Assessment of the compressive strength and strength activity index of cement incorporating fly ash

Abstract In recent years, the utilizations of industrial by-product as substitute for non-renewable material in cement and concrete production has received significant attention for sustainable development goals. In this study, fly ash blended cement was produced by replacing 5%, 10%, 15%, 20%, 25%, 30% and 35% by weight of Portland Cement with fly ash. In addition, the loss on ignition (LOI) content of fly ash, which used for the 20% replacement ratio, varies from 5 to 20% to assess the effect of unburnt carbon content in fly ash on the strength activity index of fly ash blended cement. The experimental results show that the addition of fly ash reduces the compressive strength of the mortar and strength activity index of fly ash blended cement at early ages. However, the presence of fly ash increases the strength of the mortar and the strength activity index of fly ash blended cement at longer ages when the fly ash replacement ratio is lower than 25%. The unburnt carbon in fly ash does not reduce the strength of the mortar and strength activity index of fly ash blended cement when its content does not exceed 20%.