Using Rice Husk Ash (RHA) as Stabilizing Agent for Problematic Subgrade Soils and Embankments

Arkansas produces the most of the rice in the United States. About 20% of poddy is rice husk (RH), which is burnt under controlled conditions to produce rice rusk ash (RHA). The RHA is considered an environmental hazard and a significant challenge for rice millers. However, RHA is rich in pozzolanic material, which is mainly silica. In this study, RHA is used to stabilize poor soils. Another commonly used stabilizer, hydrated lime (HL), has also been evaluated for comparison purposes. Thus, this study aimed to determine the optimum percentages of RHA, HL, or a combination of these two agents by evaluating selective physical, mechanical, and chemical properties of four subgrade soils (two from Arkansas and two from Oklahoma). Various amounts (by mass of soil) of RHA (3, 6, and 9%), HL (1, 3, and 5%), and RHA+HL have been utilized to know their optimum dosages. Routine tests including the Atterberg limits, Modified proctor, pH, California Bearing Ratio (CBR), unconfined compressive strength (UCS), free swell, and one-direction shrinkage were conducted for untreated and treated soils. Further, scanning electron microscopy (SEM) with X-ray diffractometer tests were performed to evaluate the changes in microstructure due to stabilization. Treated soils show a significant improvement in UCS and CBR data. Additionally, the free swell test also indicates a reduced swelling of treated soils. The optimum dosages of RHA and HL were found to be 6% and 3%, respectively. When these two agents were used together, a blend of 4%RHA and 1%HL was found to be the most effective in improving engineering properties  The findings of this research can significantly benefit the construction industry in Arkansas by reducing costs associated with traditional soil stabilization methods and finding a sustainable and environmentally way of using RHA.