Low-carbon expansive soil stabilisation using magnesium-activated industrial by-products

This study presents a novel, sustainable stabilisation method that alkaline-activates two industrial wastes, rice husk ash (RHA) and silica fume (SF), using low-carbon magnesium hydroxide (Mg(OH)₂). The aim is to transform these waste materials into effective binders for enhancing the strength and durability of expansive clay. The soil was treated with optimal dosages of additives (11% RHA and 7% SF, each with 3% magnesium hydroxide) and subjected to a series of geotechnical tests including unconfined compressive strength (UCS), swell potential, consolidation, and Atterberg limits after 7 and 28 days of curing. Microstructural changes were analysed using X-ray-diffraction, X-ray-fluorescence and scanning-electron-microscopy. The results demonstrated a remarkable improvement in soil properties: UCS increased by 320% and 210% for RHA and SF mixtures, respectively, after 28 days. The plasticity index was reduced by 54% (RHA) and 48% (SF), while swelling potential was nearly eliminated (up to 99.5% reduction). Compressibility also decreased significantly by 71% and 89%. Microstructural analysis confirmed that these enhancements are due to the formation of magnesium silicate hydrate and magnesium aluminate hydrate gels, which densify the soil matrix and refine its pore structure. This research successfully establishes a low-carbon, waste-valorising approach for transforming expansive soils into a stable construction medium.