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Theses (Historic Preservation) Graduate Program in Historic Preservation

2016

Architectural Precast Concrete Wall Panels: Their Technological Architectural Precast Concrete Wall Panels: Their Technological

Evolution, Significance, and Preservation Evolution, Significance, and Preservation

Grace Meloy University of Pennsylvania, [email protected]

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Meloy, Grace, "Architectural Precast Concrete Wall Panels: Their Technological Evolution, Significance, and Preservation" (2016). Theses (Historic Preservation). 608. https://repository.upenn.edu/hp_theses/608

Suggested Citation: Meloy, Grace (2016). Architectural Precast Concrete Wall Panels: Their Technological Evolution, Significance, and Preservation. (Masters Thesis). University of Pennsylvania, Philadelphia, PA.

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Architectural Precast Concrete Wall Panels: Their Technological Evolution, Architectural Precast Concrete Wall Panels: Their Technological Evolution, Significance, and Preservation Significance, and Preservation

Abstract Abstract Architectural precast concrete wall panels played an important role in mid-twentieth century architecture by providing a concrete technology that could be applied to the curtain wall system of construction utilized in this time period. Moreover, the precasting process, which enabled the controlled production of expressive facing concrete mixes and surface treatments and finishes, made this a concrete technology that could contribute to the architectural expression of the building. To promote the preservation of these panels, this thesis investigates and illuminates their historical and architectural significance in the United States in the mid-twentieth century.

There are, however, numerous technical challenges to the physical preservation of architectural precast wall panels, the most significant of which is due to their specially designed concrete mix and surface finish. Given the importance of preserving these characteristics, the general retroactive preservation action of applying patches to deteriorated concrete is unsatisfactory; instead, we must adopt a preventive approach. Towards this end, this thesis examines documents published in the United States between 1945 and 1975 that informed the design, production, and assembly of architectural precast wall panels. The information from these documents is used to trace the technological evolution of these panels and, ultimately, to identify potential material vulnerabilities and associated deterioration mechanisms to which they may be subject. This methodology provides foundational information to be used in the creation of preventive conservation plans for buildings constructed with this concrete technology.

Keywords Keywords cast stone, concrete masonry units, American Concrete Institute, Precast/Prestresse d Concrete Institute, MoSai

Disciplines Disciplines Historic Preservation and Conservation

Comments Comments Suggested Citation:

Meloy, Grace (2016). Architectural Precast Concrete Wall Panels: Their Technological Evolution, Significance, and Preservation. (Masters Thesis). University of Pennsylvania, Philadelphia, PA.

This thesis or dissertation is available at ScholarlyCommons: https://repository.upenn.edu/hp_theses/608

https://repository.upenn.edu/hp_theses/608

ARCHITECTURALPRECASTCONCRETEWALLPANELS:

THEIRTECHNOLOGICALEVOLUTION,SIGNIFICANCE,ANDPRESERVATION

GraceMeloy

ATHESISin

HistoricPreservation

PresentedtotheFacultiesoftheUniversityofPennsylvaniainPartialFulfillmentoftheRequirementsoftheDegreeof

MASTEROFSCIENCEINHISTORICPRESERVATION

2016

________________________________________AdvisorMichaelC.Henry,PE,AIAAdjunctProfessorofArchitecture________________________________________ProgramChairRandallF.Mason,PhDAssociateProfessor

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ACKNOWLEDGEMENTS

Firstandforemost, IwouldliketothankmyadvisorMichaelC.Henry,PE,AIA.He

pushedmethroughoutthisthesisprocess,andthroughoutmytwoyearsintheUniversityof

Pennsylvania’sHistoricPreservationprogrammorebroadly, toalwaysthinkcriticallyand

considerhow the gapbetweenengineeringandpreservationmaybebridged.This thesis

allowed me to explore both of these fields, and Michael Henry’s encouragement was

essential.

IwouldalsoliketothankRandallMason,FrankMatero,andtherestoftheHistoric

Preservation faculty for their guidance and support over the last two years. From their

teaching,IhavelearnedmoreaboutpreservationthanIcouldhaveeverimagined.

Additionally,Iwouldliketothankmyclassmatesforallofthewonderfulandcritical

conversationswehavehad,andIhopewewillcontinuetohave,aboutpreservationandits

placeintheworld.Ithasbeenapleasuretoworkwithyou.

Finally, I want to thank my family and friends for their efforts to appreciate my

interestinpreservingconcrete;Ihopethistopichasbecomealittlemoreintriguingafterall

ofourconversations.Inparticular,AlexHostreadandeditedmythesisinitsentirety,and

forthatIamexceedinglygrateful.

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TABLEOFCONTENTS

ACKNOWLEDGEMENTS..........................................................................................................................II

LISTOFFIGURES......................................................................................................................................V

LISTOFTABLES.....................................................................................................................................VII

CHAPTER1:INTRODUCTION...............................................................................................................1

CHAPTER2:EARLYPRECASTCONCRETEBUILDINGPRODUCTS—THEDEVELOPMENTOFARCHITECTURALPRECASTWALLPANELS..............................................6

Introduction.......................................................................................................................................................6HistoryofReinforcedConcrete..................................................................................................................6ObstaclestoArchitecturalUseofReinforcedConcrete...................................................................8ThePredecessorsofArchitecturalPrecastWallPanels................................................................12NascentArchitecturalPrecastWallPanels.........................................................................................16WorldWarIIandConcrete........................................................................................................................22Conclusion.........................................................................................................................................................23

CHAPTER3:APPLICATIONOFARCHITECTURALPRECASTWALLPANELSINMID‐CENTURYARCHITECTURE.......................................................................................................24

DevelopmentoftheCurtainWallSystem............................................................................................24FlourishingofArchitecturalPrecastWallPanels.............................................................................29ModernistArchitectsandArchitecturalPrecastWallPanels......................................................31VarietyofBuildingsandAesthetics........................................................................................................37PreservationImplications..........................................................................................................................45

CHAPTER4:LITERATUREREVIEW—PATHOLOGIESANDPRESERVATIONOFARCHITECTURALPRECASTWALLPANELS.................................................................................48

Introduction.....................................................................................................................................................48ReinforcedConcretePathologies............................................................................................................48DeteriorationofArchitecturalPrecastWallPanels........................................................................53DeteriorationDetectionMethods...........................................................................................................55CurrentArchitecturalPrecastWallPanelPreservationStrategies..........................................57ConservationStrategieswithPotential................................................................................................58TowardsaPreventiveConservationApproach.................................................................................61Conclusion.........................................................................................................................................................64

CHAPTER5:TECHNOLOGICALEVOLUTIONOFARCHITECTURALPRECASTWALLPANELS,1945‐1975................................................................................................................65

Introduction.....................................................................................................................................................65Precast’sPotential:1945‐1950................................................................................................................671950‐1965:Pre‐ACISymposium.............................................................................................................681965ACISymposium...................................................................................................................................741965‐1975:MomentumintheArchitecturalPrecastIndustry..................................................87Conclusion......................................................................................................................................................106

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CHAPTER6:METHODOLOGYFORPREVENTIVECONSERVATIONOFARCHITECTURALPRECASTWALLPANELS...............................................................................107

Introduction..................................................................................................................................................107MethodologyPart1—CategorizingIndustryLiterature............................................................107Data...................................................................................................................................................................108Discussion......................................................................................................................................................126MethodologyPart2—IdentificationofPotentialFactorsandPathstoDeterioration..127ApplicationofMethodologyandFutureSteps...............................................................................138Conclusion......................................................................................................................................................140

CHAPTER7:CONCLUSION...............................................................................................................141

BIBLIOGRAPHY...................................................................................................................................144

Mid‐centuryModern,Concrete,andItsPreservation.................................................................144HistoryofReinforcedConcrete.............................................................................................................144HistoryandDevelopmentofArchitecturalPrecastConcreteWallPanels.........................145ApplicationofArchitecturalPrecastConcreteWallPanelsinMid‐CenturyArchitecture..................................................................................................................................................146ReinforcedConcrete:PathologiesandPreservation....................................................................146ArchitecturalPrecastWallPanels:PathologiesandPreservation.........................................148PreventiveConservation.........................................................................................................................149RecommendedPracticesandOtherTechnicalDocumentsAboutArchitecturalPrecastConcreteWallPanels................................................................................................................149

INDEX......................................................................................................................................................152

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LISTOFFIGURES Figure1.DetailoftheconcretefaçadeoftheBlenheimbuildingoftheMarlborough‐BlenheimHotelinAtlanticCity,NJ(1905).

Figure2.Caststonecolumncapitols.

Figure3.An“honestlymodern”housecomposedofallconcretecomponents,includingunstuccoedexteriorwallsofconcretemasonryunits.

Figure4.TheArmostoneSystem.

Figure5.TheLockstoneSystem.

Figure6.LakeShoreDriveApartmentsbyMiesvanderRohe(Chicago,1948‐1951).

Figure7.TheSeagramBuildingbyMiesvanderRohe(NewYorkCity,1954‐1958).

Figure8.Exampleofwindow‐typemullionwallonthePanAmericanBuildinginNYC(1962).

Figure9.TheDenverHiltonHotelbyAldoCossutta(Denver,CO,1959).

Figure10.MurrayLincolnCampusCenterbyMarcelBreuerandHerbertBeckhard(UniversityofMassachusettsinAmherst,MA,1970).

Figure11.ThePanAmericanBuildingbyWalterGropiusandPietroBelluschi(NewYorkCity,1962).

Figure12.ThePhiladelphiaPoliceHeadquartersbyGeddes,Brecher,Qualls,andCunningham(Philadelphia,1962).

Figure13.TheNortheastRegionalLibrarybyGeddes,Brecher,Qualls,andCunningham(Philadelphia,1962).

Figure14.TheBuffaloEveningNewsBuildingbyEdwardDurellStoneandAssociates(Buffalo,NY,1973).

Figure15.WaltersArtMuseumadditionbyShepley,Bulfinch,Richardson,andAbbotofBostonandMeyer,Ayres,andSaintofBaltimore(Baltimore,1974).

Figure16.BankerTrustBuildingbyEmoryRothandSons(NewYorkCity,1962)

Figure17.WaterTowerInnbyHausnerandMacsai(Chicago,1961).

Figure18.TheInternationalBuildingbyAnshenandAllen(SanFrancisco,1961).

Figure19.McGawMemorialHallbyHolabird&Root&Burgee(NorthwesternUniversityinEvanston,IL,1953)

Figure20.TheOakParkHighSchool,architectunknown(Laurel,MS,c.1965).

Figure21.TheSamuelPaleyLibrarybyNolen&Swinburne(Philadelphia,1966).

Figure22.TheMiamiBeachPublicLibrarybyHerbertA.Mathes(MiamiBeach,FL,1962).

Figure23.Diagramofconcretedeterioration.

Figure24.Detailofajointthatconvolutesthepathwatermusttraveltopenetratethewallsystem.

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Figure25.Temperaturegradientthroughdifferenttypesofpanels.

Figure26.Aprecasterlayingwiremeshreinforcementontoprecastpanelbeforeapplyingthebackupconcrete.

Figure27.Imagesofdifferenttexturesthatcanbeachievedwiththeuseofformliners.

Figure28.Aprecasterhandlayingthefacingaggregateintheformwork.

Figure29.Comparisonofdifferentmethodsofexposingthefacingaggregate.

Figure30.Exampleofapositiveseatingconnectionbetweenanarchitecturalprecastwallpanelandaconcreteframe.

Figure31.Comparisonofthestrainexperiencedbythesealantmaterialinjointsofdifferentshapefactors.

Figure32.Examplesoftwo‐stagejointsystems.

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LISTOFTABLES Table1.DesignObjectives

Table2.MaterialSelection

Table3.ReinforcementDesignandMaterials

Table4.FormDesignandMaterials

Table5.CastingandConsolidation

Table6.Curing,Stripping,andStorage

Table7.SurfaceFinishesandTreatments

Table8.Transport,Handling,andErection

Table9.ConnectionDesignandMaterials

Table10.JointDesignandMaterials

Table11.Cleaning,Repairs,andCoatings

Table12.PanelDesignConditions

Table13.FacingandBackupConcreteMixConditions

Table14.ConcreteCoverandReinforcementConditions

Table15.Formwork,Casting,Curing,andSurfaceTreatmentConditions

Table16.StrippingandHandlingConditions

Table17.ConnectionandJointConditions

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CHAPTER1:INTRODUCTION

Althoughreinforcedconcrete(RC)becameoneoftheprimarystructuralmaterials

forindustrialandinfrastructuralprojectsinthelatenineteenthcentury,ittookdecadesfor

RCtobecomeanacceptedandevencelebratedarchitecturalbuildingmaterial.Vitaltothis

acceptance was the development of architectural precast concrete wall panels, which

provided architects of the mid‐twentieth century with a concrete technology that could

attainavarietyofarchitecturalexpressionsandmoreeffectivelycompetewithmid‐century

architecture’s other defining material, steel. Unfortunately, their preservation has been

inhibited, on the one hand, by a limited understanding, evident in the literature, of their

historicalandarchitecturalsignificanceand,ontheotherhand,bythenumeroustechnical

challenges associated with their physical preservation, including that of preserving the

original architectural expression of the panels. This thesis seeks to contribute to the

preservation of architectural precast concrete wall panels by addressing these

impediments.

Architectural precastwall panels are envelope components that are connected to

theprimarystructuralframeofabuilding.Theirstructuralfunctionislimitedtosupporting

theirowndeadloadandresistinglateralloads,suchaswind,andtheytherebyconformto

themid‐centurytrendofseparatingabuilding’sskinfromitsstructure.Theyaregenerally

manufacturedoff‐site,whichenablesgreatercontrolover theproductionprocessand the

quality of the product than what can be achieved with cast‐in‐place concrete, which is

subject toweather, variable curing conditions, and the inaccuracies of formwork erected

on‐site.Architecturalprecastwallpanelsarecasthorizontallyinreusableformswithathin

layer of a facing concrete typically poured first, on top ofwhich reinforcement is placed,

followedbyabackuplayerofconcrete.

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Significantly, the facing concretewas designed to fulfill an architectural function:

throughaparticularconcretemixdesignandanexpressivesurfacefinishand/ortreatment,

itisabletocontributetothearchitecturalexpressionofthebuilding.Thepanelscanalsobe

cast into interesting and artistic shapes to further add to this expression. As a result,

architectural precast wall panels contribute immensely to the character of the buildings

constructedwiththem,andpreservingtheirapplicationinmid‐centuryarchitecturewillbe

integraltothepreservationofourmid‐centuryheritagemorebroadly.

Beyond our limited awareness of architectural precastwall panels’ historical and

architectural significance, there are also numerous technical challenges to their

preservation.Thepreservationofallreinforcedconcreteischallengingbecauseoftheway

it deteriorates from the inside out, due to the corrosion of the internal reinforcement.

Corrosionresults inthevolumetricexpansionof thereinforcementand,subsequently, the

crackingoftheadjacentconcreteand,ultimately,spallingoftheconcretesurface.Whenthis

occurs, repair and conservation strategies have been limited to, most conservatively,

patching the localized section of spalling or, more liberally, demolishing the wall and

rebuilding it. Although patches preserve more historic fabric than demolition, they are

extremelydifficulttomatchandareoftenhighlyvisible,tothedetrimentofthebuilding’s

design.

The preservation of architectural precast wall panels in particular, however,

presents furtherchallenges.Precastwallpanelshave thinnersections,whichprovide less

coveroverthereinforcementandcanleadtobendingproblems.Duetothemodularityof

precastwall panel systems, there aremany joints, unlike in cast‐in‐place concretewalls.

These joints between the panels create more concrete surface area that is subject to

moisture penetration. Moreover, the connection assemblies between the panels and the

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building’s structural frame introducepaths for thermalconductionandsitesofadditional

corrosion.

Themostsignificantchallengeinpreservingarchitecturalprecastwallpanelsisdue

totheirspeciallydesignedconcretemix,surfacefinish,and/orpanelshape,whichcombine

to help define the architectural expression of the building. That this concrete technology

allowedformoreimaginativeresultsthanprecastpanels’maincompetitor,metalandglass

curtain walls, and more consistent results than could be achieved with cast‐in‐place

concrete,iswhatmadeitsoattractivetoarchitectsofthemid‐twentiethcentury.Giventhe

importanceofpreservingthisarchitecturalexpression,thegeneralretroactivepreservation

actionofapplyingpatchestodeterioratedconcreteisunsatisfactory.Instead,itisessential

that we adopt a preventive conservation approach, or a conservation approach that

attempts topredictandslowtherateofdeterioration.Bypredictingproblemsandtaking

measures to slowdeteriorationbefore thematerial integrity of this important element is

compromised, the important architectural role of precast wall panels will be more

successfullypreserved.

This thesis will first illuminate the historical significance of architectural precast

wall panels within the context of the development of reinforced concrete and its

competition with steel and, later, metal and glass curtain walls. Then, to illustrate the

architectural significance of architectural precast wall panels, this thesis will present

examples of their application in mid‐century architecture and explore their role as a

character‐defining feature.Lastly, afteremphasizing theneed forpreventiveconservation

strategies forbuildingsconstructedwitharchitecturalprecastwallpanels, this thesiswill

analyzerecommendedpracticesandothertechnicaldocumentsthatinformedtheirdesign,

production,andassemblyinordertopredictwhatmaterialvulnerabilitiesandsubsequent

deteriorationtheymaybesubjectto.Byidentifyingthepotentialarrayofthreatsthatmay

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affectthisconcretetechnology,thisthesishopestoprovideinformationthatmaybeusedin

thedevelopmentofsuchpreventiveconservationplans.

Indesigningthisthesis,severalimportantscopelimitationswereestablished.First,

this thesis will only focus on architectural precast concrete wall panels and saves the

explorationofstructuralprecastwallpanelsforfutureresearch.Similarly,sandwichpanels

will not be examined in great detail in this thesis because of the numerous challenges

particulartothattypeofwallpanel;theyshouldalsobeexploredinarelatedbutseparate

project. Second, the recommended practices and other technical documents analyzed to

predict how architectural precast wall panels may deteriorate are limited to those

publishedbetween1945and1975intheUnitedStatesduringthisperiod.Thesedateswere

determinedbasedonthesignificantuseofarchitecturalprecastwallpanelsduringthemid‐

twentiethcentury:afterWorldWarII(1945)whenarchitecturalprecastwallpanelsbegan

tobemassproducedandbeforethedeclineofmid‐centuryarchitecture(1975),theperiod

of architecture towhich architectural precastwall panels greatly contributed.This thesis

focuses on the United States because of the author’s interest in American mid‐century

architectureandherfamiliaritywithAmericanbuildingpractices.Finally,thisthesishopes

tobe thoroughbutdoesnotpretendtobeexhaustivewithrespect toreviewingallof the

documentspublishedabout thedesign,production, andassemblyof architecturalprecast

wall panels during themid‐twentieth century in the United States. However, through an

examinationof thepublicationsoforganizations suchas theAmericanConcrete Institute,

whichhasbeenandcontinuestobeoneoftheleadingauthorities inconcretetechnology,

themostinfluentialdocumentshavebeenidentifiedandreviewed.1

1It should be noted that during the research for this thesis, numerous dead ends were encountered inattemptingtofindpotentiallysignificantdocumentsaboutthedesign,production,andassemblyofarchitecturalprecast wall panels. This reveals that information about this important mid‐century architectural feature isalreadybeinglost,and,consequently,wemustbolsterourunderstandingofthisconcretetechnologywhilewestillhaveasmuchinformationaswedotobetterpreserveitinthefuture.

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Chapter 2: Early Precast Concrete Building Products—The Development of

Architectural PrecastWall Panels explores the history of reinforced concrete, significant

predecessorsofprecastpanels,andearlyprecastpanelsproducedpriortoWorldWarIIin

order to elucidate the evolution of this concrete technology and reveal its historical

significance. Chapter 3: Application of Architectural Precast Wall Panels in Mid‐Century

Architecture examines thedevelopmentof the curtainwall systemand its significance to

the application of architectural precast wall panels in mid‐century architecture. To

demonstrate the architectural significance of this concrete technology, examples of its

application in mid‐century architecture are presented, followed by a discussion of

importantimplicationsforthepreservationofarchitecturalprecastwallpanels.Chapter4:

Literature Review—Pathologies and Preservation of Architectural Precast Wall Panels

reviews thecurrentstateofknowledgeabout themechanismsofdeterioration thataffect

architecturalprecastwallpanelsandthestrategiesimplementedintheirpreservation.This

chapter exposes the shortcomings of these preservation strategies and proposes the

adoption of a preventive conservation approach. Chapter 5: Technological Evolution of

Architectural PrecastWall Panels, 1945‐1975, investigates theways inwhich the design,

production,andassemblyofthisconcretetechnologychangedoverthisthirtyyearperiod,

assemblingtheinformationthatwillbeusedtoidentifypotentialmaterialvulnerabilitiesof

architectural precastwall panels. Chapter 6:Methodology for Preventive Conservation of

Architectural Precast Wall Panels, analyzes the technological evolution of architectural

precastwall panelswithin the context of the pathologies that affect them and that affect

reinforcedconcretemorebroadly.Theresultsof thisanalysisarepresented in tablesand

diagrams that outline the various factors andpathsofdeterioration that couldaffect this

concrete technology. This information will be essential in the creation of preventive

conservationplansforbuildingsconstructedwiththisarchitecturalelement.

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CHAPTER2:EARLYPRECASTCONCRETEBUILDINGPRODUCTS—THEDEVELOPMENT

OFARCHITECTURALPRECASTWALLPANELS

INTRODUCTION

Theemergenceofreinforcedconcreteasaprimaryarchitecturalbuildingmaterial

in the mid‐twentieth century owes much to the development of architectural precast

concrete wall panels. The precasting process enabled a high level of control over the

production of this concrete technology, thereby enhancing its competitiveness with

America’spreviouslyfavoredmaterial:steel.Byexaminingthedevelopmentofarchitectural

precastwall panels, including its contribution to the architectural use and acceptance of

concrete, the historical significance of this concrete technology and the importance of

preservingitcanbefullyappreciated.

HISTORYOFREINFORCEDCONCRETE

A brief review of the history of reinforced concrete (RC) is essential for

understandingtheevolutionofarchitecturalprecastwallpanels.Afterconcrete’sinitialuse

bytheRomans, therewasa“totalneglectofconcreteconstruction”until thebeginningof

the nineteenth century when concrete emerged as a modern building material almost

simultaneouslyinEnglandandFrance,withtheUnitedStatefollowinginthesecondhalfof

thenineteenthcentury.2

Theneglectofconcretecanbepartiallyattributedtotheabsenceofagoodbinder,

which, when mixed with water, forms the paste and ultimately the matrix to bond the

coarseandfineaggregatesoftheconcretemix.Accordingly,thediscoveryofabetterbinder

2Peter Collins, Concrete:TheVision of aNewArchitecture (McGill‐Queens University Press, 2004, originallypublished1959):19.

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was essential to the development of concrete as a building material in the nineteenth

century. In 1824, such a binder was discovered by Joseph Aspdin, who patented the

formulation forwhat came to be known asPortlandcement, after the extremely durable

EnglishPortland limestone.Portlandcementwas “harder, stronger,muchmoreadhesive,

andcuredmuchmorequicklythantheordinarylimemortartowhich[theRomans]were

accustomed.”3Despitethisdiscovery,whichmadeconcretecompetitivewithotherbuilding

materials in terms of strength and durability, stone and brick remained the favored

architecturalbuildingmaterials throughout thenineteenthcentury.Asaresult,concrete’s

primary use in the nineteenth century was in industrial buildings and infrastructural

projects.

