1、523.2R-1This guide presents information on materials, fabrication, properties,design, and handling of precast concrete floor, roof, and wall units havingoven-dry unit weights of 50 pcf (800 kg/m3) or less. The concrete achievesthe low density through the use of gas-releasing agents or the mechanical
2、incorporation of air.Keywords: cellular concretes; concrete construction; concrete slabs; deflection;floors, lightweight concretes; precast concrete; prefabrication; roofs; structuraldesign; thermal conductivity; walls.CONTENTSChapter 1General, p 523.2R-21.1Objective1.2Scope1.3Definition of cellular
3、 concreteChapter 2Materials, p. 523.2R-22.1Aggregate2.2Hydraulic cement2.3Lime2.4Mixing water2.5Reinforcement2.6AdmixturesChapter 3Concrete properties, p. 523.2R-23.1Compressive strength3.2Drying shrinkage3.3Thermal insulation valuesChapter 4Design, p. 523.2R-34.1Structural analysis4.2Notation4.3All
4、owable design stresses in concrete and reinforcement4.4Deflection4.5Concrete protection for reinforcement4.6Modulus of elasticity4.7Bearing4.8Interaction between units4.9Anchorage4.10Holes and openingsChapter 5Manufacturing, p. 523.2R-45.1Curing5.2Workmanship5.3Dimensional tolerances5.4Identificatio
5、n and markingChapter 6Tests, p. 523.2R-46.1Tests of an individual flexural unit6.2Quality control, sampling and acceptance testingACI 523.2R-96Guide for Precast Cellular ConcreteFloor, Roof, and Wall UnitsReported by ACI Committee 523Fouad H. FouadChairmanLeo A. LegatskiSecretaryTheodore W. Bremner
6、Albert LitvinPhilip M. Carkner William R. MacDonaldHubert T. Dudley Henry N. MarshWerner H. Gumpertz Jan R. PrusinskiMichael Healy Leo R. RivkindGeorge C. Hoff Rudolph C. ValoreGordon D. LerchACI Committee Reports, Guides, Standard Practices, and Com-mentaries are intended for guidance in designing,
7、 planning, ex-ecuting, or inspecting construction and in preparing speci-fications. Reference to these documents shall not be made in theProject Documents. If items found in these documents are de-sired to be part of the Project Documents, they should bephrased in mandatory language and incorporated
8、 in the ProjectDocuments.ACI 523.2R-96 supercedes ACI 523.2R-68(82)(87) and became effective May 24,1996.Copyright 1997, American Concrete Institute.All rights reserved including rights of reproduction and use in any form or by anymeans, including the making of copies by any photo process, or by ele
9、ctronic or mechan-ical device, printed, written, or oral, or recording for sound or visual reproduction or foruse in any knowledge or retrieval system or device, unless permission in writing isobtained from the copyright proprietors.523.2R-2 ACI COMMITTEE REPORTChapter 7Handling, p. 523.2R-5Chapter
10、8Fire resistance, p. 523.2R-5Chapter 9 References, p. 523.2R-59.1Specified references9.2Cited referencesCHAPTER 1GENERAL1.1ObjectiveThe primary objective of this guide is to outline practicesfor design and fabrication of precast reinforced cellular con-crete (50 pcf 800 kg/m3 and under) floor, roof,
11、 and wallunits that will result in structural members of adequate loadcapacity, durability, appearance, and overall serviceabilityfor the function intended. Units covered by this Guide shouldbe protected from exposure to weather.1.2ScopeThe recommendations of this Guide apply to precast rein-forced
12、cellular concrete units, which are designed and factory-produced for use in structures. These recommendations arebased largely on the experience gained with a large variety ofunits in service. The report does not cover job site fabrication.1.3Definition of cellular concreteThis Guide includes precas
13、t concretes having oven-dryunit weights, as measured by ASTM C 495, of 50 pcf (800kg/m3) or less. The material, which is commonly referred toas cellular or aerated concrete, may be defined as:A lightweight product consisting of portland cementand/or lime with siliceous fine material, such as sand, s
14、lag,or fly ash, mixed with water to form a paste that has a homo-geneous void or cell structure. The cellular structure is at-tained essentially by the inclusion of macroscopic voidsresulting from a gas-releasing chemical reaction or the me-chanical incorporation of air or other gases (autoclave cur
15、ingis usually employed).CHAPTER 2MATERIALS2.1SandSands conforming to ASTM Specifications C 33 and C144 are acceptable.2.2Fly ashFly ash should conform to ASTM C 618.2.3Hydraulic cementsCement should conform to ASTM Specifications C 150 orC 595.2.4LimeLime should conform to ASTM C 911.2.5Foaming agen
16、tsCellular concrete foaming agents shall conform to ASTMC 796 and C 869.2.6Mixing waterMixing water for concrete should be clean and free frominjurious amounts of oils, acids, alkalies, salts, organic mat-ter, or other potentially deleterious substances.2.7AdmixturesAir-entraining, accelerating, ret
17、arding, water-reducing, orpozzolanic admixtures may be used, if desired, provided thatthey conform to ACI 318. Information on such materials isavailable in ACI Report 212.3R.Calcium chloride and accelerators containing chloridesalts should not be used when steel reinforcement or uncoat-ed aluminum m
