EFFECT OF FLY ASH ADDITION ON MECHANICAL PROPERTIES OF CONCRETE

Abstract

Although, the use of pulverised fuel ash (PFA) as cement replacement has been widely reported to enhance concrete durability against chemical attack, no enough information is published addressing the effect of high volume fly ash replacement on mechanical properties of concrete. Thus, the current experimental study was carried out to investigate the effect of PFA replacement (10, 25 and 50%) on mechanical properties of concrete. Performance of PFA concrete specimens was compared to specimens made with CEMI (42.5 N). Two different water to binder ratios (0.35 and 0.45) were used. Compressive and flexural strength were evaluated at 7, 28, 60 and 90 days of curing. Workability of fresh concrete mixes was assessed using slump test. The carbonation depths were also tested using 100 mm cube specimens at 90 days of curing. Replacement of cement by fly ash improves the workability of concrete, but causes a reduction in compressive strength and flexural strength of concrete. The reduction increases as the replacement by PFA increases. Replacement of cement by 50% PFA showed decrease in compressive and flexural strength by about 36 and 43 %, respectively compared to CEMI concrete mixes at 90 days.