Rice husks, an abundant agricultural waste generated during the rice milling process, constitute approximately 25% of the weight of rice. When burned, the hard outer coating of rice grains yields rice husk ash (RHA), a fine powder largely made up of silica (SiO2). Rice husk ash's remarkable pozzolanic activity, which allows it to mix with calcium hydroxide (Ca(OH)2) during cement hydration to produce calcium silicate hydrate (CSH), an essential component of cement that improves concrete strength and durability, has strengthened its position as a valuable additive in concrete production.

This study aims to examine the effects on concrete properties of using rice husk ash (RHA) in various grades of coarse aggregate as a partial replacement for ordinary Portland cement. Three different types of coarse aggregate with maximum sizes of 10, 15, and 20 mm and RHA ratios of 0.5%, 1%, 1.5%, 2%, 2.5%, and 3% were used to make concrete mixes for this investigation. To find out how varying replacement ratios and coarse aggregate size affected the concrete's compressive strength, a number of experiments were performed on the samples.According to the experimental results, the strength of the concrete decreases as the size of the coarse aggregate is reduced. The highest compressive strength was recorded at 2% RHA, where it reached 5.29 MPa, a 15% increase over the control 4.6 MPa for coarse aggregate size 20 mm at 90 days of age..