When does the amount of entrapped air in concrete increase?

The correct answer is that the amount of entrapped air in concrete increases as aggregate size decreases. This relationship occurs because smaller aggregate particles create more surface area relative to their volume, which can lead to increased air entrainment during the mixing process. When the aggregate is smaller, it allows for more voids and spaces that can trap air, as the particles can fit more tightly together with gaps in between.

In contrast, larger aggregates tend to reduce opportunities for air to be entrapped within the mix since they do not leave as many spaces. Also, smaller aggregates may promote a more homogeneous mix that can trap air bubbles more effectively.

Other options relate to factors that influence air content in different ways. Increased water content can lead to a higher water-to-cement ratio, which might change the way air behaves in the mix, but it does not necessarily correlate with an increase in entrapped air. Curing time is related to the hydration process of the cement and does not inherently impact the entrapped air that was present during mixing. Lastly, while higher slump indicates a wetter mix, this too does not directly imply that there will be an increase in entrapped air as it depends more on the overall mixing process and aggregate size. Thus, the most direct influence on