533R-93 Guide for Precast Concrete Wall Panelscivilwares.free.fr/ACI/MCP04/533r_93.pdf · ACI...

ACI 533R-93

Guide for Precast Concrete Wall Panels

Reported by ACI Committee 533

Donald F. Meinheit*Chairman

George F. BatyMuriel BurnsHarry A. ChambersSidney Freedman*Edward M. FrisbeeTheodore W. HuntAllan R. Kenney*Benjamin LavonVictor F. Leabu

* Editorial subcommittee

This guide presents recommendations for precast wall panels. This guideshould be used with ACI 318 “Building Code Requirements for ReinforcedConcrete” which may be legally binding. In addition to a discussion of thebasic principles of design, tolerances and materials, this guide alsodiscusses fabrication, installation, quality requirements and testing.

Keywords: admixtures; aggregates; architectural concrete; coatings; colored con-crete; concrete finishes; cracking (fracturing); curing; deflection; design; dryingshrinkage; erection; exposed aggregate concrete; fabrication; formwork; inspec-tion; joints (junction); precast concrete panels; quality control; repairs; sealants;structural design; sandwich panels; surface defects; temperature; tests; texture;tolerances; volume change; walls.

W. Calvin McCallRobert A. NunezMichael G. OlivaNavin N. PandyaTibor PatakyJames B. Quinn, Sr.Ralph C. RobinsonJoseph R. Tucker

CONTENTS

Chapter l-General considerations, pg. 533R-21.1-Introduction1.2-Purpose and scope1.3-Responsibility for precast concrete wall panels1.4-Esthetic considerations

Chapter 2-Wall panel design, pg. 533R-42.1-Introduction2.2-Design guidelines2.3-Effective dimensions

ACI Committee Reports, Guides, Standard Practices, andCommentaries are intended for guidance in designing, plan-ning, executing, or inspecting construction and in preparingspecifications. Reference to these documents shall not bemade in the Project Documents. If items found in these doc-uments are desired to be part of the Project Documents, theyshould be phrased in mandatory language and incorporatedinto the Project Documents.

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533R

2.4-Limiting dimensions for wall panels2.5-Serviceability considerations2.6-Connections and connection assemblies2.7-Provision for architectural features

Chapter 3-Tolerances, pg. 533R-93.1-General3.2-Definitions3.3-Reasons for tolerances3.4-Role of the engineer-architect3.5-Product tolerances for wall panels3.6-Erection tolerances for wall panels3.7-Interfacing considerations3.8-Clearances and tolerances for constructibility

Chapter 4-Materials, pg. 533R-224.1-Introduction4.2-Portland cement4.3-Aggregates for structural or backup concrete4.4-Facing aggregates4.5-Admixtures4.6-Insulating materials4.7-Reinforcement

Copyright 0 1993, American Concrete Institute.ACI 533R-93 became effective June 1, 1993.All rights reserved including rights of reproduction and use in any form or by

any means, including the making of copies by any photo process, or by any elec-tronic or mechanical device, printed or written or oral, or recording for sound orvisual reproduction or for use in any knowledge or retrieval system or device,unless permission in writing is obtained from the copyright proprietors.

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ACI COMMITTEE REPORT

4.8-Inserts and miscellaneous hardware4.9-Curing materials and sealers4.10-Joint sealants and fillers4.11-Chemical retarders4.12-Form release agents

Chapter 5-Panel fabrication and delivery, pg. 533R-285.1-General requirements5.2-Molds (forms)5.3-Concrete proportioning and mixing5.4-Reinforcement5.5-Concrete placement5.6-Surface finishes5.7-Concrete curing5.8-Storage5.9-Delivery

Chapter 6-Installation, pg. 533R-416.1-Planning and preparation6.2-Unloading and handling6.3-Jobsite storage6.4-Installation6.5-Cleaning6.6-Patching and repair6.7-Joint sealing (caulking)

Chapter 7-Quality requirements and tests, pg. 533R-477.1-Introduction7.2-Unacceptable defects7.3-Structural adequacy7.4-Prestressing7.5-Materials7.6-Testing plastic concrete7.7-Testing hardened concrete7.8-Documentation

Chapter 8-References, pg. 533R-538.1-Recommended references8.2-Cited references

Metric conversion, pg. 533R-55

CHAPTER l-GENERAL CONSIDERATIONS

1.1-IntroductionThe widespread popularity of concrete as a building

material can be attributed to the availability, favorableproperties and geographic distribution of its naturally-occurring mineral constituents. Concrete itself is easilyformed and molded, comparatively economical, and dur-able in its finished state. Architectural precast panel usehas increased because of the nature of concrete as amaterial and the fact that prefabricated components addto construction efficiency. In addition, by exposing decor-ative aggregates, using veneer facing materials, and byvarying sizes, shapes and textures of panels, the engineer-architect has significant esthetic possibilities for creative

response to client needs.

1.2-Purpose and scopeThis document provides guidelines for specifying,

planning, designing, manufacturing, and erecting precastconcrete wall panels. Although the focus is on precastwall panels produced in established precasting plants, siteprecasting is an option that has been used successfully ona number of projects. Tilt-up concrete, as discussed byACI 551, is a variation of site precasting. Guidanceoffered in this document should aid in establishing andmaintaining quality site production as well as plant pro-duction of precast wall panels.

The guide covers two classes of panels, either bothnon-load-bearing or load-bearing, fabricated of eithernormal or lightweight concrete. The panels may be eitherof the following types:

Solid panelsInsulated (sandwich) panelsRibbed panelsHollow-core panelsSculptured panels

In addition to reinforced panels, lightly prestressed(effective prestress, after all losses, between 150 and 225psi) and prestressed panels are covered. Structural designconsiderations briefly addressed in Chapter 2 include theuse of panels as shear wall components.

This guide is a compilation of information containedin several earlier ACI Committee 533 reports,1-44a sym-posium volume,5 committee member experience and newinformation and developments in the industry since thecommittee published its reports.

Heavy emphasis is placed on wall panels with an in-tegral exposed aggregate concrete surface finish. Smoothwall panels, as well as those having finishes of a texturedor shaped architectural surface, are included. Panelshaving natural stone veneer or ceramic veneer finishesare not covered in detail.

1.3-Responsibility for precast concrete wall panels1.3.1 General - Contractual agreements should assign

responsibilities so as to avoid later debate and contro-versy. This can be particularly troublesome when partiesinvolved disagree on basic definitions and decisionsoriginating from the specifying agency.

A special report of an ad hoc committee for theresponsibility for design of precast concrete structureshas been published.6 This report makes recommendationson assignment of authority and responsibility for designand construction of precast concrete structures.

This guide covers the design of panels by the designprofessional, referred to as the engineer-architect*

* As defined by ACI 117, engineer-architect or architect-engineer refers to the“architect, the engineer, architectural firm, engineering firm, issuing project draw-ings and specifications, or adminstering the work under contract specifications anddrawings, or both."

PRECAST WALL PANELS 533R-3

throughout the text. Since there are minimum designrequirements and methods of design peculiar to precastconcrete wall panels, Committee 533 presents supple-mental design guidelines which should be used withACI 318, the provisions of which may be legally binding.Handling and erection procedures vary widely, and guide-lines for these operations should correspond with localpractices but be consistent with Chapter 2 of this guide.Overlapping responsibilities for the structural design ofwall panels may introduce conflicts between engineer-architect and general contractor, regarding shop drawingreview, design for handling, erection stresses, in-placeloads, and adequacy of connections. It is essential thatwork assignments and responsibilities be clearly definedin the contractual arrangements.

1.3.2 Structural design - The engineer-architect canbenefit from preconstruction contact with panel produc-ers. Since most precasters maintain an engineering staffto prepare shop drawings, the engineer-architect shouldinteract with this group to obtain constructive advice andsuggestions concerning local practice, production details,and manufacturing capabilities. When possible, this dis-cussion should take place during the initial design phasesof a construction project. Once a job is released forbidding and the structural concepts have been estab-lished, changes may not be possible.

1.3.3 Reinforcement for handling and erection - It iscommon practice for the engineer-architect to rely on themanufacturer for development of handling techniquesand for providing any additional reinforcement requiredto withstand handling or erection stresses. The engineer-architect may wish to review calculations for handlingstresses.

The contract documents may require the manufacturerto accept responsibility for design of panels to resist theloads shown on the engineer of record’s design drawings,provided sufficient information is shown on these draw-ings, and to resist other loads that occur during stripping,handling, shipping and erection. In this case, it iscommon for the contract documents to require that thedesign calculations and erection drawings provided by thepanel manufacturer be signed by a professional engineerwho is either retained or employed by the manufacturer.

1.3.4 Adequacy of connections - Contract drawingsprepared by the engineer-architect should show the con-nections required and the load support points in suffi-cient detail to permit construction. Manufacturers, duringthe preparation of shop drawings, should be given theopportunity to redesign the connections if redesign willachieve more economical details that facilitate manu-facture or erection. The manufacturer should review theconnections designed by the engineer-architect forstructural adequacy and all connection redesign or anyother problem noted should be brought to the attentionof the engineer-architect. Any deviation from or discre-pancy in the approved erection drawings should be notedby the erection contractor prior to the start of erection.The general contractor should make all necessary ar-

rangements for corrections to be made by the partiesinvolved prior to start of erection.

1.3.5 Handling and erection responsibilities - Re-sponsibility for panel erection and cleaning, jointtreatment, and supply of hardware needed for handling,attachment, and bracing should be clearly defined in thecontract documents. However, contract document specifi-cations, and the specifier, should not prescribe one sub-contract because general contractors are generally moreknowledgeable of the skills and experience of the varioussubcontractors who can perform the services, and generalcontractors can more easily evaluate the economies ofthe different alternatives.

1.3.5.1 Cleaning - Specifications that require cleanpanels after installation are recommended. Cleaning neednot be the object of a separate operation (see Section6.5.2). The precast manufacturer and/or carrier are re-sponsible for delivering clean panels. After installation ofpanels, the responsibility for protecting panels fromsoiling and staining during subsequent operations shouldappropriately be the responsibility of the general con-tractor.

1.3.5.2 Furnishing attachment and handling hardware- Clip angles, inserts, bolts, and miscellaneous metalitems are required for construction with precast panels.These items may be:

. attached to the building frame. embedded in the precast panel for erector or forother trades. provided loose at the job site for connection pur-poses.

The responsibility for supplying items to be attachedto or placed in the structure to receive precast concreteunits depends on the type of structure and on local prac-tice. Specifications should indicate who is responsible forthe supply and installation of hardware. When the sup-porting frame is structural steel, erection hardware isnormally supplied and installed by the precast erector orsteel fabricator. When the building frame consists of cast-in-place concrete, hardware is normally supplied by theprecast manufacturer and placed by the general contrac-tor. Detailed hardware layout is prepared by the precastmanufacturer for approval by the engineer-architect. Oc-casionally certain special inserts or sleeves are requiredfor other trades. In these instances, the trade involved isresponsible for having such parts approved and deliveredto the panel manufacturer in time for embedment in thewall panels. These must be accompanied by the engineer-architect’s approved placement drawings and instructionsfor installation.

1.3.5.3 Execution of connections - The general con-tractor is responsible for accurately constructing bearingsurfaces and anchorages for precast elements. When apanel cannot be erected within tolerances specified in thecontract documents, the matter must be called to theengineer-architect’s attention for consideration and cor-

533R-4 ACI COMMITTEE REPORT

rection.Changes, other than adjustments within the prescribed

tolerances, can only be made after approval. Any adjust-ments affecting structural performance must be approvedby the engineer of record. No panel should be left in anunsafe support condition.

1.3.6 Shop drawing approval - Erection and shapedrawings prepared by the precast manufacturer (see Sec-tion 5.1) should be forwarded to the general contractorfor approval as to constructibility and then forwarded tothe engineer-architect who checks for conformance withthe design requirements and contract documents. Re-viewed drawings from the engineer-architect should bereturned to the manufacturer with a statement resem-bling one of the following notations:

1. Approved for conformance with the contract docu-ments. No resubmissions necessary.

2. Approved, as noted, for conformance with the con-tract documents. No resubmissions necessary.

3. Not approved; revise and resubmit.4. Rejected.

1.4-Esthetic considerationsThe manufacturing techniques and procedures covered

in this guide allow flexibility during manufacturing toachieve uniform esthetic results and concrete quality. Theuse of performance specifications for the appearance ofprecast wall panels has not been completely successful,due to the difficulty of explaining esthetic requirementsor of establishing understandable criteria for acceptance.It is recommended that reference samples be used in de-termining product characteristics and quality, rather thanwriting restrictions which may prohibit the manufacturerfrom using a process that offers the best possibility ofproducing the desired panel.

1.4.1 Design reference samples - Although full-sizesample panels are preferred, some construction specifi-cations may require that the color and texture matchsmall samples. Such samples should be at least 12 x 12 in.although larger samples may be desirable. If both facesof the panel are to be exposed, the samples should showthe finished interior surface as well as the exterior faceof the precast.

The manufacturer should submit samples to the gener-al contractor for approval of the engineer-architect, whileretaining duplicate samples. If the sample is not approv-ed, resubmissions should be made until approval isobtained. Sample approval should be in writing withreference to the correct sample code number, or theapproval may be written on the sample itself.

1.4.2 Full-size samples - Committee 533 recommends that at least 3 full-sized sample panels be specified. These sample panels should contain typical cast-in inserts, reinforcing steel, and plates as required for the project. These panels should establish the range of acceptability with respect to color and texture variations, surface defects and overall appearance. It should be

clearly stated in the contract documents how long thefull-size sample should be kept at the point of manu-facture (precasting plant) or at the job site for com-parison. Approved full-size panels should be allowed tobe used in the completed structure. If full-size samplesare required prior to or at the beginning of manufactur-ing, lead time is necessary and the construction schedulemust be adjusted accordingly. When full-size samplepanels are not specified, the first production panelsshould be submitted for inspection and approval by theengineer-architect.

CHAPER 2-WALL PANEL DESIGN

2.1-Introduction2.1.1 Scope- This guide presents design recommen-

dations for both prestressed and conventionally rein-forced concrete wall panels. Both load-bearing and non-load-bearing panels are covered.

2.1.2 Notation- The standard ACI 318 notation isused throughout this guide. Terms common to ACI 318but used in this chapter with special application to wallpanels are:

b =fc' =

heff =Ig =

k =l =r =eU =

width of cross sectionconcrete compressive strength specified at ageconsidered during designeffective thickness of membermoment of inertia of gross concrete sectionneglecting reinforcementeffective length factorlength of spanradius of gyration of cross sectionunsupported length of wall panel

2.1.3 Definitions - Precast wall panels can be differ-entiated on the basis of structural function as well aspanel configuration. The classes and types of panelscovered in this guide are defined below. Each may beeither prestressed or conventionally reinforced.

Panel classes:Non-load-bearing panel (cladding)-A precast wall

panel that transfers negligible load from other elementsof the structure; this type of panel is generally designedas a closure panel and must resist all applicable serviceand factored loads from wind forces, seismic forces, ther-mally induced forces, forces from time-dependent defor-mations, self weight and those forces resulting fromhandling, storage, transportation and erection.

Load-bearing panel-A precast wall panel that is de-signed to carry loads from one structural element toother structural elements; load-bearing panels must inter-act with other panels and the supporting structural frameto resist all applicable design loads in addition to thoselisted for non-load-bearing panels. Load-bearing panelsalso include panels designed to function as shear walls.


Panel types:Solid panel-A panel of constant thickness; an

allowance for surface texture must be made indetermining effective thickness.

Hollow-core panel-A precast panel that has voidswithin the thickness in one direction for the full length ofthe panel.

Sandwich panel-A precast panel consisting of twolayers of concrete separated by a nonstructural insulatingcore.

Ribbed panel-A precast panel consisting of a slabreinforced by a system of ribs in one or two directions.

2.2-Design guidelines2.2.1 General- Precast wall panels should be de-

signed according to Chapters 8, 9, 10, 11, 12, 16, and 18of ACI 318 except as modified in Sections 2.2.3, 2.2.4.2,2.2.5, 2.3, 2.4.2, 2.5.2 and 2.5.3 of this recommendation.ACI 318 requirements may be legally binding.

2.2.2 Forces for design - Precast wall panels should bedesigned to resist all of the following forces whereverapplicable:

l Forces developed from differential support settle-ment, deformations from creep and shrinkage, structuralrestraint and the effects of environmental temperatures.

l Forces due to construction, handling, storage, trans-portation, erection, impact, gravity dead and live loads,as well as lateral loads from soil, hydrostatic pressure,wind, and seismic action

. Local stress concentrations in the vicinity of connec-tions and applied loads must be considered.

l Forces developed from thermal movement or bow-ing as well as volume change of the panel, with respectto the supporting structure, must be considered.

2.2.3 ACI 318 provisions applicable for member design- The following sections of ACI 318 should be followedfor the design aspects enumerated, except as otherwisemodified in this guide:

Effective prestress-ACI1318, Section 18.6. The averageconcrete stress due to prestressing after losses is limitedto a range of 150 to 800 psi.

Flexure-ACI 318, Chapter 10 for nonprestressedpanels and ACI 318, Chapter 18 for prestressed panels.Requirements of ACI 318, Section 10.7 for deep beamsapply regardless of whether the member is prestressed ornonprestressed.

Shear-ACI 318, Chapter 11 for both prestressed andnonprestressed panels.

Bearing-ACI 318, Sections 10.15 and 15.8.Combined bending and axial load-ACI 318, Sections

10.3 and 10.115.

2.2.4 Combined bending and axial load2.2.4.1 General - All forces listed in Section 2.2.2

should be considered in designing wall panels for com-bined bending and axial load. Also the effects of secon-

dary forces caused by deflection, variable moment ofinertia, stiffness and duration of load should be con-sidered.

Axial forces, bending moments and shear forcesshould be determined from a rational analysis of thestructure. Considerations of member and/or joint trans-lation should be considered in the analysis.

In lieu of the procedure described above, compressionmember design may be based on the approximate pro-cedures given in Section 2.2.4.2.

2.2.4.2 Approximate evaluation of slenderness effect- Procedures described in ACI 318, Section 10.11should be followed for determining the unsupportedlength, effective length, and radius of gyration of precastwall panels.

a)

b)

c)

d)

e)

f)

The effects of slenderness may be neglected ifthe slenderness conforms to ACI 318, Sec-tion 10.11.4.1 or 10.11.4.2. For compressionmembers with slenderness k&/r greater than 150,an analysis according to Section 2.2.4.1 of thisguide should be made.The magnified moment for design of a compres-sion member should be determined according toACI 318, Section 10.11.5.1.For precast wall panels considered to be rein-forced concrete compression members by theserecommendations, the provisions of ACI 318,Section 10.11.5.2 can be used in lieu of moreaccurate calculations.For precast wall panels considered to be pre-stressed concrete compression members by theserecommendations, the provisions of Section 3.5of the PCI Design Handbook, can be used in lieuof more accurate calculations.An equivalent uniform bending moment factor,defined in accordance with ACI 318, Section10.11.5.3 should be considered for precast wallpanels braced against sideways and without trans-verse load between supports.The minimum eccentricity, according to ACI 318,Sections 10.3.5, 10.3.6, 10.11.5.4 or 10.11.5.5, asappropriate, should be considered for precastwall panels when no bending moment occurs ateither end of the panel.

2.2.5 Reinforcement- Precast wall panels are not re-quired to have lateral hoop or spiral reinforcement unlessanalysis or experience indicates this reinforcement isrequired.

Limits of reinforcement for precast wall panels shouldconform to ACI 318, Sections 7.10, 7.12, 10.9, 14.3, and18.11, except that the minimum ratio of reinforcementarea to gross concrete area should not be less than 0.001.Two-way reinforcement is not required for some essen-tially one-way panels, such as hollow-core panels.

2.3-Effective dimensions2.3.1 Effective thickness

2.3.1.1 General- The effective panel thickness for


Exposed aggregate surface

Depth of reveal

Total panelthickness(nominal)

heff!

-IL-L

i

tectural facing concrete

n

2B o n d e d i n t e r f a c el‘_. .

rctural backup concrete

heff = Total panel thickness - depth of reveal (if depthof nominal thickness)

orheff = Total panel thickness

Fig. 2.3.1.2-Effective thickness of architectural faced panels

of reveal exceeds 3%

Ih _

L- b_I

Ribbed‘b-4SolidL?.._-___-_

Hollow-core

Ig = Uncracked moment ot Inertia

h =eff

Fig. 2.3.1.3-Effective thickness of solid, hollow-core, or ribbed panels

design may be different from the total panel thickness.The following sections explain how to determine the ef-fective thickness for design purposes and Figs. 2.3.1.2,2.3.1.3 and 2.3.1.4 provide the general characteristics ofthe various effective thicknesses.

2.3.1.2 Architectural faced panels - The effectivethickness of a wall panel with an integral exposed aggre-gate surface should be determined by subtracting thedepth of aggregate reveal from the total panel thicknessif the depth of aggregate reveal exceeds 3 percent of thetotal thickness. The effective thickness of a wall panelwith a noncomposite facing should not include the separ-

ate facing thickness.2.3.1.3 Solid, hollow-core, and ribbed panels - The

effective panel thickness should be determined by Eq. (2-1).

(2-1)

where Ig is the uncracked moment of inertia accountingfor voids or ribs, if they exist.


Wythe 1

Insulation

, I . I . .

‘: ’ ‘*. . -I

Wythe 2 f. .

Mechanical Connectorh3

heff= h1 + h2 +h3 (if wythes are fully composite)

heff = h1 or h3 (if wythes are not considered composite)

Fig. 2.3.1.4-Effective thickness of sandwich panels

2.3.1.4 Sandwich panels - The effective thicknessof a sandwich panel may be assumed equivalent to theeffective thickness of the two wythes plus insulation onlyif mechanical shear connectors capable of developing fullcomposite action are used to connect the interior andexterior wythes. In such cases the effective thickness maybe determined from Eq. (2-1).

If the insulation core is cellular lightweight concrete orlightweight concrete made with mineral aggregates, theshear transfer through the insulation core must not ex-ceed the shear allowed by the strength of the insulatingconcrete core.

When only partial composite action between wythesexists, and loadings are from lateral forces or long-termsustained loads, the two wythes should be considered asseparate members unless testing is conducted to verifypanel behavior. See Section 2.4.2 for limitations on themaximum slenderness ratio of the load-bearing wythe.

2.3.1.5 Panels of irregular shape - Panels notconforming to the configurations listed in this sectionmay have the effective thickness determined by analysisor testing.

2.3.2 Effective width - If concentrated loads or bend-ing moments are applied to the top and bottom of a wallpanel, the effect of local stress in the vicinity of theapplied concentrated load or bending moment should beinvestigated. The effective width should be determined bya rational analysis.

In lieu of a rational analysis, the effective width for aconcentrated load may not exceed the center-to-centerdistance between supports, nor the width of the loadedportion plus six times the wall panel effective thicknesson each side of the concentrated load.

In lieu of a rational analysis, the effective width forconcentrated bending moments may not exceed the effec-tive thickness of the wall panel or the width of the corbelat the point of concentrated bending moment, whicheveris greater, plus three times the effective wall panelthickness each side of the concentrated bending moment.

2.4-Limiting dimensions for wall panels2.4.1 General- Limiting dimensions for precast wall

panels should be based on requirements of concreteplacement, protection of prestressed and nonprestressedreinforcement, fire resistance, member and local stability,deflection, handling, transportation and concretecracking.

2.4.2 Distance between supports - Spacing of lateralsupports for a precast wall panel loaded in flexure onlyshould not exceed 50 times the effective width of thecompression flange or face.

The maximum slenderness (ke,lr) of a precast wallpanel should not exceed 200.

The spacing between lateral supports of a precastpanel carrying axial load and bending moment should notexceed 50 times the effective width of the compressionface or flange.

Lateral bracing should be attached to the compressionregion of the member cross section needing lateral sup-port unless it can be shown that other portions of thecross section have sufficient stiffness to brace themember.

2.5-Serviceability considerations2.5.1 General - The action of service loads on deflec-

tions perpendicular and parallel to the wall panel mustbe considered. Fatigue, impact (if any), cracking, and in-plane lateral stability at service load conditions must beaccounted for in design.

2.5.2 Computed permissible deflections - Precast wallpanel dimensions should be chosen so that under serviceload conditions, the deflection of any point on the panelmeasured from its original position should not exceed thelimits given in Table 2.5.2. In calculating the deflection,the nonlinear behavior of the materials and/or the struc-tural member should be recognized.

Table 2.5.2-Deflection limits for precast wall panels

Deflection to be Deflectionmember considered limitation

Load-bearingprecast wallpanels

Immediate deflection due 1/240 but notto combined effects of greater than 3/4prestress, if any, self in.weight, and superimposeddead load. 1/360 but notImmediate deflection due greater than 3/4to live load. in.

Non-load-bearing That part of the total de- 1/480 but notprecast wall panel flection after the installa- greater than 3/4elements likely to tion of the non-load-bear- in.be damaged by ing element (the sum oflarge deflection the long time deflection

due to all sustained loadsand the immediate deflec-tion due to live load

2.5.3 Cracking2.5.3.1 Acceptability of cracking - Although precast

wall panels typically undergo far less cracking than cast-in-place concrete, they are not generally crack free. Com-putations based on current engineering practice assume


that cracks will occur in a concrete member even thoughthey may not be visible to the naked eye. It is the controland acceptability of these cracks that must be evaluated.If the crack width is narrow, not over 0.010 in., thestructural adequacy of the casting will remain unim-paired, as long as corrosion of the reinforcement isprevented. Therefore, if the reinforcement is coated forcorrosion resistance, wall panels containing cracks up to0.005 in. wide for surfaces exposed to weather and 0.010in. wide for surfaces not exposed to the weather shouldbe acceptable. The limitation on crack size specified isfor structural reasons. The esthetic limitation will dependon the texture of the surface and the appearance re-quired. On coarse textured surfaces, such as exposed ag-gregate concrete, and on smooth surfaces comparable tothe best cast-in-place structural concrete, the structurallimitation would be aesthetically acceptable. For smoothsurfaces of high quality it may be desirable to limit crack-ing in interior panels to 0.005 in. In addition, it should benoted that cracks will become even more pronounced onsurfaces receiving a sandblasted or acid etch finish.

