Strength variation of OPC-rice husk ash composites with percentage rice husk ash

This work investigated the variation of OPC-Rice Husk Ash (RHA) composites strength with percentage RHA. 231 concrete cubes, 231 sandcrete cubes, and 231 soilcrete cubes of 150mm x 150mm x 150mm were produced at percentage OPC replacement with RHA of 0% (control), 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, and 50% and crushed to obtain their compressive strengths at 3, 7, 14, 21, 28, 50, and 90 days of curing. For concrete, the 90-day strength values decreased from 30.00N/mm² at 5% RHA to 26.50N/mm² at 15% RHA to 21.50N/mm² at 35% RHA to 16.80N/mm² at 50% RHA, while the control value was 27.00N/mm². The 90-day strength values also decreased from 11.70N/mm² at 5% RHA to 6.40N/mm² at 50% RHA for sandcrete while the control value was 11.20N/mm². Soilcrete strength values decreased from 10.50N/mm² at 5% RHA to 5.00N/mm² at 50% RHA while the control value was 10.00N/mm². The results suggest that, with good quality control of the concreting process, 5% to 30% OPC replacement with RHA could be suitable for reinforced concrete works and 35% to 50% for minor works in concrete. Also, 5% to 20% OPC replacement with RHA could be used for light load-bearing sandcrete and soilcrete works, while 25% to 50% could still be suitable for non-load-bearing works.