>page 82 above Neoprene</p><p>strips between stone blocks</p><p>open up at locations where</p><p>the stone blocks have shifted.</p><p>The East Wing of the National</p><p>Gallery of Art.</p><p>page 82 below Similar to the</p><p>exterior corner, a stain occurs</p><p>inside the building on a sign</p><p>carved in stone that bears the</p><p>building architect’s name. The</p><p>East Wing of the National</p><p>Gallery of Art.</p><p>p_070_091_chapt_5_bp 17.10.2006 18:38 Uhr Seite 83</p><p>Water Runoff</p><p>Uncontrolled water runoff on a building can</p><p>leave hideous stains on a façade. Examples</p><p>of water-runoff stains can be found in every</p><p>major city in the world. Completed in 1953,</p><p>Hall Auditorium, at Oberlin College, Ohio, pro-</p><p>vides a good example of how white marble</p><p>can be permanently stained from run-off</p><p>water. The top portion of the undulating stone</p><p>façade has marks from a soffit that does</p><p>not drip water away from the façade. Water</p><p>runoff can be attributed to poor design or</p><p>poor building maintenance.</p><p>Properly detailed drip edges can direct water</p><p>away from wall surfaces, protecting them from</p><p>discoloration. If no drips are provided, water</p><p>marks will be present on dark surfaces as well</p><p>as light ones. The headquarters of the Berlin</p><p>Water Works, House III was constructed in</p><p>2000, in strong contrast to the neighboring</p><p>Baroque buildings of Berlin. The five-story</p><p>façade is composed of broken, prism-like</p><p>forms the color of granite and is based on the</p><p>styles of Cubism. Water stains can be seen at</p><p>the changes of the planes of the façade.</p><p>84 85</p><p>Hall Auditorium at Oberlin</p><p>College, Ohio, 1953.</p><p>The top portion of the undulat-</p><p>ing stone façade has marks</p><p>from a soffit that does not drip</p><p>water away from the façade.</p><p>Hall Auditorium at Oberlin</p><p>College.</p><p>p_070_091_chapt_5_bp 17.10.2006 18:38 Uhr Seite 84</p><p>Light-colored concrete shows the worst stains.</p><p>Water runoff from large horizontal surfaces</p><p>can carry extensive amounts of dirt down the</p><p>face of a building. The Federal Chancellery</p><p>building, completed in Berlin in 2001, was</p><p>part of a “ribbon” of government buildings</p><p>running along the River Spree, uniting East</p><p>and West Berlin. This series of buildings is</p><p>architecturally linked by formal blocks with</p><p>large circular cut-outs. One façade that faces</p><p>the River Spree is badly stained from rainwa-</p><p>ter. The circular cut-out in the façade has a</p><p>large projecting ledge that collects dirt and</p><p>other air-borne debris. After rainfall, the water</p><p>runs off the sill, takes the dirt with it and</p><p>streaks down the face of the building, discol-</p><p>oring the façade. The forces of nature can</p><p>permanently stain our buildings; however, the</p><p>most troublesome marks on a building façade</p><p>in an urban environment come from human</p><p>intervention.</p><p>right After rainfall, the water</p><p>runs off the sill, takes the dirt</p><p>with it and streaks down the</p><p>face of the building, discolor-</p><p>ing the façade. The Federal</p><p>Chancellery building, Berlin,</p><p>2001.</p><p>The headquarters of the Berlin</p><p>Water Works, House III, 2003.</p><p>Water stains can be seen at</p><p>the changes of the planes of</p><p>the façade. The headquarters</p><p>of the Berlin Water Works,</p><p>House III Close up.</p><p>p_070_091_chapt_5_bp 17.10.2006 18:38 Uhr Seite 85</p><p>Vandalism</p><p>In an urban environment, graffiti and other</p><p>acts of vandalism can discolor exterior walls</p><p>wherever they are accessible; however, there</p><p>are ways of protecting the appearance of</p><p>façades. One method is to make the surface</p><p>impervious to the markings of vandals. The</p><p>four exterior walls of the Bregenz Art Museum</p><p>by Peter Zumthor are composed of shingled,</p><p>frameless translucent glass covering the</p><p>entire concrete structure. These details make</p><p>it difficult to permanently paint or mark the</p><p>exterior walls of the museum. Paint markings</p><p>can be scraped off the glass easily. Concrete,</p><p>stone and masonry surfaces are more porous</p><p>than glass and require a different strategy.</p><p>Anti-graffiti protection can be provided</p><p>through coatings specially made for concrete,</p><p>stone, and terra-cotta panels. These coatings</p><p>often take the form of a very thick paint that</p><p>prevents the graffiti spray from bonding to the</p><p>surface. The graffiti is then easy to remove.</p><p>86 87</p><p>The new Innsbruck Ski Jump,</p><p>designed by Zaha Hadid and</p><p>completed in 2002, provides</p><p>an excellent drip edge at the</p><p>window sill.</p><p>Innsbruck Ski Jump.</p><p>above Bregenz Art Museum,</p><p>Bregenz, Austria, 1997. All-</p><p>glass walls are less susceptible</p><p>to graffiti than a porous stone</p><p>or concrete wall.</p><p>page 87 These glass details</p><p>make it difficult to permanent-</p><p>ly paint or mark the exterior</p><p>walls of the museum.</p><p>Bregenz Art Museum,</p><p>Bregenz, Austria, 1997.</p><p>p_070_091_chapt_5_korr_bp 27.10.2006 14:16 Uhr Seite 86</p><p>p_070_091_chapt_5_bp 17.10.2006 18:38 Uhr Seite 87</p><p>A second strategy to combat vandalism is to</p><p>make the enclosure panels easily replaceable.</p><p>The Gary Comer Youth Center was designed</p><p>by John Ronan Architects to provide practice</p><p>and performance space for the South Shore</p><p>Drill Team and Performing Arts Ensemble</p><p>in Chicago. Completed in 2006, the building</p><p>is clad with a colorful array of architectural</p><p>fiber cement façade panels. The panels are</p><p>approximately 6.25mm (1/4 inch) thick and</p><p>riveted to a metal framing with stainless steel</p><p>fasteners. Because the building is located in</p><p>an active urban environment, the design for</p><p>the building envelope at the street level had to</p><p>consider the possibility of graffiti on the walls.</p><p>If panels are discolored beyond repair, they</p><p>can easily be replaced with panels from stock.</p><p>The Gary Comer Youth Center,</p><p>Chicago, 2006.</p><p>The building is clad with a</p><p>colorful array of architectural</p><p>fiber cement façade panels.</p><p>The Gary Comer Youth Center.</p><p>The fiber cement façade</p><p>panels can easily be replaced</p><p>if damaged from vandalism.</p><p>The</p><p>Gary Comer Youth Center.</p><p>p_070_091_chapt_5_bp 17.10.2006 18:38 Uhr Seite 88</p><p>The Pulitzer Foundation build-</p><p>ing in St. Louis provides a</p><p>coating of the anti-graffiti proj-</p><p>ect every three years. The</p><p>coating is only applied at the</p><p>lower level of the building and</p><p>is not visible after it has dried.</p><p>below IRCAM Music Exten-</p><p>sion, Paris, 1990. The office</p><p>building has been marked</p><p>with graffiti. Removal of the</p><p>marks has discolored the</p><p>terra-cotta panel system.</p><p>p_070_091_chapt_5_korr_bp 27.10.2006 14:23 Uhr Seite 89</p><p>90 91</p><p>Uniform color in raw cast-in-place concrete</p><p>can be achieved. The key is to provide consis-</p><p>tent ingredients for each pour. A concrete mix</p><p>typically consists of four major ingredients:</p><p>cement, course aggregate, sand and water.</p><p>Because Portland cement is a natural materi-</p><p>al that can come from a variety of quarries,</p><p>color consistency can be achieved only by</p><p>purchasing material that originates from the</p><p>same source. Maintaining consistent water</p><p>in the mix can be difficult because the raw</p><p>materials in concrete are often absorbent and</p><p>left uncovered in construction yards. A con-</p><p>crete mix containing highly absorbent lime-</p><p>stone aggregate can have inconsistent water</p><p>content in the mix, depending on whether or</p><p>not the limestone is wet or dry prior to mixing.</p><p>In addition to maintaining a consistent source</p><p>of Portland cement for its mix, the Pulitzer</p><p>Foundation for the Arts in St. Louis, Missouri,</p><p>provided uniformity in color for the exposed</p><p>concrete walls by selecting Merrimac stone in</p><p>lieu of limestone for aggregate. Merrimac is</p><p>an abundant local stone in the St. Louis area,</p><p>which could easily be obtained from the same</p><p>quarry for the entire project. Using 19mm</p><p>(3/4 inch) rock, 6.25mm (1/4 inch) river gravel,</p><p>and sand, Merrimac provided a non-absorbent</p><p>course and fine aggregate for the concrete</p><p>mix that aided in maintaining a consistent</p><p>water-cement ratio and thus a more uniform</p><p>color for the exposed walls.</p><p>Remedies for Concrete Discoloration</p><p>The Portland Cement Association offers</p><p>several remedies for improving discolored</p><p>concrete. These solutions are not necessarily</p><p>designed for stains caused by spillage or</p><p>application of foreign substances. The first</p><p>and typically effective remedy for concrete</p><p>discoloration is an immediate, thorough flush-</p><p>ing of the concrete surface with water. By</p><p>alternately flushing and drying the concrete</p><p>surfaces overnight, discoloration can be</p><p>reduced. Hot water is typically more effective</p><p>and scrub brushing helps to remove any</p><p>unsightly surface deposits. A power wash can</p><p>be a useful alternative to brush scrubbing;</p><p>however, this must be done with care so as</p><p>not to damage the surface of the concrete. If</p><p>water scrubbing is not effective, acids and</p><p>other chemicals can be used with care to</p><p>remove discoloration. A dilute solution of one</p><p>to two percent to 2% hydrochloric or muriatic</p><p>acid can be used to remove persistent car-</p><p>bonate efflorescence. Harsh acids can expose</p><p>the aggregate and should not be used unless</p><p>this is the desired effect. Acid washing using</p><p>weaker acids such as three percent acetic</p><p>acid or three percent phosphoric acid will also</p><p>remove efflorescence and lessen mottled dis-</p><p>coloration caused by uneven curing. Before</p><p>acid is applied, the surface must be thorough-</p><p>ly dampened with water to prevent the acid</p><p>from being absorbed deep into the concrete.</p><p>Treating a dry slab with ten percent solution of</p><p>caustic soda (sodium hydroxide) gives some</p><p>success in blending light spots with a dark</p><p>background. The sodium hydroxide solution</p><p>should be left on the surface of the concrete</p><p>for one to two days, followed by a thorough</p><p>rinsing with water.</p><p>The best method for removing most forms of</p><p>discoloration from concrete is to treat the dry</p><p>surface with a 20 to 30 percent water solution</p><p>of diammonium citrate. Treatment consists</p><p>of applying the solution to the dry surface for</p><p>about 15 minutes. The white gel formed by</p><p>the solution should be diluted with water and</p><p>continuously agitated by brushing. The gel</p><p>should be scrubbed off with water after the</p><p>If left unsealed, some stones</p><p>can stain due to standing</p><p>water.</p><p>below Staining of stone from</p><p>contact with sealants can only</p><p>be avoided by using materials</p><p>that have been successfully</p><p>tested for staining with the</p><p>stone in question.</p><p>right Stone replacement is</p><p>the only method for removing</p><p>the picture-frame effect of</p><p>sealant joint stains.</p><p>How Can Surface Discoloration</p><p>Be Avoided and Repaired?</p><p>p_070_091_chapt_5_bp 17.10.2006 18:38 Uhr Seite 90</p><p>Lessons Learned</p><p>treatment. Water curing between or after</p><p>treatments increases the treatment’s effective-</p><p>ness. Typically, two or three treatments will</p><p>do the job. Acid and other chemical washes</p><p>should be tested on a small, inconspicuous</p><p>portion of the discolored concrete to insure</p><p>the remedy is effective. The cure can, in</p><p>some cases, be worse than the disease, and</p><p>care should be taken when experimenting</p><p>with different techniques and materials. As a</p><p>general rule, the sooner the remedial methods</p><p>are applied to discolored concrete, the more</p><p>effective they will be.</p><p>Localized stains on concrete can be treated</p><p>with muriatic acid; however, it may be neces-</p><p>sary to clean all areas of the concrete with the</p><p>solution in order to provide a uniform appear-</p><p>ance. An acid wash, in addition to removing</p><p>troubling stains, may also remove the calcium</p><p>carbonate deposits that are normally left on</p><p>the surface of concrete flatwork. Removing</p><p>the calcium carbonate along with the stains</p><p>will reveal the darker underlying concrete.</p><p>Uniform treatment of all areas will minimize</p><p>the risk of an uneven finish.</p><p>Stone Discoloration</p><p>Sealers are used to prevent discoloration of</p><p>natural stone. Sealers are particularly neces-</p><p>sary for stones with high absorptions rates,</p><p>such as marble. Granite has lower absorption</p><p>rates; however, for counter tops with a pol-</p><p>ished finish, sealers need to be periodically</p><p>reapplied in order to prevent staining of the</p><p>stone. Staining of stone from contact with</p><p>sealants can only be avoided by using materi-</p><p>als that have been successfully tested for</p><p>staining with the stone in question. Stone</p><p>replacement is the only method for removing</p><p>the picture-frame effect of sealant joint stains.</p><p>As with concrete, discoloration of stone due</p><p>to dirty water runoff can be remedied with</p><p>effective details that drain water away from</p><p>vertical surfaces of the building. This is parti-</p><p>cularly important when vertical surfaces are</p><p>adjacent to large horizontal projections like</p><p>window sills. Stone that is dirty from water</p><p>runoff can be cleaned; however, without</p><p>removing the cause, discoloration is sure to</p><p>come back.</p><p>Stone replacement is the</p><p>only method for removing the</p><p>picture-frame effect of sealant</p><p>joint stains.</p><p>1</p><p>In order to minimize discoloration of concrete,</p><p>do not use calcium chloride admixtures, but</p><p>use consistent/uniformly proportioned con-</p><p>crete ingredients. Also use proper, consistent,</p><p>timely finishing and curing practices. Any dis-</p><p>ruption or change in the concrete mix, form-</p><p>work, finishing or curing can result in surface</p><p>discoloration of the concrete.</p><p>2</p><p>Some level of variation is to be expected with</p><p>concrete. Uniformity of concrete color and</p><p>texture requires consistency of mix and place-</p><p>ment. Slight variations can cause dramatic</p><p>discoloration. Discoloration is typically the</p><p>result of changes in either the concrete’s mix</p><p>composition or in the method by which the</p><p>concrete was produced.</p><p>3</p><p>In order to obtain color uniformity in a con-</p><p>crete mix, quality-control methods must</p><p>ensure that equivalent materials are used in</p><p>all pours along with equal water content. Water</p><p>can be present in absorbent materials used in</p><p>a mix, or in the surfaces onto which the con-</p><p>crete is poured. Variation in water contact can</p><p>change the color of the finished product.</p><p>4</p><p>Paint can be applied to correct discoloration</p><p>of concrete; however, this</p><p>type of surface</p><p>coating will not be as durable as finishes that</p><p>are integral to the mix.</p><p>5</p><p>Concrete designs must consider the limita-</p><p>tions of all materials used on a project. Expo-</p><p>sure to ultraviolet radiation can fade materials</p><p>with organic pigments. Inorganic materials</p><p>typically have a better resistance to fading.</p><p>6</p><p>The staining of concrete can be used as a</p><p>design feature. Controlled discoloration can</p><p>provide elegant detail to what would otherwise</p><p>be a bland, flat façade.</p><p>7</p><p>Designers must consider how water runs off a</p><p>building. Uncontrolled water runoff can leave</p><p>a building streaked with dirt and unsightly</p><p>stains.</p><p>8</p><p>Vandalism of building façades in an urban</p><p>environment must be anticipated. A variety of</p><p>non-visible solutions exist to protect building</p><p>elements from graffiti.</p><p>Silicone sealant can stain</p><p>white marble.</p><p>p_070_091_chapt_5_bp 17.10.2006 18:38 Uhr Seite 91</p><p>In the summer of 2000, Chicago experienced</p><p>a series of stone-cladding failures that height-</p><p>ened people’s awareness of its deteriorating</p><p>high-rise masonry buildings. In one incident,</p><p>large chunks of masonry from Chicago’s</p><p>La Salle Street Building fell to the street, dam-</p><p>aging cars. New York City is faced with a simi-</p><p>lar risk. The root of the problem is found not</p><p>in the stone, but in the metal connections that</p><p>tie the stone cladding to the building. This</p><p>mode of failure may be traced back to the</p><p>history of construction for these great cities.</p><p>Masonry cladding systems providing façades</p><p>in materials such as brick, limestone and</p><p>terra cotta were developed with the birth of</p><p>skeleton construction methods for high-rise</p><p>buildings in the late 1800s. Steel-frame</p><p>construction quickly replaced load-bearing</p><p>masonry walls at the turn of the century as a</p><p>means of forming taller buildings. With time</p><p>these innovative enclosures are showing their</p><p>age. The symptoms of deterioration include</p><p>cracked, delaminated, spalled, and displaced</p><p>sections of masonry. The most common</p><p>mechanism of failure for these large masonry</p><p>buildings is the corrosion of the metal fasten-</p><p>ers that support the façades.</p><p>Contemporary designers are aware of the</p><p>limited durability of these old walls and have</p><p>developed new methods of attaching stone</p><p>cladding that greatly improve corrosion resist-</p><p>ance. Today, galvanized steel or stainless steel</p><p>fasteners are used to secure stone cladding.</p><p>The aim of these new materials is to improve</p><p>the life of our building cladding systems by</p><p>limiting corrosion.</p><p>Concrete buildings are not exempt from corro-</p><p>sion problems. The success of contemporary</p><p>reinforced concrete rests on the tensile force</p><p>of embedded steel reinforcement. However,</p><p>without adequate concrete cover, steel rein-</p><p>forcement will corrode with resulting rust</p><p>stains and concrete spalls, leading ultimately</p><p>to structural damage. New developments in</p><p>concrete construction have moved toward</p><p>92 93</p><p>Corrosion</p><p>above Removal of the stone</p><p>cladding reveals the corroded</p><p>steel structure.</p><p>right Corrosion of carbon</p><p>steel can lead to terrible rust</p><p>stains.</p><p>page 93 Corner conditions</p><p>experience higher wind loads</p><p>and thermal expansion, thus</p><p>requiring the most significant</p><p>repair work.</p><p>p_092_107_chapt_6_bp 18.10.2006 11:18 Uhr Seite 92</p><p>p_092_107_chapt_6_bp 18.10.2006 11:18 Uhr Seite 93</p><p>greater corrosion resistance. Epoxy-coated</p><p>steel and stainless steel reinforcement have</p><p>added additional protection against corrosion,</p><p>as have improved concrete mixes. New prod-</p><p>ucts like fiber-reinforced concrete and fiber-</p><p>reinforced polymer (FRP) reinforcing bars are</p><p>aimed at the total elimination of steel rein-</p><p>forcement from concrete. Modern construc-</p><p>tion methods are tackling corrosion of struc-</p><p>tures; however, with the introduction of any</p><p>new product, care must be taken to avoid the</p><p>possibility of catastrophic failure in years to</p><p>come.</p><p>The masonry industry experienced a corrosion</p><p>catastrophe in the mid 1970s. A high-tensile-</p><p>strength mortar additive was developed and</p><p>marketed under the name Sarabond. Many</p><p>thought it was a breakthrough in mortar tech-</p><p>nology. Sarabond was first introduced to the</p><p>construction market in 1965 as a mortar addi-</p><p>tive that increased masonry’s flexural strength</p><p>fourfold and its tensile strength threefold over</p><p>conventional mortar. It was intended to revolu-</p><p>tionize the use of brick in high-rise construc-</p><p>tion. A laboratory cousin of Saran Wrap,</p><p>Sarabond was intended to make mortar as</p><p>strong as the bricks it joined. Made of saran</p><p>latex, it was intended to render mortar less</p><p>permeable to air and water infiltration, thus</p><p>protecting any embedded steel from corro-</p><p>sion. The hope was that this new technology</p><p>would expand the creative possibilities of</p><p>masonry for architects and engineers. The</p><p>product was used throughout North America,</p><p>from the Giraffe House at the Denver Zoo</p><p>to a United Auto Workers building in Detroit.</p><p>Sarabond had become a commonplace</p><p>additive in masonry construction. In 1977,</p><p>disaster struck as many of the projects that</p><p>used Sarabond began to have problems. In</p><p>one case, bricks from the 23-story façade of</p><p>the Central National Bank in Cleveland, Ohio,</p><p>came crashing to the street just a few years</p><p>after the building had been completed. The</p><p>bank façade was completed in 1970, using</p><p>over 1.8 million bricks, bonded together with</p><p>a mortar mix that contained Sarabond. Investi-</p><p>gation of the façade and others like it uncov-</p><p>ered a problem with Sarabond, and the issue</p><p>related to corrosion.</p><p>In traditional masonry walls, when steel rein-</p><p>forcement is embedded in conventional</p><p>cementitious mortar, a stable oxide coating</p><p>is formed over the steel surface, thereby pro-</p><p>tecting the steel from damaging corrosion.</p><p>Investigation revealed that the Sarabond</p><p>additive creates a corrosive environment for</p><p>embedded steel. Sarabond was a latex</p><p>modifier containing polyvinyl chloride (PVC).</p><p>When Sarabond was added to fresh cement,</p><p>it released chloride into the cement pores. In</p><p>sufficient concentration, chloride ions destroy</p><p>the normally protective steel oxide coating that</p><p>develops naturally over the surface reinforce-</p><p>ment in contact with cementitious mortars</p><p>and concretes; the oxide coating becomes</p><p>unstable, giving rise to damaging corrosion at</p><p>the steel surface. As steel corrodes, it gains</p><p>in volume. In a cementitious mortar, the</p><p>expansion due to uncontrolled corrosion at</p><p>the metal surface generates tension forces.</p><p>Cement mortars have little capacity to resist</p><p>these tension forces, even with the increased</p><p>strength characteristics of Sarabond, and</p><p>cracks develop in the mortar. The combination</p><p>94 95</p><p>right and below Central</p><p>National Bank, Cleveland,</p><p>Ohio, 1970. Corrosion of wall</p><p>reinforcement caused brick</p><p>walls to fall to the street just</p><p>seven years after the project</p><p>was completed.</p><p>p_092_107_chapt_6_bp 18.10.2006 11:18 Uhr Seite 94</p><p>of uncontrolled steel corrosion and cracking</p><p>of the supporting mortar leads eventually to</p><p>failure of the steel. Where steel fasteners or</p><p>ties are used, this type of failure can result in</p><p>buckling of an entire wall of bricks. Sarabond</p><p>was blamed for weakening the reinforcement</p><p>system and for causing façades to peel away</p><p>from the building and bricks to plunge to</p><p>the street below. In the case of the Central</p><p>National Bank in Cleveland, the solution was</p><p>replacement of the brick façade.</p><p>The Sarabond problem was not limited to the</p><p>project in Cleveland. In fact, the effects of</p><p>Sarabond were felt throughout North America,</p><p>including Canada. 3080 Yonge Street is</p><p>a medium-size office building in Toronto,</p><p>Ontario, which used Sarabond as an admix-</p><p>ture for its masonry façade. Similar to the Cen-</p><p>tral National Bank, façade replacement was</p><p>required. The building owners decided to</p><p>replace the brick façade with a curtainwall</p><p>composed of glass and granite. The existing</p><p>brick walls were removed during the night</p><p>and the new curtainwall was installed during</p><p>the day without</p><p>tenants vacating the space.</p><p>Test studies revealed that mortar mixtures with</p><p>Sarabond additive produced considerably</p><p>more chloride than other mixes, thereby strip-</p><p>ping away the protective oxide coating on steel</p><p>and allowing the corrosion to proceed. The</p><p>problems related to Sarabond were similar</p><p>in nature to the problems related to calcium</p><p>chloride used in the concrete industry.</p><p>Calcium Chloride</p><p>The addition of small amounts of specific</p><p>materials to concrete in order to improve the</p><p>mix property is as old as the use of cement</p><p>itself. The Romans used blood, pig’s fat and</p><p>milk as additives to pozzolanic cements to</p><p>improve their workability and durability. In</p><p>contemporary concrete, many admixtures are</p><p>used; for example, water reducers, retarders,</p><p>accelerators, and waterproofers improve dif-</p><p>ferent characteristics of the mix. An accelera-</p><p>tor increases the rate of set of the concrete</p><p>mix. Calcium chloride was found to signifi-</p><p>cantly reduce the setting time of concrete</p><p>when added to concrete mixes as pellets or</p><p>flakes or solution form. This was particularly</p><p>useful for projects requiring concrete work in</p><p>cold temperatures. Because low temperatures</p><p>increase the setting time, it allowed for faster</p><p>construction. Regardless of the temperature</p><p>or cement type, concrete mixes containing</p><p>calcium chloride will have a faster cure rate</p><p>than plain concrete. The practice was also</p><p>adopted by the precast concrete industry as</p><p>the reduced concrete setting time allowed an</p><p>increase in output from the available molds.</p><p>After years of use through the 1960s, calcium</p><p>chloride had become a common admixture to</p><p>concrete mixes. It was later determined that</p><p>chlorides in concrete increased the risk of cor-</p><p>rosion of embedded metal. After the comple-</p><p>tion of many projects, strong recommenda-</p><p>tions from the industry advised against the</p><p>use of calcium chloride and chloride-based</p><p>admixtures in reinforced concrete design. The</p><p>Brick Institute advised against chlorides as</p><p>early as 1968, indicating that their use could</p><p>lead to corrosion of metals.</p><p>Although the use of calcium chloride in con-</p><p>crete was halted in the 1970s and the produc-</p><p>tion of Sarabond was stopped in 1982, there</p><p>is still merit in sharing the story. Architects</p><p>and engineers must learn from construction</p><p>history and cautiously subscribe to innovative</p><p>new products that offer superior performance.</p><p>Innovation can come at a cost. In the case of</p><p>Sarabond and calcium chloride, the cost was</p><p>metal corrosion.</p><p>Open concrete balconies are</p><p>susceptible to reinforcement</p><p>corrosion caused by weather</p><p>and de-icing salts. Marina</p><p>Towers, Chicago.</p><p>above Giraffe House, Denver</p><p>Zoo, detail.</p><p>right Corrosion of masonry</p><p>joint. Giraffe House, Denver</p><p>Zoo.</p><p>p_092_107_chapt_6_bp 18.10.2006 11:18 Uhr Seite 95</p><p>Metal Corrosion</p><p>There are two general types of metals used</p><p>in construction: ferrous and nonferrous.</p><p>Ferrous metals (for example: cast-iron, steel)</p><p>contain iron. Ferrous metals will corrode (rust)</p><p>when exposed to water and oxygen. Corrosion</p><p>is defined as the deterioration of a material</p><p>due to interaction with its environment and,</p><p>in the case of metals, as electrochemical dete-</p><p>rioration of a metal caused by atmospheric</p><p>or induced chemical reactions. A common</p><p>chemical that structures are often exposed to</p><p>is salt (sodium chloride) since it is commonly</p><p>used for removing ice. Steel composed of</p><p>iron plus more than 10.5 percent by weight</p><p>of chromium and less than 1.2 percent by</p><p>weight of carbon is known as stainless steel;</p><p>the chromium increases the resistance to cor-</p><p>rosion. Other elements (nickel, molybdenum,</p><p>titanium, silicium, etc.) are also added to</p><p>improve the properties of the stainless steel.</p><p>It should be noted that the correct formulation</p><p>of stainless steel should be chosen according</p><p>to the aggressivity of the environment it will</p><p>experience during its lifetime. A low-grade</p><p>stainless steel will corrode in an aggressive</p><p>chloride environment. 316 series stainless</p><p>steel is one of the best grades of stainless</p><p>steel for corrosion resistance.</p><p>Alternatively, steel can be covered with a zinc</p><p>coating, typically by hot dipping, although</p><p>electrodeposition techniques are sometimes</p><p>used. The zinc layer then oxidizes in prefer-</p><p>ence to the steel, thereby providing enhanced</p><p>corrosion resistance to the steel element. This</p><p>mechanism is discussed below under the</p><p>heading “Galvanic Action.” Unsurprisingly,</p><p>this zinc-coating process is called galvanizing.</p><p>Nonferrous metals (for example: aluminum,</p><p>lead, zinc, chromium, monel, copper, bronze,</p><p>brass) contain no iron and are less susceptible</p><p>to corrosion; however, many will react with</p><p>their environment to develop a stable and pro-</p><p>tective surface coating. This surface coating</p><p>is often referred to as a patina when aging</p><p>results in an aesthetically pleasing finish. Pati-</p><p>na describes the oxide, carbonate, sulfate, or</p><p>chloride that develops on the surface of some</p><p>metals. People are most familiar with this</p><p>process through the example of old roof gut-</p><p>ters. Installed with a rich copper color, the gut-</p><p>ters become dark brown and later green in</p><p>their evolution through the patina process.</p><p>The problem with so many of the turn-of-the-</p><p>century buildings is that the stone, brick, and</p><p>worst of all the terra cotta were attached to the</p><p>building with unprotected ferrous metal.</p><p>9796</p><p>above Failure of terra-cotta</p><p>panels.</p><p>1 Crazing – Fine cracking of</p><p>the glaze finish due to thermal</p><p>expansion and contraction of</p><p>terra cotta. Moisture can enter</p><p>through the cracks.</p><p>2 Spalling – The partial loss</p><p>of masonry caused by water</p><p>trapped within the terra-cotta</p><p>unit.</p><p>3 Mortar deterioration –</p><p>Deteriorated mortar joints are</p><p>a source of water infiltration.</p><p>4 Deterioration of metal</p><p>anchoring – Deteriorated</p><p>anchoring system due to water</p><p>infiltration and rusting of</p><p>carbon steel anchor can be</p><p>severe before it is noticed. As</p><p>a result, terra-cotta blocks can</p><p>fall from the building with little</p><p>warning.</p><p>above right Terra-cotta</p><p>panels are susceptible to cor-</p><p>rosion failures.</p><p>right Close-up inspection</p><p>by certified personnel of all</p><p>high-rise-building façades</p><p>has become a requirement for</p><p>many cities with terra-cotta</p><p>panels. Sounding of terra</p><p>cotta with a rubber mallet</p><p>allows inspectors to determine</p><p>if deterioration of the sub-</p><p>strates has occurred.</p><p>p_092_107_chapt_6_bp 18.10.2006 11:18 Uhr Seite 96</p><p>Terra Cotta Deterioration</p><p>Terra cotta is Latin for “earth cooked.” In sim-</p><p>ple terms, it is baked clay. In the time between</p><p>1880 and 1930, terra-cotta cladding flour-</p><p>ished in major metropolises around the United</p><p>States. It was fireproof and could be molded</p><p>into the classic architectural styles that were in</p><p>fashion at the turn of the century. Thousands</p><p>of buildings using this fired-claybased prod-</p><p>uct, as cladding or ornament, were construct-</p><p>ed throughout the world. Downtown Chicago</p><p>alone has 245 terra-cotta-clad buildings. The</p><p>Great Depression, followed by World War II,</p><p>ended terra cotta as a contributing cladding</p><p>element. By the time major construction proj-</p><p>ects started again in the 1950s, terra cotta</p><p>and classic architectural styles had fallen out</p><p>of favor in building design.</p><p>Terra-cotta failures occur with time, following a</p><p>progressive deterioration. Initially, fine crack-</p><p>ing, called crazing, occurs in the glaze finish</p><p>of the terra-cotta element. This can occur as a</p><p>result of thermal expansion and contraction</p><p>of the piece. Moisture penetrates through the</p><p>cracks, entering the porous baked clay. The</p><p>presence of moisture and oxygen at the sur-</p><p>face of the internal steel anchor connecting</p><p>the terra-cotta block to the building structure</p><p>allows the onset of corrosion. Deterioration of</p><p>the mortar used for filling between terra-cotta</p><p>elements also provides a path for water to</p><p>migrate to the steel supports. With time, corro-</p><p>sion weakens the metal until the anchor finally</p><p>breaks. Terra cotta deterioration</p><p>can ultimately</p><p>lead to large sections of façade falling to the</p><p>ground. Terra cotta restoration can be difficult</p><p>and expensive to complete. There are a hand-</p><p>ful of companies that make classic architec-</p><p>tural terra-cotta pieces. Repair methods of</p><p>terra cotta include the use of stainless steel</p><p>replacement anchors. This technique insures</p><p>that corrosion will not be a factor in years to</p><p>come.</p><p>Terra cotta made a revival in contemporary</p><p>architecture in the 1980s. Moving away from</p><p>classic architectural molds, terra cotta took a</p><p>simpler shape and more natural color and fin-</p><p>ish. The façade of the Potsdamer Platz tower</p><p>in Berlin incorporates thin terra-cotta tubes in</p><p>its design. Unlike the traditional glazed terr</p><p>cotta, this unglazed material is made of care-</p><p>fully selected clay of higher density and</p><p>greater strength than the traditional material.