Design Factors Influencingthe Aesthetics of ArchitecturalPrecast Concrete

Sidney FreedmanDirector Architectural PrecastConcrete ServicesPrecast/Prestressed Concrete InstituteChicago, Illinois

Aesthetics is playing an increasingly important role in the design ofbuilding façades. In North America and Europe the concept thataesthetics (form) must follow function is well established. This articledemonstrates the enormous potential of architectural precastconcrete applications. The abundance of possibilities gives rise to amultitude of different forms, colors, surface finishes, andarchitectural designs. The era is long over when concrete was knownsimply as a utilitarian material. Technological innovations inconcrete composition, molds, and finishes have increased the qualityof this material, enabling it to compete with the most exclusivefaçade claddings. It is the architect’s responsibility to exploit thesevaried possibilities. The important aspects of sample selection forcolor and texture as well as the use of range samples to setproduction standards for color and texture, are illustrated. The myththat precasting leads to little flexibility in façade design no longerholds true. On the contrary, because of the inherent properties andvarieties in shape, architectural precast concrete is at the forefront ofarchitecture as one of the most flexible contemporary solutions forstructural façades.

During the last decade, aestheticshas gained considerable importance in the design of overall

structures and precast concrete components. Several factors have influenced the design of buildings andfaçades; for example, greater designfreedom, complex surfaces, use of refined and more costly materials, anddemands on quality and durability.

Aesthetics is a relative concept,especially within the context ofworldwide building design. In Europe, for example, there are considerable differences in architecturalaesthetics between the coldernorthern countries and the warmersouthern countries. The formergenerally focus on plainness in architecture, in line with Modernism,

44 PCI JOURNAL

whereas the latter on more elaborate styles.’

Today, people generally dislike seeing monotonous buildings; instead,they much prefer to see attractive andhuman scale architecture. As a result,design is increasingly governed byaesthetics. Key words for the trends inprecast architectural façade design arehuman scale, aesthetics, natural or traditional linked materials, and flexibility. However, what is most striking inthe concept of new buildings — compared to 20 years ago — is the muchgreater freedom in the design of thefaçade.

Volumes, surfaces, lines, and differences in level are becoming increasingly important. Box-shaped buildingscomposed of nearly all the same basicelements have been abandoned. Instead, the design now focuses on the“total concept” of the façade.

Arguments about the beauty of concrete by the public and client often obscure the quality of precast concretearchitecture. Consequently, architectsare concerned over public and clientacceptance. Frequently though, thepublic waits for the critics to tell themwhat they like.

Architecture focuses on space,structure and proportion. In this respect, precast concrete is ideal becauseit provides the freedom and flexibilityof shaping concrete into structure andarchitecture. In the classical periods ofstone building — the Greek, the Romanesque, the Gothic — distinctionsbetween structure, ornament, and architecture simply had no relevance.They were all carved out of the sameexternal-internal continuum of architectural mass and space. Yet, the threedimensions of structure are the essential domain of architecture.

One of the major advantages of concrete is its moldability. Because of thisfeature, concrete has become the architect’ s favorite material. Concrete isreally like the sculptor’s clay in an architect’s hands. It gives the architectgreater freedom in the design offaçades than do most other materials.The only limits are imagination andcreativity (see Fig. 1).

Architectural mass and space are defined first of all by proportions — thenfleshed in by matter and brought to

life by light and shadow. An anonymous quote states this concept well.“Beauty Itself Doth of Itself Persuadethe Eyes of Man Without an Orator.”

Architectural design determines thetexture of a completed building. Thedistance between the viewer and thefinished building determines its appearance. The building’s texture is developed by the architect’s successfuluse of light, shadow, and color in thedesign.

With respect to the form of the concrete façade elements, there is an increasing trend towards profiled elements with considerable surfaceornamentation. Stone elements, whichin the ancient Greek and Romanépoque were carved by hand tools, cannow be made again in architecturalconcrete because of modem manufacturing processes and advanced concrete technology.