Additional guidance on cracking and its causes can befound in the PCI Quality Control Manual, PCI DesignHandbook, PCI Architectural Precast Concrete, ACI224.1R, and ACI 224R.

Cracks in precast concrete panels may be classified ashairline, cleavage, or fracture cracks.

Hairline cracks are surface cracks of minute width,visible but not measurable without magnification.

Cleavage cracks are cracks not over 0.01 in. wide that,in the judgment of the inspector, penetrate at least to theplane of the nearest reinforcing steel.

Fractures are total cleavages of measurable widththrough which water may pass freely.

Crazing consists of hairline cracks in an approximatehexagonal or octagonal pattern on the surface of con-crete. These probably occur in many panels, but they arenot readily visible in exposed aggregate surfaces, or whenthe concrete is dark. They are more apparent on whitepanels, flat surfaces, and smooth finishes. Crazing cracksare of little structural importance and should not because for rejection. If the panels are to be installed in anenvironment that may be the source of considerable soil-ing, it may be advisable to avoid smooth concrete finishesin order to render the potential crazing less visible.

2.5.3.2 Crack prevention and control - Significantreductions in crack widths can be obtained by properlyselecting and locating reinforcement and by maintainingaccurate positioning of the steel during the castingoperation. Reinforcement is more effective if it consistsof more closely-spaced, smaller diameter bars or wire,particularly in thin sections. For this reason, welded wirefabric reinforcement is commonly used instead of rein-forcing bars because of the relatively close spacing, 4 to6 in. or less, of the wires.

The flexural reinforcement distribution requirementsin ACI 318, Section 10.6 should be followed for rein-forced precast or architectural wall panel surfaces not

exposed to view. If the geometry of the precast memberis more like that of a two-way slab, flexural reinforce-ment requirement of ACI 318 Section 10.6 may lead tocrack widths wider than expected.

2.5.3.3 Limit on flexural tension - For convention-ally reinforced and prestressed wall panels where theexposed surface is to remain free of discernible cracks,the maximum flexural tension in the member under loadsproduced by stripping, handling, transportation, impact,and live load effects should be less than 5g. The valueof the tensile strength of concrete should be modifiedaccording to ACI 318, Section 11.2 if lightweight aggre-gate concrete is used.

2.6-Connections and connection assemblies2.6.1 General - Wall panel units should be safely and

adequately seated and anchored by mechanical meanscapable of sustaining all loads and stresses that may beapplied to the wall panel, including positive or negativewind pressures and seismic forces where required bycode.

Whenever possible, panels should be concentricallysupported to avoid bowing and warping of panels due tostress differential between inside and outside faces of thepanel.

When the wall panel is designed to serve as a struc-tural member, it may be required to carry imposed ver-tical loads, resist bending and shear (other than thatcaused by its own weight, and volumetric changes), or itmay be designed to function as a shear wall. When wallpanels are designed to transmit load from one to anoth-er, consideration must be given to the additional loadsrequired for the design of the connection or connections.

Concepts for design of connections for precast wallpanels may be found in the PCI Design Handbook andthe PCI Design and Typical Details of Connections forPrecast and Prestressed Concrete.

2.6.2 Panel movement - Wall panel connection assem-blies should be designed to allow for panel movementcaused by volumetric change in the concrete, induced bytemperature, moisture differential, and creep in pre-stressed panels, as well as by differential movement ordrift between the building frame and wall panel units.Guidance on the design for these conditions can befound in PCI Design Handbook and Ref. 7.

2.6.3 Bearing seats- Because of the indeterminacy inthe analysis of load-transfer connection assemblies, bear-ing seats should be provided for panels weighing morethan 5000 lb.

The designer should avoid hanging the panels frominserts, anchors, or other connection devices in directtension near the top edge of the panel. Clips, clamps,welding plates, and brackets are commonly used to resisthorizontal and lateral loads. When they are intended totransfer the panel weight to the structure, rigorousanalysis is required in their design, and special pre-cautions should be enforced to ensure their properinstallation.


2.6.4 Haunches - Concrete haunches used to posi-tively seat panels should conform to shear requirementsof ACI 318, Section 11.9 and should be designed foreccentric loading and combined shear, bending, tension,and bearing stresses. The effect of eccentricity which willcause the panel to deflect should be considered in thedesign of panel reinforcement.

2.6.5 Panel inserts - The design of wall panel insertsthat are part of a connection assembly should be basedon design relationships incorporating the load factors andstrength reduction factors (# factors) specified in ACI318. The connections should not be the weak link in aprecast system. Inserts should have a factor of safety con-sistent with the insert manufacturer’s recommendation.

2.6.6 Fire resistance - Wall panel connections shouldbe fireproofed as required by local codes and have min-imum fire resistance equivalent to that required by codefor the wall panels.

2.6.7 Weld design - Potential relative movementbetween the panel and supporting structural frame oradjacent panels should be investigated when designingthe welds. The effects of possible concrete cracking dueto welding heat on the precast panel or its supportingconcrete frame should be considered in the design of theconnection assembly.

2.7-Provision for architectural features2.7.1 Glass staining or etching - Glass, like all building

materials, is subject to the effects of weathering. Whena moist material is in contact with or applied to glass, theglass surface may undergo subtle changes in the contactarea. If the coating in contact with the glass is inert andmoistureproof, the glass surface will be protected fromchanges caused by exposure to moisture. However, if thecoating material is removed, a differential surface changemay become quite visible and unattractive under somelighting and viewing conditions, even though the changeis slight. Finely divided damp materials, for example, dirtand dust, in contact with glass can cause the glass con-stituents to dissolve slightly and be redeposited at anevaporating edge resulting in staining. In addition, somesilicone sealants have ingredients that may leach out andstain the glass.

When glass (sodium calcium silicate) is exposed tomoisture, a minute amount of the glass will dissolve. Ifthe dissolved material is washed away, little change canbe seen by the human eye. But when the solution re-mains on the glass, atmospheric carbonation of the alkaliand alkaline earth silicates causes a subsequent depositof silica gel. The gel on aging and exposure to atmos-pheric acids becomes difficult to remove. When thishappens uniformly, the eye does not detect the differ-ences. However, the silica gel deposit, or the glass etchdepth need not be thicker than a wavelength of light forthe eye to detect it. Frequent washing of the windowstends to remove the gel before it becomes hard, mini-mizing staining and etching.

Directed slow-water runoff and the resultant dirt

accumulation cause the glass to be attacked nonuni-formly, and eventually the cycle of water drying, gelforming, acid atmosphere attack, and alkali washingcompounds, causes in-depth glass dissolution; no amountof cleaning or buffing will remove the stain or etch.

Staining will be more noticeable on tinted heat-ab-sorbing glass because of the greater contract between thelight color of the stain or etch and the darker color ofthe glass. There is no known difference in the composi-tion of tinted glasses, which contributes to this staining,as compared to clear glass.

2.7.2 Drip details - Directed slow-water runoff ofrainwater over building facades and dirt accumulationsometimes contributes to staining or etching of glasssurfaces. This phenomenon was briefly discussed in Sec-tion 1.4 and is more fully explained in PCI ArchitecturalPrecast Concrete. Appropriate building details can reducethe amount of water discharged to the glass. Concreteframes at window heads should, wherever possible, bedesigned so that they do not splay down and back towardthe glass unless drip details are incorporated into theframes. Without drip details, a direct, slow washdown ofthe glass should be anticipated.

The drip section should be designed in relation to theslope of the concrete surface (se Fig. 2.7.2.1). To avoida weakened section that is likely to chip, the drip shouldnot be located too close to the edge of the precast unit.The introduction of edge drips and a second drip orgutter serve as a dual line of defense against slow waterrunoff. This can be accomplished by having a cast-in dripin the panel or by the use of extrusions (either aluminumor neoprene) across the head of the window, which haveeither an integral gutter or an extended drip lip of atleast 1 in. also shown on Fig. 2.7.2.1.

2.7.3 Joint size and location - Joints between precastpanels or panels and adjacent building materials must bewide enough to accommodate anticipated panel andbuilding movements. No joint should ever be designed tobe less than 3/8 x 3/8 in. Particular care must be given tojoint tolerances in order for the joint sealant system toperform within its design capacities. For optimum perfor-mance and maximum sealant life, recommendations ofthe sealant manufacturer should be followed.

Panels less than 15 ft long may have 1/2-in. joints, butall other panels should have at least 3/4-in. joints. Cornerjoints should be 1/4 in. wider to accommodate the extramovement and bowing that occurs there. Joint widths of3/8 in. are considered highly risky for any sealant instal-lation. When joints are too narrow, adjacent panels orbuilding materials may come in contact and be subject toinduced loading, distortion, cracking, and crushing ofends.

CHAPTER 3-TOLERANCES

3.1-GeneralPrecast structures should be designed and detailed in


Design of water drip in relation toslope

SEALANT OR PLASTIC DRIP

SHALLOW HEAD

DRIP ORGUTTER

_*k

45o HEAD

DON’T

Fig. 2.7.2.1-Design of water drip in relation to slope

Drip or gutter incorporated into headsection gasket

3/8 ANCHOR WITHIN 6” EACHSIDE OF VERTICALTYP . - 2” EMBEDMENT

I

EXPERIMENTAL GUTTER INSTALLEDTO CORRECT GLASS STAINING

such a manner that the complete structure will be safe,functional, aesthetically appealing, and economical. How-ever no structure is exactly level, plumb, straight andtrue. All construction and materials should be specifiedwith permissible variations, or tolerances, limiting theextent of deviation from design values. These tolerancesrequire monitoring in order to construct the structure asdesigned. General construction tolerances for cast-in-place and precast concrete have been summarized byACI 117 and the PCI Committee on Tolerances. Thischapter presents tolerances that are specifically appli-cable to precast concrete wall panels.

Three tolerance groups should be established as partof precast concrete wall panel design. Wall panels andtheir component details should conform to:

Product tolerances (Section 3.5)Erection tolerances (Section 3.6)Interfacing tolerances (Section 3.7)

When tolerances are understood and provided for inthe design stage, the task of determining and specifyingthem is made easier. The precaster, constructor, anderector must all understand the type of allowances madein the design stage in order to construct the structure asdesigned.

3.2-DefinitionsBowing-An overall out-of-plane distortion, differing

from warping, in that while two edges of the panel mayfall in the same plane, the portion of the panel betweenthe edges can be out of the plane defined by the edges.Several bowing conditions are shown in Fig. 3.2.1.

Differential bowing may be observable when panels areviewed together on the completed structure. When twopanels bow in the same direction, the magnitude of dif-ferential bowing is determined by subtracting one bow-ing value from another. When panels bow in oppositedirections, the convex bowing is taken as positive (+) andconcave bowing is taken as negative (-) by a standardsign convention, the differential bowing is the algebraicdifference.

For example in Fig. 3.2.2 if the maximum bowing of
panel 3 was +1/4 in. and the maximum bowing of panel 4was -1/4 in., then the differential bowing between thesetwo adjacent panels is 1/2 in.
Camber-The maximum deviation in elevation from astraight line through the end points of an element; acamber deflection that is intentionally built into astructural element or formed to improve appearance orto nullify the deflection of the element under the effectsof loads, shrinkage, and creep.

Clearance-Interface space between two members iscalled clearance. Clearance is normally specified to allowfor the differing amounts of deviation that can occurwithin a tolerance envelope and to allow for anticipated

WALL PANELS 533R-11
PRECAST
CROSS SECTION CROSS SECTIONCONVEX BOWING CONCAVE BOWING

BOWING(CROSS SECTION)

g lrcExPOSED FACE0 8 (CONCAVE))

$

E .MAX. BOWING

s5

PRECAST CONCRETEPANEL-

8OWNG KLEV.1

~GTN 0F BOW(CROSS SECTION)

ELEVATION PANEL BOWED IN BOTHELEVATION & CROSS SECTION

Fig. 3.2.1-Bowing definitions for panels

C R O S S S E C T I O N O F F A C A D E

Fig. 3.2.2-Differential bowing of panels

PRECASTCONCRETEPANELS

movement caused by volume change, temperature effects, or elastic deflection.

Dimensions-There are basic (nominal) and actualdimensions. The basic dimension is shown on the con-tract drawings or called for in the specifications. Thesedimensions apply to size, location, and relative locationof the precast member within the structure. The actualdimension is the measured dimension after casting orinstallation of the precast member.

Level-A line or plane perpendicular to plumb.Plumb-A vertical direction radiating from the center

of the earth, commonly determined by a suspendedweight.

Skew-An out-of-square variation from a rectangularshape. This is normally measured by comparing thelength of the diagonals.

Surface out-of-planeness-A local smoothness variationrather than a bowing variation. The tolerance for thisvariation is usually expressed in fractions of an inch or ininches per 10 ft. The tolerance is usually checked with a10-ft straightedge or equivalent as shown in Fig. 3.2.3.

Tolerance-A permitted variation from the basicdimension or quantity as in the length, width, or depth of.a member; the range of variation permitted in maintain-ing a basic dimension should be specified.

SMOOTHNESS EXPOSED SURFACEOF PRECASTCONCRETE

10' STRAIGHTEDGE(TYP.)

. . 1/2" ROLLER (TYP.)-7

a\ --

-., ---_ (WON'T FIT ANYWHERE).

VARIATION INLOCAL SMOOTHNESS

MEASURING LOCAL SMOOTHNESS VARIATIONS

ANY SURFACE

Fig. 3.2.3-Local smoothness variations

Fig. 3.2..4-Warping definitions for panels

Variation-The difference between the actual dimen-sion or location and the basic dimension. When thepermitted variation is symmetrical, the tolerance can beexpressed as a plus-minus (+) variation from a specifieddimension or relationship.

Warping-A deviation of the panel from its originalshape or the overall variation from planeness in whichthe panel comers do not fall within the same plane.Warping tolerances are stated in terms of the magnitudeof the comer variation as shown in Fig. 3.2.4. This valueis usually given in terms of the allowable variation perfoot of distance from the nearest adjacent comer with a“not-to-exceed” maximum value of comer warping.

3.3-Reasons for tolerancesTolerances are needed for product, erection, and

interfacing for the following reasons:Structural Considerations-To ensure that the structural

design properly accounts for factors sensitive to vari-ations in dimensional control. Examples include eccentricloading, bearing areas, hardware and hardware anchoragelocations, and locations of reinforcing or prestressing


steel.Performance-To ensure acceptable performance of

joints and interfacing materials in the finished structure.Appearance- To ensure that the deviation from theo-

retical requirements will be controllable and result in anacceptable appearance. Large deviations are objection-able, whether they occur suddenly or cumulatively.

Cost-To ensure ease and speed of production anderection by having a known degree of accuracy in thedimensions of the precast members.

Legal considerations-To avoid encroaching on build-ing lines.

Contractual-To establish a known acceptability rangeand also to establish responsibility for developing,achieving and maintaining mutually agreed-on tolerancevalues.

3.4-Role of the engineer-architectThe engineer-architect should coordinate the toler-

ances for precast work with the requirements of othertrades whose work relies on or is adjacent to the precast.Tolerances should be reasonable, realistic, and withingenerally accepted limits because manufacturing anderection costs are directly related to degree of precisionrequired. Thus it is economically desirable and practicallysafer to design with maximum flexibility and to keep tol-erance requirements as liberal as possible. Tolerancesgiven in this guide are basic guidelines only. Theengineer-architect determines whether a deviation fromthe allowable tolerances affects safety, appearance orother trades.

When design involves particular features sensitive tothe cumulative effect of tolerances on individual portions,the engineer-architect should anticipate and provide forthis effect by setting a cumulative tolerance limit or byproviding escape areas where accumulated tolerances orproduction errors can be absorbed. The consequences ofall tolerances for a particular design should be inves-tigated to determine whether a change is necessary in thedesign or in the tolerance level for the design. Thereshould be no possibility of minus tolerances accumulatingso that the bearing length of members is reduced belowthe required design minimum. The engineer-architectshould in this case specify the minimum bearingdimensions.

Careful inspection of the listed tolerances reveals thatmany times one tolerance will override another. Thepermitted variation for one element of the structureshould not be such that it would require another elementof the structure to exceed its tolerances. Restrictivelysmall tolerances should be reviewed by the precaster andgeneral contractor to ascertain that they are compatiblewith other elements and that they can in fact be met. Forexample, a requirement which states that “no bowing,warping or movement is permitted” is not practical. Allinvolved in the design-construction process should under-stand that tolerances given herein are for guidance onthe range of acceptability and not an automatic standard

for rejection. If these tolerances are exceeded, the en-gineer-architect may accept the product if it meets any ofthe following criteria:

a) Exceeding the tolerance does not affect thestructural integrity or architectural performanceof the member.

b) The member can be brought within tolerance bystructurally and architecturally satisfactory means.

c) The total erected assembly can be modified tomeet all structural and architectural require-ments.

3.5-Product tolerances for wall panels3.5.1 General - Product tolerances cover the dimen-

sions and dimensional relationships of individual precastconcrete members. All tolerances should be based on adegree of accuracy which is practical and achievablewhile satisfying functional and appearance requirements,and preventing costs from becoming prohibitive. Thisrequires consideration of the amount of repetition, thesize, and other characteristics of the precast member.

Manufacturing tolerances are standardized throughoutthe precast industry and for economic reasons should bemade more exacting only where absolutely necessary. Forexample, bowing or warping tolerances for flat concretepanel members with a honed or polished finish mighthave to be decreased to 50 percent of typical tolerancesto avoid joint shadows. When design details lead to analignment problem or provide inadequate joint size, theproduct tolerance may have to be adjusted to compensatefor the joint design problems.

In establishing casting tolerances for panels, thefollowing items should be considered:

l Length or width dimensions and straightness of theprecast element will affect the joint dimension, thedimensions of openings between panels, and perhaps theoverall length of the structure.

l Panels out of square can cause tapered joints andmake adjustment of adjacent panels extremely difficult.Sealant application difficulties due to tapered joints canlead to future water leakage problems.

l Thickness variation of the precast unit becomescritical when interior surfaces are exposed to view. Anonuniform thickness of adjacent panels will cause offsetsat the front or rear faces of the panels.

3.5.2 Dimensional tolerances - Architectural precastconcrete panels should be manufactured and installed sothat the face of each panel which is exposed to view aftererection complies with the dimensional requirementsshown in Fig. 3.5.2a. Figure 3.5.2a also shows the posi-tion tolerance for cast-in items within the panel. Theseare for typical, generic panels, and the tolerances mayrequire adjustment for specific job conditions.

Cast-in grooves, reglets, or lugs that are to receiveglazing gaskets should be held relatively close to their

533R-13
PRECAST WALL PANELS
a = Overall height and width meto the mold at time of casting or neutral axis of ribbedmembers:

asured at the face adjacent

10 ft or under10 ft to 20 ft20 ft to 40 ftEach additional 10 ft

b = Thickness, total or flangec = Rib width (thickness)d = Rib to edge of flangee = Distance between ribsf = Variation (deviation) of

f l/8 in.+ l/8 in., - 3/16 in.+ l/4 in.+ l/16 in. per 10 ft+ l/4 in., - l/8 in.

2 l/8 in.f l/8 in.f l/8 in.

plane of side mold + l/32 in. per 3 in. ofdepth or + l/16 in.total, whichever isgreater

Variation from square or + l/8 in. per 6 ft ofdesignated skew (difference diagonal or + l/2 in.in length of diagonal total, whichever ismeasurements) greater Length and width ofblockouts and openingswithin one unit* *l/4 in.

h1=location and dimensions ofblockouts hidden from viewand used for HVAC andutility penetrations

i = Dimensions of haunchesj = Haunch bearing surface

f 3/4 in.+ l/4 in.

deviation from specifiedplane

k = Difference in relativef l/8 in.

position of haunch bearingsurfaces of adjacent panelsfrom specified relativeposition It 1/4 in.

1 = Bowing L/360, maximum 1 in.m = Differential bowing

between adjacent panelsof the same design l/2 in.

n = Local smoothness 1/4 in. in 10 ft

o = Warping 1/16 in. per ft of distancefrom nearest adjacentcorner, maximum 1 in.

p = Location of windowopening * l/4 in.

q = Position of plates f 1 in.r = Tipping and flushness

of plates t l/4 in.

POSITION TOLERANCES: For cast-in items, measuredform the datum line location as shown on the approvederection drawings

InsertsWeld platesHandling devicesReinforcing steel andwelded wire fabric**TendonsFlashing regletsFlashing reglets, at edge

of panelReglets for glazing

gasketsGroove width for

glazing gasketsElectrical outlets, hose

bibs, or other utilityembedded items

Openings andblockouts

Center line of blockout*Haunches, to be placed

in form

f l/2 in.f 1 in.f 3 in.

f 1/4 in.2 1/8 in.f 1/4 in.

2 1/8 in.

+- 1/8 in.

+ 1/16 in.

* 1/2 in.

2 1/4 in.f 1/4 in.

+ 1/4 in.

*Some types of window and equipment frames requireopenings more accurately placed, and when this is the case,the minimum practical tolerance should be defined with theinput of the producer.**Tolerance given should be used where position hasstructural implications or affects concrete cover, otherwiseuse + l/2 in.

Fig. 3.5.2a-Production tolerances for precast architectural wall panels

CROSS SECTION

p =a = Length f l/2 in.b = Width f 1/4 in.c = Depth f l/4 in.d = Stem width f l/8 in.e = Flange thickness + l/4 in., - l/8 in.f = Distance between stems f l/8 in.g = Stem to edge of top flange f l/8 in.h = Variation from specified

q =

r =s =

k =l =m =

n =o =

maximumVariation from specified

end squareness or skew f 1/8 in. per 12 in.Sweep (variation from straight

line parallel to center lineof member)

Members up to 40 ft long f l/4 in.Members 40 ft or longer f 3/8 in.Position of tendons f l/4 in.Position of blockouts f 1 in.Size of blockouts

Finished opening +: 1/2 in.Rough opening f 1 in.

flange squareness or skew

Position of plates f 1 in.

* l/8 in. per 12 in.

Tipping and flushness ofplates f l/4 in.

of width, + l/4 in.

Position of inserts forstructural connections f l/2 in.

Position of handling devicesParallel to length A 6 in.Transverse to length f 1 in.

Bowing L/360 maximum*Differential bowing between

adjacent panels of thesame design l/2 in. (13 mm)*

Position of flashing reglets f l/4 in.Haunches (noncumulative)

i =

j =

u1 = Bearing elevation from bottomof panel f 1/4 in.

u2 = Relative position of bearingelevation in verticaIplane f l/8 in.

u3 = Haunch bearing surfacesquareness perpendicularto applied major load A/8 in. per 18 in.,

f l/4 in. maximumv = Local smoothness any

surface Al/4 in. in 10 ft*w = Warping 1/16 in. per ft of

distance from nearestadjacent corner

t =u =

*Does not apply to visually concealed surfaces. Refer toFig. 3.2.1, 3.22 and 3.2.3 for definition.

Fig. 3.5.2b-Dimension (production) tolerances for standard precast ribbed panels used as wall panels

CROSS SECTION

PLAN

I-J-r- h

ELEVATION

a = Lengthb = Width

f 1/2 in.f l/4 in.

c = Depth f l/4 in.dt = Top flange thicknessTop flange area defined by the actual measured values ofaverage dt x should not be less than 85 percent of thenominal area calculated by dt x b nominal.db = Bottom flange thicknessBottom flangearea defined by theactual measured valuesof average db xxb shall not be lessthan 85 percent of thenominal area calculated by db nominal x b nominal.e = Web thicknessThe total cumulative web thickness defined by thesummation of actual measured values of e shall not be lessthan 85 percent of the nominal cumulative width calculatedusing summation of e nominal.f = Blockout location f 2 in.g = Flange angle 1/8 in. per 12 in.,

l/2 in. maximumh = Variation from specified end

squareness or skew f 1/2 in.i = Sweep (variation from straight line

parallel to centerline of member) f 3/8 in.j = Center of gravity (CG) of the strand groupThe CG of the strand group relative to the top of the plankshall be within 2 l/4 in. of the nominal strand group CG.

Any individual strand should be within 2 1/2 in. of nominalvertical position and f 3/4 in. of nominal horizontalposition and shall have a minimum cover of 3/4 in.k = Position of plates f 2 in.l = Tipping and flushness of plates f 1/4 in.m = Local smoothness l/4 in. in 10 ft*

n= Camber applications requiring close control ofdifferential camber between adjacent members of the samedesign should be discussed in detail with the producer todetermine applicable tolerances.

PLANK WEIGHT: Excess concrete material in the plankinternal features is within tolerance as long as the measuredweight of the individual plank does not exceed 110 percentof the nominal published unit weight used in the loadcapacity calculations.

*Doessnot apply to top deck surface left rough to receive atopping or visually concealedsurface.

Fig. 3.5.2c-Dimensional tolerances for hollow core slabs used as wall panels


correct location. Misalignment of these reglets at corners,or casting them in a warped or “racked” position willrestrict proper installation of the glazing gasket. Inaddition, gasket manufacturers place very restrictivetolerances on the groove width and surface smoothnessnecessary to obtain a proper moisture seal of the gasket.

