Which types of aggregates are commonly used in base layers?

The selection of crushed stone, gravel, sand, and recycled aggregates as commonly used materials in base layers is based on their properties and performance in construction. These materials are selected for their ability to provide stability, strength, and drainage capabilities in the base of pavements and similar structures.

Crushed stone is particularly valued because it interlocks well and provides a solid foundation due to its angular shape. Gravel, being more rounded, offers good drainage while still providing some support. Sand can fill voids in these aggregates and enhances compaction. Recycled aggregates, often sourced from demolished structures, are increasingly being utilized due to sustainability concerns and can offer comparable performance to virgin materials when processed correctly.

In contrast, the other options include materials that are typically unsuitable for use in base layers. Steel and concrete are not aggregates used in this context, as they are structural materials rather than fill materials. Clay and silt possess fine particles that retain water, leading to poor drainage and potential instability when used in base layers. Lastly, wood and organic matter can decompose over time, leading to settlement and instability, making them inappropriate for such applications.