Hot air is the weather in the period when the average temperature is more than 30 ° C for three days in the pouring of concrete (TS 1248) and in general in most regions in our country, the temperature averages are above 30 ° C. In normal weather, 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 estimated as +5 ° C. The optimum concrete casting temperature can be accepted as 10 ° C-15 ° C.
Effects of Hot Air on Fresh Concrete
It is necessary to consider hot weather conditions not only as air temperature but also as a combination of ambient and concrete temperature, humidity, wind speed, and solar radiation.
The evaporation of water affects the high-temperature wind and the relative humidity naturally has a great effect on the process of casting and the waiting process of the mixed process to the quality of the fresh concrete of the temperature. This is due to the increased risk of water, the loss of consistency, the risk of thermal cracking, the risk of forming plastic shrinkage cracks, and the risk of cold joint formation, while the durability and durability due to cracks, durability, and 28-day durations decrease. Due to color difference and cold joint, a non-aesthetic image is formed and permeability may increase.
Concrete Temperature-Thickness Relationship
It is ideal for the concrete temperature to be between 15 ° C and 20 ° C, but this is not always the case. The concrete temperature should be at least 5 ° C according to TS EN 206-1 standard. It is ideal that the concrete temperature does not exceed 32 ° C (ASTM C 94) even if this standard is not an upper limit. Generally, if the amount of water that evaporates from 1m² of concrete surface in one hour is more than 1kg, necessary precautions should be taken.
As a result of the researches, it was determined that the 28 days strengths of the concrete samples cured at 38 ° C for the first 24 hours were lower than -15 (ACI 306R).
Temperature-Resistance Relation The temperature-strength relationship between the above-cured graphs is given. As can be seen here, there is an inverse relationship between temperature and resistance, ice temperature is one of the main factors that directly interact with the strength of the concrete during casting and waiting.
Precautions for Concrete Production
The material should be stocked in inappropriate ways. For example, the aggregate should be stocked in the shade or cooled directly. Cement silos should be isolated.
Water should be stored in sealed tanks and, if possible, underground.
Water cooling systems should be used. Various alternatives are discussed below.
Concrete Cooling Systems
The water cooling system can reduce the water temperature up to 8 ºC. This system is generally preferred in the regions where the temperature is up to 30 ºC in the mid-climate zone. Water cooling systems are the most commonly used water cooling system for low cost and ease of use.
Ice machines are available in different ways. The ice produced in the manual type ice machines is added to the water tank at the concrete plant and the water is cooled. This type of machinery is high in labor but low cost and can be preferred. In Ice Type Ice machines, the ice produced is transferred directly to the concrete mixer, where the concrete is cooled by mixing with other materials. It is an efficient and professional cooling system but the most cost-effective system.
Ice Water Plant;
The new generation is the latest technology cooling system. It can reduce the amount of concrete to be used in high amounts up to 0,5 ºC. Suitable for use in climates where the air temperature rises to 50 ° C. It is fully automatic and full-time. Concrete 45 is connected to the water tank in the power plant where it cools the water. With its average cost, ease of use, and high performance, it is used in many concrete batching plants with high importance.
Measures to be Taken in Concrete Casting
The concrete temperature must be checked continuously. Excessive vibration should not be made. Casting should be carried out as soon as possible. The finishing process should be done immediately when there is no sweaty water on the surface.
Concrete casting is carried out at the lowest possible temperatures during the day.
Effect of Material Temperatures
According to the above table, the concrete temperature is 31.8 ºC according to the heat energy formula.
(Q = m.c. yapılT) What to do for a degree drop:
The cement temperature should be reduced to 2515/308 = 8.2 ºC, or;
The water temperature should be reduced to 2515/515 = 4.9 ºC, or;
The aggregate temperature should be reduced to 2515/1692 = 1.5 ºC.
What is the socket's time?
Receive socket; solidification of concrete and mortars. It is a construction term. According to this; The time of setting the fresh concrete in cold weather conditions is longer in normal temperature conditions compared to the time of setting of concrete,
Prepared by: Mr. Benna Gogcu Mechanical Engineer Linkedin: https://www.linkedin.com/in/benna-g%C3%B6%C4%9Fc%C3%BC-64a506177/