SAMPLES —

SELECTION OF COLORSAND TEXTURE

In dealing with concrete, the architect and owner need to be prepared forvariations and the slight imperfectionsinherent to the medium. Architectsseem ready to accept a significantamount of variation in natural stone,but forget that concrete is constitutedof nearly the same material. Concreteis not transformed because it is cast.Moreover, precast concrete should beviewed at a minimal distance of 20 ft(6.10 m), not examined with a magnifying glass at 10 in. (254 mm).

Initial color and texture selection isusually made from 12 x 12 in. (305 x305 mm) samples or by using the PCIColor and Texture Selection Guide.2Color selection should be made underlighting conditions similar to those

i.Baha’i Temple, Wilmette, Illinois, designed by Canadian architect LouisBourgeois. This structure, started in 1920 with final completion in 1953, is one of themost beautiful and delicately conceived buildings in the United States.

March-April 2001 45

under which the precast concrete willbe used, such as the strong sunlightand shadows of natural daylight.

If small samples are used to selectthe aggregate color, the architectshould be aware that the general ap

pearance of large areas of a buildingwall may vary from the samples (seeFig. 2). For non-planar, curved, orother complex shapes, a flat-cast sample may not represent the anticipatedappearance of the final product. Sam-

pie shapes should be selected that willoffer a reasonable comparison to theprecast units represented (see Fig. 3).

The production of uniform, blemish-free samples, which demonstrate theabilities of a single master craftsman,will be completely misleading andcould cause problems when the production personnel, using actual manufacturing facilities, have to match “thesample.” Samples should be made asnearly as possible in the same mannerintended for the actual units.

Small 12 in. (305 mm) square samples do not generally reflect the relationship between materials, finishes,shapes, casting techniques, moldtypes, thickness of concrete section,orientation of exposed surfaces duringproduction, and consolidation procedures (see Fig. 4).

Aesthetic (visual) mockups, usually4 or 6 ft (1.22 or 1.83 m) square,should be produced using standardproduction equipment and techniques.Some important variables that shouldbe controlled as close to actual castconditions include: retarder coveragerate and method of application, mixdesign and slump, admixtures, heat ofplastic and cured concrete, age, vibration, piece thickness, and method ofcleaning. This is especially importantwith light etches which are affected bychanging conditions.3

Special details such as reveal patterns and intersections, corner joinery,drip sections, patterns, color and texture, and other visual panel characteristics should be demonstrated in largeproduction samples for approval.Changes in aggregate orientation,color tone, texture, and uniformity ofreturns, can easily be noted on aesthetic (visual) mockup panels.

The objective of the visual mockupsample can also demonstrate the moredetailed conditions that may be encountered in the project (recesses, reveals, outside/inside corners, multiplefinishes, textures and veneers). Eventhis sample may not be fully representative of the exact finishes thatcan be reasonably achieved duringmass production.

Samples should be supplied for eachof the different finishes for a projectand all submitted samples should beclearly identified. When approved,

Fig. 2. Display of small samples.

Fig. 3.Display of

large scale sample.

46 PCI JOURNAL

these samples form the basis ofjudgment for the purpose of accepting the appearance of finishes.These samples should establish therange of acceptability with respectto color and texture variations, surface defects, and overall appearance. Samples should be viewed ata distance consistent with theirviewing distance on the structurebut not less than 20 ft (6.10 m).

At least three range samples of asize sufficient to demonstrate actualplanned production conditions maybe used to establish a range of acceptability with respect to: colorand texture variations, uniformityof returns, frequency, size and uniformity of air voids distribution,surface blemishes, and overall appearance (see Fig. 5). The acceptability ofrepair techniques for chips, spalls orother surface blemishes should also beestablished on these samples.

patched areas should match that ofthe adjacent surface.

