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Precautions and remedial measuresThe temperature of the ingredients, aggregates, cementand water should be kept at practical levels. Aggregatetemperature can be brought down by passing cool airover it. Water should be drawn from a cool pond or astorage drum. Pipes bringing water to the concretingspot should be buried in the earth or insulated from thedirect rays of the sun. In very hot regions, ice cubes ofknown volumes can be added to the mixing waterthisitself reduces the temperature of fresh concrete. All themixing and transporting equipment should be kept undershade and protected from getting heated up. Mixers,chutes, belts, pumps and forms can be painted white toensure the least absorption of heat.

Formwork, props, reinforcements, subgrade andsurroundings can be sprayed with cool water prior toconcreting. This ensures keeping the area around theconcreting place cool and increases the humidity. Itreduces evaporation loss from the fresh concrete andkeep its temperature low. Where the day temperaturesare abnormal, concreting can be done during thecooler hours of the day or at night.The concrete once laid should be quickly finished.

Delays and bottlenecks during concreting should beidentified in advance and totally avoided by takingproper precautions. If the finished concrete driesquickly and shrinkage cracks appear, the surface shouldbe covered by wet sacks which should be maintainedin a damp condition. Adequate personnel to finish thefreshly laid concrete should be available otherwisecold joints will form indicating inadequate bond betweentwo blocks of concrete due to the loss of moisture. In hotweather curing is a very critical operation. Regular andconstant replenishment of curing water must be main-tained. After the termination of curing, the concretesurface shoud not be exposed to hot weather immediately.It should be gradually done, say, by allowing the wetsacks to dry and removing them subsequently.

Adequate data on the temperature of the ingredients,temperature of the place where concreting is done,temperature of the fresh concrete as delivered and afterplacing in the forms should be collected so that the mixdesign can take into account the effect of these tempera-tures on the concrete strength.Sometimes water reducing retarders can he also usedas admixtures provided they do not affect the hardeningand development of strength. It is advisable not to usehigh early strength cement without taking all the above

precautions.Summary and conclusionsThe extent of the influence of hot weather on mixing,transporting, placing, compacting and finishing ofconcrete depends on the actual temperature at thework site and the relative humidity. In dry, arid placesthe reduction in water content due to evaporation andincrease in the temperature of fresh concrete is very high.The higher the temperature, the greater is the loss ofwater from fresh concrete and thus greater is the problemsassociated with concreting as enumerated in this paper.With the increase in the temperature during the courseof the day it is general practice at most constructionsites to add a known percentage of water to the originalwater-cement ratio. However, scientific mix design of con-crete should cater for the increase in demand for mixingwater by taking into account as many as possibleof the number of variables that contribute to theincrease in the demand for mixing water, aside from justan increase in the temperature of the site.References1.Summer concreting, Journal of the American ConcreteInstitute, August 1975. Proc Vol 72, p. 402.ACI Standard specifications for structural concrete forbuildings, ACI 31-72 (Revised 1975). Special publication SP-15.

American Concrete Institute, Detroit, Michigan 48219, USA.3. Concrete manual. Seventh edition. Bureau ofReclamation, US Department of Interior, Washington, 1974.

Forty years ago there were no computers or finiteelementsjust pocket books, said Dr Oleg Kerensky.Site supervision was elementary, but for all that engineersdesigned good l2ridges which were still here today.Dr Kerensky was addressing the annual luncheon meetingof the Concrete Society's South West Region at the AshtonCourt Country Club in Bristol. "I started my training indesign in 1937", he reminisced. " In those days if one waslate, one was ticked of f, and if one made a mistake one wasequally ticked off". He recalled that on his f irst job theforeman proudly reported to him that the night shift hadsaved ten bags of cement in line with his predecessor'spolicy of encouraging the saving of cement by payinga small bonus for bags not used.Today's burning subject, according to him, was thelack of productivity, in the construction industry parti-cularly. In the twenties, there was much greater producti-vity , with simpler tools and simpler methods and techniques.No labour relations policies were new, he said. They hadalways been there. But punitive methods of discipliningstaff were gone, and he told the story of an of fice boymeeting his managing director in the lift one morning."Late again, then!" said the managing director, pleasantlyenough. "So am I", replied the office boy." We must restore productivity", Dr Kerensky said"and we can do this only through respect. The ordinarymanshould respect the craftsman, the craftsman should respectthe foreman, the foreman should respect the engineer, andthe engineer should respect the accountant". Engineers

should take the blame for the lack of leadership, he wenton. Restore respect, and the problems would go.Dr Kerensky spoke of the difficult times in which welived, and concluded by com paring socialism and capitalism ."Capitalism", he said, "is the exploitation of persons bypersons, and socialism is that in reverse".

"Oleg Kerensky looks back", Concrete,April 1977, p. 29.

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Owing to heavy pressure on space, it will hethe special responsibility of contributors to mak e theirpapers as brief as possible and to exclude diligentlyall material which is not strictly essential to thetreatment of the subject in hand.

NOVEMBER 197749