Use of Rice Husk Ash and Hydrated Lime as Stabilizing Agents for Poor Subgrade Soils and Embankments

Construction costs can increase dramatically when soft and/or expansive clay is found on site. Replacing undesirable soil with more stable soil is widely practiced in many countries. The present study has focused on stabilizing poor-quality soils in Arkansas by using rice husk ash (RHA), which is agricultural waste. A commonly used stabilizing agent, hydrated lime (HL), has also been evaluated for comparison purposes. The main objective of this study is to determine the optimum percentages of RHA and HL that can stabilize the tested soil. The sample has been collected from an ongoing construction project from I-555 near Jonesboro, Arkansas. It is clay soil (CL) with low plasticity (AASHTO type A-6). The unmodified (control) and modified soils with varying dosages of RHA (3%, 6%, and 9% by weight) and HL (1%, 3%, and 5% by weight) were evaluated in the laboratory. The unmodified and modified soils are then subjected to the Atterberg limit test, modified Proctor test, pH test, and unconfined compression strength test (UCS). The UCS test was conducted with remolded specimens for seven days of curing. It was found that the liquid limit of the soil increased by 15% and 24% with the addition of 9% RHA and 5% HL, respectively. There was a great reduction in the maximum dry unit weight by 13% and 9% at 9% RHA and 5% HL, respectively. The RHA showed a slight increase in the pH of the soil to reach pH 7.75 at 9% RHA, while the pH increased dramatically by using 5% HL to reach pH 12.95. RHA showed a good amount of reduction for the soil volume change from 20% to 6% at 9% RHA. A 5% HL hydrated lime showed a reduction in the soil volume from 20% to 10%. The unconfined compressive strength increased to reach 381 and 208 psi with 9% RHA and 3% HL, respectively. Based on limited test results, 6% RHA and 3% HL are found to be the optimum dosages to improve the properties of tested soil. The findings of this research have the potential to significantly benefit the construction industry in Arkansas by reducing costs associated with traditional methods of soil stabilization.