</p><p>The rod-like sunshade elements, referred to</p><p>as “baguettes,” fasten into receptors cast into</p><p>the vertical mullions. Aluminum and galva-</p><p>nized-steel fittings attach the cladding to the</p><p>substructure. In the case of the thin terra-</p><p>cotta “baguettes,” an aluminum support tube</p><p>threads through the terra cotta, preventing</p><p>their displacement if the terra cotta breaks. By</p><p>using nonferrous connections in contempo-</p><p>rary designs, terra-cotta elements will stay on</p><p>the building and not fall to the street below.</p><p>New terra-cotta panels.</p><p>1 Glass curtainwall system</p><p>2 Terra-cotta tube,</p><p>“baguette”</p><p>3 Aluminum support</p><p>right Debis Headquarters,</p><p>Potsdamer Platz, Berlin, 1998.</p><p>below Terra-cotta “baguette”</p><p>at Debis Headquarters.</p><p>p_092_107_chapt_6_bp 18.10.2006 11:18 Uhr Seite 97</p><p>Corrosion of Fasteners</p><p>There are many accessory items that play a</p><p>role in the performance required of a masonry</p><p>wall. They include horizontal joint reinforce-</p><p>ment, metal ties, strip anchors, flexible</p><p>anchors. Stone anchors are similar in appear-</p><p>ance; however, today they are typically made</p><p>of stainless steel.</p><p>Accessory items are an important and integral</p><p>part of masonry construction. Horizontal joint</p><p>reinforcement, metal anchors, ties and fasten-</p><p>ers, and flashing materials are commonly</p><p>used in construction and are essential to the</p><p>walls’ performance. Carbon steel is the most</p><p>common material for these details. Because</p><p>carbon steel is susceptible to corrosion when</p><p>exposed to water and oxygen, steps must be</p><p>taken to protect the metal from corrosion, as</p><p>discussed above.</p><p>Alkali Silica Reaction</p><p>Throughout the world today, cladding panels</p><p>are being made of concrete mixes incorporat-</p><p>ing a variety of materials. The San Jose State</p><p>Museum is proposing polished, precast con-</p><p>crete panels using recycled glass as an aggre-</p><p>gate. There is much interest in this potentially</p><p>sustainable application for recycling glass.</p><p>However, there are technical difficulties to be</p><p>aware of, principally due to the reaction that</p><p>occurs when high silica aggregates come</p><p>into contact with cement. A reaction occurs</p><p>between reactive silica in the aggregate and</p><p>the soluble alkali products in the cement</p><p>paste forming a hygroscopic alkali-silica gel,</p><p>which swells on contact with water. This form</p><p>of corrosion is a well-known problem where</p><p>reactive aggregates have been used in con-</p><p>crete; because glass is principally reactive sili-</p><p>ca, its use as an aggregate carries the same</p><p>risk. When wet, the glass aggregate produces</p><p>alkali-silica gel when in contact with the high</p><p>alkali concrete paste. The reaction produces a</p><p>swelling of the gel that breaks the concrete,</p><p>causing a readily identifiable crazing pattern</p><p>at the surface.</p><p>The potential for reuse of waste glass as a</p><p>concrete aggregate remains interesting for</p><p>economic and environmental reasons, and</p><p>much research is being done to prevent the</p><p>occurrence of ASR. Today, much progress has</p><p>been made in solving the ASR problem, and</p><p>many decorative products are available in this</p><p>material. However, mindful of the Sarabond,</p><p>and other catastrophes, the industry currently</p><p>advises that this material not be used in struc-</p><p>tural concrete exposed to moisture.</p><p>Galvanic Action</p><p>The deterioration of one material caused by</p><p>the contact with another material is a form of</p><p>incompatibility. Galvanic action, a form of cor-</p><p>rosion, occurs when dissimilar metals are in</p><p>contact with each other and when sufficient</p><p>moisture is present to carry an electrical cur-</p><p>rent. The galvanic series describes a list of</p><p>metals arranged in order from “most reactive</p><p>to corrosion” to “least reactive to corrosion.”</p><p>The less noble a material is, the more reactive</p><p>to corrosion it will be. The further apart two</p><p>metals are on the list, the greater the polarity</p><p>that will develop and consequently the greater</p><p>the corrosion decay of the less noble anode</p><p>metal.</p><p>In reality, dissimilar metals are often in con-</p><p>tact, and frequently severe corrosion of the</p><p>most anodic metal does occur. However, the</p><p>potential danger of such contacts depends on</p><p>the relative areas of anode and cathode. Put</p><p>simply, the electrical charge from the anode</p><p>surface equals that going to the cathode sur-</p><p>face; a small anode area in contact with a</p><p>large cathode area must always be avoided,</p><p>whereas a large anode area contacting a small</p><p>cathode area would be fine as the corrosion</p><p>activity would be spread over such a large</p><p>anode surface that it would be acceptable.</p><p>For example, copper plate fastened with steel</p><p>bolts would be disastrous, whereas steel plate</p><p>fastened with copper bolts would be accept-</p><p>able – the steel corrosion would be evenly</p><p>spread over a large surface.</p><p>If an incompatible anode cathode pairing is</p><p>unavoidable, separation of the dissimilar met-</p><p>als with a neutral non-conductive material is</p><p>fundamental to preventing galvanic action.</p><p>98 99</p><p>Precast concrete panels using</p><p>recycled glass as an aggregate</p><p>can show alkali silica reaction.</p><p>Concrete cover: The concrete</p><p>base at the “City of Arts and</p><p>Sciences” in Valencia, Spain,</p><p>a complex of buildings is com-</p><p>posed of steel reinforcement</p><p>covered in concrete.</p><p>p_092_107_chapt_6_bp 18.10.2006 11:18 Uhr Seite 98</p><p>Corrosion in Concrete</p><p>Masonry and stone buildings are not alone</p><p>when it comes to corrosion problems. Con-</p><p>crete buildings are equally susceptible. Con-</p><p>crete is strong in compression, but weak in</p><p>tension. Carbon steel is typically used to pro-</p><p>vide tensile strength in concrete and hence</p><p>to improve its structural properties. A simple</p><p>example of this is the lintel at the head of a</p><p>window. Concealed within a concrete element,</p><p>the carbon steel reinforcement can exist with-</p><p>out corrosion problems; however, the rein-</p><p>forcement’s concrete cover can be degraded</p><p>either by chlorides, as previously discussed,</p><p>or by attack from carbon dioxide (CO2) in the</p><p>atmosphere. This form of attack is termed</p><p>carbonation and results from the combination</p><p>of CO2 with the water in the concrete pores</p><p>to form a weak acid (carbonic acid). With time</p><p>this acid neutralizes the high alkalinity of the</p><p>cement paste at increasing depths within the</p><p>concrete. In the case of poor quality concrete</p><p>or insufficient thickness of cover to reinforce-</p><p>ment, the advancing front of carbonated (low</p><p>Anode</p><p>(least noble)</p><p>+</p><p>Electric current</p><p>flows from positive (+)</p><p>to negative (-)</p><p>cathode</p><p>(most noble)</p><p>Magnesium, magnesium alloys</p><p>Zinc</p><p>Aluminum 1,100</p><p>Cadmium</p><p>Aluminum 2,024-T4</p><p>Steel or iron, cast iron</p><p>Chromium iron (active)</p><p>Ni-Resist</p><p>Type 304, 316 stainless (active)</p><p>Hastelloy “B”</p><p>Lead, tin</p><p>Nickel (Inconel) (active)</p><p>Hastelloy “B”</p><p>Brasses, copper, bronze, monel</p><p>Silver solder</p><p>Nickel (Inconel) (passive)</p><p>Chromium iron (passive)</p><p>Type 304, 316 stainless (passive)</p><p>Silver</p><p>Titanium</p><p>Graphite, gold, platinum</p><p>The Galvanic Series</p><p>p_092_107_chapt_6_bp 18.10.2006 11:18 Uhr Seite 99</p><p>alkali) concrete reaches the steel surface. The</p><p>stable oxide discussed at the beginning of this</p><p>chapter forms because of the high alkalinity</p><p>of cement paste. Chloride ions penetrate the</p><p>stable oxide coating and</p><p>in sufficient quanti-</p><p>ties cause pitting corrosion with localized acid</p><p>conditions. The low alkali-carbonated con-</p><p>crete provides an environment where the</p><p>presence of water and oxygen enables the</p><p>oxide coating to evolve from a stable to an</p><p>unstable form (rust). While this seems to be</p><p>an elementary reinforced concrete design</p><p>detail, it is surprising to count the number of</p><p>high profile installations where it has been</p><p>overlooked.</p><p>Completed in 2004, the extension of the</p><p>Deutsches Historisches Museum in Berlin has</p><p>several differently shaped halls on four levels</p><p>where the exhibitions take place. The south</p><p>façade is composed of an all-glass volume</p><p>and a large stonewall. There is only one win-</p><p>dow on the extension structure, above which</p><p>lies a concrete lintel. The concrete lintel</p><p>includes steel reinforcement; however, it</p><p>appears that the amount of coverage is insuffi-</p><p>cient over one of the bars. In strong contrast</p><p>to the light-colored stone façade, rust marks</p><p>have started to streak down the face of the</p><p>lintel as the steel reinforcement corrodes.</p><p>The extension of the Deutsches Historisches</p><p>Museum is not alone. Less than a mile away,</p><p>a new Parliament office building, the Paul-</p><p>Löbe-Haus, designed by Stephan Braunfels</p><p>and completed in 2001, has several locations</p><p>on the concrete façade with rust marks</p><p>from unprotected carbon steel inadvertently</p><p>exposed to the environment. These nuisance</p><p>defects are typically aesthetic only; however,</p><p>continued corrosion in certain environments</p><p>can lead to serious, even catastrophic,</p><p>structural problems.</p><p>100 101 above and right Extension</p><p>of the Deutsches Historisches</p><p>Museum, Berlin, 2004.</p><p>Signs of carbon steel corrosion</p><p>are visible above the window.</p><p>right Paul-Löbe-Haus, Berlin,</p><p>2001. Unwanted stains from</p><p>carbon steel appeared on</p><p>concrete walls shortly after the</p><p>project was completed.</p><p>p_092_107_chapt_6_bp 18.10.2006 11:18 Uhr Seite 100</p><p>Salts</p><p>A former Pan Am aircraft hanger, constructed</p><p>in Miami, Florida, during the 1980s, has a</p><p>corrosion problem that is out of control. Cor-</p><p>roding steel reinforcement is visible at the</p><p>fins of precast concrete elements over a large</p><p>percentage of the façade. Heightened corro-</p><p>sion from the salts in the ocean air may have</p><p>added to the severe corrosion exhibited on</p><p>the precast concrete panels. Over many years,</p><p>a building envelope can develop serious struc-</p><p>tural problems due to the deterioration of con-</p><p>crete due to corrosion. Salts are a corrosive</p><p>element found in coastal regions of the world</p><p>and in cities away from the ocean.</p><p>The King Building at Oberlin College, Ohio,</p><p>was constructed in 1966, with similar precast</p><p>concrete details to the Pan Am hanger in</p><p>Miami. Corrosion of the concrete panels at the</p><p>King Building is not caused by the ocean air,</p><p>but by salts applied near the entrance to melt</p><p>snow and ice in the winter.</p><p>Special care must be taken when concrete</p><p>with carbon steel reinforcement is going to be</p><p>exposed to de-icing salts. Advances in materi-</p><p>als and mix design enable the specification</p><p>of reinforced concrete that will resist even the</p><p>most aggressive environments. The key lies</p><p>in understanding the environment and the</p><p>requirements that it places on the structure.</p><p>above and right King Build-</p><p>ing, Oberlin College, Ohio,</p><p>1966.</p><p>below Highway construction</p><p>utilizes epoxy-coated rebar to</p><p>reduced corrosion caused by</p><p>de-icing salts.</p><p>below and right Corrosion of</p><p>steel reinforcement can be</p><p>unsightly and can compromise</p><p>the structural integrity of a</p><p>concrete structure.</p><p>above Aluminum will corrode</p><p>if in contact with wet concrete.</p><p>p_092_107_chapt_6_bp 18.10.2006 11:19 Uhr Seite 101</p><p>Non-Corrosive Reinforcement and</p><p>Accessories</p><p>As an alternative to carbon steel there are</p><p>several reinforcement products available to</p><p>enhance corrosion resistance.</p><p>Stainless steel reinforcement can be used as</p><p>discussed previously. When embedded in a</p><p>high-performance concrete this presents an</p><p>excellent solution for high-value structures in</p><p>aggressive environments.</p><p>Carbon steel reinforcement coated with an</p><p>epoxy resin provides another option; however,</p><p>some care must be taken in handling and fix-</p><p>ing the reinforcement to avoid damaging the</p><p>coating. Local coating damage in conjunction</p><p>with concrete contaminated by chlorides can</p><p>lead to very aggressive corrosion attack.</p><p>There is much interest in the use of reinforc-</p><p>ing bars made of fiber-reinforced polymers</p><p>(FRP). With the memories of the disasters</p><p>arising from the adoption of Sarabond and cal-</p><p>cium chloride, the industry is cautiously evalu-</p><p>ating all performance characteristics of this</p><p>material with extensive testing and trails of</p><p>prototype bridge structures.</p><p>Steel reinforcement may also be coated with</p><p>zinc by “galvanizing.” Zinc is susceptible to</p><p>corrosive attack. The corroded metal occupies</p><p>a greater volume than its original material and</p><p>exerts expansive pressures around the</p><p>embedded item. However, the corrosion prod-</p><p>uct is softer than that of steel and the coating</p><p>thickness sufficiently thin that the pressure is</p><p>not sufficient to crack concrete or masonry.</p><p>The zinc coating corrodes more readily than</p><p>steel (see the above Galvanic series) and</p><p>hence will corrode sacrificially to protect the</p><p>underlying steel surface. Calcium chloride</p><p>accelerating agents are very damaging to zinc</p><p>coatings and should not be used in reinforced</p><p>or metal-tied masonry walls; equally, zinc or</p><p>galvanized products should not be used in</p><p>marine or other environments where signifi-</p><p>cant salt concentrations can be expected</p><p>unless the designer has taken this into</p><p>account.</p><p>In addition, there are several nonferrous met-</p><p>als that are commonly used for masonry</p><p>accessories. Copper and copper alloys are</p><p>essentially immune to the corrosive action of</p><p>wet concrete or mortar. Because of this immu-</p><p>nity, copper can be safely embedded in the</p><p>fresh mortar even under saturated conditions.</p><p>Aluminum is also attacked by fresh Portland</p><p>cement mortar and produces the same</p><p>expansive pressure. If aluminum is to be used</p><p>in reinforced masonry, it should be perma-</p><p>nently coated with bituminous paint, alkali-</p><p>resistant lacquer, or zinc chromate paint.</p><p>As previously mentioned, calcium chloride or</p><p>other chloride-based admixtures should not</p><p>be used in mortar or concrete that will contain</p><p>any embedded metal. In the case of copper,</p><p>aluminum or zinc, as with steel in concrete,</p><p>102 103</p><p>below Staining of concrete</p><p>walkway was an inevitable</p><p>consequence of installing</p><p>copper cladding on Oak Park</p><p>Public Library, Chicago com-</p><p>pleted in 2003 and designed</p><p>by Nagle Hartray and Asso-</p><p>ciates.</p><p>above and right Botanical</p><p>Gardens in Barcelona,</p><p>designed by Carlos Ferrater</p><p>and completed in 1999.</p><p>Elements of the park are con-</p><p>structed with Cor-Ten steel.</p><p>The staining that occurs at</p><p>the entrance almost looks</p><p>deliberate.</p><p>p_092_107_chapt_6_bp 18.10.2006 11:19 Uhr Seite 102</p><p>the chlorides break through the metal’s natu-</p><p>ral protective oxide coating, causing corrosion</p><p>damage. The same risk applies to all high</p><p>chloride environments, such as coastal</p><p>regions; hence materials’ performance must</p><p>be carefully studied in all cases.</p><p>Galvanic corrosion can occur where different</p><p>metals contact each other; where this pres-</p><p>ents a problem, steps must be taken to electri-</p><p>cally isolate them to prevent this.</p><p>Metal Flashings</p><p>Concrete and masonry construction must</p><p>include sheet-flashing material to divert pene-</p><p>trating moisture back to the exterior of the</p><p>building. All flashing materials must be imper-</p><p>vious to moisture, resistant to corrosion, abra-</p><p>sion, puncture, and if exposed to the sun,</p><p>ultraviolet radiation. Elastomeric materials hav</p><p>e recently met all of these requirements and</p><p>provide an improved ability to be shaped and</p><p>sealed at inside corner and end dams. These</p><p>products break down under ultraviolet radia-</p><p>tion and require stainless steel extensions to</p><p>take water away from the building.</p><p>Metal</p><p>thick), except for the reentrant corners</p><p>where the thickness of the panels was</p><p>increased to 38mm (1 1/2 inches) from the</p><p>42nd floor and above. The increased stone</p><p>thickness at these locations was to compen-</p><p>sate for the higher anticipated wind loads</p><p>at the upper corners of the building. The mar-</p><p>ble panels were supported by 152mm long</p><p>(6 inches) stainless steel bent plates connect-</p><p>ed to galvanized angles that were stud bolted</p><p>into the structural steel chevron shaped</p><p>columns. The marble panels had kerfs cut</p><p>into them to receive the stainless steel bent</p><p>plate. The downturned tabs of the bent plate</p><p>provided lateral support for the stone below</p><p>and the upturned tab provided lateral/bearing</p><p>support for the stone above. Each piece of</p><p>marble was independently supported back to</p><p>the adjacent steel column. After installation,</p><p>all of the joints between the marble panels</p><p>were filled with sealant.</p><p>In 1979, inspection of the building indicated</p><p>crescent shaped cracks in approximately 230</p><p>marble panels. The observed crescent shaped</p><p>cracks occurred in the panels at the 152mm</p><p>long (6 inches) stainless steel lateral connec-</p><p>tion points. Between 1979 and 1985, the</p><p>Section through marble</p><p>connection</p><p>1 Marble panel 3cm or 4cm</p><p>(1 1/4 –1 1/2 inches)</p><p>2 Stainless steel bent plate</p><p>3 Backer rod and sealant</p><p>4 Galvanized steel angle</p><p>connection back to chevron</p><p>shaped steel column</p><p>12 13</p><p>Mock-up of original Amoco</p><p>Building façade at Construc-</p><p>tion Research Laboratory in</p><p>Miami, Florida.</p><p>p_010_021_chapt_1_bp 17.10.2006 18:03 Uhr Seite 12</p><p>building owner observed additional cracking</p><p>and bowing of the marble panels. Outward</p><p>displacement of the marble panels was found</p><p>to be as much as 28.6mm (11/8 inch). The</p><p>outward bowing of the panels was actually</p><p>an outward dishing of the stone, because the</p><p>bow occurred along the vertical and horizontal</p><p>axis of the panels. The effects were linked to</p><p>thermal cycling, because approximately 80</p><p>percent of the significantly bowed panels were</p><p>located on the south and east elevations of</p><p>the building, which unlike the west elevations</p><p>had no adjacent structures to block direct</p><p>exposure of the sun. The marble panels on</p><p>the north elevation of the building, which</p><p>received the least amount of direct sunlight,</p><p>had the least amount of outward bowing. As a</p><p>result of these observations, a more thorough</p><p>investigation of the building cladding began.</p><p>In 1985, laboratory testing was started to bet-</p><p>ter understand what was happening to the</p><p>stone. 96 marble panels were removed from</p><p>the building and tested together with 10 origi-</p><p>nal stone panels that had been stored in</p><p>the basement of the building. The results of</p><p>the laboratory flexural strength tests were</p><p>startling. The minimum flexural strength of the</p><p>virgin original marble panels was 7.52 MPa</p><p>(1.09 ksi). This was much less than the mini-</p><p>mum flexural strength of 9.65 MPa (1.4 ksi)</p><p>gathered from initial test samples of the stone</p><p>prior to construction. This proved that the</p><p>stone used on the building was not as strong</p><p>as the stone used during the preliminary sam-</p><p>ple testing for the project. This realization pro-</p><p>vided a painful reminder that stone strengths</p><p>can vary in a quarry and that testing of stone</p><p>samples during a large project needs to take</p><p>Inspection of the building indi-</p><p>cated crescent shaped cracks</p><p>were visible on the stone</p><p>panels that clad the chevron</p><p>shaped steel columns.</p><p>Amoco Building.</p><p>below Stone panels are cut</p><p>into blocks at quarry and can</p><p>vary in physical properties</p><p>depending on which part of</p><p>the quarry they are extracted</p><p>from.</p><p>p_010_021_chapt_1_bp 17.10.2006 18:03 Uhr Seite 13</p><p>place throughout the construction process.</p><p>Additional testing of the marble</p><p>panels removed from the building indicated</p><p>an average flexural strength of 5.24 MPa</p><p>(760 psi). This revealed a 40 percent loss in</p><p>strength compared to stone stored in the</p><p>basement. Through accelerated weathering</p><p>testing it was anticipated that in another ten</p><p>years on the building, the marble panels</p><p>would lose a total of about 70 percent of their</p><p>original strength. This would bring the average</p><p>flexural panel strength down to about 3.65</p><p>MPa (530 psi), and a minimum flexural</p><p>strength on the stone would be as low as 1.96</p><p>MPa (285 psi).</p><p>As the inspections continued, it became clear</p><p>that the cracking and dishing of the marble</p><p>panels on the building were accelerating at a</p><p>rapid rate. The deterioration of the stone pan-</p><p>els made them unable to withstand anticipat-</p><p>ed wind loads. The test data was supported</p><p>by in-situ load tests of 48 actual full panels on</p><p>the building where a uniform negative wind</p><p>load was simulated with hydraulic rams at the</p><p>back of the panels. Rams were temporarily</p><p>installed on the exterior wall by removing</p><p>adjacent stone panels.</p><p>Although no stone panels had fallen off the</p><p>building, the strength loss to the panels</p><p>showed no sign of stopping, making repair</p><p>options futile. Based on these findings, it was</p><p>decided to remove the marble panels from the</p><p>building. Stainless steel straps, color coated</p><p>white to match the marble color, were bolted</p><p>through the marble into the supporting angles</p><p>to prevent any failing stone from coming off.</p><p>A variety of design solutions were considered</p><p>to replace the marble. However, the consen-</p><p>sus was to maintain the existing white image</p><p>of the tower. This decision suggested three</p><p>alternate re-clad materials: white aluminum</p><p>panels, white granite panels, and a man-made</p><p>ceramic glass. Based on a variety of factors</p><p>including appearance, cost, availability, and</p><p>established track records for cladding material</p><p>on high-rise buildings, a 38mm (11/2 inch)</p><p>Mount Airy granite, quarried in North Carolina,</p><p>was selected for the re-cladding. Samples</p><p>from Mount Airy granite blocks were tested</p><p>during the fabrication process, and if results</p><p>were below minimum specifications the quar-</p><p>ried blocks were rejected.The final connection</p><p>of the granite back to the existing structure</p><p>was very similar to the original detail. For</p><p>strength and corrosion resistance, a continu-</p><p>ous stainless steel shelf angle was used to</p><p>support the stone in lieu of 152mm (6 inch)</p><p>kerfs. The angle was extruded to improve</p><p>connection tolerances.</p><p>In September 1991, approximately 20 years</p><p>after the tower was built, removal and replace-</p><p>ment of all of the original 44,000 panels was</p><p>1514</p><p>Elevation of straps used to</p><p>temporarily restrain the marble</p><p>panels. Amoco Building.</p><p>1 Panel and strap above</p><p>2 Bolt</p><p>3 Marble panel</p><p>4 Theoretical crack location</p><p>5 Stainless steel straps</p><p>6 Panel and strap below</p><p>right Temporary strapping</p><p>detail</p><p>1 Stainless steel bolt</p><p>2 Stainless steel straps paint-</p><p>ed white</p><p>3 Existing backer rod and</p><p>sealant</p><p>4 Existing marble panel</p><p>5 Existing galvanized angle</p><p>connected back to structure</p><p>6 Existing stud weld connec-</p><p>tion to stainless steel plate</p><p>The granite blocks from the</p><p>quarry were tested during the</p><p>fabrication process. If results</p><p>were below minimum specifi-</p><p>cations, the blocks were</p><p>rejected.</p><p>p_010_021_chapt_1_bp 17.10.2006 18:03 Uhr Seite 14</p><p>completed. The cost of the replacement of the</p><p>panels roughly equaled the construction cost</p><p>complete. The vast majority of the removed</p><p>panels were ground into pebbles for use as</p><p>landscaping material, or donated to groups</p><p>that manufacture small stone items. In order</p><p>to better comprehend what happened to</p><p>the stone on the Amoco Building, one must</p><p>understand the composition of marble.</p><p>Calcite Crystals</p><p>Marble primarily consists of calcite crystals.</p><p>Calcite crystals are anisotropic. Anisotropic</p><p>means that when the stone is heated the crys-</p><p>tals expand in different amounts in different</p><p>directions, and when the stone is subsequent-</p><p>ly cooled, the crystals cannot return to their</p><p>original position because they interlock. This</p><p>phenomenon often results in a permanent</p><p>expansion of the marble, increased absorption</p><p>rate, and an accompanying strength loss. With</p><p>flashings are made from a variety of</p><p>materials; however, all must have adequate</p><p>corrosion resistance to the intended environ-</p><p>ment. Galvanized steel can be used as flash-</p><p>ing material, but is subject to corrosive attack</p><p>from wet mortar unless covered with a bitumi-</p><p>nous coating. Exterior exposure requires a</p><p>heavier thickness, and concealed installations</p><p>require a thinner gauge. Typically, non-ferrous</p><p>metals are used as flashing material because</p><p>they have better corrosion resistance than car-</p><p>bon steel. Stainless steel flashings are highly</p><p>resistant to corrosion and provide good dura-</p><p>bility without the danger of staining adjacent</p><p>materials. Aluminum flashings are subject to</p><p>corrosive damage from wet mortar and should</p><p>not be used unless a durable protective coat-</p><p>ing is applied to them. Copper flashings resist</p><p>ordinary corrosive action and can be easier to</p><p>shape than stainless steel; however, they can</p><p>stain light-colored walls unless they are coated</p><p>with lead.</p><p>There are many flashing types available that</p><p>use a combination of materials to provide ade-</p><p>quate protection at lower cost. Elastomeric</p><p>coatings are the most common because of</p><p>their lower cost, durability and workability in</p><p>concealed locations. Whatever material is</p><p>chosen, a thorough evaluation of its perform-</p><p>ance in the intended micro- and macro-envi-</p><p>ronment must be undertaken.</p><p>Concrete Patina</p><p>The oxidation of metals used in enclosure sys-</p><p>tems does not necessarily create an undesired</p><p>effect. Sometimes, the oxidation of cladding</p><p>elements is expected, welcomed, and initiated</p><p>by designers. A project that encouraged a</p><p>chemical reaction on concrete is the Oskar</p><p>Reinhart Collection in Switzerland. The project</p><p>was both a renovation and an extension to an</p><p>existing museum. The existing core structure</p><p>was built as a villa in 1915, with an added res-</p><p>idential house completed in 1925. The new</p><p>extension includes three new exhibition rooms</p><p>that are wrapped tightly around the 1925</p><p>structure, and a link from the main building to</p><p>the former residential house. Completed in</p><p>1998, the extension consisted of large prefab-</p><p>Oskar Reinhart Collection.</p><p>1 Precast concrete panel</p><p>with jurassic limestone and</p><p>copper</p><p>2 Copper roofing material</p><p>3 Air space</p><p>4 Insulation</p><p>5 Through-wall base flashing</p><p>above Jurassic limestone</p><p>and copper were added to the</p><p>concrete panel mix to provide</p><p>a green patina to the wall.</p><p>Oskar Reinhart Collection,</p><p>Winterthur, Switzerland, 1998.</p><p>p_092_107_chapt_6_bp 18.10.2006 11:19 Uhr Seite 103</p><p>ricated concrete walls which form the outside</p><p>of the extension.</p><p>The exterior wall comprises a cast-in-place</p><p>20cm (73/4 inch) thick reinforced concrete</p><p>wall, an external attached 10cm (4 inch)</p><p>thick layer of insulation (rock wool), a 3cm</p><p>(11/4 inch) air gap, and a precast concrete</p><p>panel (10 and 12cm [4 and 4 3/4 inch] thick).</p><p>The concrete panels have a rich surface</p><p>derived from the unusual concrete mix. Trial</p><p>panels comprising a variety of materials were</p><p>made and observed. Two materials used in</p><p>the construction of the original villa, Jurassic</p><p>limestone and copper, were found to give the</p><p>best results. Both of these materials were</p><p>ground down and added as fine aggregate to</p><p>the concrete mix. The new walls have under-</p><p>gone an accelerated aging process, acquiring</p><p>a patina that gives the walls a discreet green</p><p>color. The wall details allow runoff water from</p><p>the copper roof to deliberately streak the walls</p><p>with copper ions to provide the desired effect.</p><p>The museum project shows how a chemical</p><p>reaction between dissimilar materials can</p><p>successfully add to the character of our build-</p><p>ings without compromising the wall system.</p><p>There are, of course, projects where the oxi-</p><p>dation of metal claddings was not expected.</p><p>Other projects have been less successful with</p><p>combining dissimilar materials.</p><p>Chemical Reaction</p><p>Metal deterioration can occur in any environ-</p><p>ment when metals come in contact with</p><p>chemically active materials. Typically, this</p><p>process can be accelerated when moisture is</p><p>present. For example, aluminum in direct</p><p>contact with concrete or mortar will corrode.</p><p>Steel in contact with certain types of treated</p><p>wood will corrode. An example of an unwant-</p><p>104 105</p><p>Burroughs Wellcome Head-</p><p>quarters, Research Triangle</p><p>Park, North Carolina, 1972.</p><p>Exterior wall and original test</p><p>mock-up.</p><p>ed chemical reaction occurred at the Bur-</p><p>roughs Wellcome Research Headquarters in</p><p>North Carolina. Completed in 1972, the build-</p><p>ing stretched expansively across a wooded</p><p>hillside ridge in North Carolina. The profile</p><p>of this large corporate headquarters building</p><p>echoes the inclines of the hills around the</p><p>site. The progressive design has received</p><p>numerous awards and has served as the</p><p>backdrop of a Hollywood film. The sloped</p><p>enclosure system for the project had prob-</p><p>lems shortly after its installation. The enclo-</p><p>sure was plagued with a transition detail that</p><p>had serious problems due to galvanic action.</p><p>The cement stucco that surrounded the win-</p><p>dow system was of magnesium oxychloride</p><p>cement plaster. The sloped glass was isolated</p><p>from the adjacent material by a zinc separa-</p><p>tor. When the stucco became wet from rain,</p><p>the oxychloride combined with the water to</p><p>make hydrochloric acid. Where water is pres-</p><p>ent and in contact with zinc, the magnesium</p><p>oxychloride initiates an intense chemical reac-</p><p>tion that causes corrosion of the sacrificial</p><p>zinc material. Ironically, the system had been</p><p>tested in a mock-up prior to fabrication. The</p><p>mock-up testing of the system used plywood</p><p>in lieu of stucco. Because the stucco system</p><p>was not being tested for water infiltration, it</p><p>was not included in the mock-up. The testing</p><p>was successful, and the compatibility issue</p><p>with the stucco was not detected. However,</p><p>within weeks of completing the enclosure on</p><p>the building, the zinc border had corroded,</p><p>allowing water to leak into the building. The</p><p>entire enclosure system was ultimately</p><p>replaced.</p><p>Ettringite</p><p>What might appear to be a stone anchor fail-</p><p>ure due to corrosion can be linked to a chem-</p><p>ical reaction caused by the improper use of</p><p>above Anchor failure due to</p><p>ettringite.</p><p>1 Drip edge above window</p><p>presents etching of glass with</p><p>runoff water.</p><p>p_092_107_chapt_6_bp 18.10.2006 11:19 Uhr Seite 104</p><p>gypsum-based grout. Grout expansion from</p><p>weather-related wet/dry cycling of the stone</p><p>can cause kerf (slot in stone to accommodate</p><p>anchor) failures. Semicircular spalls separate</p><p>from the stone panels at the failed locations.</p><p>Ettringite is formed by an expansive chemical</p><p>reaction between Portland cement and gyp-</p><p>sum under moist conditions. The expansive</p><p>conversion of Portland cement and gypsum</p><p>can force the failed kerfs apart, much like air</p><p>inflating a tire, eventually causing the stone to</p><p>fracture and weakening or destroying the con-</p><p>nection. The failure patterns are very similar</p><p>to those seen at failed kerfs due to excessive</p><p>anchor loads or damage from corrosion of</p><p>the anchor support.