UTILIZATION OF RICE HUSK ASH AS A SUSTAINABLE ADDITIVE FOR SUBBASE STRENGTH ENHANCEMENT

Abstract

Rice husk is one of the most abundant agricultural wastes in Thailand, and its conversion into rice husk ash (RHA) offers an alternative material for reducing Portland cement usage in soil stabilization. This study investigates the use of RHA as a cementitious replacement to improve subbase strength. RHA was produced through controlled combustion at 600 °C for 3 hours and mashed by ball mill grinding machine. Soil samples were stabilized with 3% binder content by weight and compacted at optimum moisture content by modified compaction effort. Cement was partially replaced with RHA at 10%, 30%, 50%, 70%, and 100% by weight. Unconfined compressive strength (UCS) and capillary rise tests were performed to evaluate strength and water absorption behavior. The results showed that 10% cement replacement with RHA achieved higher compressive strength than conventional cement stabilization at both 28 and 56 days. However, strength decreased progressively with higher RHA content, while complete cement replacement (100% RHA) resulted in weak durability under soaking conditions. Capillary rise tests indicated that the 10% RHA mixture exhibited water absorption characteristics comparable to 3% cement-stabilized soil, whereas 100% RHA behaved similarly to untreated soil. Additionally, mixtures containing 30–70% RHA showed decreasing water absorption with increased curing time. Overall, the findings suggest that RHA can partially replace cement while maintaining satisfactory mechanical and durability performance, contributing to more sustainable soil stabilization.