Dimension tolerances for standard precast ribbedpanels are shown in Fig. 3.5.2b. Dimension tolerances forhollow-core slabs used as wall panels are shown in Fig.3.5.2c. Standardized ribbed and hollow-core members,typically used for roof and floor units, are frequentlyadapted for use as wall panels. The tolerances for thesestandardized units are generally more liberal than thosefor architectural panels. If the engineer-architect cannotaccept the standard tolerances of ribbed and hollow-coreunits when using them as wall panels, they should specifyother tolerances as required or the architectural toler-ances as given in Fig. 3.5.2c.

3.5.3 Warping and bowing - Warping and bowing aredefined in Section 3.2. Nonsymmetrical placement ofreinforcement may allow warping due to lack of restraintof drying shrinkage and thermal movements. Note thatsurface out-of-planeness (also defined in Section 3.2) isdifferentiated from bowing because it is not a charac-teristic of the entire panel shape, but rather a localsmoothness variation. The tolerance for local smoothnessis checked with a straightedge or the equivalent as shownin Fig. 3.2.3. The measurement of warping is shown inFig. 3.2.4.

Table 3.5.3 shows a relationship between overall flatpanel dimensions and cross-sectional thickness. If thethickness is less than suggested in Table 3.5.3, warpingtolerances should be reviewed for the possibility ofincreasing the tolerance. Panels thinner than those inTable 3.5.3 should not automatically be subjected to thestandard tolerances for bowing and warping. Ribbedpanels and panels manufactured using aggregates largerthan 3/4 in. exposed at the surface also need further con-sideration in the establishment of bowing and warpingtolerances. Tolerances for flat panels of nonhomoge-neous materials, such as two widely different concretemixes or natural stone veneer with concrete backup,should be reviewed; these tolerances may have to beincreased or reduced to meet design criteria.

Table 3.5.3-Guidelines for panel thicknesses for overallbowing and warping tolerances

panel stiffness consistent with suggested normal panel

Paneldimensions 8 ft 10 ft 12 ft 16 ft 20 ft 24 ft 28 ft 32 ft

4 ft 3 in. 4 in. 4 in. 5 in. 5 in. 6 in. 6 in. 7 in.6 ft 3 in. 4 in. 4 in. 5 in. 6 in. 6 in. 6 in. 7 in.8 ft 4 in. 5 in. 5 in. 6 in. 6 in. 7 in. 7 in. 8 in.10 ft 5 in. 5 in. 6 in. 6 in. 7 in. 7 in. 8 in. 8 in.

3.6-Erection tolerances for wall panels3.6.1 Discussion-Erection tolerances are required for

the functional matching of the precast elements with thebuilding structure. The engineer-architect should setthem to be compatible with the desired architectural ex-pression and detail appropriate to the building structureand site conditions. Erection tolerances should be set toachieve uniform joint and plane wall conditions, consid-ering the individual element design, shape, thickness,composition of materials, and overall scale of the ele-ment in relation to the building. Erection tolerancesaffect the work of several trades and must be consistentwith the tolerances specified for those trades. It is theresponsibility of the engineer-architect to see that tol-erances are compatible.

The engineer-architect should review proposed erec-tion tolerances with the panel manufacturer and the erec-tor before erection commences. Proposed changes bymanufacturer or erector from the original plan should bestated in writing and noted on erection drawings. Agree-ment should be reached before scheduling equipment forpanel installation.

The general contractor, in consultation with theprecast concrete erection contractor, should check dimen-sions and location of the in-place structure before placingthe precast panels on the building. Any dimensional dis-crepancies that may affect erection should then bereviewed and resolved with the engineer-architect beforestarting erection. The contractor may have to makecorrections to the interfacing structure.

Location or erection tolerances for wall panels shouldbe noncumulative. The recommended tolerances are list-ed in Figs. 3.6.1 and 3.6.2. Figure 3.6.1 shows erectiontolerances for precast wall panels while Fig. 3.6.2 showserection tolerances for structural wall panels.

3.6.2 Control points and benchmarks - To ensureaccurate application of erection tolerances, the generalcontractor should establish and maintain accurate controlpoints and bench marks, in areas that will remain undis-turbed until final completion and acceptance of a project.The contractor should provide the erector with a buildingperimeter offset line at each floor approximately 2 ftfrom the edge of the floor slab and bench marks on allperimeter columns. Offset lines and bench marks should

PRECAST WALL PANELS

-8LDG.Y GRID DATUM

-4-i-

STEEL STRUCTURE

STEEL STRUCTURE

-tI

OF STEEL

h-k

P L A N

BLDG. ELEV. DATUM

--BLDG. X GRID DATUM

l l BLDG. Y DATUM

-a

ST CONCRETE PANEL

P L A N

- - BLDG X DAT

a = Plan location from building grid datum * f 1/2 in.a1 = Plan location from center line of steel ** f l/2 in.b = Top elevation measured from nominal top elevation

/PRECAST CONCRETE PANEL

d d

Exposed individual panelNonexposed individual panelExposed relative to adjacent panelNonexposed relative to adjacent panel

c = Support elevation from nominal elevationMaximum lowMaximum high

d = Maximum plumb variation over height ofstructure or 100 ft, whichever is less*

e = Plumb in any 10 ft of element heightf = Maximum jog in alignment of matching

edgesg = Joint width (governs over joint taper)h = Joint taper maximumh10 = Joint taper over 10 fti = Maximum jog in alignment of matching

faces

f 1/4 in.f 1/2 in.

1/4 in.1/2 in.

l/2 in.1/4 in.

1 in.l/4 in.

l/4 in.f l/4 in.

3/8 in.l/4 in.

l/4 in.j = Differential bowing or camber as erected between

adjacent members of the same design l/4 in.

E L E V A T I O N

* For precast buildings in excess of 100 ft tall, tolerances aand d can increase at the rate of l/8 in. per story over100 ft to aamaximum of 2 in.

**For precast elements erected on a steel frame, thistolerance takes precedence over tolerance on dimension a.

Fig. 3.6.1-Erection tolerances for precast wall panels


F

BLDG. Y GRID DATUM

a =

a1 =

b =

c =

d =

e =

f =

g =

T CONCRE

B L D G X

CAST-IN-PLACEOR PRECAST CONC

b

TE PANEL

GRID DATUM

RETE

PLAN

-i

- ;

c

BLDG. ELEV.DATUM

st

1 CAST-IN-PLACEc CONCRETE

ft ’ I P’ 1 b. * o-i

be .* 0 ' . . s,;

_----__-- _.-----

h * . I----_--_-_--_o -b--~-_*-1’ .

A‘ ‘*

. . ~ ‘0.A 0

I I .>c ,

A ’ p .

I-

v. :. b. ’ .

. .

NOM. JT. WIDTH -ct_

h-M--h-

CAST-IN-PLACE FOUNDATIONOR PRECAST CONCRETE SUPPORT

ELEVATION

Plan location from building h =

grid datum* *l/2 in. h10 =Plan location from center- i =line of steelt +I/2 in.Top elevation from nominaltop elevation

Exposed individual panel *l/2 in. j =Nonexposed individual panel *3/4 in.Exposed relative to adjacent panel l/2 in.Nonexposed relative to adjacent 3 / 4 in.panel

Bearing elevation from nominalelevation

Maximum lowMaximum high

Maximum plumb variation overheight of structure or 100 ft,whichever is less*Plumb in any 10 ft ofelement heightMaximum jog in alignment ofmatching edgesJoint width (governs overjoint taper)

Joint taper over length of panelJoint taper over 10 ft lengthMaximum jog in alignment of matchingfaces

1/2 in.3/8 in.

ExposedNonexposed

Differential bowing, as erected,between adjacent members of thesame design*

3/8 in.3/4 in.

1/2 in.

l/2 in.1/4 in.

*For precast buildings in excess of 100 ft tall, tolerances"a" and "d" can increase at the rate of l/8 in. per story over100 ft to a maximum of 2 in.$For precast elements erected on a steel frame, thistolerance takes precedence over tolerance on dimension “a.”

1 in.

l/4 in.

l/2 in.

+3/8 in.

ig. 3.6.2-Structural wall panels


be maintained until final completion and acceptance ofthe work. They may be scored into columns and floorslabs, or laid out as chalk lines and lacquered forprotection.

3.6.3 Jointproblems - Width variations between adja-cent joints can be minimized by setting out joint centerlines equally spaced along an elevation and centeringpanels between them. The larger the panels, the widerthe theoretical joint should be in order to accommodaterealistic tolerances in straightness of panel edge, in slopeof edge, and in panel width. Alignment for exteriorelements should be controlled by assuming that theoutside face of the element is critical. Variations fromtrue length or width dimensions of the overall structureare normally accommodated in the joints. Where this isnot feasible or desirable, variations should be accom-modated at the corner elements, in expansion joints, orin joints adjacent to other wall materials.

Joint widths should be designed as liberally as possibleif variations in overall building dimensions are to beabsorbed in the joints. This may be coupled with a closertolerance for variations from one joint to the next forappearance purposes. The individual joint width toler-ance should relate to the number of joints over a givenbuilding dimension. For example, to accommodate rea-sonable variations in actual site dimensions a 3/4 in. jointmay be specified with a tolerance of +: 1/4 in. but withonly a 3/16 in. differential allowed between joint widthson any one floor, or between adjacent floors.

Where a joint has to match an architectural feature(such as false joints) a _+ 1/4 in. variation from thetheoretical joint width may not be acceptable and atighter tolerance specified. Adjustment in building lengthwill then have to be accommodated at the corner panelsor in joints adjacent to other wall material.

If reasonable tolerances and adjustments have beendesigned into the construction details and are adhered to,the erector should be able to:

l minimize joint irregularities such as tapered joints(panel edges not parallel)

l minimize jogs at intersectionsl minimize nonuniformity of joint widthl maintain the proper opening dimensionsl properly construct all precast connectionsl align the vertical faces of the units to avoid offsetsl prevent the accumulation of tolerances.

A more precise installation and general improvementin appearance are thus achieved.

3.7-Interfacing considerations3.7.1 General- Interface tolerances and clearances

are those required for joining of different materials andto accommodate the relative movements between suchmaterials during the life of the building. They coverproducts installed after the precast members are in placeas well as materials installed before precast erection. The

engineer-architect should provide for proper clearances(purposely provided space between adjacent independentmaterials) between the theoretical face of the structureand the back face of the precast element. The face ofstructure may be precast concrete, cast-in-place concrete,masonry, or a structural steel frame. Adjacent materialsinclude products such as glass or subframes that areinstalled after the precast panels are in place. Theclearance space provides a buffer where erection, pro-duct, and interface tolerances can be absorbed.

Where matching of the manufactured materialsdepends on work at the construction site, interfacetolerances should equal erection tolerances. Where theexecution is independent of site work, tolerances shouldclosely match the standard tolerances for the materials tobe joined. Fabrication and erection tolerances of othermaterials must be considered in design. Precast elementsmust be coordinated with and accommodate the otherstructural and functional elements comprising the totalstructure. Unusual requirements or allowances for inter-facing should be stated in the contract documents.

3.7.2 Building frame tolerances - Erection tolerancesfor precast panels are of necessity largely determined bythe actual alignment and dimensional accuracy of thebuilding foundation and frame. The general contractor isresponsible for the plumbness, level, and alignment ofthe foundation and structural frame including the loca-tion of all bearing surfaces and anchorages for precastproducts. Many engineer-architects fail to recognize thecritical importance of controlling foundation and buildingframe tolerances. It is not uncommon to find specifica-tions which make no mention of tolerances for the struc-ture to which the precast is connected. Likewise, it is notuncommon to find architectural or structural drawings onwhich clearance dimensions fail to take into account thenormal product and erection tolerances. If precast ele-ments are to be installed plumb, square, and true, theactual location of surfaces affecting the precast elements’alignment (including the levels of floor slabs and beams,the vertical alignment of floor slab edges and the plumb-ness of columns or wall) must be known before erectionbegins.

Concrete cast-in-place frames to which precast ele-ments are attached should meet the tolerances shown inTable 3.7.2 in addition to ACI 301 or ACI 117 require-
ments. Greater variations in height of floors are moreprevalent in cast-in-place structures than in other struc-tural frames. This affects location or mating of the insertin the precast with the cast-in-place connection device.Tolerances for cast-in-place structures may have to beincreased further to reflect local trade practices, thecomplexity of the structure, and climatic conditions.
Figure 3.7 shows erection tolerances for beams and
spandrels, particularly precast element to precast ele-ment, precast to cast-in-place concrete and masonry, andprecast to steel frame.
3.7.3 Mixed construction - It should be recognizedthat ACI 117 applies only to reinforced concrete and ma-


Table 3.7.2-Supplementary tolerances for cast-in-place concrete frames to which precast concrete is to be attached

Footings, caisson caps, and pile capsVariation of bearing surface from specified elevation

Piers, columns, and walls/4 ‘Y2it-L

Deviation from the level or grades specified in the drawingsAny bay or wall length less than 20 ftAny bay or wall length greater than 20 ft

Deviation from column cross-sectional dimensionsor wall thickness

Anchor boltsVariation from specified location in planVariation from specified elevation:Anchor bolt projectionPlumbness of anchor boltFloor ElevationsVariation from specified level

l/2 in.3/4 in.

+ % in., - % in.

* l/in.2 l/2 in.

+ % in., - % in.+ l/16 in. per ft

* ‘! in. in 10 ft* % in. in 30 ft or greater length

sonry buildings, and the AISC Code of Standard Practiceonly to steel building frames. Tolerances in neither ofthese standards apply to buildings of mixed construction(for example, concrete floor slabs carried by steel beamsor concrete encased structural steel members). Obviously,the location of the face of the concrete on an encasedsteel member and the location of the steel member itselfare both critical. Since the alignment of mixed construc-tion members and encased members is not controlled byreferencing the above standards, the engineer-architectshould require that the location of all such materialscontiguous to the precast unit be controlled within somestated limits. One recommendation is that the tolerancesbe no more than those specified in ACI 301 for rein-forced concrete buildings. Should there be some doubt asto the appropriate magnitude of mixed construction tol-erances, the precast concrete manufacturer may be con-sulted for advice.

3.7.4 Steel building frames - Precast concrete panelsshould be erected as uniformly as possible around theentire perimeter of the structure to avoid pulling thesteel framing out of alignment. Steel building frameshave different tolerances from those discussed above.The tolerances for steel frame structures make it im-practical to maintain precast concrete panels in a truevertical plane. Based on the allowable steel framevariations, it would be necessary to provide for a 3 in.adjustment in connections up to the 20th story and a5 in. adjustment in connections above the 20th story ifthe engineer-architect insists on a true vertical plane.Adjustments of this magnitude in connections are noteconomically feasible. Therefore the precast concretewall should follow the steel frame.

In determining tolerances, attention should also begiven to possible deflections and/or rotation of structuralmembers supporting precast concrete. This is particularlyimportant for bearing on slender or cantilevered struc-

tural members. If the frame deflection is sensitive to thelocation or eccentricity of the connection, tolerances forlocation or eccentricity should be given. Considerationshould be given to both initial deflection and to long-term deflections caused by plastic flow (creep) of thesupporting structural members. Beam and column loca-tions should be uniform in relation to the precast unitswith a constant clear distance between the precast con-crete and the support elements.

A structural steel frame presents different erection andconnection problems from that of a concrete buildingframe. For example: structural steel cross sections, fre-quently relatively weak in torsion compared to concretecross sections, generally require that the load be applieddirectly over the web or that the connection be capableof supporting the induced torsional moment. This in turncan require a stronger connection, as well as creatingerection problems when the rolling tolerances of the steelbeam approach their limits. When detailing precast ele-ments for attachment to steel structures, allowance mustbe made in the precast element for sway in tall, slendersteel structures with uneven loading, and deflections dueto thermal effects.

Designs must provide for adjustment in the verticaldimension of precast concrete panels supported by thesteel frame. An accumulation of axial shortening ofstressed steel columns will result in the unstressed panelssupported at each floor level being higher than the steelframe connections to which they must be attached. Some-times the non-load-bearing precast elements will becomeload-bearing even though the design does not allow forload. This can result in cracking.

The clearance necessary for erection of the wall willdepend on the wall design, the dimensional accuracy ofthe building frame or other construction to which thewall is connected, and the limits of adjustment permittedby the connection details. If connections to the face of


a = Plan location variation from buildinggrid datum + 1 in.

a1 = Plan location variation from center lineof steel* + 1 in.

b = Bearing elevation variation** from nominalelevation at supportMaximum low l/2 in.Maximum high 1/4 in.

c = Maximum plumb variation over height ofelement 1/8 in. per 12 in. height

1/2 in. maximum

*For precast elements erected on a steel frame, thistolerance takes precedence over tolerance dimension a.

**Or member top elevation where member is part of aframe without bearings.

*** This is a setting tolerance and should not be confusedwith structural performance requirements set by theengineer-architect.

d = Maximum jog in alignment of matching edgesArchitectural exposed edges l/4 in.Visually noncritical edges l/2 in.

e = Joint width variation from specifiedArchitectural exposed joints f l/4 in.Hidden joints + 3/4 in.Exposed structural joint not-visually critical -t- l/2 in.

f = Bearing length*** (span direction) f 3/4 in.g = Bearing width*** f l/2 in.

Fig. 3.7-Erection tolerances for precast beams and spandrels required for proper interface with precast wall panels


spandrel beams or to columns are required, more clear-ance will be needed to install the fasteners than when theanchors are located on the top and/or bottom faces ofbeams and the sides of columns.

3.8-Clearances and tolerances for constructibility3.8.1 Suggested minimum clearances - Clearance, or

interface space between members, should be specified tofacilitate construction. Some suggested minimum clear-ances are:

Between adjacent precast member Y2 in.Between precast and

cast-in-place concrete 1 in.; 11/2 in. preferredBetween precast members and steel frame 1 in.Between precast members and the frame of

tall irregular structures 2 in.Between precast column

cladding and the column 11/2 in; 3 in. preferred

If clearances are realistically assessed, they will solvemany tolerance problems. The nominal clearance dimen-sion shown on the drawings should be equal to the actualclearance required plus the outward tolerance permittedfor the adjacent construction. The nominal clearancesshould be determined on the assumption that the con-struction will be as far out of position in the wrongdirection as is allowed. Connections should be designedto accommodate the clearance plus the inward tolerance.

3.8.2 Connection problems - Connections should havethe maximum adjustability that is structurally or arch-itecturally feasible. Closer tolerances are required forbolted connections than for grouted connections. Con-nections should provide for vertical, horizontal, andlateral adjustments of 1 in. minimum to accommodateany misalignment of the support system and the precastelements. Location of hardware items cast into, orfastened to the structure by the general contractor, steelfabricator, or other trades should be determined withspecified tolerances for all site placement. Unless someother value is specified by the engineer-architect,tolerances for such locating dimensions should be + 1 in.in all directions (vertical and horizontal) plus a slopedeviation of no more than + ‘/4 in. for the levelness ofcritical bearing surfaces.

Connection details should provide for the possibility ofbearing surfaces being misaligned or warped from thedesired plane. Adjustments can be provided by the use ofdrypack concrete, nonshrink grout, or elastomeric padsif the misalignment from the horizontal plane does notexceed 2 % in.

Where possible, connections should be dimensioned tothe nearest % in. The minimum clearance between partswithin a connection should not be less than l% in., with95 in. preferred. The minimum clearance or shim spacebetween various connection elements should be a mini-mum of 1 in.

Where a unit is not erected within the tolerances

assumed in the connection design, the structural ade-quacy of the installation should be checked and theconnection design should be modified if the tolerancesare exceeded. No element should be left in an unsafesupport condition. Adjustments in the prescribed tol-erances should be made only after approval by theengineer-architect.

CHAPTER 4-MATERIALS

4.1-IntroductionBasic materials used in the fabrication and erection of

precast concrete wall panels are the same as those usedin cast-in-place structural concrete. However, precastconcrete wall panels also make extensive use of specialmaterials, including exposed aggregates, admixtures, in-serts and specialty coatings to enhance esthetic appear-ance. This chapter describes the following materials asused in precast concrete panel construction:

Portland cementAggregates, both standard and decorative for facingAdmixturesInsulating materialsReinforcement and insertsCuring materials and sealersJoint sealants and fillersSurface retardersForm release agents

Most of these materials are considered in more detailby other ACI committees.

4.2-Portland cement4.2.1 General - Usual practice is to use white, buff, or

gray portland cement which meets ASTM C 150 require-ments for Type I or Type III. White cement usage shouldbe clearly specified, when it is required. Cement Types II,IV, and V are seldom used in precast panels. When usingany special cement it is important to take every pre-caution to assure that early concrete strengths areadequate.

4.2.2 Single source - On any given project, enoughcement for the entire project should be procured from asingle source so that all cement is the same brand andtype. Some precasters prefer to obtain a single, one-time,one-batch shipment for a given project to minimize colorvariations due to the cement. Total elimination of colorvariation is not possible since variables in other materialsand in panel manufacturing may also have some effects.

4.2.3 Storage - Dry, covered storage areas should beprovided for bulk or bagged cement. Bagged cementshould be stored off the ground, preferably on woodenpallets and out of contact with outer storage buildingwalls where condensation could occur. To avoid “packset,” bags should not be stored more than two palletshigh, or 7 ft total height. Bulk cement should be stored


1.2.3.

form4.

so that contact with tanks or walls where condensationcan occur is minimized.

4.2.4 Sampling - A sample should be taken from eachcement shipment and kept in a full, sealed container atleast 6 months or until the shipment is exhausted, in caseof problems with either strength or color uniformity.

4.3-Aggregates for structural or backup concreteNormal weight or lightweight aggregates conforming

to ASTM C 33 or C 330, respectively, should be used inbackup or structural concrete for precast panels. Gradingrequirements for a backup mix may be waived if it isintended or necessary to provide a backup concrete withmechanical or physical properties similar to that of thefacing or decorative aggregate concrete in order to min-imize bowing or warping.

Aggregates for backup concrete should be stored inclean areas that are well drained and, if possible, inidentifiable bins. The bins should be designed to avoidsegregation, contamination or intermixing of differentaggregates or aggregate sizes.

4.4-Facing aggregates4.4.1 Grading

4.4.1.1 General - Uniform aggregates used forregular concrete are usually selected by standard sievesizes to provide a balance of both fine and coarse sizes.The ideal grading is one that combines aggregate sizes toproduce the maximum weight of aggregate per unit vol-ume of concrete. Most concrete mixes are chosen withthis in mind but are often limited on the upper end ofthe coarse aggregate size by:

The dimensions of the panel to be castClear distance between reinforcementClear distance between the reinforcement and thesurfaceThe desired finish.

4.4.1.2 Gap grading of facing aggregates - Sinceprecast concrete panels frequently use exposed aggregate,the desired surface finish, appearance, and texture fre-quently dictate the grading of both the fine and coarseaggregates. Gap grading may be used to achieve a consis-tent, uniform panel face with a maximum of aggregatesurface exposed. A gap-graded combination of fine orcoarse aggregates has one or more sizes missing from therange of standard particle sizes. Producers may also electtighter or more restrictive gradings in an attempt toimprove uniformity. Common sizes of gap-graded fineaggregates are 30 to 50 mesh and 16 to 30 mesh. The useof the coarse and fine sizes combined can produce a gap-graded combination that results in less segregation anda more uniform surface finish.

4.4.1.3 Schedule of sizes - Table 4.4.1.3 shows fourdifferent size gradings established by precast industrysuppliers of aggregates for use in exposed aggregate pre-cast concrete. However, this size schedule is not univer-

sally recognized, and some aggregate producers may havetheir own standards. Panel producers should be awarethat small aggregates, 1/8 in. and smaller, may pull out ofexposed aggregate finishes during surface finishing.

4.4.2 Types and quality of facing aggregates4.4.2.1 General- Decorative facing aggregates are

normally used only in the exposed panel faces because ofcost. The thickness of the face layer depends on the sizeof aggregate, but it should be thick enough to preventthe backup concrete from showing on the exposed face.The face concrete thickness should be 1.5 times the max-imum size of coarse facing aggregate but not less than 1in.

Aggregates for facing mixes should be stocked in suf-ficient quantities from the particular source to completethe entire project. Failure to plan appropriately maycause unwanted changes in color or texture.

4.4.2.2 Specific surface color and texture - Specialaggregates selected for facing use include naturallyoccurring aggregates such as selected gravels, granites,traprock, marble, limestone, and quartz, quartzite,feldspar and obsidian. Selection should be based onperformance of the facing aggregate in approved panelsamples. Approval should be based on both manufactur-ing and esthetic acceptability.

4.4.2.3 Durability concerns - Some limestones,marbles, and sandstones are not durable on exposedexterior surfaces. All facing aggregates should haveproven service records or be shown to be acceptableunder laboratory test conditions before being used inprecast panels. Appropriate tests include petrographicexamination and expansion tests (ASTM C 227).

Facing aggregates that have passed laboratory dura-bility testing or have good service histories rarely haveproblems with alkali-aggregate reactivity. If such areaction is suspected from a new or unknown combin-ation of aggregates and cement, the aggregate should beexamined petrographically, and expansion. should notexceed ASTM C 33 limits. If the limits are exceeded, itis recommended that a low alkali cement, with a maxi-mum of 0.6 percent Na2O equivalent according toASTM C 150 or a material that has a proven record toprevent harmful expansion, that is, fly ash, be used withthat aggregate. Occasionally materials that have beenshown to prevent harmful expansion, such as fly ash, maybe used if the matrix color meets architectural appear-ance requirements.