</p><p>Gypsum grout is primarily made of gypsum</p><p>and silica sand. Known problems with gypsum</p><p>grouts exposed to moisture include softening,</p><p>washout, corrosion of embedded aluminum</p><p>and steel components, and sulfate attack of</p><p>surrounding concrete.</p><p>Concrete Etching of Glass</p><p>When water reaches a building, it is either</p><p>reflected, or absorbed, or allowed to run down</p><p>the building’s façade. When water runoff</p><p>occurs across a masonry or concrete wall, the</p><p>water can carry minerals from these surfaces</p><p>to the glass below. Water runoff containing</p><p>contaminants can damage glass. To under-</p><p>stand the chemistry involved with this process,</p><p>one must review some basic concepts. An</p><p>aqueous solution can be described on a</p><p>pH scale from one to 14, with neutral solu-</p><p>tions having a pH of seven. Materials meas-</p><p>ured below seven are considered acids, and</p><p>materials above seven are considered basic</p><p>or alkaline. If the alkalinity of a solution</p><p>reaches a pH greater</p><p>than nine, a destructive</p><p>stage of glass corrosion can begin to occur.</p><p>Fresh concrete can have a pH of 12; however,</p><p>as the concrete ages the alkalinity of the sur-</p><p>face decreases. Damage to the surface of</p><p>glass can be caused by alkalis that leach out</p><p>of precast concrete panels by rain, or the</p><p>fluorides in the wash-off from concrete floors</p><p>that have been treated for hardening with</p><p>solutions of zinc or magnesium fluorosilicates.</p><p>These materials can stain or etch the surface</p><p>of the glass if allowed to remain for an extend-</p><p>ed period of time.</p><p>The contaminating effects from runoff water</p><p>may lead to white streaks on the glass, which</p><p>is difficult to remove. The transparency of</p><p>glass can be permanently lost once the glass</p><p>surface has been severely etched. Although</p><p>concrete and stone have taken most of the</p><p>blame for unsightly glass stains and etching,</p><p>it is important to remember that many struc-</p><p>tures built of materials other than concrete</p><p>and masonry have experienced glass staining.</p><p>This staining can be explained by natural cor-</p><p>rosion of the glass.</p><p>right Image of white corrosion</p><p>marks on glass from concrete</p><p>runoff.</p><p>p_092_107_chapt_6_bp 18.10.2006 11:19 Uhr Seite 105</p><p>In stone and masonry support systems, corro-</p><p>sion problems can be avoided by selecting</p><p>reinforcements or fasteners that are compati-</p><p>ble with the micro- and macro-environment of</p><p>the building; stainless steels, coated metals,</p><p>non-ferrous metals or even plastics (subject to</p><p>their long-term performance). As most materi-</p><p>als change with time if exposed to moisture,</p><p>the goal is to keep water out. By understand-</p><p>ing how materials change, one can work to</p><p>protect them and prevent unwanted corro-</p><p>sion. Coatings vary from various paint types</p><p>(epoxy, bituminous, polyurethane …) to</p><p>anodizing, to PVDF (polyvinylidene fluoride,</p><p>brand name Kynar), to powder coating.</p><p>The concrete industry has even developed</p><p>structural concrete that does not use any</p><p>metal. The new Hindu Temple in Bartlett,</p><p>Illinois, was constructed with no metal in the</p><p>concrete at all. This was a requirement of</p><p>the Hindu monks, related to their practical</p><p>knowledge and spiritual beliefs.</p><p>The monks understood that metal will deterio-</p><p>rate with time. Inspired by the great temples</p><p>of India which were sometimes carved out of</p><p>a single rock formation, the BAPS Temple in</p><p>How Can Failures Due to Corrosion</p><p>Be Avoided?</p><p>106 107</p><p>Bartlett is free of ferrous metals that could</p><p>corrode with time. In addition to creating a</p><p>building that would last for thousands of</p><p>years, the temple space was to be free from</p><p>metal to create a space for the highest level</p><p>of concentration. It is believed that steel and</p><p>the magnetic flux associated with it can be</p><p>a minor distraction to the focused mind. The</p><p>massive concrete foundation for the temple</p><p>used a high-strength mix free of steel with a</p><p>mix of 33 percent cement and 67 percent</p><p>flyash.</p><p>right and below BAPS Tem-</p><p>ple, Bartlett, Illinois, 2004.</p><p>The only metal used on the</p><p>building structure were copper</p><p>rods used to connect the</p><p>carved marble blocks together.</p><p>p_092_107_chapt_6_bp 18.10.2006 11:19 Uhr Seite 106</p><p>1</p><p>Some material changes are expected, even</p><p>desired in our building envelopes. The color</p><p>and texture of patina can add to their charac-</p><p>ter.</p><p>2</p><p>Distress in aging masonry enclosures is often</p><p>caused by the volumetric changes in the</p><p>masonry cladding due to thermal changes</p><p>and absorption of moisture. The presence of</p><p>moisture and oxygen can lead to the corrosion</p><p>of unprotected metal support systems. Corro-</p><p>sion of steel causes a series of corrosion by-</p><p>products like iron oxide to build up around</p><p>the affected metal. The added layer of materi-</p><p>al creates expansive pressure on the sur-</p><p>rounding masonry that can cause spalling,</p><p>bowing and displacement of masonry.</p><p>3</p><p>Contemporary masonry cladding systems use</p><p>reinforcement or fasteners that are non-corro-</p><p>sive (such as stainless steel) or that have</p><p>protective coatings (such as galvanizing) to</p><p>prevent corrosion problems.</p><p>4</p><p>Admixtures for concrete and masonry are</p><p>commonly used to enhance various proper-</p><p>ties. However, new products should be used</p><p>with caution on large-scale projects. Innova-</p><p>tion without full evaluation can come at a very</p><p>high cost when problems with new products</p><p>become apparent years after the technology</p><p>has entered the market.</p><p>5</p><p>All carbon steel reinforcement in concrete</p><p>or mortar must have adequate coverage to</p><p>prevent rusting of metal. Corrosion of steel</p><p>can lead to rust stains on a building and fre-</p><p>quently structural problems if the corrosion</p><p>is left unchecked.</p><p>6</p><p>Harsh environments, particularly the pres-</p><p>ence of salt, require construction materials</p><p>(metals, concretes, mortars …) that resist the</p><p>various aggressive elements they may</p><p>encounter: chlorides, sulfates, freeze-thaw,</p><p>bacteria, wind-borne sand, sunlight, etc.</p><p>Lessons Learned</p><p>7</p><p>Corrosion of glass can occur from water</p><p>runoff over fresh concrete. Routine cleaning</p><p>of the glass will prevent permanent damage</p><p>to the surface.</p><p>8</p><p>Galvanic corrosion risks due to contact</p><p>between dissimilar metals must be assessed</p><p>during design; corrosion can be avoided by</p><p>electrical insulation between the metals.</p><p>9</p><p>Testing is essential to ensure the success of</p><p>the enclosure system; however, it is necessary</p><p>that the materials used in the testing are</p><p>the same as those used on the project. Many</p><p>times, substitute materials are employed,</p><p>assuming that their role in the testing is</p><p>inconsequential, only to find at great cost</p><p>that it was not.</p><p>10</p><p>Never use gypsum-based grout in exterior</p><p>applications or interior applications subject to</p><p>wetting, because ettringite expansion can</p><p>fracture concrete and stone at connection</p><p>points.</p><p>p_092_107_chapt_6_bp 18.10.2006 11:19 Uhr Seite 107</p><p>Innovative structures made from concrete,</p><p>masonry and stone have played a significant</p><p>role in shaping the history of modern architec-</p><p>ture. Many designs have been challenged</p><p>along the way. When Frank Lloyd Wright pre-</p><p>sented his solution for the “great hall” at the</p><p>Johnson Wax Building in 1937, he had few</p><p>supporters. The hall was to be filled with a for-</p><p>est of thin white columns, which spread out at</p><p>the ceiling like lily pads on a pond. The con-</p><p>struction engineers and building inspectors of</p><p>Racine, Wisconsin, were convinced that the</p><p>slender concrete columns with narrow bases</p><p>and hollow insides were incapable of support-</p><p>ing the roof of the building. Wright arranged</p><p>for a full-scale mock-up to be constructed,</p><p>and when the day came to test the column’s</p><p>strength, the experts watched in disbelief as</p><p>it withstood six times the weight anticipated.</p><p>A famous photograph shows the vindicated</p><p>architect below the test column loaded up</p><p>with sand bags. Since that time many incredi-</p><p>ble structures have been constructed and</p><p>a few have been plagued with structural col-</p><p>lapse. The causes of structural failure vary.</p><p>Obviously, a structural failure is related to a</p><p>lack of strength and redundancy; however,</p><p>the precise mechanism attributed to the col-</p><p>lapse is not always clear. In the case of an</p><p>earthquake, a structure’s lack of flexibility</p><p>can cause failure. Precast concrete buildings’</p><p>structures have folded like card houses under</p><p>earthquake loads due to the inflexibility of</p><p>their connections. In bridge design, too much</p><p>flexibility can trigger a failure due to excessive</p><p>oscillation. Each mode of failure challenges</p><p>the design and construction profession to</p><p>better understand building materials and how</p><p>to use them.</p><p>The lessons learned from past problems can</p><p>help shape the buildings of the future. Tradi-</p><p>tional reinforced concrete combines the com-</p><p>pressive strength of stone and the tensile</p><p>strength of steel. Concrete and masonry are</p><p>fundamental building materials and designers</p><p>are constantly trying to make them better.</p><p>Innovative products, such as ultrahigh-per-</p><p>formance concrete, have given our engineers</p><p>Structure</p><p>108 109</p><p>above The strength of a thin</p><p>concrete shell can be better</p><p>understood by the analogy of</p><p>the un-breakable egg in a</p><p>squeezing hand. The concen-</p><p>trated load of a ring will, how-</p><p>ever, break the shell easily.</p><p>right The load path for the</p><p>Tod’s Omotesando office</p><p>building in Tokyo, completed</p><p>in 2004. 30cm (12 inch) thick</p><p>concrete limbs become</p><p>increasingly slender as they</p><p>rise to the top of the building,</p><p>reflecting the loads they need</p><p>to support.</p><p>page 109 Johnson Wax</p><p>Building, Racine, Wisconsin,</p><p>1937.</p><p>p_108_129_chapt_7_bp 18.10.2006 11:35 Uhr Seite 108</p><p>p_108_129_chapt_7_bp 18.10.2006 11:35 Uhr Seite 109</p><p>and architects the chance to develop new</p><p>construction techniques. 21st-century build-</p><p>ings expose their structures with greater will-</p><p>ingness. The shapes of these structures often</p><p>resemble natural forms; like the limb of a</p><p>tree, the structural members become smaller</p><p>as they rise up through the building. Thin-</p><p>shelled structures appear to defy gravity,</p><p>spanning great distances with very thin sec-</p><p>tions. The strength of a thin concrete shell</p><p>design can be understood by simply squeez-</p><p>ing an egg in your hand. The forces on the</p><p>egg are uniformly distributed over the shell,</p><p>making it very difficult if not impossible to</p><p>crush it. Similarly, the squeezing force that the</p><p>ground exerts upon the shell of a tunnel uni-</p><p>formly compresses the structure, unable to</p><p>make it collapse. The shell structure’s design-</p><p>er must consider the loads applied to it. If the</p><p>same hand that holds the egg wears a ring,</p><p>the crown of the ring can easily puncture the</p><p>egg’s shell with the same squeezing force.</p><p>This chapter explores a series of great struc-</p><p>tures constructed of concrete, masonry and</p><p>stone. Some of the projects were successful</p><p>and some were not.</p><p>Terminal 2E at the Charles de Gaulle Inter-</p><p>national Airport, completed in 2003 at a cost</p><p>of 750 million dollars, features a stunning,</p><p>airy elliptical concrete tube structure approxi-</p><p>mately 33.5m (110 feet) wide and 305m</p><p>(1,000 feet) long. The new terminal was</p><p>intended to transform Paris into the most pow-</p><p>erful air transport hub in Europe. The build-</p><p>ing’s skin consists of a double shell assembly</p><p>with an outer layer of glass and aluminum and</p><p>an inner shell structure of reinforced concrete.</p><p>The shape of the building stemmed from the</p><p>Parisian airport authority’s requirement that</p><p>there be no intermediate interior supports to</p><p>restrict the flow of passengers through the ter-</p><p>minal. The outer skin consisted of a glass sup-</p><p>ported by metal framing, preventing air and</p><p>water from entering the terminal. The elegant</p><p>inner shell was built with prefabricated 3.66m</p><p>(12 foot) reinforced concrete ring sections.</p><p>Each 54.4 tonne (60 ton) ring section rested</p><p>above Interior view of Termi-</p><p>nal 2E, Charles de Gaulle</p><p>International Airport, complet-</p><p>ed in 2003.</p><p>p_108_129_chapt_7_bp 18.10.2006 11:35 Uhr Seite 110</p><p>on four cast-in-place reinforced concrete</p><p>pylons. The long elliptical tube was formed by</p><p>interlocking concrete sections. Each vault ring</p><p>is made up of three pieces. The top piece is</p><p>nearly horizontal, straddled by the two-side</p><p>pieces. The 30cm (12 inch) thick concrete</p><p>walls allow light into the structure with a repet-</p><p>itive series of rectangular holes that pierce</p><p>through the shell. The contractor erected each</p><p>of the sections on mobile falsework and struc-</p><p>turally tied them together. To stiffen the shal-</p><p>low vault and provide support for the outer</p><p>glass enclosure, curved steel girders embrace</p><p>the concrete shell. The tensile girders are held</p><p>away from the vault by regularly spaced,</p><p>10cm (4 inch) diameter steel struts on 20cm</p><p>(8 inch) diameter plates embedded in roughly</p><p>10cm (4 inch) deep concrete shell recesses.</p><p>Air ducts and artificial lighting for the terminal</p><p>are located between the two skins. The build-</p><p>right and below Terminal 2E,</p><p>Charles de Gaulle International</p><p>Airport, Paris. The collapsed</p><p>structure cleanly sheared</p><p>away from adjacent sections of</p><p>the double shell enclosure.</p><p>1 Terminal 2E departure</p><p>lounge, prior to collapse.</p><p>2 One large walkway access</p><p>point to the terminal penetrat-</p><p>ed the shell at the area of the</p><p>collapse.</p><p>3 Two plane-boarding walk-</p><p>ways cut through the concrete</p><p>shell in the area of the col-</p><p>lapse.</p><p>4 10cm (4 inch) steel struts</p><p>transfer concentrated loads</p><p>from the outer shell to the</p><p>inner structure.</p><p>5 Glass enclosure system in</p><p>aluminum frame supported by</p><p>steel girders.</p><p>6 Metal supports had report-</p><p>edly pierced the inner con-</p><p>crete shell structure.</p><p>p_108_129_chapt_7_bp 18.10.2006 11:35 Uhr Seite 111</p><p>ing combined complex engineering with com-</p><p>plex construction techniques. The concrete</p><p>shell structure by itself has no internal load-</p><p>bearing members; instead, it relies on the thin</p><p>shell walls to provide support.</p><p>The basic design of the terminal used tech-</p><p>nology developed for concrete-lined tunnels</p><p>to provide a column-free space on the interior.</p><p>Underground tunnels use thin concrete walls</p><p>to provide a column-free space for trains and</p><p>travelers similar to Terminal 2E; however, the</p><p>earth pressure surrounding a tunnel uniformly</p><p>compresses the structure, keeping all ele-</p><p>ments in compression. In the design of Termi-</p><p>nal 2E, these principles had to be adapted</p><p>because there was no soil on the outside of</p><p>the shell to provide uniform pressure on the</p><p>free-standing structure.</p><p>In the early morning, approximately 7 a.m. on</p><p>Sunday May 23, 2004, just 12 months after</p><p>the terminal’s opening, a large section of the</p><p>airport terminal collapsed.The 30m(98.5 foot)</p><p>long by 20m (65.6 foot) wide reinforced con-</p><p>crete section of the terminal enclosure fell,</p><p>taking with it the glass and metal tube of the</p><p>outer shell. The collapsed section cleanly</p><p>sheared away from adjacent sections of the</p><p>double shell, which remained intact. There</p><p>was some warning before the accident. At</p><p>5:30 a.m. it is reported that a large spalled</p><p>section of concrete fell from an overhead arch,</p><p>passengers reported seeing cracks appear in</p><p>the roof elements and dust falling from the</p><p>ceiling. Ninety minutes later, the roof caved in.</p><p>The area that collapsed was a section of the</p><p>terminal containing access points for three</p><p>boarding walkways. The lower sections of</p><p>three alternating concrete rings were omitted</p><p>in order to provide access for these walkways</p><p>into the departure lounge. Steel connections</p><p>transferred loads from the shortened rings to</p><p>the full ones on either side. This is a different</p><p>condition when compared to the rest of the</p><p>terminal structure.</p><p>There are many theories regarding the demise</p><p>of Terminal 2E. External forces on the building</p><p>have been ruled out, as there were no large</p><p>wind, snow or earthquake loads to trigger the</p><p>collapse. Some looked to construction prob-</p><p>lems with the base of the building for explana-</p><p>tions. Before the concourse opened, support-</p><p>ing pillars were repaired and reinforced with</p><p>carbon fibers after fissures appeared in the</p><p>concrete. This, however, was in an area away</p><p>from the collapsed section of the terminal.</p><p>Others look to the construction of the vault</p><p>itself. The elliptical arch pushed the limits of</p><p>conventional vault design, the curvature con-</p><p>tinuing beyond the vertical without conven-</p><p>tional abutments other than the reinforcing</p><p>steel hoops to stop it from spreading. Some</p><p>believe the structural design of the building</p><p>was insufficiently analyzed for all conditions</p><p>of the project. Analysts believe additional com-</p><p>puter modeling and computations should</p><p>have been completed prior to constructing the</p><p>terminal. The official report following the acci-</p><p>dent indicated simultaneous and interlinked</p><p>failure of two elements giving rise to the cata-</p><p>strophic collapse of the terminal element. At</p><p>the footbridge opening, on the north side, sev-</p><p>eral external struts appear to have punctured</p><p>the shell. Retrospective calculations showed</p><p>some struts would have been overstressed. It</p><p>is probable that this</p><p>perforation was made</p><p>possible by the prior gradual deterioration of</p><p>the concrete. The second failure was immedi-</p><p>ately opposite, on the south side of the termi-</p><p>nal. The shell edge beam appears to have</p><p>fractured, falling off its bearing to the ground.</p><p>Either mechanism could have been the trigger</p><p>to cause the collapse of the terminal. The</p><p>report also cited the extreme thermal cycling</p><p>of the reinforced concrete that could have</p><p>exacerbated initial cracking, and the lack of</p><p>redundancy in the structure.</p><p>Ironically, France has been a center for struc-</p><p>tural innovation. François Hennebique devel-</p><p>oped the concept of reinforced concrete in</p><p>the 1870s and Eugène Freyssinet invented</p><p>“prestressed” concrete in the 1920s. More</p><p>recently, Lafarge, world leaders in concrete</p><p>innovation, introduced Ductal, an ultrahigh</p><p>performance concrete mix. It would appear</p><p>that the fashion for increasingly innovative</p><p>buildings has strained the limits of safety in</p><p>France. However, there are a great number of</p><p>historical buildings that achieved everything</p><p>the Terminal 2E design desired with intuitive</p><p>structural form.</p><p>112 113</p><p>page 113 Penetrations in</p><p>the concrete structure allow</p><p>for natural light to enter into</p><p>the terminal.</p><p>Terminal 2E, Charles de Gaulle</p><p>International Airport.</p><p>p_108_129_chapt_7_bp 18.10.2006 11:35 Uhr Seite 112</p><p>p_108_129_chapt_7_bp 18.10.2006 11:35 Uhr Seite 113</p><p>114 115</p><p>p_108_129_chapt_7_korr_bp.qxd 30.10.2006 13:31 Uhr Seite 114</p><p>Structural Form</p><p>Completed in 1962, the Dulles International</p><p>Terminal provides an excellent example of a</p><p>structure that is true to its form. A huge con-</p><p>crete sheet is slung between two asymmetric</p><p>rows of concrete columns. Like a large ham-</p><p>mock suspended between leaning concrete</p><p>trees, the terminal’s structural design can eas-</p><p>ily be understood and analyzed. Invisible with-</p><p>in the concrete ceiling of the terminal are steel</p><p>suspension-bridge cables that support the</p><p>weight of the concrete roof. Since the load</p><p>from the suspension cables is quite large, it</p><p>was necessary to both heavily reinforce the</p><p>concrete columns with steel and also can-</p><p>tilever them outward to counteract the inward</p><p>acting force from the roof. The connections at</p><p>the “horse head” tops of the columns are the</p><p>most critical in the structure. Here two differ-</p><p>ent systems come together where the load</p><p>transfer is the greatest. The connection con-</p><p>sists of steel tension cables connected to a</p><p>site cast concrete beam. The concrete beam</p><p>is curved, rising in the plane at the top of the</p><p>column capitals.</p><p>The building design requirements at Dulles</p><p>are similar to those of the Terminal 2E in Paris.</p><p>In its current form, the ground floor slab is</p><p>305m (1000 feet) by 50m (164 feet) by 21m</p><p>(68 feet) high. The tarmac façade piers are</p><p>15m (50 feet) high. The piers are spaced</p><p>12.2m (40 feet) apart. Similar to Terminal 2E,</p><p>the Dulles Terminal has no intermediate interi-</p><p>or supports that would restrict the flow of pas-</p><p>sengers through the terminal. The load path of</p><p>forces is more easily understood at the Dulles</p><p>Terminal than at Terminal 2E. Forces acting</p><p>on the roof are transferred in tension to the</p><p>ends of the leaning concrete columns. The</p><p>load is transferred downward to the ground</p><p>through the massive reinforced concrete</p><p>columns. The columns are kept in equilibri-</p><p>um due to the slab between the piers, keeping</p><p>them from pulling inward. This simple yet</p><p>unique structural system allows for an</p><p>extremely open and lengthy span.</p><p>page 114 and below The</p><p>material form of Jean Nouvel’s</p><p>Torre Agbar in Barcelona,</p><p>completed in 2005, is similar</p><p>to Terminal 2E: concrete tube,</p><p>with punched openings, sur-</p><p>rounded by steel frame and</p><p>aluminum glazing system.</p><p>The structural form and load</p><p>path of this tower is completely</p><p>different than that of Terminal</p><p>2E, because of how gravita-</p><p>tional forces flow through it.</p><p>right Dulles International</p><p>Airport, Washington, D.C.,</p><p>1962.</p><p>right Different structural solu-</p><p>tions for the same objective:</p><p>column-free space</p><p>1 Terminal 2E, Charles de</p><p>Gaulle International Airport</p><p>2 Main Concourse, Dulles</p><p>International Airport</p><p>p_108_129_chapt_7_bp 18.10.2006 11:36 Uhr Seite 115</p><p>Each pier is independently supported, like a</p><p>flagpole, in all four directions giving it individ-</p><p>ual stability and structural independence. Very</p><p>deep foundations were cast into the ground in</p><p>order to make this system work. The two glass</p><p>end walls and the infill walls between the con-</p><p>crete piers are structurally independent of the</p><p>main system. The great scale of the building is</p><p>a factor in the overall stability of the structure.</p><p>The building is kept in equilibrium by the</p><p>massive weight of the roof structure. Wind and</p><p>snow loads are minimal in comparison with</p><p>these large forces. Temperature changes also</p><p>greatly affect the expansion and contraction</p><p>of components for a large structural system.</p><p>Both steel and concrete have a similar modu-</p><p>lus of elasticity. They tend to expand and con-</p><p>tract at the same rate, giving the system a con-</p><p>tinuity of deformation. When there is expan-</p><p>sion or contraction at Dulles, the caternary</p><p>shape of the spanning cables becomes flatter</p><p>or deeper to compensate. The Dulles Inter-</p><p>national Airport structure is easy to under-</p><p>stand and analyze. Other building designs</p><p>Simmons Hall at MIT. A draw-</p><p>ing using colored pencil creat-</p><p>ed to check steel reinforce-</p><p>ment became the inspiration</p><p>for the final design.</p><p>Simmons Hall at MIT, Cam-</p><p>bridge, Massachusetts, 2002.</p><p>Color coated red precast con-</p><p>crete panels identify units that</p><p>span large openings, acting</p><p>like a Vierendeel truss.</p><p>p_108_129_chapt_7_korr_bp 27.10.2006 14:40 Uhr Seite 116</p><p>have even stylishly presented elements of</p><p>their structural analysis directly on the build-</p><p>ing façade to provide a clear illustration of</p><p>the structure’s function.</p><p>Structural Analysis</p><p>The load path within a building structure is</p><p>not always easy to understand from the view-</p><p>point of someone looking up at it from the</p><p>street. In the case of Simmons Hall, at the</p><p>MIT campus, the designers offer assistance.</p><p>Completed in 2002, this large dormitory at the</p><p>edge of MIT’s campus is of overwhelming</p><p>scale. The designers sought to diminish the</p><p>appearance of the building by making it</p><p>visually “porous.” A second goal was to keep</p><p>the interior as flexible and open as possible</p><p>in order to maximize social interaction among</p><p>residents. The solution was to place the pri-</p><p>mary structure at the perimeter of the build-</p><p>ing, using a gridded, precast system dubbed</p><p>“PerCon” for “perforated concrete.” The</p><p>architect, Steven Holl, had always intended</p><p>to include color on the outer concrete façade.</p><p>Initially, the thought was to have outside col-</p><p>ors reflect inside function in the building;</p><p>however, during the design process a drawing</p><p>created to check steel reinforcement by</p><p>Amy Schreiber, an engineer from Simpson</p><p>Gumpertz & Heger Inc. Structural Engineers</p><p>(in collaboration with Guy Nordenson and</p><p>Associates), became the inspiration for the</p><p>final design. Amy’s drawing used color pencils</p><p>to identify the amount of steel reinforcement</p><p>in each respective concrete panel.</p><p>This graphical diagram was translated into the</p><p>aluminum cladding on the precast concrete</p><p>façade panels. The load path of forces at the</p><p>building perimeter is literally identified with</p><p>colors on the façade.</p><p>The building structure of Simmons Hall is</p><p>easily understood from the street. Similar to</p><p>the colored output produced by some com-</p><p>puter software programs, color is used to dif-</p><p>ferentiate various stresses on the structure</p><p>under loading. The building façade appears</p><p>to reference the computer analysis that was</p><p>used to create it. Like many modern build-</p><p>ings, the design of Simmons Hall was made</p><p>possible by the use of computer analysis.</p><p>Computers using finite element software have</p><p>provided a method for analyzing extremely</p><p>difficult statically indeterminate structures.</p><p>But what</p><p>happened before the invention of</p><p>the computers, when there was just paper</p><p>and pencil?</p><p>above and right Simmons</p><p>Hall at MIT. Precast concrete</p><p>panels lifted into place and</p><p>assembled.</p><p>right Simmons Hall at MIT.</p><p>Like a Vierendeel truss, the</p><p>precast concrete panels inter-</p><p>connect with steel reinforce-</p><p>ment to span large and small</p><p>openings.</p><p>p_108_129_chapt_7_bp 18.10.2006 11:36 Uhr Seite 117</p><p>118 119</p><p>Antonio Gaudí used models of steel chains</p><p>covered in clay, hung from the ceiling, to</p><p>design the emorfic structure of Casa Milla, in</p><p>Barcelona in 1904. Robert Maillart used static</p><p>graphics to design the innovative reinforced</p><p>concrete bridges at Salgina, Switzerland, in</p><p>1929. Perhaps the greatest modern masonry</p><p>structural designs of the 20th century come</p><p>from the work of Eladio Dieste using tech-</p><p>niques similar to those of Maillart and Gaudí.</p><p>Dieste’s work was confined to the country of</p><p>Uruguay, but otherwise had no boundaries.</p><p>The building structures provide solutions</p><p>using innovative techniques for their time and</p><p>local building experience with masonry con-</p><p>struction. One of Dieste’s greatest structural</p><p>forms was the self-supporting arch.</p><p>The Municipal Bus Terminal in Salto, Uruguay,</p><p>completed in 1974, provides a classic exam-</p><p>ple of how daring structural forms were devel-</p><p>oped prior to the advent of sophisticated com-</p><p>puter analysis. A single row of columns is all</p><p>that supports the long self-carrying vaults with</p><p>equal cantilevers of 12.2m (40 feet). These</p><p>cantilevered vaults are ideal for sheltering</p><p>travelers coming in and out of the buses at</p><p>the station. The self-carrying vault is achieved</p><p>using innovative prestressing techniques that</p><p>could be simply executed by local laborers.</p><p>Timber trusses provide the formwork for posi-</p><p>tioning the bricks on the vault. The bricks</p><p>are evenly separated by small wood strips.</p><p>Steel-reinforcing bars are placed between the</p><p>bricks, and the joints are filled with mortar.</p><p>right Computer model of seis-</p><p>mic loading of concrete build-</p><p>ing structure in contemporary</p><p>design.</p><p>Robert Maillart used static</p><p>graphics to design the innova-</p><p>tive reinforced concrete</p><p>bridges at Salgina, Switzer-</p><p>land, 1929.</p><p>p_108_129_chapt_7_bp 18.10.2006 11:36 Uhr Seite 118</p><p>above Church of Christ the</p><p>Worker, designed by Eladio</p><p>Dieste, Atlántida, Uruguay,</p><p>1960.</p><p>left Casa Milla, designed by</p><p>Antonio Gaudí, Barcelona,</p><p>1904.</p><p>p_108_129_chapt_7_bp 18.10.2006 11:36 Uhr Seite 119</p><p>A large looped prestressed steel cable is</p><p>then installed to absorb the negative bending</p><p>moment on the vault. With the vault still sup-</p><p>ported by formwork, the ends of the loop are</p><p>cast into the vault. After the lightweight con-</p><p>crete has hardened, the prestressing cable</p><p>is mechanically pinched at the mid-point of</p><p>the vault. The mid-section of the vault is then</p><p>covered with mesh and filled with lightweight</p><p>concrete to complete the roof. Although com-</p><p>plicated by contemporary developments,</p><p>prestressing has been used for thousands of</p><p>years. A good example of prestressing can</p><p>be seen in the fabrication of an old cart</p><p>wheel. The heating of the iron outer band of</p><p>the wheel prior to placing it around the cart</p><p>wheel provides a form of prestressing. As</p><p>the steel band cools, it contracts, clamping</p><p>the wood parts together. In a similar manner,</p><p>Eladio Dieste developed a method of pre-</p><p>stressing with the same inherent simplicity,</p><p>requiring no heavy equipment. Prestressing</p><p>creates much larger forces in a building</p><p>element than the element would normally</p><p>experience through normal use. What hap-</p><p>pens if the natural forces are much greater</p><p>than expected?</p><p>120 121</p><p>below Prestressing of a self-</p><p>supporting arch.</p><p>1 Lightweight concrete</p><p>2 Unbraced lightweight con-</p><p>crete</p><p>3 Prestress cable</p><p>4 Reinforcement anchor</p><p>f Force of jack</p><p>F Force of prestress</p><p>The Municipal Bus Terminal in</p><p>Salto, Uruguay, 1974.</p><p>right and below The Munici-</p><p>pal Bus Terminal in Salto.</p><p>p_108_129_chapt_7_bp 18.10.2006 11:36 Uhr Seite 120</p><p>Earthquake Loads</p><p>The dome of the Hagia Sophia, Istanbul,</p><p>Turkey, partially collapsed in 553 and 557 and</p><p>again in 989 and 1435, always as a result of</p><p>earthquakes. A dome relies on its own weight</p><p>to provide strength to its structure; however, a</p><p>dome’s rigidity makes it sensitive to soil move-</p><p>ments and differential settlements. Large</p><p>buildings that are located on or near the</p><p>world’s seismic bands must be designed to</p><p>accommodate the shifting earth below. In this</p><p>type of design, strength by itself is not enough</p><p>to resist these extreme forces. Building</p><p>designs must integrate flexibility.</p><p>The design of the Imperial Hotel of Tokyo,</p><p>completed in 1922, had to consider the risk</p><p>of earthquakes and the infernos that would</p><p>inevitably follow. Unlike traditional Japanese</p><p>construction of wood and paper architecture,</p><p>the new Imperial Hotel was constructed of</p><p>reinforced concrete, stone and brick. Frank</p><p>Lloyd Wright developed a system of founda-</p><p>tions and concrete structural supports that</p><p>balanced the load of the building on can-</p><p>tilever concrete piers. The design of the sup-</p><p>ports was not unlike the fingers that support</p><p>a tray held overhead by the hand of a waiter.