When it comes to creating a concrete mix that is both economical and high-performing, selecting the right aggregates is key. The size and shape of the aggregate particles have a major influence on the amount of cement required in the mix, and therefore, on the economy of the concrete. According to IS-456, the maximum size of coarse-grained aggregate to be used in the mixture should be determined based on recommendations. It is important to note that the shape of the aggregate particles has a greater impact on the properties of freshly mixed concrete than on those of hardened concrete. The bond strength between the aggregate particles and the 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: voids, vacuum volume, and moisture content. Void spaces between aggregate particles are known as voids, while 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 amount of moisture content in the aggregates, they can exist under any of four conditions. The physical properties of aggregates must be substantial enough to withstand external and internal physical forces.
Crush strength, impact value, abrasion resistance, and elastic modulus of the aggregate are all interrelated properties that are greatly influenced by porosity. Aggregates from natural sources that are commonly used to make normal weight concrete are usually dense and strong; therefore, they rarely limit the strength and elasticity properties of concrete. To be effective, aggregates must have substantial physical properties to withstand external and internal physical forces. 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.
Awareness of the role that aggregate plays in concrete and mortar can be fundamental to exploiting them to achieve high-performance and economical results. The selected aggregate parts are embedded in a circular test device for road wheels, and then contacted with a loaded and rotating rubber tire. However, due to increased awareness of how aggregates affect many important properties of concrete and mortar, their traditional role as inert fillers is being questioned. Aggregate is usually considered an inert filler, accounting for 60-80% of the volume and 70-85% of the weight of concrete. To produce good quality, durable concrete containing recycled concrete aggregate, test concrete mixes and close control of recycled concrete properties are often required, with mix adjustments made as needed. Alternative sources of aggregates or additional aggregate mixtures can be considered to approach an ideal gradation that provides optimal workability, pumpability, shrinkage reduction, and economy (Figure).
These different aggregate properties allow designers and contractors greater flexibility to meet their design and construction requirements. Other physical and mineralogical properties of the aggregate must be known before mixing concrete to obtain a desirable mix. Although aggregates are known to be inert fillers in concrete, their different properties have a major impact on strength, durability, workability, and economy. Due to considerable overlap between them, it is more appropriate to divide study of aggregate properties into three categories based on microstructural and processing factors.
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