4.4.2.4 Staining - Occasionally, coarse facingaggregates may contain particles with an iron contenthigh enough to result in unsightly stains. This charac-teristic usually shows up at a later date in finished panelsdue to oxidation from exposure to the atmosphere. Selec-tivity by the panel producer and a good working know-ledge of aggregate materials and their service records arecurrently the only assurance against long-term iron stainsfrom aggregates. Test for the quantity of iron bearingparticles in an untried aggregate should be made accor-ding to ASTM C 641 and the aggregates should show a


Table 4.4.1.3-Typical industry size specifications for exposed aggregate

Percent of indicated size aggregate passing

Size D size c Size B Size ASieve opening 13/8 to 7/s in. ‘h to ‘h in. % to l/4 in. ‘/4 to 3/32 in.

in. mm (35 x 22 mm) (22 x 13 mm) (13 x 6 mm) (6 x 2 mm)

11/2

13/81

‘h%‘/‘A‘/‘!

3/32

38 10035 95-10025 30-60 10022 20-40 95-10016 0 -10 30-50 10013 10 -25 95-1009 0 -10 40-70 1006 5-20 95-1003 1 -10 15-352 0 -10

stain index less than 20.4.4.2.5 Glass or ceramic aggregates-Glass or cer-

amic aggregates that may be used for bright color or forspecial effects should be nonreactive with the cementused. The “quick chemical test” in ASTM C 289 may beused for detection of glass or ceramic aggregates whichare reactive. Ceramic aggregates may exhibit brittlenessand breakdown during casting. Glass aggregates have lowabsorption and good durability, but have the disadvan-tage of low compressive strength and low bond strengthwith the cement paste. Production testing of glass andceramic faced panels is highly recommended.

4.5-Admixtures4.5.1 General- Chemical or mineral materials may be

added to the concrete mix to bring about specific changesin the mix properties. ACI 212.3R contains recommenda-tions for the use of chemical admixtures, including limitson chloride content of hardened concrete (see also Sec-tion 4.5.3). For protection of reinforcement from corro-sion, ACI 222 recommends limits the acid-soluble chlor-ide ion content in hardened concrete. All prestressedconcrete and any reinforced concrete exposed tomoisture or chloride in service falls into one category andany reinforced concrete that is dry or protected frommoisture in service falls into the other category.

4.5.2 Air-entraining agents - Air-entraining agentsshould be used in all concretes that may be exposed tofreezing and thawing cycles when saturated with water.The added protection against freeze/thaw deteriorationfar outweighs any loss of strength or density. A “normal’dosage of air-entraining agent, the amount that will pro-vide about 9 percent air in the mortar fraction of theconcrete, is recommended. Because of the unusual natureof most facing mixes, a specification for the amount ofair-entraining admixture rather than a fixed percentageof air is recommended. Refer to ASTM C 260 andC 185.

4.5.3 Mineral admixtures and pozzolans - On rare oc-casions where a particularly smooth surface is desired,the addition of fine minerals or pozzolans may be made

to the mix. The typical curing period for precast panelsis often too short to allow pozzolanic action for increasedstrength.

4.5.4 Accelerating admixtures - Accelerating admix-tures, ASTM C 494 Types C and E, reduce concrete set-ting time and produce rapid early strength gain whichcan aid in panel casting operations. Rapid strength gainmay also be accomplished with higher cement content,use of Type III high early strength cement, heated waterand aggregates, or by steam curing.

Accelerators containing calcium chloride or thiocy-anate ions may contribute to corrosion of reinforcement.Calcium chloride also affects color. The committeerecommends that accelerators containing more than 0.1percent calcium chloride be used only when it can bedemonstrated that they neither initiate nor promotecorrosion of steel in any precast panel, or adversely affectcolor of the panel.

4.5.5 Retarding admixtures - Chemicals to retard theset of concrete, ASTM C 494 Types B, D and G, are nor-mally not used in precast concrete wall panels except inhot weather. Retarders delay the time of set and allowlonger finishing time. They generally do not fit into ahigh speed casting operation.

4.5.6 Water reducing admixtures - Water reducing ad-mixtures, ASTM C 494 Types A and F, are used in pre-cast concrete wall panels where it is desirable to reducethe bleed water or to increase the workability of theconcrete without adding water. This group includes highrange water-reducers (super-plasticizers) for conditionswhere placing concrete is difficult. Laitance, bleeding andefflorescence can be minimized by reducing waterrequirements. Water reducers may be helpful in harshmixes or where gap-graded aggregates are being used.Water reducing components must meet the requirementsof ASTM C 494 Type A, and should be checked for com-patibility with the cement and with any air-entrainingadmixture to be used.

4.5.7 Coloring materials - Both pigments and dyes areused to enhance the color tone of concrete in precastpanels. It is important to have tests or performance


records that reliably indicate the color stability of anycoloring agent. Experience shows that there is generallypoor color stability with organic blacks, blues, and greens.

4.5.7.1 Pigments - Pigments commonly used tocolor concrete are finely ground natural or syntheticmineral oxides. Synthetic oxides are usually more satis-factory since they are manufactured in more shades, havemore consistent properties, give better color intensity andhave longer permanence. Synthetic pigments may possiblyreact with other products used on concrete facing mixessuch as retarders or muriatic acid. All pigments should betested prior to use and should conform to ASTM C 979.

Iron oxides produce shades of yellow, buff, tan, brown,red, maroon, and black. Chromium oxide produces greenshades. Cobalt oxide produces shades of blue. Varyingamounts of these oxides, added as a percentage of thecement content by weight, produce various shades.Amounts in excess of 5 percent by weight of cementseldom further increase color intensity. Amounts greaterthan 10 percent may adversely affect concrete quality andare not recommended.

Pigments used with white cement will produce clearerand brighter shades than if used with gray cement. Drymixing of the pigment with the cement prior to concretemixing is preferred. Some cement manufacturers can pro-vide premixed or pigmented cements.

4.5.7.2 Dyes - Organic phthalocyanine dyes havebeen successfully used to produce light to dark shades ofblue and green in concrete. While their cost per poundis high, they are used in quantities of less than 1 percentby weight of cement and can be dispensed in the mixingwater, eliminating the need for preblending. Althoughcertain organic phthalocyanine dyes work well, othersmay fade quickly upon exposure to sunlight.

4.6-Insulating materialsA wide variety of insulating materials is available to

provide the desired thermal properties for sandwich wallpanels. Since thermal conductivity usually varies withdensity of insulating material, the unit weight is used toclassify insulating materials as follows:

a) Density of 15 lb per cu ft or lessPlastic materials such as polyurethane foam boards;

polystyrene foam boards or granulesGlass materials including foamed glass boards or

granules; glass fiber battsPaper materials such as paperboard honeycombs

filled with insulating granules or aggregate;cellulose granules.

b) Density of 16 lb per cu ft to 50 lb per cu ftFoamed concrete: autoclaved cellular concrete

boards; nonautoclaved cellular concrete boardsof granules

Mineral aggregate concrete: vermiculite concreteboards or granules; perlite concrete boards orgranules.

Being very porous, many of these insulating materials

will have high initial rates of water absorption and canabsorb water from the fresh concrete placed over andaround them. Glass batts and granules should be en-closed in plastic bags to prevent absorption and rapiddrying of the surrounding concrete. Open-cell boardinsulation should have a waterproof membrane coatingapplied before use.

4.7-ReinforcementReinforcement for precast panels includes prestressing

materials, deformed bars, and welded wire fabric. Rein-forcement also includes those ribs or metal shear tiesused in three-layer sandwich panel construction to con-nect the two outer layers of concrete. The shear ties maybe made of expanded metal and are commercially pro-duced as masonry reinforcement or building studding.Metal shear ties generally incorporate diagonal membersfor proper resistance to horizontal shearing deformationin sandwich panels. Some sleeve anchors do not have dia-gonals but may still be acceptable.

4.7.1 Deformed reinforcing bars - Deformed reinfor-cing bars are manufactured by hot rolling deformationsonto steel and are made in accordance with ASTMA 615 (billet steel), ASTM A 616 (rail steel) ASTMA 617 (axle steel), and ASTM A 706 (low-alloy steel).Bars are normally used in straight lengths but can bebent to form hooks required for anchorage purposes.ASTM A 496 presents requirements for deformed wireused as concrete reinforcement.

4.7.2 Welded wire fabric - Welded wire fabric (WWF)is available in a wide variety of mesh spacings and wiregauges with both plain and deformed wire being used.WWF should be manufactured in accordance with ASTMA 185 and A 497 for plain and deformed wire, respec-tively.

4.7.3 Prestressing materials - Steel wire, bar, andstrand for prestressed concrete should meet requirementsof ASTM A 416, A 421 and A 722.

4.7.4 Corrosion protection of reinforcement - Whenesthetic considerations cause reduction of the concreteminimum cover below that ordinarily specified or recom-mended, reinforcement in thin precast concrete panels(under 4 in.) may be susceptible to corrosion. In suchcases, the long-term appearance and durability of thepanels may require corrosion protection for reinforcingmaterials or the use of stainless steel reinforcement orother reinforcement clad with copper or other metals lesslikely to corrode than uncoated reinforcing steel.

4.7.4.1 Galvanizing - Galvanized welded wire fabricis readily available and the cost premium is relatively lowin comparison to the unprotected product. Galvanizedreinforcing bars are not as readily available and the extracost may be substantial. Use of galvanized bars may beminimized or avoided by proper design, maintenance ofminimum cover, and manufacture of the panels so thatbar location, concrete placement, and consolidation areprecisely controlled. Galvanizing procedures shouldconform to ASTM A 767 and A 153, including supple-


mentary requirements.4.7.4.2 Epoxy coating - Epoxy-coated reinforcing

bars (ASTM A 775) and welded wire fabric (ASTMA 884) have been used extensively in severe exposureenvironments, but only minimally used in architecturalprecast panels. The report by ACI 222 discusses thecorrosion mechanism and corrosion protection in detail.Development length must be increased for epoxy coatedbars as required by ACI 318, Section 12.2.4.3.

These bars are very resistant to corrosion if thecoating is uniform. Bars coated when straight and sub-sequently bent have shown that bending has no effect onthe coating integrity. If the coating is damaged of non-uniform, the bars have to be touched up with commer-cially available epoxy compounds to prevent seriouscorrosion. Bar tying should be done with nylon or plasticcoated tie wire rather than black wire. Bar supportsshould be stainless steel, epoxy coated or solid plastic.

4.7.4.3 Other coatings - Other coatings available forcorrosion protection include various paints such as inor-ganic zinc-rich types, epoxy paints, and certain proprie-tary chemical compounds which combine with oxidecoatings to form a protective layer. These materials maybe brush, bath, or spray applied. In evaluating thesecoatings, known performance characteristics and test datashould be considered.

4.8-Inserts and miscellaneous hardwareInserts are items cast into the panel for lifting,

holding, or attaching the precast panel to other structuralmembers. Installing inserts after casting by drilling intoplace is not recommended unless something happened tothe cast-in inserts and a field solution is required.

Such items as channel sections, framing, studs,anchors, expansion anchors, and inserts should be madefrom materials that are permanently ductile. When rein-forcing bars are used as anchors or inserts, precautions(Section 5.4.2.3) should be followed to ensure adequatestrength and ductility when their connections are welded.Brittle materials such as grey-iron castings should not beused. Specifications for bolts include ASTM A 307,A 325 and A 490. Specifications for stud welded anchorsinclude ASTM A 108 and A 496.

4.8.1 Expansion anchors - Expansion anchors shouldconform to applicable bolt specifications and be per-formance tested in accordance with ASTM E 448. Allitems should have documented chemical and physicalproperties and be used in accordance with the manu-facturer’s recommendations and/or test data.

4.8.2 Corrosion protection - Where corrosion protec-tion is required for embedded or exposed hardware,noncorrosive materials such as stainless steel, inaccordance with ASTM A 276, or the hardware may beprotected with a coating such as zinc, cadmium, epoxy, orcorrosion resistant paint may be used. Care must betaken so that the protective coatings do not interfere withsubsequent fit of the nuts onto threaded portions of thefasteners. Hex nuts and washers, or other matching hard-

ware used with exposed insert connections, should bezinc or cadmium plated. The use of hex lock nuts withnylon locking washers is suggested.

4.9-Curing materials and sealers4.9.1 Curing materials- Although not generally used,

curing compounds are preferred over water, burlap, orother wetted coverings where additional curing of theconcrete is required. A wide range of curing compoundsis commercially available; they should be supported withtest data and user experience before acceptance. Steamcuring is discussed in Section 5.7.3.2. Curing compoundsand sealers may have to be removed if the panel surfaceis to be painted.

4.9.2 Surface sealers - The use of clear, protective,water-repellent sealers, often also referred to as coatings,to maintain panel appearance remains an area of contro-versy with panel producers. A justification for use ofsealers is the potential improvement of weathering qual-ities in urban or industrial areas. A sealer may reduceattack of the exposed concrete by airborne industrialchemicals. Laboratory exposure tests and long timeoutdoor exposure plots have yielded a wide range ofresults. Some sealers produce severe discoloration withinan exposure period varying from one week up to severalmonths. Panel surfaces that have been sealed may dis-color because: (a) some sealers attract hydrocarbons tothe surface of the sealer; (b) some sealers have littleresistance to discoloration by the sun’s ultraviolet rays;and (c) other sealers may be affected by temperatures of145 F or above.

Tests have shown that sealers do not improve resis-tance to freezing and thawing. Freeze/thaw durability isbest achieved with air-entraining agents as outlined inSection 45.2.

The use of sealers should be based on prior experienceand a careful study of test data for conditions of similarexposure. They should be applied in strict accordancewith the manufacturer’s recommendations. Sealers gener-ally should not be applied on surfaces that will be incontact with joint sealants.

4.9.2.1 Silicone sealer performance - Surfacestreated with silicone formulations vary widely in per-formance. The service life of silicone sealers iscontroversial and probably shorter than advertised.Experience with silicone sealers indicates that theyshould not be used on exposed quartz aggregates, andthat durability results with use on other aggregates aremarginal. In urban areas, some silicone sealers attractairborne hydrocarbons resulting in premature discolor-ation of white or light colored panels within a shortperiod.

Silicone sealers interfere with the bonding of patchesand prevent the bonding of joint sealants. If used,silicone-based materials should be applied only afterpatching and joint sealing are completed. Committee 533does not recommend the use of silicone-based sealers.

4.9.2.2 Other sealers - Better results have been ob-


tained with methyl methacrylate forms of acrylic resin onexposed aggregate surfaces. Satisfactory results have alsobeen achieved with other acrylic copolymers, silanes andsiloxanes.

A wider range of acceptable sealers is available on lessdelicate surfaces such as plain or ribbed concrete panels.Sealers that do not perform well on exposed aggregatesurfaces or very light colored surfaces are often accept-able on plain or ribbed concrete.

4.10-Joint sealants and fillers4.10.1 Mortars -Cement mortars are not extensible

and cannot accommodate panel movement. Althoughthey are not suitable as sealants, mortars may be used forpacking joints in connections in combination with othersealers. Mortars are ideal for the base of load-bearingpanels supported by shims.

4.10.2 Elastomeric sealants - Only elastomeric mater-ials should be used as sealants in precast panel instal-lation. Elastomeric sealants (also referred to as caulks)include polysulfides, silicones and urethanes. They maybe one- or two-part compounds but either is to be pre-ferred over oil base types. Despite higher initial cost,elastomeric sealants are preferred because of lowermaintenance costs, better weathertight joints, and longerlife. Consult ACI 504 and ASTM C 962 for detailedinformation.

Nonstaining elastomeric type joint sealants should beselected to prevent the possibility of bleeding and heavydirt accumulation. High performance one- or two-partsealants such as polysulfides, urethanes, silicones or othersealant material are recommended for weatherproofingjoints in precast panels. These sealants should withstandjoint movements of at least + 25 percent. If greater seal-ant movement capacity is required, consult with manufac-turers of low modulus sealants. The sealant selectedshould match as closely as possible the color of theprecast panel. This will reduce the visual effect ofvariations in joint dimensions.

4.10.3 Joint fillers - Backup fillers are needed in jointsto control the depth of the sealant, to facilitate tooling ofthe sealant, and to serve as a bond breaker to preventthe sealant from bonding to the back of the joint. Thefiller material should be nonstaining to the sealant.Asphaltic (bitumastic) fillers should not be used. Thesealant manufacturer can advise which filler materialswould be compatible with the selected sealant. Therecommended shape factor should be listed.

Acceptable fillers are those which compress into thejoint and respond to panel movement. A round fillerprofile provides maximum edge area with minimum crosssection for best sealant adhesion. The best filler profileis a rod of spongy or foamed material that is closed cellto prevent moisture retention. If a stiff filler materialsuch as cork, wood, hard rubber or concrete mortar mustbe used, a strip of polyethylene sheet or similar materialis recommended to break the bond between the filler andsealant.

4.11-Chemical retarders4.11.1 General - Chemical retarders are specialized

chemicals which temporarily delay the cement paste fromhardening at the surface of the precast panel. After thebase concrete of the panel hardens (normally overnight),the retarded cement paste is removed by brushing, highpressure water washing, or sandblasting to expose theaggregates. Brushing or water washing will not changethe natural look of the aggregates, but sandblasting maydull the surface.

Two types of chemical retarders are used in precastpanel fabrication. Form retarders, usually fast dryingsolvent-based materials, are applied to the form surface.These retarders are designed to resist the abrasioninherent in the placement of concrete. Surface retardersare water based materials applied to the top surface offreshly placed concrete. They are usually sprayed on withgarden-type spray applicators. Before the retarder issprayed on, additional aggregate may be placed on thesurface and troweled in to provide a more uniform fin-ished surface.

4.11.2 Depth of reveal- Form and surface type retar-ders are available to etch the concrete to different depthsallowing for design flexibility. As a general rule, theretarder should expose not more than 40 percent of thediameter of the aggregate at the surface. Retarders canbe used to produce finishes from the lightest revealwhich just removes the surface skin to deep reveals usingaggregates up to 11/2 in.

4.12-Form release agents4.12.1 General- Modern release agents are formu-

lated from a variety of ingredients to perform severalfunctions. Their primary purpose is to release the panel(aid in debonding) from the form. Other functions in-clude, minimizing or eliminating bug holes and stains,minimizing form clean up time, keeping cementitiousmaterials from building up on the form facing, notinterfering with the bonding of condstruction and/orarchitecturally esthetic materials to the hardenedconcrete surface, not degrading (and thereby causingstains) form facing materials, not staining concrete whensteam curing is used, contributing towards the productionof high visual impact concrete surfaces and being easy toapply in all seasons.

4.12.2 Chemically active release agents - Chemicallyactive release agents are the most common type. Theirreleasing ability is due to the chemical reaction of freelime from the fresh cement paste with chemicals in therelease agent coating the form surface. This chemicalreaction produces a slippery, water-insoluble soap orgrease, which provides for easy form removal. Typicallythe chemically active ingredients are fish oils, vegetableoils, animal fats, or combinations thereof.

4.12.3 Emulsion type agents - Some release agents usewater emulsions for a carrier instead of petroleumderived oil. Some emulsions are chemically active agentswhile others facilitate form release by producing a barrier


film, much like fuel oil does. Generally, emulsion typerelease agents will not harm any of the form facingmaterials that would be sensitive to petroleum derivedoils. Cold weather operations require storage and useconsiderations different from other release agents.

4.12.4 Petroleum derived agents - Release agents madeentirely from petroleum derived oil, that is, fuel oil,kerosene, etc., function by producing a barrier betweenthe form face and the concrete. This barrier type releaseagent generally causes more bug holes, staining, andpoorer form release than chemically active types.

4.12.5 Application of release agents to formwork -Release agents should be applied in a thin uniformcoating on clean dry form facings. Usually this is done byspraying. The release agent should be applied in amanner and schedule so as to avoid coating the rein-forcement.

CHAPTER 5-PANEL FABRICATIONAND DELIVERY

5.1-General requirements5.1.1 Preparation of design calculations and production

and erection drawings - The precast manufacturer pre-pares erection and production drawings for the precastpanels, complete with all necessary details for thefabrication, handling and erection of the precast pro-ducts. In order to do this the manufacturer should haveall applicable contract documents, including specifi-cations, architectural, site and structural drawings.Erection drawings and hardware from other trades mustbe provided within contractual schedules. Detailingmethods vary with the manufacturer; however, elevationsand horizontal dimensions should be shown which locateand mark each precast element and give its relationshipto windows, openings, and adjacent building components.Details should provide size, shape, dimensions and pro-files of each member. Connections, reinforcement, andindividual mark numbers should be shown. Erectiondrawings should show the following: (a) proposedsequence of erection, if required; (b) location and detailsof hardware embedded in or attached to the structuralframe; (c) method of plumbing (adjusting the verticalorientation) panels and adjusting connections and (d)handling loads and additional reinforcement due to trans-portation and erection stresses. Joint and joint sealantdetails should be shown where applicable. Further, spe-cial fittings such as stripping, lifting or erection inserts,anchoring details, reglets, cutouts, pipe sleeves, otherembedded items and openings should be carefully locatedand dimensioned.

Drawings and calculations prepared to show the aboveshould be forwarded to the general contractor and theengineer-architect for approval as recommended inSection 1.3.4.

5.1.2 Manufacturing facilities - Facilities for the pro-duction of precast panels vary widely. Production facil-

ities will be affected by the size, weight, and volume ofthe products produced and by the climate and proximityof marketing areas. At times the requirements of a speci-fic project warrant casting on the job site. A site pre-caster faces a few more problems than a plant precastersuch as: lack of tightly controlled batching conditions andless than ideal curing and protection from the elements;possible difficulty of obtaining a skilled labor force; andpossible lack of management or supervisory group exper-ienced in precasting operations. Recommendations in thisguide will help to overcome these possible deficiencies.The manufacturing facility, whether at the site or in aplant, should adequately provide the following:

. Facilities to receive and store raw materials such ascement, aggregates and reinforcing steel

. Facilities for controlled proportioning and mixing ofconcrete

. A covered area for manufacturing of molds andforms

. An area for assembly and fabrication of rein-forcement

. An enclosed or covered area (depending on theclimate) for the casting operations (see Fig. 5.1.2)

. Additional space for the finishing and curingoperations

. Adequate space for convenient and proper storage

. Equipment capable of lifting and handling panels ofthe size and weight to be manufactured

. Facilities for prestressing the precast wall panels, ifrequired

5.1.3 Production and storage areas - Facilities forbatching and mixing concrete should be in accordancewith ACI 304, providing for accurate batching of aggre-gates, cement, admixtures, and water. Equipment shouldbe available to determine the amount of free moisture inthe coarse and fine aggregates. Moisture compensationbased on devices using conductivity is known to vary withthe density of the aggregates and is not recommended.Facilities should be provided and monitored to preventfrozen aggregates being introduced into the concrete.Mixing equipment should be adequate for the size of theoperation and capable of thoroughly and uniformlymixing the concrete ingredients. Panel production areasshould be protected against rain, wind, dust, and directsunlight and have heat control to prevent concrete tem-peratures from dropping below 50 F. Panel storage areasshould afford easy access and ready handling of thestored units. The surface should be clean, hard, level, andwell-drained to permit well-organized storage, and tominimize or prevent warping, bowing, chipping, cracking,discoloration, staining or soiling of the precast panels.

5.2-Molds (forms)5.2.1 General- Wood, concrete, steel, plastics, plas-

ter, polyester resins reinforced with glass fibers andcombinations of these have all been used successfully as


Fig. 5.1.2-Precasting plant and storage yard

Fig. 5.2.1.1-Mold for casting precast panel

a mold or form material for precast panels. Variouspatterns made of rubber, pressed metal, or vacuum-formed plastic may be combined with the basic materialsfor special effects. For complicated details, molds ofplaster, gelatin, or sculptured sand have been combinedor reinforced with wood or steel, depending on the sizeof the panel to be cast. See Figs. 5.2.1.1 and 5.2.1.2.

Typically the panel producer selects the proper mold,based on considerations of cost, maintenance, method ofconsolidation, reuse, details of the panel, possible salvageand on the desired finish and texture of the product.Where the engineer-architect requires a special mold orfinish or a particular mold material, these requirementsmust be clearly set forth in the contract documents.


Fig. 5.2.1.2-Panel stripped from mold

5.2.1.1 Dimensional stability and integrity - Allmolds, regardless of material, should conform to theshape, lines and dimensions of the precast panels to beproduced They should be sufficiently rigid to meet thecasting tolerances recommended in Chapter 3. Moldsshould be sufficiently tight to prevent leakage of mortaror cement paste, and should be designed to preventdamage to the concrete from: (a) restraint as the con-crete shrinks; (b) the stripping operation when the unitis lifted from the mold; and (c) dimensional changesduring prestressing. For prestressed (pretensioned) unitsit may be desirable to design the molds strong enough tosupport the prestressing force (i.e., self-stressing forms).

In molds longer than 20 ft, allowance for shrinkageand thermal expansion or contraction should be consid-ered in the design of the master pattern and/or the mold.Master molds (described in detail in PCI ArchitecturalPrecast Concrete) are sometimes used to cast panels ofseveral different designs by pre-engineering a number ofmold adjustments (see Fig. 5.2.1.3).

F

‘_

D:ll‘.

.

TYPICAL PANEL ON UPPER FLOORSCHANGES TO:

SEVERAL VARIATIONS FROM THE SAME MOLDFOR FIRST FLOOR

ig. 5.2.1.3-Master mold for large precast panels

5.2.2 Steel molds- Steel molds are often selected forprecast members when it is anticipated that numerousassemblies and disassemblies of the mold will berequired. Properly designed steel molds have great poten-tial reusage; they need be discarded only when damaged,or when they show surface imperfections from drilling forchanges or from alteration. Steel molds should be wellbraced and examined for bulging or buckling. Dimpling,twisting, or bending may occur if the form surface is notproperly stacked for storage.

When steel plates are used for the base of the mold,it is desirable to use a single piece which has been“stretcher-leveled” in the steel plant. Joining of two ormore steel plates by welding to form a flat surface isdifficult due to distortion from the heat of the weldingoperation. If joining is required, the welds should be

ground smooth and coated with an epoxy or similarmaterial adequate to hide the joint imperfections. A testsection should be cast at the joint to determine that thejoined area can produce an acceptable finished product.

