Aggregate is a broad category of coarse to medium grained particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates. Aggregates are the most mined materials in the world. The usual range employed is between 9.5mm and 37.5mm in diameter. Fine aggregates are usually sand or crushed stone that are less than 9.55mm in diameter.
Typically the most common size of aggregate used in construction is 20mm. A larger size, 40mm, is more common in mass concrete. Aggregate occupies most of the volume of the concrete. It is the stuff that the cement paste coats and binds together.