What factors influence the need for air-entraining agents in concrete?

• A. Required air void content for durability (freeze-thaw resistance), workability, and exposure conditions
• B. Color of aggregates
• C. Temperature of mixing water
• D. Time of day

Answer: (A)

The need for air-entraining agents comes from establishing a controlled network of tiny, well-dispersed air voids in concrete to meet durability and workability requirements under the given exposure conditions. These microscopic air voids provide space for water to expand during freeze-thaw cycles, which reduces internal stresses and cracking that would otherwise occur in climates with freezing temperatures. The amount, size, and distribution of these air voids must be carefully balanced: too few won't protect against freeze-thaw damage, while too many can lower strength and hinder workability. The exposure environment—such as cycles of wetting and drying or the presence of deicing salts—drives how much air void content is needed to maintain performance. Color of aggregates, temperature of mixing water, and time of day do not determine the need for air-entraining agents.