Effect of Rice Husk Ash as Partial Cement Replacement on the Mechanical Properties of Concrete

Abstract

Rice husk ash (RHA) is increasingly explored as a sustainable supplementary cementitious material due to its high amorphous silica content and potential to reduce cement consumption and CO₂ emissions. This study evaluated the effects of RHA as a partial cement replacement on the fresh and hardened properties of concrete. Rice husk was cleaned, oven-dried, and combusted at 700 ± 10°C under controlled conditions before being ground to pass a 75 µm sieve. XRD and EDS analyses confirmed the presence of amorphous silica responsible for pozzolanic reactivity. A total of 48 concrete cubes (150 mm × 150 mm × 150 mm), representing four mixes (0%, 5%, 10%, and 15% RHA) with twelve cubes per dosage, were cast at a water–cement ratio of 0.50 and tested for slump and compressive strength at 7, 14, and 28 days. Workability increased from 4.5 cm in the control mix to 7.0 cm at 10% RHA, then decreased slightly at 15%. Compressive strength for the control increased from 13.7 MPa at 7 days to 20.65 MPa at 28 days. At 5% RHA, strength exceeded the control at 14 days (17.81 MPa) and reached 18.53 MPa at 28 days, indicating beneficial pozzolanic contribution. Higher replacements reduced strength, with 10% and 15% RHA achieving 13.50 MPa and 8.20 MPa at 28 days, respectively, due to reduced cementitious content and increased porosity. The findings demonstrate that RHA possesses moderate pozzolanic reactivity and is most effective at low replacement levels, with 5% identified as the optimal dosage for enhancing performance while contributing to sustainable concrete production.