If a prestressing force is to be applied to the form, theself-stressing form must be strong enough to resist theprestressing force without buckling or wrinkling.


5.2.3 Concrete molds- Concrete can be formed intopractically any shape and has excellent rigidity, dimen-sional stability, and the potential for a large number ofreuses. Concrete molds are manufactured by casting overa master model fabricated to very close tolerances. Thismodel may be used for the production of a series ofidentical molds. Frequently concrete molds are treatedwith epoxy, plastic resins, or paraffin wax to reduce moldrepair and to improve their release capability. Theseresins and other coatings, render the concrete nonabsor-bent and produce a more uniform finish on the precastproduct. Concrete molds may also be adapted to becomea self-stressing form for use in prestressing a concretepanel. When concrete molds are used, adequate draftshould be provided on all surfaces in the direction ofstripping or removal, so that the product may be easilylifted without damage to either the panel or the mold.

5.2.4 Wood molds - Wood molds vary from simplewooden molds (particularly applicable when relativelysmall, flat panels are being produced) to elaborate,complicated molds of unusual shapes and large dimen-sions. Molds of wood should be treated to prevent exces-sive absorption, thus contributing to uniformity of panelfinish. The treatment also tends to stabilize the formdimensions.

Periodic renovation of wooden molds is necessary, andspecial care should be exercised to ensure that multipleuse does not cause the mold to swell or bulge. Mold di-mensions should be checked after each use. Wood moldsshould not be used if steam curing is planned beforestripping. Craftsmanship and joiner-y should be of highquality to achieve joints which are not objectionable inappearance. The joint location should be preplanned,subject to approval by the engineer-architect.

5.2.5 Plastic molds - Fiber reinforced plastics pro-duced from polyester or epoxy resins have considerableapplication because they can be easily molded into com-plex shapes and can impart a great variety of patterns tothe finished product. Properly designed plastic moldshave excellent performance and reuse expectancy, andthe surface may be renovated as needed.

Fiber reinforced plastics have a fairly low modulus ofelasticity and are somewhat flexible, even though theyhave excellent tensile strength. If the mold is madeentirely of plastic, it should be well supported alongedges and flat areas. This may be accomplished by rein-forcing it with lumber, steel shapes, or other materials asan integral part of the mold construction. This type ofmold is frequently designated a “mold liner,” and requiresa “mother” mold to provide adequate support.

The high gloss finish imparted to a precast panel bysome mold surfaces and/or mold liners (generally plastic)may be desirable for indoor decoration. When used forexterior work however, the gloss may disappear, usuallyin a nonuniform manner, because of weathering. Crazingand other minor surface imperfections may be more ap-parent on this type of surface. A high gloss finish shouldbe avoided on exterior work, unless the panel producer

can show successful installations of this finish in a similarclimate.

5.2.6 Form liners - Textures ranging from muted ex-pression to bold relief are obtained with different typesof form liners (see Fig. 5.2.7). Draft must be considered
for all types of liners to prevent chipping or spallingduring stripping. Rubber matting is an effective liner,reproducing complex patterns faithfully on the concretesurface. While rubber is generally satisfactory, it shouldbe tested for possible staining or discoloration of theconcrete. Trial castings will also determine the mosteffective time for stripping to ensure that the surfaceremains intact and that the liners can be reused.
Wood liners, either boards, plywood panels, or nailed-on inserts, work well. Wood liner surfaces should besealed to prevent moisture absorption and then lightlycoated with a form release agent before casting.

Plastic sheets may be vacuum formed to provide variedpatterns on either textured or glossy-smooth concretesurfaces. The extremely fine finish of plastic formedconcrete enhances the attractiveness of integral colorsand because of high reflectivity, smaller amounts ofpigment are required to obtain a given color intensity.Glossy and smooth surfaces are best for indoor ratherthan outside exposure.

Polyethylene film laid over uniformly distributedcobblestones provides dimpled surfaces. Pieces of poly-styrene foam, shaped and attached to the form, leavedeeply impressed designs after removal from the concreteface.

5.2.7 Verification and maintenance - Molds should bechecked in detail after construction and before the firstunit is made. A complete check of the first product fromthe mold further verifies the adequacy of the mold.Checking of the mold by evaluating the product is feas-ible only where an element can positively be identifiedwith the specific mold in which it was cast.

Molds should be cleaned between castings and kept ingood condition to provide a uniform product of highquality. Steel forms must be carefully maintained to avoiddiscoloration of the concrete from iron oxides. Joints mayopen, weldments come loose, rubber sealing strips erode;wood loses its protective coating, absorbs moisture andmay swell or warp; and side rails bow due to daily pro-duction. It is therefore necessary to check the moldsregularly, at least once a week, for their soundness,surface, and dimensional stability, and to repair damagebefore it affects the quality of the product.

Forms should be reassembled within the dimensionallimitations specified for the product on the shopdrawings. The squareness of the form should be checkedby comparing diagonal measurements between the cor-ners of the form. Bulkheads, templates, and similarequipment having influence on the accuracy of dimen-sions and alignment should be regularly inspected andmaintained. If more than one form is used to produce agiven unit, a comparative dimensional check should bemade before casting of the initial precast concrete panels.


Fig. 5.2.7-Form liner relief patterns

All positioning holes or slots holding any cast-inmaterials in a given position should be checked to ensurethat continuous mold use will not create wear and exceedacceptable tolerances. When using wood molds, theseclamp-on areas should be protected with corner plates.

5.3-Concrete proportioning and mixing5.3.1 Introduction - Information on mix proportions

should be recorded and kept at the concrete batchingplant. Although the same technology used for makingcast-in-place concrete must be considered in precasting,specific mix proportions and mixing procedures differfrom those for conventional concrete, particularly in theemphasis on finish and durability of the concrete surface.Precast manufacturers usually design and control the con-crete used for the precast product because of the factorslisted below. Before a concrete mix can be properly pro-portioned, several factors must be considered:

. The finish, size and shapes of units to be cast

. The method of consolidation; must be known to de-termine the required workability

. The maximum size of the coarse aggregate

. The required compressive strength

. The required surface finish as it affects the ratio ofcoarse to fine aggregate

. Exposure to severe weather or environmental condi-tions

5.3.2 Water-cement ratio and consistency (slump) -With given quantities of cement and aggregate along withproper curing, the quantity of mixing water determinesthe strength of the concrete. Water should be held to aminimum to prevent a substantial decrease in strengthand durability. Excess water in the facing and/or backupmix may be removed before initial set by a vacuum pro-

cess, application of hygroscopic materials or low-slumpmixes.

One of the most important factors affecting coloruniformity is variation in the water-cement ratio. Thewater-cement ratio must be consistent from batch tobatch from the beginning of the project to the end or thepossibility of precast concrete panel rejects increasesbecause of lack of color uniformity. Very stiff mixes usinga minimum of cement and only enough water to hydratethe cement are economical only in terms of materialcosts. These mixes generally require more placing labor,and these added placing costs may more than offset anymaterial cost savings.

Concrete mixes should always have a consistency andworkability suitable for the conditions of the project.Heavily reinforced thin sections require more plasticmixtures than large members with little reinforcement.High-range water-reducers can increase workability whilemaintaining a relatively low water-cement ratio. It isimportant that the specifier realize that even with thesame proportions, the slump may vary with changes inclimactic conditions and normal variations in materials.Concrete mixtures using natural sand and gravel aggre-gates require less water for workability than do concretemixes using crushed sand and crushed coarse aggregate.The shape and size of the aggregate will affect waterdemand, which in turn affects the water-cement ratio.

5.3.3 Proportioning -Concrete mixes should be pro-portioned in accordance with ACI 211.1 and ACI 211.2to produce a specified compressive strength of at least5000 psi measured at 28 days on standard 6 x 12-mcylinders. Some decorative aggregates have characteristicsthat do not permit attainment of compressive strength.Caution is advised in selecting such aggregates.

The objective of proportioning is to achieve a practicalcombination of materials that will provide the required


qualities of the hardened concrete at an economical cost.Concrete mixes should be proportioned and/or evaluatedfor each individual project with respect to strength, ab-sorption, and resistance to freezing and thawing asappropriate to the intended environment.

For normal weight aggregate concrete mixes, the ratioby volume of fine aggregate to coarse aggregate usuallyis on the order of 1:3 for facing mixes, whereas standardmixes are usually in the range of 1:l to 1:2 or 1:3. Forlightweight aggregate concrete mixes, the volume ratiomay vary depending on the type of lightweight aggregateused. The aggregate producer should be consulted aboutspecific material characteristics and recommended mixdesigns. The lower ratio of fine to coarse aggregateresults in a more uniformly textured finish caused by amaximum concentration of coarse aggregate in the facingmix. All mixes for panels exposed to freeze-thaw condi-tions should include entrained air for increased dura-bility.

5.3.3.1 Facing and backup mixes - Differing aggre-gate gradings and mix proportion designs for facing mixconcretes make it impossible to specify a given percen-tage of air for these mixes. Consult the PCI Manual forQuality Control for Plants and Production of ArchitecturalPrecast Concrete Products for added information.

Standard mixes may be used as backup mixes if thephysical characteristics are similar to the facing concrete.Where a precast unit consists of a face and backup mix,the mixes should have reasonably similar shrinkage, ther-mal coefficients of expansion and modulus of elasticity toavoid undue bowing or warping. Consequently, thesemixes should have similar water-cement and aggregate-cement ratios. The combination of a normal weight facemix and a backup concrete with lightweight aggregatesmay increase the possibilities of bowing or warping.

5.3.4 Mixing -The mixing procedures used in themanufacture of precast wall panels vary due to the vari-ety of equipment and methods of panel manufacturing.

To maintain batch-to-batch uniformity, materialsshould be properly sequenced and blended duringcharging of the mixers. Good mixing practices include thefollowing:

. The mixer should be operating while all materialsare being charged.

. All admixtures should enter the mixer with the waterand be charged into the mixer at consistent times in themixing sequence. Batching air-entraining agents simul-taneously with water reducers or retarders can cause thecombination to gel.

. Pigments should be preweighed and batched frompackages that are of a size appropriate for a single batch.The aggregates and cement should be introduced to-gether.

. Where mixers of 1 cu yd capacity or less are used,the aggregates may be placed into the mixer first andthen the cement and water introduced together.

5.3.4.1 Mixing time - After all materials haveentered the mixer, they should be mixed for a minimum

of one minute, or as recommended by the mixer manu-facturer, until all ingredients are thoroughly distributedand the mix is homogeneous. All concrete should be dis-charged while the mixer drum or blades are rotating.

The required mixing time varies with characteristics ofthe concrete mix and mixer. A timer should be used toensure the same mixing time for identical sized batches.Pan-type mixers designed for horizontal countercurrentforced mixing are frequently better for very low slumpconcrete (0 to 1 in.).

5.3.4.2 Cold weather - When heated water or ag-gregates are used to warm the mix and satisfy coldweather requirements, the addition of cement should bedelayed until after the aggregates and water have enteredthe mixer and have been thoroughly mixed for at leastone minute. This allows the water or aggregates to coolsufficiently to avoid flash set when the cement is placedin the mixer.

5.3.4.3 Hot weather - If the aggregates and water,when combined, have a temperature of over 100 F, theingredients of the mix should be cooled before mixing toavoid flash set, cold joints or loss of slump. Flake ice orwell crushed ice of a size that will melt completely duringmixing should be substituted for all or part of the mixingwater. To provide products that are uniform in color, itis important that the concrete temperature be controlledbetween a maximum (90 F) and minimum (50 F)throughout all seasons of the year.

5.3.4.4 Lightweight concrete - Most lightweightaggregates should be prewetted before introduction intothe mixer. This will eliminate a loss in workability due torapid absorption of the mixing water. The lightweightaggregate (and sand, if used) and most of the water arenormally placed in the mixer and mixed thoroughlybefore the cement and remainder of water are added.

5.3.4.5 Architectural concrete - Architectural con-crete requires careful observance of good, uniform mixingpractices. Mixers must be properly cleaned after eachperiod of production. Blades or liners should be adjustedor replaced per manufacturer’s recommendations to en-sure that the mixing is sufficient and adequate. Whenfacing mixes of pigmented concrete with buff or whitecement are used in conjunction with gray cement backupconcrete, separate mixers and handling arrangements arerequired. Alternatively when separate mixers are notavailable, the equipment must be flushed several timesand completely cleaned to remove all concrete residuebefore being used for mixing where specialty cements orpigments are required.

5.4-Reinforcement5.4.1 Prestressing

5.4.1.1 General - Panels are sometimes prestressedto avoid cracks, to control warping or bowing, or to rein-force particularly large units. Firm anchorage of the pre-stressing steel in a prestressing bed or in suitablydesigned individual molds is necessary. The concretecompressive strength when the prestressing force is


released should be adequate to meet the design andhandling requirements of the precast panel. In the caseof prestressed architectural panels, special attentionshould be paid to the transfer of the prestress force tothe panel, particularly if it is a heavily sculptured precastpanel or has many openings.

Accurate location of strands is important to avoidinducing permanent bowing or warping. Strand ends mustbe recessed and backfilled with epoxy or special grout,or otherwise carefully protected to avoid corrosion.

Strands are normally tensioned in two increments. Thefirst increment applies enough load to the strands tostraighten them, eliminate slack, and provide a startingpoint for measuring the elongation. The second stressincrement is then applied until the strands reach theirfinal stress and elongation. Gauge readings and elong-ation measurements must be taken and recorded for eachstrand being stressed.

Prestressing strand, rod, or wires should never bewelded as the high temperature may produce crystalliza-tion and cause the steel to lose a considerable amount ofstrength and fail when under tension.

5.4.1.2 Stringing the strands - Strands are normallysupplied in reel-less packs where the strands may bepulled from the center of the spool. They should beplaced in the form in a way that avoids entanglementduring the stressing operation. Strands for pretensionedproducts should also be free of dirt, oil, grease or anyforeign substance which can affect their bond to con-crete. The strand chucks should be clean, well lubricatedand free from cracks, capable of anchoring the loadsinduced by the strand without allowing excessive slippage.

5.4.1.3 Jacking - Hydraulic jacks with gauging sys-tems are normally used to tension strands. The hydraulicgauges should be accurate to within 1 percent the appliedpressure. Strand force should be determined by observa-tion of jack gauge pressure and measurement of thestrand elongation. The two control measurements shouldagree with their computed theoretical values within atolerance of 2 5 percent. Additionally, these two valuesshould algebraically be within 5 percent of each other. Ifthe strand readings are not within this range, tensioningshould be stopped and corrective measures taken.

5.4.1.4 Strand detensioning - Detensioning shouldnot begin until the concrete has attained adequatestrength to resist the compressive forces induced by thestrand and to adequately bond the strand to the concretein pretensioned construction. Strand transfer is normallyundertaken when the concrete is at about 3500 psi, butthis can vary with design. Each of the strands should besimultaneously and slowly cut at each end of the panel orprestressing bed. Detensioning should be performed insuch a manner as to keep forces symmetrical about thepanel vertical and horizontal axes.

5.4.2 Reinforcement cage assemblies - Information ondetailing and placing reinforcing bars and welded wirefabric may be found in ACI 318, ACI 315, and in theConcrete Reinforcing Steel Institute publications Manual

of Standard Practice and Placing Reinforcing Bars. Rein-forcement for precast wall panels is usually preassembledinto rigid cages using a template or jig before the steelis placed in the form. Cage assemblies should be con-structed to close tolerances, and the various piecesshould be rigidly connected by tying or welding. Whencages are tied, soft stainless steel #16 gauge or heaviertie wire is desirable. Reinforcement cages should besecurely suspended from the back of the molds and heldclear of any exposed surface. The suspension system mustfirmly hold the assembly in its proper position duringconcrete placing and consolidation. Permanent spacers orchairs supported on the form of an exposed concrete sur-face may mar the appearance of the precast panel. Ifpossible, the use of chairs should be avoided. If used,spacers should be of a type and material that will notcause spalling of the concrete, rust marks, or otherdeleterious effects.

All reinforcement, at the time concrete is placed,should be free of grease, oil, wax, dirt, paint, loose rustor mill scale, or other contaminants that may reducebond between steel and concrete or stain the surface ofthe concrete. Reinforcing steel should not be bent afterbeing embedded in plastic concrete.

5.4.2.1 Welding of reinforcement - Tack welding isonly recommended for increased rigidity and should notbe indiscriminately used. When absolutely necessary,welding should be done by certified welders with writtenapproval of the engineer-architect and in accordance withthe provisions of the American Welding Society (AWS)D1.4.

If coated bars are to be welded, the coating should beremoved by acid etching and rinsing the bar in clearwater, or by mechanical means such as wire brushing,abrasive blasting, or grinding. All surfaces to be weldedshould be bright and clean. The clean area should be atleast 1 in. larger than the weld area on all sides of theweld.

Welding of galvanized reinforcement requires a specialtype of welding rod. Welding removes a portion of thezinc coating in the area of the weld. Since zinc fumes aretoxic, adequate ventilation must be provided to removefumes.

Small tack welds give substantial stability to rein-forcing bar cages but are not recommended for attach-ment to main reinforcement due to the possibility of steelcrystallization (embrittlement or metallurgical notch).Tack welds which do not become a part of permanentwelds of reinforcing steel are prohibited by AWS D1.4,unless approved by the engineer. However, tack weldingof reinforcement at locations where neither bar has astructural function should be allowed. For example,welding the ends of the outside bars (within 10 bar dia-meters from the free end of the bar) may be an aid infabrication of reinforcing cages. Reinforcing bars shouldnot be welded within 2 bar diameters or a minimum of2 in., with 3 in. preferred, from a cold bend as this canresult in unpredictable behavior of the reinforcing bar at


the bend. Tack welding must be carried out without sig-nificantly diminishing the effective steel area or thereinforcing bar area should be one-third larger thanrequired. A low heat setting should be used to reduce theundercutting of the effective steel area of the reinforcingbar.

Welding of higher strength steels should be discour-aged unless proper welding procedures, identifying typeof preheat and welding rods, are written. Welding shouldbe prohibited near prestressing steel.

5.5-Concrete placement5.5.1 Transportation- Concrete for casting precast

wall panels is transported from the mixer and placed informs by various methods depending on the precastingoperation layout or the type of panel being manufac-tured. Many precasting plants have stationary mixers anddeliver the concrete to the forms by buggies, buckets,conveyors, pumps or other equipment. Some precastingplants operate from a controlled ready-mixed concreteplant and transport the concrete by mixer trucks. Truckmixer delivery (ASTM C 94) is more often used for largevolumes of concrete. In addition to speed and economy,avoiding segregation is a prime concern in transportingconcrete. Before the delivery of a new batch of concrete,hardened concrete and foreign matter should be removedfrom the surfaces of the transportation equipment.

5.5.2 Segregation- The amount of segregation varieswith the mix consistency and the aggregate grading. Sec-ondary factors which may affect segregation are weather,as it affects consistency, and the mechanism of trans-portation. Equipment should be used that will providethe least amount of jarring and segregation from the timethe concrete is placed in the transport carrier until it isdelivered to the forms. Concrete must be discharged intothe forms while in its original mixed or plastic statewithout separation of coarse aggregate and paste.

5.5.3 Consolidation- Concrete used in the manufac-ture of wall panels should be completely and uniformlyconsolidated by internal or external vibration, byvibrating screed, by impact, or by a combination of thesemethods. Although the available consolidation systemsvary widely, most have been successful when properlyapplied. ACI 309 has presented detailed recommenda-tions for good consolidation practice and the control ofsurface defects.

Even concretes containing high-range water-reducersshould be consolidated by minimal vibration. Regardlessof the type of consolidation, the goal is to avoid seg-regation and excessive bleeding while consolidating theconcrete into a dense, uniform mass with a surface asfree of defects as possible. Four typical vibration tech-niques are described hereafter. It is recommended thatthe consolidation method be left to the panel manufac-turer.

5.5.3.1 External vibration - External vibration isusually achieved by mounting high frequency vibratorsdirectly on the forms or by using a vibrating table. These

vibrators operate at varying frequencies and amplitudes.Vibrating tables or forms should be sufficiently rigid totransmit the vibration uniformly over the entire surfaceof the panel without any form damage. A vibrating tableworks best for flat or low-profile units.

5.5.3.2 Drop-table vibration - Drop-table vibrationis used in some precasting plants to consolidate concretewith a low total water content. The drop table rises andfalls an average of 3/8 in. at a low frequency of approxi-mately 260 cycles per minute.

5.5.3.3 Internal vibration - Internal vibration isdone with a tamping type motorized jitterbug or with aspud vibrator. Spud vibrators should not be used to con-solidate facing mixes. Because backup mixes are generallythicker and stiffer, they can be placed and vibrated in thesame way as regular structural concrete using internalvibration. Vibrators should not be allowed to contactinterior form surfaces, because contact may damage theform or mar the concrete surface.

At times, a combination of external and internalvibration is required to properly consolidate the concrete.When high slump concrete is placed, segregation mayoccur. With normal weight concrete materials, the coarseaggregate tends to settle to the bottom and the fines willrise to the top. With lightweight aggregates, the oppositeoccurs.

5.5.3.4 Layering - Layering is the fourth consolida-tion procedure, based on placing differing slumps andmix proportions at different depths in the concrete. Thisprocess for consolidation is normally used for deep sec-tions, such as large returns at panel edges. A high cementcontent and high slump concrete is placed in the firstlayer, and then in subsequent layers the slump is reducedand the mix changed to provide less fines. Increasingstiffness of the mix in the succeeding layers allows forabsorption of excess water and for accommodation ofpaste from the previous layer. The color of concrete maychange as the mix design and slump change. This may besatisfactory if the return is not exposed or the color doesnot affect appearance.

5.5.4 Facing concrete- Facing concrete should becarefully placed and worked into all parts of the form.This is particularly important in external and internalcorners for true and sharp casting lines. Each batch ofconcrete should be placed as close as possible to its finalposition. The whole mass should be consolidated byvibration with as little lateral movement as possible. Thethickness of a face mix after consolidation should be atleast 1 in. or 1.5 times the maximum size of aggregate,whichever is larger. The facing concrete should be thickenough to prevent any backup concrete from showing onthe exposed face.

In deep returns, excessive air pockets are often createdon the formed surface. This can generally be overcomeby rodding the concrete at the return surface with thinround nose sticks after the concrete has been vibratedinternally. The technique of two-stage casting or sequen-tial casting is discussed in the next section.


5.6-Surface finishes5.6.1 General methods -When a precast panel project

reaches the fabrication stage, approval of both color andtexture will usually have been given. This is generallyaccomplished by submitting a small sample, or in somecases a full size unit, for approval of the engineer-architect.

Surface finishes can be achieved in many ways,depending on the desired architectural effect. Somesurface treatments or finishes are executed on plasticconcrete, some on hardened concrete.

Finishes on plastic concrete generally use one of thefollowing methods:

Chemical surface retardersBrooming, floating or troweling of the back faceWater washing and/or brushingSpecial form finishSand castingSurface texturing using formlinersClay product veneer-facesStone veneer-faces

Surface treatment of hardened concrete requires morelabor and can at times be more susceptible to variations.Available methods include:

. Hand brushing and/or power rotary brushes. Acid etching. Sand or other abrasive blasting. Honing and polishing. Bushhammering or other mechanical tooling. Artificially created broken rib texture (hammeredribs or fractured fins)

Additional finishes and further discussion of finishtreatments can be found in PCI Architectural Precast Con-crete.

Regardless of the type of finishing method, factorssuch as type and brand of portland cement, aggregates,compressive strengths (at time of final architectural fin-ishing), and curing techniques used will affect the finalappearance. When finishes remove part of the surface ofthe concrete, the resulting panel must have adequatecover over the reinforcement to prevent corrosion andstaining.

All methods of finishing must be studied for a projectbefore entering into full production. The precast manu-facturer must develop quality requirements for allarchitectural finishes before undertaking production ofsuch finishes. The finishing process must produce anacceptable uniform appearance without loss of requiredconcrete qualities. When two or more different mixes orfinishes are on the same panel, a demarcation (reveal)feature is necessary.

Panels with large or steep returns (such as channelcolumn covers and some spandrels) may be cast in sepa-rate pieces in order to achieve matching high quality

finishes on all exposed faces as well as minimize airpockets; then they are joined with dry joints as illustratedin Fig. 5.6.1. This method of casting enables all panels to

PROJECTING REINFORCEMENT

,‘I

THIRD CAST WITH PROJECTINGREINFORCEMENT CAST IN, LAPPEDWITH REINFORCEMENT IN FACE,NOT SHOWN

\_&JOI T

FINAL PROFILE RECESS TO CAMOUFLAGE JOINT

a) Separate casting stages of large returns

WEL DED

I

(a)WIREFABRIC

FACE MIX

(b)

(d)

+d ie l-- DRIP3/4 "

b) Alternate casting positionsFig.5.6. 1-Two-stage/sequentialprecasting


be cast face-down with the same aggregate orientationand concrete density using conventional precast concreteforming methods; backforming is not required. Also, acombination of face mix and backup mix can be used,rather than 100 percent face mix. If this is the indicatedproduction method, attention must be paid to suitablecorner details and reinforcement at the dry joints.Although the dry joint may not show with certain mixesand textures, a groove or quirk will help to mask thejoint. Where desired, this joint can be recessed deepenough to allow installation of a small backer rod andplacement of a 1/4 in. bead of joint sealant, Fig. 5.6.1Sometimes precautions may be necessary to ensurewatertighness of the dry joints.

