Question

Consider below statements. Identify the correct statement(s) with respect to hot and cold weather concreting.

• A. In cold weather concreting, the delay in setting time makes concrete more resistant to frost attack.
• B. Hot weather condition is normally associated with relatively lower relative humidity.

1. Both the statements are true
2. Statement A is true, but B is false
3. Both the statements are false
4. Statement B is true, but A is false

Answer 1

Correct Answer - Option 4 : Statement B is true, but A is false

Concept:

Hot Weather Concreting: Hot weather concreting is defined by ACI 305 as one or a combination of the following conditions that tend to impair the quality of freshly mixed or hardened concrete by accelerating the rate of moisture loss and rate of cement hydration.

• High ambient temperature (more than 35° C)
• High concrete temperature
• Low relative humidity
• High  wind speed

​Cold Weather Concreting: Cold Weather Concreting is defined by ACI 306 as a period when for more than three successive days the average daily air temperature drops below 4°C. There are two main problems with pouring concrete in cold winter weather.

• Concrete can freeze before it gains strength which breaks up the matrix
• Concrete sets more slowly when it is cold - very slow below 10°C; below 4°C the hydration reaction basically stops and the concrete doesn't gain strength.
• Unless concrete gains sufficient strength, it cannot resist freezing and thawing action. Hence delay in setting time doesn't make concrete more resistant to frost attack.

Hot Weather effects on concreting:

• Increased water demand for required consistency.
• Rapid evaporation of mixing water
• Rapid slump loss.
• Increased plastic shrinkage.
• Difficulty in control of entrained air.
• Possible "Cold joints".

Cold weather effects on concreting:

• Low Concrete Strength.
• Increased permeability of concrete.
• "Cold joints" formation.