Concrete Casting in Hot Weather Conditions (Part 1)
Hot weather is the weather condition in which the average temperature is above 30 °C for three consecutive days during concrete casting and the average temperature in our country is generally above 30 °C during the summer months (TS 1248).
Under normal weather conditions, the 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 casting temperature can be considered as 10 °C-15 °C.
Effects of Hot Weather on Fresh Concrete
Hot weather conditions should be evaluated not only as air temperature but also as a combination of ambient and concrete temperature, humidity, wind speed and solar radiation.
High wind and relative humidity affect the evaporation of water. Naturally, temperature has a great effect on the quality of fresh concrete during the mixing process, casting process and waiting process. This is due to the increase in water ratio, temperature loss, thermal cracking risk, plastic shrinkage crack rate and cold joint formation, and the decrease in setting time, durability and 28-day strength due to cracks. An unaesthetic appearance occurs due to color difference and cold joint, and permeability may increase.
It is ideal for the concrete temperature to be between 15 °C - 20 °C; however, this is not always the case. According to the TS EN 206-1 standard, the concrete temperature should be at least 5 °C. It is ideal for the concrete temperature not to exceed 32 °C (ASTM C 94), but this standard does not have an upper limit. Generally, if the amount of water evaporating in an hour on 1 m2 concrete surface is more than 1 kg, the necessary precautions should be taken.
As a result of the research, it was determined that the 28-day strength of concrete samples cured at 38°C for the first 24 hours was 10-15% lower than the normal situation (ACI 306R).
There is an inverse proportion between temperature and strength, in other words, it is one of the main factors that directly interact with the strength of the concrete during the pouring and waiting of the mixture. Cracks occur in the poured concrete when the optimum temperature conditions are ignored.
Precautions to be Taken in Concrete Production
Materials should be stored in ways that are suitable for the ambient conditions. For example, aggregate should be stored in the shade or cooled directly. Cement silos should be insulated.
Water should be stored in isolated tanks and, if possible, underground. Water cooling systems should be used as various alternatives to this issue.