The samples should be stored outdoors and positioned to allow a comparison with production units. Theyshould be stored adjacent to eachother to allow proper lighting (sunand shade) for daily comparisons ofthe production units for finish andexposure.

Where mockup units are notused, the precaster should requestthe architect/engineer and/or ownerto inspect and approve (sign anddate) initial production units.Larger production samples will remove uncertainties in the minds ofboth the architect/engineer andowner (see Fig. 6).To avoid possible later controver

sies, this mutual approval should precede a release for production. The architect should realize, however, thatdelays in visiting plants for such ap

I

_

-_

Fig. 5. Use of 4 ft (1 .22 m) samples to establish acceptable range of color and texture. Concrete made with 3/8 in. (9.53 mm)aggregate with retarded (left side) and acid etched (right side) finishes.

Fig. 6.This production panel was createdafter examining the samples in Fig. 5.

Fig. 4. Small samples should be used only forinitial color and texture selection.

The face of each sample should contain at least two areas of approved sizeand shape, which have been chippedout and then patched and repaired. Thecolor, texture, and appearance of

March-April 2001 47

provals may upset normal plant operations and the job schedule. The contract documents need to clearly statethe time period in which productionunits or the mockup structure shouldbe kept in the plant or jobsite for comparison purposes.

It is recommended that the contractdocuments permit the approved full-sized units to be used in the job installation in the late stages of construction. The units should remain

identifiable even on the structure, untilfinal acceptance of the project. Thepanels should be erected adjacent toeach other on the building to allowcontinued comparison, if necessary.

Uniformity of color and intensity ofshading are generally a matter of subjective individual judgment. Therefore, it is difficult to establish definitive rules for product acceptability onthe basis of appearance. At a minimum, finished face surface should

have no obvious imperfections otherthan minimal color and texture variations from the approved samples orevidence of repairs when viewed ingood typical daylight illuminationwith the unaided naked eye at a viewing distance of 20 ft (6.10 m). Appearance should not be evaluated whenlight is illuminating the surface froman extreme angle because this accentuates minor surface irregularities.

The objectives of the precast industry

Fig. 8. Merrill Lynch Corporate Campus, Englewood, Colorado.Architect: Thompson, Ventulett, Stainback & Associates, Atlanta, Georgia.

Fig. 7. TransAmerica Building,San Francisco, California.Architect: Johnson Fain Partners,Los Angeles, California. Fig. 9. Close-up detail showing simulated sandstone and limestone.

48 PCI JOURNAL

are to follow the design trends and to inform the clients and designers about thepossibilities of precast concrete. The following discussion will show the versatility of architectural precast in meeting thearchitect’s aesthetic needs. Also discussed is how almost any architecturalstyle imaginable can be expressed witharchitectural precast concrete.

For more details of these structures, alist of references is provided at the end ofthe article.

APPLICATIONS OFARCHITECTURAL

PRECAST CONCRETESimilar to a magazine cover, a

building’s exterior creates a visitor’sstrongest impression and a company’smost enduring image. Take the familiar landmark, the TransAmerica Building in San Francisco, California. Cladentirely in architectural precast concrete (see Fig. 7), the building is 48

stories tall, and capped by a 212 ft(64.6 m) spire, for a total height of853 ft (260 m). Floor-height, double-window units, weighing 3’/2 tons (3.18 t)

each, make up half of the total precastpieces used, with two variations for allcorner units. It is just one of thousandsof buildings with unique, distinctive facades that has been created with architectural precast concrete.

Fig. 8 shows the corporate campus forMerrill Lynch in Englewood, Colorado,

Fig. 11.Close-up of terminatingspandrel fin.

Fig. 10. 2777 East Camelback Office Building, Phoenix, Arizona.Architect: Daniel, Mann, Johnson & Mendenhall, Phoenix, Arizona.

