305r_91

ACI 305R-91

Hot Weather Concreting

Habib M. Zein Al-AbidienJ. Howard AllredRobert BouclinCelso A. CarbonellRobert J. FerrellRobert P. FurickRichard D. GaynorJohn Gendrich

Reported by ACI Committee 305

George R.U. Burg, ChairmanK. Fred GibbeG. Terry HarrisGeorge W. HollonRoy H. KeckFrank KozeliskiDonald B. McCaulleyMartin B. MittelacherWilliam C. MoorePaul E. Mueller

When concrete is mixed, transported, and placed under conditions ofhigh ambient temperature, low humidity, solar radiation, or wind, anunderstanding of the effects these environmental factors have on concrete properties and construction operations is required. Oncethese factors are understood, measures can be taken to eliminate orminimize undesirable effects. The most serious difficulties are expe-rienced in weather and types of construction that are unusual in theexperience of those performing the work.

on concrete

This committee report defines hot weather, lists possible potentialproblems, and presents practices intended to minimize them. Amongthese practices are such important measures as selecting materials andproportions; precooling ingredients; consideration of concrete tem-perature as placed; length of haul; facilities for handling concrete atthe site and during the early curing period; special batching, placing,and curing techniques; and appropriate testing and inspecting proce-dures in hot weather conditions. A selected bibliography is included.

Keywords: admixtures; air entrainment; concrete construction; cooling; curing;evaporation; finishes; heat pump systems; high temperature; hot weather con-struction; humidity; ice; inspection; liquid nitrogen; mixing; placing; pozzo-lans; production methods; retardants; retempering; setting (hardening); slumptests; solar radiation; strength; temperature; water content; water-reducingagents; wind velocity.

CONTENTSChapter 1-Introduction

1.1-General1.2-Definition of hot weather

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 be madein the Project Documents. If items found in these documentsare desired to be part of the project documents, they shouldbe phrased in mandatory language and incorporated into theproject documents.

Leo P. NicholsonPatrick W. Reardon, Jr.John M. Scanlon, Jr.Robert T. StackGeorge V. TeodoruLewis H. TuthillLouis R. ValenzuelaWilliam F. Wescott

1.3-Potential problems in hot weather1.4-Potential problems related to other factors1.5-Practices for hot weather concreting

Chapter 2-Effects of hot weatherproperties

2.1-General2.2-Temperature of concrete2.3-Ambient conditions2.4-Water requirement2.5-Effect of cement2.6-Supplementary cementitious materials2.7-Chemical admixtures2.8-Aggregates2.9-Proportioning

Chapter 3-Production and deliver3.1-General3.2-Temperature control of concrete3.3-Batching and mixing3.4-Delivery3.5-Slump adjustment3.6-Retempering

Acknowledgment: ACI Committee 305 expresses its gratitude and apprecia-tion to the following contributors to this report. The list comprises the Associ-ate Members who gave selflessly of their time, talents, and energy: Zwade Ber-hane, Omer Z. Cebeci, Ignacio Martin, and Dan Ravina.

These revisions involve an extensive reorganization and expansion of thedocument. The revisions focus in particular on the means of controlling tem-perature, such as the use of ice, liquid nitrogen, and other admixtures.

ACI 305R-91 replaces ACI 305R-89 effective Nov. 1, 1991.Copyright © 1991, American Concrete Institute.All rights reserved including rights of reproduction and use in any form or

by any means, including the making of copies by any photographic process, orby any electronic or mechanical device, printed, written, or oral, or recordingfor sound or visual reproduction or for use in any knowledge or retrieval sys-tem or device, unless permission in writing is obtained from the copyright pro-prietors.

305R-1

305R-2

Chapter 4-Placing and curing4.l-General4.2-Preparations for placing and curing4.3-Placement and finishing4.4-Curing and protection

Chapter 5-Testing and inspection5.1-Testing5.2-Inspection

Chapter 6-References6.1-Specified references6.2-Recommended references

MANUAL OF CONCRETE PRACTICE

Appendix A-Estimating concrete temperature

Appendix B-Methods for cooling concrete

CHAPTER 1-INTRODUCTION1.1-General

Hot weather may lead to problems in mixing, plac-ing, and curing hydraulic cement concrete that can ad-versely affect the properties and serviceability of theconcrete. Most of these problems relate to the in-creased rate of cement hydration at higher temperatureand the increased evaporation rate of moisture from thefreshly mixed concrete. The rate of cement hydration isdependent upon concrete temperature, cement compo-sition and fineness, and admixtures used.

The objectives of this report are to identify the prob-lems caused by hot weather concreting and to describepractices that will alleviate adverse effects likely to beexperienced in the absence of such practices.

This report suggests preparations and procedures toreduce the undesirable effects of hot weather concret-ing in general types of construction, such as pave-ments, bridges, and buildings. Temperature, volumechanges, and cracking problems associated with massconcretes are treated more thoroughly in ACI 207.1Rand ACI 224R.

Often specifiers establish a maximum “as placed”concrete temperature in an attempt to control strength,durability, plastic shrinkage cracking, thermal crack-ing, and drying shrinkage. However, the placement ofconcrete in hot weather is too complex to be dealt withby merely setting a simple maximum temperature, “asplaced” or “as delivered.” Concrete durability is ageneral term that is difficult to quantify, but it is per-ceived to mean resistance of the concrete to weathering(ACI 201.2R). Generally, if concrete strengths are sat-isfactory and curing practices are sufficient to avoidundesirable drying of surfaces, durability of hotweather concrete should not be greatly different fromsimilar concrete placed at normal temperature, assum-ing the presence of a desirable air-void system if it isgoing to be exposed to cycles of freezing and thawing.

If an acceptable record of field tests is not available,concrete proportions may be determined by trialbatches (ACI 301 and ACI 211.1). Trial batches shouldbe made at temperatures anticipated in the work andmixed following one of the procedures described inSection 2.9, Proportioning. The concrete supplier and

contractor are generally responsible for determiningconcrete proportions to produce the required quality ofconcrete unless specifically specified otherwise.

Concrete test specimens used for checking adequacyof laboratory mixture proportions for strength or as abasis for acceptance or quality control are cured ini-tially at 60 to 80 F (16 to 27 C), ASTM C 31. If the in-itial 24-hr curing is at 100 F (38 C), the 28-day com-pressive strength of the test specimens may be 10 to 15percent lower than if cured at the required ASTM C 31curing temperature (Gaynor, Meininger, and Khan1985). If the cylinders are allowed to dry at early ages,strengths will be reduced even further (Cebeci 1987).The making, curing, and testing of the concrete speci-mens using the correct procedures all play an impor-tant part in the orderly progress of the work.

1.2-Definition of hot weather1.2.1 For the purpose of this report, hot weather is

any combination of the following conditions that tendto impair the quality of freshly mixed or hardened con-crete by accelerating the rate of moisture loss and rateof cement hydration, or otherwise resulting in detri-mental results:

a. High ambient temperature.b. High concrete temperature.c. Low relative humidity.d. Wind velocity.e. Solar radiation.1.2.2 The effects of high air temperature, solar radi-

ation, and low relative humidity may be more pro-nounced with increases in wind velocity (see later, Fig.2.1.5). The potential problems of hot weather concret-ing may occur at any time of the year in warm tropicalor arid climates, and generally occur during the sum-mer season in other climates. Cracking due to thermalshrinkage is generally more severe in the spring andfall. This is because the temperature differential foreach 24-hr period is greater during these times of theyear. Precautionary measures required on a calm, hu-mid day will be less strict than those required on a dry,windy, sunny day, even if air temperatures are identi-cal.

1.3-Potential problems in hot weather1.3.1 Potential problems for concrete in the freshly

mixed state are likely to include:a. Increased water demand.b. Increased rate of slump loss and corresponding

tendency to add water at the jobsite.c. Increased rate of setting, resulting in greater diffi-

culty with handling, compacting, finishing, and agreater risk of cold joints.

d. Increased tendency for plastic shrinkage cracking.e. Increased difficulty in controlling entrained air

content.1.3.2 Potential problems for concrete in the hard-

ened state may include:a. Decreased 28-day and later strengths resulting

HOT WEATHER CONCRETING 305R-3

from either higher water demand and/or higher con-crete temperature levels at time of placement or duringthe first several days.

b. Increased tendency for drying shrinkage and dif-ferential thermal cracking from either cooling of theoverall structure or from temperature differentialswithin the cross section of the member.

c. Decreased durability resulting from cracking.d. Greater variability of surface appearance such as:

cold joints, color difference, due to different rates ofhydration on different water-cement ratios.

e. Increased potential for reinforcing steel corrosion.This is primarily due to increased cracking, whichmakes possible the ingress of corrosive solutions.

f. Increased permeability.

1.4-Potential problems related to other factorsOther factors that should be considered along with

climatic factors may include:a. The use of cements with increased rate of hydra-

tion.b. The use of high compressive strength concretes,

which require higher cement contents.c. The design of thin concrete sections with corre-

spondingly greater percentages of steel, which compli-cate placing and consolidation of concrete.

d. The economic necessity to continue work in ex-tremely hot weather.

e. The use of shrinkage-compensating cement.

1.5-Practices for hot weather concretingIt is important to recognize that any damage to con-

crete caused by hot weather can never be fully allevi-ated. Therefore, good judgment is necessary to selectthe most appropriate compromise of quality, economy,and practicability. The procedures used will depend on:the type of construction; the characteristics of the ma-terials to be used; and the experience of the local in-dustry handling high ambient temperature, high con-crete temperatures, low relative humidity; wind veloc-ity; and solar radiation.

The most serious difficulties occur when the person-nel placing the concrete lack experience in constructingunder hot weather conditions or in doing the particulartype of construction. Since last-minute improvisationsare rarely successful, early preventive measures shouldbe applied with the emphasis on materials evaluation,advanced planning and purchasing, and coordinationof all phases of work. Detailed procedures of mixing,placing, protection, curing, temperature monitoring,and testing of concrete during hot weather should beplanned prior to beginning hot weather concreting.Precautions should be taken to avoid plastic shrinkagecracking. The potential for thermal cracking, eitherfrom overall volume changes or from internal restraint,should be anticipated. Some of the items that should beconsidered to control cracking are: joint practices, useof increased amounts of reinforcing steel or fibers, lim-its on concrete temperature, cement content, heat ofhydration of the cement, form-stripping time, and se-

lection and dosage rate of chemical and mineral admix-tures.

The following list of practices and measures to re-duce or avoid the potential problems of hot weatherconcreting are discussed in detail in Chapters 2, 3, and4:

a. Use concrete materials and proportions with satis-factory records in field use under hot weather condi-tions.

b. Use cool concrete.c. Use a concrete consistency that permits rapid

placement and effective consolidation.d. Transport, place, consolidate, and finish the con-

crete with least delay.e. Plan the job to avoid adverse exposure of the con-

crete to the environment; schedule placing operationsduring times of the day or night when weather condi-tions are favorable.

f. Protect the concrete against moisture loss at alltimes during placing and during its curing period.

CHAPTER 2-EFFECTS OF HOT WEATHER ONCONCRETE PROPERTIES

2.1-General2.1.1 Those properties of concrete that make it an

excellent construction material can be affected adverselyby hot weather, as defined in Chapter 1. However,harmful effects may be minimized by control proce-dures outlined in this report. Strength, impermeability,dimensional stability, and resistance of the concrete toweathering, wear, and chemical attack all depend onthe following factors: selection and proper control ofmaterials and mixture proportioning, initial concretetemperatures, wind velocity, solar radiation, ambienttemperatures, and humidity conditions during placingand curing periods.

