Concreting in hot weather:Â There are some special problems involved in hot weather concreting, especially arising both form; increased rate of evaporation and fresh mix. These problems concern the mixing, placing and curing of concrete.
A high temperature of fresh concrete results in a more rapid hydration and leads therefore, to accelerated setting and to a lower strength of hardened concrete. Furthermore, rapid evaporation may caused plastic shrinkage and crazing and subsequent cooling of the hardened concrete would introduce tensile stresses. It is generally believed that plastic shrinkage is likely to occur when the rate of evaporation exceeds the rate at which the bleeding water rises the surface but it has been recently found that cracks also form due to rapid evaporation.
There are some further complications in hot weather concreting; air entraining is more difficult although this can be remedied by using larger quantities of the entraining agent. Curing also presents additional problems as the curing water tends to evaporate rapidly.
There are a number of remedial measures that can be adopted. First, the cement content should be kept as low as possible so that the heat of hydration does not unduly, aggravate the effects of high ambient temperature. The temperature of the fresh concrete can be lowered by pre-cooling one or more of the ingredients of the mix and can be used instead of some of the mixing water but it is essential to see that ice melts completely before the mixing completed.
So temperature has a lot of influence during setting on the strength. It is important to know that temperature should not be higher than about 60 F.
The evaporation of freshly laid concrete and also the evaporation of curing water can be stopped by covering the surface using polythene sheets and other suitable devices.