March-April 2001 49

which is designed to house one millionsq ft (93,000 m2) of office space in fivebuildings. The first two buildings of thiscampus are complete. The site is a 70acre (28.3 ha) tract on the highest groundfor several miles in eveiy direction, witha commanding view of the front range ofthe Rocky Mountains. Because of thishigh visibility, it became an important architectural goal that the campus create abold, striking, sophisticated, corporateimage, visible from a long distance.

The simple shape and massing wasdeveloped to reinforce the long horizontal planes stepping up the hillside.However, these simple rectangularforms also maximize space planningefficiency and accommodate the load-bearing precast concrete structural system which is prevalent in the region.

The building’s exterior was developed to address both the micro andmacro scales. The long, low, dark-gray roof was designed to resemble a

silhouette against the light-blue sky.Along with the roof, the dark-gray topfloor windows and overhanging steeltrellis sunshade complete this horizontal cap to the building. The large (30 ftwide x 40 ft high) (9.14 x 12.2 m) redportals were also devised to be ofgrand enough scale to be seen fromthe distant interstate highway.

As one approaches the buildings, interesting detail abounds (see Fig. 9).The large red portals are architectural

Fig. 13.Combination

of finishesadds interestto structure.

Fig. 12. Shriners Hospital Parking Structure, Sacramento, California. Architect: Odell Associates, Inc., Charlotte, North Carolina.

50 PCI JOURNAL

precast concrete designed to replicatenative Colorado Red Sandstone.Within these large red portals, limestone colored architectural precastconcrete tracery accentuates windowopenings. This accent establishes amore delicate handmade scale to thebuildings. The overhanging trellissunshade protects windows from theharsh Colorado sunshine whileadding fine detail and visual interestto the form.

Building a 107,000 sq ft (9940 m2)speculative office building within thehistoric Biltmore district of Phoenix,Arizona, required special attention toaesthetics to match the surroundingneighborhood (see Fig. 10). The integral aesthetics consisted of the sleeklong lines of the spandrels and a limited palette of materials. Two parts ofthe spandrels were designed; spans between the columns and the terminatingfin. The fin is a key element because it

visually terminates the building andintegrates it with the other buildingcomponents (see Fig. 11). The precastconcrete serves as a subtle, delicatedetail that complements the design asa whole.

The parking structure for theShriners Hospital in Sacramento, California, forms the gateway to the medical center complex (see Fig. 12). Thepanels’ integral horizontal band of redgranite wraps the entire building.

Fig. 15.Boldly detailed loadbearingwindow-wall units.

Fig. 14. Main entrance to Aurora Colorado Municipal Justice Center, Aurora, Colorado.Architect: Skidmore, Owings & Merrill, Washington, D.C.

March-April 2001 51

Green terra cotta medallions withinthe granite band generate further interest. Two different finishes were created by alternating the sandblastingdepths, resulting in contrasting textures, with reveals added between andaround insets and bands (see Fig. 13).The creative result is a beautiful complementary parking structure thatblends well with its environment anddoes not overwhelm the setting.

Precast concrete states its case beautifully at the Aurora Colorado Municipal Justice Center.5 The combinationof color, shape, and texture, showcases the ability of architectural precast concrete to meet the designer’simaginative demands. A large passageway frames the main entrance(see Fig. 14), involving architecturalprecast concrete which forms thecolumns and fascia beams. The projectconsists of four main parts, namely, adetention facility, the courthouse, anaddition to an existing police station,and the rotunda.

The majority of the panels are load-bearing window-wall units, which aretwo stories high and weigh 20,000 lbs(9070 kg) each. Boldly detailed withbullnoses, cornices and friezes, theircream-colored appearance succeeds inlooking like limestone. Similarly,beveled reveals up to 10 in. (254 mm)wide vertically score the centerline ofeach panel to emphasize the play ofsunlight and shadow on the building’smonumental façade (see Fig. 15).

