What is the test used to determine the air content in concrete?

The Pressure Method is the correct test used to determine the air content in concrete because it measures the volume of air within a concrete mix by utilizing a pressure chamber. This method is based on the principle that when a sample of concrete is placed in a chamber, the air bubbles within the concrete will compress when the pressure is applied. The change in volume allows for the calculation of the air content, providing critical information for ensuring the desired workability and durability of the concrete.

In contrast, the other tests listed serve different purposes: the Impact Test evaluates the toughness of materials; the Compression Test assesses the strength of concrete; and the Aggregate Test focuses on the properties of the aggregates used in the mix. Thus, while all these tests are valuable in the context of concrete and construction, the Pressure Method is specifically designed for measuring air content.