Efficacy of Rice Husk Ash for Stabilizing Poor Subgrade Soils in Arkansas

Arkansas is the leading supplier of long-grain rice in the United States. Rice husk is an agricultural waste that is burned under controlled conditions. The ash produced in the milling process of rice has a high percentage of silicate, which is a pozzolanic material and can potentially improve the properties of poor-quality soils. The main objective of this study is to evaluate the optimum amounts of rice husk ash (RHA), hydrated lime (HL), or RHA plus HL by investigating two local subgrade soils from Arkansas. The treated soils were subjected to different tests such as Atterberg limits, modified proctor, unconfined compressive strength, California bearing ratio, pH, and free swell (FS). Test results show that both RHA and HL reduce the plasticity and the maximum dry density of the soil. In contrast, the strength properties of the tested soils increased with the incorporation of either RHA or HL. The FS results showed both RHA and HL mitigated the swelling of the soils. However, HL was found to be more effective in reducing soils’ FS than RHA. The HL dramatically increases the pH of the soil, but RHA does not have a notable effect on it. Six percent RHA and 3 % HL were found to be the optimum dosages in treating clayey and silty soils. The combination of RHA and HL was capable of reducing the swelling potential as well as improving the strength properties. Considering laboratory test results and economic analysis, 4 % RHA+1 % HL is recommended for stabilizing poor clayey and silty subgrade soils.