5.6.2 Chemical surface retarders - Chemical surfaceretarders are available in varying concentrations tocontrol the depth of aggregate exposure. They may beused to treat the finished surface whether it is cast up oris on the bottom of the panel, as cast. Retarders beingconsidered for a project should be thoroughly evaluatedunder prevailing project conditions before production.The retarder selected should be compatible with the par-ticular type and source of cement, aggregates, and speci-fic mix selected for the panels. The effectiveness ofsurface retarders varies when the heat of hydration of thecement is altered. The heat of hydration may be alteredby larger concrete masses, depth of precast product,changes in temperature and/or humidity, by use ofins-ulated panels or by changing cements.

5.6.2.1 Applying the retarder - Chemical surfaceretarders are specialized chemicals that delay but do notprevent the set of the surface cement paste so that the

concrete aggregate can be easily exposed. Form retardersare usually fast drying, solvent-based materials designedto resist the abrasion inherent during the placement ofthe concrete into forms coated with a retarder. Retardersapplied to the top surface of freshly placed concrete areusually water-based materials. Both types of retarderscome with retardation strength formulated to producedifferent depths of reveal. Usually, the one selected aftersuitable testing will give 30 to 40 percent exposure of theaggregate intended to be exposed at the surface.

Retarders can be applied by roller, brush, or spray.Extreme care should be taken to ensure uniform appli-cation of the retarder to the mold or concrete surface.

Since the most suitable period for providing the finalsurface treatment may vary from 12 to 24 hours aftercasting, preliminary tests should be performed under jobconditions before planning the casting for a large con-tract. When the concrete matrix is removed by waterscrubbing or other mechanical processes, the operationshould begin immediately after stripping and before thematrix becomes excessively hard. Unformed surfaces maybe treated at anytime after initial set has taken place.Surface retarded concrete is shown in Fig. 5.6.2.1.

5.6.3 Abrasive blasting to expose aggregate - The ageof concrete for abrasive blasting is not as critical as forother methods of exposing aggregates. Ideally the con-crete should not be more than about 3 to 5 days old, andall panels should have approximately the same compres-sive strength. The concrete mix used and the compressivestrength at time of abrasive blasting affect the finalexposure, as do the grading and hardness of the abrasive.Sand or abrasive blasting will produce a muted or frosted

Fig. 5.6.2.1-Aggregate exposed using surface retarders


effect which tends to lighten the color and subdue theluster of the aggregate. The diameter of nozzle, airpressure, and type of abrasive should be determined byexperimentation.

If sand is used as the abrasive, the effect of the sand’scolor on the panel should be reviewed. With certain com-binations of blasting sand grading, pressure, and volume,some of the blasting sand can become embedded in thesurface of the concrete. In this case, a blasting sand ofsimilar color to the sand in the concrete matrix should beused. However, this situation can be minimized by achange in the amount of material that hits the surface,the grading of the blasting abrasive and the pressure atthe blasting nozzle. Once the blasting sand has beenselected, the same sand and grading should be usedthroughout the project. Surface retarders used in con-junction with sandblasting can help reduce sandblastingtime and labor.

The surface of large flat panels should be separatedinto smaller sections with rustication strips or by the useof ribs and form liners in order to minimize the visualperception of textural differences.

Materials used for blasting operations are washed sil-ica sand, certain hard angular sands, aluminum carbide,blasting grit such as power plant boiler slag, carbonizedhydrocarbon, crushed chat, and various organic grits suchas ground nut hulls and corncobs. Deep exposure of thecoarse aggregate requires a finer gradation of sand abra-sive to obtain uniform results. Trials of different abrasivematerials with sample panels are made to check the tex-ture and color tones. Sandblasted concrete having lightto medium exposure is shown in Fig. 5.6.3.

Fig. 5.6.3-Aggregate exposed by sandblasting

Exposed aggregate finishes are popular because theyare reasonable in cost and provide a good variety inappearance. This variety is achieved by varying the type,color, and size of aggregate, color of matrix, method ofexposure, and depth of exposure.

The different degrees of exposure are:

a) Light exposure - where only the surface skin ofcement and sand is removed, just sufficiently toexpose the edges of the closest coarse aggregate.

b) Medium exposure - where a further removal ofcement and sand has caused the coarse aggregateto visually appear approximately equal in area tothe matrix.

c) Deep exposure - where cement and sand havebeen removed from the surface so that the coarseaggregate becomes the major surface feature.

The extent to which aggregates are exposed or “re-vealed” is largely determined by their size. Reveal shouldnot be greater than one-third the average diameter of thecoarse aggregate particles or one-half the diameter of thesmallest sized coarse aggregate.

All sandblast operators should be protected with heavygloves, aprons or protective clothing and air-fed respir-atory protection equipment. Caution, relative to environ-mental pollution, is advised in selecting abrasive grits thatproduce very fine particles of grit after impacting the sur-face. Different equipment may be required for wetblasting.

5.6.4 Honing and polishing- Honing and polishing ofsurfaces provides a smooth exposed aggregate surface.


Honing is generally accomplished by using grinding toolsin stages, with successive degrees of grit fineness varyingfrom approximately a No. 24 coarse grit to a fine grit ofabout No. 300. Polishing can be done with finer grits.Generally, honing alone provides a sufficiently smoothsurface for precast panels.

Grinding elements are made with carborundumbonded by resin, or with diamonds set in the grindingsurfaces. The diamond elements cut faster and wearlonger, but are initially more expensive. Equipment forhoning and polishing may vary from a hand grinder to anelaborate multihead machine. Air voids in the concretesurface should be filled with a cementitious paste whenthe matrix is exposed during the initial grinding oper-ations; careful inspection is required to find and fill airvoids after initial grinding. Subsequent grinding opera-tions should be delayed until the fill paste material hasgained adequate strength. Strength of the concrete andfill past material should be 5000 psi before any grindingor polishing operations are started. Uniform appearancerequires that a minimum of concrete matrix area show,as the aggregates polish better than the concrete matrix.

5.6.5 Acid etching - Due to the many types of aggre-gates used in architectural concrete, caution on the useof acids is in order. Before acid etching a thorough studyshould be made of the effect of various concentrations ofacid used for exposing aggregates or for the cleaning ofpanels. The concrete aggregates should be quartz, gran-ite, or other acid resistant stone. Limestones, dolomites,and marbles will either dissolve or discolor when exposedto muriatic acid. Acids may increase chemical reactionbetween silicates in the aggregate and the free lime lib-erated from the cement. This may lead to calcium silicatedeposits on the panel surface if residue is allowed toharden on surface. Acid washes may also damage the gal-vanizing of exposed hardware and reinforcing bars if lessthan recommended cover is used.

When acid is applied, it must be continuously brushedor scrubbed to ensure uniform reaction with the cementsurface. Acid washing should not be done until the con-crete in the precast panel has reached a minimumstrength of 3500 or 4000 psi. All personnel exposed toany acid from the surface application method must wearprotective clothing and covering to prevent injury fromacid spattering. Acid should be completely neutralizedand flushed from the concrete with clear, clean water toprevent yellowing or other discoloration. Acid should notbe allowed to remain on the concrete surface for morethan 10 to 15 minutes as an absolute maximum. Deepetch exposure should be achieved by multiple treatmentsrather than prolonged contact.

5.7-Concrete curing5.7.1 Introduction - Curing of concrete takes place as

long as sufficient moisture is present and favorable tem-peratures are maintained. In the manufacture of precastconcrete, the initial curing usually takes place in theform. Secondary curing takes place after the product is

removed from the form. Secondary curing may be lessimportant in precast concrete because design strengthsare established to enable the panels to resist maximumstresses usually occurring during stripping and handling.Concrete mixes for precast panels generally contain TypeIII high-early-strength cement or very finely ground TypeI cement, with cement contents high enough to assureadequate strength at stripping (usually at least 3000 or3500 psi). This strength often is achieved within 12 to 16hours while the precast panel is still in the form. Addi-tional information on curing may be found in ACI 308and ACI 517.2R.

5.7.2 Curing recommendations - It is recommendedthat two different stages of curing be established forprecast panels. The first 16 to 20 hours is the initial stageand the most crucial. Steps should be taken during thisperiod to both provide heat (if necessary to maintainminimum temperatures) and to prevent loss of moisturefrom the panel. The exposed portion of the fresh con-crete in a wall panel should be covered during this initialphase.

After removal from the form, the secondary stage ofcuring should be continued until a compressive strengthof 3500 psi has been attained and confirmed by standardtests. During this period, precast panels should be pro-tected from excessive moisture evaporation and fromtemperatures below 50 F.

It may be necessary to interrupt the secondary curingto examine the surface finish and to do any requiredpatching. It cannot be overemphasized that curing at theearly ages is extremely important to the strength anddurability of the concrete panel.

5.7.3 Curing techniques - Any changes in curing tech-niques during a given production run may result inchanges in color, texture, or uniformity of the wallpanels. Therefore, curing procedures should be consistentand uniform from precast panel to precast panel as wellas from day to day. Burlap and other similar coveringsmay cause staining or discoloration on certain finishesand should be avoided in these cases. Because of theirtendency to discolor, curing compounds should not beused, except on the backs of panels before the removalof forms, or on surfaces that will receive a finish later.Since some curing compounds and sealers may interferewith adhesion of surface coverings, coatings, and jointsealants, compatibility with these materials should beinvestigated.

5.7.3.1 Curing temperature - All curing of concreteshould take place at temperatures above 50 F. If temper-atures fall below this level during the first 20 hours,either external applied heat or heat retention measuresare required. However, it must be remembered that trialmix proportions are usually prepared and tested at roomtemperatures of 70 to 75 F. When concrete is cured atlower temperatures, such as 50 F, the concrete strengthmay be lower than laboratory tests have indicated. Ifpanel curing temperatures are expected to be lower thantrial mix temperatures, some allowance should be made


for the slower gain in strength and the early formstripping time adjusted accordingly.

5.7.3.2 Steam curing - Curing with steam simul-taneously provides both heat and moisture. Where steamcuring is used, recommended procedures such as those ofACI 517 must be observed to achieve desired results.Steam should not be applied until after the initial setperiod of the particular concrete mix. The initial set(delay) period should be determined by ASTM C 403.The rate of temperature rise can be from 40 to 80degrees F per hour as long as a proper initial set (delay)period precedes the heating period.8 Maximum tempera-ture should not exceed 180 F. Cooling rates should alsobe carefully controlled. Extremely close control of steamcuring procedures is required in connection with chem-ically retarded exposed aggregate surfaces. Steam curingcan produce a greenhouse effect (dripping of moisturefrom the covering on to the panel) and induce stainingon the exposed panel surfaces.9

5.7.3.3 Curing in storage - Strength gain can con-tinue after panels are moved to the storage area. Careshould be taken to prevent rapid loss of moisture whenpanels are placed in a storage yard. When ambient rela-tive humidity is high, additional protection from rapiddrying may not be required. In areas where hot, dryweather prevails, care should be taken to allow thepanels to dry slowly.

New concrete is vulnerable to damage from even onefreeze-thaw cycle until it reaches a nominal compressivestrength of about 500 psi, since the concrete is in asaturated condition at early ages. At a typical concretestrength above 3000 psi, early freezing is not a problemand the precast concrete panels may be immediatelystored outside. However, panels of any strength will notbe durable to repeated freezing and thawing unlessadequate air entrainment is provided. Section 5.3.3recommends that all concrete mixes should be air-en-trained.

5.8-Storage5.8.1 General - Because of the wide variation in pre-

cast panel sizes and shapes as well as in the productionfacilities, there are no “standard” methods of handlingand storage. Precast panels temporarily stored in a gen-eral storage area should be supported at the blockingpoints designated on the erection drawings. Units shouldbe stored in a vertical or near vertical position. Handlingand storage procedures selected should not cause struc-tural damage, detrimental cracking, architectural impair-ment or permanent distortion when the precast memberis being: (a) lifted or stripped from the mold; (b) movedto various locations for further processing or storage; (c)turned into various positions to provide access for finish-ing and/or surfacing operations: (d) stored before deliv-ery; and (e) loaded onto delivery vehicles.

5.8.2 Protection - During storage, the manufacturershould keep the precast concrete panels in a clean, prop-erly protected area to prevent staining. This does not

mean the panels need to be a covered area or must becovered. The need for protection will depend on the con-figuration of the units, the length of storage time, andthe local environment. To protect against freezing dam-age, inserts and other embedded items should be pro-tected against penetration of water or snow during coldweather.

Storage must be planned carefully to ensure deliveryand erection of the panels in an acceptable condition.Even though the panels may require washing after erec-tion, protection may still be necessary against engineexhaust fumes or soil staining.

5.8.3 Storage of thin flat panels - Flat panels less than4 in. thick or panels with a length to thickness ratiogreater than 60 should be stored and shipped in a verti-cal or near vertical position. Two-point supports spacedapproximately at the fifth points are recommended forstorage or lifting. Protective resilient material should beprovided at points of bearing and contact. All blocking,packing, and protective material should be clean and ofa type that will not cause damage, staining, or disfig-urement of the precast panels. Blocking and supportmembers should be positioned and secured in a mannerto prevent slippage, chipping at the chains, excessivebinding, or excessive stresses. Staggered or irregularblocking should be avoided. Precast units should bestacked so they are supported on both sides to equalizeloading and to avoid overturning.

5.9-DeliveryMost precast panels are delivered over the highways

by semitrailer trucks (see Fig. 5.9). A few are shipped by
rail, barge, or other modes of transportation. Precastplant facilities do not generally restrict the size andweight of precast panels which can be produced. How-ever, shipping problems with oversize panels may greatlyincrease the cost of construction or delay completion ofthe project. Special permits are generally required whereheight, width or weight exceed specified limits. The useof lightweight aggregate concrete panels can, in manycases, minimize the impact of weight in shipping, hand-ling and erection operations. Travel may be restricted togood weather, daylight hours and weekdays. Equipment,such as lowboys or special trailers, may be required forlarge or heavy panels.
All precast panels should be delivered to the siteclearly marked as indicated on the erection drawings,with the date of production and an identifier that showsthe final position of the unit on the structure. Precastpanels should be selected from storage, loaded, anddelivered in the proper order to meet the predeterminederection sequence.

Before scheduling of delivery equipment, a field checkof the project should be made by the erector to ensurethat the foundations, walls and structure generally aresuitably constructed to receive precast panel units. Thesite should be checked for crane and delivery truck ac-cess, as well as possible field panel storage. Most panels

533R-41

Fig. 5.9-Delivery/transportation of panels

should be loaded vertically and supported on A-framesmounted to flat bed trailers. They should be supportedto minimize the effect of road shock and should besecurely fastened with all contact points protected fromdamage. Corners and returns of unusual lengths shouldbe braced from edge to edge for greater protection intransit. All material in contact with the panel should benonstaining.

If panels are shipped horizontal, they should be sup-ported at two points with the supports located at the fifthpoints of the long dimension to avoid excessive stresseswhich may be induced by twisting and/or racking of thetrailer. When the two-point support system is impractical,alternate support systems must be engineered andchecked for feasibility relative to stresses and otherpotential problems.

5.9.1 Protection during shipping - Generally, protectivecovering of a precast panel during delivery should bedetermined by the manufacturer after considering suchfactors as size, shape, type of finish, type of aggregate,the method of transportation, type of vehicle, weatherand road conditions, and distance of haul. Since manu-facturers are responsible for the condition of thedelivered product, they make the decision on wrappingunless the engineer-architect has specified a particularform of wrapping protection.

5.9.2 Economical panel sizes - Economical panel sixesdepend on the plant capability, distance to the job site,highway conditions, and shipping and erection restric-tions. For maximum economy, panels should be limitedto a height and width of 8 ft and a weight of 20,000 lb toallow for two on a truck. In some areas, heights of 13 ft6 in. are allowed without special permit, while in othersthis limit is 12 ft. Restrictions generally exist for loadsover 8 ft in width; maximum permit widths can vary from

10 to 14 ft, depending on area or city. Some areas allowoverall lengths over 70 ft with a simple permit, escortsfront and rear and travel limited to certain times of day.

CHAPTER 6-INSTALLATION

6.1-Planning and preparation6.1.1 Coordination - Early in the construction, before

panel manufacture, the panel fabricator, erector,engineer-architect, owner, and the general contractorshould hold a coordination meeting to establish theworking relationship, assure that handling techniques aresatisfactory, establish the temporary erection bracing andestablish mutually agreeable delivery schedules.

6.1.2 Access - Access conditions at the site should bereviewed, considering temporary roads for deliverytrucks and handling equipment such as cranes. Responsi-bility for sidewalks, overhead lines, barricades, truckspace at site, sequences, coordination with other trades,and panel protection should be discussed at a project co-ordination meeting. At this coordination meeting the pre-cast erector should provide his scheme for the handling,loading, transportation and erection of the panels. Tem-porary bracing of the structure, on-site storage, connec-tions, starting-location and sequence of erection relativeto building stability should be discussed.

6.1.3 Project meetings - During the precast erectionphase, the general contractor should conduct frequentproject meetings between the erector and those subcon-tractors whose work is affected by the precast. Thesemeetings will help to ensure that all necessary provisionshave been made to facilitate the erection process.

6.1.4 Contract documents - The contract documentsshould state clearly any requirements or sequencing of


erection needed to maintain building stability. Lim-itations on loading of the structure, temporary bracingrequirements, or elevation sequencing need to be clearlyshown before bidding. All details of temporary erectionbracing, temporary connections, and shoring should bereviewed by the engineer-architect. The sequence ofremoval of any temporary erection connections should beshown, since leaving these connections in place can resultin structural behavior not intended by the engineer-architect.

6.1.5 Pre-erection check - Before starting erection,bearing walls, foundations, structural frame, bearingsurfaces, notches, embedded plates, angles or bolts, andwelded connections should be checked for dimension,location, line, and grade to ensure that the area toreceive the precast panels is ready. Any modification tobearing surfaces or connection hardware should be madeby the general contractor before erection begins. Theprecast erector should also spot check the access beforescheduling the loading and handling equipment.

6.2-Unloading and handling6.2.1 General - Panels should be loaded and deliv-

ered in the erection sequence established at the projectcoordination meetings. Ideally panels should be liftedfrom the delivery trucks and placed directly in theirproper position on the building. This minimizes handlingdamage and is usually the most economical method.Many requirements in Chapter 5 concerning the handlingof panels at the fabrication plant, apply equally to jobsiteactivity.

The precast erector should set out joint location andspacing before actual panel installation. This shouldminimize differential variation in the panel joint width aswell as identify problems caused by the building or theadjacent materials being out of dimension or alignment.

6.2.2 Delivery sequence - A delivery sequence forpanels should be sufficiently flexible to allow for:

. Full loads, using reasonable “fill-out” units if neces-sary. Control of unit position on the trailer with propersupport for safety and economy. Adequate advance notice of shipment. Assurance of prompt unloading. Provision for some on-site storage

If possible, panels should be unloaded by handling ina vertical position. This is usually the situation if singlestory panels are shipped on frames in a vertical or anupright position. All chains, binders, banding, protectivepacking and bracing should be carefully removed fromaround the panels. Corners and panels with returns ofunusual length are shipped with special bracing whichshould not be removed until the precast piece has beenlifted slightly from the truck before installation. If beltsare used in unloading, only one panel at a time should beremoved. Protective material must be used between the

belts and point of contact with the panel. Gangs of pre-cast panels should not be removed with belt liftingdevices unless the panels are palletized.

The exterior panel should always be unloaded firstfrom a frame or a stack; never slide a panel out from themiddle of a stack. Balance on the trailer should be main-tained during unloading by unloading alternate sides ofthe vehicle. Remaining adjacent panels on the trailershould be tied or blocked to prevent tipping.

After delivery, a panel may require rotation into a newposition; for example a tall panel delivered on its sidemust be rotated to a vertical position. A panel may alsobe delivered flat (horizontal) and then be lifted from thedelivery vehicle and uprighted in the air. The panel isnormally rotated without being allowed to touch theground. It may be necessary to bolt a support frame tothe panel before rotating. Usually two lifting lines fromthe crane are used, although special rotating frames havebeen developed for use with one crane line.

6.2.3 Lifting devices - Lifting devices should besecured to panels in accordance with the lifting devicemanufacturer’s recommendations. Bolts must be threadedinto the inserts 2.5 bolt diameters for coil inserts and 1.5bolt diameters for ferrule inserts to prevent stripping ofthe bolt or insert threads. At least two connectionsshould be used whenever the panel is lifted, so that thepanel or the lifting line cannot spin and unscrew, causingthe lifting line to become disconnected. Bolts of properlength must be used to ensure a full embedment in thelifting device. Regardless of the load requirements, a 1/2-in. bolt should be the minimum size used for any precastpanel handling. Expansion bolts, predrilled or self-drilled,should not be used for handling and erection purposes.Occasionally inserts, bolts, or other devices are providedonly for the convenience of field handling. When thesedevices are located in finished edges or exposed surfaces,bolt and insert holes require filling and repairing. Whenthis is necessary, the engineer-architect should be advisedso that the locations and repair procedure can be ap-proved before panel fabrication. Repairs should be pro-perly executed in accordance with Section 6.6.

6.3-Jobsite storage6.3.1 General - If the jobsite storage of precast panels

is necessary to meet the established schedule, the storageareas provided should be relatively level, firm, well-drained and located where there is little chance of dam-age due to other construction activity. Recommendationsfor storage in Section 5.8 should be followed. In addition,where long-term storage is necessary, panels should becovered to protect them from accumulation of dust, dirt,or other staining materials. Covers of canvas, rubberizedsheets, heavy waterproof paper, reinforced plasticsheeting, or other protective material should be con-sidered.

The storage area may have to be stabilized so thatdifferential settlement or twisting of the stored panel willnot occur. Panels should not be stored on frozen ground


without proper safeguards to prevent uneven settlementif the ground thaws.

6.3.2 Panel support -Panels should be stored withidentification marks clearly visible and supports at theblocking points shown on the erection drawings. Panelsshould be blocked to prevent tipping. When panels areplaced against a frame or support, they should be set onprotective material laid horizontally under or betweenthe panels. This protective material should be selected sothat the blocking material will not stain the panels.Plastic chairs, chain guards, and bearing pads are readilyavailable and do not stain. Wood blocking should bewrapped in plastic sheeting to avoid wood stains that canbe serious enough to cause panel rejection. Polystyrenefoam blocking may dissolve when the solvents of sealerscontact it, leaving an unsightly patch of polystyrene thatis virtually impossible to remove without defacing thepanel. When solvent-based sealers are not used, poly-styrene foam can provide good protection if it is ofadequate size to support the imposed load.

6.3.3 Storage on a delivery vehicle - If jobsite storageis limited or of short duration, leaving the panels on thedelivery truck is often more desirable, provided theshipper will permit extended truck usage. Leaving thepanels on the truck provides a clean safe place andeliminates extra handling. This reduces possible damagecaused from multiple handling and improper jobsitestorage techniques.

6.4-Installation6.4.1 Workmanship - Workers should be properly

trained to handle and erect precast concrete panels.Methods of erection should be planned to avoid soiling,cracking, chipping and damage to built-in items. Chippingand spalling may be repaired at the jobsite after instal-lation, if done to the satisfaction of the engineer-architect.

6.4.2 Equipment - Handling equipment for precastpanel erection should be safe and reliable under allanticipated conditions to which it will be exposed. It mustnot only accomplish the handling/erection quickly andeconomically but also eliminate any possibility of hazardto personnel on the site, to the public nearby, or toproperty. Factors involved in equipment selectioninclude:

l Mobility and cost - availability and cost of thehandling equipment; cost of altering boom length ormaking other modifications; mobility needed for antici-pated site conditions; whether the panels will be walkedor carried

l Capacity required - the weights, dimensions, and liftradius of the heaviest and largest precast panel; themaximum lift height and radius and the weight to behandled at that elevation; the number and frequency oflifts

l Clearance needs - the clearance between the loadand adequate headroom in which to operate; ground

clearance and conditions of the ground on which to setthe equipment; overhead clearance of wires and adjacentbuildings.

The equipment selected must meet or exceed all pro-ject requirements and have at least a 5 percent workingmargin of reserve load capacity on every lift for unan-ticipated problems. When slings are used for panel erec-tion, the included angle between the sling lines shouldnever exceed 90 deg (or 45 deg from the vertical).

Lifting devices must be checked to assure that theircapacity and intended use conforms to the manufac-turer’s recommendation. Panels should be handled onlyat the locations and with the hardware shown on theerection shop drawings. If slings are used, the panelshould be marked so that the slings are placed in theproper location.

6.4.3 Bracing and guying - Bracing requirementsshould be established before bidding so that properallowances can be made. Necessary bracing and guyingmaterial should be delivered to the jobsite beforeerection begins. All bracing and guying methods must bedesigned to support all construction loads including wind.Building design should provide for structural stabilityduring erection of the precast panels. Until proper align-ment and final connections are made, structural stabilitymay not be achieved and bracing may be required.

When bracing/guying is used, the manufacturer’srecommendations must be followed regarding load,length, and inclined angle. Special care must be given tothe location, size and capacity of the insert in both thepanel and the deadman or floor slab. A brace/guy shouldnever be connected to a precast panel at a point lowerthan two-thirds of the panel height. Temporary bracingor guying should be arranged so that it does not interferewith other panels being erected, nor should removal ofone brace remove support from the remaining panels.Removal of temporary bracing/guying should not takeplace until the building stability has been achievedthrough other means or until authorized by the engineer-architect.

6.4.4 Alignment - Offset lines are normally marked onthe floors for multistory buildings or on foundations forsingle-story buildings. Elevations for precast panels arenormally established by setting the properly sized shimpack on the floor or beam. Shim material should have abearing capacity of approximately 1000 psi. Each panelshould be erected to meet the tolerances of Chapter 3.To hold overall building dimensions, it is necessary towork to joint center lines, permitting the joint widths tovary. If a joint size is detailed as a 1/2 in. and the paneltolerance is * 1/8 in., the joint may vary from 3/8 to 5/8 in.,provided approved connection and erection proceduresare followed.

