ACI 305R-2010 Guide to Hot Weather Concreting.pdf

1、ACI 305R-10Reported by ACI Committee 305Guide to Hot Weather ConcretingGuide to Hot Weather ConcretingFirst PrintingOctober 2010ISBN 978-0-87031-396-7American Concrete InstituteAdvancing concrete knowledgeCopyright by the American Concrete Institute, Farmington Hills, MI. All rights reserved. This m

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10、ally revised ACI Manual ofConcrete Practice (MCP).American Concrete Institute38800 Country Club DriveFarmington Hills, MI 48331U.S.A.Phone: 248-848-3700Fax: 248-848-3701www.concrete.orgACI 305R-10 supersedes ACI 305R-99 and was adopted and published October 2010.Copyright 2010, American Concrete Ins

11、titute.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 electronic ormechanical device, printed, written, or oral, or recording for sound or visual reproduc-tion or for use in any knowledge or retrieva

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13、petent to evaluate thesignificance and limitations of its content and recommendationsand who will accept responsibility for the application of thematerial it contains. The American Concrete Institute disclaimsany and all responsibility for the stated principles. The Instituteshall not be liable for

14、any loss or damage arising therefrom.Reference to this document shall not be made in contractdocuments. If items found in this document are desired by theArchitect/Engineer to be a part of the contract documents, theyshall be restated in mandatory language for incorporation bythe Architect/Engineer.

15、Guide to Hot Weather ConcretingReported by ACI Committee 305ACI 305R-10Environmental factors, such as high ambient temperature, low humidity,high wind, or both low humidity and high wind, affect concrete propertiesand the construction operations of mixing, transporting, and placing of theconcrete ma

16、terials. This guide provides measures that can be taken tominimize the undesirable effects of these environmental factors and reducethe potential for serious problems.This guide defines hot weather, discusses potential problems, and presentspractices intended to minimize them. These practices includ

17、e selectingmaterials and proportions, precooling ingredients, and batching. Othertopics discussed include length of haul, consideration of concrete temperatureas placed, facilities for handling concrete at the site, and, during the earlycuring period, placing and curing techniques, and appropriate t

18、esting andinspection procedures in hot weather conditions.The materials, processes, quality control measures, and inspectionsdescribed in this document should be tested, monitored, or performed asapplicable only by individuals holding the appropriate ACI certificationsor equivalent.Keywords: air ent

19、rainment; cooling; curing; evaporation; high tempera-ture; hot weather construction; plastic shrinkage; production methods;retempering; slump tests; water content.CONTENTSChapter 1Introduction and scope, p. 21.1Introduction1.2ScopeChapter 2Notation and definitions, p. 22.1Notation2.2DefinitionsChapt

20、er 3Potential problems and practices, p. 33.1Potential problems in hot weather3.2Potential problems related to other factors3.3Practices for hot weather concretingChapter 4Effects of hot weather on concrete properties, p. 34.1General4.2Estimating evaporation rate4.3Temperature of concrete4.4Ambient

21、conditions4.5Water4.6Cement4.7Supplementary cementitious materials4.8Chemical admixtures4.9Aggregates4.10ProportioningJames M. Aldred Darrell F. Elliot Frank A. Kozeliski Bruce G. SmithGodwin Q. Amekuedi Michael Faubel Darmawan Ludirdja Edward G. SparksPhilip Brandt Richard D. Gaynor David R. Nau Bo

22、ris Y. SteinD. Gene Daniel Antonio J. Guerra Dan Ravina Louis R. ValenzuelaKirk K. Deadrick Kenneth C. Hover Robert J. RyanJames N. Cornell IIChairG. Terry Harris, Sr.Secretary2 GUIDE TO HOT WEATHER CONCRETING (ACI 305R-10)American Concrete Institute Copyrighted Materialwww.concrete.orgChapter 5Prod

23、uction and delivery, p. 145.1General5.2Temperature control of concrete5.3Batching and mixing5.4Delivery5.5Slump adjustment5.6Properties of concrete mixtures5.7RetemperingChapter 6Placing and curing, p. 166.1General6.2Preparations for placing and curing6.3Placement and finishing6.4Curing and protecti

24、onChapter 7Testing and inspection, p. 197.1Testing7.2InspectionChapter 8References, p. 208.1Referenced standards and reports8.2Cited referencesAppendix AEstimating concrete temperature,pp. 22A.1Estimating temperature of freshly mixed concreteA.2Estimating temperature of concrete with iceAppendix BMe

25、thods for cooling fresh concrete, p. 23B.1Cooling with chilled mixing waterB.2Liquid nitrogen cooling of mixing waterB.3Cooling concrete with iceB.4Cooling mixed concrete with liquid nitrogenB.5Cooling of coarse aggregatesCHAPTER 1INTRODUCTION AND SCOPE1.1IntroductionHot weather can create problems

26、in mixing, placing, andcuring hydraulic-cement concrete that adversely affect theproperties and serviceability of the concrete. Most of theseproblems relate to the increased rate of cement hydration athigher temperature and increased evaporation rate of moisturefrom the freshly mixed concrete. The r

27、ate of cement hydrationdepends on ambient and concrete temperature, cementcomposition and fineness, amount and type of supplementarycementitious materials, and admixtures used.A maximum as-placed concrete temperature is oftenspecified in an effort to control rate of setting, strength,durability, pla

28、stic shrinkage cracking, thermal cracking, anddrying shrinkage. The placement of concrete in hot weather,however, is too complex to be dealt with by setting amaximum as-placed or as-delivered concrete temperature.Concrete durability is defined as the ability of concrete toresist weathering action, c

29、hemical attack, abrasion, or anyother process of deterioration (ACI 201.2R). Generally, ifconcrete strengths are satisfactory and curing practices aresufficient to avoid undesirable drying of surfaces, the durabilityof hot weather concrete will not differ greatly from similarconcrete placed at norma

30、l temperatures.Where an acceptable record of field tests is not available,concrete proportions can be determined by trial batches (ACI301 and 211.1). Trial batches should be made at temperaturesanticipated in the work and mixed following one of theprocedures described in Section 4.10, Proportioning.

