How do you perform an air content test in the field, and what is a typical acceptable range?

• A. Use a moisture meter
• B. Visual determination
• C. Use a field air meter (pressure method) per ASTM C231; typical acceptable range is around 4–7%
• D. Use a cylinder test

Answer: (C)

The main idea here is verifying the amount of entrained air in freshly mixed concrete right on the job site. You do this with a field air meter using the pressure method specified in ASTM C231. In practice, you take a sample of fresh concrete, place it into the field meter, close the cap, and apply pressure. The meter uses that pressure to force out the air and then calculates how much air was present in the mix. This gives an on-site reading of air content, which is important because the tiny air voids help protect the concrete from freeze–thaw damage and influence workability and strength.

A typical acceptable range for normal-weight concrete is about 4 to 7 percent air content. If the reading is too low, durability against freezing and thawing can be compromised; if it’s too high, it can reduce strength. Other methods, like using a moisture meter, making visual judgments, or performing a cylinder strength test, don’t measure the field air content in the same direct way, which is why the field air meter per ASTM C231 is the preferred approach for this purpose.