The W Hotel in San Francisco, California was conceived as a modernpiece of urban design for a prominentdowntown corner site. It is flanked onone side by boldly massed brick-facedprecast panels on the Museum ofModern Art and has, as a nearbyneighbor, an Art-Deco designed,1920s style, high-rise building. Tocompliment these prominent neighbors, the architects generated apodium and tower design with boldlymassed pure forms articulated to reflect a latent classical appearance (seeFig. 16).

Important portions of the elevations,including the main entrance, street-front restaurant, and penthouse, weremodeled as temple-like facades. Thetower was given deep V-shaped scoring to emphasize its verticality. The

Fig. 16. W Hotel, San Francisco, California.Architect: Hornberger & Worstell, San Francisco, California.

Fig. 1 7. Façade has a stone appearance with two depths of sandblasting.

52 PCI JOURNAL

precast concrete panels (finished inwhite concrete with fine, black grayand terra cotta aggregate) were formedto look like blocks of bearing stonethat resemble the granite used in manyof San Francisco’s civic structures.

-r

The appearance of stone detailingwas enhanced by treating the surfaceof the panels with two depths of sand-blasting (see Fig. 17). A mediumsandblasting of the typical surface created the look of a thermal finish, while

a light sandblasting of the back face[3 in. wide by 2 in. deep (76.2 x 50.8mm)] reveals at the lower levels, wasused to give the impression of oversized mortar joints.

The unity of pure geometric formsand bold classical articulation has successfully established this building asan anchor in this prominent site. Thissuccess was made possible by thefunctional uses of plastic and sophisticated material compositions of precastconcrete.

The University of illinois MolecularResearch Biology Building, Chicago,occupies a prominent location on thewest campus of the University of Illinois downtown Chicago campus (seeFig. 18).6 The real design challengefor the building was based on thearea’s extremely eclectic architecturalstyles. Most of the buildings date backto the 1920s and 30s and feature a variety of brick and precast design motifs. There is no dominant image toplay off. The architects’ goal was tocreate something that would be compatible with this diverse group ofbuildings yet project a distinctive campus image with visitors.

Fig. 18. University of Illinois Molecular Research Biology Building, Chicago, Illinois.Architect: Lohan Associates, Chicago, Illinois.

Fig. 1 9. Articulation of the façade creates design interest. Fig. 20. Double-helix shape staircase.

March-April 2001 53

Fig. 21.Saks Majestic

Square Complex,Charleston, South

Carolina.Architect: LS3P

Associates, Ltd.,Charleston, South

Carolina.

The architects created a lot of design interest in the articulation of thefaçade. By adding varying colors andfinishes to the panels based on eachpanel’s location, themes were pickedup from nearby buildings without detracting from the overall look (seeFig. 19). The result is that each façadeis compatible with its surroundingsand looks like it belongs in the area.

The base, a sandblasted granite aggregate finish, invites visual interestfor pedestrians. The mid levels featurean acid-etched granite aggregate thatprovides subtle, rich, red tones to integrate with the masonry on existingbuildings. The top features an acid-etched white sand with a mild pinkcast that was used primarily on laboratory sections, conveying a crisp look.Amber-tinted windows reinforce thecolor scheme.

The biggest challenge for the precaster, as well as the most striking element in the design (see Fig. 20), wasthe interior circular stairway that risesthrough the facility. This double-helixshaped stairway with a distinctivesmooth finish distinguishes itself fromthe three finishes used on the exterior.Visible from the outside of the building and illuminated at night, the stair-

way serves as a focal point for thestructure, with its double-helix designsuggesting the role of DNA in biological research.

The Saks Majestic Square Complexoccupies an entire block in the historic section of Charleston, SouthCarolina. The design challenge was tointegrate the complex into the small-scale principal retail district at theblock’s edges. The precast concreteand detailing at the corner entrancedepict the tradition of the 19th grandera of late century department stores(see Fig. 21). From the decorativeurns at the roof, to the incised lettering, to the terra cotta colored brackets,and the strong cornices at the top ofthe second floor, this finite detail wasavailable and economical by usingprecast concrete.

