In the Type IIIA designation, what does the letter A indicate?

• A. Air Entrainment
• B. Admixture
• C. Abrasion
• D. Aggregates

Answer: (A)

The A denotes air entrainment in the concrete mix. In a Type IIIA designation, this modifier shows that an air-entraining admixture has been added to create a controlled population of microscopic air voids. Those tiny voids help relieve internal pressures during freezing and thawing, improving durability and resistance to freeze-thaw damage, while also helping with concrete workability and pumpability. This is especially useful for tilt-up panels exposed to cold or wet conditions, where you want the early-strength benefits of Type III cement but with enhanced durability. The other concepts—admixtures in general, abrasion resistance, or aggregates—aren’t what the designation flags; the specific purpose of the A is to signal air entrainment.