North Carolina General Contractors Practice Exam

What is air entrainment in concrete?

1. Adding small bubbles to improve freeze expansion

2. Reducing water content for a denser mix

3. Incorporating fibers for added strength

4. Using high temperatures to accelerate setting

The correct answer is: Adding small bubbles to improve freeze expansion

Air entrainment in concrete refers to the intentional inclusion of tiny air bubbles in the mix. This process is crucial because it enhances the concrete’s resistance to freeze-thaw cycles, which can otherwise lead to cracking and deterioration. The small air bubbles created through air-entraining agents provide space for water within the concrete to expand when it freezes, minimizing internal stress and allowing the material to perform better in harsh conditions. By improving freeze expansion capabilities, air-entraining concrete significantly prolongs the lifespan and structural integrity of concrete in environments subject to temperature fluctuations. This is particularly beneficial in northern climates where freezing and thawing cycles are common. The other options discuss different enhancements or techniques related to concrete but do not pertain to air entrainment. Reducing water content leads to a denser mix but doesn't specifically add air bubbles; incorporating fibers indeed adds strength but is unrelated to air entrainment; and using high temperatures addresses setting times rather than the bubble inclusion aspect that defines air entrainment.