2.1.2 Concretes mixed, placed, and cured at elevatedtemperatures normally develop higher early strengthsthan concretes produced and cured at lower tempera-tures, but strengths are generally lower at 28 days andlater ages. Fig. 2.1.2 shows that l-day strength in-creases, and 28-day strength decreases, with increasingcuring temperature (Klieger 1958; Verbeck and Hel-muth 1968).

2.1.3 Laboratory tests have demonstrated the ad-verse effects of high temperatures and lack of curing onconcrete strength (Bloem 1954). Specimens molded andcured in air at 73 F (23 C), 60 percent relative humid-ity; and at 100 F (38 C), 25 percent relative humidity,produced strengths of only 73 and 62 percent, respec-tively, of that obtained for standard specimens moist-cured at 73 F (23 C) for 28 days. It was also found thatthe longer the delay between casting the cylinders andplacing into standard moist storage, the greater thestrength reduction. The data illustrate that inadequatecuring in combination with high placement tempera-tures impairs the hydration process and reducesstrength. The tests were made on plain concrete with-out admixtures or pozzolans that might have improvedits performance at elevated temperatures. Other re-

305R-4 MANUAL OF CONCRETE PRACTICE

Fig. 2.1.2-Effects of curing temperature on compres-sive strength of concrete (Verbeck and Helmuth 1968)

searchers determined that insufficient curing is moredetrimental than high temperatures (Cebeci 1986), andalso that required strength levels can be maintainedwhen set-retarding admixtures or other admixtures orpozzolans are used in the concrete (Mittelacher 1985;Gaynor, Meininger, and Khan 1985).

2.1.4 Plastic-shrinkage cracking is frequently associ-ated with hot weather concreting in arid climates. Itoccurs in exposed concrete, primarily in flatwork, butalso in beams and footings, and may develop in otherclimates whenever the evaporation rate is greater thanthe rate at which water rises to the surface of recentlyplaced concrete by bleeding. A method to determineevaporation rate is given in the section on testing. Highconcrete temperatures, high air temperature, high windvelocity, and low humidity, alone or in combination,cause rapid evaporation of surface water and signifi-cantly increase the probability of plastic-shrinkagecracking. In laboratory research, soon after placement(between 0 and 4 hr), and under the same ambient con-ditions, the highest rate of evaporation occurred inconcrete prepared with the lowest water content. How-ever, the total amount of water evaporated at the endof the 24 hr was always highest in mixtures having thehighest water content (Berhane 1984).

2.1.5 Plastic-shrinkage cracking is seldom a problemin hot humid climates where relative humidity is rarelyless than 80 percent. Table 2.1.5 shows, for various rel-ative humidities, the concrete temperatures that mayresult in critical evaporation rate levels and, thus, causeplastic-shrinkage cracking. The table is based on theassumption of a 10 mph (16 km/hr) wind speed and adifference in air and concrete temperature of 10 F (5.6C). The use of Fig. 2.1.5 allows evaporation rate esti-

Table 2.1.5-Typical concrete temperatures forvarious relative humidities potentially critical toplastic shrinkage cracking

Concrete temperature, Relative humidity,F (C) percent

105 (40.6) 90100 (37.8) 8095 (35.0)

85 (29.4)60

80 (26.7)5040

75 (23.9) 30

mates based on all the major factors that contribute toplastic-shrinkage cracking. The graphic method of thechart also yields ready information on the effect ofchanges in one or more of these factors. For example,it shows that concrete at a temperature of 70 F (21 C),placed at an air temperature of 70 F (21 C), with a rel-ative humidity of 50 percent and a moderate wind of 10mph (16 km/hr), will have six times the evaporationrate of the same concrete placed when there is no wind.

2.1.6 When evaporation rate is expected to approach0.2 lb/ft/hr (1.0 kg/m/hr), precautions should betaken, as explained in detail in Chapter 4. The proba-bility for plastic-shrinkage cracks to occur may be in-creased if the time of setting of the concrete is delayeddue to-the use of: slow-setting cement, an excessivedosage of retarding admixture, fly ash as a cement re-placement, or cooled concrete. Fly ash is also likely toreduce bleeding and may thereby contribute to a crack-ing tendency (ACI 226.3R). Plastic-shrinkage cracks aredifficult to close once they have occurred (see Section4.3.5).

2.1.7 The following statements summarize typical ef-fects of weather conditions on concrete during and af-ter finishing:

a. If air temperature and humidity remain the sameand the wind speed increases from 5 to 20 mph (8 to 32km/h), evaporation rate will increase by 300 percent.

b. If humidity and wind remain the same and the airtemperature changes from 60 to 90 F (16 to 32 C),evaporation rate will increase by 300 percent.

c. If air temperature and wind remain the same andthe humidity decreases from 90 to 70 percent, evapo-ration rate will increase by 300 percent.

d. If the wind speed increases from 5 to 20 mph (8 to32 km/h), if air temperature rises from 60 to 90 F (16to 32 C), and humidity decreases from 90 to 70 per-cent, the evaporation rate will increase by 900 percent.

2.2-Temperature of concrete2.2.1 Unless measures are taken to control concrete

performance at elevated temperatures, through selec-tion of suitable materials and proportions as outlined inSections 2.3 through 2.9, increases in concrete temper-ature will have the following adverse effects. Others arelisted in Section 1.3.

a. The amount of the water required to produce agiven slump increases with the time since the cementwas wetted. For constant mixing time, the amount ofwater required to produce a given slump also increases


Fig. 2.1.5-Effect of concrete and air temperatures, relative humidity, and windvelocity on the rate of evaporation of surface moisture from concrete. This chartprovides a graphic method of estimating the loss of surface moisture for variousweather conditions. To use the chart, follow the four stepsrate of evaporation approaches 0.2 lb/ft2/hr (1kg/m2

outlined above. If the/hr), precautions against

plastic shrinkage cracking are necessary (Lerch 1957)

with the temperature, as shown in Fig. 2.2.1(a) and2.2.1(b).

b. This increased water content will cause a propor-tionate decrease in strength and durability, and an in-crease in drying shrinkage.

c. Slump loss will be evident earlier after mixing andat a more rapid rate, and may make handling and plac-ing operations more difficult.

d. In an arid climate, there will be a greater proba-bility of the appearance of plastic-shrinkage cracks.

e. In sections of large dimensions, there will be anincreased rate of hydration and heat evolution that will

increase differences in temperature between the interiorand the exterior concrete. This may cause thermalcracking (ACI 207.1R).

f. Early curing will be increasingly critical and thelack of it increasingly detrimental.

2.3-Ambient conditions2.3.1 In the more general types of construction in hot

weather (as defined in Section 1.2), it is impractical torecommend a maximum limiting ambient or concretetemperature because circumstances vary widely. A limitthat would serve a specific case might be unsatisfactory


Fig. 2.2.1(a)-Effect of concrete temperature on slumpand on water required to change slump (average datafor Type I and II cements) (Klieger 1958)

in others. Accordingly, the committee can only pointout the effects of higher temperatures in concrete asmentioned in Sections 1.3 and 2.2.1, and advise that atsome temperature between about 75 and 100 F (24 and38 C), there is a limit that will be found to be most fa-vorable for best results in each hot weather operation,and such a limit should be determined for the work.Trial batches of concrete for the job should be made atthe limiting temperature selected, or at the expectedjobsite high temperature, not at the 68 to 86 F (20 to 30C) range given in ASTM C 192. Procedures involvingtesting of concrete batches at higher temperatures thanabout 70 F (21 C) may be found in Section 2.9.

2.4-Water requirement2.4.1 Water, as an ingredient of concrete, greatly in-

fluences many of its significant properties, both in thefreshly mixed and hardened state. High water temper-atures cause higher concrete temperatures, and as theconcrete temperature increases, more water is needed toobtain the same slump. Fig. 2.2.1(b) illustrates the pos-sible effect of concrete temperature on water require-ments. The extra water increases the water-cement orwater-cementitious material ratio and accordingly willdecrease the strength, durability, watertightness, andother related properties of the concrete. While perti-nent to concrete placed under all conditions, this pointsto the special need to control the use of additional wa-ter in concrete placed under hot weather conditions; seeSection 2.7.

2.4.2 Fig. 2.2.1(a) illustrates the general effects ofincreasing concrete temperature on slump of concretewhen the amount of mixing water is held constant. Itindicates that an increase of 20 F (11 C) in temperaturemay be expected to decrease the slump by about 1 in.(25 mm). Fig. 2.2.1(a) also illustrates changes in waterrequirement that may be necessary to produce a l-in.

Fig. 2.2.1(b)-Effect of temperature increase on thewater requirement of concrete (U.S. Bureau of Recla-mation 1975)

(25-mm) increase in slump at various temperature lev-els. For 70 F (21 C) concrete, about 21/2 percent morewater is required to increase slump 1 in.; for 120 F (50C) concrete, 41/2 percent more water is needed for the 1in. slump increase. The water required to change slumpmay be less if a water-reducing or high-range, water-re-ducing admixture is used (Yamamoto and Kobayashi1986).

2.4.3 Increased drying shrinkage results from greaterwater demand of the concrete. At the higher shrinkagerates, concrete becomes more susceptible to cracking.Its cracking tendency will become more severe if it un-dergoes rapid cooling from high temperatures at whichit has hardened.

2.4.4 Since water has a specific heat of about four tofive times that of cement or aggregates, the tempera-ture of the mixing water has the greatest effect per unitweight on the temperature of concrete. The tempera-ture of water is easier to control than that of the othercomponents. Even though water is used in smallerquantities than the other ingredients, cooled water willreduce the concrete placing temperature, but usually bynot more than about 8 F (4.5 C) (see Fig. 2.4.4). Thequantity of cooled water should not exceed the batchwater requirement, which will depend on the mixtureproportions and the moisture content of aggregates. Ingeneral, lowering the temperature of the batch water by3.5 to 4 F (2.0 to 2.2 C) will reduce the concrete tem-perature approximately 1 F (0.5 C). Efforts shouldtherefore be made to obtain cold water. To keep itcold, tanks, pipes, or trucks used for storing or trans-porting water should be insulated or painted white orboth. Water can be cooled to as low as 33 F (1 C) usingwater chillers, ice, heat pump technology, or liquid ni-trogen. These methods and their effectiveness are ex-plained in Appendix B.

2.4.5 Using ice as part of the mixing water has re-mained a major means of reducing concrete tempera-ture. On melting alone it will absorb heat at the rate of144 Btu/lb (335 J/g). To be most effective, the crushed,shaved, or chipped ice should be placed directly into the


Applicable to "average” mixes made with typical natural aggregates. Applicable to “average” mixes made with typical natural aggregates.Quantity of cooled water cannot exceed mixing water requirement, Quantity of cooled water cannot exceed mixing water requirement,which will depend upon moisture content of aggregate and mix proportions which will depend upon moisture content of aggregate and mix proportions

mixer as part of the added-mixing water. For maxi- slump. Unless offset by measures described in Sectionsmum effectiveness, the ice should not be allowed tomelt before it is placed in the mixer in contact with theother ingredients, but it must melt completely prior tothe completion of mixing of the concrete. For a morerapid blending of materials at the beginning of mixing,not all of the available batch water should be added inthe form of ice. Its quantity may have to be limited toabout 75 percent of the batch water requirement, whichdepends on mixture proportions and moisture contentof the aggregates. Where maximum amounts of ice orcold mixing water are required, aggregates should bewell drained to minimize free moisture. Fig. 2.4.5 illus-trates possible reductions in concrete temperature bysubstituting varying amounts of ice at 32 F (0 C) formixing water at the temperatures shown. Mixing shouldbe continued until the ice is completely melted. Crushedice should be stored at a temperature that will preventlumps from forming by refreezing of particles.

