Which type of coarse aggregate is NOT mentioned as a requirement?

The selection of coarse aggregate requirements often depends on the specific application and the standards set forth in guidelines or specifications. Among the options provided, granite is often not included as a requisite type of coarse aggregate for many standard concrete mixes. This is likely due to its natural abundance and the diverse range of geological properties that different aggregates can exhibit.

In many specifications focused on concrete mixtures, aggregates like air-cooled blast furnace slag, crushed hydraulic cement concrete, and crushed gravel are more commonly addressed because of their specific properties such as lightweight, durability, and potential for recycling. These materials have demonstrated performance advantages in various contexts, making them more relevant in the discussions around concrete mixtures.

Granite, while a common and high-quality aggregate, does not typically have the same level of regulatory scrutiny in many contexts as the other materials listed. This absence underscores why it is not explicitly mentioned as a requirement in some aggregate specifications, especially those that focus on optimizing performance characteristics or addressing specific environmental concerns.