Aggregates are inert granular materials, such as sand, gravel, or crushed stone, that are essential components of concrete. These aggregates can be found in natural deposits known as pit gravel, which consist of gravel and sand that can be easily used in concrete after minimal processing. In addition, slag and recycled concrete can also be used to meet the demand for aggregates. Construction aggregate, or simply aggregate, is a broad category of coarse-grained to medium-grained particulate material used in construction.
This includes sand, gravel, crushed stone, slag, recycled concrete, and geosynthetic aggregates. These aggregates are suitable for use in street courses, highways, and other areas exposed to traffic. Aggregates also have a relatively high hydraulic conductivity value compared to most soils, making them ideal for drainage applications such as foundation drains, French drains, septic drainage fields, retaining wall drains, and roadside drains. In concrete, aggregates occupy about 70-80% of the total volume provided by the main body.
Recycled concrete aggregate is made primarily of crushed concrete and recycled aggregate contains substantial quantities of materials other than crushed concrete. To ensure that the aggregate is inert, it is manufactured from materials that have been tested and characterized according to European waste codes. The American Society for Testing and Materials publishes an exhaustive list of specifications for various construction aggregate products. Currently, only recycled aggregates made from construction or demolition waste are recommended for use in new concrete construction. These products include specific types of coarse-grained and fine aggregates designed for uses such as additives for asphalt and concrete mixes, as well as other uses in construction.
When stone, sand, and gravel are not available, construction demand is generally met by shipping aggregates by rail, barge, or truck.