2.4.6 The rate of temperature reduction can also beestimated by using Eq. (4) or (5) in Appendix A. Formost concrete, the maximum temperature reductionwith ice is about 20 F (11 C). When greater tempera-ture reductions are required, cooling by injection ofliquid nitrogen (LIN) into the mixer holding mixedconcrete may be found to be the most expedient means.See Appendix B, Methods of Cooling Concrete, formore information. LIN does not affect the mixing wa-ter requirement, except by reducing concrete tempera-ture.

2.5-Effect of cement2.5.1 High concrete temperature increases the rate at

which cement hydrates (see later Fig. 3.2.2; ACI207.2R). As a result, concrete stiffens more rapidly andrequires more water to produce or maintain the desired

2.6.1 and 2.7, the higher water content will causestrength loss and increase the cracking tendency of theconcrete.

2.5.2 Selection of a particular cement may have a de-cided effect on the hot weather performance of con-crete, as illustrated in Fig. 2.5.2. Although the curvesare based on limited data from mixtures using differentcements in combination with a set-retarding admixture,they show, for example, that when tested at 100 F (38C), the concrete with the slowest setting cement reachestime of final setting 21/2 hr later than the concrete withthe fastest setting cement. The concrete which setsslowest at 100 F (38 C) was the fastest-setting cementwhen tested at 50 F (10 C). The figure is a good exam-ple of the difficulty of predicting performance of con-crete at different temperatures. In general, use of anormally slower setting Type II portland cement(ASTM C 150) or Type IP or IS blended cement(ASTM C 595) may improve the handling characteris-tics of concrete in hot weather (ACI 225R). Concretecontaining the slower setting cements may be morelikely to exhibit plastic-shrinkage cracking.

2.5.3 When using slower hydrating cements, theslower rate of heat development and the simultaneousdissipation of heat from the concrete result in lowerpeak temperatures. There will be less thermal expan-sion, and the risk of thermal cracking upon cooling ofthe concrete will be reduced. This is an important con-sideration for slabs, walls, and mass concretes, as dis-cussed in ACI 207.1R and ACI 207.2R. The tempera-ture increase from hydration of cement in a given con-crete mixture is proportional to its cement content.Therefore, only enough cement should be used to pro-vide the required strength and durability, and not more.Concretes which obtain high strength at an early age


Fig. 2.5.2-Effect of temperature and brand of cement on hardening characteris-tics of concrete mortars (Tuthill and Cordon 1955)

will develop high concrete temperature during initialcuring. These concretes should be given thermal pro-tection so that it will cool gradually at a rate which willnot cause them to crack.

2.5.4 Cement may be delivered at relatively hightemperatures. This is not unusual for newly manufac-tured cement which has not had an opportunity to coolafter burning or grinding of the component materials.Although only 10 to 15 percent of the weight of a con-crete mixture is cement, this is sufficient to increaseconcrete temperature about 1 F (0.5 C) for each 8 F (4C) increase in cement temperature. Therefore, it is pru-dent to place a maximum limit of about 170 F (77 C)on the temperature of cement as it enters the concrete.The particular limit will depend on the use of the con-crete. If the cement has a false set tendency, slump lossis likely to be aggravated, particularly in hot weather.

2.6-Supplementary cementitious materials2.6.1 Materials in this category include primarily fly

ash and other pozzolans (ASTM C 618), and groundgranulated blast-furnace slag (ASTM C 989). They arewidely used as partial replacements for portland ce-ment; they may impart a slower rate of setting and ofearly strength gain to the concrete, both of which aredesirable in hot weather concreting, as explained inSection 2.5.2. Faster setting cements or cements caus-ing a rapid slump loss in hot weather may perform sat-isfactorily in combination with these materials (Gay-nor, Meininger, and Khan 1985). The use of fly ashmay reduce the rate of slump loss of concrete under hotweather conditions (Ravina 1984; Gaynor, Meininger,and Khan 1985).

2.7-Chemical admixtures2.7.1 Various types of chemical admixtures (ASTM

C 494) have been found beneficial in offsetting some ofthe undesirable characteristics of concrete placed dur-ing periods of high ambient temperatures (see also ACI

212.3R). The benefits may include lower mixing waterdemand, extended periods of use, and strengths com-parable to, or higher than, those of plain concreteplaced at lower temperatures. Their effectiveness de-pends upon the chemical reactions of the cement withwhich they are used in the concrete. Admixtures with-out a history of satisfactory performance at the ex-pected hot weather conditions should be evaluated be-fore their use, as explained in Section 2.7.5. Chemicaladmixtures affect the properties of concrete as de-scribed in the following.

2.7.2 Retarding admixtures meeting ASTM C 494,Type D, requirements have both water-reducing andset-retarding properties and are widely used under hotweather conditions. They can be included in concrete invarying proportions and in combination with other ad-mixtures so that, as temperature increases, higher dos-ages of the admixture may be used to obtain a uniformtime of setting. Their water-reducing properties largelyoffset the higher water demand resulting from in-creases in concrete temperature. Since water-reducingretarders generally increase concrete strength, they canbe used, with proper mixture adjustments, to avoidstrength losses that would otherwise result from highconcrete temperatures (Gaynor, Meininger, and Khan1985; Mittelacher 1985). Compared to concrete withoutadmixture, a concrete mixture that uses a water-reduc-ing and retarding admixture may have a higher rate ofslump loss. Nevertheless, it will generally be found that,after the initial slump is increased to compensate forslump loss, the net water reduction and other benefitsare still substantial.

2.7.3 Admixtures of the hydroxylated carboxylic acidtype (ACI 212.3R, Class 3) and some types meetingASTM C 494, Type D requirements may increase theearly bleeding and rate of bleeding of concrete. Thisadmixture-induced early bleeding may be helpful inpreventing drying of the surface of concrete placed athigh ambient temperature and low humidity. However,


if the admixture reduces the tensile strength and tensilestrain capacity, plastic-shrinkage tendencies may be in-creased (Ravina and Shalon 1968b). Other admixtures(ACI 212.3R, Classes 1 and 2) may reduce bleedingrate; if drying conditions are such that crusting of thesurface blocks bleed water from reaching the surface,continued bleeding may cause scaling. Under such con-ditions, fog sprays, evaporation retardants (a materialthat retards the evaporation of bleeding water of con-crete), or both should be used to prevent crusting.Concrete that is prone to bleeding generally should bereconsolidated after most of the bleeding has takenplace. Otherwise, differential settling may occur thatcan lead to cracks over reinforcing steel and other in-serts in near-surface locations. This cracking is morelikely in cool weather with slower setting concretes thanhot weather.

2.7.4 Some high-range, water-reducing and retardingadmixtures (ASTM C 494, Type G) and plasticizing andretarding admixtures (ASTM C 1017, Type 2), oftenreferred to as superplasticizers, can provide significantbenefits under hot weather conditions when used toproduce flowing concrete. At higher slumps, heat gainfrom internal friction during mixing of the concrete willbe less (see ASTM STP 169A and ACI 207.4R). Theimproved handling characteristics of flowing concretepermit more rapid placement and consolidation, andthe period between mixing and placing can thus be re-duced. The rate of slump loss of flowing concrete mayalso be less at higher temperatures than in concrete us-ing conventional retarders (Yamamoto and Kobayashi1986). Concrete strengths are generally found to besubstantially higher than those of comparable concretewithout admixture and with the same cement content.Certain products may cause significant bleeding, whichmay be beneficial in many instances but may requiresome precautions in others (see Section 2.7.3). Air-con-tent tests will be needed before placement to assuremaintenance of proper air content. Assurance may alsobe needed that the air-void system is not impaired, ifrequired for freeze-thaw resistance of the concrete.Some high-range water-reducing retarders can maintainthe necessary slump for extended periods at elevatedconcrete temperatures (Collepardi, Corradi, and Val-ente 1979; Hampton 1981; Guennewig 1988). These willbe of particular benefit in the event of delayed place-ments or deliveries over greater distances. Other high-range water-reducing admixtures may greatly accelerateslump loss, particularly when initial slumps are lessthan 3 to 4 in. Some water-reducing admixtures cancause the concrete to extend its working time by a cou-ple of hours, followed by acceleration of strength gain.

2.7.5 The qualifying requirements of ASTM C 494afford a valuable screening procedure for the selectionof admixture products. Admixtures without a perform-ance history pertaining to the concrete material selectedfor the work should be first evaluated in laboratorytrial batches at the expected high job temperature, us-ing one of the procedures described in Section 2.9.Some high-range, water-reducing retarders may not

demonstrate their potential benefits when used in smalllaboratory batches. Further testing may then be re-quired in production-size concrete batches. During pre-liminary field use, concrete containing admixtureshould be evaluated for consistency of performance inregard to the desired characteristics in hot weather con-struction. When evaluating admixtures, properties suchas workability, pumpability, early strength develop-ment, placing and finishing characteristics, appear-ance, and effect on reuse of molds and forms should beconsidered in addition to the basic properties of slumpretention, setting time, and strength. These character-istics may influence selection of an admixture and itsdosage more than properties usually covered by mostspecifications.

2.8-Aggregates2.8.1 Aggregates are the major constituent of con-

crete, since they account for 60 to 80 percent of thevolume of normal weight concrete used in most struc-tures. Therefore, the properties of the aggregate signif-icantly affect the quality of concrete. The size, shape,and grading of the aggregate are three of the principalfactors that affect the amount of water required toproduce concrete at a given slump. Aggregate proper-ties desirable in hot weather concreting include the fol-lowing:

a. Gradation, particle shape, and the absence of un-dersized material are very important in minimizing wa-ter demand (ACI 221R). Crushed coarse aggregate alsocontributes to higher water demand, but is reported toprovide better resistance to cracking than roundedgravels (ACI 224R).

b. Favorable thermal properties. A low coefficient ofthermal expansion of an aggregate causes less expan-sion of concrete in a hot environment, less shrinkageupon subsequent cooling, and thus a lower risk of ther-mal cracking. Materials having a high rate of thermaldiffusivity dissipate internal heat of hydration of theconcrete more rapidly and help minimize peak temper-atures and thermal expansion. Thermal characteristicsof different aggregate minerals are discussed in ACI207.1R, 207.2R, 207.4R, and Ravina and Shalon(1968a).

2.8.2 Since in most concrete mixtures the coarse ag-gregate represents the ingredient of largest mass,changes in its temperature have a considerable effect onconcrete temperatures. For example, a moderate 1.5 to2 F (0.8 to 1.1 C) temperature reduction will lower theconcrete temperature 1 F (0.5 C). Under given condi-tions and temperature requirements, cooling the coarseaggregate may be an effective supplementary means toachieve desired lower temperature levels of the concrete(see Appendix B).

2.9-Proportioning2.9.1 Mix proportions may be established or ad-

justed on the basis of field-performance records in ac-cordance with ACI 318, provided the records indicate


the effect of expected seasonal temperatures and deliv-ery times.

