ASTM C231/C231M pertains to which aspect of freshly mixed concrete?

ASTM C231/C231M specifically covers the determination of air content in freshly mixed concrete using the pressure method. This standard is vital for ensuring that the correct amount of air is entrained in concrete, which can significantly affect its durability, strength, and resistance to freeze-thaw cycles. The pressure method involves applying pressure to a concrete sample to measure the volume of air it contains, thus providing an indication of the concrete's air content.

In the context of concrete quality and performance, understanding the air content is essential because excess or insufficient air can lead to issues like reduced strength or increased susceptibility to weathering. Thus, the correct identification of this standard's purpose is critical for professionals working with concrete to ensure they adhere to industry standards for high-quality construction materials.