Concrete Casting in Hot and Cold Weather

CASTING CONCRETE IN HOT AIR

The most unfavorable environment for concrete pouring is extremely hot, dry and windy weather. Excessive water loss occurs as a result of rapid evaporation in freshly placed fresh concrete. As a result, slump loss, set acceleration, air gaps and plastic shrinkage cracks occur on the surface. This adversely affects the durability of concrete. The air temperature being more than +32 C while pouring concrete requires taking precautions for concrete.

Precautions:

● Cements with low cement dosage and low heat of hydration should be preferred.

● The mixer reaching the pouring area should be emptied without waiting.

● Set retarding additives should be used.

● Night concrete casting should be preferred.

● Spraying the base and molds with water during pouring is important in order not to absorb the water in the concrete mix.

● The first screeding is done immediately after the concrete is poured, and the second gauge is applied after 30-40 minutes by sprinkling.

● It should be saturated with water for 72 hours starting from the first half hour of casting.

● Exposed concrete surfaces should be covered with wet burlap or plastic sheeting to protect them from the effects of sun and wind.

CASTING CONCRETE IN COLD WEATHER

In case the air temperature is lower than +5 C during concrete pouring, special precautions must be taken in construction, casting and maintenance works in order to obtain quality concrete. It is very dangerous to have frost while the fresh concrete sets. If the temperature of the environment where the fresh concrete is poured falls below +5 C in a day, if it drops below +5 C for 48 hours for more than a day, it should be protected against frost for 72 hours.

Precautions

● Concrete should not be poured as much as possible in weather conditions where there is a risk of frost.

● Cement with high heat of hydration, maximum allowable cement dosage and low water/cement ratio should be chosen.

● The molding time should be extended.

● Set accelerator and antifreeze should be used.

● Aggregate, cement and especially water should be heated so that the initial temperature of the concrete does not fall to the freezing value.

● The heat generated as a result of the hydration of the cement should be prevented from spreading out of the concrete. For this, appropriate insulation should be made on the outer surfaces of the molds.