</p><p>The entire structure rode on a grid of thin</p><p>concrete pins, 2.75m (9 feet) deep and</p><p>0.60m (2 feet) apart. The concrete pins</p><p>loosely connected the building to a mud sub-</p><p>strate below. Flexibility and strength are what</p><p>saved the building from the devastating Kanto</p><p>quake in 1923, just one year after its comple-</p><p>tion. A legendary telegraph from the region</p><p>back to Wright in the U.S. proclaimed: “Tokyo</p><p>is destroyed … the New Imperial Hotel still</p><p>stands.” Other works by Wright have had less</p><p>success with moving earth.</p><p>The Hagia Sophia, Istanbul,</p><p>built in the 6th century.</p><p>The Imperial Hotel of Tokyo,</p><p>completed in 1922.</p><p>p_108_129_chapt_7_bp 18.10.2006 11:36 Uhr Seite 121</p><p>Built in 1924, the Ennis-Brown House in Los</p><p>Angeles was named for its original owners,</p><p>Mabel and Charles Ennis. The home is</p><p>famous for a luxurious pool, artistic glass</p><p>doors, ironwork, and intricate concrete block</p><p>cladding. The monumental scale of the house</p><p>is softened by the human scale of the con-</p><p>crete forms, and the combination of plain and</p><p>patterned blocks. Wright believed that steel</p><p>combined with concrete could be the great</p><p>liberating element that would produce an</p><p>entirely new architecture for the 20th century.</p><p>The main part of the building is constructed</p><p>on bedrock; however, a large portion of the</p><p>house is surrounded by large concrete-block</p><p>retaining walls that support the outside</p><p>perimeter of the complex. The design of the</p><p>perimeter retaining walls has proven to be</p><p>less than adequate for the moving earth of</p><p>southern California. Plagued by a 1994 North-</p><p>ridge earthquake and a devastating series of</p><p>122 123</p><p>The Ennis-Brown House,</p><p>Los Angeles, 1924. Exterior</p><p>concrete block retaining walls</p><p>crumbled after an earthquake</p><p>and subsequent mud slides.</p><p>Church of Padre Pio, San Gio-</p><p>vanni Rotondo, Italy, 2004.</p><p>p_108_129_chapt_7_bp 18.10.2006 11:36 Uhr Seite 122</p><p>storms in 2005, the earth below the retaining</p><p>walls has washed away, taking the concrete</p><p>block walls with it. More contemporary build-</p><p>ings composed of stone blocks have been</p><p>designed to resist the forces that the Ennis-</p><p>Brown House could not.</p><p>Built as a place for Christian pilgrimage, Renzo</p><p>Piano’s Church of Padre Pio rests on land,</p><p>subject to seismic loading near the southern</p><p>heel of Italy’s “boot.” Completed in 2004, the</p><p>church is constructed with a structural system</p><p>of cream-colored limestone blocks. The goal</p><p>was to build a church of stone, yet with a</p><p>lightweight, modern structure. Capable of</p><p>sustaining the forces of an earthquake, the</p><p>slender limestone arches, which serve to sta-</p><p>bilize the building and to resist earthquakes,</p><p>are tensioned internally with continuous steel</p><p>cables. The building’s ability to flex provides a</p><p>safe response to the forces of an earthquake.</p><p>The structure is composed of two intersecting</p><p>rows of segmental arches, laid out in radial</p><p>plan. The larger arches converge in a funnel-</p><p>like form behind the pulpit. Steel struts rising</p><p>from the arches support the laminated wood</p><p>roof with its stuccoed underside and its green,</p><p>segmented outer shell of preoxidized copper</p><p>roofing. The V-shaped stainless steel struts</p><p>separate and articulate structural compo-</p><p>nents, allowing clerestory illumination of the</p><p>curved ceiling above the arches.</p><p>The calcareous stone was specially selected</p><p>from local quarries, visually examined for</p><p>obvious cavities, and tested with ultrasound to</p><p>verify the internal homogeneity of the block.</p><p>These non-destructive tests were substantiat-</p><p>ed with selected destructive testing of sample</p><p>material from the blocks. Following a careful</p><p>color match, the stone was ready for fabrica-</p><p>tion in the sophisticated composite arch</p><p>design. Relying on the precision of advanced</p><p>stone fabrication technologies stone blocks</p><p>Section through the Church of</p><p>Padre Pio showing the great</p><p>stone arches with inherent</p><p>flexibility.</p><p>p_108_129_chapt_7_bp 18.10.2006 11:36 Uhr Seite 123</p><p>were cut with extreme accuracy prior to ship-</p><p>ping to the site.</p><p>The arches are posttensioned to precompress</p><p>the stone and reduce the subsequent risks</p><p>of failure under tensional stresses. The stone</p><p>was drilled to take sleeves for steel cables.</p><p>The stone pieces were then stacked and</p><p>bonded with two-part epoxy resin and a 2mm</p><p>(1/16 inch) stainless steel space plate to ensure</p><p>a consistent junction between stones. With all</p><p>of the blocks in place, the tension cables were</p><p>mechanically inserted. The steel scaffolds</p><p>were lowered and the cables were tensioned.</p><p>The flexibility of a great structure is critical to</p><p>a building in a seismic zone; however, too</p><p>much flexibility can be hazardous to a mas-</p><p>sive structure.</p><p>Flexibility</p><p>The Tacoma Narrows Suspension Bridge,</p><p>constructed in 1940, was a graceful structure</p><p>of enormous proportions. It consisted of two</p><p>towers that supported main cables hung in a</p><p>parabolic configuration from which slender</p><p>steel deck girders were suspended by further</p><p>vertical cables. The concrete deck on which</p><p>cars drove was constructed between the two</p><p>slender girders. The girders had a depth of</p><p>2.4m (8 feet) with a span of 853m(2,800 feet)</p><p>124 125</p><p>World tectonic plates</p><p>1 Pacific Plate</p><p>2 Cocos Plate</p><p>3 Nazca Plate</p><p>4 Caribbean Plate</p><p>5 South American Plate</p><p>6 African Plate</p><p>7 Arabian Plate</p><p>8 Indo-Australian Plate</p><p>9 Eurasian Plate</p><p>10 Philippine Plate</p><p>11 North American Plate</p><p>12 Antarctic Plate</p><p>Referenced buildings</p><p>A Hagia Sophia</p><p>B Ennis-Brown House</p><p>C Imperial Hotel</p><p>D Church of Padre Pio</p><p>Interior base detail, the</p><p>Church of Padre Pio</p><p>1 Posttension cable threaded</p><p>through stone arch</p><p>2 Limestone block with seal-</p><p>able joints</p><p>3 Stainless steel V-strut</p><p>4 Concrete arch footing clad</p><p>with limestone 10cm (4 inch-</p><p>es) thick</p><p>5 Honed limestone flooring</p><p>right Advanced fabrication</p><p>techniques allowed for</p><p>the large stone to be cut</p><p>with extreme precision for</p><p>the arches of the Church</p><p>of Padre Pio.</p><p>p_108_129_chapt_7_korr_bp 27.10.2006 14:40 Uhr Seite 124</p><p>from tower to tower. The slender nature of this</p><p>deck was part of its elegance as well as its</p><p>demise. Uncontrolled oscillation was a prob-</p><p>lem from the time the bridge was completed</p><p>in July 1940. The flexible nature of the bridge</p><p>caused travelers to become motion-sick</p><p>with its movements and the bridge quickly</p><p>acquired the nickname, Galloping Gertie. On</p><p>November 7, just four months after its com-</p><p>pletion. the Tacoma Bridge was destroyed by</p><p>aerodynamic wind oscillations. The concrete</p><p>deck was said to have broken up like pop-</p><p>corn. Huge chunks of concrete broke from</p><p>the deck as oscillation of the bridge reached</p><p>its peak. Tearing itself apart, the twisting</p><p>undulations of the bridge reached an ampli-</p><p>tude of 7.5m (25 feet) before a 183m (600</p><p>foot) length of the bridge deck tore away from</p><p>the suspension cables and plunged into the</p><p>water below. The collapse of the Tacoma Nar-</p><p>rows Bridge became even more infamous as</p><p>its destruction was caught on film. How could</p><p>such a bridge deck twist and jump like a rub-</p><p>ber band under relatively normal winds, and</p><p>how could it have been avoided? The princi-</p><p>pal cause of the failure was later understood</p><p>to stem from the aerodynamic behavior of the</p><p>bridge deck; essentially, the slender deck sec-</p><p>tion caused it to behave like an aircraft wing,</p><p>inducing the destructive undulating motion.</p><p>Bridge designers of today carry out routine</p><p>wind tunnel testing during the design phase</p><p>of a project to avoid such disasters. There</p><p>was a device that could have saved Galloping</p><p>Gertie, after it had been constructed with the</p><p>faulty design. Unfortunately, it was developed</p><p>40 years after its steel frame collapsed into</p><p>the Tacoma Narrows.</p><p>Tuned Mass Dampers</p><p>A tool developed to correct oscillations of</p><p>structures, similar to those experienced by the</p><p>Tacoma Narrows Bridge, are tuned mass</p><p>dampers. These prevent progressive increase</p><p>in the magnitude of aerodynamic oscillations.</p><p>The technique allows for span oscillations</p><p>to be counteracted by means of a dynamic</p><p>damper. This was successfully done for the</p><p>first time on a bridge in 1990 to damp oscilla-</p><p>tions of the Bronx-Whitestone Bridge in New</p><p>York. A tuned dynamic damper is also used</p><p>above The replacement</p><p>bridge for the Tacoma Narrows</p><p>was redesigned with deep</p><p>open truss members that allow</p><p>wind to pass through them.</p><p>The construction of the sec-</p><p>ond design was completed in</p><p>1950.</p><p>below The Tacoma Narrows</p><p>Suspension Bridge, built in</p><p>1940 across Puget Sound in</p><p>Washington, was the first of its</p><p>type to use plate girders to</p><p>support the concrete roadbed.</p><p>With this new thin design,</p><p>wind was diverted above and</p><p>below the structure.</p><p>p_108_129_chapt_7_bp 18.10.2006 11:36 Uhr Seite 125</p><p>in tall-building construction to avoid the</p><p>inconvenience of airsickness to the tenants</p><p>and protect the building from eventual col-</p><p>lapse. A tuned damper consists of a large</p><p>mass that is allowed to float on the top of a</p><p>structure. The mass is connected to the struc-</p><p>ture by steel springs and shock absorbers.</p><p>In its early stages, mass dampers were set on</p><p>thin layers of oil that would allow for their free</p><p>movement. When the structure starts oscillat-</p><p>ing, the damper tends to stay in the same</p><p>location because of its large mass and allows</p><p>the structure to slide under it as it floats by.</p><p>When this happens, the springs on one side</p><p>of the damper become longer and pull the</p><p>structure back, while those on the opposite</p><p>side become shorter and push it back to</p><p>its original position. In order to be effective,</p><p>the mass of the damper must be tuned to</p><p>have the same period as that of the structure.</p><p>Hence the name “tuned mass damper.”</p><p>Tuned mass dampers are also used to remove</p><p>oscillations due to the movement of large</p><p>groups of pedestrians crossing flexible struc-</p><p>tures.</p><p>The Seonyu Footbridge, completed in 2002,</p><p>provides a recent example of a tuned mass</p><p>damper used in a very slender bridge struc-</p><p>ture. The design of the footbridge provides a</p><p>pedestrian link from the city of Seoul, to</p><p>Seonyu Footbridge, Seoul,</p><p>2002.</p><p>1 Ultrahigh-performance</p><p>precast concrete structure</p><p>2 Tuned mass damper</p><p>concealed below bridge deck</p><p>to reduce later motion of</p><p>bridge</p><p>p_108_129_chapt_7_bp 18.10.2006 11:36 Uhr Seite 126</p><p>Sunyudo Island in the Han River. Potential</p><p>vibration of such a slender arch had to be</p><p>considered. In order to maintain comfort for</p><p>pedestrians crossing over the bridge, the</p><p>design included shock-absorbing tuned mass</p><p>dampers at the top of the arch. These limited</p><p>the horizontal acceleration to 0.2m/sec</p><p>(0.66 feet/sec) and the vertical acceleration</p><p>to 0.5m/sec (1.64 feet/sec). In addition to</p><p>the use of new structural technology, the foot-</p><p>bridge uses a relatively new type of building</p><p>material: ultrahigh-performance concrete.</p><p>The</p><p>ribs of the deck slab are prestressed by</p><p>12.5mm (1/2 inch) diameter monostrands. The</p><p>arch is composed of six segments, three on</p><p>each side. Each of the segments was prefabri-</p><p>cated in an area next to the final location of</p><p>the arch. Diaphragms were added at the ends</p><p>of each segment. The segments are 20–22m</p><p>(65.6–72.2 feet) long and curved. Each of the</p><p>sections is formed from 22.5m3 (803 cubic</p><p>feet) of concrete, cast in a metal mold. During</p><p>the casting operations, the fluidity of the con-</p><p>crete mix is constantly checked and con-</p><p>trolled. After casting a segment, it is cured in</p><p>the mold for 48 hours at 35º C. The segment</p><p>is then lifted to a heat treatment chamber,</p><p>where it is steam-cured at 90º C for 48 hours.</p><p>The six completed segments are positioned</p><p>in sequence on scaffolding, supported by</p><p>a river barge. The segments on each of the</p><p>half spans are stitched together and then</p><p>prestressed before the tendon ducts are</p><p>grouted up.</p><p>The slender nature of the bridge was made</p><p>possible not only by the tuned mass dampers,</p><p>but by the use of ultrahigh-performance con-</p><p>crete, a product developed by Lafarge with</p><p>the trade name Ductal.® The 1.2m (4 foot)</p><p>wide deck is slightly greater than 2.5cm</p><p>(1 inch) thick. The bridge’s slender support</p><p>structure was made possible by the resulting</p><p>Phaeno Science Center,</p><p>Wolfsburg, Germany, 2005.</p><p>Self-compacting concrete was</p><p>used to construct ten cone-</p><p>shaped support elements.</p><p>p_108_129_chapt_7_bp 18.10.2006 11:36 Uhr Seite 127</p><p>reduction in dead load from the deck. Using</p><p>ultrahigh performance in place of traditional</p><p>concrete approximately halved the amount of</p><p>material required.</p><p>Ultrahigh-performance Concrete</p><p>Ultrahigh-performance concrete contains</p><p>extremely strong fibers that in effect make the</p><p>mixture self-reinforcing. Trademarked as</p><p>Ductal, this material in its finished form is very</p><p>dense and resistant to cracking and chipping.</p><p>The material has excellent strength character-</p><p>istics and can be used to create very thin</p><p>structural members that do not require con-</p><p>ventional steel reinforcement.</p><p>Ultrahigh-performance concrete incorporates</p><p>metallic or organic fibers and is highly ductile.</p><p>Contrary to the traditionally brittle nature of</p><p>concrete, ultrahigh-performance concrete</p><p>can bend while continuing to carry load. Its</p><p>strength is six to eight times greater than con-</p><p>ventional concrete. Compressive strengths</p><p>equal to 230 MPa (33.35 ksi) can be achieved</p><p>without reinforcement. Flexural strength as</p><p>high as 60 MPa (8.70 ksi) allows the material</p><p>to undergo significant transformation without</p><p>breaking. Ultrahigh-performing concrete is</p><p>just one of a number of new concrete prod-</p><p>ucts used in construction today.</p><p>Self-compacting Concrete</p><p>To create the complex geometry of the cones</p><p>and other curved and sharp-edged portions</p><p>of a building, engineers can specify self-com-</p><p>pacting concrete, which does not need to</p><p>be vibrated when poured. Self-compacting</p><p>concrete was ideal for Zaha Hadid’s Phaeno</p><p>Science Center in Wolfsburg, Germany,</p><p>completed in 2005. In fact, many structural</p><p>forms may not have been possible if this</p><p>type of construction was not available. The</p><p>new science center is supported by ten cone-</p><p>shaped elements. Resembling the profile of</p><p>an elephant’s foot, each cone rises up through</p><p>the underground parking garage to support</p><p>the elevated floor of the main hall. The main</p><p>hall consists of 6,040m2 (65,000 square feet)</p><p>128 129</p><p>of exhibition space. Five of the cone struc-</p><p>tures continue upward to support the roof</p><p>above the exhibition hall. The building’s form</p><p>is incredibly complex with continuously</p><p>changing geometry. The heavily reinforced</p><p>cone elements were made possible with the</p><p>use of self-compacting concrete.</p><p>Self-compacting concrete is made with a sys-</p><p>tem of optimized aggregates, cements, and</p><p>admixtures including a “polycarboxylate ether</p><p>superplasticizer” which keeps the concrete</p><p>mix extremely fluid during the pouring process</p><p>without compromising strength. Self-consoli-</p><p>dating concrete fills all the voids, effortlessly</p><p>requiring no mechanical vibration once it is</p><p>in place, either to eliminate air pockets or to</p><p>ensure even distribution of the aggregate.</p><p>Autoclaved Aerated Concrete (AAC)</p><p>An important factor to consider in designing a</p><p>building structure is fire resistance. During a</p><p>fire, structural elements must provide support</p><p>for fleeing occupants as well as rescue teams</p><p>that enter the building. Cementious materials</p><p>provide excellent fire-resistant capabilities,</p><p>but can be very heavy. Autoclaved aerated</p><p>concrete (AAC) is intended to bring the fire</p><p>resistance properties of concrete to light-</p><p>weight building products.</p><p>Autoclaved aerated concrete (AAC) is com-</p><p>posed of cement-lime, water, finely ground</p><p>sand or fly ash. Aluminum flake is added to</p><p>the mix, generating gas bubbles that increase</p><p>the volume and therefore reduce the density</p><p>of the liquid. The expanded, hardened mix</p><p>is cut or shaped and then cured in an auto-</p><p>clave. An autoclave is like a giant pressure</p><p>cooker. The end result is a building material</p><p>that is so light it floats. In addition to fire</p><p>resistance, AAC blocks provide improved</p><p>insulation values for heat and sound. Prod-</p><p>ucts like autoclaved aerated concrete, ultra-</p><p>high-performance concrete and self-compact-</p><p>ing concrete are changing the way designers</p><p>are thinking about concrete. It can be light,</p><p>flexible, and cast into amorphic forms.</p><p>Phaeno Science Center.</p><p>Self-compacting concrete</p><p>support elements.</p><p>p_108_129_chapt_7_bp 18.10.2006 11:36 Uhr Seite 128</p><p>The structural collapse at the Charles de</p><p>Gaulle Airport should not restrict the way</p><p>architects think about buildings. As in the</p><p>case of the Tacoma Narrows Bridge, solutions</p><p>can be found for all problems as we advance</p><p>the art of buildings. As architects, engineers</p><p>and builders strive for innovation, there is</p><p>always a risk of failure. New building types</p><p>and forms should not be dismissed solely by</p><p>the thought that they are implausible. If this</p><p>were so, our world would be without works</p><p>like the “great hall” at the Johnson Wax Build-</p><p>ing in Racine, Wisconsin. However, the scruti-</p><p>nizing of structural solutions is an important</p><p>part of the process and should not be dis-</p><p>missed. In France, there is a distinction</p><p>between civil engineering works and build-</p><p>ings. However, there is no distinction between</p><p>complex projects. While complicated bridges</p><p>undergo peer review, no such procedure was</p><p>applied to the Charles de Gaulle Terminal.</p><p>Concrete has always been a good material to</p><p>protect buildings from structural collapse due</p><p>to fire. New construction techniques have</p><p>improved its performance even more. Insulat-</p><p>ed Concrete Forms (ICFs) containing flame</p><p>retardant additives can improve the fire resist-</p><p>ance of concrete walls in addition to providing</p><p>greater resistance to sound transmission. The</p><p>insulated forms are not removed after pouring</p><p>the wall, but stay in place to improve the walls</p><p>ability to resist fire and sound transmission.</p><p>Although higher in cost, concrete walls made</p><p>with insulated concrete forms are challenging</p><p>the wood and metal stud wall industry by</p><p>giving builders a fast and economical way to</p><p>make concrete walls with added value.</p><p>Computer modeling and analysis has brought</p><p>confidence to new forms and daring shapes</p><p>in architectural structures. Designers need to</p><p>develop structural solutions that have clearly</p><p>understood load paths, and new systems</p><p>must be thoroughly tested. New materials like</p><p>ultrahigh-performance concrete should be</p><p>used with a complete understanding of its</p><p>potential and limitations.</p><p>1</p><p>Innovative structural systems and their com-</p><p>ponents should be thoroughly tested with</p><p>mock-ups to confirm structural analysis.</p><p>2</p><p>The load path of a structural element should</p><p>be clearly understood and the effects of the</p><p>environment (e.g. thermal expansion) fully</p><p>taken into consideration. Unforeseen forces</p><p>can cause failures in concrete</p><p>and masonry</p><p>structures.</p><p>3</p><p>Structural analysis prior to the invention of</p><p>computers used graphic statics and physical</p><p>models to predict the strength of unique</p><p>building forms before construction.</p><p>4</p><p>Buildings designed to resist earthquake loads</p><p>must be flexible and provide redundant con-</p><p>nections.</p><p>5</p><p>Too much flexibility in a structure can cause</p><p>motion sickness for occupants and lead to</p><p>structural collapse. The use of tuned mass</p><p>dampers can limit the oscillation of a struc-</p><p>ture under loading.</p><p>6</p><p>New concrete mixtures like ultrahigh-perform-</p><p>ance concrete have been developed for</p><p>greater strength and flexibility. These products</p><p>are challenging designers to rethink how to</p><p>use concrete in architecture.</p><p>Lessons Learned How Can Structural Failures</p><p>Be Avoided?</p><p>above ICF wall construction</p><p>during and after fire testing</p><p>right Insulated Concrete</p><p>Form (ICF)</p><p>p_108_129_chapt_7_bp 18.10.2006 11:36 Uhr Seite 129</p><p>The Monadnock Building in Chicago, complet-</p><p>ed in 1891, represents the last unreinforced</p><p>monolithic, load-bearing brick construction for</p><p>a high-rise building. Towering 16 stories, with</p><p>walls ranging from 30cm (12 inches) at the</p><p>top and 1.8m (6 feet) at the ground floor, the</p><p>Monadnock Building marked the culmination</p><p>of a construction method that soon thereafter</p><p>would become out of date.</p><p>With the birth of steel skeleton structures and</p><p>the curtain wall, the outer walls of buildings</p><p>became much thinner and non-load-bearing</p><p>as buildings became taller. Like wearing a</p><p>T-shirt on your body, the building envelope is</p><p>separated from the building structure. For</p><p>concrete, stone, and masonry façades, cavity</p><p>and curtain wall construction provided a</p><p>barrier method that could stop air and water</p><p>infiltration while at the same time creating the</p><p>familiar appearance of a load-bearing wall.</p><p>The change spurred new debates regarding</p><p>leakage. Many people believe that cavity wall</p><p>construction is superior to the traditional solid</p><p>wall construction that preceded it. Others</p><p>claim that solid walls are a better method of</p><p>construction. Critics of the solid load-bearing</p><p>walls complain about header courses that</p><p>extend the full width of the wall section. Those</p><p>critics believe such details facilitate leakage</p><p>of air and water into the building and provide</p><p>very little thermal separation from the exterior.</p><p>Water can track its way through the solid wall</p><p>and air can blow through cracks, making old</p><p>buildings cold, drafty, and damp, similar to</p><p>an old castle.</p><p>New construction methods are intended to</p><p>remedy these leakage problems. Any inciden-</p><p>tal moisture that finds its way through the</p><p>outer wall is captured at the base through-</p><p>wall flashings and weeped to the outside,</p><p>keeping the new buildings dry. By properly</p><p>separating the inner and outer walls with</p><p>insulation, the building can be kept warm</p><p>in the winter and cool in the summer. As a</p><p>whole, the veneer wall systems of today have</p><p>proven to be effective; however, basic princi-</p><p>Leakage</p><p>above Unlike the Monadnock</p><p>Building, the exterior walls of</p><p>modern towers cover the</p><p>building structure much like a</p><p>T-shirt drapes over a body.</p><p>right and page 131 The Mon-</p><p>adnock Building in Chicago,</p><p>completed in 1891, was con-</p><p>structed with a load-bearing</p><p>exterior wall that grew to 1.8m</p><p>(6 feet) at the ground floor.</p><p>130 131</p><p>p_130_151_chapt_8_bp 18.10.2006 12:03 Uhr Seite 130</p><p>p_130_151_chapt_8_bp 18.10.2006 12:03 Uhr Seite 131</p><p>ples are to be followed, or else modern build-</p><p>ings can quickly become like drafty, leaky old</p><p>castles.</p><p>The Vontz Center for Molecular Studies at the</p><p>University of Cincinnati was completed in</p><p>1999. The Center consists of three occupied</p><p>floors containing a variety of offices and labo-</p><p>ratories. Easily distinguished from other</p><p>masonry buildings on campus, the Vontz Cen-</p><p>ter has multi-story windows that protrude the</p><p>exterior façade in irregular shapes around the</p><p>building. The building appears as if it has</p><p>been overinflated and the brick exterior walls</p><p>appear to pillow outward. The brick walls are</p><p>non-load-bearing walls, with weeps at the</p><p>heads and sills of the panels. The bowing of</p><p>the walls is not a defect, but the preconceived</p><p>sculptural form of an exterior assembly con-</p><p>structed of prefabricated masonry panels.</p><p>The building was reportedly intended to be</p><p>finished in a reflective metallic material, but</p><p>due to a variety of considerations, including</p><p>cost, the masonry alternative was developed.</p><p>Other buildings on the campus use a similar</p><p>brick material in their façades. However, these</p><p>buildings have been constructed in more</p><p>132 133</p><p>right Complicated building</p><p>geometry has contributed</p><p>to water infiltration issues at</p><p>the Vontz Center for Molecular</p><p>Studies at the University of</p><p>Cincinnati, Ohio, 1999.</p><p>below White efflorescence</p><p>on interior masonry walls is</p><p>an indication that the building</p><p>may have water infiltration</p><p>problems. Vontz Center for</p><p>Molecular Studies.</p><p>p_130_151_chapt_8_bp 18.10.2006 12:03 Uhr Seite 132</p><p>traditional rectangular forms, without bowing</p><p>walls and tilted windows. The irregular transi-</p><p>tions resulting from the complex geometric</p><p>conditions may be linked to water infiltration</p><p>problems at the Vontz Center.</p><p>Masonry veneer walls can always be expected</p><p>to allow water to penetrate the outer wythe of</p><p>the façade. Composed of a multitude of mor-</p><p>tar joints, it would be impractical to expect the</p><p>exterior skin of a brick wall to stop all water</p><p>from getting past the face of the wall for the</p><p>lifespan of the building. In a traditional cavity</p><p>wall assembly, infiltrating water typically trav-</p><p>els down the inside face of the exterior brick,</p><p>where it is weeped at the base of the wall via a</p><p>through-wall flashing. What might appear as a</p><p>simple concept can become much more diffi-</p><p>cult to achieve with transitions that cut</p><p>through a wall at angles.</p><p>Because of the Vontz Center’s irregular shape,</p><p>the wall, window, and skylight transitions were</p><p>very difficult to execute. In addition, the major-</p><p>ity of the precast panels were prefabricated,</p><p>making through-wall flashing difficult to inte-</p><p>grate with sloped skylights and window head</p><p>conditions. In an effort to simplify these transi-</p><p>tions, it appears that some of the flashings</p><p>were applied to the surface of the masonry in</p><p>lieu of penetrating through the wall assembly.</p><p>For example, the skylight transition to the</p><p>masonry wall appears to be a surface-mount-</p><p>ed flashing connected to the outside wythe of</p><p>brick. If the flashing does not extend all the</p><p>way through the cavity, infiltrating water can-</p><p>not be directed to the exterior. Evidence of</p><p>water migration can be seen on the interior</p><p>masonry walls which are covered with a white</p><p>efflorescence powder. Brick veneer systems</p><p>typically provide a weepage path to the out-</p><p>side of the building. Weep vents are installed</p><p>at the base of an exterior wall to weep water</p><p>out of the cavity. The Vontz Center actually has</p><p>an installation of a masonry weep on the inte-</p><p>rior face of the masonry wall. For any building</p><p>envelope, it is critical to provide clear weepage</p><p>paths to the exterior for infiltrating water. For</p><p>concrete, masonry, and stone veneer walls,</p><p>understanding the basic concepts of exterior</p><p>wall construction is essential for creating a</p><p>leak-free building.</p><p>Solid Masonry Walls</p><p>Solid masonry walls consist of multiple wythes</p><p>of masonry interwoven to produce the exterior</p><p>load-bearing structure of a building. Because</p><p>the wall is the building structure, there is no</p><p>need to provide expansion joints or separate</p><p>the exterior wall from the building structure.</p><p>Solid masonry wall construction is not com-</p><p>pletely gone. Some feel it has advantages and</p><p>continue to use it in construction. Critics of</p><p>veneer walls claim a load-bearing structure</p><p>with a 10cm (4 inch) thick facing material can</p><p>limit the design possibilities for a masonry</p><p>wall. Cross bond, block bond, Gothic bond,</p><p>and other configurations that involve stag-</p><p>gered</p><p>patterns of brickwork to decorate walls</p><p>are not possible with a brick veneer wall.</p><p>Flashing details</p><p>1 Surface-applied flashings</p><p>do not allow weeping water to</p><p>be shed to the exterior.</p><p>2 Through-wall flashings</p><p>capture penetrating water and</p><p>weep it to the exterior.</p><p>right and above Skylight</p><p>flashing detail appears to be</p><p>surface-applied to masonry</p><p>in lieu of penetrating through</p><p>masonry wall. Vontz Center</p><p>for Molecular Studies.</p><p>right Masonry weep vents</p><p>can be found on the interior</p><p>face of the brick wall.</p><p>Vontz Center for Molecular</p><p>Studies.</p><p>p_130_151_chapt_8_bp 18.10.2006 12:03 Uhr Seite 133</p><p>Large projections and recesses that give a</p><p>façade depth, shadow, and texture are only</p><p>possible within narrow parameters for a</p><p>veneer wall. For this reason, many of our mod-</p><p>ern buildings appear flat. A solid masonry wall</p><p>frees the architect from having to deal with</p><p>concealment of the indispensable expansion</p><p>joints, and other peculiarities of contemporary</p><p>brick veneer and cavity wall construction.</p><p>The Lévi-Strauss School in Köpenick, Berlin,</p><p>has made a return to modern construction</p><p>with solid masonry walls. Completed in 2000,</p><p>the exterior of the building is constructed with</p><p>a complex, beautifully detailed masonry wall,</p><p>filled with interweaving layers of brick. In order</p><p>to meet German code requirements for ther-</p><p>mal protection, the exterior and interior</p><p>masonry are different. The outer masonry</p><p>work must be resistant to weathering and</p><p>frost, while the inner must be distinguished by</p><p>higher compressive strength coinciding with a</p><p>greater proportion of perforations. Poroton</p><p>bricks used on the interior provide the neces-</p><p>sary thermal requirements. In order to prevent</p><p>water damage, the bricks must be set into the</p><p>mortar without air pockets. Expansion joints</p><p>are not required, because the outer wall is</p><p>load-bearing and monolithic.</p><p>Single Wythe Construction</p><p>Single wythe construction consisting of con-</p><p>crete masonry units is often used as a cost-</p><p>saving measure for some building types. Sin-</p><p>gle wythe construction has tried to prevail</p><p>with advances in brick and block technology.</p><p>Chemically treated concrete masonry block</p><p>units are fabricated with a water repellent</p><p>agent that prevents water from penetrating the</p><p>surface of the material. The problem with this</p><p>type of system is that numerous joints related</p><p>to a concrete masonry unit wall must be con-</p><p>sidered in the design. These joints provide an</p><p>avenue for moisture to penetrate a building</p><p>134 135</p><p>Masonry wall construction</p><p>1 Solid masonry wall</p><p>2 Cavity masonry wall</p><p>Lévi-Strauss School, Köpenick,</p><p>Christoph Mäckler Architekten,</p><p>Berlin, 2000.</p><p>right and page 135</p><p>Lévi-Strauss School.</p><p>The construction photograph</p><p>shows the solid masonry</p><p>walls.</p><p>below Single whyte construc-</p><p>tion in a warehouse applica-</p><p>tion.</p><p>p_130_151_chapt_8_korr_bp 27.10.2006 15:18 Uhr Seite 134</p><p>p_130_151_chapt_8_bp 18.10.2006 12:03 Uhr Seite 135</p><p>enclosure with or without the water repellent</p><p>agent. Water can track its way to the interior</p><p>because there is no cavity separation. Single</p><p>wythe construction is common in warehouse</p><p>applications, where large areas need to be</p><p>enclosed with few openings at low cost. These</p><p>types of systems provide a minimal barrier for</p><p>water infiltration unless they incorporate an</p><p>internal drainage system that weeps water to</p><p>the exterior. In the case of precast concrete</p><p>panels, a dual seal with an internal gutter sys-</p><p>tem can be used to provide a second line of</p><p>defense for preventing air and water infiltra-</p><p>tion. Precast panels can include a layer of</p><p>insulation in the middle of the panel. These</p><p>so-called “sandwich” panels try to achieve an</p><p>effect similar to cavity wall construction in a</p><p>unitized element.