Suitability of Crushed Sand as Fine Aggregate in Concrete

Abstract

As the main construction material concrete is, there are several aspects of it which should be assessed to make the concrete quality better and also to solve the pertaining problems in the field of concrete production. For example, the production of constituent materials of concrete like cement, aggregate, fly ash and construction chemicals, quality and durability, construction technology, maintenance, sustainability, skill development, research & development, etc.

The strict environmental laws are restricting mining of river sand. Due to that it became necessary to transport the natural sand from longer distance. It will lead to add energy cost. In most of the states, mining of river sand is restricted or banned. There will be presence of inorganic salts of chloride & sulphate and other organic salts and impurities in natural sand. Due to presence of the chloride and sulphate salts, strength and durability properties of concrete as well as reinforcement are affected adversely resulting in shorter life of structure. The amount of salt is further increased in rainy season.

Rock crushed to the required grain size distribution is termed as crushed sand or Manufactured sand (M-sand). In order to arrive at the required grain size distribution the coarser stone aggregates are crushed in a special rock crusher and some of the crushed material is washed to remove fines.

Generally the crushed sand contains high fines, whereas lesser amount of clay and silt. Rock dust is the major component of these fines. The effects of particle texture and shape of fine aggregates are more predominant than effects of coarse aggregates in concrete. Better interlocking of particles can be achieved by using angular shape of fine aggregates, which could lead to improvement in strength of cement concrete. The crushed sand possesses high angularity and when used in cement concrete produces less workability due to increased surface area. Dosage of admixtures as per manufacturers recommendations are not much effective in manufactured sand mortars, as in case of mortars with natural sand fine aggregates, which even when used in high dosages, failed to attain the flowability or air content observed in natural sand mortar.

From work carried out till the date, it is observed that the workability of concrete is tend to reduce as the percentage replacement of natural sand by crushed sand is increase. It maybe due to the presence higher amount of fine particles in the crushed sand than natural sand.

The results of compressive strength test has indicated that replacing the natural sand by half of the volume by crushed sand can lead to increment in compressive strength of concrete. But beyond the half amount of volume, compressive strength is tend to reduce than that of the control concrete.