Laboratory investigation on the effects of blended crushed and natural aggregates on the fresh and hardened property of c-25 concrete

Abstract

Aggregates play a major role in determining the fresh and hardened properties of concrete. Various studies have been conducted on different types of natural coarse aggregate to determine the effectiveness of their use in concrete. Effort toward consuming locally available natural source and to investigate the engineering property of aggregate should be accepted or rejected in accordance to specification and standards has initiated the studies on river gravel as blending with crushed coarse aggregate material for the conventional concrete around the Jimma Zone and the study investigated the use of crushed stone sand as supportable alternative to natural river sand by blending together that is being conventionally used as fine aggregate in cement concrete. The research program was divided into two main phases. First: the aggregate tests were carried out in accordance with the appropriate ES, ASTM, AASHTO, ACI, and BS. During laboratory test carried out, the aggregate quality test from Bulk Density, Specific Gravity, Absorption, Aggregate Impact Value moisture content, and silt content were conducted. In the second phase, Mix Design was carried out. In each case, cubes' compressive strength test and beam flexure tests were conducted. The study showed that, blended crushed coarse aggregate with river gravel coarse aggregate at 0%, 10%, 20%, 30%, 40% and 50% and blended natural sand with manufactured sand at 0%, 10%, 20%, 30%, 40% and 50% have a compressive strength of 31.91Mpa,32.85Mpa 33.05Mpa,33.95Mpa,32.85Mpa and 30.77Mpa respectively at the age of 28 day of curing. On the other hand, at 0%, 10%, 20%, 30%, 40% and 50% blending of crushed coarse aggregate with river gravel coarse aggregate and blended at 0%, 10%, 20%, 30%, 40% and 50% natural sand blend with manufactured sand have a flexural strength 3.13Mpa, 3.14Mpa, 3.19Mpa, 3.41Mpa, 3.06Mpa and 2.93Mpa respectively at the age of 28 day of curing. In addition to this, the concrete mix having a slump value 52mm,46mm, 40mm, 32mm, 24mm, and 20mm for 0%, 10%, 20%,30%,40% and 50% blending of crushed coarse aggregate with river gravel coarse aggregate and natural sand blended with manufactured sand respectively. All percentage of the blended of river gravel coarse aggregate with crushed coarse aggregate and manufactured sand blended with natural sand satisfies the specified compressive strength of concrete (fc). But the optimum compressive strength was achieved at the blended percentage of 30%. Hence it is recommended to blend up to 30%.