Geotechnical improvement of soils by rice husk ash in Caspian Region, Northern Iran

Abstract

Soil stabilization using additive materials is a fundamental technique in geotechnical engineering. Common stabilizers include lime, cement, rice husk ash (RHA), pozzolans, micro-silica, aluminum sulfate, and fly ash. Given the increasing emphasis on sustainable materials, this study focuses on RHA-a pozzolanic material widely available in northern Iran as a promising soil stabilizer. RHA's abundant supply, ease of processing, and costeffectiveness make it suitable as a partial or complete replacement for cement in various soil stabilization applications. The research outlines RHA's production process using different curing methods by altering the time and temperature of combustion and the rate of cooling process, while the chemical characterization was determined through X-ray florescence (XRF) and scanning electron microscopy (SEM) analysis. Furthermore, to assess the capability of RHA in soil stabilization, unconfined compressive strength (UCS) test was performed on the treated sandy clay soil specimens after 7 and 28 days curing period. The findings revealed that the RHA obtained from burning at 500 °C for 12 hours and rapidly cooled shows the highest pozzolanic activity while gradual cooling has a negative effect on it. The UCS test results showed that adding 15% of RHA-cement, with equal proportions, to the sandy clay soil could enhance the compressive strength by over 2.7 MPa. Results indicate that incorporating RHA not only improves soil stabilization and reduces cement usage, but also offers environmental benefits by repurposing an agricultural byproduct that would otherwise go to waste. These findings provide practical guidelines for implementing eco-friendly soil stabilization practices in the Caspian region and similar ecological zones.