2.9.2 Selection of ingredients and their proportionsshould be guided by their contribution to satisfactoryperformance of the concrete under hot weather condi-tions (ACI 211.1 and 211.2). Cement content should bekept as low as possible but sufficient to meet strengthand durability requirements. Inclusion of supplemen-tary cementitious materials, such as fly ash or slag,should be considered to delay setting and to mitigatethe temperature rise from heat of hydration. Use ofwater-reducing and retarding admixtures or high-range,water-reducing and retarding admixtures can offset in-creased water demand and strength loss which mightotherwise be caused by higher concrete temperatures.High-range, water-reducing retarders formulated forextended slump retention should be considered if longerdelivery periods are anticipated. From economicallyavailable aggregates, those selected should result inlower water demand during mixing, and impart favor-able thermal properties to the concrete. Unless requiredotherwise, concrete should be proportioned for a slumpof not less than 3 in. (75 mm) to permit prompt place-ment and effective consolidation in the form.

2.9.3 The performance of the concrete mixtures pro-posed for the work should be verified under conditionsapproximating the delivery time and hot weather envi-ronment expected at the project. Trial batches used toselect proportions are normally prepared in accordancewith ASTM C 192. The method requires concrete ma-terials to be at room temperature [in the range of 68 to86 F (20 to 30 C)]. However, trial batches should alsobe performed at the expected maximum placing tem-perature with consideration of using a mixing and agi-tating period longer than that required in ASTM C 192to help define the performance to be expected.

2.9.4 In determining mix proportions using labora-tory trial batches, a procedure for estimating the slumploss during the period between first mixing of the con-crete and its placement in the form is suggested in Pro-cedures A and B, following, adopted from ACI 223 onshrinkage-compensating concrete. These methods werefound to produce a rate of slump loss similar to thatexpected for a 30 to 40 min delivery time.

Procedure A1. Prepare the batch using ASTM C 192 procedures,

but add 10 percent additional water over that normallyrequired.

2. Mix initially in accordance with ASTM C 192 (3-min mix followed by a 3-min rest and 2-min remix).

3. Determine the slump and record as initial slump.4. Continue mixing for 15 min.5. Determine the slump and record as estimated

placement slump. Experience has shown this slumpcorrelates with that expected for 30 to 40 min deliverytime. If this slump does not meet the specification lim-its, either discard and repeat the procedure with an ap-propriate water adjustment or add water to give the re-quired slump and then test the concrete.

6. Determine other properties of fresh concrete (tem-perature, air content, unit weight), and mold strengthtest specimens.

Procedure B1. Prepare the batch using ASTM C 192 procedures

for the specified slump.2. Mix in accordance with ASTM C 192 (3-min mix,

3-min rest, and 2-min remix) and confirm the slump.3. Stop the mixer and cover the batch with wet bur-

lap.4. After 20 min, remix 2 min, adding water to pro-

duce the specified slump. The total water (initial waterplus the remix water) can be expected to equal that re-quired at the batch plant to give the required jobsiteslump.

5. Determine other properties of fresh concrete (tem-perature, air content, unit weight), and mold strengthtest specimens.

2.9.5 As an alternative method, use of full-size pro-duction batches may be considered for verification ofmixture proportions, provided the expected high tem-perature levels of the concrete can be attained. Thismay be the preferred method when using admixturesselected for extended slump retention. It requires care-ful recording of batch quantities at the plant and ofwater added for slump adjustment before sampling.Sampling procedures of ASTM C 172 should be strictlyobserved.

CHAPTER 3-PRODUCTION AND DELIVERY3.1-General

It is important that production facilities and proce-dures are capable of providing the required quality ofconcrete under hot weather conditions at productionrates required by the project. Satisfactory control ofproduction and delivery operations should be assured.Concrete plant and delivery units should be in goodoperating condition. Intermittent stoppage of deliveriesdue to equipment breakdown can be much more seri-ous under hot weather conditions than in moderateweather. In hot weather concreting operations, con-crete placements may be scheduled at times other thanduring daylight hours. Night-time production requiresextra vigilance from plant personnel for quality controland safe operations.

3.2-Temperature control of concrete3.2.1 Concrete can be produced in hot weather with-

out maximum limits on placing temperature and willperform satisfactorily if proper precautions are ob-served in proportioning, production, delivery, placing,and curing. As part of these precautions, an effortshould be made to keep the concrete temperature as lowas practical. Using the relationships given in AppendixA, it can be shown, for example, that the temperatureof concrete of usual proportions can be reduced by 1 F(0.5 C) if any of the following reductions are made inmaterial temperatures:


Fig. 3.2.2-Influence of temperature of concrete ingredients on concrete tempera-ture. Calculated from equations in Appendix A

a. 8 F (4 C) reduction in cement temperature.b. 4 F (2 C) reduction in water temperature.c. 2 F (1 C) reduction in the temperature of the ag-

gregates.3.2.2 Fig. 3.2.2 shows the influence of concrete in-

gredients on concrete temperature. Since the greatestportion of concrete is aggregate, reduction of aggregatetemperature brings about the greatest reduction in con-crete temperature. Thus, all practical means should beemployed to keep the aggregates as cool as possible.Shaded storage of fine and coarse aggregates, andsprinkling and fog spraying of coarse aggregates stock-piles under arid conditions will help. Sprinkling ofcoarse aggregates can reduce aggregate temperature byevaporation and direct cooling (Lee 1987). However,wetting of aggregates tends to cause variations in sur-face moisture and thereby complicates slump control.Above-ground storage tanks for mixing water should beprovided with shade and thermal insulation. Silos andbins will absorb less heat if coated with heat-reflectivepaints. Painting mixer surfaces white to minimize solarheat gain will be of some help. Based on 1 hr deliverytime on a hot, sunny day, concrete in a clean whitedrum should be 2 to 3 F (1 to 1.5 C) cooler than in ablack or red drum and 0.5 F (0.3 C) cooler than in acream-colored drum. If an empty drum stands in thesun for an extended period before concrete is batched,

the heat stored in the metal drum would produce con-crete temperatures 0.5 to 1 F (0.3 to 0.5 C) lower for awhite drum than a yellow or red drum. Spraying thedrum with water before batching or during delivery hasbeen suggested as a means of minimizing concrete tem-perature, but it can be expected to be of only marginalbenefit.

3.2.3 Setting up the means for cooling sizeableamounts of concrete production requires planning wellin advance of placement and installation of specializedequipment. This can include chilling of batch water bywater chillers or heat pump technology as well as othermethods, such as substituting crushed or flaked ice forpart of the mixing water, or cooling by liquid nitrogen.Delivery of the required volume of cooling materialsshould be assured for each placement. Details of esti-mating concrete temperatures are provided in Appen-dix A. Various cooling methods are described in Ap-pendix B. The general influence of the temperature ofconcrete ingredients on concrete temperature is calcu-lated from the equations in Appendix A, and shown inFig. 3.2.2.

3.3-Batching and mixing3.3.1 Batching and mixing is described in Chapters 4

and 5 of ACI 304R. Procedures under hot weatherconditions are no different from good practices under


normal weather conditions. However, particular atten-tion should be given to producing concrete for correctslump and other specified properties to avoid its rejec-tion for noncompliance with applicable specifications.The interruption in the placement caused by rejectionmay cause the formation of a cold joint or seriousproblems in finishing. Testing of concrete must be dili-gent and accurate so that results represent the true con-dition of the concrete.

3.3.2 For truck-mixed concrete, initial mixing at thebatch plant will allow a general verification of the con-dition of the concrete, primarily its slump, before itleaves the plant. Generally, centrally mixed concretecan be visually inspected as it is being discharged intothe transportation unit. Slump can easily change due tominor changes in materials and concrete characteris-tics. For example, an undetected change of only 0.5percent moisture content of the aggregates couldchange slump by 1 to 2 in. Control is also complicatedby the limited accuracy even of advanced systems ofaggregate moisture determination due to an error rangeof about 0.5 percent. For this reason, operators oftenbatch concrete in a drier condition to avoid producinga slump higher than specified; a small water additionmay be needed at the jobsite.

3.3.3 Hot weather conditions and extended haulingtime may indicate a need to split the batching processby batching the cement at the jobsite, or layering thematerials in the mixer drum at the plant to keep someof the cement dry and then mixing the concrete afterarrival at the jobsite. These methods may, on occasion,offer the best solution under existing conditions. How-ever, a better controlled concrete can usually be pro-vided when materials are batched at the regular plantfacility. By using some effective retarding admixtures atappropriate dosages, preferably in combination withcementitious material of slow-setting characteristics,concrete can be maintained in a placeable condition forextended periods even in hot weather (see Section 2.7).Field experience indicates that concrete set retardationcan be extended further by separately batching the re-tarding admixture with a small portion of mixing wa-ter, 1 to 2 gal/yd (5 to 10 l/m ), after the concrete hasbeen mixed for several minutes. These admixtures, to-gether with the cementitious materials and other ingre-dients proposed for the project, should be evaluated inthe field for desired properties.

3.3.4 Under hot weather conditions, the amount ofmixing at mixing speed of the mixer should be held toa minimum to avoid any unnecessary heat gain of theconcrete (ACI 207.4R). For efficient mixing, mixersshould be free of buildup of hardened concrete and ex-cessive wear of mixer blades. As soon as the concretehas been mixed to a homogeneous condition, all fur-ther drum rotation should be at the lowest agitatingspeed of the unit, or a speed recommended by themixer, or by the admixture manufacturer if an admix-ture is used. Usually the drum should not be stoppedfor extended periods because of the possible problemsif the concrete stiffens rapidly or sets in the drum.

3.3.5 Specifications governing the total number ofrevolutions of the drum usually set a limit of 300 revo-lutions for truck mixers. This limit may be waived un-der the following conditions requiring further thoroughmixing of the concrete: separate addition of high-range,water-reducing admixtures, or direct injection of liquidnitrogen into the mixer as a means of lowering the con-crete temperature, or if the concrete retains its worka-bility without the addition of water.

3.4-DeliveryCement hydration, temperature rise, slump loss, ag-

gregate grinding, and either loss or, occasionally, gainof air content all occur with the passage of time; thusthe period between mixing and placement of the con-crete should be minimized. The dispatching of trucksshould be coordinated with the rate of placement toavoid delays in arrival or waiting periods until dis-charge. On major concrete placements, provisionsshould be made to have good communications betweenthe jobsite and concrete-production facility. Majorplacements should be scheduled during periods of lowerurban traffic loads. When placement is slow, consider-ation should be given to reducing load size, using set-retarding admixture, or using cooled concrete.

3.5-Slump adjustmentFresh concrete is subject to slump loss with time,

whether it is used in moderate or hot weather. Withgiven materials and mix proportions, the slump changecharacteristics between plant and jobsite should be es-tablished. With the limitations on accurately predictingslump, as explained in Section 3.3.2, uncertainty intraffic, and the timing of placing operations, operatorsneed to batch concrete in a drier condition to avoid aslump higher than specified. If on arrival at the jobsitethe slump is less than the specified maximum, addi-tional water may be added if the maximum allowablewater content is not exceeded. When water is added tobring the slump within required limits, the drum orblades must be turned an additional 30 revolutions ormore, if necessary, at mixing speed. For expeditiousplacement and effective consolidation, structural con-crete should have a slump of 3 or 4 in. Slump increasesshould be allowed when chemical admixtures are used,providing the admixture-treated concrete has the sameor lower water-cement or water-cementitious materialratio and does not exhibit segregation potential.

