How is the air content measured in the field for FDOT concrete?

• A. By estimating the air content from mix proportions.
• B. Using a moisture meter to assess air.
• C. With an air meter (pressure or volumetric method) per ASTM C231/C173, ensuring equipment is calibrated and test performed correctly.
• D. Measuring the air content after 7 days.

Answer: (C)

Air content is determined on fresh concrete using an air meter, following standardized procedures. In the field, there are two accepted methods: the pressure method (ASTM C231) and the volumetric method (ASTM C173). Both involve taking a representative sample of freshly mixed concrete, running the test with calibrated equipment, and calculating the percentage of air by volume. This measurement is crucial for ensuring the concrete has the proper air-void system to resist freeze–thaw damage and to ensure satisfactory durability and performance. Other options aren’t appropriate: you can’t reliably estimate air content from mix proportions, a moisture meter doesn’t measure air content, and air content is a property of fresh concrete, not something measured after several days.