The size and shape of the aggregate particles have a major influence on the amount of cement needed in a concrete mix, and thus, its economy. To create an economical concrete mix, it is recommended to use the largest feasible coarse-grained aggregates for the structure, as suggested by IS-456. It is important to note that the shape and size of aggregate particles have a greater impact on the properties of freshly mixed concrete than those of hardened concrete. The strength of the bond between aggregate particles and cement paste depends on their surface texture, roughness, and porosity. Specific gravity values are also taken into account when designing a concrete mix.
The bulk density of aggregates is determined by three factors. The voids between aggregate particles are known as voids. The vacuum 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 moisture content in aggregates, they can exist in any of four conditions.
Crush strength, impact value, abrasion resistance, and elastic modulus of aggregate are interrelated properties that are greatly affected by porosity. Aggregates from natural sources used to make normal weight concrete are usually dense and strong, so they rarely limit the strength and elasticity properties of concrete. This is a summary of the most important factors to consider when selecting and dosing concrete aggregate. The aggregate acts mainly as an inert filler, but has secondary influences on various properties of concrete and mortar. To produce good quality, durable concrete containing recycled concrete aggregate, it is often necessary to test concrete mixes and closely monitor the properties of old recycled concrete, making adjustments to the mix as needed.
Aggregate is usually considered an inert filler, accounting for 60-80% of the volume and 70-85% of the weight of concrete. The mineralogical composition of aggregate affects its crushing strength, hardness, elastic modulus, and solidity, which in turn affect various properties of hardened concrete containing this aggregate. The selected aggregate parts are embedded in a circular test device for road wheels and then contacted with a loaded and rotating rubber tire. The shape and texture of aggregate affect properties of fresh concrete more than hardened concrete. Understanding the role that aggregate plays in concrete and mortar can be essential for achieving desired properties in high-performance yet economical mixes. For effective performance, aggregates must have sufficient physical properties to withstand external and internal physical forces.
Due to considerable overlap between them, it is more appropriate to divide the study of aggregate properties into three categories based on microstructural and processing factors. Other physical and mineralogical properties of aggregate must be known before mixing concrete to obtain a desirable mix. These different aggregate properties give designers and contractors maximum flexibility to meet their design and construction requirements. However, due to increasing awareness of the role that aggregates play in determining many important properties of concrete and mortar, traditional view of aggregate as an inert filler is being questioned. Alternative sources of aggregates or additional aggregate mixtures can be considered to approach the ideal gradation that provides optimal workability, pumpability, shrinkage reduction, and economy (Figure).