18、embers are embedded in or in contact withthe concrete.2.8Reinforcement2.8.1Reinforcement should be weldable steel conform-ing to ASTM Specifications A 615, A 82, or A 185. Electri-cal resistance spot welding is usually employed to fabricatethe reinforcing steel cage or mesh. All welding should con-f
19、orm to AWS D12.1.2.8.2Reinforcement in cellular concrete units should beprotected by a corrosion-inhibiting coating such as a latex-modified portland cement slurry or hot dipped zinc coating.CHAPTER 3CONCRETE PROPERTIES3.1Compressive strengthLow-density concrete used in precast reinforced cellularco
20、ncrete floor, roof, and wall units should have a minimumcompressive strength of 300 psi (2.07 MPa). The compressivestrength of these units should be determined by ASTM C 495,ASTM C 513, or ASTM C 796, whichever is applicable.3.2Drying shrinkageThe potential drying shrinkage of cellular concretesshou
21、ld be determined on three specimens, in accordancewith ASTM C 426 or ASTM C 341. The average dryingshrinkage should not be in excess of 0.20 percent. The testshould be conducted employing either a test specimen cutfrom a manufactured unit that is unreinforced or at least hasno steel reinforcement in
22、 the longitudinal direction or mold-ed from the same batch of concrete from which the units aremade. The specimens should be 2 in. x 2 in. (50 mm) in crosssection and of sufficient length to provide the 10 in. (254mm) gage length required. Specimens should be conditionedby immersion in water at 73 2
23、 F (23 1.1 C) for 48 hr.Length measurements should commence immediately uponremoval from the water3.3Thermal insulation valuesThe thermal conductivity of cellular concrete should bemeasured by means of the Guarded Hot Plate (ASTM C 177)or the Heat Flow Meter (ASTM C 518). When test data for aspecifi
24、c concrete are not available, Table 3.3 may be used asa general guide.PRECAST CELLULAR CONCRETE 523.2R-3CHAPTER 4DESIGN4.1Structural analysisThe design of the concrete units covered by this Guideshould be made with reference to permissible stresses, ser-vice loads, and the accepted linear elastic th
25、eory of design.4.2NotationEc = static modulus of elasticity of concreteEs = modulus of elasticity of steel = 29,000,000 psi(200 GPa)fc = allowable compressive stressfc = compressive strength of concrete specimen at 28days unless otherwise specifiedh = vertical distance between lateral wall supportsI
26、 = moment of inertiaL = span length of slab or beamn = Es/Ect = thickness of unitvs = allowable shear stressw = total load per unit length of beam or per unit areaof slabD = deflection4.3Allowable design stresses in concrete andreinforcement4.3.1For steel reinforcement, the design allowablestresses
27、should not exceed one-half of the specified yieldstrength, with a maximum of 24,000 psi (165 MPa).4.3.2The design allowable stresses in the concreteshould conform to the requirements Appendix A of ACI 318,except as noted belowa.Unreinforced web shear stress vcpermitted should notexceed 0.03 fc.b.Wal
28、lsAllowable compressive stress in concrete forprecast cellular concrete load-bearing walls should not ex-ceed the followingfc= 0.2fc1(h/40t)3Non-load-bearing partitions or curtain walls should belimited to an h/t ratio of not greater than 48, with the maxi-mum height and length of the wall not excee
29、ding 20 and 40feet respectively.4.4DeflectionPrecast reinforced cellular concrete units used as floors androofs shall not exceed either of two deflection limitations:I. The maximum deflection requirements of the LocalBuilding Code, andII. The maximum deflection requirements recommendedby Table 9.5(b
30、) of ACI 318.In no case should the span-depth ratio exceed 30, norshould the thickness be less than 2 in. (50 mm). For this pur-pose the thickness of a topping should not be included incomputing the depth.4.5Concrete protection for reinforcementDue to the high porosity of cellular concretes, the rei
31、nforc-ing bars must receive a rust-resistant coating before casting.The minimum clear cover should be1/2in. (12 mm), com-posed of cellular concrete and any coating that has been ap-plied to the steel reinforcement. The protective cover for firehazard should be at least that necessary to comply with
32、localbuilding codes or other applicable codes.4.6Modulus of elasticityThe modulus of elasticity should be determined in accor-dance with ASTM C 469, except that the specimens may berectangular prisms, and only the results of the first cycle ofloading should be utilized. Strains may be measured by us
33、eof electrical resistance strain gages, mechanical strain mea-suring devices, or dial gages attached to a suitable frame.Maximum strains should not exceed 0.001.It is possible to determine Ecand n by direct measurementof deflection of production members, in accordance withASTM E 72. Using the deflec
34、tion formula = 5wL4/384EcIa value for EcI can be calculated. By trial and error calcula-tions for I of the uncracked transformed section, using as-sumed values of n, a value for Eccan be calculated. Correctvalues of Ecand n are obtained when the relationship Es/Ecis equal to the assumed value for n.