6.4.5 Connections - Connections should be compat-ible with both precast and supporting frame tolerances,be simple in detail, and easily adjustable in the field tomeet special project conditions. Connections should allow


erection to proceed independent of ambient temperaturewithout temporary protection measures. They should beas standardized as possible in order to minimize plantand field erection quality control problems. Once agreedupon by the engineer-architect, the erector, and theprecast supplier, the typical connections selected shouldbe shown on the shop drawings submitted before panelfabrication.

6.4.5.1 Bolted connections - Connections should bedesigned so that members can be safely secured to thestructure in a minimum amount of time without com-pleting alignment and all adjustments. Bolted connectionsare positive immediately and allow for adjustment with-out tying up large handling equipment. Care must betaken during adjustment to prevent damage to either thepanels or the adjacent building materials.

Standardized attachment hardware (clip angles, bolts,and shims) helps to minimize errors and control inven-tory. Regardless of the load requirements, a 1/2-in.diameter bolt should be the minimum size used. Clipangles should be slotted or have oversized holes to allowfor product tolerances and building movement.

6.4.5.2 Welded connections - Where welded con-nections are required, welding should be done in accor-dance with AWS D1.l and with the erection drawings.These drawings should show the type, size, length ofweld, sequence, minimum preheat, interpass temperature,weld location and, if critical, the type of electrode. Panelsmay be shimmed while the initial tack welding is done.Bracing or other provisions must be adequate to safelyhold the panel in position while the handling equipmentis released and adjacent panels are placed.

Before temporary bracing is released, the designatedfull weld should be in place at every connection in theprecast panel. To minimize staining, all loose slag anddebris should be removed immediately after the weldingis complete. Panel finish and surrounding materials mayrequire protection from sparks and smoke stain. Non-combustible shields should be used to protect exposedconcrete surfaces during welding.

6.4.5.3 Post-tensioned connections-Post-tensioning,either vertical and/or horizontal, may be used for fieldconnection of precast panels using either bonded or un-bonded tendons. Bonded tendons are installed in pre-formed voids or ducts; they are made monolithic with themember and protected from corrosion by grouting afterthe stressing operation is completed. The grout must fillall voids in and around the tendon for its entire length.Unbonded tendons are connected to the precast panelonly through the anchorage hardware. Anchorage devicesfor all post-tensioning systems must be aligned with thedirection of the axis of the tendon at the point ofattachment. Concrete surfaces against which the anchor-age devices bear must be in the plane of the tendon andnormal to the tendon direction. Post-tensioning opera-tions require personnel properly qualified and exper-ienced with the stressing procedures and equipment to beused.

6.4.5.4 Dowels and grouting - The strength of adowel connection in tension or shear depends on theembedded length and the developed bond. Since place-ment of a portland cement grout or epoxy grout is re-quired during erection, use of dowel connections usuallyslows down the erection and may be costly.

For doweled or grouted connections, setting shims arelocated and grout holes are filled just before setting pre-cast panels. The concrete in and adjacent to the groutholes should be damp or in a saturated surface dry condi-tion. Grout consistency should permit displacement ofsome grout when panels are placed in position. Wheregrout beds are required, the panels may be set on shimsand dry-packed with mortar later. Panels may also be setonto fresh grout with the elevation controlled by shims.Excess grout should be removed if it interferes with otherconstruction activities. Use of epoxy and cementitiousgrouted connections should be avoided when the ambienttemperature is below 40 F. Mixing and installation ofepoxy grouts must be in strict accordance to the manu-facturer’s instructions. In selecting methods of dowelingand grouting, consideration must be given to how thefinal joint will be made and how the corners will bejoined. Adjustments to the precast panel after the initialset of the grout may destroy the grout bond and reducethe connection strength. Doweled and grouted connec-tions should only be used where they are part of thestructural design concept.

6.5-Cleaning6.5.1 Protection- Panels should be delivered to the

jobsite in a clean and acceptable condition. The erectorshould recoat all welds and abraded steel with a rustinhibitor or, in cases of galvanized plates, with a coldgalvanizing coating. The erector is normally responsiblefor any chipping, spalling, cracking and other damage tothe precast panels after delivery to the jobsite. The gen-eral contractor assumes responsibility for panel protec-tion after panel erection.

Any mortar, grout, plaster, stains, or other matter anddroppings on the panels during the course of generalconstruction should be immediately washed off with cleanwater or cleaned as otherwise required. Rainwater orwater from construction hoses can wash across buildingmaterials and cause discoloration of exposed precastpanels.

Arrangements should be made by the general contrac-tor to provide protection for adjacent materials (such asglass and aluminum) which may be damaged by welding.Otherwise the adjacent materials should not be installeduntil the panels are in place, repaired, and cleaned.

If cleaning is required, exposed panel faces should bewashed with a cleansing agent mixed with hot water.Panels should be thoroughly rinsed with clear water afterwashing. A good fiber brush should be used for cleaning.Normal procedure is to begin cleaning panels from thetop of the building downward. Individual panels arecleaned by starting at the precast panel bottom and


working up. After first washing from the bottom to thetop, the panels should be rinsed and then washed fromtop to bottom, followed by a second rinse with clearwater. Cleaning solutions must never be allowed to dryon the concrete surface that will be exposed to view. Thefinal finish should be sound and have exposed concretefree of all laitance, dirt, stains, smears, or otherblemishes.

6.5.2 Stubborn stains- If stains remain after cleaningwith a stiff brush and cleansing agent, the surface of thepanel should be thoroughly wetted with clear water andthen scrubbed with a dilute solution of muriatic acid. Theconcentration of this solution may be increased to a max-imum of 5 percent muriatic acid, but weaker solutionsshould be tried first. A thorough washing with clear watershould immediately follow the scrubbing. Acid cleaningcannot be done on honed and polished surfaces or ifthere are soluble aggregates such as limestone or marbleon the panel face. Acid cleaning may change the appear-ance of sandblasted surfaces. Care must be taken to pre-vent damage to adjacent material corrodible by the acid.Glass and aluminum trim are especially susceptibleduring acid scrubbing and washing. Repeated applicationsof a cleaning acid on the exposed surface of the precastpanel may change the color or texture of the panel. Theeffect on appearance may necessitate extensive washingof all project panels. Other commercial cleaners may bedesirable in lieu of acid. Because muriatic (hydrochloric)acid may leave a yellow stain on white concrete, a 3 to 5percent phosphoric acid solution may be preferable onwhite or very light concrete panels.

6.5.3 Sandblasting and steam cleaning - High pressuresandblasting and steam cleaning are also common waysto clean panels. An experienced operator should beengaged for sandblasting of precast panels. Sandblastingmay dull the aggregate or change the color or texture sothat it no longer matches the remainder of the structure.A small area, preferably on the mockup panel, should betried and approved before proceeding with the work.

6.5.4 Sealers - If panels that have been sealed beforeshipping to the site require cleaning, it may be necessaryto remove the sealer and recoat the panel after cleaning.Surface sealers should never be reapplied until all repairsand cleaning have been completed.

6.6-Patching and repair6.6.1 General - Minor chipping of precast panels

during transportation and handling at the jobsite can beexpected. Damaged panels can be repaired after erection,but major spalls or cracks require an engineering eval-uation. Repair work requires expert craftsmanship if theend result is to be both structurally sound and pleasingin appearance. Careful planning is required to determinewhether the repairs can economically match the existingsurface concrete both in color and texture and be struc-turally sound. In some cases, it may be more feasible torecast the panel. All patching and repairs should be fullycured, cleaned, and dry before installation of sealant in

the joints between panels. General guidelines for repairof concrete are found in ACI 546. The repairs shouldconform to the contract documents and be architecturallysatisfactory. Gross variations in color and texture ofrepairs from the adjacent surfaces may be cause forrejection and a request for replacement of the panel.

6.6.2 Repair considerations - A certain amount ofrepair is routinely expected on architectural panels.Evaluate the imperfections in the concrete to determineif repairs should be attempted. Repairs can accentuatethe flaws, rather than remove them. Slight color vari-ations can be expected. Attempt hand tooling of surfaceblemishes before undertaking patch repairs. Needlescaling, bushhammering, or other mechanical tooling canbe effective in blending in offsets or variations in colorand texture.

Use the jobsite mockup or a damaged reject panel todevelop a patch mix design and practice repair andtexture techniques. In most cases, it is better to completethe preparation of all finishes on the precast panel beforebeginning any patching or repairs. Recent repair areascan be damaged if repairs are made ahead of the panelfinishing. Epoxy-filled crack repairs should be donebefore sandblasting. Blasting before the epoxy work willcause the crack to have rounded edges, and it will bemore difficult to minimize the crack appearance.

Cure all patches and repair areas. These will requirebetter curing and greater weather protection than theoriginal concrete. Proper tools, staging or scaffolds, andsafety or protection equipment should be set for allfinishing personnel. Patch mix designs and finishing tech-niques should be documented so that new workers cantake over repairs if others leave the project.

6.6.3 Chips and spalls - Chips, spalls, and areas ofunsound concrete may be prepared with a hand-held orpneumatic chisel. The repair area should be chipped outto a depth of 1.5 times the maximum size of aggregate toassist in physically holding the patch mix in place. Alldust must be brushed or blown from area to be repaired.The entire area to be repaired, as well as adjacent sur-faces, should be prewetted before applying a recom-mended bonding agent. A stiff predesigned patch mixshould be applied onto repair area and compacted formaximum density by dry tamping.

Large repair areas will need coarse aggregate in thepatch mix or the aggregate must be hand placed androdded into the patching grout. Strike the repair arealevel and add any surface texturing while the concrete isstill plastic. Begin curing immediately. If the spalled-outpiece of concrete is available and fracture surfaces stillmate, the easiest repair is to adhere the spalled concreteback into place using an epoxy adhesive. The fracturedsurface of the panel and spalled piece should both bepainted with the epoxy adhesive. Apply enough epoxy sothat some epoxy will squeeze out when the mated piecesare clamped together. Use an epoxy with enough vis-cosity to prevent sagging or running on vertical surfaces.It may be necessary to drill through the spalled piece and


into the precast panel to set pins or bars to increaseanchorage.

6.6.4 Crack repair- Panels may crack during trans-portation and erection. Structural and visual acceptabilityof cracks should be determined by the engineer-architectand owner (crack acceptability is discussed in Section2.5.3.1). The repair method for a crack depends on itssize, location, and the engineering problems causing thecrack. Cracks that are nonworking or have no significantstructural problems may be chipped or routed out andrepaired in the same way as chips and spalls (Section6.6.3).

Cracks that are relatively short but that requirestructural repair may be chipped or routed out to aminimum depth of 1.5 times the aggregate size and filledwith a nonsagging epoxy adhesive or stiff mortar. Wherethe crack is on the exposed finish face of the panel, theepoxy repair preparation may be taken deeper into thepanel to allow for application of a surface patch mix tomatch adjacent surfaces.

6.6.4.1 Epoxy injection- Longer or deeper crackrepairs may require epoxy injection using a low viscosity100 percent solids material. The epoxy color (amber,gray, white or pigmented) should closely match theexposed concrete surface. This approach can be used onall cracks wider than about 0.002 in. Epoxy injectiondepends on temperature of the concrete and viscosity ofthe epoxy. The typical epoxy repair procedure is to:

. Clean the cracked area thoroughly.

. Drill holes for entry ports along the crack one-halfthe thickness of the precast panel and space entry portsalong crack at intervals approximately equal to thethickness of the panel.

. Provide a temporary surface seal with either wax,grout, hydraulic cement or epoxy resin sealant.

. Inject low viscosity 100 percent solids epoxy intoports beginning with the bottom or lowest port. A pres-sure of 90 psi is usually recommended.

. Continue to inject at lowest port until epoxy flowsfrom the next highest port along the crack.

. Plug each injector port after it has been filled.

Continue the procedure until the entire crack has beenfilled. After the epoxy has cured, remove the temporarysurface seals, ports, and extra epoxy. Surface texturizingor sandblasting of the repaired concrete area will benecessary to remove all traces of epoxy or the surfaceseal coat. Further, more detailed, information can befound in ACI 503R and ACI 503.1.

6.7-Joint sealing (caulking)6.7.1 Joint preparation- Before application of a

sealant, concrete surfaces should be sound, smooth, cleanand free of all mortar, dust, or other contaminants suchas form release agents that may affect adhesion. Somesealant materials cannot be applied to wet surfaces; nosealants should be applied to a frozen surface. Use of astiff wire brush, light grinding or sandblasting followed by

air blowing may be necessary to remove surface contam-inants. After cleaning of the joint area, the joint shouldbe wiped with a cloth dampened with an oil-free solvent,or as recommended by the sealant manufacturer. To en-sure good adhesion between the sealant and the panelconcrete surface, some sealant manufacturers recommenda primer. The sealant and primer combination should beas recommended by the manufacturer. Some primersleave an amber stain if brushed along the exposed panelface. Removal of this stain often requires mechanicalmeans and is expensive. Sealers or sealants should not beapplied directly over silicone or acrylic waterproofmaterials. Further information can be found in ACI504R.

6.7.2 Sealant installation- Sealant application shouldbe scheduled when the exterior temperature is from 40to 90 F. Installation temperature may vary dependingupon sealant material, humidity, and protection available.In cold weather, the joint and the sealant may be heateddepending upon the manufacturer’s recommendations.

It is desirable to use the minimum amount of sealantto make a satisfactory joint. A relatively thin bead is lesslikely to fail than a thick bead because the thin bead candeform more uniformly. For joints up to 1/2 in. wide, thedepth of the sealant should equal the width. For widerjoints, the depth should equal half the width, but notmore than 1/2 in.

Sealant material should be delivered in the manufac-turer’s original sealed containers with labels intact.Recommendations of the manufacturer should always befollowed regarding mixing, surface preparation, priming,pot life and installation procedure. Good workmanshipby qualified experienced sealant applicators is the mostimportant factor required for satisfactory performance.To ensure quality control, sealant subcontractors mayprefer to mix all two-part sealants at their businesses,load into cartridges, and then flash freeze the cartridgesbefore delivery to the jobsite. If done properly, this willeliminate dust, dirt or moisture contamination. Thesealant (caulking) gun should have a nozzle of propersize and should provide sufficient pressure to completelyfill the joint. Joint filling should be done carefully andcompletely, thoroughly working the sealant into the joint.The sealant should be smoothed and neatly tooled toeliminate air pockets or voids. Since some solutions usedto facilitate tooling, have discolored lightly coloredconcrete surfaces, tools should be used dry or wettedonly with water when working next to these surfaces. Thefinal surface of the tooled sealant should fill the joint, besmooth and free of ridges, wrinkles, sags and air pocketsas much as possible. All sealant smears, primers, solventsand other materials used in caulking or sealant workshould be removed immediately and entirely from adja-cent surfaces as the work progresses. Use the solvent orcleaning agent recommended by the sealant manufac-turer, so long as it does not discolor the exposed surfaceof the precast panel.

Backup fillers used in joints to control the depth of

RECESSED VERTICAL BUTT JOINT

HORIZONTALJOINT

ALTERNATIVE PROFILE

RECESSED HORIZONTAL OR VERTICAL BUTT JOINT

Fig. 6.7.2-One-stage joints

ALTERNATIVE PROFILE

FLUSH BUTT JOINT(LEAST DESIRABLE) RECESSED CORNER JOINT

\_ 1/2” x MAX.AGGREGATE OR 3/4" MIN.

CORNER JOINT DETAIL JOINTS IN PANELS WITH NARROW RIBS

2- 1/2" MIN.3” PREFERRED

sealant should be installed in the joint with a minimum compression of 30 percent. If heavy-wall, hollow-coretubing, block, and rod stock are used as fillers, theyshould be compressed and rolled into the joint in such away as to avoid linear stretching. Filler rods or blocksshould not be twisted or braided during installation.

The sealant joints described above are called one-stagejoints. Several typical situations are shown in Fig. 6.7.2.

6.7.3 Two-stage joints - When a two-stage joint (seeexamples in Fig. 6.7.3) is used, proper venting and drain-
ing are absolutely necessary. All horizontal joints shouldhave vent tubes, generally located at the junction of thehorizontal and vertical joints. Venting prevents water(either from penetration or from condensation) from col-lecting between the wall structure and facing panels orwithin the panel joints, if both the exterior and interiorfaces of the panels are sealed.
Vent tubes should be 1/4 to 3/8-in. inside diameter poly-vinyl chloride or other nonstaining materials. The venttube should slope down to the exterior face of the paneland must penetrate the joint backup filler so that itallows for free movement of air between the outsideenvironment and the cavity. A minimum of two venttubes per panel or spacing at 6 to 10 ft on center shouldbe used. Vents should project at least 1/4 in. (6 mm)beyond the sealant exterior face.

When installing a two-stage joint, apply the interior airseal or sealant first. This will minimize the escape ofwarm moist air from the interior to the joint cavity,

thereby condensation.6.7.4 Fire-resistant joints - When installing a fire-

resistant joint system, the fire-resisting blanket should beinstalled under a minimum of 10 to 15 percent compres-sion.10

CHAPTER 7-QUALITY REQUIREMENTSAND TESTS

7.1-Introduction7.1.1 General - An effective quality assurance and

quality control program in the manufacturing of precastpanels benefits the precaster by reducing the cost ofrepairing or remaking products due to errors in fabri-cation. Quality control also reduces the chance of struc-tural failure due to reinforcing bars being omitted ormislocated. Precast erectors benefit when panels meettolerances so they do not have to spend extra timelooking for a satisfactory way to erect out-of-tolerancepanels. Overall benefits to the owner accrue in receivinga structure that meets the requirements within the agreedupon budget. The main objective of the quality assuranceand quality control (QA/QC) program is to provide com-prehensive production inspection and testing so thatpanels will be made within project tolerances and incompliance with the job specifications.

7.1.2 Materials - Project materials should be evalu-ated as they arrive to assure that they meet the specifica-


(a) Two-stage joint-horizontal-using gasket (b) Two-stage joint-horizontal-using field-molded sealants

MINIMUM" PER INCH)

SEALANT (IF USED) MUST BEDISCONTINUED AT INTERVAL S(VERTICAL JOINTS) TO DRAIN AREABETWEEN IT AND AIR SEAL

(c) Minimum requirement for elementary two-stage joint

(d) Two-stage joint-vertical-using field-moldedsealants

SEALANT --

BACKING --

1 1/2"

1-1/2" -i-t t

HORIZONTALSEALANT BEAD

t%!!;E

SOME DESIGNSWILL NOT USEHORIZONTA L -BEAD.

HORIZONTAL VERTICAL

(20 DEG.SLOPE PREFER4 BL E)

(e) Modified two-stage joint with air chamber

,112’; MIN.----. __ ____

- - -.

SEALANT DISCON DAT HORIZONTAL JOINTS

* REVERSE SEALANT AND BACKER ROD WHENINSTALLED FROM FRONT t

EXTERIORFACE

EXTERIOR INTERIOR

CONTINUOUS AIRTIGHT SEALSLOPING GUTTER TOVERTICAL JOINT (OPTIONAL)

AIR CHAMBER (OPTIONAL)

AIRTIGHT HORIZONTA L AN D VERTICAL INTERIOR

HORIZONTAL JOINT-m AIR SEA L - CONTINOUS AT INTERSECTIONS

FLOOR VERTICALLY

SLOPE TO EXTERIOR

AIR CHAMBER ( OPTIONAL)

SECTION ATVERTICAL JOINT

/c4”MlN.-mj

PROFILE ATAIR CHAMBER

PANEL PROFIL EWHERE AIR CHAMBER

IS TERMINATED

Fig. 6.7.3-Two-stage joints


tions. Inspection records should be kept in a concise,clear form and filed for future reference. Most projectsrequire only minimal testing for concrete compressivestrength and absorption and will not require overlydetailed inspection of materials. However, there areinstances where extensive complicated testing, inspection,and control procedures are needed. This type of sophis-ticated quality control is beyond the scope of this guide.

7.1.3 QA/QC - Quality assurance and quality control(QA/QC) programs can simplify and improve the interre-lation among owner, engineer-architect, contractor, andpanel fabricator. In such a program, forms, reinforce-ment, and embedments should be inspected before con-crete placement. The face finish of the panel should beinspected after the panel is cured and stripped from theform. The finish surface of the panels should beinspected for compliance with project requirements forcolor uniformity and texture before shipment. Inspectionprocedures should be designed so that panel productioncan proceed at a prescheduled pace with minimum delay.

A good quality control program is simple and con-sistent. Complicated plant procedures and controls leadto uncertainty and confusion. All persons concerned withproduction and inspection should be fully familiar withspecification provisions including the specified tolerances.It is when tolerances are not properly identified andanticipated that they are most likely to cause delay andpanel rejection.

7.1.4 Product finish- There will always be some vari-ation in the color, texture, and finish from panel topanel. Acceptable panels should show no obvious surfacedefects, other than minor color and texture variations,when seen in good typical lighting at a distance of 20 ft.

The final appearance of the product is difficult toevaluate because it is normally subject to the personalinterpretation of the engineer-architect or owner. Wherethere is a great concern about the color, texture, oruniformity of the panel, the owner should require mock-up panels or samples as recommended in Section 1.4.Once the owner or engineer-architect has inspected thesamples and selected an acceptable range of finish andtexture, the inspector has a tangible standard forreference.

7.2-Unacceptable defectsCracks can usually be repaired. The precast fabricator

should have an opportunity to make repairs before anypanels are rejected. The following list gives definitions ofunacceptable panel defects that should not remain on thefinished panels:

Casting defects-Excessive bug holes (air voids) on theexposed surface; casting lines evident from differentplacements and poor consolidation; areas of backup con-crete bleeding through the facing concrete; foreignmaterial embedded in the panel face; reinforcementshadow lines

Stains-rust or other stains; blocking stains or acid

stains evident on the exposed surfaceIrregularities-ragged or irregular edges; visible form

joints or irregular surfacesNonuniform color and texture-panels not matching the

approved samples for uniformity of color within a panelor from panel to panel; nonuniformity of aggregate color;adjacent flat and return surfaces with greater differencein exposure than the approved samples

Cracks and repairs-cracks or repairs visible at 30 ftafter final installation and finish.

7.3-Structural adequacyPrecast panels should be inspected carefully to assure

that they are structurally sound. When the inspector findscracks, chips, or spalls in a panel and is unsure of theirimpact, he should refer the problem to the engineer-architect so that the condition may be evaluated. Eventhough repairs may be structural, all repairs should matchthe surrounding concrete and meet architectural require-ments.

7.4-PrestressingPrestressing procedures are described in Section 5.4.1.

The strand must be kept untangled and free of anymaterial that will affect bond to concrete. Strand chucksshould be clean, well lubricated, and free of cracks.

Hydraulic jacks with gauging systems are normallyused to tension the strand. Gauge readings and elonga-tion measurements should be taken and recorded foreach strand being stressed. The gauges, which should beaccurate to within 1 percent of the applied pressure,should be calibrated a minimum of once a year, orwhenever there is cause to question the accuracy of thejack load.

7.5-Materials7.5.1 General - The panel materials should be con-

tinuously evaluated to assure that they meet theirrespective specifications. In some cases, the materialevaluation program involves only obtaining and reviewingmill or material supplier reports. However, in othersituations, it may include extensive testing.

7.5.2 Reinforcing steel- Reinforcing steel should bechecked to see if it is the proper size and grade. If thereinforcing steel is to be used as an anchor for weldedembedment assemblies, the carbon equivalent shouldmeet AWS D.l.4 requirements.

7.5.3 Welded assemblies - Welded embedment assem-blies should be inspected to assure that the assembliesare fabricated properly with the correct size plates andnumber of anchors. Welding procedures should be moni-tored to assure that welds have adequate strengths.

7.5.4 Concrete - In many instances, concrete for pre-cast wall panels is batched at the site of panel fabricationbecause of the use of special cements and aggregates.The control and testing of this concrete is the respon-sibility of the precaster.

7.5.4.1 Cement -Cement should be evaluated for


its strength producing characteristics. The cement sup-plier should provide a certified mill test report with eachshipment and also data as outlined in ASTM C 150. Milltest reports should be kept for at least 2 years. It is alsobeneficial to obtain a 10 lb sample from each deliveryand store it in an air-tight container for possible futureevaluation in case strength or color problems occur.

7.5.4.2 Aggregates - Normal weight coarse aggre-gates and fine aggregates should meet the requirementsof ASTM C 33, except for gradation of aggregates usedin the face mix. Structural lightweight aggregates shouldmeet the requirements of ASTM C 330. All aggregatesshould be sampled in accordance with ASTM D 75,tested for grading in accordance with ASTM C 136, andfor specific gravity in accordance with ASTM C 128.Aggregate tests should be made for every 200 cu yd ofconcrete produced, but not less often than once every 2weeks.

7.5.4.3 Admixtures - Admixtures should meet oneof the following specifications:

ASTM C 618 for mineral admixturesASTM C 260 for air-entraining admixturesASTM C 494 for chemical admixtures

Chemical admixture materials should be evaluated inthe laboratory or in trial batches in the field to assurecompatibility with the cement used in the concrete. If theadmixtures are to be used in architectural precast con-crete, they should be evaluated for their effect on theconcrete color and the consistency of color.

7.5.4.4 Mixing water -If the water comes from amunicipal water system, it may be used in concrete with-out further testing. If the water comes from an unqual-ified source, it should be tested for use in concrete byobtaining a chemical analysis and by making 2-in. mortarcubes as described in ASTM C 109. Baseline data shouldbe obtained using a proven water source. If the 7- and28-day compressive strengths of concrete made with theunproven water source equal 90 percent of the compan-ion control, the water is satisfactory for use in concrete.