3.6-RetemperingRetempering is defined as “additions of water and

remixing of concrete, or mortar which has lost enoughworkability to become unplaceable or unsaleable” (ACI116). Laboratory research, as well as field experience,shows that strength reduction and other detrimental ef-fects are proportional to the amount of retemperingwater added. Therefore, water additions in excess ofthe proportioned maximum water content or water-ce-mentitious material ratio to compensate for loss ofworkability should be prohibited. Adding chemical ad-


mixtures, particularly high-range, water-reducing ad-mixtures, may be very effective to maintain workabil-ity.

CHAPTER 4-PLACING AND CURING4.1-General

4.1.1 In many respects the requirements for good re-sults in hot weather concrete placing and curing are nodifferent than in other seasons. The same necessitiesexist:

a. That concrete be handled and transported with aminimum of segregation and slump loss.

b. That concrete be placed where it is to remain.c. That the concrete be placed in layers shallow

enough to assure vibration well into the layer below andthat the elapsed time between layers be minimized toavoid cold joints.

d. That joints be made on sound, clean concrete.e. That finishing operations and their timing be

guided only by the readiness of the concrete for them,and nothing else.

f. That curing be conducted in such a manner that atno time during the prescribed period will the concretelack ample moisture and temperature control to permitfull development of its potential strength and durabil-ity.

4.1.2 Details of placing and curing procedures aredescribed in ACI 304, 308, and 309R. It is the purposeof this chapter to point out the factors peculiar to hotweather that can affect these operations and the result-ing concrete and to recommend what should be done toprevent or offset their influence.

4.2-Preparations for placing and curing4.2.1 Planning hot weather placements - At an early

stage of the project, plans should be made for mini-mizing the exposure of the concrete to adverse condi-tions. Whenever possible, placing of slabs should bescheduled after roof structure and walls are in place tominimize problems associated with drying winds anddirect sunlight. This will also reduce thermal shockfrom rapid temperature drops caused by wide day andnight temperature differences or cold rain on concreteheated by the sun earlier in the day. Under extreme hotweather conditions, scheduling concrete placements atother than normal hours may be advisable. Pertinentconsiderations include ease of handling and placing,and avoiding the risk of plastic shrinkage and thermalcracking.

4.2.2 Preparing for ambient conditions - Personnelin charge of construction should be aware of the dam-aging combinations of high air temperature, direct sun-light, drying winds, and high concrete temperature inadvance of concrete placements. Monitoring of localweather reports and routine recording conditions at thesite, including air temperature, sun exposure, relativehumidity, and prevailing winds, are available. Thesedata, together with projected or actual concrete tem-peratures, enable supervisory personnel through refer-ence to Fig. 2.1.5 to determine and prepare the re-

quired protective measures. Equipment should also beavailable at the site for measuring the evaporation ratein accordance with Section 5.1.2.

4.2.3 Properties of concrete mixtures - The proposedmixtures should be suitable for expected job condi-tions. This is particularly important when there are nolimits on placing temperatures, as is the case in mostgeneral construction in the warmer regions. Use of ce-ments or cementitious materials that perform well un-der hot weather conditions, in combination with water-reducing and retarding admixtures, can provide con-crete of required properties (Mittelacher 1985). Whenusing high-range, water-reducing and retarding admix-tures, products should be selected which provided ex-tended slump retention in hot weather (Collepardi,Corradi, and Valente 1979; Guennewig 1988). In dryand windy conditions, the setting rate of concrete usedin flatwork should be adjusted to minimize plastic-shrinkage cracking or crusting of the surface, with thelower layer still in a plastic condition. The type of ad-justment depends on local climatic conditions, timingof placements, and concrete temperatures. A change inadmixture dosage or formulation can often provide thedesired rate of set.

4.2.4 Temperature control of concrete - If limitingtemperatures govern the delivery of the concrete, avail-ability of temperature-controlled concrete should beascertained in advance. Cooling of the concrete will re-quire installation of special equipment and assurance ofa ready and ample supply of cooling materials such asice or liquid nitrogen (LIN) for the anticipated concretevolume and placement rate. The specification of amaximum temperature limit should provide for a tol-erance that will allow continuation of a placement inprogress if placing temperatures above the limit are ob-served in individual batches. Maintaining a continuousflow of concrete to the jobsite is important to avoid thepossible development of a cold joint. Thermometersused to determine acceptance of temperature-con-trolled concrete should be calibrated in accordance withASTM C 1064.

4.2.5 Expediting placements - Preparations must bemade to transport, place, consolidate, and finish theconcrete at the fastest possible rate. Delivery of con-crete to the job should be scheduled so it will be placedpromptly on arrival, particularly the first batch. Manyconcrete placements get off to a bad start because theconcrete was ordered before the job was ready andslump control was lost at this most critical time. Traf-fic arrangements at the site should insure easy access ofdelivery units to the unloading points over stable road-ways. Site traffic should be coordinated for a quickturnaround of concrete trucks. If possible, large orcritical placements should be scheduled during periodsof low urban traffic loads.

4.2.6 Placing equipment - Equipment for placing theconcrete should be of a suitable design and have amplecapacity to perform its functions efficiently. All equip-ment should have adequate power for the work and bein first-class operating condition. Breakdowns or de-


lays that stop or slow the placement can seriously af-fect the quality and appearance of the work. Arrange-ments should be made for the ready availability ofbackup equipment. Concrete pumps, if used, must becapable of pumping the specified class of concretethrough the length of line and elevation at requiredrates per hour. If placement is by crane and buckets,wide-mouth buckets with steep-angled walls should beused to permit rapid and complete discharge of bucketcontents. Adequate means of communication betweenbucket handlers and placing crew should be provided toassure that concrete is charged into buckets only if theplacing crew is ready to use the concrete without delay.Concrete should not be allowed to rest exposed to thesun and high temperature before placing it into theform. To minimize the heat gain of the concrete duringplacement, delivery units, conveyors, pumps, and pumplines should be kept in the shade if possible. In addi-tion, pump lines should be provided with a coat ofwhite paint. Lines can also be cooled by covering withdamp burlap, kept wet with a soaker hose, or similarmeans.

4.2.7 Consolidation equipment - There should beample vibration equipment and manpower to consoli-date the concrete immediately as it is received in theform. Procedures and equipment are described in ACI309R. Provision should be made for an ample numberof standby vibrators-at least one standby for eachthree vibrators in use. On sites subject to occasionalpower outages, portable generators should be availablefor uninterrupted vibrator operation. Apart from theunsightliness of poorly consolidated concrete, insuffi-cient compaction in the form may seriously impair thedurability and structural performance of reinforcedconcrete.

4.2.8 Preparations for protecting and curing the con-crete - Arrangements should be made for ample watersupply at the site for wetting subgrades, fogging forms,reinforcement work in progress under arid conditions,and for moist-curing if applicable. The fog nozzles usedshould produce a fog blanket. They should not be con-fused with common garden-hose nozzles, which gener-ate an excessive washing spray. Pressure washers with asuitable nozzle attachment may be a practical means forfogging on smaller jobs. Materials and means should beon hand for erecting temporary windbreaks and shadesas needed to protect against drying winds and directsunlight. Plastic sheeting or sprayable compounds forapplying temporary moisture-retaining films should beavailable to reduce moisture evaporation from flat-work between finishing passes. Means should also beprovided to protect the concrete against thermalshrinkage cracking if it is likely to become exposed torapid temperature drops. Finally, the materials andmeans for the curing methods selected should be read-ily available at the site to permit prompt protection ofall exposed surfaces from drying upon completion ofthe placement.

4.2.9 Preparing incidental work - Due to faster set-ting and hardening of the concrete in hot weather, the

timing of various final operations as saw-cutting jointsand applying surface retarders becomes more critical;therefore, these operations must be planned in ad-vance. Provisions should be made for the timely saw-ing of the contraction joints in flatwork. This is to pre-vent the building of shrinkage stresses before the cut-ting of the joints.

4.3-Placement and finishing4.3.1 General - Speed-up of placement and finishing

materially reduces hot weather difficulties. Delays in-crease slump loss and invite the addition of water tooffset it. Each operation in finishing should be carriedout promptly when the concrete is ready for it. Theconcrete should not be placed faster than it can beproperly consolidated and finished. If the placing rateis not coordinated with the available work force andequipment, the quality of the work will be marred bycold joints, poor consolidation, and uneven surfacefinishes.

4.3.2 Concrete consistency - A precondition for suc-cessful hot weather concreting is the use of concrete ofa consistency that allows prompt placement and rapidand effective consolidation in the form. Unless otherconsiderations govern, the concrete should have aslump of 3 or 4 in. At lower slumps, the rate of con-crete placement is reduced, and the concrete absorbsmore heat from the environment. Cement hydrationand stiffening rate of the concrete are thereby acceler-ated, thus compounding slump loss problems and thedifficulties in placing the concrete.

4.3.3 Placing formed concrete - In hot weather, it isusually necessary to place concrete in shallower layersthan those used in moderate weather to assure coverageof the lower layer while it will still respond readily tovibration. The interval between monolithic wall anddeck placements (to let the wall concrete develop itssettlement shrinkage) becomes very short in hotweather. This interval may be extended by the judi-cious use of set-retarding admixtures.

4.3.4 Placement of flatwork - Before depositing con-crete for flatwork on grade, the subgrade should bemoist, yet free of standing water and soft spots at thetime of concreting. In placing concrete slabs of anykind, it may be necessary in hot weather to keep theoperation confined to a small area and to proceed on afront having a minimum amount of exposed surface towhich concrete is to be added. A fog nozzle should beused to cool the air, to cool any forms and steel imme-diately ahead, and to lessen rapid evaporation from theconcrete surface before and after each finishing opera-tion. Excessive fog application (which would wash thefresh concrete surface or cause surplus water to cling toreinforcement or stand on the concrete surface duringfloating and troweling) must be avoided. Other meansof preventing moisture loss include spreading and re-moving impervious sheeting or application of sprayablemoisture-retaining films between finishing passes. Theseprocedures may cause a slight increase of the concretetemperature in place due to restricting evaporative


cooling. Generally, the benefit from reducing moistureevaporation is more important than the increase ofconcrete temperature (Berhane 1984).

4.3.5 Plastic-shrinkage cracks - Without protectionagainst moisture loss, plastic-shrinkage cracks may oc-cur, as described in Section 2.1.5. In relatively massiveplacements, revibration before floating can sometimesclose this type of cracking. Before the concrete reachesfinal set, the cracks can frequently be closed by strikingthe surface on each side of the crack with a float. Theaffected area is then retroweled to level finish. It servesno lasting purpose to merely trowel a slurry over thecracks, since these are likely to reappear if not firmlyclosed and immediately covered to avoid evaporation.

