Compressive Strength Performance of Concrete Partially Blended with Rice Husk ASH

This study examines the compressive strength performance of concrete partially blended with Rice Husk Ash (RHA) as a supplementary cementitious material. Concrete cubes of dimension 150 mm x 150 mm x 150 mm were produced using a 1:2:4 mix ratio at varying water-cement ratios (0.50to0.70), with RHA replacing cement at 5%, 10%, 15%, 20% and 25% by weight. Materials used include UNICEM Ordinary Portland Cement (Grade 32.5), river sand from Unwana beach, crushed stone aggregate (10to20 mm) from Akpoha, and potable water. Sieve analysis confirmed the fine aggregate falls within BS Zone I. Slump tests were performed on fresh concrete, and compressive strength was determined at 28 days curing age using a 2000 kN compression machine. Results show that workability (slump) increased with increasing RHA content and water-cement ratio, though all mixes exhibited very low workability. Compressive strength decreased progressively with increasing RHA replacement, from 21.8 N/mm2 at 5% RHA to 10.10 N/mm2 at 25% RHA. The 5% RHA blend achieved Grade C20 concrete, making it suitable for use in reinforced concrete construction. This study recommends a maximum of 5% RHA as a partial cement replacement for structural concrete works, and up to 10% for mass concrete applications. The use of RHA as a cement substitute offers environmental and economic benefits by reducing CO2 emissions and the overall cost of concrete production.