Air-entraining:

Air-entraining:

• A. Increases compressive strength
• B. Decreases permeability
• C. Improves the working life of concrete
• D. Speeds up curing

Answer: (C)

Air-entraining agents introduce a large number of tiny, evenly distributed air bubbles in fresh concrete. These micro air voids act as cushions that improve the flow and cohesion of the mix, reducing friction between the paste and aggregates and helping to control segregation and bleeding. This makes the concrete easier to place and finish and, importantly for practice, keeps it workable for a longer period before it stiffens, which is what “working life” refers to. While air voids also contribute to better freeze–thaw durability, they do not speed up curing, and they are not used to increase early compressive strength (in fact, they can slightly reduce strength early on).

Air-entraining agents introduce a large number of tiny, evenly distributed air bubbles in fresh concrete. These micro air voids act as cushions that improve the flow and cohesion of the mix, reducing friction between the paste and aggregates and helping to control segregation and bleeding. This makes the concrete easier to place and finish and, importantly for practice, keeps it workable for a longer period before it stiffens, which is what “working life” refers to. While air voids also contribute to better freeze–thaw durability, they do not speed up curing, and they are not used to increase early compressive strength (in fact, they can slightly reduce strength early on).