Aggregate is a composite material that is used in construction and consists of inert materials such as sand, gravel, crushed stone, slag and recycled aggregates. It is the most important and economical factor in building materials to increase their strength, distribute the load and increase the volume of concrete. Aggregates represent between 60 and 75% of the total volume of concrete and are available in almost ready-to-use form from natural resources. The properties that define the quality of the aggregate are of crucial importance for its use.
These properties depend on the bedrock, which can be igneous, sedimentary or metamorphic. The aggregate comprises large chunks of material in a composite, commonly coarse-grained gravel or crushed rocks and fine materials. For greater workability and economy, as reflected in the use of less cement, the fine aggregate must have a rounded shape. Fine aggregate generally consists of sand, crushed stone, or crushed slag screens; coarse-grained aggregate consists of gravel (pebbles), broken stone fragments, slag, and other coarse-grained substances.
Aggregates should be clean, hard, and free of absorbed chemicals or coatings of clay and other fine materials when added to cement to obtain a good concrete mix. The purpose of fine aggregate is to fill the voids in the coarse-grained aggregate and act as a workability agent. It is this type of aggregate which is used in standard proportions of performance in heavy weight concretes. Recycled aggregates are also used as a partial substitute for natural aggregates in composite materials. Aggregate is used in buildings and constructions to be mixed with cement, bitumen, lime and gypsum to make concrete or mortar.
In those situations, if not readily available, suitable rock types are crushed to the desired particle sizes to produce coarse-grated aggregates.