Hot Weather Concreting

 Hot Weather Concreting - Any operation of concreting done at atmospheric temperatures above 40°C or any operation of concreting (other than steam curing) where the temperature of concrete at time of its placement is expected to be beyond 40°0.

Effects Of Hot Weather On Concrete : Effects of hot weather on concrete, in the absence of special precaution, may be briefly described as follows:

a) Accelerated Setting - High temperature increases the rate or setting of the concrete. The duration of time during which the concrete can be handled is reduced. Quick stiffening may necessitate undesirable retempering by addition of water. It may also result in cold joints.

b) Reduction in strength - High temperature results in the increase of the quantity of mixing water to maintain the workability with consequent reduction in strength.

c) Increased tendency to crack - Either before or after hardening plastic shrinkage cracks may form in the partially hardened concrete due to rapid evaporation of water. Cracks may be developed in hardened concrete either by increased drying shrinkage resulting from greater mixing water used or by cooling of the concrete from its elevated initial temperature.

d) Rapid Evaporation of Water during curing period - It is difficult to retain moisture for hydration and maintain reasonably uniform temperature conditions during the curing period.

e) Difficulty in Control of air content in air-entrained concrete -It is more difficult to control air content in air-entrained concrete. This adds to the difficulty of controlling workability. For a given amount of air-entraining agent hot concrete will entrain less air than concrete at normal temperatures.

Temperature control of concrete ingredients and concrete:

1. Shading stockpiles from direct rays of the sun.

2. If cold water is available, heavy spraying of coarse aggregate immediately before use may also be done to have a direct cooling action.

3. The use of cold mixing water will effect a moderate reduction in concrete placing temperatures.

4. The effect of mixer surface exposed to sun should be minimized by painting mixer drum yellow or white and spraying it with cool water.

5. Form, reinforcement and sub grade shall be sprinkled with cooled water just prior to placement of concrete

6. Concrete placement may be restricted to the evening or night when temperature is lower and evaporation is less.

7. Immediately after consolidation and surface finish concrete shall be protected from evaporation of moisture.