ACI Cold & Hot Weather Concreting 2

Question 1

When concreting in cold weather, what is the minimum concrete temperature recommended by ACI 306 for sections greater than 12 inches thick?

Accepted Answer

45°F (7°C)

Answer

ACI 306 specifies a minimum placed concrete temperature of 45°F for sections greater than 12 inches thick, as thicker sections retain heat better.

Question 2

During hot weather concreting, which admixture type is most commonly used to counteract accelerated setting?

Accepted Answer

Type B retarding admixture

Answer

Type B retarding admixtures slow the hydration reaction, offsetting the accelerated setting caused by high temperatures.

Question 3

What is the primary risk of using calcium chloride as an accelerator in cold weather concrete containing embedded steel?

Accepted Answer

It promotes corrosion of the reinforcement

Answer

Calcium chloride is a chloride-based accelerator that can initiate and accelerate corrosion of embedded steel reinforcement.

Question 4

In hot weather, why should concrete be placed as quickly as possible after mixing?

Accepted Answer

To avoid loss of slump and premature stiffening

Answer

High temperatures accelerate hydration, causing rapid slump loss and premature stiffening if placement is delayed.

Question 5

Which curing method is particularly effective in cold weather because it provides both insulation and moisture retention?

Accepted Answer

Insulating blankets with moisture underneath

Answer

Insulating blankets placed over wet burlap or plastic sheeting trap both heat and moisture, satisfying cold-weather curing requirements simultaneously.

(ACI) American Concrete Institute Concrete Finisher Practice Test

(ACI) American Concrete Institute Concrete Finisher Practice Test

ACI Cold & Hot Weather Concreting 2