</p><p>Cavity Wall Construction</p><p>Cavity wall construction consists of an outer</p><p>wythe of concrete or masonry separated from</p><p>the building structure by a cavity. Typically in</p><p>new constructions, cavity walls have an outer</p><p>wythe of masonry and an inner wythe of con-</p><p>crete block. When the inner wythe is substitut-</p><p>ed with wood or metal framing covered with a</p><p>sheathing material, the wall is referred to as</p><p>“veneer wall;” however, the cavity concept</p><p>remains.</p><p>The outside face of the cavity or veneer</p><p>assembly is expected to allow some amount of</p><p>water through it with time. A breach in the</p><p>outer barrier can come from a poorly executed</p><p>joint or the natural aging of the façade. With</p><p>time, water is expected to pass through the</p><p>outer barrier, run down the inside face of the</p><p>outer wall and weep to the exterior via a</p><p>through-wall flashing. The inner wythe or</p><p>sheathing is covered with an air and water</p><p>barrier to keep the inside dry.</p><p>Cavity walls typically have an air space in the</p><p>cavity to allow the free flow of water to the</p><p>flashings below. Older buildings used weep</p><p>ropes to wick the water out of the cavity. How-</p><p>ever, plastic and reticulated foam weeps are</p><p>more popular because they provide greater</p><p>longevity. The outer wythe of the cavity wall</p><p>can be brick, clay tile, concrete block, or</p><p>stone, anchored to one another with metal ties</p><p>which span the open collar joint. The two</p><p>wythes together can be designed as a unified</p><p>load-bearing element, but the exterior wythe is</p><p>usually designed as a non-structural veneer.</p><p>Cavity walls have many advantages including</p><p>water resistance and improved thermal per-</p><p>formance. Continuous insulation within the air</p><p>space in the cavity provides an excellent ther-</p><p>mal barrier between the building structure</p><p>and the exterior. Brick veneers are used for</p><p>reduced cost and speed of erection. Although</p><p>cavity wall construction requires multiple</p><p>trades, the erection of a wood or steel struc-</p><p>ture can occur much more quickly than a</p><p>solid masonry wall. For these systems, the</p><p>building can be enclosed and the brick façade</p><p>can follow. The merits of cavity wall and</p><p>veneer wall construction are rooted in the con-</p><p>cept of a second line of defense.</p><p>136 137 above Onterie Center,</p><p>Chicago, 1986. Cracks in con-</p><p>crete can allow water infiltra-</p><p>tion.</p><p>right Second line of defense</p><p>for concrete façade</p><p>1 Water can infiltrate a con-</p><p>crete enclosure through crack</p><p>in the wall.</p><p>2 Water is captured by</p><p>through-wall flashing at head</p><p>of windows.</p><p>3 Water is directed to exterior</p><p>through weeps.</p><p>p_130_151_chapt_8_bp 18.10.2006 12:03 Uhr Seite 136</p><p>Second Line of Defense</p><p>There are basically three methods used to</p><p>prevent leakage to the inside of the building in</p><p>a building enclosure. The first method is to</p><p>simply prevent water from penetrating the</p><p>outer barrier of enclosure. Reliance on a sin-</p><p>gle source of protection against water leakage</p><p>is a plan prone to eventual failure. The second</p><p>method is to screen the water at the outer skin</p><p>and provide an internal drainage system to</p><p>carry any incidental moisture out of the build-</p><p>ing enclosure (for instance, cavity wall system</p><p>or gutter and weep system). A third method of</p><p>enclosure design is pressure equalization.</p><p>This type of enclosure has small holes in the</p><p>outer skin of the building to prevent a pres-</p><p>sure differential at the outer layer where exten-</p><p>sive water is present.</p><p>Pressure-equalized Wall Construction</p><p>Pressure-equalized wall construction attempts</p><p>to reduce water penetration by eliminating the</p><p>air pressure differential across the outer barri-</p><p>er, with a “rainscreen design.” A rainscreen</p><p>consists of an outer layer of material separated</p><p>by a minimum 19mm (3/4 inch) drainage cavity</p><p>followed by an airtight moisture barrier at the</p><p>back of the cavity. The rainscreen drainage</p><p>cavity is wide enough to break the capillary</p><p>action and surface tension of water such that</p><p>gravity will pull the water that gets behind the</p><p>exterior, cladding down-and-out through weep</p><p>holes at the base. The outer barrier contains</p><p>openings to ensure that the internal cavity of</p><p>the enclosure will have the same pressure as</p><p>the exterior. Weepage at the base of these sys-</p><p>tems is critical to draining incidental</p><p>water that</p><p>can penetrate any of the pressure equalization</p><p>holes. For a stone wall with a rainscreen</p><p>design, joints can be left completely open on</p><p>the outer face of the wall. For a masonry wall,</p><p>pressure equalization holes can be achieved</p><p>with small vents in the head joints at the top of</p><p>a wall with weep holes at the base of the wall.</p><p>These holes at the top serve to vent out the</p><p>cavity. This type of system prevents water from</p><p>being sucked into a building by an internal</p><p>pressure differential. Pressure-equalized</p><p>design is particularly important in high-rise</p><p>Pressure equalization prevents</p><p>driving rain from infiltrating.</p><p>P1 Exterior pressure</p><p>P2 Interior pressure</p><p>right and below In rainscreen</p><p>design, open stone joints will</p><p>not allow water into the build-</p><p>ing.</p><p>p_130_151_chapt_8_bp 18.10.2006 12:03 Uhr Seite 137</p><p>construction where the enclosure system is</p><p>susceptible to the forces of stack effect. Stack</p><p>effect occurs when high-rise buildings act like</p><p>chimneys in the wintertime. Hot air will rise</p><p>through these towers, creating an inward draft</p><p>through the lower floors. This flow of air cre-</p><p>ates an internal pressure on the enclosure</p><p>system which draws air and possibly water</p><p>through any holes in the exterior skin. Good</p><p>seals at the perimeter air barrier will reduce</p><p>the amount of air infiltration into the building.</p><p>Compartmentalization</p><p>A key component of any weepage system is</p><p>compartmentalization. The system’s ability to</p><p>weep water out of the building is dependent</p><p>on limiting the enclosure area above the</p><p>weeps. For example, weeps at the base of a</p><p>30-story office building should not be expect-</p><p>ed to accommodate all 30 floors. Compart-</p><p>mentalization is not just based on a building</p><p>skin’s surface area. The direction of the wind</p><p>can influence the amount of rain that will</p><p>cover a façade. Because wind pressure is</p><p>inconsistent over the entire building surface,</p><p>building exteriors should be compartmental-</p><p>ized at more frequent intervals in high wind</p><p>areas – for example, near the corners and the</p><p>top. Enclosure systems that cover large areas</p><p>(e.g. high-rise buildings) require compart-</p><p>mentalization in order to ensure that internal</p><p>drainage systems will not overload the design</p><p>and allow water to back up into the building.</p><p>Flashings</p><p>The majority of leakage problems in buildings</p><p>can be traced to poorly executed transitions</p><p>between varied materials. The success of a</p><p>good transition is rooted in properly installed</p><p>flashings. Flashings are used to marry one</p><p>building system to another and shed water</p><p>away from the building. Consistent with the</p><p>concept of a second line of defense, most</p><p>exposed flashings are covered with a metal</p><p>counter flashing over the base flashing to</p><p>improve its durability. Flashings are typically</p><p>completed with a monolithic, impermeable</p><p>material like metal or rubber. The susceptibili-</p><p>138 139</p><p>right and below The Max-</p><p>Planck-Institut für Infektions-</p><p>biologie in Berlin, completed</p><p>in 1999, has a monumental</p><p>entrance hall. The brick</p><p>façade, which does not weep</p><p>at the diagonal, leads to</p><p>trapped water that stains</p><p>the façade.</p><p>Base flashing</p><p>1 Window sill without base</p><p>flashing</p><p>2 Window sill with base flash-</p><p>ing to direct water to the exte-</p><p>rior</p><p>above Compartmentalization:</p><p>The corners and the tops</p><p>of a building are exposed to</p><p>greater wind pressure and</p><p>hence more rain. These areas</p><p>should be compartmentalized</p><p>at more frequent intervals to</p><p>reduce the risk of overloading</p><p>the internal weepage system.</p><p>right Kulturzentrum Gasteig,</p><p>Munich, 1985. Library build-</p><p>ing with weeps in header joints</p><p>of diagonal masonry wall.</p><p>p_130_151_chapt_8_bp 18.10.2006 12:03 Uhr Seite 138</p><p>ty of window systems to water infiltration can</p><p>be greatly improved by providing a weeped</p><p>through-wall flashing under them. This added</p><p>detail will prevent infiltrating water from the</p><p>window system from finding its way into the</p><p>building. An upturned leg of the flashing will</p><p>keep driving rain from leaking back into the</p><p>interior. If properly detailed and executed,</p><p>flashing details can provide a path for the</p><p>inevitable leakage to exit a building enclosure.</p><p>If flashing details are not executed properly,</p><p>they will trap water, which can cause damage</p><p>to the masonry and lead to further moisture</p><p>penetration into the building.</p><p>Weeps and Baffles</p><p>Drainage holes are required to leak infiltrating</p><p>water out of the system. Baffles are used to</p><p>prevent water infiltration through the weeps</p><p>by driving rain. Baffles can be made of a foam</p><p>material but must be dense and secure to</p><p>prevent insects from infiltrating the system</p><p>and nesting. Spiders are notorious for spin-</p><p>ning their webs across elegant façades on</p><p>high-rise buildings. Pressurized cavities within</p><p>the enclosure system provide insects with</p><p>shelter from harsh natural elements like rain,</p><p>sun, high winds, and snow. Baffles can pre-</p><p>vent insects from entering weep holes. If the</p><p>enclosure system cavity has loose construc-</p><p>tion debris or corroded metals, weep holes</p><p>can be marked by stains. The design of any</p><p>enclosure cavities must anticipate the entry of</p><p>water and provide a clean method of draining</p><p>through weeps.</p><p>Residential complex for gov-</p><p>ernment employees, Berlin,</p><p>completed in 1999. The apart-</p><p>ments have masonry weeps</p><p>and vents to allow moisture</p><p>out of the wall.</p><p>Baffled weeps are often used</p><p>to prevent insect infestation</p><p>into the wall.</p><p>p_130_151_chapt_8_bp 18.10.2006 12:03 Uhr Seite 139</p><p>140 141</p><p>Stick Systems</p><p>Stick systems represent enclosures that are</p><p>assembled in the field using individual com-</p><p>ponents: mullions, gaskets, fasteners, stone,</p><p>and glazing. Stick systems can allow for con-</p><p>siderable variation in-situ. Because much of</p><p>the material is cut to fit on-site, this type of</p><p>system can quickly be erected onto a building</p><p>structure from elements shipped to the site.</p><p>Stick systems are dependent on quality con-</p><p>trol on the job site and are labor-intensive.</p><p>Unitized Systems</p><p>Unitized systems are factory-assembled units</p><p>that are shipped to the site with all of the</p><p>major components intact. Stone, concrete</p><p>and masonry materials can be used in this</p><p>type of system. For large buildings with exten-</p><p>sive stone cladding, unitized curtain walls pro-</p><p>vide a segmented assembly that affords some</p><p>of the same principles used in cavity wall con-</p><p>struction and often include pressure equaliza-</p><p>tion and rainscreen design. Units are typically</p><p>modular, one-unit wide and one-floor tall, for</p><p>attachment to the building structure with</p><p>adjustable anchors. Unitized systems boast of</p><p>having better quality control because the units</p><p>are assembled with glass and stone in the</p><p>controlled environment of a factory.</p><p>Sealant Joints</p><p>By their very nature, building enclosures con-</p><p>sist of multiple elements of material joined</p><p>together. The individual elements can be</p><p>bricks, stone panels, or precast concrete</p><p>walls. Although the exterior material can vary</p><p>the material itself, it is rarely the source of</p><p>water infiltration. Problems occur at the joints</p><p>between elements. These joints represent the</p><p>weak link in water barriers. The control of</p><p>water leakage through joints is often depend-</p><p>ent on sealant.</p><p>Sealant failure can be cohesive or adhesive.</p><p>Cohesive failure occurs when the movement</p><p>capacity of the joints surpasses the designed</p><p>movement capacity of the sealant. Cohesive</p><p>failures can be avoided by using durable</p><p>sealants and by detailing joints to accommo-</p><p>date anticipated movements. The joint width-</p><p>to-depth ratio is critical. Typically, the width-</p><p>to-depth ratio should be 2:1. Sealant manu-</p><p>facturers provide guidelines about how their</p><p>product is to be installed, and should be con-</p><p>sulted regarding atypical conditions. Properly</p><p>installed sealant joints should only have adhe-</p><p>sion to two sides of the joint. Three-sided</p><p>adhesion will prevent the joint from expanding</p><p>properly. Backer rod or bond breaker material</p><p>is used to ensure a joint can accommodate</p><p>movements.</p><p>large thermal cycles, some marbles can trans-</p><p>form into very fine sugar-like particles through</p><p>granulation.</p><p>In the case of some thin white marble panels,</p><p>if the outside face of a panel is heated to a</p><p>higher temperature than the inside, the outer</p><p>face of the panel will expand more than the</p><p>inside face. This explains the dishing out</p><p>of the panels. On a building constructed in</p><p>a northern climate, it is not surprising that</p><p>panels facing north will have the least amount</p><p>of dishing. These panels receive the least</p><p>amount of thermal exposure on the exterior</p><p>face of the stone. Although white marbles</p><p>have been used for centuries in architecture,</p><p>two factors have led to the dramatic effects</p><p>of thermal hysteresis on contemporary build-</p><p>ings: the stone thickness and the climate.</p><p>Stone Thickness</p><p>The first factor in understanding how hystere-</p><p>sis affects our modern buildings is to consider</p><p>the evolution of stone in the history of con-</p><p>struction. In early times, large blocks were</p><p>used for the construction of buildings. The</p><p>Pantheon completed in Rome in 125 A.D. was</p><p>built with 1.2m (4 feet) thick stone walls and</p><p>1.9m (6 foot 2 inch) diameter solid stone</p><p>columns. During the Medieval (9th through</p><p>15th century) and Renaissance periods (15th</p><p>through 16th century) the use of solid blocks of</p><p>stone in walls was converted into stone-faced</p><p>walls consisting of random stone rubble set</p><p>in a mass of mortar between inner and outer</p><p>faces of stone ashlar. With the advent of skele-</p><p>ton steel frame construction in the late 1800s,</p><p>the use of thick load-bearing walls evolved into</p><p>Flexural strength of marble panels at Amoco Building</p><p>Condition Original design Actual panels Difference</p><p>samples for building installed on building</p><p>Original strength 9.65 Mpa (1.4 ksi) 8.69 MPa (1.26 ksi) ——</p><p>Minimum Average</p><p>7.52 MPa (1.09 ksi) 22% less</p><p>Minimum than specified</p><p>After aging 5.79 MPa (840 psi) 3.65 MPa (530 psi) ——</p><p>(40% loss) Average</p><p>1.17 MPa (170 psi)</p><p>Minimum 80% less</p><p>(90% loss) than specified</p><p>above The Pantheon stone</p><p>walls were constructed with</p><p>1.2m (4 feet) thick stone</p><p>blocks. The stone panels that</p><p>enclosed the Lincoln Bank</p><p>of Rochester, New York, were</p><p>25mm (1 inch) thick.</p><p>p_010_021_chapt_1_bp 17.10.2006 18:03 Uhr Seite 15</p><p>p_010_021_chapt_1_bp 17.10.2006 18:03 Uhr Seite 16</p><p>thinner non-load-bearing walls. The Empire</p><p>State Building, towering over 300m (1,000</p><p>feet) in the air was constructed in 1930 with</p><p>wall thickness measured in inches and not</p><p>feet. More than 5,600m3 (200,000 cubic feet)</p><p>of limestone and granite were cut into panels</p><p>and connected back to the steel structure.</p><p>As our buildings reached to greater heights,</p><p>it became very important to reduce the weight</p><p>of cladding materials. The lighter the cladding</p><p>material, the less steel structure would be</p><p>required to support it. Building designs were</p><p>aggressively trying to reduce the stone thick-</p><p>ness of façades in order to reduce building</p><p>costs. When the cladding wall or curtain-</p><p>wall design principles were combined with</p><p>improved stone fabrication equipment and</p><p>techniques in the 1960s, the result was the</p><p>start of 3cm (1 1/4 inch) thick stone panels</p><p>to skin our buildings.</p><p>Around this time, the Lincoln Bank of</p><p>Rochester, New York, wanted to provide its</p><p>city with an elegant tower clad in expensive</p><p>stone. The 20-story building design had a</p><p>square plan with columns at the perimeter</p><p>that fanned out at the street level on all four</p><p>sides. The Lincoln Bank Tower was completed</p><p>in 1970 using Carrara marble to clad the 48</p><p>swooping columns. Because of the building’s</p><p>unique form, the stone panels varied in width</p><p>and height. The original design considered</p><p>5cm (2 inch) thick stone and connected to</p><p>two-story-high steel cages, which were to</p><p>hang alternatively from the external columns</p><p>of the building’s structural frame. The final</p><p>design was revised to 2.5cm (1 inch) thick</p><p>panels hung from one-story-high cages, which</p><p>were much lighter than the original design.</p><p>Unfortunately, the fate of the Lincoln Bank</p><p>cladding was similar to the Amoco Building</p><p>in Chicago. Within 10 years of completion,</p><p>the thin stone panels were dishing outward,</p><p>requiring a full replacement.Unlike the Amoco</p><p>Building, Lincoln Bank decided to re-clad the</p><p>columns using lightweight aluminum in lieu</p><p>of heavier granite material. Because of the</p><p>unique shape of the building, the retrofit of</p><p>aluminum panels required a total of 13,000</p><p>panels, which were individually computer-de-</p><p>signed and fabricated to clad the 48 columns</p><p>by Antamex, a Canadian-based curtainwall</p><p>company. No two of the panels were identical.</p><p>The demise of the Rochester Bank and</p><p>Amoco Tower cladding was linked to the thick-</p><p>ness of the stone as well as their climatic con-</p><p>ditions. This leads to the second contributing</p><p>factor which is thermal cycling.</p><p>Thermal Cycling</p><p>The second factor contributing to hysteresis,</p><p>thermal cycling, is linked to the use of a</p><p>southern-based building material in an unsuit-</p><p>able (northern) climate. As the calcite crystals</p><p>in white marble transform with temperature</p><p>The desire to reduce the</p><p>weight of cladding elements</p><p>was linked with improved</p><p>stone fabrication equipment</p><p>in the 1960s to produce</p><p>thin stone panels to skin our</p><p>building.</p><p>above The 48 swooping</p><p>columns were re-clad with</p><p>aluminum panels. A total of</p><p>13,000 panels were individu-</p><p>ally computer-designed and</p><p>fabricated to fit onto the exist-</p><p>ing metal framework.</p><p>right The re-cladding of the</p><p>Lincoln Bank of Rochester,</p><p>New York, originally completed</p><p>in 1970, required a lightweight</p><p>solution that would not add</p><p>excessive weight to the exist-</p><p>ing metal support framing and</p><p>building structure.</p><p>page 16 The Lincoln Bank of</p><p>Rochester was clad with thin</p><p>marble panels, fixed to a com-</p><p>plex metal cage work.</p><p>p_010_021_chapt_1_bp 17.10.2006 18:04 Uhr Seite 17</p><p>variation, stone panels can change from flat</p><p>plates to round dishes. It appears that the</p><p>greater the temperature differential on the</p><p>stone, the greater the effect on the panels. In</p><p>no project was this more evident than in the</p><p>use of Italian marble in the northern climate of</p><p>Helsinki, Finland.</p><p>Finlandia Hall was constructed between 1967</p><p>and 1971. The main part of the building rises</p><p>like a white tower with inclined roofs. The</p><p>design of the large volume above the auditori-</p><p>um was intended to improve the acoustics by</p><p>providing a resonance space above the seat-</p><p>ing area. The cladding material used to cover</p><p>this monumental building was not indigenous</p><p>to the northern lands of Finland. The design-</p><p>ers wanted this performing arts building to</p><p>have a direct link to Mediterranean culture.</p><p>Not by accident, the cladding material select-</p><p>ed was from a quarry in the Apennine Moun-</p><p>tains above Carrara, Italy. The marble cladding</p><p>had a maximum panel size of 140cm and was</p><p>3cm thick (55 x 1 1/4 inches). Each panel was</p><p>fixed by four pins. The pins were inserted</p><p>35cm (14 inches) in from the edges. Thus</p><p>each panel was connected to four adjacent</p><p>panels, overlapping at half the panel height.</p><p>Similar to the Amoco Tower and the Rochester</p><p>Bank building, the marble skin of Finlandia</p><p>Hall was doomed to failure.</p><p>In July 1991, safety nets were hung along the</p><p>length of Finlandia Hall to protect pedestrians</p><p>from potential cladding failures from above.</p><p>Similar to other projects, the stone panels on</p><p>the north face did not suffer from the same</p><p>dishing as panels on the east, west, and south.</p><p>What is unique about Finlandia Hall is not the</p><p>problem, but the solution. The government</p><p>officially protected Finlandia Hall in 1993,</p><p>declaring that the exterior should be kept</p><p>“equivalent to the original”. The appearance</p><p>of the marble was required to resemble the</p><p>original stone, even down to the pattern of the</p><p>stone veins rising diagonally from the left to</p><p>the right on the panels.</p><p>18 19</p><p>The government officially</p><p>protected Finlandia Hall in</p><p>Helsinki in 1993, declaring</p><p>that the exterior should</p><p>Adhesive failures occur when the bond</p><p>between the sealant and substrate releases.</p><p>This is displayed when sealant peels off of</p><p>stone, leaving no remnant of the sealant on</p><p>the stone. Adhesion failures can be prevented</p><p>on a building by testing the sealant’s adhesive</p><p>quality to anticipated substrates. It is not</p><p>uncommon to use primers in order to allow</p><p>sealant to bond to some substrates. Clean</p><p>dry substrates are also important to achieving</p><p>good adhesion. The surface preparation of the</p><p>substrate is critical to providing an effective</p><p>seal. Primers are typically employed on sub-</p><p>strates that require mechanical cleaning,</p><p>such as brick, stone, and concrete. Most</p><p>sealants should not be installed at tempera-</p><p>tures below freezing or in damp weather.</p><p>Sealant substrate contamination and subse-</p><p>quent loss of sealant adhesion are difficult to</p><p>avoid entirely, since invisible films of airborne</p><p>debris can accumulate between cleaning,</p><p>priming, and sealant application. Even wiping</p><p>a surface with solvent to clean it prior to</p><p>applying the sealant can lower its surface</p><p>temperature, thus causing a film of moisture</p><p>condensation that will impair or prevent</p><p>sealant adhesion.</p><p>left Stick system:</p><p>1 Anchor</p><p>2 Mullion</p><p>3 Horizontal rail (gutter</p><p>section at window head)</p><p>4 Spandrel panel</p><p>5 Horizontal rail (window</p><p>sill section)</p><p>6 Vision glass</p><p>7 Interior mullion trim</p><p>right Unitized system:</p><p>1 Anchor</p><p>2 Pre-assembled framed</p><p>unit</p><p>Sealant joint width-to-depth</p><p>ratio</p><p>1 Effective sealant joint</p><p>2 Ineffective sealant joint</p><p>p_130_151_chapt_8_korr_bp 27.10.2006 15:20 Uhr Seite 140</p><p>Perfect seals are difficult to achieve even in a</p><p>factory setting. Time and weather will adverse-</p><p>ly affect sealants and gaskets that make up</p><p>joinery details. The best plan for keeping</p><p>water out of the building is to provide a sec-</p><p>ond line of defense. Back-up systems, such</p><p>as through-wall flashings, are useful in drain-</p><p>ing infiltrated water out of the system. Tech-</p><p>niques like pressure equalization move pri-</p><p>mary seals away from the outside surface,</p><p>protect from the environment, and reduce the</p><p>amount of water on these joints.</p><p>Dual Seals</p><p>Reliance on an exposed single barrier of</p><p>sealant to prevent water penetration into an</p><p>enclosure is the single most common source</p><p>of contemporary building enclosure problems.</p><p>Despite improved sealant technology and</p><p>installation techniques, a single sealant barrier</p><p>is only effective if it maintains its original seals.</p><p>There are many problems that can lead to</p><p>sealant failure – including weathering, poor</p><p>workmanship during installation, incompatibil-</p><p>ity, improper mix design, preparation of sub-</p><p>strates, ultraviolet radiation. An enclosure</p><p>design that relies on single seals for protection</p><p>lacks the level of redundancy required for a</p><p>leak-free building. A dual seal design provides</p><p>a continuous outer and inner seal at all transi-</p><p>tion details. The outer seal can fail, and the</p><p>system will still resist water and air infiltration.</p><p>A dual seal system allows the primary seal</p><p>(the one on the inboard side of the system) to</p><p>be sheltered from rain, sun, and birds. All of</p><p>the elements could adversely affect its per-</p><p>formance. The outer seal can be seen as a</p><p>sacrificial element.</p><p>Water Damage</p><p>Penetrating water can be a nuisance for build-</p><p>ing occupants. A leaking window can chip</p><p>paint. Infiltrating water at the base of a wall</p><p>can stain carpeting. However, the worst water</p><p>damage on a building can be hidden from</p><p>view and trapped inside the wall system.</p><p>Completed in 1986, the Imperial Polk County</p><p>Courthouse in Bartow, Florida, is a ten-story</p><p>concrete-frame structure clad with brick</p><p>veneer and clay tile roofing. With a reasonable</p><p>construction budget of 35 million dollars, the</p><p>courthouse was expected to serve its commu-</p><p>nity for many years but it did not. Instead,</p><p>it proved to be an infamous example of how</p><p>much damage infiltrating water can do to a</p><p>building. The courthouse was plagued with</p><p>serious water infiltration shortly after comple-</p><p>tion. Leaks from the clay tile roofing system</p><p>and brick veneer flashing intersections led</p><p>to water damage on the interior. At the same</p><p>time, the brick veneer on the tower had devel-</p><p>oped severe cracks and bulges. Pieces of</p><p>masonry literally fell off of the building. Com-</p><p>plicated by problems with the HVAC system</p><p>and the use of a vinyl wall covering at the</p><p>perimeter of the building, the courthouse</p><p>showed chronic symptoms of “sick building</p><p>syndrome” and was vacated in 1991, just</p><p>five years after opening.</p><p>Although the building is an extreme example</p><p>of construction-related problems, the water</p><p>infiltration through the brick veneer is a classic</p><p>example of a failure that occurs on many</p><p>buildings. The exterior wall consisted of brick</p><p>veneer, cavity space, reinforced concreted</p><p>masonry units (CMU), insulation, gypsum</p><p>wallboard, and vinyl wall coving. The veneer</p><p>was supported on relieving angles bolted to</p><p>the spandrel beams of the concrete structure.</p><p>Window perimeter calking</p><p>1 Dual seals provide a sec-</p><p>ond line of defense against</p><p>water infiltration</p><p>Adhesion failure of sealant on</p><p>stone.</p><p>right Roof flashing, Imperial</p><p>Polk County Courthouse in</p><p>Bartow, Florida</p><p>1 Initial design of flashing</p><p>at roof transition was surface-</p><p>applied to masonry wall</p><p>2 Revised detail of flashing</p><p>was stepped to provide</p><p>through-wall flashing to effec-</p><p>tively weep water</p><p>p_130_151_chapt_8_bp 18.10.2006 12:03 Uhr Seite 141</p><p>Water leakage through the brick veneer wall</p><p>occurred primarily at window openings and</p><p>at roof-to-wall intersections. The transition</p><p>details at the courthouse had four major prob-</p><p>lems. First, the flashing material proved to</p><p>have poor durability. Composed of PVC, the</p><p>flashing material became brittle within three</p><p>years of installation – particularly in areas</p><p>where it had been folded or manipulated, the</p><p>flashing began to split. Second, many of the</p><p>window flashings failed to shed water to the</p><p>exterior. In most cases, they did not extend all</p><p>the way to the face of the veneer. Third, end</p><p>dams were not provided at terminal edges,</p><p>and the flashings did not turn up behind the</p><p>window sill to prevent water from tracking</p><p>back into the building. Finally, the flashing at</p><p>the intersection of the brick veneer and the</p><p>side (rake edge) of the sloped roof did not</p><p>provide a through-wall flashing. Similar to the</p><p>Vontz Center in Ohio, flashing of the sloped</p><p>roof consisted of a metal termination bar sur-</p><p>face- mounted to the face of the masonry</p><p>wall. With no through-wall flashing to collect</p><p>water flowing down the inside face of the</p><p>cavity wall, water infiltration was inevitable.</p><p>In order to stop the air and water infiltration</p><p>that riddled this building, the entire brick</p><p>veneer with its windows was removed. A rub-</p><p>berized asphalt membrane was applied to the</p><p>exterior face of the CMU back-up wall, and</p><p>new copper flashings were installed around</p><p>the entire perimeter of the window openings.</p><p>The flashing system with an upturned leg was</p><p>sealed to the window frames and the rubber-</p><p>ized asphalt membrane was adhered to the</p><p>flashings. In order to be effective, the flashing</p><p>at the roof was installed in a step manner to</p><p>follow the slope of the roof and the masonry</p><p>mortar joints. The flashing was integrated</p><p>into the mortar bed and head joints of the</p><p>brick veneer. All the vinyl wall covering was</p><p>removed from the interior face of the dry wall</p><p>and replaced with a breathable latex paint.</p><p>It was important to establish a vapor barrier</p><p>on the warm side of the insulation (in this</p><p>case, the outside was the warm side), and</p><p>removal of the wall paper was necessary to</p><p>prevent a double vapor barrier from trapping</p><p>moisture within the wall system. After three</p><p>years of work, remedial construction costs</p><p>were approximately two-thirds of the original</p><p>building cost.</p><p>The cracking and bulging of the brick veneer</p><p>at the courthouse was the result of ineffective</p><p>and missing relieving joints in</p><p>better suited for pressure-</p><p>relieving joints in clay masonry walls, where</p><p>expansion is anticipated to compress the filler.</p><p>146 147</p><p>Sankt Florian Church Center</p><p>in Riem, Munich, 2004. The</p><p>expansion joints and control</p><p>joints for the building are an</p><p>integral part of the design and</p><p>provide a method for articulat-</p><p>ing the sign of the cross on</p><p>the church tower.</p><p>p_130_151_chapt_8_bp 18.10.2006 12:03 Uhr Seite 146</p><p>Differential Movement of Building</p><p>Structure</p><p>Sometimes the structural frame may move in</p><p>the opposite direction of the expanding exteri-</p><p>or skin due to shortening of the building</p><p>structure. Column shortening and concrete</p><p>creep can reduce the height of the building,</p><p>whereas the building façade can grow with</p><p>thermal expansion. These differential move-</p><p>ments accumulate with long or tall walls, cre-</p><p>ating a potential masonry façade stress many</p><p>times greater than from normal gravity or wind</p><p>loads on a façade. Localized failures are char-</p><p>acterized by bowing, by horizontal cracks at</p><p>shelf angles, by vertical cracks near corners,</p><p>and spalling at other points where stresses</p><p>are concentrated. Flexible joint material must</p><p>be intermittently provided in horizontal joints</p><p>to alleviate these stresses and allow the build-</p><p>ing structure to move without damage to the</p><p>masonry.</p><p>When masonry walls are built directly on top</p><p>of concrete foundations that extend above</p><p>grade, thermal and moisture expansion of the</p><p>masonry can work against the drying shrink-</p><p>age of the concrete, causing extension of the</p><p>masonry wall beyond the corner of the foun-</p><p>dation or cracking the foundation. When the</p><p>concrete cracks with lower temperatures, the</p><p>tensile strength of the masonry may not be</p><p>sufficient to move the wall back with it, and</p><p>cracks form in the masonry near the corners.</p><p>Flashing often serves as a bond break</p><p>between the foundation and the wall to allow</p><p>each to move independently.