Good quality aggregate must be clean, hard, strong, and have durable particles. It should also be free of any absorbed harmful chemicals, clay coatings, or other contaminants that could affect cement hydration or reduce paste-aggregate bonding. The size and shape of the aggregate particles play an important role in the amount of cement required in the concrete mix and, consequently, the economics of the concrete. IS-456 recommends using the largest feasible coarse-grained aggregates for the structure when preparing economical concrete mixes.
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 taken into account when designing the concrete mix. The bulk density of aggregates is determined by three factors.
Void spaces 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.