Aggregates is a broad category of coarse to very fine grained particulate material. They are used in construction or as commodity in production of many different materials. It includes sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates.
Construction aggregates are the most mined materials in the world. Aggregates are a component of composite materials such as concrete and asphalt concrete. The aggregate serves as reinforcement to add strength to the overall composite material.
Aggregates are also used as base material under foundations, roads and railroads. In other words, aggregates are used as a stable foundation or road/rail base with predictable, uniform properties (e.g. to help prevent differential settling under the road or building). They are also used as a low-cost extender that binds with more expensive cement or asphalt to form concrete.
Very fine ground aggregates also serve as fillers e.g. for mortars, in the glass industry, paint production, etc.