Which test method does ASTM C173 describe?

The correct answer is the Standard Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method, as outlined in ASTM C173. This method specifically addresses how to measure the air content in freshly mixed concrete using a volumetric approach, providing a way to ensure that the concrete mix contains the appropriate amount of air for optimal strength and durability.

This testing method is vital in concrete construction because the air content of a mix can significantly affect its workability, strength, and overall performance. By utilizing the volumetric method described in ASTM C173, engineers and builders can accurately determine the air content, which is crucial for meeting the specifications required for various applications, particularly in areas susceptible to freezing and thawing cycles.

The other options pertain to different aspects of concrete testing. For instance, the measurement of temperature or compressive strength focuses on other critical parameters but does not relate to air content specifically. Therefore, while they are important in the overall assessment of concrete, they do not align with the specific description provided in ASTM C173.