MECHANICAL PROPERTIES OF CONTROL AND FLY ASH BLENDED CONCRETE USING COAL WASHERY REJECTS AS PARTIAL REPLACEMENT OF COARSE AGGREGATE

During coal washing process, large quantities of impurities so called coal washery rejects (CWR) are getting accumulated and posing disposal problems. As the construction industry is the feasible application to reuse waste materials, this investigation is mainly intended to study the mechanical properties of control concrete (CC) and fly ash (FA) blended concrete using coal washery rejects (CWR) as partial replacement of coarse aggregate. In M 25 grade of CC, CWR was used at different replacement levels (0%, 20%, 30%, 40% and 50%). For these replacement levels, compressive, splitting tensile, flexural, bond strength and modulus of elasticity properties were determined at different curing periods and compared to M 25 grade of CC. It is observed that the increase of CWR replacement level decreased the mechanical properties of CWR based concrete. Slight decrease in compressive strength was observed up to 30% of CWR replacement. But beyond 30%, the decrease was very much significant. As 28 days compressive strength of 30% CWR concrete is nearer to that of M 25 grade CC, the 30% CWR (CWR_30) was considered as optimum concrete. To enhance the strength and durability properties, fly ash was used in CWR_30 concrete at different replacement levels of cement (10%, 20% and 30%). Though the decreasing trend was observed with the increasing fly ash replacement, the mechanical properties of FCWR based concrete up to 20% were slightly higher than that of CWR_30 concrete at 28,56 and 112 days. Whereas, the mechanical properties of 30% FCWR based concrete were slightly less that of CWR_30 concrete at 28, 56 and 112 days, but these values are comparable to CWR_30. From the results, it is concluded that the concrete mixes FCWR_20 and FCWR_30 can be recommended sustainable M 25 grade of concrete