31、 Theconcrete supplier is generally responsible for determiningconcrete proportions to produce the required quality ofconcrete unless specified otherwise.If the initial 24-hour curing is at 100F (38C), the 28-daycompressive strength of the test specimens may be 10 to 15%lower than if cured at the req

32、uired ASTM C31/C31M curingtemperature (Gaynor et al. 1985). If the cylinders areallowed to dry at early ages, strengths will be reduced evenfurther (Cebeci 1987). Therefore, proper curing of the testspecimens during hot weather is critical, and steps should betaken to ensure that the specified proce

33、dures are followed.The effects of high air temperature and low relativehumidity are more pronounced with increases in wind speed.The potential problems of hot weather concreting can occurat any time of the year, but generally occur during thesummer season. Drying conditions can occur even at loweram

34、bient temperatures, with slower set times, lower relativehumidity, and wind, all of which are conducive to higherevaporation. Precautionary measures required on a windy,sunny day will be stricter than those required on a calm,humid day, even if air temperatures are identical.1.2ScopeThis guide ident

35、ifies problems associated with hot weatherconcreting and describes practices that alleviate these potentialadverse effects. These practices include suggested preparationsand procedures for use in general types of hot weatherconstruction, such as pavements, bridges, and buildings.Temperature, volume

36、changes, and cracking problemsassociated with mass concrete are treated more thoroughly inACI 207.1R, 207.2R, and 224R.CHAPTER 2NOTATION AND DEFNITIONS2.1NotationE = evaporation rate, lb/ft2/h (kg/m2/h)ea= water vapor pressure in mmhg (psi) in the airsurrounding the concrete obtained by multiplyingt

37、he saturation vapor pressure at the temperature ofthe air surrounding the concrete by the relativehumidity of the air. Air temperature and relativehumidity are measured approximately 1.2 to 1.8 m(4 to 6 ft) above the concrete surface on thewindward side and shielded from the suns rayseo= saturation

38、water vapor pressure in mmhg (psi) inthe air immediately over the concrete surface, at theconcrete temperature. Obtain eofrom Table 4.2(a)or (b)es= saturation vapor pressure, kPa (psi)r = (relative humidity percent)/100T = temperature, C (F)Ta= air temperature, F (C)GUIDE TO HOT WEATHER CONCRETING (

39、ACI 305R-10) 3American Concrete Institute Copyrighted Materialwww.concrete.orgTc= concrete (water surface) temperature, F (C)V = average wind speed in km/h (mph), measured at0.5 m (20 in.) above the concrete surfaceW = mass of water evaporated in kg (lb) per m2(ft2) ofwater-covered surface per hour2

40、.2DefinitionsACI provides a comprehensive list of definitions throughan online resource, “ACI Concrete Terminology,” http:/terminology.concrete.org. The definition provided hereincomplements that resource.hot weatherone or a combination of the followingconditions that tends to impair the quality of

41、freshly mixedor hardened concrete by accelerating the rate of moistureloss and rate of cement hydration, or otherwise causingdetrimental results: high ambient temperature; high concretetemperature; low relative humidity; and high wind speed.CHAPTER 3POTENTIAL PROBLEMSAND PRACTICES3.1Potential proble

42、ms in hot weatherPotential problems for concrete in the freshly mixed stateinclude:Increased water demand;Increased rate of slump loss and correspondingtendency to add water at the job site;Increased rate of setting, resulting in greater difficultywith handling, compacting, and finishing, and a grea

43、terrisk of cold joints;Increased tendency for plastic shrinkage and thermalcracking; andIncreased difficulty in controlling entrained air content.Damage to concrete caused by hot weather can never befully alleviated. Potential deficiencies to concrete in thehardened state can include:Decreased stren

44、gths resulting from higher water demand;Increased tendency for drying shrinkage and differentialthermal cracking from either cooling of the overallstructure, or from temperature differentials within thecross section of the member;Decreased durability resulting from cracking; andGreater variability o

45、f surface appearance, such as coldjoints or color difference, due to different rates ofhydration or different water-cementitious materialratios (w/cm).3.2Potential problems related to other factorsOther factors that should be considered along withclimatic factors include:Cements with different and i

46、ncreased rate of hydration;High-early-compressive-strength concrete, which requireshigher cement contents;Thin concrete sections with correspondingly greaterpercentages of steel, which complicate placing andconsolidation of concrete;Economic necessity to continue work in extremely hotweather; andUse

47、 of shrinkage-compensating cement.3.3Practices for hot weather concretingGood judgment is necessary to select procedures thatappropriately blend quality, economy, and practicability.The procedures selected will depend on type of construction,characteristics of the materials being used, and the exper

48、ienceof the local industry in dealing with high ambient temperature,high concrete temperatures, low relative humidity, and highwind speed.The most serious difficulties occur when personnelplacing the concrete lack experience in constructing underhot weather conditions or in doing the particular type

49、 ofconstruction. Last-minute improvisations are rarelysuccessful. Early preventive measures should be appliedwith the emphasis on materials evaluation, advanced planningand purchasing, and coordination of all phases of work.Planning in advance for hot weather involves detailedprocedures for mixing, placing, protecting, curing, andtesting of concrete. Precautions to avoid plastic shrinkagecracking are important. The potential for thermal cracking,either from overall volume changes or from internalrestraint, should be ant