35、Table 3.3 Thermal conductivity of various low-density concretesOven-dry unit weightThermal conductivity (k factor)*Oven dry Air drypcfkg/m3k W/mK k W/mK20 320 0.60 0.09 0.83 0.1230 480 0.83 0.12 1.10 0.1640 640 1.10 0.16 1.40 0.2050 800 1.40 0.20 1.80 0.26*Representative values for oven dry and air
36、dry materials. These values should not vary more than 5 percent. They areintended as design (not specification) values for materials in normal use. For the conductivity of a specific concrete,the user may obtain the value supplied by the producer or secure the results of test. “k” is in units Btu in
37、./hr ft2F (SIequivalent is in W/mK).523.2R-4 ACI COMMITTEE REPORT4.7BearingThe allowable bearing unit stresses should be as providedfor in Appendix A of ACI 318.4.8Interaction between unitsThe concrete roof and floor units should be detailed andconstructed to provide interaction with adjacent units,
38、 thuspermitting the transfer of loads without differential displace-ment. Interaction between adjacent roof units may be omit-ted provided that the maximum difference in deflectionbetween units is not greater than1/8in. (3.2 mm) under anycondition of load for which the units are designed. Where aflo
39、or system that provides interaction between units, sup-ports partition walls parallel to the unit, or will be subjectedto heavy concentrated loads, such loads may be consideredto be uniformly distributed over not more than two identicalunits on each side thereof, but not over a greater total widthth
40、an 0.4 of the clear span distance.4.9Anchorage4.9.1 Cross rodsAll tensile steel reinforcement should beanchored by a minimum of two cross rods welded in accor-dance with AWS D12.1 and located within 8 in. (200 mm)from each end and spaced at least 3 in. (75 mm) apart. Addi-tional cross rods should be
41、 spaced at intervals not exceeding40 in. (1 m). For compressive steel reinforcement, at least onecross rod should be placed 4 in. (100 mm) from each end. Ad-ditional cross rods should be spaced at intervals not exceeding40 in. (1 m). The area of the cross rods should be no less thanone third the are
42、a of the longitudinal steel reinforcement.4.9.2 Weld shear strengthA weld in shear should devel-op a minimum of one-half the specified yield strength of thelongitudinal steel times its cross-sectional area.4.10Holes and openingsHoles may be drilled or cut providing the steel reinforce-ment area in a
43、 unit is not reduced in excess of 30 percent.Slabs immediately adjacent to the cut slab should be made toact monolithically with the cut slab, either by keying, weld-ing, doweling, or other mechanical means. Engineering cal-culations should be provided for cut slabs.CHAPTER 5MANUFACTURING5.1CuringAf
44、ter molding, the units are normally cured by high-pres-sure steam curing (autoclaving) or by atmospheric steamcuring. However, other processes may be used that preventthe loss of water during curing, and that result in the attain-ment of all minimum values of mechanical properties recom-mended in th
45、is guide.5.2WorkmanshipThe mix, gradation of the aggregate, and workability shouldbe such as to insure complete filling of the form and intimatebond between the concrete and all steel reinforcement. Thefinished product should have a uniformly textured surface,and be essentially free of flaws and cra
46、cks that would detractfrom its appearance and structural performance.5.3Dimensional tolerancesDimensional tolerances should be as listed for precast con-crete in ACI 117.5.4Identification and markingAll units should bear a permanent identifying symbol aswell as a mark indicating the top of the unit
47、and its orientation.The identifying symbol should be the same one used for theunit in the manufacturers literature. It should be shown in atable on the erection drawings, together with the length, type,and size of unit, and the amount, size, and arrangement of allreinforcement. The tabulated informa
48、tion should be completeenough to permit the calculation of the load capacity of theunit.CHAPTER 6TESTS6.1Tests of an individual flexural unitWhen an individual unit designed by the working stressmethod is to be tested as a simple span beam, the zero pointfor deflection measurements should be under t
49、he total deadload to be carried. The maximum 24 hr midspan deflectiondue to a test load of twice the service live load (with mini-mum test loads of 80 and 60 psf 3.8 and 2.9 kPa for floorsand roofs respectively) should not exceed1/160of the span.The residual deflection immediately after removing the testload should not exceed1/400of the span. Such units shouldthen be tested to complete failure. The test load at failureshould be not less than two times the sum of dead and servicelive loads, nor le
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