Sustainable Soil Stabilization Using Alkali-Activated Rice Husk Ash

Rice husk ash (RHA), a pozzolanic byproduct of rice milling, poses environmental risks if not disposed of properly. This study explores the use of RHA and alkali-activated RHA (AARHA) as eco-friendly stabilizers for highly plastic expansive clayey soil. AARHA was made by treating RHA with sodium hydroxide (NaOH) at 1M and 2M concentrations. Energy-dispersive X-ray spectroscopy analysis of RHA confirmed the presence of a significant proportion of silicon and oxygen. These elements combine to form silica, which governs the pozzolanic nature of RHA, making it an ideal material for geopolymer formation. Scanning electron microscopy images showed that RHA particles are fine and irregular, forming a porous structure with a large surface area, which enhances the chemical reactivity of RHA with NaOH for geopolymer formation and soil grain binding. Physical tests included compaction, free swell index, and unconfined compressive strength after 3, 7, and 28 days of curing. Test results showed that adding RHA and AARHA reduced the maximum dry density, improved strength, and lowered swelling. Alkali activation enhanced the performance of RHA in clay soil stabilization, making it a useful, sustainable way to recycle the agro-waste. The best results were achieved with 15% AARHA (2M NaOH), which gave about six times more strength and around half the swelling compared to untreated soil.