</p><p>Brick parapet wall can be particularly trouble-</p><p>some because, with two surfaces exposed,</p><p>they are subject to temperature and moisture</p><p>extremes much greater than the building wall</p><p>below. Differential expansion can cause para-</p><p>pets to bow or crack horizontally at the roof</p><p>line. Although through-wall flashing at the roof</p><p>line can improve resistance to water infiltra-</p><p>tion, it creates a plane of weakness that may</p><p>only amplify the problems. If parapets must</p><p>be part of the building design, extra precau-</p><p>tions are needed. All expansion joints must</p><p>extend through the parapet and space addi-</p><p>tional joints halfway between those running</p><p>the full height of the building. Adding steel</p><p>reinforcement helps to counteract the tensile</p><p>forces created and prevent excessive move-</p><p>ment in the parapet. The same material</p><p>should be used for the entire thickness of the</p><p>parapet.</p><p>Fixing Cracks</p><p>When exterior stone wall panel expansion</p><p>joints are missing or filled solid, the results</p><p>can be disastrous. The 152.4m (500 foot) tall</p><p>Metro Dade Center in Miami, Florida, was</p><p>constructed in 1985 to house county offices.</p><p>It is clad with approximately 8,700 limestone</p><p>panels that are 10cm (4 inches) in thickness.</p><p>The panels are attached to the building’s</p><p>reinforced concrete frame with stainless steel</p><p>anchor supports. They range in size from</p><p>1.5m (5 feet) high and 0.61m (2 feet) wide</p><p>and weighing 255kg (600 pounds), to 3m</p><p>(10 feet) high and 1.5m (5 feet) wide, weigh-</p><p>ing 977.5kg (2,300 pounds). In 1987,</p><p>cracks were detected in the building’s lime-</p><p>stone façade after a piece of stone fell to</p><p>the ground. The cause of the cracked panels</p><p>was linked to the system’s inability to accom-</p><p>modate vertical and horizontal movement</p><p>between the panels and the concrete frame.</p><p>The differential movement was created pri-</p><p>marily from the building structure’s concrete</p><p>shrinkage and creep, and thermal expan-</p><p>sion/contraction of the limestone relative to</p><p>the concrete frame.</p><p>right and below Unity Temple,</p><p>Oak Park, Illinois, 1905, shows</p><p>isolated cracks in the exterior</p><p>walls even after extensive</p><p>restoration work in 2002.</p><p>p_130_151_chapt_8_bp 18.10.2006 12:03 Uhr Seite 147</p><p>Normally in the construction of cavity wall or</p><p>curtainwall assemblies, differential movement</p><p>is incorporated by “soft” sealant joints</p><p>between panels to absorb movement without</p><p>introducing large forces into the panels. The</p><p>Metro Dade Center was constructed with few</p><p>true soft joints. Most of the joints were inad-</p><p>vertently filled with mortar behind the sealant</p><p>face seal. The mortar effectively blocked the</p><p>expansion joints. As the building’s concrete</p><p>frame shrank slightly due to normal column</p><p>shortening, the limestone façade did not</p><p>shrink. The accumulation of stress in the pan-</p><p>els and their anchors resulted in the building</p><p>façade stone to crack and ultimately fall off of</p><p>the building. Hard shims had been placed at</p><p>the corner panel locations and had inadver-</p><p>tently been left in place and not removed after</p><p>the stone had been set in place. The 42.6m</p><p>(140 feet) long exterior wall suffered from</p><p>extensive cracking at the corners. In some</p><p>cases, the stone panels on one face of the</p><p>building were pushed out beyond those of the</p><p>adjacent façade, and anchors were peeling off</p><p>triangular pieces of stone. In order to solve</p><p>the problem, corner panels were replaced</p><p>and a continuous expansion joint was</p><p>installed.</p><p>The engineering firm of Simpson Gumpertz</p><p>& Heger was hired to solve the problem.</p><p>To resolve the vertical expansion problem,</p><p>horizontal joints between stone panels were</p><p>cut to provide a gap of a minimum 3mm</p><p>(1/8 inch) and filled with sealant. Approximate-</p><p>ly 15,000 new anchors were installed. All of</p><p>the original limestone panels were retained,</p><p>except for 44 panels which were significantly</p><p>cracked. These panels were replaced with</p><p>new stone.</p><p>148 149</p><p>right Metro Dade Center in</p><p>Miami, Florida, 1985.</p><p>below Metro Dade Center.</p><p>Corner cracks in stone.</p><p>p_130_151_chapt_8_bp 18.10.2006 12:03 Uhr Seite 148</p><p>Design drawings for enclosure systems typi-</p><p>cally stay in the two-dimensional world of plan</p><p>and drawing sections. However, since water</p><p>moves laterally within enclosures, finding the</p><p>path of least resistance, these drawings can</p><p>limit the review of water infiltration weakness.</p><p>Isometric drawings of corner and transition</p><p>joints help tell the story of how seal continuity</p><p>of an enclosure is obtained. No matter how</p><p>impressive a building enclosure system may</p><p>appear on paper, a laboratory test of the typi-</p><p>cal details is a useful tool in uncovering</p><p>unwanted problems that could be found in</p><p>the field.</p><p>In addition to following the principles dis-</p><p>cussed in this chapter, testing is the best</p><p>method for determining whether water infiltra-</p><p>tion will occur on a large wall system. Labora-</p><p>tory testing includes a review of the thermal,</p><p>structural, air, and water performance of an</p><p>enclosure. It also helps to confirm erection</p><p>tolerances and sequence of installations. The</p><p>most common type of failure for mock-up</p><p>testing is water infiltration; however, designers</p><p>should not be discouraged by this fact. Labo-</p><p>ratory testing should be seen as a tool in the</p><p>design process. Modifications in the design</p><p>are far easier to achieve in this setting than</p><p>after the enclosure has been installed on the</p><p>building.</p><p>Mock-up Testing</p><p>Many think of mock-up testing as a method</p><p>for verifying the enclosure’s ability to meet</p><p>minimum standards of performance. This is</p><p>true, but it can also be the final design tool</p><p>prior to fabrication of the system. Many modi-</p><p>fications to the system can occur at the mock-</p><p>up, which improve the performance and</p><p>appearance of the enclosure. In the end, it is</p><p>important that the tested assembly accurately</p><p>imitates the actual design and that it is</p><p>assembled in the same manner as intended</p><p>on the actual building. If possible, the individ-</p><p>uals responsible for the erection of the enclo-</p><p>sure on the building should be involved with</p><p>the construction of the mock-up. While it is</p><p>not possible</p><p>to replicate every condition on</p><p>the building, at least the size of the mock-up</p><p>must be large enough to include all major ele-</p><p>ments and perimeter transition conditions. It</p><p>is not usually necessary to repeat the actual</p><p>building frame used to support the enclosure</p><p>but it is crucial that all actual details of the</p><p>enclosure are incorporated into the mock-up.</p><p>Laboratory testing can be done to verify sound</p><p>transmission, fire resistance, vapor transmis-</p><p>sion, resistance to seismic loads, overall con-</p><p>densation resistance, and thermal transmis-</p><p>sion. The major reasons for laboratory testing</p><p>can be summarized as follows:</p><p>1</p><p>To verify the resistance of the enclosure</p><p>against air leakage. The purpose of this test</p><p>is to measure the amount of air leakage into</p><p>the system. Industry standards identify a max-</p><p>imum of allowed infiltration per unit of area</p><p>of an assembly. Excessive heat or cold into</p><p>the building can tax a building’s mechanical</p><p>system. It is impossible for an assembly to</p><p>be completely airtight. Air infiltration should</p><p>be tested before the wall is wetted. Trapped</p><p>water within a test specimen could reduce</p><p>the detectable air leakage on a mock-up.</p><p>Excessive air leakage in a building may cause</p><p>physical discomfort and energy loss to the</p><p>occupants.</p><p>2</p><p>To verify the effectiveness in controlling water</p><p>penetration. Resistance to air and water infil-</p><p>tration can only be determined through test-</p><p>ing. The test intends to simulate an enclosure</p><p>subjected to high winds combined with heavy</p><p>rainfall. The assembly is subjected to a prede-</p><p>termined internal pressure to simulate the</p><p>force of wind on the enclosure. Water is</p><p>sprayed on the assembly at a specified rate</p><p>for a given time period. Failure of the test</p><p>occurs when water appears on the inside sur-</p><p>face of the enclosure during the course of the</p><p>test. Controlled water inside the system that</p><p>weeps to the exterior is allowed. A second</p><p>method of testing for water penetration into a</p><p>building is the dynamic pressure test. Dynam-</p><p>ic testing is used to determine if water will</p><p>infiltrate an assembly when exposed to a pul-</p><p>sating pressure. The in-and-out turbulent flow</p><p>of air occurring during a storm is typically</p><p>Glass failure at 4.3 MPa</p><p>(90psf) pressure test on win-</p><p>dows in façade mock-up.</p><p>An airplane engine is used</p><p>with a sprat rack for dynamic</p><p>water infiltration mock-up test-</p><p>ing.</p><p>How Can Leakage Be Avoided?</p><p>p_130_151_chapt_8_bp 18.10.2006 12:03 Uhr Seite 149</p><p>simulated by using an airplane propeller</p><p>engine in conjunction with water spray racks.</p><p>Because of the turbulent nature of the pres-</p><p>sure, water may penetrate a system, which</p><p>would not show up in the uniform static air</p><p>pressure test. It is recommended that the</p><p>water infiltration test should be repeated after</p><p>structural loading to confirm that minor</p><p>deflections in the system will not trigger leak-</p><p>age into the building.</p><p>3</p><p>To verify the structural adequacy of the enclo-</p><p>sure under wind loads. The strength and stiff-</p><p>ness of framing members may be determined</p><p>by engineering analyses and calculations.</p><p>However, the structural performance test is</p><p>the final check to find out if the composite</p><p>assembly meets the design loads. Pressuriz-</p><p>ing a test chamber encased by the enclosure</p><p>system being tested simulates wind loads.</p><p>Inward and outward forces are achieved by</p><p>drawing air in or out of the chamber. Failure</p><p>of this test consists of fracture of any individ-</p><p>ual element or deflection beyond the estab-</p><p>lished maximum under loads equal to or less</p><p>than the design loads.</p><p>Field Installation</p><p>Laboratory testing can help identify major</p><p>design errors and various installation chal-</p><p>lenges, such as sequencing, building toler-</p><p>ances, and workmanship. It is advantageous</p><p>for the workers involved with assembling the</p><p>laboratory mock-up to be represented later on</p><p>the actual site to supervise the installation of</p><p>the enclosure. For custom systems, this may</p><p>be a requirement for the project. Mock-up</p><p>testing cannot verify many quality control</p><p>measures, which are carried out on the job</p><p>site. For example, when installers are pushed</p><p>to complete work on the building quickly in</p><p>adverse weather, the quality can suffer. For all</p><p>of these situations, it is recommended to pro-</p><p>vide random testing in the field to ensure the</p><p>system on the building is as good as the sys-</p><p>tem that passed the laboratory tests. Field</p><p>testing is not exclusive to large-scale projects</p><p>and can be as simple as spraying the exterior</p><p>joinery at random locations with water from a</p><p>hose and looking for seepage into the build-</p><p>ing. Points of leakage can be identified and</p><p>corrected.</p><p>The most critical time to complete field testing</p><p>is at the beginning of a project. Early testing</p><p>can eliminate these faults before the remain-</p><p>der of the installation is completed. Field test-</p><p>ing when the first units of an enclosure are</p><p>installed can uncover any faults with the</p><p>assembly of the system. Random field testing</p><p>of the system as the project progresses will</p><p>help verify that quality control has been main-</p><p>tained throughout the process. Atypical con-</p><p>ditions not part of laboratory testing can be</p><p>reviewed for air and water infiltration. Field</p><p>testing is also important to ensure that transi-</p><p>tions to adjacent systems have been properly</p><p>executed. Random sealant adhesion field</p><p>testing is important to verify that substrates</p><p>are being prepared properly. These tests con-</p><p>firm that the seals are being installed as</p><p>designed and that the sealant material is cur-</p><p>ing properly.</p><p>Large masonry buildings did not stop with the</p><p>Monadnock building. An 18-story masonry</p><p>150 151</p><p>above and right Masonry</p><p>tower at Potsdamer Platz,</p><p>Berlin, 2000.</p><p>p_130_151_chapt_8_bp 18.10.2006 12:03 Uhr Seite 150</p><p>1</p><p>Through-wall flashings used in cavity wall</p><p>construction allows for porous cracking</p><p>masonry walls to remain leak-free. Water pen-</p><p>etrating the outer masonry wythe will fall</p><p>through the cavity and weep out of the cavity</p><p>through flashing material at the base.</p><p>2</p><p>Sloppy installation of masonry with excessive</p><p>mortar droppings can lead to closing the cavi-</p><p>ty and water problems. Clogging of weeps and</p><p>filling the cavity with mortar will allow moisture</p><p>to bridge the cavity and find its way into the</p><p>building. Expansion joints filled with mortar</p><p>will be ineffective and cause serious damage</p><p>to the façade.</p><p>3</p><p>Flashing details that are not properly end</p><p>dammed and extended to the exterior surface</p><p>of the building will lead to uncontrolled leak-</p><p>age and masonry deterioration. Uncontrolled</p><p>leakage can produce masonry anchor failures</p><p>due to excessive corrosion.</p><p>4</p><p>Flashings must be effectively installed to pre-</p><p>vent concealed leakage. Systems should</p><p>not rely on window frame construction to be</p><p>water-tight. Use complete window flashing</p><p>assemblies, including pan flashings beneath</p><p>windows, to capture water that may often leak</p><p>into the exterior wall.</p><p>5</p><p>Do not rely on a single line of sealant to pre-</p><p>vent leakage. In order to minimize the risk of</p><p>water infiltration, provide a second line of</p><p>defense. The exterior seals of building enclo-</p><p>sures are going to leak.The question is, where</p><p>does the water go once it gets past the first</p><p>barrier? Properly designed and installed sys-</p><p>tems direct the water back to the exterior.</p><p>6</p><p>Large areas must be compartmentalized to</p><p>prevent an overload on the system. Areas that</p><p>receive greater amounts of wind are also sus-</p><p>ceptible to greater amounts of water and will</p><p>require additional compartmentalization.</p><p>Lessons Learned</p><p>7</p><p>Laboratory and field testing are the best meth-</p><p>ods of ensuring a leak-free condition at win-</p><p>dow and curtainwall transitions.</p><p>8</p><p>The worst water damage can be in areas you</p><p>cannot see. Mold growth inside a wall can</p><p>destroy a building. Proper location of a vapor</p><p>barrier is critical to not trapping water. A dou-</p><p>ble vapor barrier can lead to trapped moisture</p><p>and mold growth.</p><p>building completed in 2000 at Potsdamer</p><p>Platz, Berlin, continues the tradition. The</p><p>masonry spire mirrored by the Sony Tower</p><p>form an ironic gateway to Potsdamer Straße.</p><p>The dark red brick façade with small window</p><p>openings is in strong contrast to the all-glass</p><p>façade of the Sony Tower. The facing and</p><p>relief structure as well as the staggered design</p><p>is modeled on the skyscrapers of the 1930s</p><p>and 1940s in North America; however, the</p><p>building shows all of the standard joints</p><p>requirements of a contemporary masonry</p><p>façade. With properly installed through-wall</p><p>flashings, weeps and expansion joints, con-</p><p>crete, masonry, and stone can be leak-free.</p><p>Field water test of cement fiber</p><p>panel and window system</p><p>transition. Gary Corner Youth</p><p>Center, Chicago, 2006.</p><p>p_130_151_chapt_8_bp 18.10.2006 12:03 Uhr Seite 151</p><p>152 153 Acknowledgments</p><p>A book that describes the lessons learned</p><p>from concrete, stone and masonry problems</p><p>could not have been completed without the</p><p>cooperation and shared knowledge of many</p><p>design professionals and people from the</p><p>construction industry. I would like to extend</p><p>my gratitude to those architects, builders, and</p><p>individual experts that contributed information</p><p>to my research. This book was intended to</p><p>educate people about the limitations of build-</p><p>ing materials, with the intent to reduce the</p><p>risk of problems in the future. I received</p><p>valuable information from many qualified</p><p>individuals, including Steve Morby of the</p><p>Pulitzer Foundation for the Arts who explained</p><p>to me how to make “Ando Concrete”, Terry</p><p>Collins of the Portland Cement Association</p><p>who taught me how to get rid of “pinto con-</p><p>crete”, and Larry Weldon of Goettsch Partners</p><p>who instructed me on just about everything</p><p>else. So much of the credit for the book</p><p>goes to Ria Stein for faithfully advising me on</p><p>the content, A.A. Sakhnovsky for graciously</p><p>reviewing the text prior to publication, and</p><p>to Gabrielle Pfaff for elegantly laying out the</p><p>chapters. A special thanks to photographer</p><p>Carl-Magnus Dumell for providing me with</p><p>fabulous photographs and insights of Finlan-</p><p>dia Hall in Helsinki. My final thanks goes</p><p>to the Graham Foundation for Advanced</p><p>Studies in the Fine Arts who kindly sponsored</p><p>this publication.</p><p>p_152_160_bp 18.10.2006 12:46 Uhr Seite 152</p><p>About the Author</p><p>Patrick Loughran was born in 1964 and grew</p><p>up in Oak Park, Illinois. He studied Civil</p><p>Engineering at the University of Notre Dame</p><p>in South Bend, Indiana, where he received</p><p>his Bachelor of Science degree in 1986.</p><p>He then obtained a Master of Architecture</p><p>degree from the University of Illinois at Urbana</p><p>Champaign, Illinois in 1990. He proceeded to</p><p>work for several architectural practices in</p><p>Chicago and has been employed at Goettsch</p><p>Partners since 1994 where he is responsible</p><p>for the design and detailing of curtainwalls,</p><p>skylights, and canopy structures. In 1999,</p><p>he traveled to Europe on a Francis J. Plym</p><p>Traveling Fellowship and was awarded the</p><p>Young Architect Award from the American</p><p>Institute of Architects one year later. His first</p><p>book, “Falling Glass”, summarizes several</p><p>years of research on glass building enclosure</p><p>problems. In 2005, Patrick received a grant</p><p>from the Graham Foundation to research</p><p>the innovations and limitations of concrete,</p><p>masonry, and stone. His studies have been</p><p>compiled into his second book, “Failed</p><p>Stone”.</p><p>p_152_160_bp 18.10.2006 12:46 Uhr Seite 153</p><p>Selected Bibliography</p><p>Preface</p><p>Anderson, Stanford (ed.); Eladio Dieste. Innovation in</p><p>Structural Art, Princeton Architectural Press, New</p><p>York, 2004</p><p>Casciato, Maristella (ed.); Stone in Modern Buildings.</p><p>Principles of Cladding, Preservation Technology</p><p>Dossier 6, April 2003, DOCOMOMO, 2003</p><p>Foster, Mary Christin; The Cathedral of Our Lady</p><p>of the Angels. A House of Prayer for All Peoples,</p><p>Editions du Signe, Strasbourg, 2005</p><p>Levin, Michael; “Jerusalem of Gold”, Canadian Archi-</p><p>tect Magazine, May 2003, p 32–37</p><p>Thermal Hysteresis</p><p>Amrhein, James E. and Michael W. Merrigan; Marble</p><p>and Stone Slab Veneer, second edition, Masonry</p><p>Institute of America, 1989</p><p>Casciato, Maristella (ed.); Stone in Modern Buildings.</p><p>Principles of Cladding, Preservation Technology</p><p>Dossier 6, April 2003, DOCOMOMO, 2003</p><p>Chin, Ian R. (ed.); Recladding of the Amoco Building</p><p>in Chicago, Proceeding from Chicago Committee on</p><p>Highrise Buildings, November 1995</p><p>Cox, Ernie Jr.; “Amoco Tower’s Fate May Be Carved in</p><p>Stone”, Chicago Tribune, May 22, 1988, Business</p><p>Section, p 4</p><p>Dorris, Virginia Kent; “Anchoring Thin-Stone Veneers”,</p><p>Architecture Magazine, December 1993</p><p>Hoigard, Kurt R. (ed.); Dimension Stone Cladding,</p><p>Design Construction, Evaluation, and Repair, Stock</p><p>Number: STP 1394, ASTM International, 2000</p><p>Johnson, Paul G. (ed.); Performance of Exterior Build-</p><p>ings, Stock Number: STP 1422, ASTM International,</p><p>2003</p><p>Levy, Matthys and Mario Salvadori; Why Buildings</p><p>Fall Down. How Structures Fail, W.W. Norton &</p><p>Company, New York, 2002</p><p>Lorenzi, Rossella; “A Flawed Material. Michelangelo’s</p><p>David Said Flawed”, Discovery News, September</p><p>12, 2005</p><p>Pope-Hennessy, John; Italian High Renaissance and</p><p>Baroque Sculpture, Phaidon, London, 1996</p><p>Impact</p><p>Fortner, Brian; “Symbol of Strength”, Civil Engineer-</p><p>ing – ASCE, Vol. 74, No. 10, October 2004, p 37– 45</p><p>Hoke, John Rat; Architectural Graphic Standards,</p><p>ninth edition, Ramsey/Sleeper, John Wiley & Sons,</p><p>New York, 1994</p><p>Jodidio, Philip; Santiago Calatrava, Benedikt Taschen</p><p>Verlag, Köln, 1998</p><p>Levin, Michael; “Jerusalem of Gold”, Canadian Archi-</p><p>tect Magazine, May 2003, p 32–37</p><p>Levy, Matthys and Mario Salvadori; Why Buildings</p><p>Fall Down. How Structures Fail, W.W. Norton &</p><p>Company, New York, 2002</p><p>Nashed, Fred; Time-Saver Details for Exterior Wall</p><p>Design; McGraw Hill, New York, 1995</p><p>Stephens, Suzanne; “Eisenman’s Memorial to the</p><p>Murdered Jews of Europe”, Architectural Record,</p><p>July 2005, p 120–127</p><p>Efflorescence</p><p>Beall, Christine; Masonry Design and Detailing for</p><p>Architects, Engineers, and Builders, Prentice-Hall,</p><p>Englewood, New Jersey, 1984</p><p>Flynn, Larry; “Sculpture by Wind and Water. National</p><p>Museum of the American Indian”, Building Design</p><p>& Construction, May 2005, p 22–31</p><p>Nashed, Fred; Time-Saver Details for Exterior Wall</p><p>Design; McGraw Hill, New York, 1995</p><p>Slaton, Deborah and Lisa Backus; “Efflorescence”,</p><p>The Construction Specifier, January 2001</p><p>“Efflorescence”, Trowel Tips, Information from Portland</p><p>Cement Association, 2004</p><p>Surface Defects</p><p>Amrhein, James E. and Michael W. Merrigan; Marble</p><p>and Stone Slab Veneer, second edition, Masonry</p><p>Institute of America, 1989</p><p>Arets, Wiel; University Library in Utrecht, “Black-</p><p>and a lot of light”, Detail, No. 3, May/June 2005,</p><p>p 308 –321</p><p>Arets, Wiel; University Library – Utrecht. The Nether-</p><p>lands, Wiel Arets Architect & Associates, The Plan,</p><p>Architecture & Technologies in Detail Magazine,</p><p>No. 8, December 2004/January 2005, p 52–61</p><p>Amelar, Sarah; “Church of Padre Pio of Pietrelcina,</p><p>Italy”, Architectural Record, November 2004,</p><p>p 184–195</p><p>Basham, Kim D.; “Concrete Cracking: It Happens.</p><p>Here’s how to fix it”, L&M Concrete News, Summer</p><p>2006, Vol. 6, No. 3, L&M Construction Chemicals,</p><p>2006</p><p>Beasley, Kimball J.; “Masonry Façade Stress Failures”,</p><p>The Construction Specifier, February 1988</p><p>Bennett, David; Exploring Concrete Architecture. Tone</p><p>Texture Form, Birkhäuser, Basel, 2001</p><p>Bennett, David; The Art of Precast Concrete, Colour</p><p>Texture Expression, Birkhäuser, Basel, 2005</p><p>Betsky, Aaron; “Dark Clouds of Knowledge”, Architec-</p><p>ture Magazine, April 2005, p 52–61</p><p>Foster, Mary Christin; The Cathedral of Our Lady</p><p>of the Angels, A House of Prayer for All Peoples,</p><p>Editions du Signe, Strasbourg, 2005</p><p>Francisco, Jamie; “Image Seen Giving Occasion to</p><p>Pray”, Chicago Tribune, April 26, 2005, Section 2,</p><p>p 1</p><p>Gregory, Rob; “Process, Ancient and Modern”, The</p><p>Architectural Review, January 2004, p 54– 59</p><p>Iovine, Julie V.; “Building a Bad Reputation”, New York</p><p>Times, August 8, 2004, p 1, 27, 28</p><p>Nehdi, Moncef;</p><p>“Cracking in Building Envelopes”,</p><p>Wall & Ceiling Magazine, August 1998, p 40– 52</p><p>Malone, Sara; “Concrete: the Once & Future Liquid</p><p>Stone”, Archi Tech Magazine, March/April 2005,</p><p>p 52– 55</p><p>Mäckler, Christoph (ed.), Material Stone. Construction</p><p>and Technologies for Contemporary Architecture,</p><p>154 155</p><p>p_152_160_bp 18.10.2006 12:46 Uhr Seite 154</p><p>Birkhäuser, Basel, 2004</p><p>Pfeifer, Günter and Antje M. Liebers, Per Brauneck,</p><p>Exposed Concrete.Technology and Design,</p><p>Birkhäuser, Basel, 2005</p><p>Pollock, Naomi R.; “Tod’s Omotesando Building,</p><p>Japan”, Architectural Record, June 2005, p 78– 85</p><p>Pearson, Clifford A.;”Phaeno Science Center,</p><p>Germany”, Architectural Record, February 2006,</p><p>p 70– 81</p><p>Reese, Nancy I. Z. and Phil Geib; “Danger From</p><p>Above”, Chicago Tribune, July 16, 2000, p 14–15</p><p>Russel, James S.; “Agbar Tower, Barcelona”, Architec-</p><p>tural Record, December 2006, p 88– 95</p><p>Architectural Precast Concrete, second edition, Pre-</p><p>cast/Prestressed Concrete Institute, 1989</p><p>Guide for Surface Finish of Formed Concrete, As-Cast</p><p>Structural Concrete prepared by ASCC Education</p><p>and Training Committee, Hanley–Wood, LLC Addi-</p><p>son, IL 60101, 1999</p><p>Discoloration</p><p>Baumeister, Nicolette; Architektur neues München,</p><p>Verlagshaus Braun, Berlin, 2004</p><p>Futagawa, Yukio (ed.); Tadao Ando Details 3, A.D.A.</p><p>EDITA, Tokyo, 2003</p><p>Kamin, Blair; ”New Youth Center in Grand Crossing –</p><p>A Beacon of Optimism”, Chicago Tribune, June 4,</p><p>2006, Tempo Section, p 1</p><p>Kosmatka, Steven H.; “Discoloration of Concrete –</p><p>Causes and Remedies”, Concrete Technology</p><p>Today, Vol. 7, No. 1, April 1986, Portland Cement</p><p>Association, p 3– 5</p><p>Sims, B.D.; “Pinto Concrete: Is There a Cure?”, Con-</p><p>crete Technology Today, Vol. 17, No. 1, March</p><p>1996, Portland Cement Association, p 4– 5</p><p>Corrosion</p><p>Beall, Christine; Masonry Design and Detailing for</p><p>Architects, Engineers, and Builders, Prentice-Hall,</p><p>Englewood, New Jersey, 1984</p><p>Bey, Lee; “The trouble with terra-cotta”, Chicago Sun-</p><p>Times, October 18, 1998, p 31A</p><p>Freedman, Sidney and N.R. Greening; “Glass Stains</p><p>Causes and Remedies”, Modern Concrete, April</p><p>1979, p 36–72</p><p>Grimm, Clayford T.; “Falling Brick Façades”, The Con-</p><p>struction Specifier, March 2000</p><p>Hoke, John Rat; Architectural Graphic Standards,</p><p>ninth edition, Ramsey/Sleeper, John Wiley & Sons,</p><p>New York, 1994</p><p>Kamin, Blair; ”Terra Stricken”, Chicago Tribune,</p><p>March 4, 1999, Tempo Section, p 1</p><p>Laska, Walter; Masonry and Steel Detailing Handbook,</p><p>The Aberdeen Group, 1993</p><p>Nashed, Fred; Time-Saver Details for Exterior Wall</p><p>Design; McGraw Hill, New York, 1995</p><p>Myers, James C.; “Lessons Learned from Damaging</p><p>Interactions Between Masonry Facades and Build-</p><p>ing Structures”, Simpson Gumpertz and Heger,</p><p>Arlington, MA</p><p>Olson, Eric K. and Mauro J. Scali; “Problems in Precast</p><p>Concrete Facades: Looking Past the Obvious”, Con-</p><p>crete Repair Bulletin, May/June 1999</p><p>Prudon, Theodore H. M.; “Saving Face”, Architecture,</p><p>November 1990</p><p>Ramachandran, V. S.; ”Calcium Chloride in Concrete”,</p><p>Canadian Building Digest, January 1, 1974</p><p>Rewert, Thomas L.; “The Danger from Above”, Struc-</p><p>tural Engineer Magazine, October 2000</p><p>Richards, Cindy; “Terra Cotta Threat Shuts City Block”,</p><p>Chicago Tribune, October 10, 1988</p><p>Structure</p><p>Anderson, Stanford (ed.); Eladio Dieste. Innovation</p><p>in Structural Art, Princeton Architectural Press,</p><p>New York, 2004</p><p>AAMA TIR-A9-1991, Metal Curtain Wall Fasteners,</p><p>Architectural Aluminum Manufacturers Association,</p><p>1983</p><p>Croft, Catherine; Concrete Architecture, Gibbs Smith,</p><p>2004</p><p>Crumley, Bruce; “Why Did Charles de Gaulle Take</p><p>a Fall?”, TIME Europe Magazine, June 2, 2004</p><p>Dernie, David; New Stone Architecture, McGraw Hill,</p><p>New York, 2003</p><p>Imhof, Michael and Krempel, Leon; Berlin New</p><p>Architecture, A Guide to New Buildings from 1989</p><p>to Today, Michael Imhof Verlag, Petersberg, 2005</p><p>Post, Nedine M.; “Seismic Design, Quake Engineering</p><p>Moves Toward Era of Empowerment”, Engineering</p><p>News Record, April 17, 2006</p><p>Indiana Limestone Handbook, Indiana Limestone</p><p>Institute of America, 2000</p><p>Levy, Matthys and Mario Salvadori; Why Buildings</p><p>Fall Down. How Structures Fail, W.W. Norton &</p><p>Company, New York, 2002</p><p>Pfeiffer, Bruce Brooks; Frank Lloyd Wright,</p><p>Benedikt Taschen Verlag, Köln, 2003</p><p>Reina, Peter; “Airport Roof Failure Blamed on</p><p>Process”, Engineering News Record, February 21,</p><p>2005</p><p>Risling, Greg; ”Wright Home’s Oneness with Hill is</p><p>Undermined by Rains”, Chicago Tribune, March 6,</p><p>2005</p><p>Ryan, Raymund; ”Kinetic Monolith, Student Resi-</p><p>dences, Boston Massachusetts, USA”, The Archi-</p><p>tectural Review, January 2004, p 36– 40</p><p>Smith, Craig S.; “Roof Collapses at Paris Airport,</p><p>Killing 5”, The New York Times, May 24, 2004</p><p>Smith, Craig S.; “New Cracks Stop Search at Terminal</p><p>After Collapse”, The New York Times, May 25, 2004</p><p>Wyatt, Caroline; ”Paris Terminal ‘Showed Movement’”,</p><p>BBC News, May 26, 2004</p><p>Leakage</p><p>AAMA 501-83, Methods of Test for Metal Curtainwalls,</p><p>Architectural Aluminum Manufacturers Association,</p><p>1983.