Hot air is the weather condition (TS 1248) when the average temperature is above 30 ° C for three consecutive days during concrete pouring and in general, the average temperatures in summer months are above 30 ° C in our country.
In normal weather, concrete casting temperature is defined as + 5 ° C to + 30 ° C (TS 1247).
The fresh concrete temperature at the time of delivery can be determined between the user and the manufacturer (TS EN 206-1). The fresh concrete temperature at the time of delivery is foreseen as + 5 ° C. The most suitable concrete pouring temperature can be considered as 10 ° C-15 ° C.
Effects of Hot Air on Fresh Concrete
It is necessary to evaluate hot weather conditions not only as air temperature but as a combination of ambient and concrete temperature, humidity, wind speed, and solar radiation.
The high-temperature wind and relative humidity affect the evaporation of the water. Naturally, the temperature has a great effect on the quality of the fresh concrete in the mixed process, the casting process, and the waiting process. This is due to the increase in the rate of water, temperature loss, the risk of thermal cracking, the rate of plastic shrinkage cracks, and cold joint formation, while the setting time, durability and 28-day strength due to cracks decrease. Due to color difference and cold joint, non-aesthetic appearance is formed, permeability may increase.
It is ideal for the concrete temperature to be between 15 ° C - 20 ° C; but this is not always the case. The concrete temperature should be minimum 5 ° C according to TS EN 206-1 standard. It is ideal if the concrete temperature is not above 32 ° C (ASTM C 94), although this standard does not have an upper limit. Generally, 1m2 of concrete surface in one hour necessary precautions if the amount of water evaporated from the area is more than 1 kg it should be taken.
Curing at 38° C for the first 24 hours as a result of researches
It has been determined that the 28-day strength of the concrete samples obtained is 10-15% lower than the normal situation (ACI 306R).
There is an inverse proportion between temperature and strength, that is, one of the main factors that directly interact with the strength of the concrete during the mixture pouring and waiting.
Concrete poured by ignoring the optimum temperature conditions
cracks caused by heat.
Precautions To Be Taken In Concrete Production
Materials should be stored in inappropriate ways. This, for example, Aggregate should be stored in the shade or must be cooled directly. Cement Silos should be insulated.
Water in insulated tanks and underground if possible it should be maintained.
It should use water cooling systems. Various alternatives on this subject are listed below, respectively.
Benna GOGCU
Mechanical Engineer