Rice Husk Derived Nanosilica for Sustainable Soil Stabilisation A Review of Geotechnical Applications

The environmental effect identified with conventional lime and cement-based soil stabilisation have intensified the search for eco-friendly alternatives in geotechnical engineering. Agricultural waste-derived nanomaterials, particularly rice husk-derived nanosilica (RH-NS), have emerged as promising sustainable stabilisers due to its high pozzolanic reactivity and waste valorisation potential. This review critically examines recent advances (2020–2026) on the synthesis, characterization, stabilisation mechanisms, engineering performance, sustainability implications, and implementation challenges of RH-NS for soil stabilisation, based on peer-reviewed studies from major databases. Rice husk, an abundant agricultural by-product containing 15–22% amorphous silica and can be converted into highly reactive nanosilica (15–50 nm) through acid leaching-pyrolysis, mechanical milling, or precipitation methodologies. The incorporation of RH-NS into weak soils enhances unconfined compressive strength up to 4–5 times of its original strength, reduces swelling potential up to 88%, improves California Bearing Ratio, and decreases hydraulic conductivity. These improvements stem from nanosilica's high specific surface area (150–350 m²/g) and its pozzolanic reactivity, which promote calcium silicate hydrate (C-S-H) and calcium aluminium silicate hydrate (C-A-S-H) gel formation. However, challenges including nanoparticle agglomeration, non-uniform dispersion, long-term durability concerns, high production costs, and limited field-scale validation remain barriers to widespread adoption. Tropical lateritic soils remain understudied despite their prevalence in developing countries. Emerging techniques such as hybrid stabilisation with other agro-wastes, functionalized nanosilica, and life-cycle assessment frameworks show promise for enhancing sustainability and field applicability. Future research should prioritize field validation, durability testing, standardized synthesis protocols, and cost reduction strategies to transition RH-NS from laboratory research to routine geotechnical practice.