Effect of Water-Cement Ratio on the Mechanical Properties of Blended Cement Containing Bottom Ash and Limestone

Abstract

This paper presents investigation on the effect of water requirement on compressive/ flexural strength of hardened cement mortar of ordinary portland cement (OPC) blended with 10% Limestone (L) and 10% coal bottom ash (BA) by weight  ( 80C- 10L-10 BA). The water-cement ratio is one of the most important parameters that affect the performance (mechanical properties) of mortar, thus obtaining the best water requirement translates to the best mechanical properties. Class C bottom ash and Limestone (L) were used to partially replace Portland cement at 10% each by weight. The blended cement containing limestone and coal bottom ash and OPC were prepared at different water-cement ratios ranging from 0.35 to 0.55. Mortar mixtures were prepared for the blended cement and OPC control. 2, 7, 28, 60 days-compressive and flexural strengths of the mortar mixtures were determined. The strength results were compared to those of OPC and relative strengths are reported. It was observed that the compressive/flexural strength in comparison with the OPC control at water-cement ratio w/c = 0.4 was equivalent while at 0.45 and 0.50, the compressive strength experienced a reduction followed by compressive strength increment at 0.55. This can be attributed to the slow nature of the pozzolanic reaction which did not show effect until the water-cement ratio reached 0.55. But after 7 days, the pozzolanic reaction showed its effect with increment in flexural and compressive strength all through. At 28 days the compressive and flexural strengths were 40.85MPa and 9.34MPa respectively which were higher than OPC control for compressive and flexural strength of 33.85MPa and 8.92MPa respectively. It was observed that as the water-cement ratio was increased from 0.40 to 0.55 both blended cement and the control experienced increment in the compressive and flexural strength.

Keywords: Compressive / Flexural strength, Water-cement ratio, Bottom ash, Limestone, Ternary cement