Nevertheless, because concrete had the potential to “be cheaper than traditional

masonryconstruction”andtobeusedasa“fireproofing”materialfortheincreasinguseof

iron in building construction, there was a sustained interest in its development.4While

muchexperimentationandtestingoccurredinEuropeinthemid‐nineteenthcentury,vital

totheassertionofconcrete’sstructuralandeconomicadvantageswasthedevelopmentof

reinforced concrete at the end of the nineteenth century, largely due to important

experimentationintheUnitedStates.Throughhis investigationsbetween1871and1872,

WilliamE.Warddemonstratedthatthecombinationofironandconcretewouldresultina

compositeassemblywithimprovedstrength.Healsorecognizedthatplacingtheironnear

the bottom of a concrete beamwould effectively increase the tensile capacity.5Thaddeus

Hyatt confirmed that the thermal coefficients of expansion and contraction for iron and

3Edward Allen and Joseph Iano, FundamentalsofBuildingConstruction:MaterialsandMethods (Hoboken, NJ:JohnWiley&Sons,2009),516.4Bill Addis and Michael Bussell, “Key Developments in the History of Concrete Construction” in ConcreteBuildingPathology,ed.SusanMacdonald(Oxford:BlackwellScienceLtd,2003),18.5Collins,Concrete,57.

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concretearethesame,demonstratingthesafetyofthiscompositematerialinfires.6Ernest

LeslieRansome,unlikehiscontemporaries,actuallytriedtoexploitRCinAmerica,despitea

growingpreferenceforironandsteelconstruction.7InFrance,FrancoisHennebiquemade

anessentialcontributiontothedevelopmentofRCwhenhispatentforreinforcedconcrete

in1892substitutedsteelforironreinforcement.8Bythebeginningofthetwentiethcentury,

textbooksonreinforcedconcretewereincirculation,makingthematerial’spropertiesand

methods of production accessible and enabling continued experimentation with this

material.Despite theseadvancements inRC technologyand theadvantages itoffered, the

acceptanceofRCasanarchitecturalmaterialwasnotyetcomplete.

OBSTACLESTOARCHITECTURALUSEOFREINFORCEDCONCRETE

In the United States, there were numerous barriers to the architectural use of

reinforcedconcrete.BecausetheU.S.didnothaveanestablisheddomesticcementindustry

until the end of the nineteenth century, the high cost of importing cement from Europe

madetheuseofconcretelesseconomicalthanotherbuildingmaterials,likesteel.9Cast‐in‐

place reinforced concrete was also an entirely new type of material with no “handicraft

traditiontoguidepractitioners,”andalthoughtheactualplacementofconcretedidnotrely

on skilled labor, the fabrication and erection of the formworknecessary for cast‐in‐place

concrete requiredan immenseamountof craft labor.10Thisnecessity for skilled labor for

RC construction did not conform to America’s industrial principle: the drive to remove

skilledlaborfromtheconstructionsitetoincreaseefficiencyanddecreasecost.Instead,as

6Ibid.,59.7Ibid.,61.8Ibid.,65.9Morris,PrecastConcreteinArchitecture,79.10Donald Friedman,HistoricalBuildingConstruction:Design,Materials,andTechnology, (New York, NY:W.W.Norton&Company,Inc.,2010),133.

9

theU.S.workedon the challenge of designing and constructing taller buildings, iron, and

latersteel,becametheprimarymaterialusedinthisarchitecturebecauseofitsavailability

andtheabilitytofactory‐producestandardizedmembers.Thus,steelbecamethepreferred

structural building material in America’s building industry and “established a virtually

impregnable ascendancy.”11Even as other countries realized concrete’s potential for

fireproofingsteelconstruction,Americareliedonitsestablishedmethodofusingterracotta

slabs.12

The most significant barrier to concrete’s architectural use in the United States,

however,was its appearance. Stone, brick, andwood remained theprimary architectural

building materials, and concrete’s aesthetic could not compete with the familiar and

engrainedaestheticofthesematerials,aswellaswiththeirnaturalabundanceattheendof

the nineteenth century. As a result, although the establishment of a domestic cement

industry in the latter part of the nineteenth century helped to enhance the economy of

concrete construction in the U.S., RC continued to be relegated to industrial and

infrastructural projects. In order tomake RCmore competitivewith steel, the American

ConcreteInstitutewasestablishedin1904todisseminateinformationaboutconcreteand

publish standards and manuals.13In 1916, the Portland Cement Association was also

founded to promote the use and quality of cement and concrete in America’s building

industry.14

Asreinforcedconcretebecamemoreestablishedasabuildingmaterial in theU.S.,

and thestructuralandeconomicadvantagescouldno longerbe ignored,architectsbegan

experimenting with concrete as an architectural material. In the U.S., initially, the

11Collins,Concrete,86.12Ibid.,56.13Friedman,HistoricalBuildingConstruction,132.14“AboutPCA,”PCA,lastaccessed10March2016,http://www.cement.org/.

10

architecturaluseof concrete generally consistedof casting concrete to imitate traditional

masonrymaterials, as seen in the production of cast stone. RC also began to be used in

architectureasastructuralmaterial,althoughitwastypicallycoveredwithveneersofmore

conventional materials, such as stone and brick. European architects, such as Auguste

Perret,madesignificantcontributionstotheexpressionofconcreteasitsownarchitectural

materialintheearlytwentieth‐century,althougheventheseexampleswerefairlyisolated.

IntheUnitedStates,“themoststrikinglyrationalattempttoexploitboththestructuraland

aestheticvaluesofconcretewasmadein1905,whentheBlenheimbuildingwasaddedto

the Marlborough‐Blenheim Hotel in Atlantic City, NJ.”15Designed by architects Price and

McLanahan of Philadelphia, the Blenheim building was the largest reinforced concrete

building in theU.S. at the timeandemployeda concrete facadewith terracottadetails to

avoid“sham”coveringsandexpresstheconcreteitself[Figure1].

15Collins,Concrete,87.

11

Figure1.DetailoftheconcretefaçadeoftheBlenheimbuildingoftheMarlborough‐Blenheim

HotelinAtlanticCity,NJ(1905).16

Determininghowtoexpressconcreteasanarchitecturalmaterialcontinuedtobea

challenge into the twentieth century. In Europe, it was only after World War I and the

maturationofthemodernarchitecturalstyle,whichpromotedthearchitecturalexpression

ofconcreteas itsownmaterial, thatconcretebecameaprimaryarchitecturalmaterial. In

theUnitedStates,thetransitiontoRCasaprimaryarchitecturalmaterialdidnotoccuruntil

afterWorldWarII.

16Photocourtesyof:Collins,Concrete,Plate23.

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THEPREDECESSORSOFARCHITECTURALPRECASTWALLPANELS

BytheendofthenineteenthcenturyintheUnitedStates,theindustrialproduction

ofprecastconcretebuildingelements,whetherarchitecturalorstructural,wasrecognized

tobeonestrategytomakeconcreteamorecompetitivebuildingmaterial,fortheprecasting

process facilitated standardization and more closely aligned with America’s industrial

principle.Twoimportantpredecessorsofarchitecturalprecastwallpanelswerecaststone

andconcretemasonryunits(CMU).Althoughbothweredevelopedinthesecondhalfofthe

nineteenth century and were products of precasting, the two materials served distinct

functions and contributed differently to the development of architectural precast wall

panels.

Cast stone was developed in the second half of the nineteenth century with the

establishmentof thedomesticcement industryandwasasuccessfulattempt tomake the

useofconcreteinarchitectureacceptable—bycastingittoimitatenaturalstone.Toachieve

thisimitation,theconcretemixwasdesignedtoimitatethecolor,texture,andevenveining

of stone, and the concrete was then cast into custom molds. Cast stone had distinct

advantagesovernaturalstone,includingtheabilitytobemoldedtotheshapesrequiredby

thedesignand,throughtheuseofreinforcement,tocreatelong,load‐bearingspans.17The

productionofcaststoneasveneer,block,andornamentalsocateredtothestyleofthetime,

the City Beautiful movement, which called for large Neo‐Classical columns and

ornamentation[Figure2].18

17GrahamTrue,DecorativeandInnovativeUseofConcrete (Scotland,UK:WhittlesPublishing,2012),56;WyattB.Brummitt,“CastStone,”AmericanBuilder(1June1928):97.18Ibid.,94.

13

Figure2.Caststonecolumncapitols.19

Still,certaincharacteristicsofcaststonewouldpreventitsprolongedsuccess.First

and foremost, although cast stone was cast off‐site, its casting was very specialized and

requiredanimmenseamountofcraftskill.Thecreationofthemoldsthemselvesrequired

expertworkmanship, and theywere often not reused,which limited the efficiency of the

productionprocess.20Similarly,allcastingswere“madealittleover‐sizesothattheymaybe

finisheddowntopreciselythedimensionrequired”;becausesuchfinishingrequiredskilled

carvers,thisaddedtotheamountofskilledlaborinvolvedintheproductionprocess.21The

curingprocess,whilecontrolledandabletoachieveahighlevelofquality,requiredatleast

twoweeksbeforethecaststonehadgainedsufficientstrengthtobestrippedfromthemold,

19Photocourtesyof:Brummitt,“CastStone,”95.20Brummitt,“CastStone,”95.21Ibid.,97.

14

which in turncreated longerproductioncycles.22Caststonealsoconformedto traditional

masonryconstruction,requiringskilledmasonsforitsassembly,and,therefore,ignoredthe

trend towards the separation of skin and structure beginning in the late nineteenth and

earlytwentiethcentury.23Thelaborintensityandinefficiencyofcaststoneproductionled

to the cast stone industry’s decline during the Great Depression, as material production

becamemoreandmoremechanized.24Theunderstandingofsurfacefinishesandaesthetic

mix design, however, ultimately provided the foundational knowledge used in the

expressionofarchitecturalprecastwallpanels.

Concurrentlywiththedevelopmentofcaststone,concretemasonryunitsbeganto

bemanufactured.Unlikecaststone,CMUweregenerallycastwithoutanexpressivesurface

finish. Additionally, CMU were cast in quantity by machines into standardized sizes,

although themass production of CMUdid not begin until the beginning of the twentieth

century.25Before 1915, CMU were used mostly for foundation, basement, and partition

walls,butafterthefirsttwodecadesofthetwentiethcenturyandtheimprovedproduction

ofCMU,thepopularityofthisconcretetechnologygrew.26Onearticleclaimedthattheuse

of concretemasonryunits and tile increased 670percent between 1920 and 1923.27The

popularityofCMUreflectedthepublic’sgrowingconfidenceinconcreteasamaterialtobe

used in architecture, although thearchitectural expressionof concretewasnot solvedby

CMU:thesurfacewasoftenstuccoedforbothaestheticreasonsandto increasethewater

22Ibid.23AdrienneB. Cowden andDavidP.Wessel, “Cast Stone” inTwentiethCenturyBuildingMaterials:HistoryandConservation(LosAngeles,CA:GettyConservationInstitute,2014),57.24Ibid.25PamelaH.Simpson,HarryJ.Hunderman,andDeborahSlaton,“ConcreteBlock”inTwentiethCenturyBuildingMaterials:HistoryandConservation(LosAngeles,CA:GettyConservationInstitute,2014),47.26Ibid.27“Growing Use of Concrete Products: Concrete Masonry and Other Products are in Growing Demand forStrength,BeautyofFinish,andFireResistance,”AmericanBuilder37/3(1June1924):369.

15

resistanceoftheCMU.28Evenso,a1933articleadvertisingan“honestlymodern”concrete

houseconveyseffortstoexpressconcreteasitsownarchitecturalmaterial[Figure3].29

Figure3.An“honestlymodern”housecomposedofallconcretecomponents,including

unstuccoedexteriorwallsofconcretemasonryunits.30

Notably, the use of concrete masonry units—which were inexpensive, could be

producedmoreefficientlythancaststone,couldbeinstalledmorequicklythantraditional

materials (such as fired claymasonry),were fireproof, and required littlemaintenance—

exemplifiesakeyfactorinconcrete’sintroductionintoarchitecturalsettings:thepromotion

of its use by organizations such as Portland Cement Association in the economic

28WyattB.Brummitt, “SolveBuildingProblemswithConcreteMasonry,”AmericanBuilder44/3 (1December1927):102.29“An‘HonestlyModern’ConcreteHouse:ACenturyofProgressinConcreteBuildingShowninNewDesignbyWyatt B. Brummitt andWal‐Ward Harding for Portland Cement Association, Chicago,”AmericanBuilderandBuildingAge55/3(1June1933):56.30Photocourtesyof:“An‘HonestlyModern’ConcreteHouse,”56.

16

construction of houses. Numerous articles encouraged the use of CMU in the creation of

economical houses and professed their beauty and serviceability.31Because reinforced

concrete was having difficulty competing with steel construction in commercial

architectural settings, “the propaganda of the cementmanufacturers in theUnited States

tendedtoconcentratemoreonhousing.”32Thus,inadditiontoprovidingknowledgeabout

mass and mechanized production, the CMU industry also profoundly affected the

developmentofarchitecturalprecastwallpanelsbyestablishingapathforthearchitectural

use of concrete. Still, because CMU also aligned with traditional load‐bearing wall

construction, its architectural usewas inherently limited as constructionmoved towards

theseparationofskinandstructure.

Thus,despitecreatinganarchitecturalniche forconcrete, theadvantagesof these

two types of concrete technology were outweighed by the remaining obstacles to the

widespread architectural use of concrete, including the continued preference for steel

construction in the U.S. and concrete’s reliance on load‐bearing wall construction.

Nonetheless, the production of cast stone and CMU created the foundation for the

productionofarchitecturalprecastwallpanelsbyproviding important informationabout

surface finishes and treatments and the casting process and by establishing a path for

architecturalprecastwallpanels’useintheconstructionofhouses.

NASCENTARCHITECTURALPRECASTWALLPANELS

Theevolutionofarchitecturalprecastwallpanelsstemmedfromtheneedtosatisfy

two separateobjectives thatwouldultimatelymake this concrete technology competitive

31A.J.R. Curtis, “Most Popular of 500 Dwellings: A Successful Five Room House Plan and Some Reasons forFollowingItatMorganPark,aSuburbofDuluth,”AmericanBuilder34/5(1February1923):104.32Collins,Concrete,89.

17

with other architectural buildingmaterials. The first objectivewas tomake this concrete

technology aesthetically pleasing. The second was to align it with the trends of the

American building industry in the early twentieth century, which included reducing the

amountofskilledlaborneededon‐site,enablingfasterconstruction,separatingtheskinof

buildings from their structure, and standardizing the components of construction. The

knowledge of mix design and surface finishes and treatments honed by the cast stone

industrycontributedgreatly to the firstobjective. Indeed,manycaststonemanufacturers

becameprecastersbecauseof theirunderstandingof thecastingprocess,mixdesign,and

surface finishes and techniques.33To achieve the second objective, however, precastwall

panelsdeviatedfromcaststoneandconcretemasonryunits.

Althoughprecastpanelswereseenasearlyas1875whenW.H.Lascellespatented

his system for reinforcedpre‐cast construction,which includedpre‐cast slabswhose face

could look likewall tiling, the development of precast panels really began in the second

decade of the twentieth century.34Some of the pioneers included Ernest Leslie Ransome

whose“RansomeUnitSystem,”patentedin1911,incorporatedprecastwallpanelswithina

whole system of precast building components.35John E. Conzelman also attacked the

question of how to make building construction more efficient through prefabrication

between 1910 and 1916, during which time he took out more than fifty patents for his

concrete“UnitSystem.”36

Precastwall panelswith an expressive architectural finish trulydevelopedwithin

thenichepreparedbyCMUtomakeeconomicalandattractivehousing.Thiswasthe first

settinginwhicharchitecturalprecastwallpanelscoulddemonstratetheeaseoftheirwall

33CowdenandWessel,“CastStone,”57.34Collins,Concrete,42.35Morris,PrecastConcreteinArchitecture,81.36Ibid.

18

system construction, the advantages of precasting and the quality that could be achieved

through this process, and the opportunity for individuality and beauty. A review of

moderate‐costhouseconstructionmethodsandequipment in theAugust1935volumeof

ArchitecturalRecordadvertisesfourseparateprecastwallsystems.TheArmostoneSystem,

developed by ConcreteHousing Corporation, advertised awall system composed of 1 in.

thick precast panels three feetwide by story height that used cementmortar to seal the

panels[Figure4].37Thesepanels,whichwerestiffenedwithverticalribs,wouldbestuccoed

ontheexteriortoachieveanappealingaesthetic.

Figure4.TheArmostoneSystem.38

37“Moderate‐CostHouseConstructionandEquipment,”ArchitecturalRecord78/2(August1935),112.38Photocourtesyof:“Moderate‐CostHouseConstructionandEquipment,”112.

19

In contrast, the Lockstone System by Ernest H. Lockwood from Pasadena, California,

advertised a hybrid wall system composed of smaller precast panels that formed the

formwork forpouredconcretewalls.Theprecastpanels,whichwere1½ in. thick,12 in.

tall,and36in.wide,wereadvertisedasbeing“attractivelyfinishedinthemould…need[ing]

nofurthertreatment”[Figure5].39

Figure5.TheLockstoneSystem.40

39Ibid.,113.40Photocourtesyof:“Moderate‐CostHouseConstructionandEquipment,”113.

20

John J. Earley’s mosaic concrete precast panels were also advertised in this review. The

mosaicconcretepanels,whichwere2in.thickandapproximately9ft.highand4to10ft.

wide, were produced with a colorful exposed facing aggregate surface and required no

additionaltreatment.41

ThedevelopmentofarchitecturalprecastpanelsintheU.S.owesmuchtothework

of John J. Earley and theEarley Studio.Through their experimentation in the 1930swith

exposedaggregateprecastpanels,knownasMoSai,theydiscoveredinvaluableinformation

about the precasting process and potential finishes and surface treatments.42Like other

precasters at the time and in light of the Great Depression, Earley explored the use of

precast panels and professed their production as the best way to construct affordable,

efficient, and beautiful housing.43He believed that through the use of concrete, and in

particular precast wall panels, housing could be “within the reach of every family” in

America and provide the security desperately needed after the Stock Market Crash of

1929.44 The design of these houses also demonstrates Earley’s recognition of the

importanceofminimizingthefootprintofthebuilding’swalls tomaximizetheareaofthe

interior space, a consideration thatwould become very important in the development of

curtainwallsystems.45

Earley continued to explore theuseofMoSai, improving thematerial’sproperties

andproductionthroughtesting.Thecreationofseveralprominentstructures,suchasthe

EdisonMemorialTowerinNewJersey(1938)andtheadministrationbuildingsattheDavid

W.TaylorModelTestingBasinnearWashington,DC(1938),ledtotheincreasedvisibilityof

41Ibid.,111.42Earley’sarchitecturalprecastpanelswerecalledMoSai,inreferencetomosaics,toacknowledgethe“artistic,craftsman‐qualityofthisproduct”(Cellini,3).Byexposingtheaggregateoftheconcretemix,thesurfaceoftheMoSaipanelswerereminiscenttoearlyItalianmosaics.43JohnJ.Earley,“ArchitecturalConcreteMakesPrefabricatedHousesPossible,”JournaloftheAmericanConcreteInstitute(May‐June1935):514.44Ibid.45Ibid.,518.

21

thisconcrete technology.46Finally,withEarley’sprominentrole in theAmericanConcrete

Institute, of which he became president in 1939, research and publications about

architecturalprecastwallpanelsand theirproductionbegan tobepushed forward in the

field.47

Despite these promising beginnings, the earnest development of architectural

precast panels and recognition of their potentialwould not be realized until afterWorld

War II and the dominance of the curtain wall system over traditional load‐bearing

construction.Suchanenvironmentwouldenabletheriseinuseofarchitecturalprecastwall

panels.

WORLDWARIIANDCONCRETE

WorldWar II was a pivotal moment for the architectural use of concrete in the

UnitedStates.First,tosupportthewareffort,America’spreferredbuildingmaterial,steel,

was rationed for general use. The rationing of steel finally justified the serious and

sustainedconsiderationof concrete inarchitectural settings, and, inparticular, theuseof

precaststructuralframecomponents.48Furthermore,duetothewar,thenumberofskilled

construction trades available to buildwith traditionalmaterials, such as stone andbrick,

was limited.49Without this skilled labor, the less skilled assembly of precast concrete

systems,includingarchitecturalprecastwallpanels,becameappealingandeconomical.

Second, with the coming of World War II, many European architects fled the

ContinentandimmigratedtoAmerica.Thesearchitectsbelievedinanddesignedaccording

46Sidney Freedman, “Architectural Precast Concrete” in Twentieth Century Building Materials: History andConservation.(LosAngeles,CA:GettyConservationInstitute,2014),77.47JennaCellini,“TheDevelopmentofPrecastExposedAggregateConcreteCladding:TheLegacyofJohnJ.EarleyandtheImplicationsforPreservationPhilosophy,”UniversityofPennsylvaniaMaster’sThesis(2008),69.48Morris,PrecastConcreteinArchitecture,93.49MichaelA.Tomlan,“BuildingModernAmerica:AnEraofStandardizationandExperimentation”inTwentieth‐centuryBuildingMaterials:HistoryandConservation(LA,CA:GettyConservationInstitute,2014),8.

22

to thenewstyleofmodernarchitecture thataccommodatedconcreteand itsappearance.

The philosophy of modern architecture had matured after World War I in Europe and

proposed a break with the past through the rejection of ornamentation, utilization of

simple,rationalforms,andrelianceonobjectiveproblemsolving.50Concretefitnicelyinto

thisphilosophyandbecameadefiningmaterialofthestyle,especiallygiventhepromotion

ofconcretebytheprominentarchitectLeCorbusier.LeCorbusierdemonstratedconcrete’s

place in the new style, and consequently in architecture, by recognizing the “remarkable

adaptabilityofconcrete…withitssculpturalandstructuralpotential.”51

AlthoughthetranslationofthematuremodernstyletotheUnitedStatesprovideda

place for architectural reinforced concrete, the contributions of one important American

architectcannotbeignored.Throughhisexperimentationwithreinforcedconcrete,Frank

LloydWrighthelpedtointroducebothmodernmaterialsandmodernarchitecturalideasto

theU.S.WithworkssuchastheJohnsonWaxAdministration(Racine,WI,1936‐1939)and

FallingWater (Bear, PA, 1936),Wright illustrated the potential of reinforced concrete in

American architecture.52Moreover, Wright helped to reveal the aesthetic potential of

exposingspeciallyselectedaggregateonconcrete’ssurface,atechniquethatwould“become

by far the most widely used precast concrete surface finish.”53Despite such strides,

however, Frank LloydWright alone did not instigate thewidespread architectural use of

concrete.

Instead, the influx of European architects into the United States fundamentally

changed the architectural perspective on concrete. Many of these architects, including

numerous German architects such as Walter Gropius, Ludwig Mies van der Rohe, and

50Mark Gelernter, AHistory of American Architecture: Buildings in Their Cultural and Technological Context(Hanover:UniversityPressofNewEngland,1999),237.51“LeCorbusier’sLoveforConcrete,”ConcreteInternational(1March2015):38.52KennethFrampton,ModernArchitecture:ACriticalHistory(London:ThamesandHudsonLtd.,1980),188.53Morris,PrecastConcreteinArchitecture,89.

