STUDY ON BEHAVIOUR OF CONCRETE UNDER PARTIAL REPLACEMENT OF CEMENT BY RICE HUSK ASH (RHA) AND FLY ASH (FA) WITH THE EFFECT OF SODIUM CHLORIDE AND SULPHURIC ACID

Abstract

This study examines the mechanical and durability performance of concrete incorporating Rice Husk Ash (RHA) and Fly Ash (FA) as partial replacements for cement under aggressive chemical environments. Cement was replaced by RHA and FA at varying proportions of 0%, 5%, 10%, 15%, and 20%, both individually and in blended combinations, to evaluate their influence on concrete behavior. The prepared concrete specimens were subjected to standard mechanical tests, including compressive strength, split tensile strength, flexural strength, and water absorption at curing periods of 7, 28, and 56 days. To assess durability characteristics, the specimens were exposed to 5% Sodium Chloride (NaCl) solution and 2% Sulphuric Acid (H₂SO₄) solution after curing. Experimental results revealed that the incorporation of supplementary cementitious materials significantly improved the long-term performance of concrete. Among all mixes, the combined replacement of 10% RHA and 10% FA achieved the optimum compressive strength of 32.6 MPa at 28 days, demonstrating enhanced pozzolanic activity and improved microstructural densification. Exposure to NaCl solution slightly increased the strength of blended concrete due to pore refinement and salt deposition within voids. In contrast, H₂SO₄ exposure resulted in considerable deterioration of strength and surface quality because of acid attack on cement hydrates. However, blended concrete exhibited superior resistance to acid attack, with only 11.2% strength reduction compared to 18.4% in conventional concrete. The findings confirm that RHA and FA can effectively enhance both the mechanical properties and durability of concrete while promoting sustainable utilization of industrial and agricultural waste materials.