Concept: Aggregate: ● 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 in any particular mix of concrete 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. The maximum size of coarse aggregate that can be used in a mix depends on the size, shape, and reinforcing bar of a member, It should not-to-exceed by these guidelines- a) of the clear spacing between reinforcing bar and clear cover. b) the thickness of the concrete section.