The overall architectural effect ofthe precast panels on Plaza MoliereDos 22 in Mexico City, where formand meaning are integrated, gives thebuilding a distinguished appearancethat communicates dignity and sobriety (see Fig. 22). The project, whichhas become a landmark symbol, includes a three-story shopping mall andan 11-story office building in the heartof a major business district. The use of

architectural precast concrete panels toclad the buildings created a distinctivelook, resembling rough-hewn stones.The panels also comprise the creativegeometric shapes that make the complex stand out.

The stone texture of the panels wasachieved by using rubber form liners,taken from natural rocks in a basaltrock quarry (see Fig. 23). Detailed engineering and intricate forms wereneeded to produce panels with deepreveals in false joints and interlockinglateral ends that eliminated any visiblevertical joints. The horizontal, vertical,and slanted corner panels were cast inone piece, producing a true “cornerstone” appearance.

This project is well detailed and itfeatures interesting textures and forms— which are fairly complicated. Theangles, circles, and curved surfaces allare done in a very competent and interesting way. The architect and precaster captured the feel, texture, andwarmth of hand-hewed stone. A visitor comes away feeling that’s exactlywhat it is.

The facades of the four-story, blocklong, John Pappajohn Business Administration Building at the Universityof Iowa in Iowa City, are articulated

54 PCI JOURNAL

Fig. 22.Plaza MoliereDos 22, MexicoCity, Mexico.Architect:Sordo Madaleno yAssociados, S.C.,Mexico, D. F.,Mexico.

by a harmonious rhythm of pilastersand windows, symmetry, and classicaldetail (see Fig. 24). The scale andfeeling of the exterior reflect the graceand serene neo-classicism of nearbyearly 19th Century structures.

The architectural precast concretecomponents for this project were manufactured with a blend of white andgray cement, a small amount of buffpigment, a light colored limestone ag

gregate, and an evenly colored naturalbuff sand. All of the precast panelswere lightly acid-washed.

The precast material’s extraordinaryflexibility allowed considerable designfreedom in the detailing of the elements. For example, the pedimentedentry gates are executed with classicaldetailing (see Fig. 25). This traditionaldesign interpretation is juxtaposedwith the contemporary elements in the

façade. Here, the precast concrete ismolded in a modem way, creating astepped, animated façade rather thanan unrelenting flat surface. The precast concrete has an especially strongexpression in the rusticated base of thebuilding, which conveys the strength,solidity and mass of the structure.

The color adjustability of the precastconcrete provided great flexibilitywith the color palette. The architectsmatched the color of surroundingstructures very closely, which was extremely important in helping this largenew building blend harmoniously withits neighbors.

As with many college campuses,Duke University’s West Campus inDurham, North Carolina, features ageneral architectural theme and manyvariations on that theme.8 Due tochanging tastes, cost constraints, andmaterial availability, a variety of styleshave been created through the years.But the new Terry Sanford Institute ofPublic Policy has re-established astrong design sense (see Fig. 26).

The older campus buildings arerichly detailed with pitched roofs,Gothic towers and window tracery.The new building manages to recallthe original stone Gothic motif of theFig. 23. Form liners were used to achieve stone texture of panels.

March-April 2001 55

Architect: Neumann Monson Architects, Iowa City, Iowa.

campus by combining German limestone pieces, which were set into thearchitectural precast panels duringfabrication. The German limestonereplicates the coloring and texture ofthe original Duke stone. It connectsboth visually and symbolically to theold campus.

Fig. 25.Classic

detailing ofpedimentedentry gates.

Calakmul Corporate Center in aMexico City suburb is a corporatecenter and landmark symbol for a newdevelopment area (see Fig. 27). Thebuilding is integrated to the landscapeby the use of architectural precast concrete panels in an innovative form andexpression. The pyramid-shaped

building holds exhibition areas, showrooms and a multiple-use auditorium.

