154141Coarse Aggregate

Some important properties like crushing strength, the maximum size, flake, and elongation indices should be carefully controlled while selecting the aggregate for HPC. As the tensile strength of concrete is of prime importance, it is necessary to reduce the flaky and elongated particles to reduce the weaker zones in the concrete. This is achieved by screening the aggregate through specially designed sieves.

Strict control of coarse aggregate strength is important for HPC. HPC possesses good interfacial bonds between the coarse aggregate and the cement matrix, resulting in the fracture crack usually passing through the aggregate, rather than the interfacial zone under the loading. The aggregate strength typically determines the final strength of HPC. Thus, when making HPC, the aggregate compressive strength should not be less than the required compressive strength of HPC.

Many studies have shown that crushed stone was preferable in HPC than rounded gravel. The most likely reason for this is the greater mechanical bond that can develop with angular particles. The ideal aggregate should be clean, cubical, angular, 100% crushed aggregate with a minimum of flat and elongated particles.

Equidimensional particles from crushing of either dense limestones or igneous rocks, of plutonic type (viz., granite, syenite, diorite, gabbro, diabase) are generally satisfactory as coarse aggregate.

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