An overview of rice husk ash as a waste by-product material for sustainable soil stabilization

Expansive soils, particularly those with high clay content, exhibit significant swelling and shrinking properties, which may be undesirable for civil engineering applications. These changes in soil properties cause problems in field projects; therefore, improving the soil properties before construction is often required. This review provides a systematic evaluation of rice husk ash (RHA) or its use in combination with other agents as a sustainable material for soil stabilization, with a focus on improving the properties of clayey soil particles. In addition, through analysis of the published data using the PRISMA method, this review not only determines the optimal RHA percentage for soil stabilization but also highlights the environmentally valuable benefits of RHA as a waste by-product, which decreases construction costs and addresses disposal problems. The impact of RHA on index properties, compaction parameters, free swelling, Unconfined Compressive Strength (UCS), California Bearing Ratio (CBR), and shear properties of naturals and treated soils was investigated. The results showed that the plasticity index and free swells of the treated soils declined with the addition of RHA ratios. Additionally, the UCS, CBR, and shear strength of the treated soils were also improved with the addition of RHA contents. However, the addition of RHA led to a decrease in Maximum Dry Density (MDD) and an increase in Optimum Moisture Content (OMC), a result that must be carefully managed in geotechnical applications. The reviewed studies show that the optimal RHA content for soil stabilization is 5-20%.