Aggregate is a material used in building and construction to mix with cement, bitumen, lime, gypsum, or other adhesive to form concrete or mortar. It provides bulk, stability, wear or erosion resistance, and other desired physical properties to the finished product. Aggregates are composed of large and coarse-grained particles that form the basic structural members of concrete. The gaps between the larger particles are filled with smaller particles, and the voids between the smaller particles are filled with even smaller particles.
Finally, the gaps between the finer grains are filled with cement. The better the aggregate is classified (i.e., the better the particle size distribution), the more solidly all the voids will be filled and the denser and stronger the concrete will be. Aggregates help make concrete mixes more compact and reduce the consumption of cement and water, contributing to the mechanical strength of concrete. In general construction, aggregates are used to provide drainage, fill voids, protect pipes, and provide hard surfaces.
They are also used in water filtration and wastewater treatment processes. Water will seep through a ditch filled with aggregates more quickly than through the surrounding soil, allowing surface water to drain from an area. This technique is often used along roads to disperse water collected from the asphalt surface. The purpose of aggregates within this mixture is to provide a rigid skeletal structure and reduce the space occupied by the cement paste.