Aggregate is a term for any particulate material. It includes gravel, crushed stone, sand, slag, recycled concrete, and geosynthetic aggregates. Aggregate may be natural, manufactured or recycled. Aggregates make up some 60 -80% of the concrete mix. They provide compressive strength and bulk to concrete.
Aggregates are selected for their durability, strength, workability and ability to receive finishes. For a good concrete mix, aggregates need to be clean, hard, strong particles, free of absorbed chemicals or coatings of clay, and other fine materials that could cause the deterioration of concrete.
Aggregates are divided into either coarse or fine categories.
- Coarse aggregates are particulates that are greater than 4.75m. The usual range 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. Larger aggregate diameters reduce the quantity of cement and water needed.