</p><p>Deason, J.P., T.A. Tsongas and C.R. Cothem; Environ</p><p>mental Engineering Policy, Vol. 1, No. 1, July 1998,</p><p>p 37– 45</p><p>Dow Corning, Weatherproofing Sealant Guide, Dow</p><p>Corning Corporation, October 1994</p><p>LaTona, Raymond W. and Thomas Schwartz; ”Cladding</p><p>Systems Against the Wall”, Architecture, May 1990,</p><p>p 129–131</p><p>LeVoguer, Brian; “Details and Execution: The Road</p><p>to Quality Air Barriers”, Construction Canada, July</p><p>1996, p 10–12</p><p>Kerr, Dale D.; “Controlling Rain and Wind”, Architec-</p><p>ture, October 1994, p 117–119</p><p>Kieren, Martin; New Architecture Berlin 1990 – 2000,</p><p>Jovis, Berlin, 1998</p><p>Loughran, Patrick; Falling Glass. Problems and</p><p>Solutions in Contemporary Architecture, Birkhäuser,</p><p>Basel, 2003</p><p>Mäckler, Christoph (ed.), Material Stone. Construction</p><p>and Technologies for Contemporary Architecture,</p><p>Birkhäuser, Basel, 2004</p><p>Ting, Raymond; “Evolution of Curtain Wall Design</p><p>Against Water Infiltration”, January 1997, p 34– 36</p><p>Sturdevant, John R.; “What Makes a Good Curtain-</p><p>wall?”, Progressive Architecture, February 1994,</p><p>p 70–77</p><p>Wright, Gordon; “Inappropriate Details Spawn Cladding</p><p>Problems”, Building Design & Construction, January</p><p>1996, p 56– 60</p><p>p_152_160_bp 18.10.2006 12:46 Uhr Seite 155</p><p>Index</p><p>111 South Wacker, Chicago 32</p><p>Aalto, Alvar 6</p><p>Absorbent formwork 57</p><p>Absorption rate 69</p><p>Accelerated weathering test 21</p><p>Acid wash 91</p><p>Adhesive failure 140</p><p>Admixtures 75, 91, 95, 128</p><p>Aggregates 8, 75, 90, 128</p><p>Aggregate transparency 52, 74</p><p>Alfred P. Murrah Federal Building, Oklahoma City</p><p>24–25, 26</p><p>Algae growth 83</p><p>Alkali hydroxide solutions 77</p><p>Alkali silica reaction 98</p><p>American Institute of Architects 82</p><p>American-mist granite 43</p><p>Amoco Building, Chicago 11, 12, 13, 14, 21</p><p>Ando, Tadao 68</p><p>Anisotropic 15</p><p>Antamex 17</p><p>Anti-graffiti protection 86, 88</p><p>Arets, Wiel 59</p><p>ArkHouse 80</p><p>Auditorium Parco della Musica, Rome 34, 35, 36–37</p><p>Autoclaved aerated concrete (AAC) 128</p><p>Baffles 139</p><p>Bagging 69</p><p>BAPS Temple, Bartlett, Illinois 106</p><p>Berlin Water Works, Headquarters, Berlin 84, 85</p><p>Berlin Zoo 67</p><p>Blast design 8, 26–28, 29, 33</p><p>Blowholes 69</p><p>Blue Cross Blue Shield of Illinois, Chicago 22, 23</p><p>Botanical Gardens, Barcelona 102</p><p>Braunfels, Stephan 100</p><p>Bregenz Art Museum, Austria 86, 87</p><p>Bronx-Whitestone Bridge, New York 125</p><p>Bugholes 51, 52, 58</p><p>Burroughs Wellcome Research Headquarters,</p><p>North Carolina 104</p><p>Bush hammering 33, 62</p><p>Calatrava, Santiago 7, 79, 99</p><p>Calcite crystals 15</p><p>Calcium chloride 74, 91, 95, 102</p><p>Canadian Embassy, Washington, D.C. 44– 45, 46</p><p>Carbon steel connections 6</p><p>Carbon steel reinforcement 102, 107</p><p>Carrara alpha grey marble 12</p><p>Carrara white marble 6, 10, 17, 20, 21</p><p>Casa Milla, Barcelona 118, 119</p><p>Cast-in-place concrete 28, 48, 50, 51, 52, 56, 57, 59,</p><p>68, 111</p><p>Cathedral of Our Lady of the Angels, Los Angeles</p><p>8, 39, 56</p><p>Cavity wall 130, 136, 140, 151</p><p>Cement wash 57</p><p>Central National Bank, Cleveland, Ohio 94, 95</p><p>Chamfered corners 31</p><p>Charles de Gaulle International</p><p>Airport, Terminal 2E,</p><p>Paris 8, 110-113, 115, 129</p><p>Chemical staining 79-80</p><p>Chemical washes 91</p><p>Chipping 66, 67, 128</p><p>Church of Christ the Worker, Atlántida, Uruguay 119</p><p>Church of Padre Pio, San Giovanni Rotondo, Italy</p><p>122, 123–124</p><p>Cohesive failure 140</p><p>Colored concrete 77–79</p><p>Compartmentalization 138, 151</p><p>Concrete patina 103 –104</p><p>Concrete repair 69</p><p>Construction Research Laboratory, Miami 12</p><p>Contemporary Arts Center, Cincinnati, Ohio 77</p><p>Corrosion 92–107</p><p>Cor-Ten steel 102</p><p>Crystallization 38, 46, 47</p><p>Curling of concrete slabs 54, 55</p><p>Curtain wall 8, 17, 130, 140, 151</p><p>David, sculpture by Michelangelo 20</p><p>Debis Tower, Potsdamer Platz, Berlin 97</p><p>Debris mitigation 26, 33</p><p>Denver Zoo, Giraffe House, Colorado 94</p><p>Deutsches Historisches Museum, Berlin 100</p><p>Dieste, Eladio 9, 118, 119, 120</p><p>Dio Padre Misericordioso, see Jubilee Church</p><p>Discoloration 70 –91</p><p>Dual seals 141</p><p>Ductal 112, 127, 128</p><p>Ductility 24, 28–30, 33</p><p>Dulles International Airport, Washington, D.C. 62, 63,</p><p>115 –117, 129</p><p>Earthquake loads 112, 121-124, 129, 149</p><p>Eberswalde Technical School, Eberswalde near Berlin</p><p>81</p><p>Efflorescence 34– 47, 76, 132</p><p>Eiteljorg Museum of American Indians and Western</p><p>Art, Indianapolis 83</p><p>Engineering Research Center, University of Cincinnati,</p><p>Ohio 143–144</p><p>Ennis-Brown House, Los Angeles 122–123, 124</p><p>E.N.S.A.D., Ecole Nationale Supérieure des Arts</p><p>Décoratifs, Paris 8</p><p>Epoxy resin 102, 124</p><p>Epoxy-coated steel 94</p><p>Etching of glass 105</p><p>Ettringite 104 –105, 107</p><p>Expansion joints 143, 144, 145, 146, 148, 151</p><p>Fading 91</p><p>Federal Campus Building, Oklahoma City 27–28</p><p>Federal Chancellery, Berlin 85</p><p>Ferrater, Carlos 102</p><p>Fiber-reinforced concrete 62</p><p>156 157</p><p>p_152_160_korr_plotter 27.10.2006 15:26 Uhr Seite 156</p><p>Fiber-reinforced polymer (FRP) 94, 102</p><p>Field installation 150–151</p><p>Finishes 67</p><p>Finlandia Hall, Helsinki 6, 18 –19, 20</p><p>Fins 52</p><p>Fire resistance 128, 129, 149</p><p>Fissures 66</p><p>Flashings 138–139, 141, 142, 151</p><p>Flexibility 121, 124-125, 129</p><p>Form scabbing 52</p><p>Freeze thaw testing 21, 67</p><p>Freyssinet, Eugène 112</p><p>Galloping Gertie, see Tacoma Narrows Suspension</p><p>Bridge</p><p>Galvanic action 96, 98, 104</p><p>Galvanic corrosion 102, 107</p><p>Gary Comer Youth Center, Chicago 88</p><p>Gaudí, Antonio 118, 119</p><p>General Motors Building, New York 20– 21</p><p>Getty Center, Los Angeles 73</p><p>Goettsch Partners 9, 32, 33</p><p>Graffiti 86, 88</p><p>Graves, Michael 143</p><p>Greenhouse effect 70, 76</p><p>Guggenheim Museum, New York 79</p><p>Hadid, Zaha 86, 128</p><p>Hagia Sophia, Istanbul 121, 124</p><p>Hall Auditorium, Oberlin College, Ohio 84</p><p>Hennebique, François 112</p><p>Herzog and de Meuron 81</p><p>Hessel Museum, CCS Bard College, New York 9</p><p>High cement mortar 38</p><p>Holl, Steven 117</p><p>Holocaust Memorial, Berlin 31, 32</p><p>Honeycombing 48, 50, 51– 52, 69</p><p>Hydrophobic layer 83</p><p>Igneous rock 65, 67</p><p>Impact 22– 33</p><p>Imperial Hotel, Tokyo 121, 124</p><p>Imperial Polk County Courthouse, Bartow, Florida</p><p>141–142</p><p>Inclusions 65</p><p>Indiana Limestone Institute 29</p><p>Innsbruck Ski Jump, Austria 86</p><p>Insulated concrete forms (ICF) 129</p><p>International Masonry Institute 67</p><p>IRCAM Music Extension, Paris 89</p><p>Iron oxide 75, 107</p><p>Israeli Foreign Ministry 8, 28–29</p><p>Jay Pritzker Pavilion at Millenium Park, Chicago</p><p>48, 49, 54</p><p>Johnson Wax Building, Racine, Wisconsin 108, 109,</p><p>129</p><p>Jubilee Church, Rome 70 –73</p><p>Jurassic limestone 104</p><p>Kahn, Louis 51</p><p>Kasota domilitic limestone 43</p><p>King Building, Oberlin College, Ohio 101</p><p>Kulturzentrum Gasteig, Munich 138</p><p>Kunstmuseum Liechtenstein, Vaduz, Liechtenstein</p><p>64, 65</p><p>Lafarge 112, 127</p><p>La Salle Street, Chicago 92</p><p>Layer marks 55</p><p>Leakage 130–151</p><p>Léon Wohlhage Wernik Architekten 64</p><p>Lévi-Strauss School, Köpenick, Berlin 134, 135</p><p>Lincoln Bank of Rochester, New York 16, 17</p><p>Low-alkali cement 47</p><p>Mäckler, Christoph 134</p><p>Maillart, Robert 118</p><p>Marciano, Rémy 78</p><p>Marina Towers, Chicago 95</p><p>Masonry tower, Potsdamer Platz, Berlin 150</p><p>Mather Tower, Chicago 6</p><p>Max-Planck-Institut für Infektionsbiologie, Berlin 138</p><p>Mel and Joan Perelman Wing, see Eiteljorg Museum</p><p>Merrimac stone 68, 90</p><p>Met Lofts, Los Angeles 77</p><p>Metal corrosion 96</p><p>Metal flashings 102</p><p>Metamorphic rock 65, 67</p><p>Metropolitan Correctional Center, Chicago 40, 41</p><p>Metropolitan Museum of Art, New York 84</p><p>Mexican Embassy, Berlin 62</p><p>Miami Dade Center, Miami 147–148</p><p>Michelangelo 20</p><p>Mock-up 12, 29, 61, 69, 104, 129, 150–151</p><p>Mold 151</p><p>MOMA, Museum of Modern Art, New York 30, 31</p><p>Monadnock Building, Chicago 130, 131, 150</p><p>Mortar joints 38–39</p><p>Mount Airy granite 14</p><p>Municipal Bus Terminal, Salto, Uruguay 118, 120</p><p>Murrah Building, see Alfred P. Murrah Federal Building</p><p>Mustakivi School and Community Center, Helsinki 80</p><p>Nagle Hartray and Associates 102</p><p>National Gallery of Art, East Wing, Washington, D.C.</p><p>75, 82, 83</p><p>National Museum of the American Indian, Washington,</p><p>D.C. 42, 43</p><p>New building bloom 34, 43</p><p>Non-absorbent formwork 57</p><p>Non-absorbing forms 76</p><p>Non-ferrous metals 96, 97</p><p>Nordenson and Associates 117</p><p>Nouvel, Jean 115</p><p>Offsets 52</p><p>Oklahoma City bombing 33, see also Alfred P. Murrah</p><p>Federal Building</p><p>One South La Salle Street, Chicago 92</p><p>Onterie Center, Chicago 136</p><p>Oskar Reinhart Collection, Winterthur, Switzerland 103</p><p>Our Lady of the Angels, see Cathedral of Our Lady</p><p>of the Angels</p><p>Painting concrete 79</p><p>Palace of Justice, Bordeaux 30</p><p>Palazzo Vecchio, Florence 20</p><p>Pantheon, Rome 15, 57, 69</p><p>Paul-Löbe-Haus, Berlin 100</p><p>Perforated concrete 117</p><p>Phaeno Science Center, Wolfsburg, Germany 59, 60,</p><p>61, 127, 128</p><p>Phenolics 77</p><p>Photoengraved concrete 8, 81</p><p>Piano, Renzo 123</p><p>Piazza della Signora, Florence 20</p><p>Pinakothek der Moderne, Munich 74</p><p>Pinto concrete 70, 73</p><p>Polishing 64, 69</p><p>Polycarboxylate ether 61, 128</p><p>Portland cement 34, 38, 39, 47, 90, 105</p><p>Portland Cement Association 73, 90</p><p>Post-damage resistance 25</p><p>Potsdamer Platz, Berlin, see Debis Tower</p><p>Precast concrete 8, 58-59, 62, 64, 69, 116, 117</p><p>Precast concrete sandwich panels 80</p><p>Precast panels 8, 136</p><p>Pressure-equalized wall 137–138, 141</p><p>Prestressed steel cable 120</p><p>Prestressing 120, 127</p><p>Progressive collapse 24, 25-26, 28, 33</p><p>Public Library, Oak Park, Illinois 102</p><p>Pulitzer Foundation of the Arts, St. Louis 68, 89, 90</p><p>Rainscreen design 137, 140</p><p>Reinforcement marks 55</p><p>Regenstein Center for African Apes, Lincoln Park Zoo,</p><p>Chicago 33</p><p>Release agent 76, 77</p><p>Residential complex for government employees,</p><p>Berlin 139</p><p>Resin 66, 69, see also Epoxy resin</p><p>Rhône-Alpes TGV station, Lyon Airport 6, 7</p><p>Ronan, John 88</p><p>Ross Barney + Jankowski Architects 27</p><p>Ruffi Gymnasium, Marseilles 78</p><p>Salgina, Switzerland 118</p><p>Salk Institute for Biological Studies, La Jolla, California</p><p>50–51, 52, 53, 64</p><p>Salt hydration distress (SHD) 38</p><p>Sandblasting 62, 69</p><p>Sankt Florian Church Center, Riem, Munich 145 –146</p><p>San Nicola Stadium, Bari, Italy 76</p><p>Sarabond 6, 94, 95, 102</p><p>Scaling 55</p><p>Schreiber, Amy 117</p><p>Sealant joints 140–141, 148, 151</p><p>Sedimentary rock 65, 67</p><p>Self-compacting concrete (SCC) 48, 61, 127, 128</p><p>Seonyu Footbridge, Seoul 126–127</p><p>p_152_160_korr_plotter 27.10.2006 15:26 Uhr Seite 157</p><p>Shrinkage 54, 145–146, 147</p><p>Sick building syndrome 141</p><p>Silicone sealant 91</p><p>Simmons Hall at MIT, Cambridge, Massachusetts 116</p><p>Simpson Gumpertz & Heger 117, 148</p><p>Single wythe construction 134, 136</p><p>Skateboarders 32, 33</p><p>Smooth-form concrete 58</p><p>Snow loads 112, 116</p><p>Sodium sulfate 38</p><p>Solid masonry walls 133–134</p><p>Soluble compounds 47</p><p>Sozialverband Deutschland, Headquarters, Berlin</p><p>62, 64</p><p>Spalling 40, 46, 48, 55, 57, 107</p><p>Stand-off distance 25</p><p>Stainless steel 96, 103, 107, 123, 124</p><p>Stainless steel fasteners 92, 147</p><p>Stainless steel reinforcement 94</p><p>Stains 70, 77, 84, 85, 90, 91, see also Chemical</p><p>staining</p><p>Stick systems 140</p><p>Stone discoloration 91</p><p>Structural analysis 117– 118, 120, 129</p><p>Structural collapse 112, 129</p><p>Structural form 115–117</p><p>Structural redundancy 23, 33, 112</p><p>Suicide bombers 26</p><p>Sulfide 75</p><p>Super white exposed</p><p>concrete 70</p><p>Superplasticizer 8, 61, 128</p><p>Surface defects 48– 69</p><p>Tacoma Narrows Suspension Bridge, Washington</p><p>State 124 –125, 129</p><p>Terra-cotta 6, 9, 66, 67, 89, 96, 97</p><p>Terrazo 64</p><p>Thermal hysteresis 6, 10–21</p><p>Tie bar 55</p><p>Tie holes 55, 56</p><p>Through-wall flashing 130, 133, 136, 139, 141, 142,</p><p>151</p><p>Tod’s Omotesando office building, Tokyo 108</p><p>Torre Agbar, Barcelona 114, 115</p><p>Trowel burn 76</p><p>Tuned mass dampers 125 –128, 129</p><p>Ultrahigh performance concrete 108, 112, 126, 127,</p><p>128, 129</p><p>Ultrahigh strength concrete 48</p><p>Unitized systems 140</p><p>Unity Temple, Oak Park, Illinois 57, 147</p><p>University Library, Utrecht 58, 59</p><p>University of Cincinnati School of Architecture and</p><p>Interior Design, Ohio 39</p><p>University of Oulu, Linnannmaa District, Finland</p><p>144, 145</p><p>Vandalism 86 – 89, 91</p><p>Vapor barrier 142, 151</p><p>Veining patterns 66</p><p>Veneer wall 130, 133, 136, 141, 142</p><p>Virta Palaste Leinonen 144</p><p>Vontz Center for Molecular Studies, Cincinnati, Ohio</p><p>44, 132–133, 142</p><p>Walt Disney Concert Hall, Los Angeles 66</p><p>Washington Monument, Washington, D.C. 82</p><p>Water-cement ratio 73, 90</p><p>Water runoff 84 –85, 91, 104, 105, 107</p><p>Weeps 138, 139, 151</p><p>Wicking 44– 45</p><p>Wind loads 150</p><p>World tectonic plates 124</p><p>Wright, Frank Lloyd 57, 79, 108, 121, 122, 147</p><p>Zumthor, Peter 86, 87</p><p>Zwarts, Kim 59</p><p>158 159</p><p>p_152_160_korr_plotter 27.10.2006 15:26 Uhr Seite 158</p><p>Illustration Credits</p><p>Antamex Curtainwall Company 16</p><p>American Architectural Manufacturers Association,</p><p>AAMA 140 top</p><p>Carl-Magnus Dumell, www.dumell.net cover photo,</p><p>18, 19</p><p>Construction Research Laboratory (CRL) 12 top,</p><p>101 bottom, 104 bottom, 149 bottom</p><p>Diamond and Schmitt Architects Incorporated,</p><p>www.dsai.ca 28 bottom, 29 bottom</p><p>Don Schapper, Aldon Chemical 38</p><p>Ed Allen 119 top</p><p>Encarta.msn.com 24 top</p><p>Formtech, Insulated Concrete Forms, courtesy of</p><p>Kevin Grogan 129</p><p>The Frank Lloyd Wright Foundation, Taliesin West,</p><p>Scottsdale, AZ 121 bottom</p><p>Getty Images 111 top</p><p>Steve Hall, Hedrich Blessing,</p><p>www.hedrichblessing.com, courtesy of Ross Barney</p><p>+ Jankowski Inc Architects 27 top</p><p>Illustration redrawn from detail on page 11-2 and</p><p>page 5-3 of Ian R. Chin; Recladding of the Amoco</p><p>Building in Chicago, Proceeding from Chicago Com-</p><p>mittee on Highrise Buildings, November 1995 12,</p><p>14 top</p><p>Jan Bitter courtesy of Jan Bitter Fotografie</p><p>www.janbitter.de 58 top and bottom right</p><p>James Steincamp, James@Steincampphotography.com</p><p>32 bottom, 34 top</p><p>Johnson Architectural Images, AJ1507; © Artifice Inc.</p><p>108 bottom</p><p>Lisa Krichilsky 21</p><p>Kevin A. O'Connor, AIA, Ross Barney + Jankowski</p><p>Inc Architects 26, 27 bottom</p><p>Kim Zwarts (design of pattern on precast mould at</p><p>University Library Utrecht) 58 bottom right</p><p>Léon Wohlhage Wernik Architekten 64</p><p>Galvin Loughran 71, 84</p><p>Liam Loughran 57 bottom</p><p>Mary Margaret Loughran 95, 102 top, 104 middle,</p><p>114, 115 bottom</p><p>Mike Giso 17 bottom left and bottom right</p><p>Nabih Youssef Associates 118 bottom</p><p>Nicholas Stanos 20 middle</p><p>Oklahoma Publishing Company (OPUBCO)</p><p>www.newsok.com 24 bottom</p><p>O’Mally Creadon Productions 122 top</p><p>Pavlo Berko 87 bottom</p><p>Pennie Sabel, courtesy of Building Stone Institute</p><p>13 bottom, 14 bottom, 16, 17 top, 124 middle right</p><p>Philippe Rualt, courtesy of Remy Marciano Architecte</p><p>DPLG 78</p><p>Pulitzer Foundation 68, 69 top</p><p>Jay Williams, AIA 116 top, 117 top</p><p>John Ronan Architect 88 top</p><p>Randy Chapple AIA 90 top</p><p>R. Van Petten AIA 94</p><p>Scott Seyer AIA 9, 10 right, 11 (photo rendering of</p><p>300 east Randolph Expansion)</p><p>Simpson Gumpertz & Heger Inc. 116 bottom,</p><p>117 bottom middle, 148</p><p>Shutterstock.com 10, 15, 20 top, 22, 32 top, 51 top,</p><p>70 top, 73 top, 76 top, 82 left, 86 bottom, 110 top,</p><p>113, 121 top, 125</p><p>Stanford Anderson (ed.) Eladio Dieste. Innovation</p><p>in Structural Art 118 top, 119 top, 120</p><p>Tim Griffith, www.timgriffith.com, courtesy of Diamond</p><p>and Schmitt Architects Inc. 28 top, 29 top</p><p>Travis Soberg 48 left</p><p>Wiel Arets Architects 58 bottom left</p><p>Virta Palaste Leinonen Architects 144</p><p>Ductal 126 top</p><p>Stefan Müller, courtesy of Christoph Mäckler</p><p>Architekten 135</p><p>Christoph Mäckler Architekten 134 bottom right</p><p>ArkHouse Architects 80</p><p>Illustration redrawn from Christine Beall; Masonry</p><p>Design and Detailing, For Architects, Engineers,</p><p>and Builders, Prentice-Hall, Englewood, New Jersey</p><p>1984 36, 46 bottom left, 47 left</p><p>Illustration redrawn from detail on page 187 of</p><p>Günter Pfeifer and Antje M. Liebers, Per Brauneck,</p><p>Exposed Concrete.Technology and Design, Birk-</p><p>häuser, Basel, 2005 56 left</p><p>Illustration redrawn from detail on page 406 and</p><p>page 187 of Christine Beall; Masonry Design and</p><p>Detailing for Architects, Engineers, and Builders,</p><p>Prentice-Hall, Englewood, New Jersey 1984</p><p>46 bottom and 47 left</p><p>Image redrawn from detail on page 64 of James E.</p><p>Amrhein and Michael W. Merrigan; Marble and</p><p>Stone Slab Veneer, second edition, Masonry Insti-</p><p>tute of America, 1989 20</p><p>Image redrawn from detail on page 262 of Matthys</p><p>Levy and Mario Salvadori; Why Buildings Fall Down.</p><p>How Structures Fail, W.W. Norton & Company,</p><p>New York, 2002 25</p><p>Image redrawn from detail on page 31A of Lee Bey;</p><p>“The trouble with terra-cotta”, Chicago Sun-Times,</p><p>October 18, 1998 96</p><p>Image redrawn from detail on page 31 of Indiana</p><p>Limestone Handbook, Indiana Limestone Institute of</p><p>America, 2000 45</p><p>Images redrawn from the information on the website</p><p>of the Renzo Piano Building Workshop,</p><p>www.renzopiano.com 36 bottom, 37 bottom</p><p>All other illustrations were provided by the author.</p><p>p_152_160_korr_plotter 27.10.2006 15:26 Uhr Seite 159</p><p>Graphic design: Gabrielle Pfaff, Berlin</p><p>Engineering review and copy editing: Richard Palmer,</p><p>Palmer Consulting, Divonne-les-Bains, France</p><p>A CIP catalogue record for this book is available from</p><p>the Library of Congress, Washington D.C., USA</p><p>Bibliographic information published by Die Deutsche</p><p>Bibliothek</p><p>Die Deutsche Bibliothek lists this publication in the</p><p>Deutsche Nationalbibliografie; detailed bibliographic</p><p>data is available in the internet at http://dnb.ddb.de.</p><p>This work is subject to copyright. All rights are</p><p>reserved, whether the whole or part of the material</p><p>is concerned, specifically the rights of translation,</p><p>reprinting, re-use of illustrations, recitation, broad-</p><p>casting, reproduction on microfilms or in other ways,</p><p>and storage in data banks. For any kind of use, per-</p><p>mission of the copyright owner must be obtained.</p><p>© 2007 Birkhäuser – Publishers for Architecture,</p><p>P.O. Box 133, CH-4010 Basel, Switzerland</p><p>Part of Springer Science+Business Media</p><p>Printed on acid-free paper produced from chlorine-</p><p>free pulp. TCF</p><p>Printed in Germany</p><p>ISBN-13: 978-3-7643-7329-0</p><p>ISBN-10: 3-7643-7329-6</p><p>http://www.birkhauser.ch</p><p>9 8 7 6 5 4 3 2 1</p><p>Front cover: Detail of Finlandia Hall, Helsinki</p><p>∞</p><p>p_152_160_bp 18.10.2006 12:46 Uhr Seite 160</p><p>FS</p><p>front-matter</p><p>01Thermal Hysteresis</p><p>02Impact</p><p>03Efflorescence</p><p>04Surface Defects</p><p>05Discoloration</p><p>06Corrosion</p><p>07Structure</p><p>08Leakage</p><p>back-matter</p><p>be</p><p>kept “equivalent to the origi-</p><p>nal”.</p><p>The re-clad Finlandia Hall</p><p>remains stark white as com-</p><p>pared to the neighboring hotel</p><p>re-clad in white granite.</p><p>page 19 above Finlandia Hall</p><p>was constructed between</p><p>1967 and 1971 using white</p><p>Carrara marble with a distinc-</p><p>tive stone veining pattern ris-</p><p>ing diagonally from the panels.</p><p>below Finlandia Hall. Photo</p><p>of bowing replacement panels</p><p>taken in the winter of 2006.</p><p>p_010_021_chapt_1_bp 17.10.2006 18:04 Uhr Seite 18</p><p>In 1997, re-cladding of Finlandia Hall with</p><p>white marble was started. Work was complet-</p><p>ed in May 1999. In total, 7,000m2 (75,320</p><p>square feet) of panels were replaced at a cost</p><p>of over 3 million Euros. In autumn 2001, just</p><p>three years after Finlandia Hall had been re-</p><p>clad, it was realized that new panels were</p><p>bending. Measurements have shown that the</p><p>renovated walls of Finlandia Hall have deterio-</p><p>rated. The reduction in the strength of the</p><p>marble since the slabs were replaced is</p><p>20–30 percent. Panels installed in autumn</p><p>1998 are bowed more than those installed the</p><p>following spring. The reason for this can be</p><p>attributed to the cold winter in Finland in</p><p>1998–99. The story of the cladding at Finlan-</p><p>dia Hall demonstrates the irrational loyalty a</p><p>community can have for great works of archi-</p><p>tecture.</p><p>p_010_021_chapt_1_bp 27.10.2006 15:56 Uhr Seite 19</p><p>The history of the famous Renaissance mas-</p><p>terpiece David may shed some light on how</p><p>thermal hysteresis can be avoided in white</p><p>marble. In 1464, the Overseers of the Office</p><p>Works (Operai) made plans to commission a</p><p>series of twelve large Old Testament sculp-</p><p>tures for the buttress of the cathedral of Santa</p><p>Maria Del Fiore in Florence. Two sculptures</p><p>had been created by Donatello and his assis-</p><p>tant Agostino de Duccio, and they planned to</p><p>create a David for the project. A large marble</p><p>block, more than 5m (17 feet) tall, was carved</p><p>from a quarry and Agostino began to shape</p><p>the legs, feet and chest of the figure. For rea-</p><p>sons unknown, Agostino’s association with the</p><p>project ceased with the death of his master</p><p>Donatello in 1566, and Antonio Rossellino</p><p>was commissioned to take up where Agostino</p><p>had left off. Shortly thereafter, Rossellino’s</p><p>contract was terminated, and the large block</p><p>of marble lay dormant, exposed to the ele-</p><p>ments, in the yard of the cathedral workshop</p><p>for 25 years. In 1501, a young Michelangelo,</p><p>only 26 years old, was given the contract</p><p>to complete the massive biblical hero. He</p><p>worked on the project for a little more than</p><p>three years, prior to its unveiling in front of</p><p>the Palazzo Vecchio on Piazza della Signoria.</p><p>Although the sculpture had a reputation of</p><p>being of poor quality, it remained there until</p><p>1873, when it was moved indoors to the</p><p>Academmia gallery in Florence. How could</p><p>the sculpture of David be left exposed to the</p><p>elements for over 300 years with no signs</p><p>of thermal hysteresis? The re-cladding of</p><p>Finlandia Hall showed visible deterioration</p><p>after less than three years. Obviously, the cli-</p><p>mate of Florence has far smaller thermal</p><p>cycles than the streets of Helsinki; however,</p><p>a closer examination of the stone will also</p><p>reveal a difference.</p><p>The veining of the marble at Finlandia Hall</p><p>was a prominent feature of the stone. The</p><p>original stone as well as the replacement stone</p><p>had a distinctive pattern with veins rising diag-</p><p>onally from the left to the right on the panels.</p><p>The grain size of David is far less visible to the</p><p>eye. The fine grain size is the most distinct</p><p>property of the marble used for David. Studies</p><p>suggest that the grain texture, veining and</p><p>clear contours produce lower strength and</p><p>prove less durable than slightly veined mar-</p><p>bles. The stone used to create David had very</p><p>little grain as opposed to the stones used on</p><p>the architectural projects discussed. Have</p><p>there been examples of white marble on</p><p>buildings that have not failed? The answer is</p><p>yes, and the successful projects are linked to</p><p>unique installation techniques and quarried</p><p>white marble stone with special material</p><p>properties.</p><p>Installation Techniques</p><p>Installation techniques can contribute to the</p><p>success of white marble on buildings. In the</p><p>late 1980s, stone-faced composite panels,</p><p>consisting of 5mm (1/5 inch) thick stone panels</p><p>adhered to 4cm (11/2 inch) honeycombed alu-</p><p>minum, fiberglass, or sheet steel core began</p><p>to be used on the exterior walls of buildings.</p><p>An early example of this innovative technique</p><p>using Carrara marble was completed at the</p><p>new hall at the Fiera in Carrara. The building</p><p>design required lighter loads than could be</p><p>obtained with traditional 3cm (11/4 inch) pan-</p><p>els. This led to the decision to use thin mar-</p><p>ble, 4mm (3/16 inch) thick, bonded to a honey-</p><p>comb backing which tests have proven to be</p><p>surprisingly resistant to flexure, even after frost</p><p>treatment in an aggressive environment.</p><p>Another project that has had success with thin</p><p>white marble in a northern climate is an office</p><p>building in the town of Karjaa, which is west</p><p>of Helsinki. The building was completed at</p><p>about the same time as Finlandia Hall, with</p><p>its façades made from Carrara marble. There</p><p>is no visible evidence of dishing on this build-</p><p>ing. Many would speculate that the façade</p><p>used material much thicker than the 3cm</p><p>(11/4 inch) used at Finlandia Hall. In truth,</p><p>the material is thinner. Similar to the hall at</p><p>the Fiera in Carrara, the façade is made of</p><p>composite panels consisting of 1cm (3/8 inch)</p><p>thick stone with a 3cm (11/4 inches) concrete</p><p>back-up system. The marble slab was pre-</p><p>bowed by sandblasting the back of it until</p><p>there was 4mm (3/16 inch) of bowing prior to</p><p>attaching to the concrete substrate. As the</p><p>20 21</p><p>David’s replacement.</p><p>Michelangelo’s David, carved</p><p>from a solid block of white</p><p>Carrara marble, was moved</p><p>indoors after being exposed</p><p>to the elements for over</p><p>300 years.</p><p>General Motors Building,</p><p>New York City, 1968.</p><p>Clad with white marble, with</p><p>no signs of thermal hysteresis.</p><p>below Marble slabs support-</p><p>ed by precast concrete panels</p><p>similar to the ones used for the</p><p>General Motors Building.</p><p>1 Marble veneer panel</p><p>2 Impervious isolation sheet</p><p>3 Stainless steel pin in drilled</p><p>holes</p><p>4 Precast concrete panel</p><p>How Can Thermal Hysteresis Be Avoided?</p><p>p_010_021_chapt_1_bp 17.10.2006 18:04 Uhr Seite 20</p><p>concrete panel shrank with drying, the stone</p><p>slab was straightened. Lastly, the General</p><p>Motors Building in New York City was suc-</p><p>cessfully clad with white marble in 1968. The</p><p>perimeter hexagonal columns of this 50-story</p><p>building were covered with domestically quar-</p><p>ried 2.2cm (7/8 inch) thick Georgia white mar-</p><p>ble connected to precast concrete panels.</p><p>To date, the building has not experienced the</p><p>severe affects of thermal hysteresis. The Gen-</p><p>eral Motors Building stands as a reminder that</p><p>not all white marble cladding is the same.</p><p>Stone Testing</p><p>In order to predict which stones will suffer</p><p>the effects of hysteresis, laboratory-simulated</p><p>accelerated weathering testing is used to</p><p>estimate the loss of strength in materials as</p><p>a result of exposure to the weather. This issue</p><p>is still being debated in the stone industry.</p><p>There are critics that believe that durability</p><p>(accelerated weathering) test procedures have</p><p>no relationship to natural weathering. There</p><p>is wide diversity between the durability test</p><p>procedures preferred by the European Coun-</p><p>tries and freeze thaw testing used in the</p><p>United States.</p><p>What is important to remember is that exten-</p><p>sive testing was completed for the Amoco</p><p>Building. However, the decision to use a build-</p><p>ing material that lost 40 percent of its strength</p><p>due to freeze thaw cycling was still made.</p><p>Testing alone will not avoid the problem. What</p><p>the Amoco project lacked was a historic exam-</p><p>ple/precedent of thin 3cm (11/4 inch) white</p><p>Carrara marble installed on metal framing in</p><p>a northern city. They desired to use a Mediter-</p><p>ranean stone on a large-scale project without</p><p>confirming its suitability for the Chicago cli-</p><p>mate. Amoco was not a small Italian Villa con-</p><p>structed of marble blocks; it was an 80-story</p><p>office tower with a steel structure located just</p><p>off the shores of Lake Michigan in Chicago. It</p><p>can be dangerous to borrow design elements</p><p>from buildings of the past without including</p><p>the construction methods or climate consider-</p><p>ations from which they came.</p><p>Stone faced composite panels</p><p>with a thin layer of stone</p><p>adhered to a honeycombed</p><p>aluminum core has proven to</p><p>be resistant to flexure, even</p><p>after frost treatment in an</p><p>aggressive environment.</p><p>Lessons Learned</p><p>1</p><p>Stone is a natural material, and by its very</p><p>nature is prone to material property variation.</p><p>Marbles have an enormous range in initial</p><p>strength properties and vary considerably in</p><p>weathering characteristics. It is important to</p><p>verify that the materials supplied to the site</p><p>meet the project design requirements. The</p><p>flexural strength of the marble supplied and</p><p>installed on the building should not be less</p><p>than the minimum specified flexural design</p><p>strength. This occurred at the Amoco project.</p><p>Quality control testing of the actual material</p><p>being supplied should therefore be undertak-</p><p>en to ensure continued compliance with the</p><p>required strength as calculated from design.</p><p>2</p><p>The use of thin marble panels on buildings</p><p>in the late 1960s was relatively new, and</p><p>therefore the in-service behavior of this type</p><p>of stone on buildings had no history. The use</p><p>of thin marble panels has led to complete</p><p>façade replacement on several large-scale</p><p>projects throughout the world. If stone is used</p><p>in an exterior application for a large project,</p><p>it is advisable to select a stone that has per-</p><p>formed well over time in a similar circum-</p><p>stance.</p><p>3</p><p>If loss of material strength (hysteresis) is a</p><p>concern, and if stone panels are going to be</p><p>exposed to large temperature variation, mate-</p><p>rial testing of stone should include accelerat-</p><p>ed weathering tests.</p><p>4</p><p>In keeping with the history of the use of stone</p><p>in architecture, the thickness of stone used</p><p>for exterior walls on buildings has been</p><p>reduced substantially. The most dramatic</p><p>decreases from 10.2cm (4 inches) to 3cm</p><p>(11/4 inches) occurred during the last 40</p><p>years. Extensive research on material proper-</p><p>ties, including durability, must parallel the</p><p>advancement in fabrication techniques.</p><p>Large-scale projects must consider the ramifi-</p><p>cations of technical advancements prior to</p><p>embarking on innovative installation tech-</p><p>niques.</p><p>5</p><p>Marble has been successfully used as a</p><p>building material for hundreds of years, and</p><p>as a consequence its general physical proper-</p><p>ties and in-service behavior are known. How-</p><p>ever, the successful historical use of marble</p><p>was based upon its being utilized in thick</p><p>blocks or as thick panels of about 10.2cm</p><p>(4 inches) or greater in bearing type walls.</p><p>The Amoco Building used 3cm (11/4 inch)</p><p>thick, non-load-bearing marble panels.</p><p>6</p><p>Not all marble claddings are alike. The</p><p>General Motors Building in New York utilized</p><p>thin stone panels to clad its tower, but select-</p><p>ed domestic marble and a different anchoring</p><p>system than Amoco to secure the panels to</p><p>the structure. The General Motors building</p><p>has not required re-cladding.</p><p>p_010_021_chapt_1_bp 17.10.2006 18:04 Uhr Seite 21</p><p>People have the perception that brick, con-</p><p>crete and stone walls are impenetrable. This</p><p>perception comes from historic buildings</p><p>constructed with solid masonry walls 30cm</p><p>(12 inches) in thickness. World War II bunkers</p><p>were constructed with concrete walls meas-</p><p>ured in feet and not inches. Today’s modern</p><p>construction rarely uses this type of wall</p><p>assembly. Concrete structures have become</p><p>much thinner with innovative ultrahigh per-</p><p>forming concrete and fiber reinforcement sys-</p><p>tems, sometimes less than 2.5cm (1 inch)</p><p>thick. Masonry construction has moved to</p><p>non-load-bearing veneer walls comprising a</p><p>9.21cm (3 5/8 inch) wythe with stone cladding</p><p>panels typically 3.18cm (11/4 inch) in thick-</p><p>ness, or sometimes thinner. Designers have to</p><p>anticipate how building materials are going to</p><p>be used and misused. Careful consideration</p><p>must be made toward maintaining material</p><p>finishes. Everything, from luggage to shovels,</p><p>will dull sharp edges. A building element ade-</p><p>quately designed to resist a uniformly distrib-</p><p>uted wind load can fracture due to the large</p><p>concentrated load of a shopping trolley or</p><p>skateboard.</p><p>Some types of structures have historically</p><p>been at risk to blast effects because of the</p><p>nature of what is inside them. For example,</p><p>a grain-processing facility can be at risk due to</p><p>the concentration of the combustible grain</p><p>dust particles. Or a chemical plant can be at</p><p>risk because of the volatility of the compounds</p><p>it produces. Today, buildings are at risk due</p><p>to terrorism. In a fraction of the time it takes</p><p>to blink an eye, the impact of 4,000 pounds of</p><p>explosives in a parked car can destroy the</p><p>face of a building. The impact of bombs has</p><p>become a force to be considered in many</p><p>façade designs. Building hardening has</p><p>22 23</p><p>Impact</p><p>A grain-processing facility can</p><p>be at risk to blast effects due</p><p>to the concentration of the</p><p>combustible grain dust parti-</p><p>cles.</p><p>page 23 Stand-off distances</p><p>can be achieved by installing</p><p>bollards or planters around the</p><p>perimeter of buildings. Blue</p><p>Cross Blue Shield of Illinois</p><p>Headquarters, Chicago, 1997.</p><p>In 1/16</p><p>th of the time it takes to</p><p>blink, the impact from an</p><p>explosion can destroy the face</p><p>of an entire building.</p><p>p_022_033_chapt_2_bp 17.10.2006 18:05 Uhr Seite 22</p><p>p_022_033_chapt_2_bp 17.10.2006 18:05 Uhr Seite 23</p><p>moved into the forefront of enclosure design.</p><p>As we move to designing against bursts</p><p>of force, the criteria for acceptability have</p><p>evolved. While breakage is allowed, safety</p><p>of life is the priority. The design goal relates</p><p>to structural redundancy, ductility and pre-</p><p>venting progressive collapse. For Americans,</p><p>the classroom for many of these concepts</p><p>was in the town of Oklahoma City at the site</p><p>of the Murrah Federal Building bombing.</p><p>On April 19, 1995, the Alfred P. Murrah</p><p>Federal Building was destroyed by a truck</p><p>bomb. The truck, which carried thousands</p><p>of pounds of explosives, was located less</p><p>than 3m (10 feet) from the front of the build-</p><p>ing. The Murrah Building and site proved</p><p>to be ill prepared for this type of impact. The</p><p>bombing forced the United States Govern-</p><p>ment and America to rethink how its govern-</p><p>ment buildings should be designed against</p><p>acts of terrorism, and concrete and stone</p><p>were part of the solution. Following the Murrah</p><p>Federal Building collapse, three major design</p><p>considerations have been developed for build-</p><p>ings of higher-level security: maintaining</p><p>stand-off distance to a building, preventing</p><p>progressive collapse to a building structure,</p><p>and minimizing debris mitigation.</p><p>24 25</p><p>right and below Murrah</p><p>Building, Oklahoma City.</p><p>Façade destruction due to</p><p>impact.</p><p>p_022_033_chapt_2_korr_bp 27.10.2006 15:44 Uhr Seite 24</p><p>Stand-off Distance</p><p>The intensity of a bomb blast is much higher</p><p>near the detonation of the blast and dramati-</p><p>cally reduces with distance away from this</p><p>point. The first criterion to consider in design-</p><p>ing new federal buildings was to prevent</p><p>unwanted vehicles accessing a defined safety</p><p>corridor around the structure. This is achieved</p><p>by locating the building away from access</p><p>roads, and providing barriers to prevent unau-</p><p>thorized vehicles from coming close to it.</p><p>There are many elements of blast design that</p><p>will almost surely be unpredictable, including</p><p>the nature, location and intensity of the blast.</p><p>Given this, it is unlikely that even the most</p><p>rigorous design concept could ensure that</p><p>structural damage could be prevented. The</p><p>second consideration is to prevent a progres-</p><p>sive collapse.