Figure 4-14. Effects of high temperature on concrete
compressive strength at various stages.
In hot weather, the tendency for cracks to form increases both before and after hardening. Rapid water
evaporation from hot concrete can cause plastic shrinkage cracks even before the surface hardens. Cracks can
also develop in the hardened concrete because of increased shrinkage due to a higher requirement and because of
the greater difference between the high temperature at the time of hardening and the low temperature to which the
concrete later drops.
Cooling Concrete Materials
The most practical way to obtain a low concrete temperature is to cool the aggregate and water as much as
possible before mixing. Mixing water is easier to cool and is also more effective, pound for pound, in lowering
concrete temperature. However, because aggregate represents 60 to 80 percent of the concrete' total weight, the
concrete temperature depends primarily on the aggregate temperature. Figure 4-15 shows the effects of the
mixing water and aggregate temperatures on the temperature of fresh concrete. You can lower the temperature of
fresh concrete by--
Using cold mixing water. In extreme cases, you can add slush ice to chill the water.
Cooling. Cool coarse-aggregate by sprinkling, thereby avoiding too much mixing water.
Insulating. Insulate mixer drums or cool them with sprays or wet burlap coverings. Insulate water supply
lines and tanks or painting them white.