This study evaluates the use of rice husk ash (RHA) as a partial replacement for ordinary Portland cement (OPC) component to address the environmental and managerial challenges posed by underutilization of RHA and cement production. Therefore, RHA was subjected to slow-pyrolysis process to obtain amorphous ash and was subsequently mixed with cement in incremental steps of 5%, ranging from 0% to 25%. The objective is to determine the optimal RHA-based OPC blend that could substitute existing cement components while maintaining or enhancing performance. RHA was produced using pyrolysis kiln. Control sample were based on CEM IV 32.5N BP cement, while gypsum, pozzolana, and clinker used were sourced from Hima Cement Factory in Kasese District, Uganda. The materials were proportioned in varying ratios of clinker or pozzolana with RHA, then milled using a ball mill to produce different ash-based OPC blends. Each treatment was replicated three times and tested for Blaine fineness, compressive strength, setting time, water demand and durability. Tukey’s pairwise post hoc test revealed no significant differences in compressive strength for several RHA replacement in both pozzolana (P-values = 0.062, 0.486, 0.122, 0.880, 0.230, 0.292) and clinker (P-values = 0.999, 0.059, 0.458) scenarios. However, Blaine fineness and water demand generally increased with higher RHA replacement levels, while setting time showed a decreasing trend. The acid forming ions in all cement samples registered values well below the threshold limits. These findings suggest that RHA is effective supplementary cementitious material for sustainable and cost-effective cement production.