Sustainable Soil Stabilization Approach Utilizing Rice Husk Ash and Hydrated Lime for Enhancing Poor Subgrade Soil in Arkansas

Abstract

Soils with a significant proportion of clay or silt tend to have poor geotechnical characteristics (such as volumetric change and low strength) when exposed to varying moisture contents. The chemical stabilizers currently used are costly and have negative effects on the environment. Arkansas, in the United States, is the leading producer of rice in the country. During rice production, ~20% of the harvested grain consists of rice husk (RH). The rice milling process produces ash with a considerable amount of silicate. Research is being conducted to address the environmental concerns associated with its disposal in Arkansas, as there is growing interest in using rice husk ash (RHA) as a stabilizing additive for problematic soils. For RHA to be effective, an activator such as lime may be needed. The present study focuses on investigating the effectiveness of RHA in stabilizing substandard soils, as no prior study has used RHA as a stabilizing agent in the United States. Additionally, the research aims to determine the optimal proportions of RHA, hydrated lime (HL), or a combination of both. The study employs varying percentages of RHA (3%, 6%, and 9%) and HL (1%, 3%, and 5%) in a unary system. In the binary system, 3%, 4%, and 5% of RHA are combined with 1% HL. The study includes a range of routine tests, such as assessments of Atterberg limits, modified proctor compaction, pH levels, California bearing ratio (CBR), unconfined compressive strength (UCS), and free swell (FS). Furthermore, results from scanning electron microscopy (SEM) coupled with X-ray diffractometer analyses demonstrated significant improvements in UCS and CBR values for the treated soils, indicating enhanced strength and stability. Moreover, the FS test reveals a reduction in swelling characteristics for the stabilized soils. It was found the optimal dosages of RHA and HL were 6% and 3%, respectively. Notably, when RHA and HL were combined, a blend of these two stabilizing agents exhibited the most promising results in terms of improving the swelling. The optimum percentage of the combined stabilizing agents was 4% RHA + 1% HL. The findings of this proof-of-concept research hold substantial potential for the construction industry in Arkansas, offering cost-effective alternatives to conventional soil stabilization methods while promoting the sustainable and environmentally conscious use of RHA.