4.4-Curing and protection4.4.1 General - After completing placing and finish-

ing operations, efforts must continue to protect theconcrete from high temperature, direct sunlight, lowhumidity, and drying winds. If possible, the workshould be kept in a uniformly moderate temperaturecondition to allow the concrete to develop its fullstrength potential. High initial curing temperatures aredetrimental to the ultimate strength to a greater degreethan high placing temperatures (Bloem 1954; Barnes,Orndorff, and Roten 1977; Gaynor, Meininger, andKhan 1985). Procedures for keeping exposed surfacesfrom drying must be promptly commenced, with amplecoverage and continued without interruption. Failure todo so may result in excessive shrinkage and cracking,and will impair the surface durability and strength ofthe concrete. Curing should be continued for at leastthe first 7 days. If a change in curing method is madeduring this period, it should be done only after theconcrete is 3 days old. The concrete surface should notbe permitted to become dry during the transition. Thevarious methods of curing are described in ACI 308.The concrete should also be protected against thermalshrinkage cracking from rapid temperature drops, par-ticularly during the first 24 hr. This type of cracking isusually associated with a cooling rate of more than 5 F(3 C) per hour, or more than 50 F (28 C) in a 24-hr pe-riod for concrete with a least dimension less than about12 in. (300 mm). Concrete exposed to rapid cooling hasa lower tensile strain capacity and is more susceptible tocracking than concrete that is allowed to cool at aslower rate (ACI 207.4R). Hot weather patterns likelyto cause thermal cracking include wide day and nighttemperature differences and cold rain. Under theseconditions, the concrete should be protected by placingseveral layers of waterproof paper over the concrete, orby using other insulating methods and materials de-scribed in ACI 306.

4.4.2 Moist-curing of flatwork - Of the differentcuring procedures, moist-curing is the best method fordeveloping the strength of concrete and minimizingearly drying shrinkage. It can be provided by ponding,covering with clean sand kept continuously wet, orcontinuous sprinkling. This will require an ample water

supply and disposal of the runoff. When sprinkling isused, care must be taken that erosion of the surfacedoes not occur. A more practical method of moist-cur-ing is that of covering the prewetted concrete with im-pervious sheeting or application of absorptive mats orfabric kept continuously wet with a soaker hose or sim-ilar means. Suitable coverings are described in ACI 308.These materials should be kept in contact with the con-crete surface at all times. Alternate cycles of wettingand drying must be avoided because this may result inpattern cracking. The temperature of water used forcuring must be as close as possible to that of the con-crete to avoid thermal shock.

4.4.3 Membrane curing of flatwork - Use of liquidmembrane-forming compounds is the most practicalmethod of curing where job conditions prohibit moist-curing. The membranes restrict the loss of moisturefrom the concrete, thereby enhancing its strength, du-rability, and the surface wearability of floors and pave-ments. On concrete surfaces exposed to the sun, heatreflecting white pigmented compounds should be used.The capability for moisture retention varies consider-ably between products. For use under hot weather con-ditions, a material should be selected which providesbetter moisture retention than required by ASTMC 309. It limits the moisture loss in a 72-hour period tonot more than 0.55 kg/m2, when tested in accordancewith ASTM C 156. Some agencies have set a more re-strictive limit of 0.39 kg/m2 of moisture loss in a 72-hrperiod. On flatwork, application should be started im-mediately after disappearance of the surface watersheen after the final finishing pass. When applied byspraying, the spray nozzles should be held or posi-tioned sufficiently close to the surface to assure amplecoverage and prevent wind-blown dispersion. Manualapplication should be in two passes, with the secondpass proceeding at right angles to the first application.Most curing compounds should not be used on anysurface against which additional concrete or other ma-terials are to be bonded, unless the curing material willnot prevent bond or unless removal of the curing ma-terial is assured before subsequent bonded construc-tion.

4.4.4 Curing of concrete in forms - Forms should becovered and kept continuously moist during the earlycuring period. Formed concrete requires early access toample external curing water for strength development.This is particularly important when using high-strengthconcrete having a water-cement or water-cementitiousmaterial ratio of less than about 0.40 (ACI 363R). Theforms should be loosened, as soon as this can be donewithout damage to the concrete, and provisions madefor the curing water to run down inside them. Duringform removal, newly exposed surfaces should promptlyreceive a uniformly wet cover. A continuous flow ofcuring water over the concrete may prevent or moder-ate development of high-temperature levels that wouldotherwise result from the heat generated by cement hy-dration. For example, if there is little heat loss, formedconcrete 12 to 18 in. (0.3 to 0.5 m) thick can be ex-


pected to reach a maximum temperature of 12 F per100 lb/yd of cement (9 C per 100 kg/m) above the in-itial concrete temperature at an age from 18 to 72 hr(see ACI 207.1R). Cracking may occur when the con-crete cools rapidly from a high peak temperature and isrestrained from contracting. In more massive membersand if the internal temperature rise cannot be con-trolled by available means, the concrete should be giventhermal protection so that it will cool gradually at arate that will not cause the concrete to crack. Afterform removal, form tie holes can be filled and any nec-essary repairs made by uncovering a small portion ofthe concrete at a time to carry on this work. These re-pairs should be completed in the first few days afterstripping, so the repairs and tie-hole fillings can curewith the surrounding concrete. At the end of the curingperiod (7 days should be minimum; 10 days is better),the covering should be left in place without wetting forseveral days (4 days is suggested), so that the concretesurface will dry slowly and be less subject to surfaceshrinkage cracking. The effects of drying can also beminimized by application of a sprayable compound atthe end of the moist-curing period.

CHAPTER 5-TESTING AND INSPECTION5.1-Testing

5.1.1 Tests on the fresh concrete sample should beconducted and specimens prepared in accordance withASTM Standard Test Methods C 31, C 138, C 143,C 172, C 173, C 231, and C 1064 so that they will be asrepresentative as possible of the potential strength andother properties of the concrete as delivered. High tem-perature, low relative humidity, and drying winds areparticularly detrimental to the relatively small volumeof concrete used for making tests and molding speci-mens. Leaving the sample exposed to hot sun, wind, ordry air can seriously impair the accuracy and useful-ness of test results.

5.1.2 It is sometimes desirable to conduct tests suchas slump, air content, concrete temperature, and unitweight more frequently than for normal conditions. Inhot weather it is sometimes desirable to conduct addi-tional tests, including temperatures of the materials;initial and final time of set; slump loss; ambient tem-perature; and relative humidity where the concrete isbeing placed.

5.1.3 The most important factor affecting plasticshrinkage is the evaporation rate, which can be esti-mated from Fig. 2.1.5 with the prevailing temperature,relative humidity, and wind velocity. The evaporationrate can be more closely determined by evaporatingwater from a cake pan having an area of about 1 ft2

(0.093 m2). The pan is filled with water and weighedevery 15 to 20 min to determine the evaporation rate,which is equal to the weight loss of water from the pan.A gram scale of at least 2500 g capacity graduated to0.1 g is satisfactory.

5.1.4 Particular attention should be given to the pro-tection and curing of strength test specimens used as abasis for acceptance of concrete. Due to their small size

in relation to most parts of the structure, test speci-mens are more readily influenced by changes in ambi-ent temperatures. Extra effort is needed in hot weatherto maintain strength test specimens at a temperature of60 to 80 F (16 to 27 C) and to prevent moisture lossduring the initial curing period, in accordance withASTM C 31. If possible, the specimens should be pro-vided with an impervious cover and placed in a temper-ature-controlled job facility immediately after molding.If stored outside, exposure to the sun should be avoidedand the cooling effect of evaporating water should beused to help provide the required curing condition. Thefollowing methods for nonpotentially absorptive testmolds have been found practical:

a. Embedding in damp sand. Care should be taken tomaintain sand in continuously moist conditions (not tobe used for cardboard molds).

b. Covering with wet burlap. Care should be taken tomaintain burlap in a continuously moist condition andout of contact with the concrete.

c. Continuous fog sprays. Care should be taken toprevent interruptions of the fog spray.

d. Total immersion in water (not to be used for card-board molds). Specimens may be immersed immedi-ately in saturated limewater after molding. Becausespecimens are made with hydraulic cement, whichhardens under water, specimen cylinders need not becovered with a cap, but generally they are, as a precau-tionary measure to prevent external damage.

5.1.5 Molds must not be of a type that is potentiallyabsorptive and expands when in contact with moistureor when immersed in water. Merely covering the top ofthe molded test cylinder with a lid or plate is usuallynot sufficient in hot weather to prevent loss of mois-ture and to maintain the required initial curing temper-ature. During the transfer to the testing facility, thespecimens should be kept moist, and also be protectedand handled carefully. They should then be stored in amoist condition at 73.4 ± 3 F (23 ± 1.7 C) until themoment of test.

5.1.6 Specimens in addition to those required for ac-ceptance may be made and cured at the jobsite to assistin determining when forms can be removed, whenshoring can be removed, and when the placement canbe placed in service. Unless specimens used for thesepurposes are cured at the same place and as nearly aspossible under the same conditions as the placement,results of the tests can be misleading.

5.2-Inspection5.2.1 The numerous details to be looked after in

concrete construction are covered in ACI 311.1R and311.4R. The particular effects of hot weather on con-crete performance and the precautions to be taken tominimize adverse effects have been previously dis-cussed. Project inspection of concrete is necessary toinsure compliance with these additional precautions andprocedures. Adequate inspection is also necessary toverify and document this compliance. The need forsuch measures as spraying of forms and subgrade;

HOT WEATHER CONCRETING

cooled concrete; providing sunshades, windscreens, orfogging and the like; and minimizing delays in place-ment and curing should be anticipated.

5.2.2 Air temperature, concrete temperature (ASTMC 1064), general weather conditions (clear, cloudy),wind velocity, relative humidity, and evaporation rateshould be recorded at frequent intervals. In addition,the following should be recorded and identified withthe work in progress so that conditions relating to anypart of the concrete construction can be identified at alater date:

• All water added to the mixture with correspond-ing mixing times.

• Time batched, time discharge started, and timedischarge completed.

• Concrete temperature at time of delivery and af-ter placing concrete.

• Observations on the performance and appearanceof concrete as delivered and after placing in forms.

• Slump of concrete as delivered.• Slump of concrete as discharged.• Protection and curing:

a. Methodb. Time of applicationc. Rate of applicationd. Visual appearancee. Duration of curing

These observations should be included in the perma-nent project records.

CHAPTER 6-REFERENCES6.1-Specified references

The documents of the various standards-producingorganizations referred to in this document are listedwith their serial designation, including year of adop-tion or revision. The documents listed were the latest ineffect at the time this document was revised. Sincesome of these documents are revised frequently, gener-ally in minor detail only, the user of this documentshould check directly with the sponsoring group if it isdesired to refer to the latest revision.

