Which test is commonly used to determine the air content of fresh concrete?

• A. A compression-based test.
• B. The slump test.
• C. The Schmidt hammer test.
• D. The pressure method (ASTM C231) or the volumetric method (ASTM C173) as an alternative.

Answer: (D)

Air content in fresh concrete is a key factor for durability, especially inFreeze–thaw environments. To measure it, we use tests specifically designed for fresh concrete that quantify the volume of air voids. The pressure method (ASTM C231) places a concrete sample in a sealed air meter and uses pressure changes to determine how much air is present. The volumetric method (ASTM C173) uses a calibrated air meter to separate and measure the volumes of air and concrete in a known container. Either method provides a direct percentage of air content.

The other tests don’t assess air content. A compression-based test looks at how well hardened concrete resists loads, the slump test gauges workability, and the Schmidt hammer test estimates surface hardness after curing. None of these give the air void content of the fresh mix, which is why the pressure or volumetric methods are the standard choices for this measurement.