Problems Encountered in Hot Weather Concreting:

Following are the problems encounter within hot weather concreting:

Reduction in Strength

Concrete cured and produced at higher temperature generally develops higher early strength than normally produced concrete but the eventual strengths are lower. High temperature causes greater evaporation and hence requires increase of mixing water, consequently decreasing the strength. The effect of simultaneous reduction in the relative humidity, it is seen that specimens moulded and cured in air at 23ºC and 60% relative humidity and at 38ºC and 25% relative humidity attained strengths of only 73% and 62% respectively, in comparison along with the specimens which are moist-cured at 23ºC for 28 days.

Accelerated Setting

Rapid hydration takes place due to higher temperature causing accelerated setting. This results in reducing the handling time of concrete and also lowering the strength of hardened concrete. The workability of concrete decreases and hence water requirement increases with the increase in the temperature of concrete. It has been found in which an approximately 25mm decrease in slump has resulted from 11ºC increase in concrete temperature. The addition of water without proper adjustments in mix proportions adversely affects the quality of concrete.

Rapid Evaporation During Curing

A rapid initial hydration results in a poor microstructure of gel, which is possibly more porous, resulting in a huge proportion of the pores remaining unfilled. This decrease the strength of concrete. The hydration of cement takes place only in water-filled capillaries so it is imperative that a loss of water by evaporation from the capillaries be prevented. Water lost internally by self-desiccation has to be replaced by water from outside.

Difficulty in Controlling the Air Content

It is very difficult to control the air content in air-entrained concrete at higher temperature. Because of this control of workability is difficult. For a given amount of air-entraining agent, hot concrete entrains less air than does concrete at normal temperature.

Increased Tendency to Cracking

The rate of evaporation depends on the ambient temperature, relative humidity, wind speed and concrete temperature. More rapid evaporation leads to plastic shrinkage cracking, and subsequent cooling of hardened concrete introduces tensile stresses.