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305R-99 Hot Weather Concreting - bpesol.com

ACI 305R-99 supersedes ACI 305R-91 and became effective October 27, 1999. Copyright 2000, American concrete 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 electronic ormechanical device, printed, whitten, or oral, or recording for sound or visual repro-duction or for use in any knowledge or retrieval system or device, unless permission inwriting is obtained from the copyright proprietors. ACI Committee Reports, Guides, Standard Practices, andCommentaries are intended for guidance in planning, design-ing, executing, and inspecting construction. This documentis intended for the use of individuals who are competentto evaluate the significance and limitations of its contentand recommendations and who will accept responsibilityfor the application of the material it contains.

curing hydraulic cement concrete. These problems can adversely affect the properties and serviceability of the con-crete. Most of these problems relate to the increased rate of cement hydration at higher temperature and increased evap-oration rate of moisture from the freshly mixed concrete. The

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Transcription of 305R-99 Hot Weather Concreting - bpesol.com

1 ACI 305R-99 supersedes ACI 305R-91 and became effective October 27, 1999. Copyright 2000, American concrete 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 electronic ormechanical device, printed, whitten, or oral, or recording for sound or visual repro-duction or for use in any knowledge or retrieval system or device, unless permission inwriting is obtained from the copyright proprietors. ACI Committee Reports, Guides, Standard Practices, andCommentaries are intended for guidance in planning, design-ing, executing, and inspecting construction. This documentis intended for the use of individuals who are competentto evaluate the significance and limitations of its contentand recommendations and who will accept responsibilityfor the application of the material it contains.

2 The AmericanConcrete Institute disclaims any and all responsibility for thestated principles. The Institute shall not be liable for any lossor damage arising to this document shall not be made in contractdocuments. If items found in this document are desired bythe Architect/Engineer to be a part of the contract documents,they shall be restated in mandatory language for incorporationby the Architect/Engineer. 305R-1 Hot Weather ConcretingACI 305R-99 concrete mixed, transported, and placed under conditions of high ambienttemperature, low humidity, solar radiation, or wind, requires an under-standing of the effects these environmental factors have on concrete prop-erties and construction operations. Measures can be taken to eliminate orminimize undesirable effects of these environmental factors.

3 Experience inhot Weather with the types of construction involved will reduce the poten-tial for serious problems. This committee report defines hot Weather , lists possible potential prob-lems, and presents practices intended to minimize them. Among these prac-tices are such important measures as selecting materials and proportions,precooling ingredients, special batching, length of haul, consideration ofconcrete temperature as placed, facilities for handling concrete at the site,and during the early curing period, placing, and curing techniques, andappropriate testing and inspecting procedures in hot Weather conditions. Aselected bibliography is revisions involve an editorial revision of the document. The revi-sions focus in particular on the effects of hot Weather on concrete properties,and the use of midrange water-reducing admixtures and extended set-con-trol admixtures in hot : air entrainment; cooling; curing ; evaporation; high tempera-ture; hot Weather construction; plastic shrinkage; production methods;retempering; slump tests; water 1 Introduction, p.

4 Definition of hot Potential problems in hot Potential problems related to other Practices for hot Weather concretingChapter 2 Effects of hot Weather on concrete properties, p. Temperature of Ambient Water Effect of Supplementary cementitious Chemical ProportioningChapter 3 Production and delivery, p. Temperature control of Batching and mixingReported by ACI Committee 305 Robert J. RyanChairmanKenneth B. RearSecretaryMuwafaq A. Abu-ZaidD. Gene DanielAlexander LeschinskyBijan AhmadiRichard D. GaynorWilliam C. MooreJ. Howard AllredJohn G. GendrichDan RavinaZawde BerhaneG. Terry Harris, M. ScanlonKarl P. BrandtBarry L. HousealVictor H. SmithTerence M. BrowneFrank A. KozeliskiGeorge V. TeodoruJoseph G. CabreraMark E. LeemanHabib M. Zein Al-AbidienJames N.

5 Cornell, II 305R-2 ACI COMMITTEE Slump Properties of concrete RetemperingChapter 4 Placing and curing , p. Preparations for placing and Placement and curing and protectionChapter 5 Testing and inspection, p. InspectionChapter 6 References, p. Referenced standards and Cited referencesAppendix A Estimating concrete temperature, p. 305R-19 Appendix B Methods for cooling fresh concrete , p. 305R-19 CHAPTER 1 GeneralHot Weather may create problems in mixing, placing, andcuring hydraulic cement concrete . These problems canadversely affect the properties and serviceability of the con- crete . Most of these problems relate to the increased rate ofcement hydration at higher temperature and increased evap-oration rate of moisture from the freshly mixed concrete .