23

Marcel Breuer, filled leadership positions in American design schools and “shaped the

future of American architecture at its source, in the education of the next generation of

architects.”54

CONCLUSION

Thus,bytheendofWorldWarII,thearchitecturaluseofconcretebegantoflourish

intheUnitedStates.Between1946and1969,theU.S.experiencedthelongestcontinuous

periodofgrowthinthenation’shistory,andduringthatperiod,reinforcedconcretebecame

thematerialofchoice.55Althougharchitecturalprecastwallpanelswouldgreatlycontribute

tothisshift,essentialtothewidespreaduseofarchitecturalprecastpanelswasthechange

inbuildingassembliesfromload‐bearingwallstotheseparationofabuilding’sskinfromits

structure.

54Ibid.55Tomlan,“BuildingModernAmerica,”9.

24

CHAPTER3:APPLICATIONOFARCHITECTURALPRECASTWALLPANELSINMID‐

CENTURYARCHITECTURE

DEVELOPMENTOFTHECURTAINWALLSYSTEM

Beginninginthelatenineteenthcentury,wallassembliesbegantochange:theskin

ofthebuildingwasseparatedfromitsstructure.Thisseparationledtotheemergenceofthe

curtainwallsystem—awallassemblythatseparatestheexteriorfromtheinteriorspaceof

thebuildingandsupportsnothingbut itself.56The transition towards curtainwallspartly

arose from the challenge of creating taller buildings while simultaneously maximizing

rentablefloorspace.Forexample,theMonadnockBuildingbuiltinChicagoin1893metthe

requirementsofatallerbuilding,butits6ft.deepbearingwallsgreatlyreducedtheamount

ofrentablespaceperthefootprintofthebuilding.57Assteelandconcreteframesdeveloped

forthegravityloadspreviouslybornebyload‐bearingwalls,thewallcouldbereducedtoa

thin skin that supported itself and resistedweather and lateral loads such aswind. This

separation encouraged both greater interior flexibility and the rationalization of the

building process by separating the erection of the structure from the installation of the

building’sskin.58

PietroBelluschi’sEquitableSavingsandLoanBuildinginPortlandOregon(1948)is

oftencreditedasbeingthepioneerbuildingincurtainwallconstruction.59Likemostearly

curtainwalls,thiscurtainwallwascomprisedofmetalwindowframingandglazing.Ludwig

Mies vanderRohe, a leader inmid‐centurymodern architecture, spearheaded theuseof

56WilliamDudleyHunt,TheContemporaryCurtainWall(NewYork:F.W.DodgeCorp,1958),1.57Ibid.,5.58Theodore H.M. Prudon, FAIA, Preservation ofModernArchitecture (Hoboken, NJ: John Wiley & Sons, Inc.,2008),111.59DavidThomasYeomans,“TheArrivaloftheCurtainWall,”PreservingtheRecentPast,3‐140.

25

curtain walls and greatly contributed to the evolution of this technology.60His steel and

glasscurtainwalldesignfor860‐880LakeShoreDriveApartmentsinChicago(1948‐1951)

demonstrates his early commitment to this technology, and his subsequent designs for

othermetalandglasscurtainwallsforbuildingsliketheEsplanadeApartmentBuildingsin

Chicago(1953‐1956)andtheSeagramBuildinginNewYorkCity(1954‐1958)conveythe

prominentplacecurtainwalltechnologyhadinmodernarchitecture[Figure6and7].Given

this prominence, in order for concrete to stay competitive with metal and glass curtain

walls, a form of concrete would have to be developed that could alignwith this type of

buildingassembly.

60MellonHallHistoricStructureReport(UniversityofPittsburgh:ArchitecturalStudiesProgramDocumentationandConservationStudio,Spring2013),65.

26

Figure6.LakeShoreDriveApartmentsbyMiesvanderRohe(Chicago,1948‐1951).61

61Photo courtesy of: Werner Blaser, Mies van der Rohe: Lake Shore Drive Apartments (Basel, Switzerland:Birkhäuser–PublishersforArchitecture,1999),41.

27

Figure7.TheSeagramBuildingbyMiesvanderRohe(NewYorkCity,1954‐1958).62

Architectural precast wall panels had numerous advantages over cast stone,

concretemasonry units, and even cast‐in‐place concrete. First, the precasting process of

architecturalprecastwallpanelsachievedahighlevelofqualitybecauseofthecontrolled

production environment, which enabled better surface finishes and/or treatments. The

processwasalsofarmoreefficient:thetableorfloorheightatwhichthepanelswerecast

both simplified and accelerated the casting operation, there was minimum formwork

becauseitwasreused,andreinforcementcouldbeplacedmoreeasilythanincast‐in‐place

62Photocourtesyof:WernerBlaser,MiesvanderRohe(Basel,Switzerland:Birkhäuser–VerlagfürArchitektur,1997),163.

28

concrete.63Additionally,throughtheintroductionofearlystrengthconcrete,thecuringtime

could be greatly reduced and twenty‐four‐hour production cycles were not uncommon,

unlikethetwo‐week‐longcuringtimeforcaststone.64Mostimportantly,thoseotherforms

ofconcretereliedonload‐bearingwallsystemswhilethethincross‐sectionandlargearea

ofarchitecturalprecastwallpanelscouldbereadilyadaptedtothecurtainwallsystem.

Despite these advantages over other concrete technologies, architectural precast

wallpanelshadimportantobstaclestoovercomebeforetheycouldeffectivelycompetewith

metalandglasscurtainwalls.Initially,theiruseincurtainwallsystemswaslimitedbythe

materials‐handling equipment available: because of the lack of mobile cranes and other

efficientmaterials‐handlingequipment,constructionofprecastconcretecurtainwallswas

slower than the construction of metal and glass curtain walls, which often could be

assembled from within the building.65The production of metal and glass curtain wall

systemsalsoexploited“theseeminglypre‐emptivepotentialofprecision,mass‐production

‘machine‐age’technology,”fittingneatlyintotheUnitedStates’industrializationofbuilding

construction.66In the years after World War II, the issue of more efficient handling

equipmentwas resolved through the introduction of rubber‐tiredmobile cranes and the

introduction of lightweight aggregate concrete mixes, which made panels lighter.67

Additionally, improvedmethods inproductionhelped to enable themass‐production and

standardization of architectural precast wall panels. Thus, through the development of

architectural precast panels, the concrete industry provided a concrete technology that

couldcompetewithmetalandglasscurtainwallsinitsabilitytobemass‐produced,butalso

63“PrecastConcrete:WallPanels.”PortlandCementAssociation(October1954),10.64Ibid.65Freedman,“ArchitecturalPrecastConcrete,”78;Hunt,TheContemporaryCurtainWall,6.66Morris,PrecastConcreteinArchitecture,96.67Ibid.,95.

29

in its “exceptionalresistancetowind,rain,and fire”andthevarietyof formsand finishes

thatcouldbeachievedwithprecasttechnology.68

FLOURISHINGOFARCHITECTURALPRECASTWALLPANELS

Thepopularityofarchitecturalprecastpanelsincreasedinthe1950sand1960sdue

tobetterhandling/erectingequipment,improvedmethodsofproduction,andthecontinued

development of new techniques andmaterials.One innovation that improvedproduction

was theutilizationofShokbeton (or shockedconcrete),whichwasanewcastingmethod

that enabled the consolidation of no‐slump concrete mixes through repetitive and fast

raising and dropping of the form.69Improvements in casting technology and handling

equipmentalsomadelargerpanelspossible,whichmadeconstructionfasterandrequired

fewer joints and connections. The development of the window‐type mullion wall panel

which introduced glazing into architectural precast wall panels, made this concrete

technologyevenmorecompetitivewithmetalandglasscurtainwalls[Figure8].70Similarly,

thedevelopmentofsandwichpanels,whichareprecastpanelsconsistingoftwoouterfaces

ofconcretethatsandwichacoreofinsulativematerial,providedatypeofprecastpanelthat

addressed growing concerns for heating and air‐conditioning costs.71Also importantwas

the realization of the “structural economies to be gained from utilizing the primary

structuralpotentialofprecastconcreteunits,”whichfurthermaximizedtherentablefloor

68Ibid.,96.69T.W.Hunt,“PrecastConcreteWallPanels:HistoricalReview,”SymposiumonPrecastConcreteWallPanels,ACIPublicationSP‐11(1965):13.70VictorLeabu, “PrecastConcreteWallPanels:DesignTrendsandStandards.”SymposiumonPrecastConcreteWallPanels,ACIPublicationSP‐11(1965),37.71D.W.PfeiferandJ.A.Hanson,“PrecastConcreteWallPanels:FlexuralStiffnessofSandwichPanels,”SymposiumonPrecastConcreteWallPanels,ACIPublicationSP‐11(1965):67.

30

space by eliminating theneed for an entirely separate structural framewhile retaining a

thinwallsection.72

Figure8.Awindow‐typemullionwallpanelisherebeinghoistedintoitsplaceonthePan

AmericanBuildinginNYC(1962).Window‐typemullionwallpanelsintegratedglazinginto

theprecastpanel,makingarchitecturalprecastwallpanelsmorecompetitivewithmetaland

glasscurtainwalls.73

72Morris,PrecastConcreteinArchitecture,156.73Photocourtesyof:Morris,PrecastConcreteinArchitecture,162.

31

The most significant reason for architectural precast panels’ rise in popularity,

however,wasthevarietyofsurfacetexturesandpatternsandexteriordesignsthatcouldbe

acquired,arangethatgenerallycouldnotbeachievedaseconomicallyinothermaterials.74

Althoughnearlyallsurfacefinishesandtreatmentsthatwereultimatelyusedinthe1950s

and 1960s were established by the early twentieth century, the improved precasting

process provided enough control to optimize their implementation.75Similarly, as form

technology advanced and incorporated different materials, such as steel and fiberglass

reinforced plastics, the variety of shapes that could be accomplished with architectural

precastpanelswasmarketedasbeing“limitedonlybytheimaginationofthearchitectand

designer.”76

Therefore, although the increased speed of construction and high quality of the

productmade architectural precastwall panels competitivewithmetal and glass curtain

walls,itwasthediversityinshapes,colors,andtexturesthatmadethisconcretetechnology

thepreferredmaterialforcurtainwalls.77Toillustratetherangeofaestheticsthatcouldbe

achievedwitharchitecturalprecastwallpanels,aswellastheiradaptationtocurtainwall

assembly,thefollowingsectionspresentexamplesoftheiruseinmid‐centuryarchitecture.

MODERNISTARCHITECTSANDARCHITECTURALPRECASTWALLPANELS

The first architecturally significant building to incorporate architectural precast

wall panels was the Denver Hilton Hotel in Denver, Colorado [Figure 9]. Constructed in

1959 and designed by I.M. Pei & Partners, this building “represented the first fully

74Freedman,“ArchitecturalPrecastConcrete,”78.75Morris,PrecastConcreteinArchitecture,9076Leabu,“PrecastConcreteWallPanels:DesignTrendsandStandards,”37.77Freedman,“ArchitecturalPrecastConcrete,”78.

32

consistent use of concrete in the U.S.: a precast skin enclosing a concrete structure.”78

Utilizingstory‐highpanels,thedesignofthebuildingworkedtoovercomesomeoftheearly

aesthetic challenges precast wall panel systems presented, such as how to attractively

incorporatethejointsbetweenthepanels.79AldoCossutta,thechiefarchitectoftheDenver

HiltonHotel, decided to design “into the surface a gridwith a pattern of deep reveals: a

traceryof shadow lines engenderingall the joints and relegating them toa lesser role.”80

Theconcretemixofthepanelsusedsandandgravelsievedfromthesoilexcavatedonthe

site, and the surface of the panels was lightly etched with acid to expose the natural

aggregate.81

Figure9.TheDenverHiltonHoteldesignedbyAldoCossuttainDenver,CO(1959).82

78AldoCossutta“FromPrecastConcretetoIntegralArchitecture,”ProgressiveArchitecture(October1966):196.79Morris,PrecastConcreteinArchitecture,160.80Cossutta,“FromPrecastConcretetoIntegralArchitecture,”198.81Ibid.,196.82Photocourtesyof:“SheratonDenverDowntownHotel:I.M.PeiTower,”Sheraton,lastaccessed25April2016,http://www.sheratondenverdowntown.com/im‐pei‐tower.

33

Marcel Breuer also had a particular interest in precast technology. Breuer and

Herbert Beckhard designed the Murray Lincoln Campus Center at the University of

MassachusettsinAmherst,Massachusetts(1970),whichconsistsofthreedifferenttypesof

precast panels connected to a structural frame and exterior end walls of cast‐in‐place

concrete[Figure10].83Theten‐storytowerdemonstratesthevarietyofshapesthatcanbe

achievedwitharchitecturalprecastpanels.

Figure10.MarcelBreuerandHerbertBeckhard’sMurrayLincolnCampusCenteratthe

UniversityofMassachusettsinAmherst,MA(1970)demonstratesonasinglestructurethe

varietyofshapesthatcanbeachievedwitharchitecturalprecastwallpanels.84

83“ThreePrecastBuildingsfromtheOfficeofMarcelBreuerandAssociates,”ArchitecturalRecord(March1973):118.84Photocourtesyof:“ThreePrecastBuildingsfromtheOfficeofMarcelBreuerandAssociates,”118‐119.

34

Walter Gropius, founder of the Bauhaus, and Pietro Belluschi, architect of the

EquitableBuilding inPortland,Oregon,designed thePanAmericanBuilding inNewYork

City[Figure11].85Constructedin1962,thefifty‐seven‐storytoweriscladwith9,000story‐

highprecastconcretewindowunitsfacedwithexposedquartzaggregate.86

Figure11.ThePanAmericanBuildinginNewYorkCity(1962),designedbyWalterGropius

andPietroBelluschi,iscladwith9,000story‐highprecastwindowunits.87

85ChristopherGray,“Streetscapes/TheMetLifeBuilding,OriginallythePanAmBuilding;CriticsOnceCalledItUgly; Now They’re Not Sure,” The New York Times (7 October 2001),http://www.nytimes.com/2001/10/07/realestate/streetscapes‐metlife‐building‐originally‐pan‐am‐building‐critics‐once‐called‐it.html?pagewanted=all.86Morris,PrecastConcreteinArchitecture,161.87Photocourtesyof: “AirRights:PanAmBuilding,”ThePanAmHistoricalFoundation, lastaccessed25April2016,http://www.panam.org/the‐jet‐age/370‐air‐rights‐the‐pan‐am‐building‐2.

35

In Philadelphia, the architectural firm Geddes, Brecher, Qualls, and Cunningham

explored theuseofprecastpanels.Oneof theirmost famous structures, thePhiladelphia

PoliceHeadquarters(1962),utilizesthree‐storytallstructuralprecastpanels[Figure12].88

Figure12.ThePhiladelphiaPoliceHeadquarters(1962)isGeddes,Brecher,Qualls,and

Cunningham’smostfamousstructure,theexteriorofwhichconsistsofthree‐storytall

structuralprecastwallpanels.89

Geddes, Brecher, Qualls, and Cunningham also explored the use of architectural precast

panelsintheirdesignfortheNortheastRegionalLibraryinPhiladelphia(1962)[Figure13].

Thepanelsofthispubliclibrary,whichwereattachedtoastructuralcast‐in‐placeconcrete

88Morris,PrecastConcreteinArchitecture,155.89Photo courtesy of: Save the Roundhouse and found in Nicole Anderson, “Pending Sale of Philadelphia’sRoundhouse Police Headquarters Spurs Campaign for Landmark Status,”TheArchitectNewspaper (22March2013), http://archpaper.com/2013/03/pending‐sale‐of‐philadelphias‐roundhouse‐police‐headquarters‐spurs‐campaign‐for‐landmark‐status/.

36

frame, are composed of gray cement with an aggregate of white quartz and “Riverdale”

stonefromNewJersey.90Thepanelswerefinishedwithalow‐pressuresandblasttoexpose

theaggregate,andacolorlesssiliconewaterrepellantcoatingwasappliedtotheirexterior

afterinstallation.91

Figure13.Geddes,Brecher,Qualls,andCunningham’sdesignfortheNortheastRegional

LibraryinPhiladelphia(1962)iscladwitharchitecturalprecastwallpanels,adetailofwhich

isshowninthisimage.92

90“PrecastPanelsonaFrame,”ProgressiveArchitecture(September1964):157.91Ibid.92“PrecastPanelsonaFrame,”156.

37

VARIETYOFBUILDINGSANDAESTHETICS

The use of architectural precast wall panels was easily adapted to a variety of

building types. The Buffalo Evening News Building (1973), which is currently on

DOCOMOMO’s register of significant modern buildings, was designed by Edward Durell

StoneandAssociates.Thelargeandweightyexposedaggregateprecastwallpanels,which

were connected to a cast‐in‐place concrete structural frame, juxtapose the airinessof the

roof, which appears to float in space above the precast panels and the deeply recessed

windowsdesignedinthem[Figure14].93

Figure14.TheBuffaloEveningNewsBuilding,designedbyEdwardDurellStoneand

Associates(1973),iscladwithmassivearchitecturalprecastpanels.94

93“The Buffalo EveningNewsBuilding,” DOCOMOMO‐US, lastmodified 3May 2014, http://www.docomomo‐us.org/register/fiche/buffalo_evening_news_building.94Photocourtesyof:RobertM.Metz,BuffaloEveningNewsPhotoCollectionfrom6January1973foundon“TheBuffalo Evening News Building,” DOCOMOMO‐US, last accessed 25 April 2016, http://www.docomomo‐us.org/register/fiche/buffalo_evening_news_building.

38

The Walters Art Museum addition in Baltimore, Maryland (1974), which was

designedbyShepley,Bulfinch,Richardson,andAbbotofBostonandMeyer,Ayres,andSaint

of Baltimore, was constructed to provide much needed gallery space for the Baltimore

museum[Figure15].95Theprimaryelevationsof theadditionutilizedprecastpanelsasa

brisesoleil,whichspanthewidthoftheelevationsandaresuspendedseveralfeetfromthe

exteriorwallofthebuilding.Theconcretemixofthesepanelscomplimentsthestoneofthe

original museum building, and the panels are finished on the street‐facing side with

striationstocreateaninterestingtexture,whiletheaggregateisexposedonthepanelside

facingthemuseum,whichcanbeseenfromthegalleryspaceswithin.

Figure15.TheprecastpanelsoftheWaltersArtMuseumadditioninBaltimore,MD,designed

byShepley,Bulfinch,Richardson,andAbbotofBostonandMeyer,Ayres,andSaintof

Baltimore(1974),formabrisesoleil(photobyauthor).

95 “From Art Gallery to Art Museum,” The Walters Art Museum, last accessed 9 February 2016,http://thewalters.org/about/history/gallery.aspx.

39

Numerousskyscraperswereconstructedwitharchitecturalprecastwallpanels. In

NewYorkCity,theBankerTrustBuilding(1962),whichwasdesignedbyEmoryRothand

Sons,wasconstructedwithstory‐highwindowwallunits[Figure16].96Thesepanelswere

composedofawhitequartzaggregateinawhitecementmatrixandwerefinishedtoexpose

theaggregate.97

Figure16.Oneofthestory‐highwindowunitsisseenherebeinghoistedontotheelevationof

theBankerTrustBuildinginNewYorkCity,designedbyEmoryRothandSons1962).98

96Morris,PrecastConcreteinArchitecture,161.97Hunt,“PrecastConcreteWallPanels:HistoricalReview,”11.98Photocourtesyof:Morris,PrecastConcreteinArchitecture,161.

40

In Chicago, the Water Tower Inn (1961), which was designed by Hausner and Macsai,

illustrates the texture that could be achieved with architectural precast panels: the

vertically staggered story‐high window boxes create a distinctive elevational pattern

[Figure17].99

Figure17.ThewindowunitscladdingtheWaterTowerInninChicago,designedbyHausner

andMacsai(1961),createadynamicelevationpattern.100

99Morris,PrecastConcreteinArchitecture,163.100Photocourtesyof:Morris,PrecastConcreteArchitecture,163.

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InSanFrancisco,architecturalprecastpanelsformtheundersilloftheribbonwindowson

the International Building (1961), designed by Anshen and Allen [Figure 18].101These

panelsweredesignedwithare‐entrantcornersurface,whichcreatesinterestingshadows

anddepthonthebuilding’selevations.

Figure18.TheelevationsoftheInternationalBuildinginSanFrancisco,byAnshenandAllen

(1961),aredefinedbyalternatinglayersofglazingandprecastundersills,whosereentrant

cornerdesigncreatesinterestingshadowsanddepth.102

101Ibid.,164.102Photo courtesy of: Thomas found on “International Building,” Archikey.com, last accessed 25 April 2016,http://archikey.com/building/read/2799/International‐Building/663/.

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Schools, universities, and libraries also utilized architectural precast panels.

Designed by the firm of Holabird & Root & Burgee, the McGaw Memorial Hall at

Northwestern University in Evanston, Illinois (1953), is an early example of the use of

architectural precastwall panels in a university setting [Figure 19].103The panels, which

wereclampedtoasteelframe,aresolidarchitecturalprecastwallpanels8”thickand8’4”

square in area.104The Oak Park High School in Laurel, Mississippi (c. 1965, architect

unknown),conveysthegrowinguseofcolorinarchitecturalprecastpanels[Figure20].105

AtTempleUniversityinPhiladelphia,Nolen&Swinburne’sSamuelPaleyLibrary(1966)is

clad with story‐high exposed aggregate panels [Figure 21].106Finally, the cylindrical

auditorium of theMiami Beach Public Library in Florida, designed byHerbert A.Mathes

(1962),demonstratesthetexturesandpatternsthatcanbeachievedusingsculpturedsand

thatistranslatedtotheprecastpanelsurfaceduringcasting[Figure22].107Theendresultis

adynamicexteriorthatcouldnotbeachievedinanyothermaterial.

103 “McGaw Hall,” University Archives: Northwestern Architecture, last accessed 17 April 2016,http://digital.library.northwestern.edu/architecture/building.php?bid=12.104“PrecastConcrete:WallPanels,”PCA,9.105Hunt,“PrecastConcreteWallPanels:HistoricalReview,”8.106Amelia Brust, “Board Approval Signals New Chapter for Library,” The Temple News (19 March 2012),http://temple‐news.com/news/board‐approval‐signals‐new‐chapter‐for‐library/.107David Rifkind, “A Story Told in Fragments,”Miami’s Community Newspapers, last accessed 1 April 2016,http://communitynewspapers.com/miami‐beach‐featured/a‐story‐told‐in‐fragments/;Hunt, “Precast ConcreteWallPanels:HistoricalReview,”1.

43

Figure19.McGawMemorialHallbyHolabird&Root&Burgee(1953)isanearlyexampleof

solidprecastwallpanels.108

Figure20.TheOakParkHighSchoolutilizescoloredarchitecturalprecastwallpanelsonthe

school’sfaçade.109

108Photo courtesy of: “McGawHall,” University Archives: Northwestern Architecture,” last accessed 25 April2016,http://digital.library.northwestern.edu/architecture/image.php?iid=124&all=123,129,128,130,124,126,127,121,122,125.

44

Figure21.TheSamuelPaleyLibrary,designedbyNolen&Swinburne(1966),iscladwithsolid

exposedaggregatepanels.110

109Hunt,“PrecastConcreteWallPanels:HistoricalReview,”8.110Photo courtesy of: “Paley Library, Temple University,” Preservation Alliance, last accessed 25 April 2016,http://www.preservationalliance.com/directory/mcmar/index.php/inventory/detail/220.