American Concrete Institute C 143116R-90

201.2R-77(Reapproved 1982)207.1R-70(Reaffirmed 1980)207.2R-86

C

207.4R-80

211.1-89

211.2-81

Cement and ConcreteTerminologyGuide to Durable Concrete

Mass Concrete

Effect of Restraint, VolumeChange, and Reinforcement onCracking of Massive ConcreteCooling and Insulating Systemsfor Mass ConcreteStandard Practice for SelectingProportions for Normal,Heavyweight, and MassConcreteStandard Practice for Selecting

211R-84

212.3R-89

221R-84

223-83

224R-80-(84)

225R-85

226.3R-87301-89

304R-85

306R-88308-81 (Revised 86)

311.1R (SP2)311.4R-88318-83R-86

363R-84

ASTMC 31-88

C 42-87

C 138

150-86

156-80a

C 172-82

C 173

C 192-88

305R-17

Proportions for StructuralLightweight ConcreteGuide for the Use of NormalWeight Aggregates in ConcreteChemical Admixtures forConcreteGuide for the Use of NormalWeight Aggregates in ConcreteStandard Practice for the Useof Shrinkage-CompensatingConcreteControl of Cracking inConcrete StructuresGuide to the Selection and Useof Hydraulic CementsUse of Fly Ash in ConcreteSpecifications for StructuralConcrete for BuildingsGuide for Measuring, Mixing,Transporting, and PlacingConcreteCold Weather ConcretingStandard Practice for CuringConcreteManual of Concrete InspectionGuide for Concrete InspectionBuilding Code Requirementsfor Reinforced ConcreteState-of-the-Art Report onHigh Strength Concrete

Standard Practice for Makingand Curing Concrete TestSpecimens in the FieldStandard Test Method forObtaining and Testing DrilledCores and Sawed Beams ofConcreteStandard Test Method for UnitWeight, Yield, and AirContent (Gravimetric) ofConcreteStandard Test Method forSlump of Hydraulic CementConcreteStandard Specification forPortland CementStandard Test Method forWater Retention by ConcreteCuring MaterialsStandard Practice for SamplingFreshly Mixed ConcreteStandard Test Method for AirContent of Freshly MixedConcrete by the VolumetricMethodStandard Practice for Makingand Curing Concrete TestSpecimens in the Laboratory

C


C 231

C 309-81

C 403-88

C 494-86

C 595-86

C 618-87

C 803-82

C 900-87

C 918-80

C 989-88

C 1017-85

C 1064-86

STP 169A

Standard Test Method for AirContent of Freshly MixedConcrete by the PressureMethodStandard Specification forLiquid Membrane-FormingCompounds for CuringConcreteStandard Test Method forTime of Setting of ConcreteMixtures by PenetrationResistanceStandard Specification forChemical Admixtures forConcreteStandard Specification forBlended Hydraulic CementsStandard Specification for FlyAsh and Raw or CalcinedNatural Pozzolan for Use as aMineral Admixture in PortlandCement ConcreteStandard Test Method forPenetration Resistance ofHardened ConcreteStandard Test Method forPullout Strength of HardenedConcreteStandard Test Method forDeveloping Early AgeCompression Test Values andProjecting Later-Age StrengthsStandard Specification forGround Granulated Blast-Furnace Slag for Use inConcrete and MortarsStandard Specification forChemical Admixtures for Usein Producing Flowing ConcreteStandard Test Method forTemperature of Freshly MixedPortland-Cement ConcreteSignificance of Tests andProperties of Concrete andConcrete-Making Materials,1966, 571 pp.

The preceding references are available from:

American Concrete InstituteP.O. Box 19150Detroit, MI 48219

American Society for Testing and Materials1916 Race StreetPhiladelphia, PA 19103

6.2-Recommended referencesBarnes, B. D.; Orndorff, R. L.; and Roten, J. E., Dec. 1977,

“Low Initial Curing Temperature Improves the Strength of ConcreteTest Cylinders,” ACI JOURNAL, Proceedings V. 74, No. 12, pp. 612-615.

Berge, Olav, July 1976, “Improving the Properties of Hot-MixedConcrete Using Retarding Admixtures,” ACI JOURNAL, ProceedingsV. 73, No. 7, pp. 394-398.

Berhane, Zawde, Mar. 1983, “Compressive Strength of Mortar inHot-Humid Environment,” Cement and Concrete Research, V. 13,No. 2, pp. 225-232.

Berhane, Zawde, Nov.-Dec. 1984, “Evaporation of Water fromFresh Mortar and Concrete at Different Environmental Conditions,”ACI JOURNAL, Proceedings V. 81, No. 6, pp. 560-565.

Bloem, Delmar, Dec. 1954, “Effect of Curing Conditions onCompressive Strengths of Concrete Cylinders,” Publication No. 53,National Ready Mixed Concrete Association, 15 pp.

Bloem, Delmar, July 1960, “Plastic Cracking of Concrete,” Engi-neering Information, National Ready Mixed Concrete Assn., 2 pp.

Bulletin du Ciment, E. G. Portland, Aug. 1953, “Hot Cement,”V. 21, No. 20, 6 pp (in French).

Carlson, Roy W., and Thayer, Donald P., Aug. 1959, “SurfaceCooling of Mass Concrete to Prevent Cracking,” ACI JOURNAL ,Proceedings V. 56, No. 2, pp. 107-120.

Cebeci, O. Z., 1986, “Hydration and Porosity of Cement Paste inWarm and Dry Environment,” 8th International Congress on theChemistry of Cement, Rio de Janeiro, V. III, pp. 412-416; 423-424.

Cebeci, O. Z., July 1987, “Strength of Concrete in Warm and DryEnvironment,” Materials and Structures, Research and Testing (RI-LEM, Paris), V. 20, No. 118, pp. 270-272.

Clark, Roy R., June 1957, “Mass Concrete Control in DetroitDam,” ACI JOURNAL, Proceedings V. 53, No. 12, pp. 1145-1168.

Collepardi, Mario; Corradi, Mario; and Valente, Michele, Jan.1979, “Low-Slump-Loss Superplasticized Concrete,” TransportationResearch Record 720, Transportation Research Board, Washington,D.C., pp. 7-12

Concrete Products, Mar. 1968, “Gifford-Hill Furnished Concreteon-the-Rocks,” V. 71, No. 3, pp. 60-61.

Constructional Review (Sydney), Aug. 1961, “Concreting in HighTemperatures,” V. 34, No. 8, pp. 37-38.

Cordon, William A., and Thorpe, J. Derle, Aug. 1965, “Controlof Rapid Drying of Fresh Concrete by Evaporation Control,” ACIJOURNAL, Proceedings V. 62, No. 8, pp. 977-985.

Davey, N., Oct. 1933, “Influence of Temperature upon theStrength Development of Concrete,” Building Research TechnicalPaper No. 14, Department of Scientific and Industrial Research,London.

Fintel, Mark, and Khan, Fazlur R., Dec. 1965, “Effects of Col-umn Exposure in Tall Structures-Temperature Variations and theirEffects,” ACI JOURNAL, Proceedings V. 62, No. 12, pp. 1533-1556.

Freedman, S., May 1969, “Hot Weather Concreting,” ModernConcrete, V. 33, No. 1, pp. 31-36, and 38.

Gaynor, Richard D.; Meininger, Richard C.; and Khan, Tarek S.,1985, “Effects of Temperature and Delivery Time on Concrete Pro-portions,” Temperature Effects on Concrete, STP-858, ASTM, Phil-adelphia, pp. 68-87.

Glover, Robert E., Nov.-Dec. 1934, “Flow of Heat in Dams,” ACIJOURNAL, Proceedings V. 31, No. 2, pp. 113-124.

Guennewig, Tom, Mar. 1988, “Cost-Effective Use of Superplasti-cizers,” Concrete International: Design & Construction, V. 10, No.3, pp. 31-34.

Hampton, James S., 1981, “Extended Workability of ConcreteContaining High-Range Water-Reducing Admixtures in HotWeather,” Developments in the Use of Superplasticizers, SP-68,American Concrete Institute, Detroit, pp. 409-422.

Harris, D. P., June 1956, “Concreting Problems and Methods inHot Climates,” Reinforced Concrete Review (London), V. 4, No. 2,pp. 95-125.

Hersey, A. T., May 1968, “Experimental Research in Abuse of4000 psi Concrete,” ACI JOURNAL, Proceedings V. 65, No. 5, pp.379-383.

Ikeda, T., and Mizoguchi, Y., Aug. 1962, “Effects of Climate onProperties of Ready-Mixed Concrete,” Cement and Concrete, No.186 (in Japanese).

Irwin, Harry, Feb. 15, 1956, “Producing Cooled Concrete,” Pre-sented at the 26th Annual Convention, National Ready Mixed Con-crete Association, 5 pp.


Jaegermann, C. H., and Glucklich, J., Apr. 1968, “Effect of HighEvaporation during and Shortly after Casting on the Creep Behaviorof Hardened Concrete,” Proceedings, Colloquium, Physical andChemical Causes of Creep and Shrinkage of Concrete, RILEM, Paris.

Jaegermann, C. H., and Glucklich, J., 1968, “Effect of PlasticShrinkage on Subsequent Shrinkage and Swelling of the HardenedConcrete,” Proceedings, Colloquium on the Shrinkage of HydraulicConcretes, RILEM/Cembureau, Paris, V. 1 (published by InstitutoEduardo Torroja, Madrid).

Jaegermann, C. H., and Ravina, D., 1967, “Effect of Some Ad-mixtures on Early Shrinkage and Other Properties of Prolonged-Mixed Concrete Subjected to High Evaporation,” Proceedings, In-ternational Symposium on Admixtures for Mortar and Concrete(Brussels, 1967), RILEM, Paris, pp. 319-350.

Jessing, Jorn, 1956, “Influence of Weather Factors on Heat En-ergy Level-A Case of Calculation,” Reprint No. 73, Danish Na-tional Institute of Building Research, Copenhagen, 64 pp.

Kameta, Y., and Sinozawa, K., Sept. 1963, “Effects of CuringConditions of Hot Weather Concreting on Compressive Strength ofConcrete,” Paper No. 89, Architectural Inst. of Japan (in Japanese).

Kelly, T. M., and Bryant, D. E., 1957, “Measuring the Rate ofHardening of Concrete by Bond Pullout Pins,” Proceedings, ASTM.V. 57, pp. 1029-1042.

Klieger, Paul, June 1958, “Effect of Mixing and Curing Tempera-ture on Concrete Strength,” ACI JOURNAL, Proceedings V. 54, No.12, pp. 1063-1081. Also, Research Department Bulletin 103, Port-land Cement Association.

Koda, T. et al., Aug. 1965, “Study on Hot Weather Concreting,”Laboratory Paper, Nihon Cement Company, Tokyo (in Japanese).

Lee, Michael, July 1987, “New Technology in Concrete Cooling,”Concrete Products, V. 89, No. 7, pp. 24-26, 36.

Lerch, William, 1955, “Hot Cement and Hot Weather ConcreteTests,” Portland Cement Association, Chicago, 9 pp.

Lerch, William, Feb. 1957, “Plastic Shrinkage,” ACI JOURNAL,Proceedings V. 53, No. 8, pp. 797-802.

Martin, Ignacio, 1971, “Effect of Environmental Conditions onThermal Variations and Shrinkage of Concrete Structures in theUnited States,” Designing for Effects of Creep, Shrinkage, andTemperature in Concrete Structures, SP-27, American Concrete In-stitute, Detroit, pp. 279-300.

Mather, Bryant, Aug. 1987, “The Warmer the Concrete the Fasterthe Cement Hydrates,” Concrete International: Design & Construc-tion, V. 9, No. 8, pp. 29-33.

Mittelacher, Martin, 1985, “Effect of Hot Weather Conditions onthe Strength Performance of Set-Retarded Field Concrete,” Temper-ature Effects on Concrete, STP 858, ASTM, Philadelphia, pp. 88-106.

Mowery, S. A., Aug. 1966, “Hazards of Hot-Weather Concret-ing,” Civil Engineering, ASCE, V. 236, No. 8, pp. 56-57.

National Ready Mixed Concrete Association, June 1962, “CoolingReady Mixed Concrete,” Publication No. 106, Silver Spring, 7 pp.

Oliver, Eduardo A., June 1982, “Controlling Ready-Mixed Con-crete Operations in Hot, Humid Climates,” Concrete International:Design & Construction, V. 4, No. 6, pp. 30-32.

Olivieri, Elmer, and Martin, Ignacio, 1963, “Curing of Concrete inPuerto Rico,” Revista, Colegio de Agricultura y Artes Mecanicas,Universidad de Puerto Rico, Mayaguez.

