What method would you use to measure the air content of freshly mixed concrete?

The pressure method is widely recognized for measuring the air content in freshly mixed concrete due to its accuracy and reliability. This method involves using a specific device known as an air meter, which operates on the principle of measuring the change in pressure within a sealed chamber. When a fresh concrete sample is placed in the chamber, air bubbles present in the mixture will alter the pressure readings. By comparing the initial pressure with the pressure after the sample is introduced and processed, one can accurately determine the volume of air in the concrete.

This method is particularly effective because it can assess both the total air content and trapped air, which is significant for ensuring quality and durability in concrete mixtures. The pressure method is standardized in many concrete testing procedures, making it a reliable choice for construction and quality control professionals.

In contrast, the volumetric method, while also a valid technique, relies more on the comparison of volumes to determine air content, which can be less precise than pressure readings in certain contexts. The mechanical aggression method and centrifuge method are not standard practices for measuring air content in concrete and are not recognized as practical for this purpose, which further emphasizes the correctness of using the pressure method for accurate measurements.