North Carolina General Contractors Practice Exam

Which substance is commonly used as a retarder in concrete mixing?

1. Sucrose

2. Calcium chloride

3. Gypsum

4. Sand

The correct answer is: Sucrose

Sucrose is commonly used as a retarder in concrete mixing because it helps to delay the setting time of the concrete. Retarders are particularly useful in hot weather or when delays are anticipated between mixing and pouring, allowing for greater workability and preventing the mix from hardening too quickly. By slowing down the hydration process, sucrose allows for more time to place and finish the concrete, which can lead to improved quality and performance of the cured concrete. Calcium chloride, while it can be used to accelerate the setting time of concrete, serves a different function than retarders do. Gypsum is primarily used in cement to control the setting time but is not typically added directly to concrete as a retarder. Sand, being an aggregate component, does not have a role in altering the setting characteristics of concrete itself, hence it is not related to the retarding properties necessary for mixing.