Portland Cement Association, 1966, “Hot Weather Concreting,”Concrete Information Sheet IS 14.02T, Skokie, 4 pp.

Public Roads, Feb. 1961, “Symposium on Water-Reducing Re-tarders for Concrete,” V. 31, No. 6, 29 pp.

Ravina, Dan, Apr. 1984, “Slump Loss of Fly Ash Concrete,”Concrete International: Design & Construction, V. 6, No. 4, pp. 35-39.

Ravina, D., and Shalon, R., 1968a, “Shrinkage of Fresh MortarsCast Under and Exposed to Hot Dry Climatic Conditions,” Pro-ceedings, Colloquium on Shrinkage of Hydraulic Concrete, RILEM/Cembureau, Paris, V. 2, (published by Instituto Eduardo Torroja,Madrid).

Ravina, Dan, and Shalon, Rahel, Apr. 1968b, “Plastic Shrinkageand Cracking,” ACI JOURNAL , Proceedings V. 65, No. 4, pp. 282-291.

Ravina, Dan, and Shalon, Rahel, 1970, “Effect of Elevated Tem-perature on Portland Cement,” Temperature and Concrete, SP-25,American Concrete Institute, Detroit, pp. 275-290.

Roberts, H. H., June 1951, “Cooling Materials for Mass Con-crete,” ACI JOURNAL, Proceedings V. 47, No. 10, pp. 821-832.

Ruud, Frederick O., Jan. 1965, “Prediction and Control ofStresses in Concrete Block,” ACI JOURNAL, Proceedings V. 62, No.1, pp. 95-104.

Shalon, R., and Ravina, D., 1960, “Studies in Concreting in HotCountries,” Proceedings, International Symposium on Concrete andReinforced Concrete in Hot Countries (RILEM, Paris, V. 1, 46 pp.(published by Building Research Station, Israel Institute of Technol-ogy, Haifa).

Seidel, K., 1955, “Experiences in Concreting with Hot Cement,”Schriftenreihe der Arbeitsgruppe Betonstrassen, Forschungsgesell-schaft fur das Strassenwesen, No. 6, pp. 17-22 (in German). Also,Foreign Literature Study No. 145, Portland Cement Association.

Seidel, K., Jan. 1955, “Use of Warm Cement in Concreting Jobs(Uber die Verwendung von Warmem Zement beim Betonieren),” Ze-ment-Kalk-Gips (Wiesbaden). V. 44, No. 1, pp. l-6 (in German).

Teodoru, George, 1987, “New Proposals for the ACI 305 Hot-Weather Concreting” Recommendations, RILEM Symposium Mate-rials and Structures/Research Orientation and Industrial Needs, Bo-logna, pp. 147-153.

Tuthill, Lewis H., and Cordon, William A., Nov. 1955, “Proper-ties and Uses of Initially Retarded Concrete,” ACI JOURNAL, Pro-ceedings V. 52, No. 3, pp. 273-286.

U.S. Bureau of Reclamation, Denver, 1952, “Effect of InitialCuring Temperatures on the Compressive Strength and Durability ofConcrete,” Report No. C-625, 7 pp.

U.S. Bureau of Reclamation, 1975, Concrete Manual, 8th Ed.,Denver, 627 pp.

Venuat, M., 1967, “Properties of Hot Cements, Cooled or Aer-ated (Propriétés des ciments chauds, refroidis ou eventes),” Techni-cal Publication No. 167, Centre d’Etudes et de Récherches de l'In-dustrie de Liants Hydrauliques, Paris, 39 pp. (in French).

Verbeck, G. J., and Helmuth, R. H., 1968, “Structure and Physi-cal Properties of Cement Pastes,” Proceedings, Fifth InternationalSymposium on the Chemistry of Cement, Tokyo, V. III, pp. l-32.

Walz, K., Sept. 1955, “Use of Hot Cement-A Bibliography of 15References (Verwendung von heissem Zement-Literatur Zusammen-stellung),” Zement-Kalk-Gips (Wiesbaden), V. 44, No. 9, pp. 315-319(in German).

Yamamoto, Y., and Kobayashi, S., Jan.-Feb. 1986, “Effect ofTemperature on the Properties of Superplasticized Concrete,” ACIJOURNAL, Proceedings V. 83, No. 1, pp. 80-87.

APPENDIX A-ESTIMATING CONCRETETEMPERATURE

A1 Equations for estimating temperature T of freshly mixed con-crete are shown in the following.

Without ice (U.S. customary and SI units)

0.22(TaW a + T cW c) + TwW w + TaW w a

0 . 2 2 ( Wa + WC) + Ww + Ww a

(1)

With ice (U.S. customary units)

0 .22(T aW a + TcW c) + Tw W w + TaW w a - 1 1 2 Wi

0 . 2 2 ( W a + WC ) + Ww + Wi + Ww a

(2)

With ice (SI units)

0.22(TaW a + TcW c) + Tw W w + TaW w a - 79 .6Wi

0 . 2 2 ( W a + Wc) + Ww + Ww + Wi + Ww a

(3)


T =T =T =

W =W =W =W =W =T a =T c =T w =

T i =

W a =W c =W w =W wa =W =

temperature of aggregatetemperature of cementtemperature of batched mixing water from normal supplyexcluding ice (Note: The temperature of free and absorbedwater on the aggregate is assumed to be the same tempera-ture as the aggregate. All temperatures are in deg F or C.)dry weight of aggregatesweight of cementweight of batched mixing waterweight of free and absorbed moisture in aggregatesweight of icetemperature of aggregatetemperature of cementtemperature of batched mixing water from normal supplyexcluding icetemperature of ice. (Note: The temperature of free and ab-sorbed water on the aggregate is assumed to be the sametemperature as the aggregate. All temperatures are in deg For C.)dry weight of aggregateweight of cementweight of batched mixing waterweight of free and absorbed moisture in aggregate at Ta

weight of ice(Note: All weights are in lb or kg.)

A2 Eq. (2) and (3), for estimating the temperature of concrete withice in U. S. customary or SI units, assume that the ice is at its melt-ing point. A more exact approach would be to use Eq. (4) or (5),which includes the temperature of the ice.

With ice (U. S. customary units)

T =0.22(T aW a + TcW c) TwW w

0 . 2 2 ( Wa + WC ) + Ww + Wi + Ww a

T aW w a - W i (128 - 0.5T i)

0 . 2 2 ( Wa + Wc) + Ww + Wi + Ww a

With ice (SI units)

T =0.22(T aW a + TcW c) TwW w

0 . 2 2 ( Wa + WC ) + Ww + Wi + Ww a

T aW w a - Wi(79.6 - 0 .5T i) 0 . 2 2 ( Wa + Wc) + Ww + Wi + Ww a

(4)

(5)

APPENDIX B-METHODS OF COOLINGCONCRETE

The summary is limited to a description of methods suitable formost structural uses of concrete. Methods for the cooling of massconcrete are explained in ACI 207-4R.

B1 Cooling with chilled mixing water - Concrete can be cooled toa moderate extent by using chilled mixing water; the maximum re-duction in concrete temperature that can be obtained is about 10 F (6C). The quantity of cooled water cannot exceed the mixing water re-quirement, which will depend upon the moisture content of aggre-gates and mixture proportions. The method involves a significant in-vestment in mechanical refrigeration equipment and insulated waterstorage large enough for the anticipated hourly and daily productionrates of cooled concrete. Available systems include one that is basedon heat-pump technology, which is usable for both cooling and heat-ing of concrete. Apart from its initial installation cost, this systemappears to offer cooling at the lowest cost of available systems forcooling mixing water.

B2 Liquid nitrogen cooling of mixing water - Mixing water can bechilled rapidly through injection of liquid nitrogen into an insulatedholding tank. This chilled water is then dispensed into the batch. Al-ternatively, the mixing water may be turned into ice slush by liquid

nitrogen injection into the mixing water stream as it is discharged intothe mixer. The system enables cooling by as much as 20 F (11 C). Theratio of ice to water in the slush must be adjusted to produce thetemperature of concrete desired. Installation of this system requiresinsulated mixing water storage, a nitrogen supply vessel, batch con-trols, and auxiliary equipment. Apart from installation costs, thereare operating expenses from liquid nitrogen usage and rental fee forthe nitrogen supply vessel. The method differs from that by directliquid nitrogen injection into mixed concrete described in B4.

B3 Cooling concrete with ice - Concrete can be cooled by using icefor part of the mixing water. The amount of cooling is limited by theamount of mixing water available for ice substitution. For most con-crete, the maximum temperature reduction is about 20 F (11 C). Forcorrect proportioning, the ice must be weighed. Cooling with blockice involves the use of a crusher/slinger unit, which can finely crusha block of ice and blow it into the mixer. A major obstacle to the useof block ice in many areas is insufficient supply. Costs of using blockice are: the cost of ice including transportation, refrigerated storage,handling and crushing equipment, additional labor, and if required,provisions for weighing the ice. An alternative to using block ice is toset up an ice plant near the concrete plant. As the ice is produced, itis weighed, crushed, and conveyed into the mixer. It may also beproduced and used as flake ice. This system requires a large capitalinvestment.

B4 Cooling mixed concrete with liquid nitrogenB4.1 Injection of liquid nitrogen into freshly mixed concrete is

an effective method for reduction of concrete temperature. The prac-tical lower limit of concrete temperature is reached when concretenearest the injection nozzle forms into a frozen lump; this is likely tooccur when the desired concrete temperature is less than 50 F. Themethod has been successfully used in a number of major concreteplacements. The performance of concrete was not adversely affectedby its exposure to large amounts of liquid nitrogen. Cost of thismethod is relatively high, but it may be justified on the basis of prac-tical considerations and overall effectiveness.

B4.2 Installations of the system consist of a nitrogen supply ves-sel and injection facility for central mixers, or one or more injectionstations for truck mixers. The system can be set up at the construc-tion site for last-minute cooling of the concrete before placement.This avoids temperature gains of cooled concrete in transit betweenthe concrete plant and jobsite. Coordination is required in the dis-patching of liquid nitrogen tanker trucks to injection stations for thetimely replenishing of gas consumed in the cooling operations. Thequantity of liquid nitrogen required will vary according to mixtureproportions and constituents, and the amount of temperature reduc-tion.

B5 Cooling of coarse aggregatesB5.1 An effective method of lowering the temperature of the

coarse aggregate is by cool water spraying or inundation. Since thecoarse aggregate is the largest ingredient in a standard concrete mix-ture, reducing the temperature of the aggregate approximately 2 ±0.5 F (1.1 ± 0.28 C) will lower the final concrete temperature ap-proximately 1 F (0.5 C). To use this method, the producer must haveavailable large amounts of chilled water and the necessary water-cooling equipment for production requirements. This method is mosteffective when adequate amounts of coarse material are contained ina silo or bin so that cooling can be accomplished in a short period oftime. Care must be taken to evenly inundate the material so thatslump variation from load to load is minimized.

B5.2 Cooling of coarse aggregate can also be accomplished byblowing air through the moist aggregate. The air flow will enhanceevaporative cooling and can bring the coarse aggregate temperaturewithin 2 F (1 C) of wet bulb temperature. Effectiveness of the methoddepends on ambient temperature, relative humidity, and velocity ofair flow. The added refinement of using chilled air instead of air atambient temperature can reduce the coarse aggregate temperature toas low as 45 F (7 C). However, this method involves a relatively highinstallation cost.

This report was submitted to letter ballot of the committee and approved inaccordance with ACI standardization procedures.