North Carolina General Contractors Practice Exam

Which chemical is typically used as an accelerator when mixing concrete?

1. Sucrose

2. Calcium chloride

3. Water

4. Fly ash

The correct answer is: Calcium chloride

Calcium chloride is commonly used as an accelerator in concrete mixing because it enhances the rate at which concrete sets and develops strength. When added to the concrete mix, calcium chloride helps to accelerate the hydration process, which is particularly beneficial in colder weather when the curing process may be slowed down. By promoting faster curing, it allows projects to be completed more quickly and reduces the risk of freezing before the concrete has adequately set. The other substances listed serve different roles. Sucrose is often used as a retarder rather than an accelerator, helping to slow down the setting time in certain situations. Water is essential for mixing concrete but does not act as an accelerator. Fly ash is typically used as a supplementary cementitious material to improve long-term strength and durability but does not accelerate the strength gain in the same manner as calcium chloride. Thus, calcium chloride is specifically recognized for its accelerating properties in the context of concrete mixing.