45

Figure22.ThepanelsusedontheMiamiBeachPublicLibrary,designedbyHerbertA.Mathes

(1962),illustratetheexpressivetexturethatcouldbeachievedwitharchitecturalprecastwall

panels.111

PRESERVATIONIMPLICATIONS

Thepreservationofmid‐centurymodernarchitecturehasbecomeaninitiativewith

increasing support across the United States, spearheaded by organizations such as

DOCOMOMOandtheirUnitedStateschapter.Atthenationallevel,theNationalParkService

and National Trust for Historic Preservation have been giving increasing attention to

significant mid‐century modern architecture, including buildings constructed with

architecturalprecastpanels.Additionally,localorganizationshavebeguninventoryingand

highlighting mid‐century modern architecture, such as Philadelphia’s Preservation

111 Photo courtesy of: “Miami Beach Public Library,” Albert Vrana, last accessed 25 April 2016http://albertvrana.com/library.html.

46

Alliance’sMid‐CenturyModern Initiative andMontgomery County’sMontgomeryModern

programinMaryland.

Despite such initiatives, however, there has been considerable resistance to the

preservationofmid‐century architecturedue to new challenges it presents. For example,

mid‐centuryarchitectureisgenerallynotassignedthesameaestheticvaluethatisassigned

tootherhistoricbuildingslikeDraytonHallinCharleston,SouthCarolina,andrequiresthat

wecriticallyreconsiderourcurrentmodelsofpreservation.Mid‐centuryarchitecturealso

has difficult associations with, for instance, slum clearance and urban renewal; the

successfulandmeaningfulpreservationofsucharchitecturewillrequirethatwefigureout

how to live with and, more importantly, learn from these histories. Lastly, the building

assembliesofmid‐centuryarchitecturearegenerallymorecomplicatedandvulnerablethan

those of traditional architecture, since they are often thin, have many joints and

connections,andarecomprisedofmultipletypesofmaterials,andtheythereforepresent

significant conservation challenges. Due to all of these factors, the preservation of mid‐

century architecture must be preceded by more complex and nuanced preservation

solutions and a re‐evaluation of preservation philosophy to address its current

shortcomings.

Asapartofthisendeavortopreservemid‐centuryarchitecture,thesignificanceof

architectural precast wall panels must be made visible. This concrete technology is

historicallysignificantbecauseitplayedanimportantroleinforgingaplaceforconcretein

the architecture of this period and ensuring the material’s successful competition with

contemporarymetalandglasscurtainwallsystems.Moreover,as illustratedbytheabove

examples, the variety of architectural expressions achieved with precast wall panels

throughtheuseofdifferentconcretemixes,surfacefinishes,surfacetreatments,andpanel

shapes make this concrete technology architecturally significant as a character‐defining

47

feature of the buildings constructed with it.112To conserve this architectural feature

successfully,however,thetechnicalchallengesofitspreservationmustbeaddressed.

112Character‐defining featuresare those features thatcontribute to thevisualcharacterofabuildingandcan“include theoverall shapeof thebuilding, itsmaterials, craftsmanship,decorativedetails, interior spaces andfeatures, as well as the various aspects of its site and environment” (NPS Preservation Brief #17, 1). If acharacter‐defining feature were altered or demolished, the character of the building would be negativelyaffectedandthebuilding’ssignificanceand/orintegritywouldbecompromised.

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CHAPTER4:LITERATUREREVIEW—PATHOLOGIESANDPRESERVATIONOF

ARCHITECTURALPRECASTWALLPANELS

INTRODUCTION

This chapter presents information about the state of knowledge regarding the

deterioration mechanisms that affect reinforced concrete generally and architectural

precast wall panels specifically, as well as the strategies currently utilized in their

preservation.Significantly, thesestrategiesare fairly limitedanddonot tend toprioritize

themostimportantpartofthisconcretetechnology:thearchitecturalexpressionobtained

throughthespeciallydesignedfacingconcretemixandthesurfacefinishand/ortreatment

appliedtoit.

REINFORCEDCONCRETEPATHOLOGIES

Asareinforcedconcreteassembly,architecturalprecastwallpanelsaresubject to

the pathologies that affect general reinforced concrete, and, therefore, these pathologies

mustbe reviewed.Althoughwell‐designed and executedRC canbe an extremelydurable

material—itsstrengthandperceiveddurabilityweretheprimarycharacteristicsthatmade

it anattractivebuildingmaterial,particularly for industrial and infrastructuralprojects—

theporousnatureofconcrete,thevulnerabilityofthesteelreinforcement,andthetenuous

compatibility between the two inevitably lead to the deterioration of the assembly. The

pathologies that these lead to are influenced by both internal and external factors.113For

example,when considering architectural precast panels, someof the internal factors that

should be considered include type of aggregates used, water‐cement ratio, type of

113BryantMather,“ConcreteDurability,”Cement&ConcreteComposites26(2004):3.

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reinforcement,andcastingmethod.Someoftheexternalfactorsthatshouldbeconsidered

include climate, interior building environment, joints betweenpanels, and connections to

the structural frame. Consequently,when determining the pathologies that affect a given

buildingassembly,itisessentialtoconsidertheexternalenvironment,thecharacteristicsof

theassembly,andthecharacteristicsofthematerialsthemselves.

Themostcommonmechanismofdeteriorationaffectingreinforcedconcreteisthe

corrosion of the internal steel reinforcement, which leads to a loss of material and

structural integrity due to cracking and spalling. Corrosion is an electrochemical process

thatoccursthroughtwoprimaryreactions:theanodicreactionandthecathodicreaction.In

thecaseofsteelreinforcementwithinconcrete,theprocessbeginswiththeanodicreaction,

asthesteeldissolvesintheporewateroftheconcreteandgivesupelectrons.However,to

preserveelectricalneutralityofthesteelreinforcement,theelectronsgivenupduringthe

anodic reaction must be accepted elsewhere on the steel surface; this is the cathodic

reaction,whichoccurs throughareactionwithoxygenandwater.Forcorrosion tooccur,

theflowofelectronsbetweenthesetworeactionsmustbesustainedbythepresenceofan

electrolyte,which, inthiscase, istheporewateroftheconcreteagainstthesurfaceofthe

steelreinforcement.Withtheproductionofcorrosionproducts(rust),thesteelexpandsin

volume,causingcrackingandultimatelyspallingoftheconcretecover.114

Innormalcircumstances,thenecessaryandsufficientfactorsthatmustbepresent

for corrosion to occur are moisture, oxygen, and an electrolyte.115In the case of steel

reinforcement in concrete, however, corrosion cannot occur until the surface of the steel

114John Broomfield, Corrosion of Steel in Concrete:Understanding, Investigation, and Repair (New York, NY:Taylor&Francis,2007),8.115The concept of necessary and sufficient factors was developed by Samuel Harris in his book BuildingPathologies:Deterioration,Diagnostics,andIntervention(2001).Theconceptisthatifallofthesenecessaryandsufficient factorsofacertainpathologyarepresent, then themechanismofdeteriorationwilloccur; ifoneormore necessary and sufficient factor is absent, the mechanism will not occur. This is an extremely helpfulconcept to utilizewhen applying knowledge aboutmechanismsof deteriorations and attempting to diagnoseassociatedpathologies.

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reinforcement isdepassivated.At the timeof construction, thepHof concrete is typically

between 12 and 13.5.116At this pH level, the steel forms “a very thin, protective oxide

knownasapassivelayer,”whichprotectsthereinforcementfromcorrosion.117

There are two primaryways the passive layer is destroyed: carbonation and the

introduction of chloride ions. As mentioned previously, concrete is a porous material

composedofwater, cement, andcoarseand fineaggregates.Whenwaterandcementare

mixed to create thepaste that binds the coarse and fine aggregates, a hydration reaction

occurs, which results in the formation of hydroxides.118As carbon dioxide from the air

penetratestheconcrete,acarbonationreactionoccursbetweenthehydroxideandcarbon

dioxide,resultingintheformationofcarbonatesandthereductionoftheconcrete’spH.119

Asthehydroxideionsnearthesurfacecarbonate,carbondioxidemustpenetratedeeperto

react with available hydroxide ions within the concrete. The furthest depth at which

carbonationhasoccurred is called thecarbonation front,andwhen the carbonation front

reaches the reinforcement, the passive layer breaks down due to the lower pH. The

following diagram illustrates the carbonation of concrete and the resultant deterioration

[Figure23].Theprocessofcarbonationcanbeexpeditedbyfactorssuchasahighwater‐

cement ratio, low cement content, a short curing period, low strength concrete, highly

permeable/porouspaste,andinsufficientreinforcementcover.120

116John Broomfield, “The Identification and Assessment of Defects, Damage and Decay,” inConcreteBuildingPathology,ed.SusanMacdonald(Oxford,UK:BlackwellScienceLtd.,2003),142.117Ibid.118SusanMacdonald,“Introduction”inConcreteBuildingPathology,ed.SusanMacdonald(Oxford,UK:BlackwellScienceLtd.,2003),3.119PortlandCementAssociation,“TypesandCausesofConcreteDeterioration,”IS536,3.120Ibid.,3.

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Figure23.Thisdiagramillustratesonewayinwhichreinforcedconcretecandeteriorate:the

concretecoverbeginstocarbonate,whichultimatelydepassivatesthereinforcementandleads

toitscorrosion.Throughtheprocessofcorrosionandtheproductionofcorrosionproducts,

theconcretecoverbeginstocrackandsubsequentlyspall(diagrambyauthor).

A second cause of reduced alkalinity of concrete and depassivation of the steel

reinforcement’ssurfaceistheintroductionofchlorideionsintotheconcrete.Chloridecan

be introducedtoconcrete indeicingsalts,admixtures thatcontainchloride,andseawater

(in liquidorvapor forms), and the ions travel through thepore structureof the concrete

towards the reinforcement.As thechloride ioncontent reachesa critical thresholdat the

steelreinforcement(approximately0.4%byweightofcement),thepassivelayerisbroken

downandthereinforcementbecomessusceptibletocorrosion.121

Other pathologies that help to enable the corrosion of the internal reinforcement

and/or cause cracking of the concrete cover include the chemical reaction of aggregates,

aggressivechemicalexposure,presenceofbiologicalmatteronthesurfaceoftheconcrete,

and damage resulting from freeze‐thaw cycling. The presence of soluble silicates in the

aggregatecanresultinalkali‐silicareactionsbetweensilicaintheaggregatesandhydroxide

inthecementpaste,whichresultsintheformationofagelthatabsorbsmoisture,expands,

121Broomfield,“TheIdentificationandAssessmentofDefects,DamageandDecay,”144.

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and can lead to the cracking of the concrete cover.122In addition to chloride attack, as

describedabove,concretecanbesubjecttoacidandsulfateattack,amongotherchemicals.

Acidsreactwiththecalciumhydroxidesofthecementpastetoformwater‐solublecalcium

compounds that leach out of the concrete, increasing the porosity of the concrete and

removing latent hydroxides for carbon dioxide to react with.123Sulfates, which can be

introduced through groundwater and soil, reactwith the hydroxides of the cement paste

andresultintheformationofettringite,anexpansivesubstancethatcausescrackingofthe

concrete.124Micro‐biologicalgrowthonthesurfaceoftheconcretecanproduceverystrong

acids that canbotherode thesurfaceof theconcrete,making itvulnerable toweathering

and carbonation, and penetrate the concrete cover, depassivating the reinforcement and

enablingcorrosiontooccur.125

Factors external to the concrete material itself, such as poor detailing, poor

drainage, problematic finishes, inadequate design for actual loadings, and inadequate

maintenance can also exacerbate the pathologies described above. For example, poor

drainagecanleadtotheintroductionofsulfatesthroughgroundwaterandtheformationof

ettringite,andinadequatedesignforactualloadingscanleadtothedevelopmentofinternal

stresses,whichresultsincracksthatexpeditecarbonationandexposethereinforcementto

additional moisture and oxygen. Because external factors such as these can significantly

contribute to the deterioration of RC, they must be identified through surveys and

conditionsassessmentsandtheirinfluencemustbeminimized.

122Ibid.,148.123PCA,“TypesandCausesofConcreteDeterioration,”6.124Broomfield,“TheIdentificationandAssessmentofDefects,DamageandDecay,”149;A.Darimont,“Concrete–Pathology–SecondaryPrecipitations,”MicroscopyResearchandTechniques25(1993):179.125ShipingWei, et. al., “Microbiologically InducedDeterioration of Concrete – A Review,”BrazilianJournalofMicrobiology,44/4(2013):1003.

53

DETERIORATIONOFARCHITECTURALPRECASTWALLPANELS

In addition to the pathologies that affect general reinforced concrete, there are

numerousmechanismsofdeteriorationuniquetoarchitecturalprecastwallpanelsdueto

their composition and the nature of the wall system they comprise. First, there are

importantgeometricconsiderations.Architecturalprecastwallpanelshaveacross‐section

that is much thinner than cast‐in‐place concrete walls. The narrow cross‐section makes

panelsvulnerabletobowinganddistortion,whichcanleadtocrackingandexposureofthe

reinforcement.126Italsoprovideslessconcretecoveroverthepanel’sreinforcement,which

can lead to faster carbonation of the concrete and, subsequently, depassivation of the

reinforcement.127Upon depassivation, the reinforcement becomes susceptible to the

corrosionprocess,whichcanresultinthecrackingoftheconcretecover.Thevulnerability

ofthereinforcementcanbeamplifiedbyaggregatereactionsofthefacingconcrete,suchas

alkali silica reaction, which leads to cracking and easier penetration of carbonation.128

Insufficientormisplacedreinforcementcanalsoleadtocrackingofthepanel.129Moreover,

thethinnercross‐sectionofarchitecturalprecastwallpanelsmakesthemmoresensitiveto

temperaturechangesandresultsintheexpansionandcontractionofthepanel.Ifthispanel

movement is sufficiently restrained, the panel can experience deflection and subsequent

cracking.130

Second,theproductionprocessspecifictoarchitecturalprecastwallpanelscanlead

to the development of cracks in various ways. For example, cracks can develop due to

improper trowelling of the facing concrete during the castingprocess or due to concrete

126R.J.Folic, “ClassificationofDamageand ItsCausesasApplied toPrecastConcreteBuildings,”MaterialsandStructures24(1991):276.127Ibid.,277.128M.A. Ozol and D.O. Dusenberry, “Deterioration of Precast Concrete Panels with Crushed Quartz CoarseAggregateDuetoAlkaliSilicaReaction,”ACISP131‐22DurabilityofConcrete(March1992):412.129Folic,“ClassificationofDamage,”278.130Ibid.

54

shrinkage occurring during the curing process. Themethod of curing—in particular, the

process of steam curing—has also been identified as a cause of cracking.131Architectural

precastwallpanelsmayalsodevelopcrackswhilebeingstrippedfromtheformorduring

handlingandtransportation.132

Third,unlikecast‐in‐placeconcretewalls,architecturalprecastpanelwallsystems

arecharacterizedbyconnections,includingtheseatconnectionofthepanel,thetie‐backto

the structural frame, and connections to control lateral movement, and are bounded by

joints.Jointandconnectionzonesaretheareasofarchitecturalprecastwallpanelsystems

withthelargestnumberofoccurrencesofdamage.133Connectionareasaremadevulnerable

due to factors such as unintended forces introduced into thewall system and accidental

eccentricitiesoccurringduringtheproductionanderectionphases;thesecanoverloadand

weaken the connection material, ultimately leading to connection failures.134If the

connectionmaterialisexposedtomoistureandbeginstocorrode,thevolumetricexpansion

of theconnectioncancompress thematerialof thepanelaround it, resulting in fractures,

chipping, and excessive wall movement.135Corrosion of the connection material is a

particularconcerngiventhat,historically,connectionsweretypicallyfabricatedwithnon‐

corrosionresistantmaterials.Recognitionofthisvulnerabilityledtotheuseofhot‐dipped

galvanized steel connection assemblies, but these too can eventually corrode, especially

whenincontactwithdissimilarmetals,mortar,orconcrete.136

Theperformanceofthejointsandthejointmaterialbetweenarchitecturalprecast

wall panels can also significantly contribute to the deterioration of the panel. If the joint

material deteriorates, the panel’s ability to accommodate differential movement can be131Ibid.,279.132BrianJ.Pashina,“CrackRepairofPrecastConcretePanels,”ConcreteInternational(August1986):24.133Folic,“ClassificationofDamage,”281.134Ibid.,282.135GeorgeL.Maness,“PreventingWallDeterioration,”JournalofPropertyManagement56/5(Sep/Oct1991):35.136Ibid.,36.

55

impededandleadtocrackingandchipping.Deterioratedjointmaterialalsopresentsmore

opportunities for moisture to move along the surface of the panels, which can result in

erosionofthecementpasteand,consequently,increasedconcreteporosity.137Additionally,

deterioration of the jointmaterial allows air andmoisture to penetrate thewall system,

whichcanleadtoproblemsofcondensationonthebacksideofthepanel.138Condensation

can cause discoloration of the panels and corrosion of the connections.139Freeze‐thaw

cycles will also affect condensation and other moisture in the wall system and cause

expansionandcontractionofthepanel,spalling,anddelamination.140

All of these pathologies andmethods of deterioration lead to cracking,which can

irreversiblydamagetheappearanceofarchitecturalprecastwallpanels.Thus, inorderto

protectthedistinguishingexpressivefinishand/ormixofarchitecturalprecastwallpanels,

preservation efforts should attempt to prevent cracking and other deterioration

mechanismsthatdamagetheappearanceofarchitecturalprecastwallpanels.

DETERIORATIONDETECTIONMETHODS

Because deterioration generally occurs from the inside out, it is essential to the

preservation of historic reinforced concrete that we understand the condition of the

concretebelowthesurface.Thereareavarietyofsurveyingstrategiesthatcanbeemployed

to attempt to do this. Unfortunately, surveying is usually only instigated by visible and,

therefore, significant signs of deterioration. Once implemented, however, surveying

techniques can point to areas of incipient deterioration and be used to prevent further

137PaulE.GaudetteandDeborahSlaton,“PreservationofHistoricConcrete,”PreservationBriefs15(Washington,DC:NationalParkService,HeritagePreservationServices,2007):6.138ToddA.Gorrell,“CondensationProblemsinPrecastConcreteCladdingSystemsinColdClimates,”JournalofTestingandEvaluation39/4(2010):1.139Maness,“PreventingWallDeterioration,”34.140Ibid.

56

deterioration. Hammer testing, chain dragging, and impact‐echo testing are used to

determineareasofdelamination,orareasof incipientspalling.Hammertestingandchain

dragging involve listening to the pitch and tone these instruments make when struck

againsttheconcretesurface,whileimpact‐echotestinginvolvesmeasuringthereflectionof

transient pulses between an internal delamination and the exterior of the concrete.141

Carbonation testing assesses the depth of the carbonation front by applying

phenolphthalein to the cross section of core samples taken from the concrete. The

application of Nonlinear Resonant Ultrasound Spectroscopy has also been studied as a

meanstonon‐destructivelydeterminethedepthofthecarbonationfront.142Mappinghalf‐

cell potentials is used to understand where areas of corrosion may be located.143This

techniqueworksbymeasuringtheelectrodepotentialacrossaconcretesurfacerelativetoa

referenceelectrode.Ifthesteelisstillpassive,thepotentialmeasuredwillbesmall(e.g.0to

‐200mV),butifthepassivelayerhasbeencompromised,thepotentialmeasuredwillbea

larger negative number (e.g. > ‐350mV).144Ground (or sound) penetrating radar can be

used to characterize concrete thickness, estimate concrete cover over the reinforcement

and its approximate location, estimate the size of the rebar, and determine locations of

voidsanddelaminations.145

Despite the useful information that can be obtained with these surveying

techniques,theyhavesignificantlimitations.Inadditiontoquestionsabouttheiraccuracy,

almost all of these techniques are often expensive and require a trained professional to

141Linnea M. Linton, “Delamination in Concrete: A Comparison of Two Common Nondestructive TestingMethods.”APTBulletins36/2‐3(2005):22.142F. Bouchaala, et. al., “CarbonationAssessment in Concrete byNonlinearUltrasound,”CementandConcreteResearch41(2011):558.143GaudetteandSlaton,“PreservationofHistoricConcrete,”8.144JohnP.Broomfield,CorrosionofSteelinConcrete:UnderstandingofSteelinConcrete(NewYork,NY:Taylor&Francis,2007),45.145Giovanni Leucci, “Ground Penetrating Radar: An Application to Estimate Volumetric Water Content andReinforcedBarDiameterinConcreteStructures,”JournalofAdvancedConcreteTechnology10(2012):411.

57

execute them. Moreover, they can only show what is presently there and have limited

predictivevalue.Furtherresearchisthereforerequiredtoenhancetheutilityofthesetools.

CURRENTARCHITECTURALPRECASTWALLPANELPRESERVATIONSTRATEGIES

Despite the numerous deterioration mechanisms that can damage architectural

precastwallpanelsandtheenhancedconcernforpreservingtheoriginalmaterial,thereare

few repair or conservation strategies available that specifically address these needs. The

repairandconservationof architecturalprecastpanels relyheavilyoncleaning thepanel

surface, replacing joint sealants, sealing cracks, and patching localized areas of spalling.

Withrespecttopatchinginparticular,workmanshipisextremelyimportanttothesuccess

of the repair and the patch location must be well prepared: any exposed internal

reinforcementmust be cleaned and the concrete surfacemust be prepared to accept the

patchmaterial.146The patchmaterial should be compatible with the original concrete in

characteristicssuchascompressivestrength,modulusofelasticity,andthermalexpansion,

and the characteristicsof thepatchmaterial, suchasbonding strength,permeability, and

drying shrinkage, must be evaluated to ensure a successful patch. When patching

aesthetically significant concrete, the mix of the patching material should be carefully

formulatedtomatchtheappearanceoftheoriginalconcrete;toachieveasuccessfulmatch,

it is imperative to prepare numerous samples and conduct mock‐ups on‐site. Even with

extensive efforts to match the repair’s mix with the original concrete, patches often

stubbornly standout andhaveapropensity to fail prematurely, especially if thematerial

surroundingapatchisvulnerabletothesamedeteriorationthatcausedtheoriginalspall.

146ACICommittee546,GuidetoConcreteRepair(Detroit,MI:AmericanConcreteInstitute,2014).

58

The repair of concrete facades, including architectural precast wall panels, also

oftenincludestheapplicationofaprotectivecoatingtopreventcarbonationandprotectthe

interioroftheconcrete.147Protectivecoatings,however,cangreatlychangetheappearance

of an historic concrete structure and irreversibly alter the original surface finish of the

concrete.

CONSERVATIONSTRATEGIESWITHPOTENTIAL

Therearesomeconservationmethodsthathavethepotentialtomoresuccessfully

preserve the appearance of architectural precast wall panels by attempting to slow and

even reverse the factors that enable corrosion, and therefore cracking, to occur:

impregnationtreatments,electrochemicalrealkalization,andcathodicprotection.Whileall

threeofthesemethodshelppreventfuturecorrosion,vitaltotheirsuccessisthepatching

of any damaged sections of concrete to minimize reinforcement exposure. Additionally,

although all of these treatments can be extremely effective, they are also expensive and

requireexpertiseintheirexecution.148

Impregnation treatments are a conservation method borrowed from the

conservation of stone. The treatment involves applying a chemical formulation to the

surface of the reinforced concrete and allowing the formulation to penetrate the cross

section of the concrete through the material’s pore network. 149 The objective of

impregnation treatments as applied to reinforced concrete is to “[reduce] the materials

porosity close to the reinforcement, in order to improve its pull‐out strength and

behavior…[andreduce]thematerialsporosityandpermeability, inorderto improvetheir147DavidReid‐SimmsandJohnKeble,“FaçadeConcreteRepairstoUK’sDecentHomesStandard,”Concrete42/1(Feb2008):32;DamianMeyers,“FaceLiftforCarPark,”Concrete40/5(June2006):37.148GaudetteandSlaton,“PreservationofHistoricConcrete,”15.149Elisa Franzoni, et. al., “Improvement of Historic Reinforced Concrete/Mortars by Impregnation andElectrochemicalMethods,”Cement&ConcreteComposites49(2014):51.

