What type of aggregates is unsuitable for the pressure method used in determining air content?

High porosity aggregates are unsuitable for the pressure method used in determining air content because they can trap air within their porous structure. This entrapment can lead to inaccuracies in the measurement of air content, as the air bubbles within the aggregates themselves might not be accounted for in the overall mixture volume. The pressure method relies on measuring the volume of air that can be displaced, aiming for a clean and reliable read on the air content in the concrete or aggregate sample.

When dealing with high porosity aggregates, the inherent nature of their structure complicates the measurement process. Ideally, aggregates used in this method should not contain numerous voids that could interfere with the accurate measurement of air content. Other types of aggregates, such as those that are fully saturated or those that have small particle sizes, might still be manageable under this testing method, as they do not present the same challenges associated with air entrapment as high porosity aggregates do. Heavy aggregates, while having their own specific characteristics, do not fundamentally alter the parameters for obtaining accurate air content readings through the pressure method.