Which of the following problems are observed during the pouring of freshly prepared concrete in hot weather?

(i) Rapid rate of hydration of cement

(ii) Quick setting and early stiffening

(iii) Greater plastic shrinkage

(iv) More finishing times

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.

1. High ambient temperature (more than 35° C)
2. High concrete temperature
3. Low relative humidity
4. High wind speed

Hot Weather effects on concreting:

• Increased water demand for required consistency.
• Quick setting and early stiffening
• Rapid evaporation of mixing water
• Rapid slump loss.
• Increased plastic shrinkage.
• Difficulty in control of entrained air
• Rapid rate of hydration of cement.
• Minimal finishing time

Additional Information

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.

1. Concrete can freeze before it gains strength which breaks up the matrix
2. 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.
3. 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.

Cold weather effects on concreting:

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