59

resistance to aggressive agents,” such as chloride ions and additional carbonation.150

Franzoni,et.al.,testedtheeffectivenessofimpregnatingreinforcedconcretewithasolution

ofethylsilicateinorganicsolvent,aformulationusedintheconsolidationofhistoricstone,

andfoundthatthetreatmentwaseffectiveinbothreducingtheconcrete’ssusceptibilityto

carbonation and improving the corrosion resistance of the internal reinforcement.151

Significantly,theefficacyofthetreatmentwasfoundtoincreasewithmoreporousconcrete

because the treatment could impregnate thematerialmore thoroughly. Impregnationhas

beenusedintheconservationofarchitecturalconcretebecauseitdoesnotchangethecolor

ofor forma filmon thesurfaceof theconcrete,butmoreresearchmustbeconducted to

understandhowthistreatmentaffectsdifferentsurfacefinishesand/ortreatments.152

CathodicprotectionisamethodbywhichthesteelreinforcementinRCisprotected

from further corrosion: through the introduction of a superficial source of electrons, the

anodic reaction on the reinforcement ceases. There are two types of cathodic protection

systems: the impressed current system and the sacrificial anode system. The impressed

currentsystemisanactivesystemthatworksby“passingasmalldirectcurrent(DC)froma

permanent anode on top of or fixed into the concrete to the reinforcement.”153The

sacrificialanodesystemisapassivesystemthatisusedlessoftenandinvolvesconnecting

thesteelreinforcementtoalessnoble,orsacrificial,metalonwhichtheanodicreactionwill

occur, with the result that the secondary metal corrodes rather than the steel.154While

these methods of cathodic protection can be extremely effective at slowing the rate of

corrosion, they have distinct disadvantages. The impressed current system requires an

150Ibid.,57.151Ibid.,58.152SaijaVarjonen,JussiMattila,JukkaLahdensivu,andMattiPentti,“ConservationandMaintenanceofConcreteFacades: Technical Possibilities and Restrictions,” Research Report 136 (Tampere University of Technology:InstituteofStructuralEngineering,2006):15.153Broomfield,CorrosionofSteelinConcrete,141.154Ibid.,144.

60

immense amount of monitoring, adjustment, and maintenance to ensure long‐term

protectionandisveryexpensivetoinstall.155Thesacrificialanodesystemislessexpensive,

buttheanodemustbereplacedwheneveritisdepletedfromtheanodicreactioninorder

for the treatment to remain effective. Thus, both systems of cathodic protection are

permanent,oftenaltertheappearanceofthebuilding,andmustthemselvesbemaintained

to ensure successful protection of the reinforced concrete. Radaelli, et. al., studied the

effectiveness of installing a cathodic protection system on slender carbonated concrete

elements using a few localized galvanic anodes.156The study examined this particular

method as a way of protecting corroding reinforcement in situations where the

preservationof theoriginalsurface, shape,andmaterial is important,but they foundthat

thecostsofthissystemwereprohibitivelyexpensivetobeusedpreventively,althoughthe

system has the potential to be used “where and when corrosion has initiated and

propagatesduetocarbonation.”157

Electrochemical realkalization is a technique that aims to restore the alkalinity of

carbonatedreinforcedconcretetoreinstatetheprotectivepassivelayeraroundtheinternal

reinforcement. This objective is achieved by either soaking the concrete in an alkaline

solution or by applying an external current to the steel reinforcement by way of a

temporaryanodesystem,whichisplacedonthesurfaceoftheconcrete.158Unlikecathodic

protection, electrochemical realkalization using an external current is a temporary

treatment technique and does not affect the surface of the concrete after the treatment

155GaudetteandSlaton,“PreservationofHistoricConcrete,”15.156ElenaRedaelli,et.al., “CathodicProtectionwithLocalisedGalvanicAnodes inSlenderCarbonatedConcreteElements,”MaterialsandStructures47(2014):1839.157Ibid.,1854.158Ibid.;LucaBertolini,MaddalenaCarsana,andElenaRedaelli,“ConservationofHistoricalReinforcedConcreteStructuresDamagedbyCarbonationInducedCorrosionbyMeansofElectrochemicalRealkalisation,”JournalofCulturalHeritage9(2008):377.

61

apparatusisremoved.159Nevertheless,thisisalsoanexpensiveandcomplexconservation

method and has only been used sporadically in the conservation of architectural

concrete.160

Although all of the preservation strategies described above can help to reduce

futuredeteriorationand repairdamage thathasoccurred, their implementationhasbeen

reactiveinnature.Thus,theydonotpreventorslowdowntherateofdeteriorationbefore

damage has occurred. Adopting an approach that predicts and prevents deterioration,

ratherthanreactstoit,willultimatelypreservearchitecturalprecastwallpanelsthemost

successfully.

TOWARDSAPREVENTIVECONSERVATIONAPPROACH

Preventiveconservation isanapproachtoconservationbasedon identifyingways

topreventorslowdowndeterioration.Typically,conservationandrestorationcampaigns

are enacted in reaction to significant deterioration that necessitates large conservation

efforts to save the object or structure. Such conservation and restoration campaigns are

expensive, and, by delaying action until deterioration is so severe as to require large

conservationcampaigns,thereisagreatriskoflosingoriginalfabricandintegrity.

The concept of preventive conservation as a distinct approach to preservation is

fairlynew: publications about this approachbegan to appear in the late 1980s and early

1990s. This approach has been most frequently applied to the preservation of object

collections in museums, although it has been slowly gaining popularity in building

preservation.Inthearenaofobjectcollections,preventiveconservationreliesontheability

to control the environment inwhich the objects are located to attain the perfect balance

159Ibid.160Varjonen,et.al.,“ConservationandMaintenanceofConcreteFacades,”16.

62

betweentemperature,relativehumidity, lightexposure,etc.161Inthisway,variousthreats

caused by an imbalance of the above factors can be minimized and the mechanisms of

deterioration can be better predicted. For buildings, however, utilizing a preventive

conservation approach is extremely complex and relies on systems thinking to try to

understandhowallof thepotentialmechanismsofdeteriorationand theirnecessaryand

sufficientfactorsrelate.162Tobegintounderstandabuildingasasystem,thecomponentsof

the building and the factors that affect it must be understood; the condition of these

componentsmustthenbeassessedandultimatelymonitoredtobegintopredictthreats.163

Forthisreason,preventiveconservationasappliedtobuildingsisoftenaboutmaintenance.

Unfortunately, many building stewards often minimize regularmaintenance due to tight

budgetsandtheinabilitytoseethebenefitsofmaintenanceoverashortperiodoftime.164

In contrast, large preservation campaigns appear to be more important and gratifying

despite their expense and the fact that they put the historic fabric of the building in

jeopardy.165

Nevertheless,apreventiveconservationapproachisthemosteffectiveapproachfor

preserving architectural precast wall panels because of their important architectural

expression and the way they generally deteriorate from the inside out. The successful

preservation of buildings constructed with this concrete technology requires an

understanding of concrete pathologies in general coupled with an understanding of the

building’s context and history in order to begin to predict potential mechanisms of

161JeffreyLevin,“PreventiveConservation,”TheGettyConservationInstituteNewsletter7/1(Spring1992):1.162Robert Waller and Stefan Michalski, “Effective Preservation: From Reaction to Prevention,” The GettyConservationInstituteNewsletter19/1(Spring2004):8.163Hugo Entradas Silva and Fernando M.A. Henriques, “Preventive Conservation of Historic Buildings inTemperate Climates. The Importance of a Risk‐Based Analysis on the Decision‐Making Process,” EnergyandBuildings107(2015):26.164Nigel Dann and Timothy Cantell, “Maintenance: From Philosophy to Practice,” Journal of ArchitecturalConservation11/1(2005):42;JeffreyLevin,“PreventiveConservation,”2.165Levin,“PreventiveConservation,”2.

63

deterioration. Such predictions should be accompanied by conditions assessments and

monitoring,aswellasamaintenance/conservationplanthataimstopreventdeterioration

fromoccurring—keeping thenecessary and sufficient factors formechanisms to occur at

bay.Minimalresearchhasbeenperformedontheapplicabilityofpreventiveconservation

plans to historic concrete structures in general. However, Chew et. al. proposes a

methodology for evaluating curtain wall and cladding facades, which could be generally

applied tobuildingsconstructedwitharchitecturalprecastwallpanels.Thismethodology

provides a framework to aid in identifying technical risk factors associated with design,

building profile, environment and usage, construction quality, maintenance quality, and

customersatisfaction.166Utilizingsuchanevaluationmethodologyforregularinspectionof

historic concrete structures, in conjunction with the use of nondestructive evaluation

techniquesandmonitoring,asexploredbyGoncalvesinherthesis“CorrosionPreventionin

Historic Concrete: Monitoring the Richards Medical Laboratory,” can greatly enhance a

building steward’s ability to predict and prevent deterioration.167Indeed, the successful

preservation of all historic concrete structures is dependent upon our ability to predict

problems.

By adapting Jeffrey Levin’s framework for preventive conservation of object

collections, the essential stages of developing preventive conservation plans can be

identified as 1) identifying possible threats to the structure, 2) substantiating the risk of

these threats toprioritize them,3) identifyingcost‐efficientmeans tomeasure theriskof

thesethreats,and4)developingmethodstoreduceoreliminatetheriskofthesethreats.168

In essence, this thesis contributes to the first stage of this framework by identifying

166M.Y.LChew,S.S.Tan,andK.H.Kang,“ATechnicalEvaluationIndexforCurtainWallandCladdingFacades,”StructuralSurvey22/4(2004):211.167Ana Paula A Gonçalves, “Corrosion Prevention in Historic Concrete: Monitoring the Richards MedicalLaboratory,”UniversityofPennsylvaniaMaster’sThesis(1January2011),14.168Levin,“PreventiveConservation,”3.

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potential threats to architectural precast wall panels and predicting deterioration. It is

importanttonote,however,thatthethreatsidentifiedinthisthesis,whicharederivedfrom

anevaluationofpastrecommendedpracticesandothertechnicaldocuments,mustalsobe

accompanied by a thorough investigation of the specific building in question and its

environmenttocreateacomprehensiveunderstandingofthebuildingasasystem.

CONCLUSION

Architecturalprecastwallpanels are subject to a variety ofpathologies, including

those that occur in general reinforced concrete and those that arise from the unique

compositionofthisconcretetechnology.Becauseofthesignificantappearanceanddesign

ofarchitecturalprecastwallpanels, thecurrentreactiveconservationstrategiesofsealing

and patching damaged architectural precastwall panels are inadequate and result in the

loss of original fabric,which reduces the integrity of the architecture anddiminishes the

evidenceofthisimportantconcretetechnology.Instead,effortsshouldbemadetopredict

andpreventdeteriorationratherthanrespondtoit.Tosuccessfullypredictandslowdown

the deterioration of architectural precast wall panels, the factors thatmay contribute to

theirdeteriorationmustbeidentified.Asthefirststepinthisprocess,wemustunderstand

thetechnologicalevolutionofarchitecturalprecastwallpanels.

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CHAPTER5:TECHNOLOGICALEVOLUTIONOFARCHITECTURALPRECASTWALL

PANELS,1945‐1975

INTRODUCTION

Beginningintheearlytwentiethcentury,thetrendtowardsstandardizationofthe

building industry resulted in thepublicationof standards and guidance to ensure quality

and competitiveness in the production of building materials. Although the impetus for

standardizationofthebuildingindustryintheUnitedStateswasthedevelopmentofmetals,

standardizationofallbuildingmaterialsbecame imperativewith theendofWorldWar II

and the construction boom that followed.169Recommended practices and other technical

documents that were published to inform the design, production, and assembly of

architectural precast wall panels between 1945 and 1975 provides us with valuable

informationaboutthisconcretetechnologyanditstechnologicalevolution.

Reviewingtheindustryliteraturereveals,however,thatthroughoutthisthirty‐year

periodtheindustrywashesitanttomakespecificrecommendationsorestablishstandards

outofdeferencetothejudgmentandexperienceofindividualprecasters.Thesignificance

ofprecasters’ artistic contribution in thedesignof the concretemix and the executionof

finishes and surface treatments was greatly appreciated, and it was recognized that

“attempts todefine this intangiblepropertyofworkmanship [could] result in restrictions

that prohibit the manufacturer from using a process that offers the best possibilities of

success.”170For this reason, recommendations and guidance about topics such asmixing,

casting, finishesandsurfacetreatments,andformworkaremorelimitedincomparisonto

guidance about design objectives,material selection, reinforcement, handling, connection

169Tomlan,“BuildingModernAmerica,”9.170LeabuandAdams, “Fabrication,HandlingandErectionofPrecastConcreteWallPanels,”ACIJournal (April1970):313.

66

design and materials, and joint design and materials. The variability resulting from the

judgment and experience of the individual precasters, aswell as the limited information

aboutparticular areasof theproductionprocess,makes thepreservation of architectural

precastwall panelsmore difficult. Analyzing the documents that resulted from this push

towardsstandardization is all themore important,however,because theyhelp toconvey

thestateofandchangesinknowledgeacrossthistimeperiod,therebyprovidinginvaluable

informationtobeusedinthepreservationofthisconcretetechnology.

Themajority of the documents consulted from this periodwerepublishedby the

AmericanConcreteInstitute(ACI)andconveyACI’sdedicationtothisconcretetechnology.

Specifically, the vast majority of the documents were published by ACI Committee 533,

whichwas founded in 1964 andwas dedicated to “supplement[ing] existing information

with those practices and methods peculiar to precast concrete wall panels.”171Several

documents were also published by the Precast/Prestressed Concrete Institute (PCI), but

these documents are from after 1966 when PCI started its own committee, the Plant

Production of Architectural Precast Concrete Products Committee, which aimed to

contribute to the improvement and standardization of the architectural precast industry.

Finally,thePortlandCementAssociation(PCA)publishedaselectfewdocumentsdedicated

to the production and assembly of architectural precast wall panels. By analyzing these

documents tounderstand the technologicalevolutionofarchitecturalprecastwallpanels,

wecanbegintoconsiderthewaysinwhichthisconcretetechnologymaybevulnerable.It

shouldberemembered,however,thatthissurveyisnotexhaustiveandthevulnerabilities

drawnfromitarenotexclusivebutratherprovideathoroughstartingpoint.

Importantsubjectstoconsiderintheevolutionofarchitecturalprecastwallpanels

include design objectives, thematerials used, the form design andmaterials,methods of

171Ibid.,312.

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casting and consolidation, type and placement of reinforcement, curingmethods, surface

finishesandtreatments,strippingfromtheform,storage,transporttotheconstructionsite,

handling and erection, connection design and materials, joint design and materials, and

cleaning, repairs, and coatings. Exploring the issues associatedwith testing architectural

precastwall panels, improving their thermal value, preventing bowing andwarping, and

preventing damage to the panel appearance during production and assembly are also

significanttoourunderstandingofthisconcretetechnology.

PRECAST’SPOTENTIAL:1945‐1950

Between 1945 and 1950, the only article published by ACI that discussed

architectural precast wall panels was written by A.C. Grafflin in 1948. Promoting the

productionofprecastbuildingelements,includingarchitecturalprecastwallpanels,Grafflin

emphasizedtheuseofprecastasawaytostandardize,simplify,andmechanizeconcrete’s

role inthebuildingindustry.172Tofurtherpromotetheuseof“cementstone”(thetermhe

applied toprecast concrete,perhaps to smooth the transition from theuseof cast stone)

Grafflin compared this method of concrete construction to its competitor, steel

construction.Heclaimedthatthecostofconstructionwithcementstonewascomparableto

non‐fireproofed structural steel and “at least 20 percent less than steel fire‐proofed, or

poured‐in‐place concrete.”173This single article did not, however, provide any technical

information about the production and assembly of architectural precast wall panels,

therebyillustratingtheindustry’slimitedinterestinthistechnologybefore1950.

172A.C. Grafflin, “Cementstone Precast Construction,” Journal of the American Concrete Institute (November1948):193.173Ibid.,202.

68

1950‐1965:PRE‐ACISYMPOSIUM

Beginninginthe1950s,publicationsabouttheproduction,design,andassemblyof

architecturalprecastwallpanelsbegantoappearwithmoreregularity.Between1950and

1965,themajorityofthearticleswerepublishedbyACIandwrittenbythemenwhowould

formACI’sCommittee533in1964.ACI’sincreasedattentiontothistechnologyconveysthe

concreteindustry’sgrowinginterestindevelopingandstandardizingarchitecturalprecast

wall panels. This growing interest is also reflected by the Portland Cement Association’s

1954publicationspecificallyaboutprecastwallpanelsandthepublicationofthe1958book

TheContemporaryCurtainWallbyWilliamDudleyHunt,whichexaminesthepropertiesand

significance of curtain wall systems and the materials they are made of, including

architecturalprecastwallpanels.

Many of the general problems in the design, production, and assembly of

architecturalprecastwallpanelswere identified in theseearlypublications.Forexample,

the challengeof optimizing the size of thepanel simultaneously to reduce thenumberof

joints but also to accommodate contemporary handling equipment and transportation

methodswasestablishedasasignificantdesignconsiderationinthe1950s.Smallerpanels

hadtheadvantagesofbeingeasilyhandledandkeepinglateralmovementwithinacceptable

limits,whichVictorLeabu,oneoftheleadingmembersofACICommittee533,highlighted

asbeinga significantdesignconsideration to improvepanelperformanceand reduce the

potential for deflection and cracking.174Larger panels, however, had distinct economic

advantages,suchasrequiringfewerjointsandfewerhandlingactions,whichledtoatrend

174Victor F. Leabu, “Problems and Performance of Precast Concrete Wall Panels,” Journal of the AmericanConcreteInstitute(October1959):287.

69

throughout thisperiodtowardstheiruse; later improvements inhandlingequipmentand

therisinguseoflightweightaggregateshelpedtoenablethisdevelopment.175

By the 1960s, durability became a primary concern in the design of architectural

precast wall panels. In 1964, ACI Committee 533 recommended that the facing concrete

have a compressive strength of at least 5000 psi at 28 days to ensure the panel’s

durability.176The Committee also recommended the introduction of air entrainment into

thepanel’sconcretemixtoimprovedurability,althoughaspecificfixedaircontentwasnot

recommendeddue to thevarietyofmixesused in theproductionof architecturalprecast

panels.177

Many of the publications from this period offered guidance about how to reduce

crackingduringtheproductionprocessandinstorage.Forinstance,toimprovethequality

of thepanelsbefore their storage in theyard, and, consequently, to reducecracking,PCA

promoted the use of steam curing, the removal of excesswater by vacuum from thewet

concrete,ortheapplicationofcuringcompounds.178Inthissamepublication,PCAclaimed

that broom or swirl finishes helped to reduce surface cracking.179To enable earlier

strippingandreducecrackingresultingfromthisprocess,bothPCAandACICommittee533

promoted the use of high strength concrete.180The use of high strength concrete also

resulted in themore reliable reuse of the panel forms,which then increased production

efficiency.Finally,PCAemphasizedtheimportanceofevenlydistributingstressesduringall

handlingactionstoreducecracking.181

175Thomas S. Gilbane, “Precast Concrete Panel Multistory Construction,” Journal of the American ConcreteInstitute(May1950):730.176J.A.Hanson,“TestsforPrecastWallPanels,”JournaloftheAmericanConcreteInstitute(April1964):377.177Ibid.,378.178“PrecastConcrete:WallPanels,”PCA,12.179Ibid.,15.180Ibid.,12;Hanson,“TestsforPrecastWallPanels,”376.181“PrecastConcrete:WallPanels,”PCA,12

70

As early as the 1950s, publications recognized the problem of variations in color

betweenadjacentpanelsanddiscolorationofindividualpanels.Toreducesuchvariations,

Leabu recommended in his 1959 publication that the production of panels should be as

consistent as possible, including using cement and aggregates from the same sources

throughoutagivenproject.Healsosuggestedthatmeasuresshouldbetakeninthefieldto

minimizeshadevariations,suchasmatchingindividualpanelsbeforeerection.182

During this period, much attention was already being given to the design of

connections.Inits1954publication,PCAestablishedconnectiondesignfundamentals:they

mustbefireresistant,enabletheaccuratealignmentofthepanels,beprotectedtoprevent

corrosion, accommodate lateralmovement, andaccommodate thedeadand live loads for

which the panels were designed.183To achieve these objectives, the connection material

mustbeductileandstrong.184Theplacementofconnectionassemblieswasalsoaconcern,

withclaimsthatanchorinsertsinthefaceofthepanelscouldmarthesurfaceandshould,

therefore,beavoided.185Still,theunderstandingoftheproblemsassociatedwithconnection

assemblieswas limited. For example,protecting connections toprevent corrosionmerely

meant protecting them from the atmosphere,without consideration of the importance of

moisture and vapor penetrating the wall system. Similarly, welded connections were

perceived as unproblematic, although this perception changed considerably with

experience.186

Thesignificanceofjointstothesuccessofarchitecturalprecastwallpanelsystems

wasalsoemphasizedduringthisperiod.Intheir1962publication,W.HowardGerfenand

John R. Anderson stressed the importance of designing joints to accommodate the

182Leabu,“ProblemsandPerformanceofPrecastConcreteWallPanels,”289.183“PrecastConcrete:WallPanels,”PCA,8‐12.184Leabu,“ProblemsandPerformanceofPrecastConcreteWallPanels,”297.185“PrecastConcrete:WallPanels,”PCA,12.186Ibid.,10.

71

movementofthepanelscausedbytheirexpansionandcontractiontoavoidjointfailure.187

Additionally, theyhighlighted the role of joints in preventingwater frompenetrating the

wallsystem,promotingdesignsthatcreatedmoreconvolutedpathsforwatertotravelover

square‐endedpanels[Figure24].188

Figure24.Detailofajointthatconvolutesthepathwatermusttraveltopenetratethewall

system.189

By1964,theproblemoftestingarchitecturalprecastwallpanelsbecameapparent,

withtheresultthatthenewlyformedACICommittee533dedicatedanentirearticletothis

topic.Atthetime,therewerenotestsspecifictoarchitecturalprecastwallpanelsandtheir

performance, so a variety of tests for reinforced concrete were adapted to this specific

187W. Howard Gerfen and John R. Anderson, “Joinery of Precast Concrete,” Journalof theAmericanConcreteInstitute(October1962):1435.188Ibid.,1437.189Photocourtesyof:GerfenandAnderson,“JoineryofPrecastConcrete,”1436.

