Good quality aggregate must be clean, hard, strong, and have durable particles that are free of absorbed harmful chemicals, clay coatings, or other contaminants that can affect cement hydration or reduce paste-aggregate bonding. The size and shape of the aggregate particles are important for the amount of cement required in the concrete mix and, therefore, the economics of the concrete. To prepare an economical concrete mix, it is recommended to use the largest feasible coarse-grated aggregates for the structure. According to IS-456, this is the best way to decide the maximum size of coarse-grained aggregate to be used in the mix of P, C, C & R, C, C.
The shape and size of the aggregate particles have a greater influence on the properties of freshly mixed concrete than those of hardened concrete. The development of a strong bond between the aggregate particles and the cement paste depends on the surface texture, surface roughness and surface porosity of the aggregate particles. Specific gravity values are also used when designing the concrete mix. The bulk density of aggregates is determined by three factors.
Voids between aggregate particles are known as voids. The void volume is equal to the difference between the gross volume of the aggregate mass and the volume occupied by the particles alone. Depending on the amount of moisture content in the aggregates, it can exist under any of four conditions.