The cube-shaped building is eightstories high, topped with a penthouse,and will be used as corporate offices.Waterfalls cascade onto the floor inside the circular openings of the fourwalls, then flow into reflecting poolsin the main plaza.

The building is conceived like a harmonic complex of volumes linkedwith space, relating the parts to thewhole. This was made possible bycombining shapes, symbols, and precast materials in a monumental structure. Three elemental forms, namely,the square or cube, the triangle orpyramid, and the circle or sphere exemplify forms and volumes of theideal platonic solids. The ideal conception was to combine these basicforms.

The architectural symbolism hasstriven to communicate the earth as animaginary square pointing towards thesolstice corners; the sky as a circlerepresenting the heavenly dome withthe circular movement of the stars;and the pyramid as representing a visual and metaphysic language of fireand light.

The combination of white and gray-crushed marble aggregates and sandmixed with white and gray cement,was used to match the surroundinglandscape and the design concept ofnatural stone — crucial in giving thebuildings the right color blend. The architect sought texture and brightness

• •

L.I_

_______

Fig. 24. John Pappajohn Business Administration Building, University of Iowa, Iowa City, Iowa.

56 PCI JOURNAL

Fig. 26. Terry Sanford Institute of Public Policy, Duke University, Durham, North Carolina.Architect: Architectural Resources Cambridge, Inc., Cambridge, Massachusetts.

Fig. 27. Calakmul Corporate Center, Mexico City, Mexico. Architect: Agustin Hernandez N., Mexico, D.F., Mexico.

March-April 2001 57

for the desired reflection of light byusing a medium-deep surface textureachieved with pneumatic chisel tools.The marble chips shone when the skinwas broken off the precast panels. Thearchitect also requested that slightcolor variation be randomly added tothe panels in order to attain the naturalpyramid stone effect.

customized elements makes precastconcrete different from any other exterior cladding material.

Take Columbus Ohio’s Center ofScience & Industry, for instance. Thisstructure was designed as an ellipticalcurve that includes a discontinuous“clothoid” curve from ground to roof(see Fig. 28). Each quadrant of pre

Fig. 28. Center of Science & Industry (COSI) in Columbus, Ohio. Architect: Arata Isozaki & Associates, Tokyo, Japan.

Project Architect: NBBJ Architects, Columbus, Ohio.

As can be seen, improvements infabricating processes allow architectural precast concrete to be created inalmost any color, form, or texture —

whatever is most aesthetically pleasing. In addition, concrete’s moldability offers the freedom to sculpt thestructure’s façade in very imaginativeways. This ability to achieve totally

Fig. 29. Museum of Modern Art, San Francisco, California. Project Architect: Mario Botta, Lugano, Switzerland.

Architect of Record: Helimuth, Obata and Kassabaum, San Francisco, California.

58 PCI JOURNAL

cast panels making up the façade wasplaced along segments of six curves toproduce the elliptical shape. The wallpanels also curve vertically into thebuilding along segments of two othercircular curves.

Structurally, the curved panels actas loadbearing members to support theroof. Conceptually, this building’slook combines two distinct aspects ofarchitecture: its universal grammar,such as basic geometry and general organization of space, and the acknowledgment of incorporating local materials and site restraints.

Precast concrete can be faced creatively with a wide variety of othercladding materials. Architects are incorporating the pleasing appearancesof traditional cladding materials suchas dimensional stone, brick, tile, andeven terra cotta, with the strength, versatility, and economy of precast concrete. For example, the patternedfaçade of the San Francisco Museumof Modern Art has 1 in. (25.4 mm)thick brick on 9 in. (229 mm) thickprecast concrete panels (see Fig. 29).b0

Most panels measure 10 x 28’/z ft(3.05 x 8.69 m) and contain 1500 to2300 bricks per panel.