72

concretetechnology;these,however, ledtoinconsistentandevencontradictoryresults.190

To complicate matters further, the variety of panel types and concrete mixes made

prescribed testsproblematic. Inanattempt toovercome thesechallenges,ACICommittee

533proposedsimple,basictestsbywhichthequalityanddurabilityofarchitecturalprecast

wall panels could bemeasured.191These testsmeasured the compressive strength of the

concrete, which was used as a measure of the panel’s durability, and Committee 533

recommendedtheuseof6x12in.cylinderor4in.cubesamples.The4in.cubesamplesize

deviated from the cube sample size of 2 in. used in the testing of normal structural

reinforced concrete to accommodate the large coarse aggregate in the facing concrete.192

ACICommittee533recognized,however, that thesecompressivestrengthtestscouldstill

provideunreliableresultsandthereforepromotedcore testsof theactualconcrete in the

panel as the most dependable test.193Tests for freeze‐thaw were seen as unnecessary

because of the vertical position of the panels in thewall system,whichwas inaccurately

thought to sufficiently protect the panels from becoming saturated and susceptible to

freeze‐thawdamage.194

Theimportanceofimprovingthethermalvalueofarchitecturalprecastwallpanels

toremaincompetitivewithmetalandglasscurtainwallswasestablishedduringtheperiod

between1950and1965.Thedevelopmentofsandwichpanels,aswellaspanelsmadeof

lightweightconcrete,aimedtoenhancethethermalvalueofprecastpanels.195Inhis1959

article, Leabu acknowledged some of the problems in sandwich panels that had to be

resolvedfortheirfuturesuccess,includingthethermalbridgescreatedbytheribsandsolid

190Hanson,“TestsforPrecastWallPanels,”370.191Ibid.192Ibid.,372.193Ibid.,375.194Ibid.,376.195Leabu,“ProblemsandPerformanceofPrecastConcreteWallPanels,”288.

73

concretesectionsconnectingtheouterwythesofconcreteandthecondensationcausedby

thetemperaturegradientsenabledbythepaneldesign[Figure25].196

Figure25.Temperaturegradientthroughdifferenttypesofpanels.197

Relatedly, Leabu quickly identified bowing andwarping as a problemwithmany

precastpanels,especiallysandwichpanels.198Hehighlightedsomeofthecausesofbowing

andwarping,suchasthetemperatureandmoisturedifferentialsacrossthecross‐sectionof

thepanelandcuringshrinkage,whichwasthoughttobeexacerbatedbycastingpanelsina

flat, horizontal position since this causes uneven curing and evaporation of moisture

throughoutthedepthofthepanel.199

196Ibid.,297;“PrecastConcrete:WallPanels,”PCA,9.197Photocourtesyof:Leabu,“ProblemsandPerformanceofPrecastConcreteWallPanels,”292.198Ibid.,291.199Ibid.,296.

74

Many topicswere given almostnoattentionduring theperiodbetween1950and

1965. For instance, there was no discussion about the mixing of the facing and backup

concrete,thedesignofandmaterialusedforthepanelformwork,andmethodsofcasting,

producing particular surface finishes and surface treatments, storage, or handling and

erection. Minimal attention was granted to the type, placement, or cover of panel

reinforcement,whichwasgenerallyplacedattheinterfacebetweenthefacingconcreteand

backup concrete during casting. One article from 1950 revealed a concern for corrosion

protectionofreinforcement inthinprecastconcretesections,althoughthisstudywasnot

specific to architectural precast panels. The study, which was inspired by the Navy’s

extensive use of precast technology in the construction of its warehouses, attempted to

identifythecorrosionrateofsteelreinforcement inthinprecastconcretesections,but its

resultscouldnotestablishafunctionalrelationshipbetweenthecross‐sectionalareaofthe

reinforcement and the rateof corrosion.200These gaps inknowledgebegan tobe filled in

withthemostcomprehensivepublicationonarchitecturalprecastwallpanelstodate:the

1965ACISymposium.

1965ACISYMPOSIUM

In 1965, ACI Committee 533 hosted a symposium focused on the subject of

architecturalprecastwallpanels.TheSymposiumandthepublicationsthatresultedfromit

providedanimmenseamountofinformationaboutthedesign,production,andassemblyof

thisconcretetechnologythatwouldultimatelyspiketheinterestoftheconcreteindustry.

Committee 533 presented information focused onmaterials and tests; design trends and

standards; themanufacturingprocess; bowing,warpage, andmovement; and the flexural

200D.H.Pletta,E.F.Massie,andH.S.Robins,“CorrosionProtectionofThinPrecastConcreteSections,”JournaloftheAmericanConcreteInstitute(March1950):525.

75

stiffness of sandwich panels. To provide context, Committee 533 also presented a brief

historicalreviewoftheuseofarchitecturalprecastwallpanelsandacommentaryontheir

use in mid‐century architecture. Reviewing these documents reveals how the industry

aimed to improve this concrete technology to ensure its sustained use in mid‐century

architecture.

DesignObjectives

The 1965 Symposium reiterated the precast panel industry’s reliance on the

experience and judgment of precasters and the difficulty of establishing a standardized

design practice or recommended design guide, but it also acknowledged the need to

standardizetheindustrytoensurequality.201Duringthe1965Symposium,ACICommittee

533 highlighted the major quality aspects that must be achieved, including good

consolidation, high strength, low moisture absorption, a pleasing appearance, and

resistance to freeze‐thawdamage.202To attain this quality, Committee 533 presented the

followingpreliminarydesignrecommendations:

Panel design should consider concrete shrinkage, temperature differential, creep,

prestressing,handlinganderectionloads,andeccentricloadswhennecessary;

Theeffective section for thedifferent typesofpanelsmustbedefined to facilitate

calculations;

Theheighttothicknessratioshouldbelessthanorequalto50toavoidbuckling;

201Leabu,“PrecastConcreteWallPanels:DesignTrendsandStandards,”31.202Phillip W. Gutmann, “Precast Concrete Wall Panels: Manufacturing Processes,” Symposium on PrecastConcreteWallPanels,ACIPublicationSP‐11(1965),52.

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Allowable deflection should be less than h/240 and no greater than ¾ in. (as

opposedtothestandardh/360forotherstructuralmembers);and,

The clear distance between lateral supports should not exceed 32 times the least

widthofthecompressionflangeoreffectivepanelthickness.

MaterialSelection

Forthefirsttime,ACIrecommendedspecificmaterialstobeusedintheproduction

ofarchitecturalprecastwallpanels, includingwhiteorgrayportlandcement(Types I, IA,

III, or IIIA), normalweight or lightweight structural aggregate (withmaximumaggregate

sizenotexceeding¾in),andairentrainmenttoimprovethedurabilityofthepanels.203For

the facing concrete, which can be composed with aggregates such as limestone, quartz,

marble, granite, glass, and ceramics, Committee 533 made particular recommendations.

First,tomaximizeeconomyofproduction,thefacingconcreteshouldonlybethickenough

topreventthebackupconcretefromshowing.Second,thefacingaggregateshouldbegap‐

gradedtoobtainthedesiredaestheticforexposedaggregate finishes—arecommendation

resulting from the extensive experimentation of the Earley studio.204Third, hard, durable

aggregates with service records should be used to avoid alkali reactivity and similar

problems.Finally, the recommendedminimum5000psi compressive strengthat28days

remainedfromearlierarticles,withtheadditionthatfacingconcreteshouldcontain6bags

ofcementpercubicyardofconcrete formaximumdensityandminimumpermeability.205

For thebackupconcrete,bycontrast,Committee533recommendedaminimum4000psi

compressivestrength,arecommendationfirstpresentedinthe1965Symposium,although

203J.A.HansonandD.P. Jenny, “PrecastConcretePanels:MaterialsandTests,”SymposiumonPrecastConcreteWallPanels,ACIPublicationSP‐11(1965),21.204Cellini,“TheDevelopmentofPrecastExposedAggregateConcreteCladding,”52.205HansonandJenny,“PrecastConcretePanels:MaterialsandTests,”23.

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they also cautioned that the properties of the backup concrete should be comparable to

thoseofthefacingconcretetominimizetheeffectsofdifferentialproperties.206Despitethe

higherstrengthrequirement,thefacingconcretemixtendedtohaveahigherslump(4to6

in.)toachieveworkabilityforplacement,whilethebackupconcretewasdriertoabsorbthe

excesswaterfromthefacingconcretemix.207

ACI Committee 533 also presented information about the use of admixtures. To

attainhighearlystrengths,Committee533recommendedusingTypeIIIcementandagood

curingmethodinsteadofacceleratingadmixtures.TheCommitteedidnotrecommendthe

useofretardingadmixtures,whilewater‐reducingadmixturescouldbeusedtoreducethe

water content of the facing concrete while maintaining a high level of workability.208

Pigmentscouldbeaddedtoobtaincoloredconcrete,butCommittee533recommendedthat

thepigmentcontentbelimitedto5%,forcontentsoverthisvaluedidnotintensifythecolor

further.209Moreover,pigments shouldbeadded to the cement in thedry state andmixed

withwhitecementstoattainmorevibrantcolors.

ReinforcementDesignandMaterials

Recommendationsaboutreinforcementwerenotintroducedintopublicationsuntil

the1965Symposium.TheinformationpresentedintheSymposiumrevealedthatavariety

of types of reinforcement were already used in precast panels, including structural,

intermediate,andhighstrengthdeformedbars;blackorgalvanizedwirefabricwithawide

variety of mesh spacings and wire gages, and the recent development of mesh with

206Ibid.,21.207Ibid.,23.208Ibid.,24.209Ibid.,25.

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deformed wire.210The Symposium highlighted that the precast industry relied on the

“MinimumRequirementsforThin‐SectionPrecastConcreteConstruction”(ACI525‐63)for

reinforcementplacementandcoverrequirements.211Fromthispublication,whichwasnot

architecturalprecastpanelspecific,theminimumcoverforreinforcementwas3/8in.,and

forpanelslessthan3in.thick,2x2wiremeshwasrecommended[Figure26].212Galvanized

meshwasrecommendedforminimumcover,butforcoversgreaterthan¾in.,galvanized

reinforcementwasdeemedunnecessary.

Figure26.Aprecasterlayingwiremeshreinforcementontoaprecastpanelbeforeapplying

thebackupconcrete.213

210Ibid.211Ibid.212At this time, the recommended concrete cover for beams and girderswas 1½ in, according to the 1963BuildingCodeRequirementsforReinforcedConcrete.213Photocourtesyof:Gutmann,“PrecastConcreteWallPanels:ManufacturingProcesses,”50.

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FormDesignandMaterials

Information about formwork for architectural precast wall panel materials and

design was also first presented in depth at the 1965 Symposium. Good formwork was

stressed as being essential to the quality of the panel, and the choice ofmaterial should

considercost,maintenance,re‐use,detail,andsalvageabilityoftheform.214Theformdesign

was dependent upon draft allowances, desired panel texture, consolidation techniques,

mass production schedules, and locally available talent.215Commonmaterials used at the

timeoftheSymposiumincludedconcrete,wood,andsteel.Concreteasaformmaterialwas

gainingpopularitybecauseitcouldaccommodatenumerousreusesandhadminimaljoints,

which could produce undesirable results and remained a problem with wood and steel

forms.216Polyester resins reinforcedwith glass fiberwere also becoming amorepopular

formmaterial.

ACICommittee533discussedtheuseofformlinerstoachievevariouspatternsand

textureson the surfaceof theprecastpanel. Commonmaterials included rubbermatting,

wood,vacuum‐formedplasticsheets,andpolyethylenefilmlaidoveruniformlydistributed

cobblestone[Figure27].217TheCommitteecautionedthatwoodlinersneededtobesealed

topreventexcessivelossofmoisturefromthefacingconcrete,andarchitectsandengineers

wereremindedthatglossy‐surfaceconcreteshouldnotbeexposedtotheexterior.

214HansonandJenny,“PrecastConcretePanels:MaterialsandTests,”26.215Gutmann,“PrecastConcreteWallPanels:ManufacturingProcesses,”48.216Geoffrey A. Collens, “Precast Concrete Wall Panels: Architectural Commentary,” Symposium on PrecastConcreteWallPanels,ACIPublicationSP‐11(1965),116.217HansonandJenny,“PrecastConcretePanels:MaterialsandTests,”27.

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Figure27.Imagesofdifferenttexturesthatcanbeachievedwiththeuseofformliners.218

CastingandConsolidation

At the 1965 Symposium, ACI Committee 533 explained that the most popular

methodof casting architectural precastwall panelswas in a horizontal positionwith the

facingconcretepouredfirst,followedbythebackupconcrete,thesamemethoddeveloped

bytheEarleyStudio.TheCommitteealsorecognizedalternativemethods,suchaspouring

thefacingconcreteontopofthebackupconcrete,whichwasthepreferredcastingmethod

for panels finished with a broom.219To achieve a specific architectural expression, the

decorative aggregate of the facing concrete may be placed first, followed by the facing

concrete’scementmatrix,whichwouldthenbeconsolidatedintheform,withcaretakento

not disturb the location of the aggregate [Figure 28].220Committee 533 discussed the

218Photocourtesyof:ACICommittee533,GuideforPrecastConcreteWallPanels,32.219HansonandJenny,“PrecastConcretePanels:MaterialsandTests,”23.220Gutmann,“PrecastConcreteWallPanels:ManufacturingProcesses,”49.

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differentmethodsofconsolidation:externalvibration,internalvibration,andthemethodof

concreteconsistencyvariation(inwhichconsolidationisachievedbylayingprogressively

drier mixes to accommodate a high slump facing concrete), as well as the invention of

shockedconcreteanditspotentialforcreatingwell‐consolidatedpanels.221

Figure28.Aprecasterhandlayingthefacingaggregateintheformwork.222

Inadditiontotheformlinersusedtocreatedifferenttextures,thefacingaggregate

could be exposedduring castingwith the use of chemical retarders; could be sprayedor

brushedontothesurfaceoftheformoraretarder‐impregnatedmaterialcouldbeplacedon

theform’ssurfacebeforethe facingconcretewasplaced.223TheCommitteerecommended

thatafterthepanelwascured,amildwashof5to10percentmuriaticacidbeappliedtoits

221Photocourtesyof:Gutmann,“PrecastConcreteWallPanels:ManufacturingProcesses,”51.222Gutmann,“PrecastConcreteWallPanels:ManufacturingProcesses,”50.223Ibid.,48.

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surface to clean and brighten the colored aggregate; the surface should be flushed with

water immediately after the acid wash. To achieve deep reveals, the Symposium

recommendedtheuseofsandtocreatepositiveformsforthepanels.224

Curing,Stripping,andStorage

Curing methods were not described in detail at the 1965 Symposium, although

Committee533warned thatpanels shouldonlybe removedafter sufficient strengthgain

andbe immediately set up against a framing system. Strippingusually occurred eighteen

hours after casting, but the timingwas truly dependent upon the type of panel face, the

desired degree of aggregate exposure, the ambient temperature of the plant, the water‐

cement ratioof the concrete, and the curing techniques employed.225Committee533 also

underlined the importance of the precaster’s experience in determining the timing of

stripping.

SurfaceTreatments

AttheSymposium,Committee533recognizedthatexposedaggregatewasthemost

popularsurfacefinishforarchitecturalprecastwallpanels,althoughitalsodiscussedother

surface finishes briefly. The most common surface treatments to expose the facing

aggregate were hand brushing, applying powered rotary brushes, bush hammering,

grinding,sandblasting,oracidetching[Figure29].226Tobrightentheaggregates,Committee

533recommendedthatallofthesesurfacetreatmentsbefollowedbyanacidwashingthree

tosevendaysaftercasting. Italsoemphasized theneed tomakemockups forall surface

224Ibid.225Ibid.,52.226Ibid.

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finishes, whether achieved during the casting process or through surface treatments, to

confirmthattheaestheticachievedcompliedwiththevisionofthearchitectandengineerof

theproject.227

Figure29.Comparisonofdifferentmethodsofexposingthefacingaggregate:ontheleft,the

aggregateisexposedusingsurfaceretardersontheform,whileontheright,theaggregateis

exposedaftercuringusingsandblastingequipment.228

227Ibid.228Photocourtesyof:ACICommittee533,GuideforPrecastConcreteWallPanels,37‐38.

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Transport,Handling,andErection

At the Symposium, Committee 533 gave minimal attention to considerations of

transporting panels between the precasting facility and the job site, although it did

recommendthatinsertsusedforliftingdevicesduringfabricationorerectionbedesigned

for100percentimpact.229TheCommitteealsodiscussedtheproblemofbreakagesduring

handling,which delayed the construction process, and highlighted the continued need to

balancetheabilitiesofthehandlingequipmentwiththesizeofthepanelandthedesireto

reducethenumberofjointsinthewallsystem.230Toincreaseefficiencyontheconstruction

site and minimize the potential for miscommunication, Committee 533 encouraged the

reductionofthenumberoftradesinvolvedintheerectionprocess.231

ConnectionDesignandMaterials

TheSymposiumoutlinedthevariousloadsthatconnectiondesignshouldconsider,

including wind loads with equal positive and negative pressures. 232 This latter

recommendationrecognizedthesignificantloadthatsuctioncausedbywindcouldimpart

on the panel connections. To protect connection materials against corrosion, Committee

533 began recommending the use of materials treated to resist corrosion, such as

galvanizedsteel.Connections,anchors,andinsertsmustalsobemadeofsufficientlyductile

materials to allow for limited panel movement caused by shrinkage and moisture and

temperaturechangessothattherewouldbevisibledeformationbeforefracture.233Finally,

Committee533presentedspecificconcernsaboutweldedconnections,namelythatwelded

229Leabu,“PrecastConcreteWallPanels:DesignTrendsandStandards,”44.230Collens,“PrecastConcreteWallPanels:ArchitecturalCommentary,”116.231Ibid.,90.232Leabu,“PrecastConcreteWallPanels:DesignTrendsandStandards,”39.233Ibid.,44.

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connectionsneedtoprovideadequatetolerances,theconnectionsmustbedetailedinsuch

awayastoallowspace foreasywelding,andscorchmarksonthe finishedsurfaceof the

panel from fieldwelding connectionsmust be avoided.234At the time of the Symposium,

Committee533gavenoconsiderationtohowweldedconnectionscouldbeprotectedfrom

corrosion.

JointDesignandMaterials

Specific jointmaterialsand theiradvantagesanddisadvantageswerediscussed in

the1965Symposium.Forexample,cementmortarsshouldbeavoidedbecausetheycannot

accommodatethemovementofthepanels.235Committee533promotedtheuseofmastics

and thermosetting plastics because they can accommodate movement much better,

althoughmasticshadashortservicelifewhilethermosettingplasticsgenerallyperformed

betterandrequiredlessmaintenance.236

Cleaning,Repairs,andCoatings

Thesuccessofprotectivecoatingswascontentiousatthistime,fortestingindicated

that coatingsdidnot, in fact, increase thepanels’ resistance tomoisturepenetration and,

therefore, frostaction.Instead,experiencerevealedthatcoatingsmadeitmoredifficultto

repair the face of the panel and could discolor the panel significantly, although they did

makecleaningthepanels’surfaceeasier.237

234Collens,“PrecastConcreteWallPanels:ArchitecturalCommentary,”117.235HansonandJenny,“PrecastConcretePanels:MaterialsandTests,”28.236Ibid.237Ibid.

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Testing

Testing remained an important issue, and at the Symposium, Committee 533

recommended the same 6x12 in. cylinder and 4 in. cube sample sizes that it originally

proposed in its 1964 article for compressive strength tests. The Committee also

recommended a vibration test (ASTM C31 and C192) for low slump or zero‐slump

concrete.238Durabilitytestscontinuedtobeconsideredunnecessaryduetotheinfrequency

ofpanel saturation, butCommittee533 recognized that a testormethod todetect facing

aggregate with a sufficient iron content to stain the surface of the panel needed to be

developedbecausethatamountwasuntraceablethroughconventionaltests.239

BowingandWarpage

Finally, bowing and warpage continued to be a significant problem and was

addressedextensively in the1965Symposium.Theresultsofvarious investigationswere

presented in the Symposium, including the fact that panels “always deflect outward

regardlessofwhetherthetemperatureishigherorlowerinsidethanoutside,whetherthe

panel is solid or sandwiched, or whether the panel is cast face down for the exposed

aggregatepanelsor cast faceup for the regular concretebroomed surface.”240Committee

533alsofoundthatthefollowingcontributedtotheproblemofbowing:largerpanelsizes,

the curing position in the yard, temperature and moisture differential across the cross‐

sectionofthepanel,anddifferentialshrinkageofthefacingandbackupconcretemixes.241

This section of the Symposium warned against the use of intermediate connections to

238Ibid.,21.239Ibid.,23.240Sheng,“PrecastConcreteWallPanels:Bowing,Warpage,andMovement,”62.241Ibid.,58.

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controldeflection,however,becauseaconcentrationofstressescouldoccuratthesepoints

andresultinthedevelopmentofvisiblecracks.242

1965‐1975:MOMENTUMINTHEARCHITECTURALPRECASTINDUSTRY

1965becameapivotalyearforthearchitecturalprecastpanel industryduetothe

significant impactof theSymposium.The influenceof theSymposiumisevidencedbythe

numerousorganizationsthatwereestablishedimmediatelyafterwardstopromotetheuse

ofarchitecturalprecastwallpanelsandimprovetheirproductionandquality,includingthe

NationalPrecastConcreteAssociation,whichwas founded in1965, and theArchitectural

Precast Association, which was founded in 1966.243What was then known as the

PrestressedConcrete Institute (PCI)addedprecast to itsmission in1966andcreated the

Plant Production of Architectural Precast Concrete Products Committee to “introduce a

plantcertificationprogramforarchitecturalprecastconcreteproductions”tocontributeto

thequalityassuranceofthisconcretetechnology.244ThePCICommitteewantedtopublisha

manualforguidanceonqualitycontrol,plantfacilities,materials,production,erection,and

creation of samples, all the while recognizing the challenge of balancing recommended

standardswith the diverse needs of individual plant operations resulting from themany

geographical locations and circumstances of precast production.245Through its numerous

publications, thePCICommittee and itsmembers’ contribution to thedesign,production,

andassemblyofarchitecturalprecastwallpanelswassecondonlytoACICommittee533’s

contribution.

242Ibid.,62.243“AboutNPCA:OurMission,”NPCA, lastaccessed7March2016,http://precast.org/npca/;“AboutUs,”APA,lastaccessed7March2016,http://www.archprecast.org/index.php/about‐us#history.244JohnF.Downing,“AManualforQualityControl,”PCIJournal(April1968):58.245Ibid.

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DesignObjectives

After ACI Committee 533’s 1965 Symposium, the design objectives for precast

panels became more nuanced, emphasizing the significance of stresses induced during

handling and the relationship between the panel units and the structural frame.246

Particularly because of the stresses imposed on the panels during handling, high

compressive strengths in excess of service requirements were recommended. 247

Conveniently, such high strengths enabled the “more satisfactory attainment of

architectural finishes.”248C.H.Raths,amemberof thePCICommittee,alsohighlighted the

importanceofdesigningtheshapeofthepaneltoaccommodateallofthedifferentstagesof

handling,includingstrippingfromtheform.249Afterthe1965Symposium,thefirstfactors

of safetywere recommended: thepanel shouldbedesignedwitha factorof safetyof2.5,

insertsused inhandling shouldbedesignedwith a factor of safety of 4, and connections

shouldbedesignedwithafactoryofsafetyofatleast3.250

DurabilityremainedaprimaryconcernaftertheSymposium,particularlythatofthe

facingconcrete,althoughtheperceptionfromtheearly1960s,thattheverticalpositionof

the panel would reduce the potential for saturation and therefore freeze‐thaw damage,

persisted. In 1967, an article published by Raths explicitly established the production of

crack‐free panels as a primary goal in panel design. He proposed that this goal could be

achievedthroughhighcompressivestrengthsandsuccessfulreinforcementdesign.251

246C.H.Raths,“ProductionandDesignofArchitecturalPrecastConcrete,”PCIJournal(June1967):19;C.H.Raths,“EngineeringDesignofArchitecturalPrecastConcrete,”PCIJournal(April1968):83.247VictorF.LeabuandJ.A.Hanson,“QualityStandardsandTestsforPrecastConcreteWallPanels,”ACIJournal(April1969):271.248Ibid.249Raths,“EngineeringDesignofArchitecturalPrecastConcrete,”78.250Ibid., 81; Richard C. Adams and Victor Leabu, “Design of Precast ConcreteWall Panels,”ACI Journal (July1971):513;Ibid.,512.251Raths,“ProductionandDesignofArchitecturalPrecastConcrete,”29.

