In an F3 exposure situation, what is the target air percentage for a concrete mixture with a ¾ in. maximum aggregate size?

In an F3 exposure situation, the target air content for a concrete mixture with a maximum aggregate size of ¾ inch is set to ensure durability, especially in environments susceptible to freeze-thaw cycles and the presence of de-icing salts. The American Concrete Institute (ACI) and other relevant standards designate a target air content percentage to provide adequate concrete performance under these conditions.

For larger aggregate sizes, the required air content generally decreases because larger aggregates have fewer voids, and thus less air is needed to achieve the specified level of resistance to freezing and thawing. With a maximum aggregate size of ¾ inch, the target air content is typically around 6%. This percentage helps to create an ideal microstructure within the concrete that enhances its ability to resist damage from freeze-thaw cycles, while also balancing workability and strength.

Choosing 6% as the target air content aligns with industry standards for F3 exposure conditions. Higher or lower percentages would not provide the optimal balance needed for both durability and performance. The other options—4%, 8%, and 10%—are either too low or too high for this specific exposure classification and aggregate size, potentially compromising the concrete's effectiveness in resisting environmental stresses.