Architectural precast concrete manufacturers have responded to the demand for more color choices by offering a wide variety of colorfulingredients. Various cement matrixcolors, a multitude of colorful stoneaggregates and sands, and a widerange of stable pigments allow the designers to create exactly the colorneeded. Fig. 30 shows the occasionaluse of two or more different colored-mix recipes in a single precast piece.

A designer can achieve strikinglydifferent colors and textures from asingle precast mix simply by varyingthe finish treatment. The single concrete mix shown in Fig. 31 has threedifferent finishes. This multiple-finishtechnique offers an economical, yeteffective, way to heighten aestheticinterest.

Signs of age etched in city grime areoften a disconcerting note in an era ofeternal youth. Discussions of measuresused to counteract atmospheric stainelicit, for the most part, a “We can livewith it” attitude. Sloping sills just invite soot to lay on them, and the rain is

Fig. 30. Several different mixes are used in a single panel.

Fig. 31.From left to right,the finishes areacid etched,sandblastedand retarded.

Fig. 32.Aesthetics can bedestroyed by lack

I ofdetailingforweather.

March-April 2001 59

going to streak the face (see Fig. 32).Stains from weathering can be reducedby proper detailing. There is a needfor designers to make provisions forcarrying down rainwater to minimizestreaking.

CONCLUDING REMARKSMany of the issues discussed in this

article affect the ultimate application

of architectural precast concrete in anyspecific design. If a precaster influences a job, it is important that the architect find the most qualified producer. This is because the technologyof precasting is quite complex. However, with the right precaster, the ensuing quality and aesthetics of the jobwill be well worth the effort.

This article has attempted to showhow the proper use of architectural

precast concrete can produce aesthetically pleasing structures. Today, thetechnology is sufficiently advancedwhereby a large variety of solutionsare avaibable to the architect.

Long ago, Goethe said that, “Themain challenge of any art is to causeby appearance, the illusion of a higherreality.” As the new century begins,those wise words will continue to haverelevance.

REFERENCES

I. van Acker, A., “The Relationship Between Aesthetics and Design Worldwide in Precast Concrete Structures,” Betonwerk +

Fertigteil-Technik, Wiesbaden, Germany, No. 4, 1990, pp.125-130.

2. Architectural Precast Concrete Color and Texture SelectionGuide, Precast/Prestressed Concrete Institute, Chicago, IL,1992, 258 pp.

3. Freedman, Sidney, “Successful Planning with ArchitecturalSamples,” ASCENT, Summer 1996, pp. 36-40.

4. Duffy, Tom, and Robison, Mark, “Architectural Precast Concrete Beautifies Shriners Hospital for Children in Sacramento,” PCI JOURNAL, V. 44, No. 2, March-April 1999, pp.14-25.

5. Freedman, Sidney, “Loadbearing Architectural Precast Concrete Wall Panels,” PCI JOURNAL, V. 44, No. 5, September-October 1999, pp. 92-115.

6. Anderson, Floyd, D., Nijhawan, Jagdish, and Kelley, Tom,“Precast Concrete Delineates Biology Lab Inside and Out,”PCI JOURNAL, V. 43, No. 2, March-April 1998, pp. 32-41.

7. “Architectural Precast Concrete Plays Key Role in Construction of the University of Iowa John Pappajohn Building,” PCIJOURNAL, V. 40, No. 3, May-June 1995, pp. 14-23.

8. Freedman, Sidney, “Stone Veneer-Faced Precast ConcretePanels,” PCI JOURNAL, V. 45, No. 4, July-August 2000, pp.72-99.

9. Isozaki, Arata, Scott, Jerome, Doyle, Thomas, and Cummings,Jerry, “Uniquely Curved Precast Concrete Panels Define NewCenter of Science & Industry (COSI),” PCI JOURNAL, V. 44,No. 5, September-October 1999, pp. 48-59.

10. Freedman, Sidney, “Clay Product-Faced Precast Concrete Panels,” PCI JOURNAL, V. 39, No.1, January-February 1994, pp.20-36.

60 PCI JOURNAL