6 Therate of cement hydration is dependent on concrete tempera-ture, cement composition and fineness, and admixtures report will identify problems created by hot weatherconcreting and describe practices that will alleviate thesepotential adverse effects. These practices include suggestedpreparations and procedures for use in general types of hotweather construction, such as pavements, bridges, and build-ings. Temperature, volume changes, and cracking problemsassociated with mass concrete are treated more thoroughly inACI and ACI maximum as placed concrete temperature is oftenused in an effort to control strength, durability, plastic-shrinkage cracking, thermal cracking, and drying placement of concrete in hot Weather , however, is toocomplex to be dealt with by setting a maximum as placed or as delivered concrete temperature.

7 concrete durabilityis a general term that is difficult to quantify, but it is per-ceived to mean resistance of the concrete to weathering ( ). Generally, if concrete strengths are satisfactory andcuring practices are sufficient to avoid undesirable drying ofsurfaces, durability of hot Weather concrete will not differgreatly from similar concrete placed at normal presence of a desirable air-void system is needed if theconcrete is going to be exposed to freezing an acceptable record of field tests is not available, con- crete proportions may be determined by trial batches (ACI301 and ACI ). Trial batches should be made at temper-atures anticipated in the work and mixed following one of theprocedures described in Section , Proportioning. The con- crete supplier and contractor are generally responsible fordetermining concrete proportions to produce the requiredquality of concrete unless specified to ASTM C 31/C 31M, concrete test specimensmade in the field that are used for checking adequacy of lab-oratory mixture proportions for strength or as a basis foracceptance or quality control should be cured initially at60 to 80 F (16 to 27 C).

8 If the initial 24 h curing is at 100 F(38 C), the 28-day compressive strength of the test speci-mens may be 10 to 15% lower than if cured at the requiredASTM C 31/C 31M curing temperature (Gaynor et al 1985).If the cylinders are allowed to dry at early ages, strengths willbe reduced even further (Cebeci 1987). Therefore, properfabrication, curing , and testing of the test specimens duringhot Weather is critical, and steps should be taken to ensurethat the specified procedures are followed. Definition of hot For the purpose of this report, hot Weather is anycombination of the following conditions that tends to impairthe quality of freshly mixed or hardened concrete by acceler-ating the rate of moisture loss and rate of cement hydration,or otherwise causing detrimental results: High ambient temperature; High concrete temperature; Low relative humidity; Wind speed; and Solar The effects of high air temperature, solar radiation,and low relative humidity may be more pronounced with in-creases in wind speed (Fig.)

9 The potential problems ofhot Weather Concreting may occur at any time of the year inwarm tropical or arid climates, and generally occur duringthe summer season in other climates. Early cracking due tothermal shrinkage is generally more severe in the spring andfall. This is because the temperature differential for each 24 hperiod is greater during these times of the year. Precautionarymeasures required on a windy, sunny day will be more strictthan those required on a calm, humid day, even if air temper-atures are Potential problems in hot Potential problems for concrete in the freshly mixedstate are likely to include: Increased water demand; Increased rate of slump loss and corresponding ten-dency to add water at the job site; Increased rate of setting, resulting in greater difficultywith handling, compacting, and finishing, and a greaterrisk of cold joints; Increased tendency for plastic-shrinkage cracking.

10 And Increased difficulty in controlling entrained air Potential deficiencies to concrete in the hardenedstate may include: Decreased 28-day and later strengths resulting from 305R-3 HOT Weather Concreting either higher water demand, higher concrete tempera-ture, or both at time of placement or during the firstseveral days; Increased tendency for drying shrinkage and differen-tial thermal cracking from either cooling of the overallstructure, or from temperature differentials within thecross section of the member; Decreased durability resulting from cracking; Greater variability of surface appearance, such as coldjoints or color difference, due to different rates ofhydration or different water-cementitious material ratios(w/cm); Increased potential for reinforcing steel corrosion making possible the ingress of corrosive solutions; and Increased permeability as a result of high water con-tent, inadequate curing , carbonation, lightweight aggre-gates, or improper matrix-aggregate Potential problems related to other factorsOther factors that should be considered along with climat-ic factors may include: Use of cements with increased rate of hydration; Use of high-compressive-strength concrete , whichrequires higher cement contents.


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