7.5.4.5 Pigments- The pigment supplier shouldcertify that pigments or other coloring agents are resis-tant to lime and other alkalies and conform to ASTMC 979. A simple test can be made by mixing 20 parts ofcement with one part of the pigment, using sufficientwater to form a buttery paste. The samples should bekept moist and observed for several days. If considerablefading occurs, the pigments are unsuitable. Under thesetest conditions, it is possible for the test samples todevelop efflorescence. The efflorescence should beremoved with dilute muriatic (hydrochloric) acid or 5percent phosphoric acid followed by copious washingwith water before the true color can be evaluated. Ittakes time to test the durability of a color under theinfluence of light and sometimes a special artificial lightcan be used to accelerate aging. Pronounced fading of acolored mortar upon exposure to sunlight for 1 month is

evidence that the pigment is unsuitable.

7.6-Testing plastic concrete7.6.1 Consistency- The consistency of concrete

should be tested at least once per day for each mix used.A significant variation in consistency is a good indicatorof variations from batch to batch in the air content, or achange in aggregate moisture content, grading or density.Two of the more common methods for measuring con-crete consistency are the slump test and the Vebe consis-tometer.

7.6.1.1 Slump - The slump test is an easy, fairlyquick test which provides reliable information about theconsistency of concrete. ASTM C 143 provides detailedinstructions on the proper test procedure. A tolerance ofup to 1 in. above the maximum specified slump may beallowed for individual batches provided the slump vari-ation does not affect the appearance or other qualities ofthe concrete beyond the specification limits. Concrete oflower than usual slump may be used provided that it canbe properly placed and consolidated.

7.6.1.2 Consistometer - The Vebe consistometersubjects the concrete to a slump test on a vibrating table(see ACI 211.3). The measure of the concrete consistencyis the time, in seconds, required to consolidate the slumpcone mass into a 93/8 in. diameter mass. Concretes thatrequire a Vebe time of more than 61/2 seconds may bedifficult to consolidate properly with internal vibration.Concretes with Vebe times of less than 41/2 seconds haveexcellent consolidation characteristics.

7.6.2 Air content- The air content of air-entrainedconcrete should be tested at least once a day for eachmix design whenever strength test specimens are made.An air content check should also be made when any ofthe following changes occurs:

. The slump varies more than + 1 in. . Temperature of the concrete varies more than *

10 F. Finishing difficulties develop. Bleeding appears or increases. Aggregate grading changes significantly. There is a change in concrete mix design yield

7.6.3 Unit weight- Unit weight tests of backup con-crete should be carried out at least once per week foreach mix design used regularly, except for lightweightconcrete which should be tested daily. When air contenttests are made, it is usually quite easy to also determinethe plastic unit weight of the concrete.

7.6.4 Temperature- The temperature of plastic con-crete should be recorded whenever strength specimensare cast. In addition, concrete temperatures should berecorded at the start of operations each day and at fre-quent intervals in hot or cold weather. An armored ther-mometer accurate to _+ 2 F should remain in the sampleuntil the reading stabilizes.

7.7-Testing hardened concrete


7.7.1 General -Concrete mixes should meet the dura-bility specifications and achieve the compressive strengthcriteria outlined in ACI 318, Chapter 4. Generally pre-cast concrete develops strength in excess of the require-ments for in-place loads. These higher compressivestrengths allow earlier stripping for reuse of forms, moresatisfactory attainment of architectural finishes, as well ascrack resistance during handling and installation.

7.7.2 Durability -Due to the vertical orientation ofmost panels, critical saturation is seldom reached andfreeze-thaw durability has rarely been a major problem.When durability tests are deemed desirable for precastconcrete panels, the tests should follow the procedures ofASTM C 666. A minimum allowable durability factor of70 is recommended. Air entrainment is recommended forpanels subject to freeze-thaw conditions, but a specifiedfixed air content level is not recommended (see Section4.5.2).

7.7.3 Absorption - A water absorption test of theproposed facing mixes may provide an early indication ofweathering or potential staining properties of the con-crete. For the concrete strengths normally specified forarchitectural precast concrete, a reasonable water absorp-tion should not be a problem unless cement-rich or high-slump nonsuperplasticized mixes or both are used.

7.7.3.1 Procedure for absorption tests - Specimensshould be tested after the concrete is 28 days old. Thespecimens should be dried in an oven at a temperaturebetween 180 and 225 F until the loss in weight in 24hours is less than 0.1 percent. Test samples should beallowed to cool to room temperature, weighed, and thensubmerged in water to one-half the specimen height.After 24 hours they should be submerged in water untilthe water is flush with the specimen top. The watershould in both cases be maintained between 65 and 75 F.After another 24 hours, the specimens should be re-moved, the surface water wiped off with a damp cloth,and specimens weighed on a scale which has a resolutionof 0.1 gram. The percentage absorption is the differencebetween wet weight and oven-dry weight, divided by thedry weight and multiplied by 100. This value may betransformed to volume percentage based on the unitweight of the concrete tested. The maximum water ab-sorption for normal weight concrete face mixes shouldnot exceed about 14 percent by volume.

The specimens should be clean and free of partingagent, form release agent or sealer. Care should be takennot to mix any of these agents into the concrete.

7.7.4 Test specimens- Confusion and discrepanciesexist in the selection of the size and shape of test spe-cimens. Many precast plants prefer 4 x 8-in. or 6 x 12-in.cylinders. Others prefer 4-in. or 6-in. cubes for evaluatingabsorption and compressive strength. Generally thesmaller specimens-the 4 x 8-in. cylinder and the 4-mcube-are not used when the maximum size of aggregatein the concrete mix is over 1.0 in. Test specimens shouldbe consolidated, cured, and finished similarly to theproducts they represent.

7.7.5 Molds - Molds for making test specimensshould comply with applicable requirements of ASTMC 31 and C 470. Heavy gauge reusable steel molds,rather than single-use molds of paper or lightweightmetal or plastic, are preferred. Any molds that becomedistorted or do not comply with the dimensional re-quirements of the appropriate ASTM specification shouldbe discarded.

7.7.6 Compressive strength test specimens7.7.6.1 Test cylinders - Samples for strength tests

should be taken on a strictly random basis as specified byASTM C 172. If choice of times of sampling or thebatches of concrete to be sampled are selected on thebasis of appearance, convenience, or other possiblybiased criteria, statistical concepts lose their validity. Nomore than one test should be taken from a single batchand water should not be added after the sample is taken.

Four compression specimens should be made daily foreach individual concrete mix (whether facing or backupmix), or for each 40 cubic yards of any one mix wherethe daily consumption exceeds this volume. Two speci-mens should be used to determine the stripping strength,particularly if the mix is new and its history not wellknown. However, one specimen may be sufficient as pro-duction progresses. For face mixes, the specimens nor-mally required for determining stripping strength may beomitted when the air temperature is higher than 50 F.

Test specimens should be made and stored as near aspossible to the location where they will be cured inaccordance with ASTM C 31. Consolidation and finishingprocedures should closely follow ASTM C 31 and C 192requirements.

Capping procedures should be as specified in ASTMC 617 except when fast-setting high strength sulfur com-pounds, specially manufactured for capping, are used.Compression testing may be performed after the recom-mended cure time for the capping compound.

7.7.6.2 Cube test specimens - Most of the require-ments of Section 7.7.7.1 can be applied directly to cubepreparation and testing. Some slight deviations will berequired in the consolidation of the concrete as a resultof different specimen size and shape. When using cubes,it is reasonable to place the concrete in a single 4-in.layer for the 4-in. cube and two 3-in. layers for a 6-in.cube. Tamping or external vibration should be done inaccordance with the appropriate ASTM specification.Similar to the restrictions for 4-in. cylinders, internalvibration should not be used to consolidate either size ofcube.

Measured compressive strength for cubes is generallyhigher than that obtained with concrete cylinders madefrom the same concrete. Cube data correlation should bemade to standard 6 x 12 in. test cylinders if cubes are tobe consistently used as the quality control specimen. Ifno correlation is available, it is recommended that 80percent of the measured cube strength be used as an esti-mate of the strength of the same concrete when testedusing cylinders.


7.7.6.3 Curing considerations - In the manufactureof precast panels, initial curing of the concrete usuallytakes place in the forms. Test specimens should be curedwith and by the same methods as the units they representup to the time of stripping the product from the form ormold. If the precast panel is to be steam cured, the testspecimen mold should be capable of withstanding ele-vated temperature without significant distortion.

When the precast panels are removed from theirforms, the test specimens should also be removed fromtheir molds and placed in a continuous moist conditionat 73.4 & 3 F. This is the secondary stage of curing. Analternate method for secondary curing may provide thebest measure of the potential strength of a particularconcrete mix. This method calls for approximately twodays of continuous moist curing after removal of thespecimens from the molds, followed by storage at approx-imately 50 percent relative humidity until the test sampleis tested. Since this is not an ASTM designated proce-dure, it should be considered only after the engineer-architect evaluates ambient weather conditions for theproject area.

7.7.7 Tests of finished panels - When questions ariseabout adequate strength of a panel or series of panels,the quality of the actual concrete can best be establishedby core tests. Alternate methods such as rebound ham-mer, pullout tests, and penetration probe tests have beenused along with pulse velocity testing. Depending on theproblem, some equipment and procedures may be betterthan others in determining the strength of the concretein the panel.

7.7.7.1 Core tests - Acceptance tests for compres-sive strength in the past have been limited to the takingof cores. Test cores should always be prepared, condi-tioned, tested and reported in accordance with the re-quirements of ASTM C 42. The average strength of threerepresentative cores should be at least 85 percent of thespecified strength. No single core should be less than 75percent of that specified. The length-to-diameter ratio ofthe core sample should be as close to 2:l as possible.Any core showing evidence of damage before testingshould not be tested and replaced with another coresample.

The engineer-architect should select the location fordrilling cores where they will least impair the strength ofthe structure and the exposed surface finish. Cores holescan often be adequately patched without damage to theappearance or integrity of a precast panel. When pos-sible, cores should be drilled so that the core test load isapplied in the same direction as the service load. Oftentop drilling of core samples minimizes or eliminates dam-age to the panel face. Since almost all architecturalprecast panels are cast flat, top coring of the panelproduces a representative sample of concrete. Corestaken perpendicular to the face of the panel may be upto 15 percent weaker than cores taken parallel to theface of the panel.

Cores should be drilled with a diamond bit to avoid an

irregular cross section and damage from drilling. If thecore sample must be broken, wooden wedges should beused to minimize the likelihood of damage. Allow anextra 2 in. of core length at the broken end to permitsawing off ends to plane surfaces before capping.

7.7.7.2 Rebound hammer- Impact (rebound) ham-mer tests should not be used as acceptance tests forprecast panels, but they are of value for qualitativecomparisons at the plant for the same job. The reboundhammer test, conducted in accordance with ASTMC 805, can be used to locate areas of lower strengthconcrete or to track day-to-day variations in the pro-duction concrete strength.

7.7.7.3 Pullout tests- The pull-out test, asdescribed in ASTM C 900, provides a direct indication ofthe tensile strength of the in-place concrete. This testinvolves drilling into hardened concrete and installing anexpansion anchor or embedding an anchor disc duringcasting of the concrete. The expansion anchor or embed-ded anchor disc is pulled out perpendicular to the con-crete surface, bringing with it a truncated cone ofconcrete. A relationship between pullout force and com-pressive strength of the concrete can be developed for aparticular project by means of laboratory tests. Gooddata correlation between field and laboratory compres-sion tests is required for this test to give valid results.These tests are typically done on the back of the precastpanel where minimum repair is needed.

7.7.7.4 Penetration probe- The penetration probetest, conducted according to ASTM C 803, is relativelynondestructive, reasonably accurate, and economical.However, an established relationship between the com-pressive strength and probe test results must bedeveloped for each of the different concrete mixes usedin the precast panels. Once the background comparisontesting on concrete cores and cylinders has been done,the probe test can give reliable results. Since the amountof penetration is inversely proportional to the strength ofconcrete, a reading of concrete compressive strength isimmediately obtained. Each probe leaves only a smallhole which can be easily filled with an epoxy patchingcompound.

7.7.7.5 Pulse velocity- The principle of the ultra-sonic test (ASTM C 597) is that the velocity of longi-tudinal ultrasonic pulses traveling in solid concretedepends on the density and the elastic properties of theconcrete. The test is not a substitute for other methodsof evaluating compressive strength, but it is a goodmethod for detection of cracks and cavities, for examin-ation of panel damage due to frost, fire, or chemicalattack and for assessment of the relative general qualityof concrete.

The test requires access to both sides of the panel. Itsuse for approximating in-place concrete strength by non-destructive means is limited to those cases where con-crete is sufficiently strong to allow pulse transmission atvelocities greater than 11,500 ft/sec. Correlations havebeen established between pulse velocity and such proper-


ties of concrete as density, the static modulus of elasticity, and the dynamic modulus of elasticity. The measured pulse velocity is an average velocity if the facing and backup concrete are significantly different.

7.8-Documentation Record keeping is an essential part of any quality

control program. Management should establish, distri- bute, and update operational procedures for record keeping so that every person employed in the precasting operation knows what documentation is required. The documentation need not be elaborate; it may require only an outline or the completion of a simple data form. But it is an important part of implementing quality control through control of materials, control of concrete mixes, control of production, control of handling, and control of technical services.

Precasters should develop a rational system of analy- zing the production test results and keeping records onmaterials, breakage/damage, and rejection/rework. Dataconcerning inspection and test results should be recordedand reviewed particularly when evaluating new materialsand products. Record keeping must be such that thecharacteristics of all precast panels can be identified witha specific mark number that may be tied to a certainmold or form on a specific date.

CHAPTER 8-REFERENCES

8.1-Recommended references

American Concrete Institute117

211.1

211.2

211.3

212.3R222R224R224.1R

301

304R

304.2R304.3R

308309R309.2R

315

Standard Specifications for Tolerances forConcrete Construction and MaterialsStandard Practice for Selecting Proportions forNormal, Heavyweight and Mass ConcreteStandard Practice for Selecting Proportions forStructural Lightweight ConcreteStandard Practice for Selecting Proportions forNo-Slump ConcreteChemical Admixtures for ConcreteCorrosion of Metals in ConcreteControl of Cracking in Concrete StructuresCauses, Evaluation and Repair of Cracks inConcrete StructuresSpecifications for Structural Concrete forBuildingsRecommended Practice for Measuring, Mix-ing, Transporting and Placing ConcretePlacing Concrete by Pumping MethodsHigh Density Concrete: Measuring, Mixing,Transporting and PlacingStandard Practice for Curing ConcreteGuide for Consolidation of ConcreteIdentification and Control of Consolidation-Related Surface DefectsDetails and Detailing of Concrete Reinforcement

318 Building Code Requirements for ReinforcedConcrete

318R Commentary for Building Code Requirementsfor Reinforced Concrete

503R Use of Epoxy Components with Concrete503.1 Standard Specification for Bonding Hardened

Concrete, Steel, Wood, Brick and OtherMaterials to Hardened Concrete with Multi-Component Epoxy Adhesive

504R Guide to Joint Sealants for Concrete Struc-tures

517.2R Accelerated Curing of Concrete at Atmos-pheric Pressure-State of the Art

546R Guide for Repairing Concrete Bridge Super-structures

551R Tilt-Up Concrete Structures

American Society for Testing and MaterialsA 36A 108

A 128

Specification for Structural SteelSpecification for Steel Bars, Carbon, Cold-Finished, Standard QualitySpecification for Steel Castings, AustenticManganese

A 153

A 185

Specification for Zinc Coating (Hot-Dip) onIron and Steel HardwareSpecification for Steel Welded Wire, Fabric,Plain, for Concrete ReinforcementSpecification for Stainless and Heat-ResistingSteel Bars and Shapes

A 276

A 307

A 325

A 416

A 421

A 490

A 496

A 497

A 516

A 582

A 615

A 616

A 617

A 706

A 722

Specification for Carbon Steel Bolts and Studs,60,000 psi TensileSpecification for High-Strength Bolts forStructural Steel JointsSpecification for Uncoated Seven-Wire Stress-Relieved Steel Strand for Prestressed ConcreteSpecification for Uncoated Stress-RelievedWire for Prestressed ConcreteSpecification for Heat-Treated, Steel Structur-al Bolts, 150 ksi (1035 MPa) Tensile StrengthSpecification for Steel Wire, Deformed, forConcrete ReinforcementSpecification for Welded Deformed Steel WireFabric for Concrete ReinforcementSpecification for Pressure Vessel Plates, Car-bon Steel, for Moderate- and Lower-Temper-ature ServiceSpecification for Free-Matching Stainless andHeat-Resisting Steel Bars, Hot-Rolled orCold-FinishedSpecification for Deformed and Plain Billet-Steel Bars for Concrete ReinforcementSpecification for Rail-Steel Deformed andPlain Bars for Concrete ReinforcementSpecification for Axle-Steel Deformed andPlain Bars for Concrete ReinforcementSpecification for Low-Alloy Steel DeformedBars for Concrete ReinforcementSpecification for Uncoated High-Strength

533R-54

A 767

A 775

A 779

A 884

C 31

C 33C 42

C 94C 109

C 136

C 143

C 150C 172C185

C 227

C 260

C 289

C 330

C 331

C 403

C 470

C 494

C 597

C 617

C 618

C 641

C 666

C 803

C 805

Steel Bar for Prestressing ConcreteSpecification for Zinc-Coated (Galvanized)Bars for Concrete ReinforcementSpecification for Epoxy-Coated ReinforcingSteel BarsSpecification for Steel Strand, Seven Wire Un-coated Compacted, Stress-Relieved for Pre-stressed ConcreteSpecification for Epoxy-Coated Steel Wire andWelded Wire Fabric for ReinforcementTest Methods of Making and Curing ConcreteTest Specimens in the FieldSpecification for Concrete AggregatesMethods of Obtaining and Testing DrilledCores and Sawed Beams of ConcreteSpecification for Ready-Mixed ConcreteTest Method for Compressive Strength of Hy-draulic Cement Mortars (Using 2-in. or 50-mmCube Specimens)Test Method for Size and Bulk Density of Re-fractory Brick and Insulating FirebrickTest Method or Slump of Portland CementConcreteSpecification for Portland CementMethod of Sampling Freshly Mixed ConcreteTest Method for Air Content of HydraulicCement MortarTest Method for Potential Alkali Reactivity ofCement-AggregateCombinations(Mortar-BarMethod)Specification for Air-Entraining Admixturesfor ConcreteTest Method for Potential Reactivity of Aggre-gates (Chemical Method)Specification for Lightweight Aggregates forStructural ConcreteSpecification for Lightweight Aggregates forConcrete Masonry UnitsSpecification for Time of Setting ConcreteMixtures by Penetration ResistanceSpecification for Molds for Forming ConcreteTest Cylinders VerticallySpecification for Chemical Admixtures forConcreteTest Method for Pulse Velocity Through Con-creteStandard Practice for Capping CylindricalConcrete SpecimensSpecification for Fly Ash and Raw or CalcinedNatural Pozzolan for Use as a Mineral Admix-ture in Portland Cement ConcreteTest Method for Staining Materials in Light-weight Concrete AggregatesTest Method for Resistance of Concrete toRapid Freezing and ThawingTest Method for Penetration Resistance ofHardened ConcreteTest Method for Rebound Number of Hard-

C 900

C 962C 979

D 757E 488

ened ConcreteTest Method for Pullout Strength of HardenedConcreteGuide for Use of Elastomeric Joint SealantsSpecification for Pigments for Integrally Col-ored ConcretePractices for Sampling AggregatesTest Method for Strength of Anchors in Con-crete and Masonry Elements

American Institute of Steel ConstructionCode of Standard Practice: For Steel Building and

Bridges

American Welding SocietyAWS Dl.l Structural Welding Code - SteelAWS D1.4 Structural Welding Code - Reinforcing

Steel

Concrete Reinforcing Steel InstituteManual of Standard PracticePlacing Reinforced Bars

Precast/Prestressed Concrete InstitutePCI Design Handbook: Precast and Prestressed Con-

crete, Fourth Edition, (MNL-120)Manual for Quality Control for Plants and Production

of Architectural Precast Concrete (MNL-117)Manual for Quality Control for Plants and Production

of Precast and Prestressed Concrete Products, ThirdEdition (MNL-116)

Tolerances for Precast and Prestressed Concrete (JR-307)

Design and Typical Details of Connections for Precastand Prestressed Concrete, Second Edition, (MNL-123)

Architectural Precast Concrete, Second Edition,(MNL-122)

PCI Drafting Handbook - Precast and PrestressedConcrete, Second Edition (MNL-119)

Model Building CodesUniform Building Code

8.2-Cited references1. ACI Committee 533, “Quality Standards and Tests

for Precast Concrete Wall Panels, ACI JOURNAL, Pro-ceedings, V. 66, April 1969.

2. ACI Committee 533, “Selection and Use of Mater-ials for Precast Concrete Wall Panels,” ACI JOURNAL,

Proceedings, V. 66, Oct. 1969.3. ACI Committee 533, “Fabrication, Handling and

Erection of Precast Concrete Wall Panels,” ACIJOURNAL, Proceedings, V. 67, April 1970, p. 310-340.

4. ACI Committee 533, “Design of Precast ConcreteWall Panels,” ACI JOURNAL, Proceedings, V. 68, July1971, p. 504-513.

5. ACI Committee 533, “Symposium on Precast Con-crete Wall Panels,” ACI Special Publication SP-11,


American Concrete Institute, Detroit, Michigan, 1965,143 pp.

6. PCI Board Ad Hoc Committee for Responsibilityfor Design of Precast Concrete Structures, “Recommen-dations on Responsibility for Design and Construction ofPrecast Concrete Structures,” PCI Journal, V. 33, No. 4,Jul.-Aug. 1988, pp. 44-52.

7. Gaylord, Edwin H., Jr. and Gaylord, Charles N (editors), “Structural Engineering Handbook,” Third Edition, McGraw-Hill Publishing, 1990.

8. Pfeifer, Donald W., and Landgren, Robert, “Energy-

Efficient Accelerated Curing of Concrete for Plant-Produced Prestressed Concrete,” PCI Journal, V. 23 No.2, Mar.-Apr. 1982, pp. 94-107.

9. Greening, N.R. and Landgren, J.R., “SurfaceDiscoloration of Concrete Flatwork,” Journal of theP.C.A. Research and Development Laboratories, V. 8, No.3, Sept. 1966, pp. 34-50.

10. Gustaferro, A.H. and Abrams, M.S., “Fire Tests ofJoints between Precast Concrete Wall Panels: Effects ofVarious Joint Treatments,” PCI Journal, V., 20, No. 5,Sept./Oct. 1975.

METRIC CONVERSION

Conversion to International System of Units (SI)

To convert from to-

Lengthinch (in.)inch (in.)foot (ft)yard (yd)

millimeter (mm)meter (m)meter (m)meter (m)

Areasquare foot (sq ft)square inch (sq in.)square inch (sq in.)square yard (sq yd)

Volumecubic inch (cu in.)cubic foot (cu ft)cubic yard (cu yd)gallon (gal) Can. liquid*gallon (gal) Can. liquid*gallon (gal) U.S. liquid*gallon (gal) U.S. liquid*

Forcekipkippound (lb)pound (lb)

Pressure or Stresskips/square inch (ksi)pound/square foot (psf)pound/square inch (psi)pound/square inch (psi)pound/square foot (psf)

Masspound (avdp)ton (short, 2000 lb)ton (short, 2000 lb)graintonne

square meter (sq m) 0.09290square millimeter (sq mm) 645.2

square meter (sq m) 0.0006452square meter (sq m) 0.8361

cubic meter (cu m) 0.00001639cubic meter (cu m) 0.02832cubic meter (cu m) 0.7646

liter 4.546cubic meter (cu m) 0.004546

liter 3.785cubic meter (cu m) 0.003785

kilogram (kgf) 453.6newton (N) 4448.0

kilogram (kgf) 0.4536newton (N) 4.448

magapascal (MPa)? 6.895kilopascal (kPa)T 0.04788kilopascal (kPa)t 6.895

megapascal (MPa)? 0.006895kilogram/square meter (kgf/sq m) 4.882

kilogram (kg) 0.4536kilogram (kg) 907.2

tonne (t) 0.9072kilogram (kg) 0.00006480kilogram (kg) 1000

mu1tiply by

25.40.02540.30480.9144

Mass (weight) per Lengthkip/linear foot (klf)pound/linear foot (plf)pound/linear foot pIf)

Mass per volume (density)pound/cubic foot (pcf)pound/cubic yard (pcy)

Bending Moment or Torqueinch-pound (in.-lb)foot-pound (ft-lb)foot-kip (ft-k)

Temperaturedegree Fahrenheit (deg F)degree Fahrenheit (deg F)

OtherSection modulus (in.3)Moment of inertia (in.4)Coefficient of heat transfer

(Btu/ft2h/F)Modulus of elasticity (psi)Thermal conductivity

(But(Btu-in.ft2/h/F)Thermal expansion in./in./FArea/length (in.2/ft)

* One U.S. gallon equals 0.8321 Canadian gallont A Pascal equals one newton/square meter

ACI 533R-93 was submitted to letter ballotaccording to Institute balloting procedures.

of the committee and was approved

kilogram/meter (kg/m) 0.001488kilogram/meter (kg/m) 1.488newton/meter (N/m) 14.593

kilogram/cubic meterkilogram/cubic meter

newton-meter 0.1130newton meter 1.356newton-meter 1356

degree Celsius (C) tc=(tF-32)/1.8degree Kelvin (K) tk=(tF+459.7)/1.8

mm3

mm4

W/m2/C 5.678MPa 0.006895

(Btu-in./ft2/h/F) Wm/m2/C 0.1442mm/mm/C 1.800

mm2/m 2116.80

16.020.5933

16.387416.231

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