Cement Replacement by Fly Ash in Concrete

The potential for using fly ash as a supplementary cementitious material in concrete has been known almost since the start of the last century. Historically, fly ash has been used in concrete at levels ranging from 15% to 25% by mass of the cementitious material component. The actual amount used varies widely depending on the application, the properties of the fly ash, specification limits, and the geographic location and climate. There has been lot of research took place over using fly ash as additive in cement, admixture in concrete and cement replacement material in concrete. But most of the research has been limited to few percentages of cement replacement for concrete of fewer grades. An experimentation program is carried out to see the effect of fly-ash on compressive strength of different high grades concrete for different proportions of fly ash and different curing periods. Different grades of concrete mixes with varying percentage of fly ash content were prepared and the effects of fly ash on mechanical properties of fresh and hardened concrete have been investigated. The compressive strength of concrete was measured for 7, 28 and 45 days and compaction factor is taken as a measure of workability. A different comparative study is done consisting of rate and strength as parameters. Compressive strength of concrete at different proportions of cement being replaced by fly ash has been checked and results have been found effective and applicable. Hence, a comparative study is done and use of fly ash as a cement replacement in concrete can be analyzed and compared. The paper aims to study the effects of Fly ash as partial replacement of cement in concrete and ascertain the optimum proportion of fly ash for different grades of concrete which is acceptable, applicable and economical. This paper studies the variation in compressive strength of different grades of concrete at different percentages of fly ash and at different curing periods.