ACI Concrete Field Testing Technician - Grade I Practice Exam

The pressure method of determining air content can be used on concrete made with what type of aggregate?

1. Lightweight aggregate

2. Relatively dense aggregate

3. High porosity aggregate

4. Recycled aggregate

The correct answer is: Relatively dense aggregate

The pressure method of determining air content in concrete is best suited for mixtures that utilize relatively dense aggregates. This method relies on the principle that changes in air volume can be measured by the pressure exerted by the trapped air in the concrete sample. Relatively dense aggregates provide a stable matrix that allows for accurate measurements, as the density supports the containment of air bubbles without excessive pressure changes that could skew results. While lightweight aggregates can create a different air content profile due to their inherent properties, they may not yield reliable results with the pressure method due to their lower density and different structural characteristics. High porosity aggregates, on the other hand, could introduce complexities in measurement because their porous nature can significantly affect the distribution and volume of air. Recycled aggregates, though potentially usable in other contexts, may also have variable densities and surface characteristics that could complicate a consistent and accurate application of the pressure method. Thus, utilizing relatively dense aggregates is essential for achieving reliable and repeatable measurements of air content through this method in concrete mixtures.