Strength, Durability, and Microstructural Characteristics of Binary Concrete Mixes Developed with Ultrafine Rice Husk Ash as Partial Substitution of Binder

This study investigates the utilization of ultrafine Rice Husk Ash (RHA) as a partial replacement for cement in concrete to enhance its properties and sustainability. The effects of ultrafine RHA on fresh and hardened concrete properties and the microstructure of the resulting binary mixtures were examined. Test results indicate that the incorporation of ultrafine RHA considerably decreases the slump of concrete mixtures. Mixture having 15% replacement of cement with ultrafine RHA shows a 43% increase in compressive strength at 90 days of concrete age. Furthermore, at the same replacement level, a 31% reduction in moisture sorption, a 27% reduction in drying shrinkage, and a 23% reduction in mass loss due to abrasion are recorded. Acid resistance tests show that the mix with 15% ultrafine RHA loses only 12% of its compression strength after exposure to H₂SO₄ at 56 days of age, in comparison to the 29% loss in the control mix. SEM, EDX, and XRD analyses confirm a denser microstructure, increased silica content, and enhanced pozzolanic activity in ultrafine RHA-modified mixes. These findings suggest that ultrafine RHA is a viable supplementary cementitious material, offering significant environmental and performance benefits to the resulting concrete mixtures.