</p><p>Progressive Collapse</p><p>When the nine-story Murrah Building col-</p><p>lapsed, 168 people were killed. It has been</p><p>estimated that a least 80percent of the deaths</p><p>were caused by the structure collapsing on</p><p>occupants who might have otherwise survived</p><p>the bomb blast. The Murrah Building’s con-</p><p>crete structure was adequately constructed for</p><p>traditional building loads. It was designed to</p><p>resist forces from wind, snow, people and</p><p>everything normally found in a building. It had</p><p>not been designed to resist an explosion at its</p><p>doorstep. In response to the Murrah Building</p><p>collapse, several structural design changes</p><p>have been incorporated into the design of fed-</p><p>eral buildings for the United States Govern-</p><p>ment. In simple terms, blast design allows</p><p>local structural damage to occur but designs</p><p>against progressive collapse. This can be</p><p>achieved through redundant design and duc-</p><p>tile material behavior. For example, if a column</p><p>were damaged or even eliminated in an explo-</p><p>sion, what would this do to the structure?</p><p>The Murrah Building had a transfer girder</p><p>running across the face of the structure at the</p><p>second floor, which transferred the weight of</p><p>ten building columns to five columns down to</p><p>the ground. The failure of one column meant</p><p>three failed; with the failure of two, as many as</p><p>seven could fall. Localized damage is expect-</p><p>ed in a bomb blast; however, by preventing</p><p>progressive collapse, designers hope to limit</p><p>damage and save lives. In blast design suffi-</p><p>cient redundancy must be available in all</p><p>major structural elements, including beams,</p><p>girders, columns, and slabs. All are to assume</p><p>the loads carried by adjacent damaged or</p><p>removed elements. Post-damage resistance is</p><p>typically provided by the cantilever or cater-</p><p>nary action to hold the damaged zone in place</p><p>to facilitate rescue efforts. Transfer girders are</p><p>less likely to be used in this type of design</p><p>because they increase the potential for a cata-</p><p>strophic failure.</p><p>Designers are asked to put a greater emphasis</p><p>on the overall ductile behavior of a structure</p><p>in response to blast loading. Steel is the most</p><p>probable material to consider, because by</p><p>its very nature it is ductile. Steel bends and</p><p>deforms elastically prior to failing. If a building</p><p>were not designed for blasts, a traditional steel</p><p>frame would perform better than concrete</p><p>because steel has equal capacity in tension</p><p>and compression, whereas concrete has</p><p>capacity only in compression.</p><p>For example, in a simple reinforced concrete</p><p>beam not designed for blasts, reinforcement</p><p>only penetrates the supporting columns</p><p>for a determined number of inches based</p><p>on the length of the span. To resist normal</p><p>The Murrah Building destruc-</p><p>tion came from a truck filled</p><p>with 4,000 pounds of explo-</p><p>sives parked less than 3m</p><p>(10 feet) from the face of the</p><p>building.</p><p>p_022_033_chapt_2_bp 17.10.2006 18:05 Uhr Seite 25</p><p>loading, the majority of the steel reinforcement</p><p>would be located near the bottom of the beam</p><p>section (the tension zone) with the upper little</p><p>or no reinforcement near the top (the com-</p><p>pression zone). If a blast were to occur below</p><p>such a simple reinforced concrete frame, the</p><p>resulting force would push the beam up and</p><p>possibly push its supporting columns outward.</p><p>The upward force on the beam reverses its</p><p>reinforcement needs causing it to lose its</p><p>structural integrity and fail catastrophically.</p><p>The short lengths of reinforcement penetrating</p><p>the columns would not resist the outward</p><p>movement of the columns, giving a second</p><p>mode of catastrophic failure. With little or</p><p>no reinforcement of concrete in the top of the</p><p>beam or inadequate reinforcement penetrat-</p><p>ing the columns, the frame would fail. With</p><p>additional reinforcement, it has a chance of</p><p>staying in place.</p><p>Concrete structures can be designed for blast</p><p>by using continuous reinforcement to tie</p><p>the building together vertically and laterally.</p><p>By doing this, there are alternative load paths</p><p>implicit within a design. The alternative path</p><p>method makes it possible for loads within a</p><p>building to be redistributed when individual</p><p>members are damaged or removed. This type</p><p>of design can be implemented even if the</p><p>exact nature of the threat is unknown. For</p><p>example, if internal columns are accessible</p><p>to the public but cannot be approached by</p><p>vehicles, they can be made sufficiently robust</p><p>to resist the threats delivered by individual</p><p>suicide bombers.</p><p>Debris Mitigation</p><p>The fragmentation and propulsion of building</p><p>components pose a great threat to life. Using</p><p>architectural elements and systems that do</p><p>not fragment during an explosion can remove</p><p>this threat. Flying projectiles can cause as</p><p>much harm as the explosion. New blast</p><p>designs understand this, incorporating special</p><p>frames and laminated glass to resist the force</p><p>of an explosion without dislodging. If exposed</p><p>to a blast, this type of glazing system will</p><p>break; however, it will stay in one piece in</p><p>its specially designed frame. Debris mitigation</p><p>must be considered in all elements of a proj-</p><p>ect, including the solid walls that surround</p><p>buildings.</p><p>Blast Design</p><p>Shortly after the attack on the Murrah Build-</p><p>ing, the United States Government began</p><p>reviewing its design criteria to incorporate</p><p>blast requirements and other security meas-</p><p>ures in its buildings. The facility to replace</p><p>the Murrah Building was to symbolize the</p><p>strength and accessibility of the United States</p><p>2726</p><p>right The stone barrier wall</p><p>at the main entrance</p><p>1 Form tie voids to be grout-</p><p>ed solid</p><p>2 25 x 25mm (1 x 1 inch)</p><p>steeel mesh</p><p>3 15.2 x 15.2cm (6 x 6 inch)</p><p>welded wire fabric (wwf)</p><p>secured to form ties</p><p>4 Stone</p><p>5 Structural cast in place</p><p>concrete wall</p><p>6 Grout</p><p>Construction of stone barrier</p><p>wall at Oklahoma Federal</p><p>Campus Building, Oklahoma</p><p>City.</p><p>right Stone barrier wall mock-</p><p>up, Oklahoma Federal Cam-</p><p>pus Building.</p><p>below Stone barrier wall</p><p>close-up view.</p><p>p_022_033_chapt_2_bp 17.10.2006 18:05 Uhr Seite 26</p><p>Government. The goal of the design was to</p><p>look strong but not be oppressive. Security</p><p>measures were to be transparent because the</p><p>new federal building in Oklahoma City was to</p><p>be open to the public as before.</p><p>The building structure would be one of the</p><p>first new federal office buildings requiring</p><p>blast protection. Designed by the architectural</p><p>firm of Ross Barney + Jankowski, the Federal</p><p>Campus Building in Oklahoma City is a</p><p>16,815m2 (181,000 square foot) office build-</p><p>ing occupying the southern block of a two-</p><p>block site. The site topography influenced the</p><p>design of the building in such a way that the</p><p>east wing of the building is three stories in</p><p>height while the west side is four. To allow as</p><p>much daylight as possible into the heart of this</p><p>large floor plan, a large elliptical courtyard was</p><p>incorporated into the design. A large window,</p><p>1.5 x 3.35m (5 x 11 feet), in the concrete</p><p>walls, enabled the building interior to receive</p><p>a good deal of natural sunlight.</p><p>The use of stone on the building façade pro-</p><p>vided a sense of strength and permanence to</p><p>the building’s exterior. It also provided a physi-</p><p>cal connection to this region of the country.</p><p>All of the stone on the barrier walls came from</p><p>sites within the state of Oklahoma. The use</p><p>of stone in the design of the Federal Campus</p><p>brought with it a unique design challenge.</p><p>In the aftermath of the Murrah bombing, the</p><p>Federal Government rewrote its security and</p><p>blast mitigation guidelines. In light of these</p><p>revised guidelines, traditional hand-set stone</p><p>might dislodge from the wall during an explo-</p><p>sion. The concern was that the presence of</p><p>cavities and voids between the stone and a</p><p>back-up wall created a weak point in the sys-</p><p>tem in the event of a blast.</p><p>A new stone-setting technique, eliminating</p><p>the voids in the wall, had to be developed for</p><p>this project. In order to minimize debris in the</p><p>event of a blast, 27.58 MPa (4,000 psi) grout</p><p>was required to secure the veneer stone to</p><p>the concrete wall. The problem was how to</p><p>achieve a monolithic pour. How could the con-</p><p>tractor ensure that the high-strength</p><p>grout</p><p>would flow around the voids in the stone?</p><p>Learning from several mock-ups, the solution</p><p>was a new method for constructing a stone</p><p>wall. The process involved attaching 3.8cm</p><p>(11/2 inch) thick furring strips to the face of a</p><p>Front entrance to the</p><p>Oklahoma Federal Campus</p><p>Building, 2004.</p><p>The ground floor plan of the</p><p>Oklahoma Federal Campus</p><p>Building provides a perimeter</p><p>of bollards and a stone wall at</p><p>the main entrance to protect</p><p>the face of the building.</p><p>p_022_033_chapt_2_bp 17.10.2006 18:05 Uhr Seite 27</p><p>cast-in-place concrete wall, attaching a wire</p><p>mesh to those strips, and installing an outside</p><p>form 9cm (3.5 inches) away from the mesh.</p><p>Stones were then placed in the 9cm (3.5 inch)</p><p>void in 0.6m (2 foot) lifts. Grout was poured</p><p>into the system in two lifts. The grout filled</p><p>the voids between the concrete wall, the wire</p><p>mesh and the stone. Once all the lifts were</p><p>completed, the wall was sandblasted to reveal</p><p>the integral stone facing. A stone sealer was</p><p>applied to the finished wall to restore the color</p><p>and sheen of the local stone.</p><p>In seeking to protect building occupants, the</p><p>Oklahoma Federal Campus design addressed</p><p>four primary concerns: perimeter protection,</p><p>progressive collapse prevention, debris mitiga-</p><p>tion, and hardened internal partitions. Many</p><p>details of the building’s design are not avail-</p><p>able to the public. The standoff distances from</p><p>unsecured areas are at least 15m (50 feet),</p><p>and the concrete walls and windows are</p><p>designed to resist blast loadings from those</p><p>distances. Cast-in-place concrete walls 30cm</p><p>(12 inches) thick form the building’s perimeter</p><p>on the façades closest to the streets. The exte-</p><p>rior walls are load-bearing and enable forces</p><p>to arch over any damaged portions. This alter-</p><p>native path approach provides for the redistri-</p><p>bution of loads resulting from the removal of</p><p>any single column. An important considera-</p><p>tion in this type of enclosure is not only</p><p>strength but ductility.</p><p>Ductility</p><p>Stone and concrete can provide the strength</p><p>required for blast design. However, the goal for</p><p>many building designers is to prevent building</p><p>occupants from having to work in dark, ugly</p><p>concrete bunkers buried under the ground.</p><p>The Israeli Foreign Ministry, completed in</p><p>2002 in Jerusalem, was designed to meet</p><p>this challenge by the architectural firm of Dia-</p><p>mond and Schmitt. Their solution provided</p><p>blast design with ductility. A ductile material is</p><p>capable of being stretched or deformed with-</p><p>out fracturing. Ductility is an important char-</p><p>acteristic in blast design. Stone and concrete</p><p>are not ductile materials unless they are com-</p><p>bined with metals like steel and aluminum.</p><p>The public building complex at the Israeli For-</p><p>eign Ministry is configured to accommodate</p><p>elements appropriate to the State of Israel</p><p>and its ceremonial functions. In ceremonial</p><p>fashion there is an atrium and reception hall</p><p>for heads of state and dignitaries. This was a</p><p>structure that had to be both beautiful and</p><p>safe. The innovative design of the wall assem-</p><p>bly for the reception building consists of a</p><p>structure that permits light penetration while</p><p>maintaining heightened security requirements.</p><p>The stone wall system has been designed</p><p>specifically to resist the horizontal thrust that</p><p>would result from an exterior bomb blast.</p><p>The central structure of the atrium consists of</p><p>12 concrete columns that support a skylight</p><p>roof above. A steel frame is bracketed off of</p><p>these columns to provide a secondary outer</p><p>structure. This second structure consists of</p><p>20 x 10cm (7 4/5 x 3 9/10 inch) elliptical steel</p><p>columns that support the barrier wall. This</p><p>barrier wall is enclosed by 30 horizontal alu-</p><p>minum channels, which carry 3cm (11/4 inch)</p><p>onyx panels.</p><p>Directly behind the stone panels are a series</p><p>of vertical airplane-gauge stainless steel</p><p>wires that are suspended from a flexible 5cm</p><p>(2 inch) diameter steel pipe. The wall system</p><p>has been designed to resist an exterior blast,</p><p>which would be absorbed by the stone and</p><p>secondary aluminum structure. Wooden</p><p>screens located along the walkways in the</p><p>atrium provide additional protection for occu-</p><p>28 29</p><p>Israeli Foreign Ministry,</p><p>Jerusalem, 2002. Exterior view</p><p>of onyx blast-resistent wall.</p><p>below Detail of stone con-</p><p>nection back to metal framing</p><p>during construction.</p><p>page 29 below Israel Foreign</p><p>Ministry, façade section.</p><p>1 Perforated metal sunscreen</p><p>2 Steel sunscreen support</p><p>3 Catwalk</p><p>4 Hollow steel section skylight</p><p>5 Steel beam</p><p>6 Tapered concrete column</p><p>7 Wood screen</p><p>8 Sand blasted glass floor</p><p>9 Steel channel</p><p>10 Onyx panels</p><p>11 Stone floor</p><p>12 Elliptical steel columns</p><p>13 Glazing</p><p>14 Concrete floor</p><p>p_022_033_chapt_2_korr_bp 27.10.2006 15:42 Uhr Seite 28</p><p>pants by catching smaller pieces of debris</p><p>during an explosion. The screens also allow</p><p>visitors to pass through the ceremonial space</p><p>without disrupting events in the atrium area</p><p>below. Although the wall would be destroyed</p><p>in a large blast, the main structural elements</p><p>and people inside the building would be pro-</p><p>tected. Testing of this system was necessary</p><p>to verify the performance of this innovative</p><p>enclosure system. A full-scale mock-up of the</p><p>façade was constructed in the desert outside</p><p>of Jerusalem. A controlled bomb blast pushed</p><p>the mock-up stone inwards and onto the wire</p><p>net, causing the cables to go into tension. The</p><p>pipe on which the wires were strung collapsed</p><p>further, absorbing energy from the explosion.</p><p>Although the stone was fractured by the bomb</p><p>blast, this was expected and the test was</p><p>successful. It proved the ductile nature of the</p><p>entire system. In this case, stone breakage</p><p>due to impact is expected. However, in some</p><p>projects it can be an unnecessary problem</p><p>with some building enclosure systems.</p><p>Stone Breakage</p><p>Unlike blast design, traditional enclosure</p><p>designs provide façades to resist uniformly</p><p>distributed loads on a façade without break-</p><p>ing. Although a 1.44 kPa (30 psf) wind load</p><p>can quickly add up to thousands of pounds</p><p>in force over a large area, a much smaller</p><p>1.11 kN (250 pound) concentrated load can</p><p>be the breaking point of a façade panel that</p><p>has been cut too thin.</p><p>The Indiana Limestone Institute strongly rec-</p><p>ommends that Indiana Limestone be milled to</p><p>dimensions not less than 5.08cm (2 inches).</p><p>In contrast, the trend in Continental Europe</p><p>has been to use considerably thinner lime-</p><p>stone, usually between 3 and 4cm (11/4 –11/2</p><p>inches). When using thin limestone cladding,</p><p>considerable caution is required if thickness is</p><p>to be reduced. Unlike many other commonly</p><p>used cladding stones such as granite, lime-</p><p>stone may suffer considerable weathering</p><p>during the lifespan of the building. Given that</p><p>limestone usually exhibits significantly lower</p><p>Israel Foreign Ministry, interior</p><p>view of onyx wall.</p><p>9</p><p>1</p><p>2</p><p>3</p><p>4</p><p>5</p><p>6</p><p>7</p><p>8</p><p>10</p><p>12</p><p>11</p><p>14</p><p>13</p><p>p_022_033_chapt_2_korr_bp 27.10.2006 15:42 Uhr Seite 29</p><p>compressive and flexural strength than gran-</p><p>ite, on thin panels this weathering and conse-</p><p>quent loss of strength may lead to rapid failure</p><p>in service as the stone becomes unable to</p><p>sustain imposed structural or wind loads.</p><p>The loss of a few millimeters in thickness from</p><p>a 10cm (3 9/10 inch) thick stone wall may</p><p>be acceptable but in a 3cm (11/4 inch) thick</p><p>veneer panel this may prove disastrous.</p><p>Completed in 1998, the new Palais de Justice</p><p>building in Bordeaux provides seven unique</p><p>courtrooms, administrative offices, and a large</p><p>public space leading to the courtrooms. The</p><p>seven courtrooms are pod-shaped, timber-</p><p>clad volumes, supported by concrete pilotis.</p><p>The wooden courtrooms combine high-tech</p><p>geometry with traditional construction materi-</p><p>als. Recent developments in computerized</p><p>machinery were essential to the production of</p><p>the complex curves and acoustic perforation</p><p>of the internal maple-veneered finishes.</p><p>The base of the building consists of a lime-</p><p>stone wall. Using the same stone as the origi-</p><p>nal Palace</p><p>of Justice building, the designers</p><p>tried to make a connection between the two</p><p>very different buildings. In an effort to match</p><p>the stone of the old Palace of Justice, the new</p><p>stone was sandblasted. This gave the stone</p><p>a weathered appearance and texture similar</p><p>to the original weathered building. However,</p><p>the new stone cladding was made of thin</p><p>stone panels and smaller stone blocks than</p><p>were used with the old Palace of Justice. It</p><p>is believed that the loss of thickness due to</p><p>sandblasting contributed to a design that</p><p>could not resist the impact loads often found</p><p>at the street level of a building. The stone at</p><p>the base of the new building underwent regu-</p><p>lar breakage and had to be replaced with</p><p>thicker stone.</p><p>Many times the thickness and finish of the</p><p>stone are correctly designed. However, the</p><p>impact loads imposed on it are too large, for</p><p>example construction loads. In 2002, the</p><p>MOMA in New York underwent a major addi-</p><p>tion. The historic sculptural garden was con-</p><p>verted into a construction site with equipment</p><p>and materials not considered in the original</p><p>design of the paving system constructed in</p><p>1953. The stone paving has received consid-</p><p>erable damage during the new construction</p><p>process. Some of the large thick granite</p><p>paving blocks have literally cracked in half.</p><p>Thickness and finish are not the only factor</p><p>in maintaining an architectural material’s</p><p>appearance. Edges are the most susceptible</p><p>area of a stone, concrete or masonry wall.</p><p>30 31</p><p>Section of Palace of Justice</p><p>building.</p><p>1 Limestone base had a his-</p><p>tory of breakage due to small</p><p>impact loads.</p><p>right The Palace of Justice,</p><p>Bordeaux, 1999.</p><p>below The new Palace of</p><p>Justice building, completed in</p><p>1999, was constructed with a</p><p>stone base composed of pan-</p><p>els that were cut too thin and</p><p>broke easily under contact.</p><p>below right The original</p><p>Palace of Justice building was</p><p>constructed of large stone</p><p>blocks that have weathered</p><p>with time.</p><p>p_022_033_chapt_2_bp 17.10.2006 18:05 Uhr Seite 30</p><p>Edges</p><p>Sharp edges are often desired, but difficult to</p><p>produce and maintain in concrete, stone and</p><p>masonry. As designers strive for crisp corners</p><p>to their building elements, they must consider</p><p>how building materials will perform against the</p><p>force of impact. Traditional corner details in</p><p>concrete and stone often incorporate miters</p><p>and eased edges to allow for some physical</p><p>abuse by the end users. Other projects want</p><p>sharp edges that challenge the end users’</p><p>ability to maintain it.</p><p>The Holocaust Memorial, completed in</p><p>December 2004 in Berlin, is designed with</p><p>2,711 gray precast concrete pillars with sharp</p><p>corner edges. The field of pillars is composed</p><p>of 0.91 x 2.44m (3 x 8 foot) pillars or stiles of</p><p>varying heights ranging from approximately</p><p>0.46 to 4.57m (1 foot 6 inches to 15 feet).</p><p>Consistently separated by a 0.91m (3 foot)</p><p>wide path paved in small cubic blocks embed-</p><p>ded in gravel, the pillars provide a rolling</p><p>topography over the 20,235m2 (5 acre) site.</p><p>An underground Information Center with exhi-</p><p>bition galleries, seminar room, a bookshop</p><p>and offices is covered with a cast-in-place cof-</p><p>fered ceiling that repeats the contours of the</p><p>large precast blocks above. All of the concrete</p><p>in the space was left unfinished to contribute</p><p>to the exhibit’s stark appearance.</p><p>The concrete stiles are composed of rein-</p><p>forced, self-compacting concrete that was</p><p>prefabricated off-site. Each stile was reviewed</p><p>against an approved prototype before it was</p><p>shipped to the site and lowered into place with</p><p>a crane. The color uniformity, finish, and cor-</p><p>ner details are greatly aided by the self-com-</p><p>pacting concrete that fills all voids in a tightly</p><p>fabricated precast concrete formwork. The</p><p>sharp corners were for the most part intact</p><p>after installation; however, they have suffered</p><p>minor defects with normal abrasion from con-</p><p>struction and general use.</p><p>Typically sharp corners are hard to maintain</p><p>with a brittle material like concrete. Traditional</p><p>cast-in-place corners can be weaker because</p><p>water leaks out of formwork corners, reducing</p><p>the water available for full concrete hydration.</p><p>Chamfered corners are typically used to</p><p>improve seals and provide a less vulnerable</p><p>edge to impact forces. Chamfered edges are</p><p>made with triangular strips. They make strip-</p><p>right Holocaust Memorial,</p><p>Berlin, 2004.</p><p>right Section through the</p><p>Memorial.</p><p>1 Seminar Room</p><p>2 Foyer</p><p>3 Room of Names</p><p>4 Room of Families</p><p>The MOMA expansion in New</p><p>York City brought large con-</p><p>centrated loads on the garden</p><p>pavers. The result was broken</p><p>paving blocks.</p><p>p_022_033_chapt_2_korr_bp 27.10.2006 15:43 Uhr Seite 31</p><p>ping the form easier and prevent corners from</p><p>leaking cement paste. The finished product</p><p>is also less vulnerable to abrasion. Sharp</p><p>corners are best achieved with watertight, pre-</p><p>cisely fabricated corners. If the joints are not</p><p>tight and concrete mix water escapes from</p><p>the form, color variation and material strength</p><p>loss can occur. For this reason sharp corners</p><p>are more susceptible to breakage. The corners</p><p>at the Holocaust Memorial are in very good</p><p>condition; however, chipped edges are fairly</p><p>frequent.</p><p>One of the most difficult edges to maintain in</p><p>architecture is a bench in a public plaza.</p><p>Skateboarders have scarred our urban fabric</p><p>with grind marks. Challenging the abilities of</p><p>our youths, designers have developed a multi-</p><p>tude of skateboard deterrent details to solve</p><p>the problem. By using stepping curbs and</p><p>benches, or applying metallic speed bumps</p><p>to these surfaces, designers hope to prevent</p><p>the impact of sport enthusiasts.</p><p>The 111 South Wacker office building in</p><p>downtown Chicago, completed in 2005 by</p><p>Goettsch Partners, combines a series of</p><p>inconspicuous design features to deter skate-</p><p>boarders from marking the benches and</p><p>planters at the base of the building. On the</p><p>north side of the building, separating the side-</p><p>walk from an ultratransparent cable wall sys-</p><p>tem, a series of stepped curved stone bench-</p><p>es have proven to be uninviting to the skate-</p><p>board community. By curving the edges of the</p><p>benches in both section and plan, skate-</p><p>boarders have found the site unusable and</p><p>have moved on to other locations in the city.</p><p>32 33</p><p>right In contrast to the Holo-</p><p>caust Memorial concrete</p><p>blocks, beveled edges reduce</p><p>the risk of chipping at a gar-</p><p>den sculpture west of Munich.</p><p>below The 111 South Wacker</p><p>office building, Chicago, has</p><p>skateboard-proof walls which</p><p>are stepped, non-continuous</p><p>and curved in two dimensions.</p><p>p_022_033_chapt_2_bp 17.10.2006 18:05 Uhr Seite 32</p><p>Stone, concrete and masonry are obviously</p><p>very durable materials, able to resist impact</p><p>loads; however, as the thickness of these</p><p>materials is reduced with innovations in mate-</p><p>rial fabrication, designers must understand</p><p>that they become more vulnerable to impact</p><p>failure. Architectural details must consider</p><p>potential impacts at street level from luggage</p><p>to skateboarders. Specific finishes and pro-</p><p>files are better able to take abuse. For exam-</p><p>ple, a thermal (rough finish) on stone will hide</p><p>abrasions better than a polished finish.</p><p>Blast design has become a factor in many</p><p>new buildings, and stone, concrete or mason-</p><p>ry is typically part of the solution. Structural</p><p>considerations including redundancy, ductili-</p><p>ty, and debris mitigation can all be used to</p><p>provide a system that resists progressive col-</p><p>lapse. By providing steel embedded in con-</p><p>crete, contemporary projects combine ductili-</p><p>ty with fire resistance. Both of these are criti-</p><p>cal for the impact of an explosion. In many</p><p>cases, the enclosure is sacrificial, providing</p><p>permanent deformation in order to absorb the</p><p>hazardous forces of an explosion. Life safety</p><p>is the goal for this type of design solution.</p><p>It is expected that damage will occur to the</p><p>building elements. The concrete and stone</p><p>elements will break. The goal of the system</p><p>is safety and security of people and property</p><p>near and inside</p>concrete 70Superplasticizer 8, 61, 128Surface defects 48– 69Tacoma Narrows Suspension Bridge, Washington State 124 –125, 129Terra-cotta 6, 9, 66, 67, 89, 96, 97Terrazo 64Thermal hysteresis 6, 10–21Tie bar 55Tie holes 55, 56Through-wall flashing 130, 133, 136, 139, 141, 142, 151Tod’s Omotesando office building, Tokyo 108Torre Agbar, Barcelona 114, 115Trowel burn 76Tuned mass dampers 125 –128, 129Ultrahigh performance concrete 108, 112, 126, 127, 128, 129Ultrahigh strength concrete 48Unitized systems 140Unity Temple, Oak Park, Illinois 57, 147University Library, Utrecht 58, 59University of Cincinnati School of Architecture and Interior Design, Ohio 39University of Oulu, Linnannmaa District, Finland144, 145Vandalism 86 – 89, 91Vapor barrier 142, 151Veining patterns 66Veneer wall 130, 133, 136, 141, 142Virta Palaste Leinonen 144Vontz Center for Molecular Studies, Cincinnati, Ohio 44, 132–133, 142Walt Disney Concert Hall, Los Angeles 66Washington Monument, Washington, D.C. 82Water-cement ratio 73, 90Water runoff 84 –85, 91, 104, 105, 107Weeps 138, 139, 151Wicking 44– 45Wind loads 150World tectonic plates 124Wright, Frank Lloyd 57, 79, 108, 121, 122, 147Zumthor, Peter 86, 87Zwarts, Kim 59158 159p_152_160_korr_plotter 27.10.2006 15:26 Uhr Seite 158Illustration CreditsAntamex Curtainwall Company 16American Architectural Manufacturers Association, AAMA 140 topCarl-Magnus Dumell, www.dumell.net cover photo,18, 19Construction Research Laboratory (CRL) 12 top, 101 bottom, 104 bottom, 149 bottomDiamond and Schmitt Architects Incorporated, www.dsai.ca 28 bottom, 29 bottomDon Schapper, Aldon Chemical 38Ed Allen 119 topEncarta.msn.com 24 topFormtech, Insulated Concrete Forms, courtesy of Kevin Grogan 129The Frank Lloyd Wright Foundation, Taliesin West, Scottsdale, AZ 121 bottomGetty Images 111 topSteve Hall, Hedrich Blessing, www.hedrichblessing.com, courtesy of Ross Barney+ Jankowski Inc Architects 27 topIllustration redrawn from detail on page 11-2 and page 5-3 of Ian R. Chin; Recladding of the AmocoBuilding in Chicago, Proceeding from Chicago Com-mittee on Highrise Buildings, November 1995 12,14 topJan Bitter courtesy of Jan Bitter Fotografie www.janbitter.de 58 top and bottom rightJames Steincamp, James@Steincampphotography.com 32 bottom, 34 topJohnson Architectural Images, AJ1507; © Artifice Inc.108 bottomLisa Krichilsky 21Kevin A. O'Connor, AIA, Ross Barney + Jankowski Inc Architects 26, 27 bottomKim Zwarts (design of pattern on precast mould at University Library Utrecht) 58 bottom rightLéon Wohlhage Wernik Architekten 64Galvin Loughran 71, 84Liam Loughran 57 bottomMary Margaret Loughran 95, 102 top, 104 middle, 114, 115 bottomMike Giso 17 bottom left and bottom rightNabih Youssef Associates 118 bottomNicholas Stanos 20 middleOklahoma Publishing Company (OPUBCO) www.newsok.com 24 bottomO’Mally Creadon Productions 122 topPavlo Berko 87 bottomPennie Sabel, courtesy of Building Stone Institute13 bottom, 14 bottom, 16, 17 top, 124 middle rightPhilippe Rualt, courtesy of Remy Marciano Architecte DPLG 78Pulitzer Foundation 68, 69 topJay Williams, AIA 116 top, 117 topJohn Ronan Architect 88 topRandy Chapple AIA 90 topR. Van Petten AIA 94Scott Seyer AIA 9, 10 right, 11 (photo rendering of 300 east Randolph Expansion)Simpson Gumpertz & Heger Inc. 116 bottom, 117 bottom middle, 148Shutterstock.com 10, 15, 20 top, 22, 32 top, 51 top, 70 top, 73 top, 76 top, 82 left, 86 bottom, 110 top,113, 121 top, 125Stanford Anderson (ed.) Eladio Dieste. Innovation in Structural Art 118 top, 119 top, 120Tim Griffith, www.timgriffith.com, courtesy of Diamond and Schmitt Architects Inc. 28 top, 29 topTravis Soberg 48 leftWiel Arets Architects 58 bottom leftVirta Palaste Leinonen Architects 144Ductal 126 topStefan Müller, courtesy of Christoph Mäckler Architekten 135Christoph Mäckler Architekten 134 bottom rightArkHouse Architects 80Illustration redrawn from Christine Beall; MasonryDesign and Detailing, For Architects, Engineers, and Builders, Prentice-Hall, Englewood, New Jersey1984 36, 46 bottom left, 47 leftIllustration redrawn from detail on page 187 of Günter Pfeifer and Antje M. Liebers, Per Brauneck,Exposed Concrete.Technology and Design, Birk-häuser, Basel, 2005 56 leftIllustration redrawn from detail on page 406 and page 187 of Christine Beall; Masonry Design andDetailing for Architects, Engineers, and Builders,Prentice-Hall, Englewood, New Jersey 198446 bottom and 47 leftImage redrawn from detail on page 64 of James E. Amrhein and Michael W. Merrigan; Marble andStone Slab Veneer, second edition, Masonry Insti-tute of America, 1989 20Image redrawn from detail on page 262 of Matthys Levy and Mario Salvadori; Why Buildings Fall Down.How Structures Fail, W.W. Norton & Company, New York, 2002 25Image redrawn from detail on page 31A of Lee Bey; “The trouble with terra-cotta”, Chicago Sun-Times,October 18, 1998 96Image redrawn from detail on page 31 of IndianaLimestone Handbook, Indiana Limestone Institute ofAmerica, 2000 45Images redrawn from the information on the website of the Renzo Piano Building Workshop, www.renzopiano.com 36 bottom, 37 bottomAll other illustrations were provided by the author.p_152_160_korr_plotter 27.10.2006 15:26 Uhr Seite 159Graphic design: Gabrielle Pfaff, BerlinEngineering review and copy editing: Richard Palmer,Palmer Consulting, Divonne-les-Bains, FranceA CIP catalogue record for this book is available fromthe Library of Congress, Washington D.C., USABibliographic information published by Die DeutscheBibliothekDie Deutsche Bibliothek lists this publication in theDeutsche Nationalbibliografie; detailed bibliographicdata is available in the internet at http://dnb.ddb.de.This work is subject to copyright. All rights arereserved, whether the whole or part of the material is concerned, specifically the rights of translation,reprinting, re-use of illustrations, recitation, broad-casting, reproduction on microfilms or in other ways,and storage in data banks. For any kind of use, per-mission of the copyright owner must be obtained.© 2007 Birkhäuser – Publishers for Architecture, P.O. Box 133, CH-4010 Basel, SwitzerlandPart of Springer Science+Business MediaPrinted on acid-free paper produced from chlorine-free pulp. TCF Printed in GermanyISBN-13: 978-3-7643-7329-0ISBN-10: 3-7643-7329-6http://www.birkhauser.ch9 8 7 6 5 4 3 2 1 Front cover: Detail of Finlandia Hall, Helsinki∞p_152_160_bp 18.10.2006 12:46 Uhr Seite 160FSfront-matter01Thermal Hysteresis02Impact03Efflorescence04Surface Defects05Discoloration06Corrosion07Structure08Leakageback-matter
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Phone: +8215934114615

Job: Hospitality Director

Hobby: tabletop games, Foreign language learning, Leather crafting, Horseback riding, Swimming, Knapping, Handball

Introduction: My name is Kelle Weber, I am a magnificent, enchanting, fair, joyous, light, determined, joyous person who loves writing and wants to share my knowledge and understanding with you.