For normal concreting operations the temperature of concrete should vary between 150C to 250C to enable it to attain its full ultimate strength within 28 days. In case concreting is carried out in extreme hot weather conditions, the rate of hydration of cement gets accelerated and the water in the concrete mix dries out rapidly. This in turn results in formation of stresses which cause shrinkage cracks and damage to the concrete.
The adverse effects of hot weather can be minimized by taking following precautions while concreting in extreme hot weather conditions.
1. Use Retarding Admixture
Add retarding agents in concrete to lower the rate of hydration of cement.
2. Lower the Temperature of Aggregate
Keep the temperature of concrete ingredient as low as possible. Temperature of aggregate may be lowered by stockpiling the aggregate in shaded areas and also by sprinkling cold water on the stock piles.
3. Lower the temperature of Water
Use cold water for making concrete. In certain cases, crushed ice may be used to bring down the temperature of water and to obtain concrete mix having temperature within desirable limits.
4. Fast Transporting of Concrete
The mixed concrete should be transported and placed in position within the shortest possible time, so as to minimize the losses due to evaporation and rise of temperature.
5. Sprinkling Over Formwork and Reinforcement
Sprinkle cold water over the formwork and reinforcement just before the placement of concrete. This prevents the loss of water from concrete due to absorption by these materials.
In case of construction of roads, sprinkle water over the prepared sub-grade before placing concrete.
6. Placing of Concrete at Night
Schedule the time of placing of concrete in night when the ambient temperature is very low as compared to day time.
7. Speed Up the Work
The work should be executed with utmost speed, since delays will affect the concrete adversely due to hot weather conditions.
8. Protection from Direct Sun Rays
After placing in positions, the concrete surface should be adequately protected from exposure to direct sun rays by erecting sunshades.
9. Protection from Wind
Erect wind breaks over the finished concrete surface so as to protect the concrete surface from wind.
10. Cure Continuously
The concrete should be continuously cured with sufficient water during the first few hours and thereafter the surface should be kept moist for the full duration of curing.