89

At the beginning of the 1970s, there was an increasing concern for coordinating

tolerances to ensure successful panel design and joint system design, including the

tolerancesbetweenpanelsandadjacentmaterials,betweenpanelsandthebuildingframe,

and for panel movement.252A 1971 publication by ACI Committee 533 revealed a new

appreciationforthepotentialvarietyofeccentricitiesimposedonthepanelfromsupport,

connection, line of load applications, variations in flatness, unsymmetrical cross‐sections,

total deflection, etc.253Consequently, Committee 533 recommended that these loads

becomeaprimaryconsiderationinthepaneldesign.

By1975,therewasstillnostandardpublishedbyACInorauniversalspecification

toguidethedesign,production,andassemblyofarchitecturalprecastwallpanels.Thelack

of such a standard or universal specification resulted from the fact that techniques

continuedtovarygreatlyamongreliablemanufacturers—afactthatrevealsthecontinued

significance of craftsmanship to this industry.254Determining the optimal balance of

economical and practical to achieve the required strength, durability, volume constancy,

surfacefinish,andworkabilityreliedonboththeexperienceofprecastersandcalculations

andtests.255

MaterialSelection

In the years following the 1965 ACI Symposium, concerns about reducing color

variations between panels and increasing durability continued to orient the

recommendationsformaterials.Forexample,FayLawson,amemberofthePCICommittee,

revealed that white cement was problematic because it was more easily stained by the

252LeabuandAdams.“Fabrication,HandlingandErectionofPrecastConcreteWallPanels,”327.253AdamsandLeabu,“DesignofPrecastConcreteWallPanels,”506.254LeabuandAdams,“Fabrication,HandlingandErectionofPrecastConcreteWallPanels,”313.255Ibid.,320.

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forms. 256 ACI Committee 533 recommended that aggregates vulnerable to

weathering/deterioration should be avoided to reduce discoloration.257 Additionally,

natural sand and gravel aggregates were recommended for having less shrinkage and

producingmoreworkableconcrete,althoughcrushedaggregatewasrecognizedtohavea

greaterbondwithcementpasteandbetteraggregateinterlock.258

ACICommittee533addedtotheirrecommendationsaboutadmixturesintheyears

following the 1965 Symposium. They recommended in 1969 a “normal” amount of air‐

entrainingagent,oradosagethatwouldprovide19±3%air ina1:4(cementtosandby

weight)standardsandmortar,although therecontinued tobedeference to thevarietyof

mixturesusedintheproductionofarchitecturalprecastwallpanels.259In1969,Committee

533 continued to recommend using Type III cement and good curing methods over

accelerating admixtures to achieve high early strength, but it advised against the use of

retarding admixtures to prolong workability.260In the same article, the Committee

recommendedtheuseofwater‐reducingadmixturestoreducebleedingwateror increase

workability, but only if adequate consolidation could be achieved.261Mineral admixtures

andpozzolanscouldbeusedtoobtainasmoothconcretesurface,andbythelate1960s,it

wasrecognizedthatnotonlydidpigmentamountsexceeding5%notaddtotheintensityof

thecoloroftheconcrete,butamountsabove10%couldbeharmfultotheconcretemix.262

256Lawson,“PanelDiscussiononProductionandQualityControlforArchitecturalPrecastConcrete,”70.257LeabuandHanson,“QualityStandardsandTestsforPrecastConcreteWallPanels,”271.258VictorF.LeabuandDanielP. Jenny, “SelectionandUseofMaterials forPrecastConcreteWallPanels,”ACIJournal(October1969):815.259LeabuandHanson,“QualityStandardsandTestsforPrecastConcreteWallPanels,”274;LeabuandAdams,“Fabrication,HandlingandErectionofPrecastConcreteWallPanels,”320.260LeabuandJenny,“SelectionandUseofMaterialsforPrecastConcreteWallPanels,”816.261Ibid.,817.262Ibid.

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Mixing

Theprocessofmixingthevariousingredientsofthefacingandbackupconcretewas

not discussed at length in any publication until the 1970s. One of the 1970s documents

publishedbyACICommittee533 inpreparation fora standarddedicated toarchitectural

precast wall panels highlighted the fact that within the precast industry there was an

immenseamountofvarietyinmixingprocedures.263Inthenever‐endingattempttoensure

the quality of the architectural precastwall panel product, the Committee recommended

onlyahandfulofrulesthatshouldbefollowedtoachievedesirableresults:

Themixershouldonlybeoperatingwhileallmaterialsarecharged;

Toobtainahomogeneousmix,afterall thematerialshaveenteredthemixer,they

should be mixed for a minimum of 1 minute or as recommended by the mixer

manufacturer;

If,duetocoldweather,theaggregateorwaterhasbeenheated,cementshouldbe

added only after the aggregate andwater have entered themixer and have been

thoroughlymixedforatleast1minute;

Lightweightaggregatesshouldbepre‐wetted;and,

Themixershouldbeproperlyloaded—notabovecapacity—andthoroughlycleaned

aftereachperiodofproduction.264

263LeabuandAdams,“Fabrication,HandlingandErectionofPrecastConcreteWallPanels,”321.264Ibid.

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ReinforcementDesignandMaterials

After the Symposium, more attention was given to the design and placement of

reinforcement.Topreventbending,thePCICommitteerecommendedthatreinforcementbe

centeredinthecrosssectionratherthanatthefacingandbackupconcreteinterface.265In

1967,PCIrecommendedamoreconservative1in.coveroverallsteelreinforcement,while

ACICommittee533recommendedacoverofa½in.ina1969publication,anincreasefrom

the 3/8 in. recommended in the 1965 Symposium.266Both organizations recommended

using galvanized reinforcement in scenarios where the cover was the minimum

recommendedcoverorless.Thetypesofreinforcementusedinarchitecturalprecastpanels

appearstohaveexpandedgreatlyafterthe1965Symposiumandincludedbillet‐steel,rail‐

steel,andaxle‐steeldeformedbars;hightensilestrengthsteelwires,rods,andstrandsfor

prestressingpurposes;oras‐drawnorgalvanizedweldedwirefabric,smoothordeformed,

withavarietyofmeshspacingsandwiregages.267PCIadvisedthatthereinforcementmust

bedesignedtoaccommodatethestressesinducedbystripping,handling,storage,shipping,

erecting,andwindandotherin‐placeloads.268

By1975,therewasheightenedattentiontothecausesofreinforcementcorrosion.

In 1970, ACI Committee 533 recognized that corrosion could be caused by inadequate

qualityofconcreteduetoimpropermixproportioning,improperconsolidationofconcrete,

inadequate cover by design or misplacement of reinforcement, excessive use of calcium

chloride, or a combination of these factors.269As a result, they recommended the use of

weldedwire fabric toachievebettercover, theuseofgalvanizedreinforcementwhen the

recommendedminimumcover(½in.accordingtoACIand1in.accordingtoPCI)couldnot265Raths,“ProductionandDesignofArchitecturalPrecastConcrete,”30.266Ibid.;LeabuandJenny,“SelectionandUseofMaterialsforPrecastConcreteWallPanels,”817.267LeabuandJenny,“SelectionandUseofMaterialsforPrecastConcreteWallPanels,”817.268Raths,“ProductionandDesignofArchitecturalPrecastConcrete,”19.269LeabuandAdams,“Fabrication,HandlingandErectionofPrecastConcreteWallPanels,”321.

93

be achieved, and the importance of accurately placing reinforcement.270Additionally, to

controlcrackinginpanelslessthan6in.thick,Committee533proposedplacingatleasttwo

layersofreinforcementandplacingadditionalreinforcementalongtheedgesof thepanel

andaroundanyopeningsinthepanel.271Significantly,in1970,Committee533increasedits

recommendedminimumcoverfrom½in.(presentedin1969)to¾in.andrecognizedthe

need to consider the environment towhich the concrete surfacewas exposed, including

whetheritwasexposedtooceanatmosphereoraggressiveindustrialfumes,todetermine

theappropriateamountofcover.272

FormDesignandMaterials

Wood,steel, concrete,and fiber‐glass‐reinforcedplasticscontinued tobe themost

popular formmaterials,whilemoldsofplaster, gelatin, or sculptured sandwereused for

morecomplicateddetails.273AccordingtoACICommittee533,fiber‐glass‐reinforcedplastic

formshadthebestoverallperformance,buttheyhadtobewellsupportedalongedgesand

flatareas toprevent formdistortiondue to the flexibilityof theplastic.274Concrete forms

hadexcellentrigidityanddimensionalstabilityandallowedfornumerousreuses,although

carehadtobetakenduringstripping.Toimprovetheformreleaseandfacilitatestripping,

theformcouldbetreatedwithepoxyorotherplasticresins.275Woodformstendedtoshow

theirwear and tearmorequickly than theother formmaterials andhad tobe treated to

prevent excessive absorption and nonuniform finish. Steel molds were more difficult to

modify and obtain dimensional control, although theywere good formultiple assemblies

270Ibid.,322.271AdamsandLeabu,“DesignofPrecastConcreteWallPanels,”511.272LeabuandAdams,“Fabrication,HandlingandErectionofPrecastConcreteWallPanels,”321.273Raths,“ProductionandDesignofArchitecturalPrecastConcrete,”19.274LeabuandAdams,“Fabrication,HandlingandErectionofPrecastConcreteWallPanels,”318.275Ibid.

94

anddisassemblies.276Forall forms, adimensional toleranceof±1/8 in.wasproposedby

PCI.277Additionally, form liners continued to be a primaryway of obtainingpatterns and

texturesonthesurfaceofarchitecturalprecastpanels,althoughtherewascautionagainst

theuseof some liners, such as rubbermatting, for they could stainordiscolor thepanel

surface.278

CastingandConsolidation

Thedesiretogivedeferencetoprecastersandtheirmethodsofproductionappears

tohavecontinuedwellaftertheSymposium,forlittleinformationaboutthecastingprocess

was presented in the publications from between 1965 and 1975. Still, in its 1970

publication,ACICommittee533presentedimportantconsiderationsfortheformdesignto

ensure high quality during casting: the form should achieve recommended casting

tolerances by being sufficiently rigid, prevent leakage of the mortar or cement paste by

being sufficiently tight, and prevent damage to the concrete from panel shrinkage and

stripping.279Consolidationwasstillachievedthroughexternalvibration,internalvibration,

ortheadjustedslumpandmixmethod.280

SurfaceFinishesandTreatments

Documents published during this period by PCI in particular emphasized the

importance of effective communication between precasters, architects, and engineers,

276Ibid.277Raths,“ProductionandDesignofArchitecturalPrecastConcrete,”20.278LeabuandJenny,“SelectionandUseofMaterialsforPrecastConcreteWallPanels,”817.279LeabuandAdams,“Fabrication,HandlingandErectionofPrecastConcreteWallPanels,”317.280Ibid.,323.

95

especiallyforobtainingthedesiredsurfaceappearance.281Thetypesofsurfacefinishesand

treatments did not change immensely after the 1965 Symposium, however, although

publications presented the range of finishes, applied either to plastic concrete during

castingorhardenedconcreteaftercuringandstripping:

PlasticConcrete

o Chemicalsurfaceretarders;

o Brooming;

o Floatingortroweling;

o Specialformfinishes;and,

o Scrubbing,brushing,andsurfacetexture;

HardenedConcrete

o Handbrushingand/orpowerrotarybrushes;

o Beltsanding;

o Acidetching;

o Sandorotherabrasiveblasting;

o Honingandpolishing;

o Bushhammeringorothermechanicaltooling;and,

o Artificiallycreatedbrokenribtexture.

Considerationsabouthowsurfacefinishesandtreatmentsrelatedtootherpartsof

the production and assembly process became more significant after the 1965 ACI

Symposium. For example,ACICommittee533 advised that the choiceof surface finishor

281Richard E. Cavanaugh, “Contractor Considerations for Architectural Precast Concrete,” PCI Journal (April1968):85.

96

treatmentmustconsiderthehandlingrequirementsofthepanels.Additionally,whilegap‐

graded facing aggregates continued to be preferred for exposed aggregate finishes,

Committee 533 found that using a grade of aggregates with a more restrictive size

limitation could improveboth the uniformityof the surface and its durabilitydue to less

segregation and better contact between the aggregate and matrix.282Information about

whattoavoidalsobecamemoreprominent.Forinstance,ACICommittee533warnedthat

glass aggregatesused to createbright colors couldpossibly reactwith cement and cause

problems.283The Committee recognized that acid etching must be used with caution

becauseofthepotentialfortheacidtoreactwiththefacingaggregateorcement,resulting

inthebuildupofcalciumsilicatedepositsonthesurfaceofthepanel.284Acidetchingcould

also potentially damage galvanized reinforcement without sufficient cover. Similarly, the

Committeeadvisedthatthecompressivestrengthofblastingequipmentusedtoexposethe

facing aggregate, such as sandblasting,must be considered to ensure the adequate cover

andprotectionofthereinforcement.

Curing,Stripping,andStorage

Curingintheform,whichusuallyoccurredforoneday,hadtobehighlycontrolled

topreventexcessiveevaporation,whichcouldcreate tensilestressesat thesurfaceof the

panel and cause cracking. Due to the use of high early strength cement or high Type I

cementcontents,ACICommittee533 identified the initial curing in the formasbeing the

mostimportant.285Incontrast,thecuringthatoccurredafterformstrippinghadtocompete

282LeabuandAdams,“Fabrication,HandlingandErectionofPrecastConcreteWallPanels,”319.283LeabuandJenny,“SelectionandUseofMaterialsforPrecastConcreteWallPanels,”816.284Ibid.,324;LeabuandJenny,“SelectionandUseofMaterialsforPrecastConcreteWallPanels,”818.285LeabuandAdams,“Fabrication,HandlingandErectionofPrecastConcreteWallPanels,”325.

97

withtheneedsofthesurfacetreatmentsemployed.286Thebasicmethodsofcuringincluded

supplying additional moisture (immersion, sprinkling, or wet coverings), prevention of

moistureloss(waterproofpaperorplasticsheets),oraccelerationofstrengthgainthrough

the addition of heat.287Although the initial curing phase was the most significant for

strength gain, Committee 533 still recommended that the panels be protected from

excessive evaporation or temperatures below 50°F after stripping and surface

treatments.288

Form stripping became a primary concern after the 1965 Symposium, and

publicationsacknowledgedthestressesthattheprocesscouldimposeonthepanelandthe

potentialdamageitcouldcause.PCIwarnedthatcrackingcouldoccurduringstrippingdue

to either thermal shock ormishandling.289PCI also identified shrinkage of the unit, form

suction,andstainingoftheunitduringformreleaseasbeingsignificantproblems.290

Essential to the stripping, handling, and erection process was the placement of

handlinginsertsinthepanels.Suchinsertscouldbeboltedtothepanels,whichPCIclaimed

in1967wasthemostcommonpractice,orwirecableinsertscouldbecastintothepanel.291

Testingindicatedthatsuchinsertshadagreatercapacitywhenloadedinpureshearthan

whenloadedindirecttension.Fortunately,manyinsertmanufacturerscouldprovideuseful

testinformationabouttheirproducts.292

Finally,muchmoreinformationaboutthestorageofpanelswaspresentedafterthe

1965Symposiumdue to itsacknowledgedconnection topanelbowingandwarpage. Ina

286Ibid.287Ibid.288Ibid.,326.289Raths,“ProductionandDesignofArchitecturalPrecastConcrete,”20.290A.A.Roy,“PanelDiscussiononArchitecturalandEngineeringDesignofArchitecturalPrecastConcrete,”PCIJournal(April1968):92;Lawson,“PanelDiscussiononProductionandQualityControlforArchitecturalPrecastConcrete,”70.291Raths,“ProductionandDesignofArchitecturalPrecastConcrete,”26.292Raths,“EngineeringDesignofArchitecturalPrecastConcrete,”82.

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1967article,PCIrecommendedthatunitsalwaysbesupportedatonlytwopointsandwith

proper blocking in a given plane to avoid distortion.293ACI Committee 533 advised that

storageconditions, evenon the job site,mustprevent soiling, aswell as the rapid lossof

moistureandfreezing,whichcouldcausedeflection.294Tominimizehandling,andtherefore

breakages, the storage of the panels should consider how the units would ultimately be

transported.295

Transport,Handling,andErection

PCIrecommendedthatpanelsbesupportedonlyattwopointsduringtransportand

inallhandlingactions toavoiddistortion.296Duringshipping,which typicallyoccurredby

semitrailer trucks over highways, ACI Committee 533 advocated that panels be loaded

vertically, supported on ‘A’ frames, and stored in such a way as to protect against road

shock.297TheCommitteealsoproposedthatpanelsshouldalwaysbehandled inavertical

positionandallhandlingshouldoccurinmidairtoavoiddamagingthepanels.298

ConnectionDesignandMaterials

Afterthe1965Symposium,informationaboutconnectionsbecameveryprominent

inpublicationsbecauseoftheirsignificanceintheperformanceofarchitecturalprecastwall

panelsystems.Thetypesofconnectionsutilizedinpanelwallsystemsincludedclipangles,

slottedinserts,bolts,orconcretehaunchescastontothebackofthepanels.299Connections

293Raths,“ProductionandDesignofArchitecturalPrecastConcrete,”21.294LeabuandAdams,“Fabrication,HandlingandErectionofPrecastConcreteWallPanels,”326and331.295Raths,“ProductionandDesignofArchitecturalPrecastConcrete,”21.296Ibid.297LeabuandAdams,“Fabrication,HandlingandErectionofPrecastConcreteWallPanels,”330.298Ibid.299Ibid.,333.

99

could be made from steel, pressed steel, or malleable cast iron.300To adequately

accommodatelateralmovement,PCIproposed½in.asapracticaldimensionaltolerancein

1967.301Ina1968publication,PCIpromotedthestandardizationofconnectionsforagiven

project to increase construction efficiency. 302 To similarly increase efficiency, ACI

Committee533recommendedin1970thatconnectionsbedesignedtoallowforadjustment

inthefield,easyaccessduringerection,fastsecurement,andlimitedpanelmovementafter

installation.303

Numerousspecificrecommendationsaboutconnectiondesignwerepresentedafter

the1965Symposium.For instance,bothPCI andACICommittee533proposed that good

connectiondesigninvolvedsupportingpanelsatonelevel—oronlytwopoints—tokeepthe

panelcross‐sectionincompression,and,ideally,locatingthemainpanelsupportfairlyclose

to thebottomedgeof thepanel to allow forproperboltingandapositive seating, rather

than hanging the panel from connection angles and clamps [Figure 30].304The design of

connectionsshouldalsoattempttominimizethetransferofbuildingloadstothewallpanel

and the development of restraint forces resulting from temperature changes, wind, or

gravityloads.305

300VictorF.Leabu,“ConnectionsforPrecastConcreteWallPanels,”ACIPaperSP22‐8(1969):98.301Raths,“ProductionandDesignofArchitecturalPrecastConcrete,”33.302Raths,“EngineeringDesignofArchitecturalPrecastConcrete,”79.303LeabuandAdams,“Fabrication,HandlingandErectionofPrecastConcreteWallPanels,”333.304Ibid.,30;Leabu,“ConnectionsforPrecastConcreteWallPanels,”101.305Raths,“EngineeringDesignofArchitecturalPrecastConcrete,”79.

100

Figure30.Exampleofapositiveseatingconnectionbetweenanarchitecturalprecastwall

panelandaconcreteframe.306

Thematerialsusedforconnectionsshouldbepermanentlyductiletoaccommodate

panelmovement,andpublicationsstressedtheimportanceofavoidingcoatingsthatcould

causeembrittlementofthematerial.Thevulnerabilityofconnectionmaterialstolong‐term

corrosion despite their lack of exposure to the exterior environment finally began to be

appreciated,whichresultedinanincreasinguseofstainlesssteel,galvanizedmaterials,or

cadmium plated materials. Significantly, stainless steel was not recommended as a

306Photocourtesyof:Leabu,“ConnectionsforPrecastConcreteWallPanels,”100.

101

connection material until ACI Committee 533’s 1969 article about precast panel

connections.307Problemswithwelded connections also began to be appreciated after the

1965 Symposium. In 1968, PCI highlighted the discovery that welded connections could

havereducedcapacitywhenexposedtoexteriortemperaturesbelow0°F,andin1969,ACI

Committee533warned that thehighheat fromweldingcouldcausedamage to thepanel

and/or supporting concrete frame through the sudden expansion of the concrete

material.308

JointDesignandMaterials

Likewiththedesignofconnections,muchmorespecificguidelinesforthedesignof

joints were presented after the 1965 Symposium. In 1968, PCI recognized that

weatherproofing the joints between the panels and between the panels and other wall

elements was essential to the performance of the wall system.309To achieve successful

weatherproofing, the joint material must be installed with good workmanship and be

flexible to accommodate panel movement. Cement mortar, mastics, and elastomeric

materials remained the primary joint materials, although PCI only recommended that

cementmortars be used in situationswhere therewould be negligible panelmovement.

After the Symposium, there were new developments in elastomeric materials, including

thermoplastics (cold‐applied, solvent, or emulsion types) and thermosetting elastomerics

(chemicallycuringorsolventreleasetypes).310

Jointsystemscouldeitherbefield‐molded,whichPCIclaimedwaspreferablewhen

the joint width and movement were nominal, or premolded, which PCI claimed was307Leabu,“ConnectionsforPrecastConcreteWallPanels,”102.308Roy, “Panel Discussion on Architectural and Engineering Design of Architectural Precast Concrete,” 93;Leabu,“ConnectionsforPrecastConcreteWallPanels,”100.309R.J.Schutz,“DesignofJointsinPrecastConcreteWallPanels,”PCIJournal(October1966):60.310RaymondJ.Schutz,“ArchitecturalPrecastConcreteJointDetails,”PCIJournal(March‐April1973):25.

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preferableandmoreeconomicalwhenpanelmovementwassevereorthejointwidthwas

exceptionallywide (greater than 1½ in.).311In 1966, PCI Committeemember R.J. Schutz

proposedthatthedesignoffield‐moldedjointsystemsshouldbedeterminedbytheshape

factor of the joint, or the depth‐to‐width ratio, with the best performing and most

economicaljointbeingasshallowaspossible[Figure31].312

Figure31.Comparisonofthestrainexperiencedbythesealantmaterialinjointsofdifferent

shapefactors.Themostshallowjoint,1”x½”experiencestheleaststrain,withSmax=32%.313

311Schutz,“DesignofJointsinPrecastConcreteWallPanels,”64.312Ibid.,61.313Photocourtesyof:Schutz,“DesignofJointsinPrecastConcreteWallPanels,”61.

