What ASTM standard is used for measuring air content in concrete?

The correct choice is based on the specific purpose of the ASTM C231 standard, which outlines the procedures for determining the air content of freshly mixed concrete using the pressure method. This method involves measuring the air that is entrained within the concrete mix, which is essential for understanding the workability and durability of the concrete. The air content is a critical factor that affects the performance of concrete in various conditions, particularly in preventing damage from freeze-thaw cycles.

Standards like ASTM C150 relate to the specification for portland cement, while ASTM C31 covers the standard practices for making and curing concrete test specimens in the laboratory. ASTM C330 deals with lightweight aggregates for structural concrete but does not address air content measurement. Therefore, ASTM C231 is the appropriate standard for this specific testing method, highlighting its importance in ensuring that the concrete meets the necessary quality requirements.