Construction Supervisor License Practice Exam

When does concrete for a foundation need to be air-entrained?

1. A. When it is subject to freezing and thawing during construction.

2. B. When it is being placed under water.

3. C. When higher strengths are needed.

4. D. To prevent separation of aggregate during placement.

The correct answer is: A. When it is subject to freezing and thawing during construction.

Concrete for a foundation needs to be air-entrained when it is subject to freezing and thawing cycles. This is crucial for maintaining the integrity and durability of the concrete over time, particularly in climates where temperatures frequently fluctuate around the freezing point. Air-entraining agents create tiny air bubbles within the concrete mix, which provide space for water to expand when it freezes. This expansion is significant because, without these air pockets, the concrete can crack and deteriorate as the water freezes and thaws. The importance of air entrainment in freeze-thaw conditions stems from the fact that water can infiltrate the concrete. When the temperature drops and the water freezes, it expands, putting internal stress on the concrete. Air-entraining helps mitigate this risk by allowing for that expansion without causing damage to the concrete structure. In contrast, while the other scenarios presented in the options might involve specific challenges, they do not require air-entrainment for the same protective reason against the freeze-thaw cycle. For instance, placing concrete under water focuses more on flowability and curing concerns, while higher strengths are typically related to the concrete mix design rather than air content. Preventing separation of aggregate is more about ensuring proper consolidation and workability of the mix, rather