103

Thejointshapefactorshouldbebasedonthepanelsizeandcoefficientofexpansion

of the panel material, and PCI recommended that ½ in. be the minimum width for any

joint.314PCIalsoadvisedthatthejointmaterialshouldhavealowmodulusofelasticityso

thatitwillelongatewithoutpullingoffthesurfaceofthepanel.Especiallyforfield‐molded

joint systems,PCIcautionedagainst thepotential forcompressionset,or theset that can

occur after the joint material has been in compression and does not fully recover after

release. Premolded joint systems could be constructed using sheets or tubesmade from

neopreneorbutylrubber,whichwouldbebondedtothesidesofthejointslotswithgap‐

fillingepoxyadhesiveornon‐sagfield‐moldedsealant.315PCIwarnedthatpremoldedjoints

should only be subjected to bending and flexing and not stretching to prevent joint

failure.316Forbothtypesofjointsystems,PCIrecommendedthatcarebetakentoalignthe

jointshorizontallyandvertically foraestheticreasonsandtoguidewateralongthe joints

ratherthanthefaceofthepanels.Inalaterpublicationfrom1973,PCIrecommendedthat

joints be located where there was maximum panel thickness and in response to an

understanding of the weather patterns for the structure.317To ensure their success, the

jointsmustbeproperlypreparedpriortotheinstallationofthejointmaterial,includingthe

applicationofajointprimerandbackupfiller,whichcontrolledthedepthofthesealantand

actedasabondbreaker.

Finally, during this latter period, cavity walls became more popular, adding

complexitytothewallsystem.Aprimaryconsiderationwastheneedtoventthecavityand

ACICommittee533promotedtheplacementofventtubesinallhorizontaljointsofthewall

system in order to do so.318The two‐stage rain screen joint system resulting from cavity

314Schutz,“DesignofJointsinPrecastConcreteWallPanels,”63.315Ibid.,64.316Ibid.,66.317Schutz,“ArchitecturalPrecastConcreteJointDetails,”14.318LeabuandAdams,“Fabrication,HandlingandErectionofPrecastConcreteWallPanels,”335.

104

wall design becamemore popular than the conventional one‐stage joint system andwas

seen as the most effective system in separating and controlling both the exterior and

interiorairandhumidityconditions[Figure32].319

Figure32.Examplesoftwo‐stagejointsystems.320

319Schutz,“ArchitecturalPrecastConcreteJointDetails,”13.320Photocourtesyof:Schutz,“ArchitecturalPrecastConcreteJointDetails,”17.

105

Cleaning,Repairs,andCoatings

In1970,ACICommittee533prescribed that, after installation,anyexcessmortar,

plaster,extrashims,etc.beremovedandthepanelscleaned.321Cleaningcouldbeachieved

simplywithsoappowderdissolvedinboilingwaterfollowedbyathoroughrinsewithclear

water.Forparticularlydifficultstains,however,ACICommittee533recommendedtheuse

ofdilutedmuriaticacidorsteamcleaningandsandblasting,althoughcareshouldbetaken

with either of thesemethods because they could potentially alter the appearance of the

panels.322After cleaning the panels, damage caused during handling or installation was

repairedon‐site.ACICommittee533advisedthatthequalityoftherepairwascontingent

on theweatherandcuring conditionsof the repairmaterial.323Protective coatings,which

wouldbeappliedaftercleaningandrepairs,remainedcontroversialduetoconcernsabout

spallingoftheconcretesurfaceanddiscolorationofthepanels.324

Testing

Although testing continued to be a concern in the years following the 1965

Symposium, few new recommendations were presented. In addition to the

recommendationspresentedintheSymposium,ACICommittee533proposedin1969that

absorption testsbeadapted for thepurposesofunderstanding theabilityofarchitectural

precastwallpanelstoresistdirtadherence,stainingfromsoftaggregates,fadingofcolors,

andotherissuesthatcouldalterthepanels’appearance.325In1968,PCIwasintheprocess

of testing different coatings to try to solve the problem of discoloration caused by their

321LeabuandAdams,“Fabrication,HandlingandErectionofPrecastConcreteWallPanels,”332.322LeabuandAdams,“Fabrication,HandlingandErectionofPrecastConcreteWallPanels,”336.323Ibid.,324.324LeabuandJenny,“SelectionandUseofMaterialsforPrecastConcreteWallPanels,”819.325LeabuandHanson,“QualityStandardsandTestsforPrecastConcreteWallPanels,”274.

106

application,althoughnofurtherinformationabouttheresultsofthistestingwerepresented

before1975.326

BowingandWarpage

Bowing and warping also continued to be a significant problem. After the 1965

Symposium,additionalcauseswereidentified,includingunsymmetricalpanelsectionsand

differencesbetweenfacingconcreteandbackupconcreteproperties.327

CONCLUSION

The industry literature reveals how the design, production, and assembly of

architecturalprecastwallpanels changedbetween1945and1975anddemonstratesnot

onlytheindustry’sdesiretoimproveandstandardizetheirproductbutalsoimportantgaps

in the literature. The information presented in this chapter provides the foundation for

understandingthetechnicalaspectsofthisconcretetechnologyandpredictinghowitcould

deteriorate.Theresultsofthisevaluationarepresentedinthefollowingchapter.

326Lawson,“PanelDiscussiononProductionandQualityControlforArchitecturalPrecastConcrete,”73.327Leabu,“ConnectionsforPrecastConcreteWallPanels,”95.

107

CHAPTER6:METHODOLOGYFORPREVENTIVECONSERVATIONOFARCHITECTURAL

PRECASTWALLPANELS

INTRODUCTION

Understandingthehistoricalandarchitecturalsignificanceofarchitecturalprecast

wallpanelsisessentialtotheirpreservation,forsuchunderstandingwillleadtoheightened

awarenessandultimatelygreaterappreciationforthisconcretetechnology.Still,thisthesis

seekstoalsocontributetothephysicalconservationofarchitecturalprecastwallpanelsby

identifying potential threats that may affect them. These threats were identified by

analyzingthetechnologicalevolutionofarchitecturalprecastwallpanels(Chapter5)within

the context of reinforced concrete pathologies and the current understanding of how

architecturalprecastwallpanelsdeterioratepresentedintheliteraturereview(Chapter4).

Thedataandresultsof thisevaluationarepresentedbelow, tobeused in thecreationof

preventiveconservationplans.

METHODOLOGYPART1—CATEGORIZINGINDUSTRYLITERATURE

Theprimaryconsiderationforthepreservationofarchitecturalprecastwallpanels

is preventing or reducing the amount of cracking. Cracking not onlymakes panelsmore

susceptible tosubsequentdeterioration,butalsonegativelyaffects theappearanceof this

architectural feature and can lead to spalling and loss of original fabric. To prevent such

deterioration,theparticularvulnerabilitiesofarchitecturalprecastwallpanelsduetotheir

design, production, and assembly must be identified. The specific recommendations and

guidancefromthedocumentsdiscussedinChapter5canprovideuswiththisinformation.

108

DATA

Theinformationderivedfromthismethodologyisorganizedintotables[Tables1‐

11]basedonthefollowingsubjects:

DesignObjectives[Table1]

MaterialSelection[Table2]

ReinforcementDesignandMaterials[Table3]

FormDesignandMaterials[Table4]

CastingandConsolidation[Table5]

SurfaceFinishesandTreatments[Table6]

Curing,Stripping,andStorage[Table7]

Transport,Handling,andErection[Table8]

ConnectionDesignandMaterials[Table9]

JointDesignandMaterials[Table10]

Cleaning,Repairs,andCoatings[Table11]

Within each subject table, the recommendations are further organized into sub‐

categories.Forexample,withinthe“Materials”category,theinformationisorganizedinto

general information about materials, information about cement, information about

aggregates,and informationaboutadmixtures.Additionally, the information ispresented

withrespecttothetimeperiodofitspublication,dividedintofourperiods:pre‐1965ACI

Symposium, 1965 ACI Symposium, 1965‐1969, and 1970‐1975. Finally, the individual

recommendationsareclassifiedbasedonwhethertheyareindicativeofgeneraltrendsin

theindustry,technicalguidance,orstandards,andtheyarecolorcodedasfollows:

109

There are some assumptions and simplifications that must be addressed in

evaluating these recommendations and guidance, however. First, an important

simplification in reading the tables is that the first period inwhich information about a

particular topic is presented indicates that no information in previous periods was

presented about that topic. For example, in “Design Objectives,” a standard for the

minimum compressive strength of the backup concrete is first presented in the 1965

Symposium.Thismeansthatnoinformationaboutthistopic(thecompressivestrengthof

the backup concrete) was presented in any earlier publications. Second, if a

recommendationispresentedinacertaintimeperiod,itisassumedthatthatinformation

isrelevantforthesubsequenttimeperiods,unlessanewrecommendationaboutthesame

topic ispresented. For example, in “DesignObjectives,” the standard fordeflection tobe

less than h/240, which was presented initially in the 1965 Symposium, is assumed to

remain a standard for the subsequentperiodsof 1965‐1969 and1970‐1975becauseno

new standard was presented in the industry literature. Lastly, recommendations about

howtopreventdiscolorationordamagetothepanelappearancearenotincludedinthese

tables unless the recommendation or guidance could also contribute to the physical

deteriorationofthepanel.

126

DISCUSSION

Reviewing the numerous publications from between 1945 and 1975 reveals

significantgapsintheircontent.Forexample,whileACIdedicatedanentirecommitteeto

thistechnology,itdidnotrecognizearchitecturalprecastwallpanelsasbeingseparatefrom

other reinforced concrete. Consequently, it must be remembered that the design,

production, and assembly of architectural precast wall panels were within the larger

contextof reinforced concreteproductionand assembly, though thedocuments reviewed

herefocusontheissuesspecifictoarchitecturalprecastwallpanel.Additionally,although

construction with architectural precast wall panels reduced the amount of skilled labor

needed on‐site, the production of this concrete technology required skilled labor in the

precastingplant.Thepublicationsfromthistimeperiodrepeatedlystatethesignificanceof

the precasters’ workmanship on the quality of the panels and claim specifications and

standards may not be appropriate given the need to rely on the experience of the

precasters.EvidenceofthishesitationisthefactthatACIdidnotpublishaguide,letalonea

standard,dedicated toarchitecturalprecastwallpanelsuntil1992(ACI533R‐93).Due to

thisdeferencetotheprecasters’ judgmentandexperience, thepublications frombetween

1945 and 1975 gloss over particular areas of production, such as casting methods,

consolidationmethods,andsurfacefinishesandtreatments.

Otherinterestingfindingsincludethefollowing:generally,notmuchattentionwas

given to the thickness of the panels,which varied from8 in. in earlier panels to 5 in. on

averageinmid‐centuryarchitecturetoasthinas3 in.or less inparticularapplications.328

Giventhesesmalldimensions,thicknesswasonlyconsideredwithrespecttotheheightto

thicknessratioasitaffectedthepanel’spotentialforbending.Variationsinthicknesswere

328Leabu,“ProblemsandPerformanceofPrecastConcreteWallPanels,”287.

127

rarely recommended, presumably to keep material to a minimum. Additionally, it is

significant that stainless steel was not recommended as a connection material until the

1970s,andstainlesssteelwasneverformallyrecommendedtobeusedasareinforcement

materialduring this thirty‐yearperiod.Similarly, therecommendedconcretecoverswere

extremelyshallow,evenincomparisontotherecommendedcoversat thetime forbeams

and girders,whichwas1½ in.329In general, the inadequateprotection against corrosion

during this period exemplifies the limited understanding of its significance in the

deterioration of reinforced concrete. Another interesting discovery was the more liberal

deflection limits assigned to architecturalprecastwallpanels, despite thedesire to avoid

cracking. For typical reinforced concretemembers, themaximum allowable deflection is

length(orheight)dividedby360.Incontrast,themaximumdeflectionarchitecturalprecast

wallpanelscouldexperience,accordingtothepublicationsfrombetween1945and1975,

was length (or height) divided by 240. This more liberal deflection limit further

demonstratesanarrowunderstandingofhowsignificantdeflectionandbowingaretothe

conditionanddeteriorationofarchitecturalprecastwallpanels.

METHODOLOGYPART2—IDENTIFICATIONOFPOTENTIALFACTORSANDPATHSTO

DETERIORATION

From these recommendations, specific factors that could influence deterioration

have been identified. The potential paths to deterioration to which these factors may

contributeareillustratedinthediagramsbelow[Table12‐17],specificallyoutliningpaths

towardscracking(inred).ThefactorsidentifiedfromTables1‐11havebeengroupedbased

on how they contribute to a particular condition (in blue) and are listed below that

329ACI Committee 318, BuildingCodeRequirements forReinforcedConcrete, (Detroit, MI: American ConcreteInstitute,1963),33.

128

condition. For example, the factors that contribute to the condition of “shallow concrete

cover” include a thin facing concrete layer, inappropriate placement of reinforcement,

impropercastingmethods,andimproperconsolidationmethods.

Thefollowingdiagramsshouldbereadusingthearrowsandthedescriptorsabove

oronthearrowtounderstandhowthedifferentstepstowardsdeteriorationrelate.These

diagramsborrowfromDonellaH.Meadows’systemdiagramsinher2008bookThinkingin

Systemstoconveyhowexternalfactorsenableorexacerbatethedeteriorationprocess.The

genericsystembelowcanhelptoillustratehowtoreadthem:

ConditionX,enabledbythepresenceofA,causesY.YincreasestheoccurrenceofZ,whichis

exacerbatedbythepresenceofB.

138

APPLICATIONOFMETHODOLOGYANDFUTURESTEPS

To begin to create a preventive conservation plan for an individual building built

witharchitecturalprecastwallpanelsusing the informationpresentedabove, thedateof

thebuilding’sconstructionandthetypeofpanelsusedmustbeidentified.Thisinformation

shouldthenbecomparedtotherecommendationsandguidelinesfromthattimeperiodto

understand the industry literature that informed thedesign,production, andassemblyof

thepanelsusedonthebuilding.Thisinformationmustthenbecomparedwiththepotential

factorsandpathstodeteriorationthathavebeenoutlinedhere.Itisessential,however,that

aconditionsassessmentisconductedinadditiontothisarchivalandhistoricalresearchand

analysis,so thatpertinentexternal factorscanbe identifiedaswellasanypeculiaritiesto

thearchitecturalprecastwallpanelsofthebuildingthatdonotconformwiththeindustry

literaturefromthattimeperiod.

Aftercreatingthisfoundationofinformation,whichwillhelptopointtowardsareas

ofconcern,thearchitecturalprecastwallpanelsystemmustbesurveyedandmonitoredto

learnhowitsconditionchangeswithtimeofdayandseason.Monitoringandsurveyingcan

be performed with the tools presented in Chapter 4. Depending on these findings,

conservationmethodsmaybeimplementedinanefforttopreventfurtherdeteriorationor

topreventdeterioration from starting. For example, if surveying confirms that the facing

concrete layer is only ¾ in. thick, which is also the only cover over the ungalvanized

reinforcement, a realkalization treatment could be administered to protect the

reinforcement fromcarbonation.Similarly, if surveyingconfirms that agapgraded facing

aggregatewasused,resultinginaporousfacingconcrete,animpregnationtreatmentcould

beutilizedtoprotecttheinternalreinforcementandreducefurthercarbonation.

139

Moreresearchmustbeconducted,however,toimprovebothsurveyingtechniques

and current preservation strategies. Key to the success of these tools and treatment

methods is getting ahead of deterioration. The surveying tools available provide only a

limitedviewunderneaththesurfaceoftheconcrete,wherethemostcriticalinformationis

located. Consequently, the accuracy and variety of toolsmust be enhanced.More studies

must also be performed to determine how conservation methods such as cathodic

protection and realkalization may be successfully applied to architectural precast wall

panels to both address their unique composition and characteristics and to protect their

architecturalexpression.

While the information provided in this thesis will be able to contribute to the

creationofpreventiveconservationplanstopreservearchitecturalprecastwallpanels,the

realityisthatreplacementofpanelsmaybenecessaryincertainsituations.330Becausethis

concrete technology is mass‐produced, pathologies have the potential to be pandemic

across a given project—or a given time period. The technological evolution presented in

Chapter 5 and the recommendation tables presented in this chapter reveal problematic

recommendations during different time periods. For example, in the late 1960s, ACI

recommended only a ½ in. minimum cover over reinforcement. If this recommendation

wereexecutedincombinationwithabatchof facingaggregatessusceptibletoalkalisilica

reaction, the facing concrete on the panels of that entire project would be particularly

vulnerable to cracking and spalling. Replacement of the architectural precastwall panels

wouldbemoreeconomicalandsafe,and,throughcarefuldesignandunderstandingofthe

originaltechnology,thiscouldhavethepotentialtopreservetheoriginaldesignintentmore

effectively,whichwasbasedonuniformityandconsistency.Nonetheless,effortsshouldbe

330AnneE.Weber,PaulE.Gaudette,andRobertF.Ambruster,“JohnJ.Earley’sMosaicConcrete:MeridianHillParkandEdisonMemorialTower,”ConcreteInternational(October2011):31.

140

madetopreservetheoriginalfabric—theevidenceofthissignificantconcretetechnology—

beforereplacementisdeemednecessary.

CONCLUSION

There are numerous technical challenges to the physical preservation of

architecturalprecastwallpanels.Theinformationprovidedinthissectionabouthowthey

couldpotentiallydeteriorate, incombinationwithconditionsassessmentsandmonitoring

of individual buildings constructed with them, can be used to create thorough and

successfulpreventiveconservationplans.

141

CHAPTER7:CONCLUSION

Architecturalprecastconcretewallpanelsplayedasignificantroleintheacceptance

ofconcreteasanarchitecturalmaterialanditssubsequentemergenceasadefiningmaterial

of mid‐twentieth century architecture in the United States. This concrete technology

assumed this role because of the efficiency and quality achieved through the precasting

process,thevarietyofsurfacefinishesandarchitecturalexpressionsthatcouldbeachieved

relative to cast‐in‐place concrete, and the competitiveness of architectural precast wall

panelswithmetalandglasscurtainwall systems. Inparticular,becauseof theexpressive

concretemixand/orfinishofarchitecturalprecastwallpanels,thisconcretetechnologyhas

becomeacharacter‐definingfeatureforbuildingsconstructedwithit,asevidencedbysuch

structuresastheDenverHiltonHotel, theNortheastRegionalLibraryinPhiladelphia,and

theBuffaloEveningNewsBuilding.Consequently,thepreservationofarchitecturalprecast

wallpanelsandthebuildingsconstructedwiththemisessentialtothepreservationofmid‐

centuryarchitectureandourunderstandingofthisperiodofarchitecture.

Appreciationfortheirhistoricalandarchitecturalsignificance,however,iscurrently

lacking, and this must be rectified to ensure a preservation interest in this important

architecturalelement.Toelucidate thehistorical significanceof architecturalprecastwall

panels, their history is explored within the context of reinforced concrete and its

architecturaluseinAmerica.Thisexplorationinvolvesexaminingthedevelopmentofcast

stoneandconcreteblock,twoimportantprecastpredecessors;revealingthesignificanceof

World War II to the architectural use of reinforced concrete; and demonstrating the

importanceofcurtainwallconstructiontothesuccessofarchitecturalprecastwallpanels.

Similarly, to illustrate their role as character‐defining features in mid‐twentieth century

architecture, examples of their application are presented. These applications reveal

142

modernistarchitects’interestinarchitecturalprecastwallpanelsandtheiradaptabilitytoa

widerangeofbuildingtypesanddesigns.Moreover,thebuildingsandtheimagespresented

display the variety of architectural expressions that could be achievedwith architectural

precastwallpanels.

Although acknowledging and understanding the historical and architectural

significanceofarchitecturalprecastwallpanelswillbolsteraninterestinpreservingthem,

therearenumerouschallengestotheirphysicalpreservationthatmustbemet.Aswithall

historicconcretestructures,thephysicalpreservationofarchitecturalprecastwallpanelsis

extremelycomplex.Significantly,currentpreservationstrategies inadequatelyaddressthe

importance of preserving the original facing concrete mix and the surface finish and/or

treatment applied to architectural precast wall panels. Preserving this architectural

expression,however, isessential topreserving thisconcrete technologyandthebuildings

constructedwithit.Thus,topreserveasmuchhistoricfabricaspossible,wemustadopta

preventive conservation approach rather than rely on reactive conservation strategies,

which jeopardize the integrity of architectural precastwall panels. Towards this end, the

potential factors that may contribute to their deterioration have been identified by

examining publications providing technical information, guidance, and recommendations

aboutthedesign,production,andassemblyofthisconcretetechnologyfrombetween1945

and 1975. Reviewing these publications reveals the concrete industry’s struggle not to

restricttheartisticresultsachievedthroughtheexperienceandjudgmentoftheindividual

precasterswhilestillstandardizingthisconcretetechnology’sproductionandassemblyto

ensurethequalityof thepanelsproducedand,subsequently, theircompetitiveness in the

building industry. Still, reviewing this industry literature enables us to identify potential

factorsandthemechanismsofdeteriorationtheyleadto,whichprovidesuswithinvaluable

information to be used in the creation of preventive conservation plans for buildings

143

constructed with architectural precast wall panels. These efforts must be met, however,

with increased research in surveyingandpreservation techniques toprovide the tools to

effectivelyimplementpreventiveconservationplans.

Ultimately, tracing the historical and architectural significance of architectural

precastconcretewallpanelswillhelp todemonstrate theirvalueand increase interest in

their preservation. But this alone is not enough: successfully preserving this significant

architectural feature requires that we understand how this concrete technology has

changedovertime,sothatwemaypredictandpreventitsdeteriorationinthefuture.

144

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INDEX aggressivechemicalexposure,51alkali‐silicareactions,51AnshenandAllen,v,41ArmostoneSystem,v,18BankerTrustBuilding,v,39Belluschi,Pietro,v,24,34Blenheimbuilding,v,10,11Breuer,Marcel,v,23,33BuffaloEveningNewsBuilding,v,37,141carbonation,50,52,53,58,59,60,138caststone,10,12‐17,27,67,141cathodicprotection,58,60,139chlorideions,50,51,59concretecover,51,53,56,78,128concretemasonryunits,12,14‐17,27,concreteshrinkage,54,75Conzelman,John,17corrosion,2,49,51,53‐56,58,59,70,74,84,92,100,127

Cossutta,Aldo,v,32,146curtainwallsystem,5,21,24,28DenverHiltonHotel,v,31,32,141DOCOMOMO,37,45domesticcementindustry,8,9,12Earley,John,20,21,76,80EdwardDurellStoneandAssociates,v,37electrochemicalrealkalization,58,60EmoryRothandSons,v,39freeze‐thaw,51,72,75,88Geddes,Brecher,Qualls,andCunningham,v,35,36

Gropius,Walter,v,22,34handlingequipment,28,29,68,84HausnerandMacsai,v,40Hennebique,Francois,8Holabird&Root&Burgee,v,42,43Hyatt,Thaddues,7

impregnationtreatments,58InternationalBuilding,v,41Lascelles,W.H.,17LeCorbusier,22LockstoneSystem,v,19Mathes,HerbertA.v,42,45McGawMemorialHall,v,42,43MiamiBeachPublicLibrary,v,42,45MiesvanderRohe,Ludwig,v,22,24,26,27

modernarchitecturalstyle,11MoSai,20MurrayLincolnCampusCenter,v,33Nolen&Swinburne,v,42,44NortheastRegionalLibrary,v,35,36,141OakParkHighSchool,v,42,43PanAmericanBuilding,v,30,34passivelayer,50,51,56,60Perret,Auguste,10PhiladelphiaPoliceHeadquarters,v,35Portlandcement,7PortlandCementAssociation,9,15,28,50,66,68

Ransome,ErnestLeslie,8,17SamuelPaleyLibrary,v,42,44Shepley,Bulfinch,Richardson,andAbbot,v,38

Shokbeton,29steel,1,3,6,8,9,16,21,24,25,31,42,48,49,51,54,56,59,60,67,74,79,84,92,93,99,100,127

WaltersArtMuseumaddition,v,38Ward,WilliamE.,7,15WaterTowerInn,v,40window‐typemullionwallpanel,29WorldWarII,4,5,11,21,23,28,65,141Wright,FrankLloyd,22