EFFECT OF RICE HUSK ASH ON COMPRESSIVE STRENGTH AND WORKABILITY OF CONCRETE

Abstract

Concrete is the most widely used construction material globally, but its production relies heavily on Portland cement, contributing to significant CO₂ emissions and creating a substantial environmental burden. Rice husk ash (RHA), an abundant agricultural by-product with high silica content and pozzolanic potential, presents a promising opportunity for partial cement replacement, offering environmental and economic benefits. This study investigates the partial replacement of cement with RHA in concrete mixes, evaluating its effect on compressive strength and workability. Replacement levels were limited to 0%, 2%, 4%, and 6% by weight, as higher RHA contents require increased burning to produce sufficient ash, raising processing costs and offsetting the economic benefits of this substitution. Concrete specimens were cast at each replacement level and tested for compressive strength at 7 and 28 days. Compressive strength decreased gradually with increasing RHA content: the 28-day strength for control, 2%, 4%, and 6% replacement levels was 21.73 MPa, 20.03 MPa, 19.39 MPa, and 19.1 MPa, respectively. Workability also declined slightly, with slump values of 45 mm, 43 mm, 41 mm, and 40 mm for the same replacement levels. Despite this reduction, the results suggest that RHA substitution up to 6% is a technically viable strategy, offering meaningful reductions in cement consumption and associated CO₂ emissions, along with the beneficial reuse of agricultural waste, while maintaining acceptable mechanical performance.