Optimum Utilization of Rice Husk Ash for Stabilization of Sub-base Materials in Construction and Repair Projects of Forest Roads

Forest roads play an important role in forest management, timber transportation and forest protection. However, minimum standards are considered for pavement materials due to the traffic volume and economic situation of forestry projects. Therefore, this paper aims to (a) evaluate the role of Rice Husk Ash (RHA) as a soil stabilizer of sub-base layer to improve the quality of materials and (b) determine the optimum utilization among 10 combinations of soil, lime and RHA regarding the environmental factors. The results of laboratory studies on soil A–6 (AASHTOO classification) indicates a general decrease in the maximum dry density (MDD) and an increase (21.9%) in optimum moisture content (OMC) with increase in RHA content. Adding RHA (9%) causes a decrease (13.3%) in liquid limit and plasticity index (PI) of soil. However, this improving effect is not as much as the influence of lime. The California bearing ratio (CBR) of stabilized soil in both saturated condition and optimum water content was 28% and 37.5% more than the natural soil, respectively. The maximum unconfined compressive strength (UCS) values were recorded for 9% RHA, 237 KN m after 28 days curing time, which was 23 KN m more than the natural soil. According to the results, the combination of Soil+4% Lime+9% RHA could be used as the optimum consumption of materials for stabilization of sub-base layer in construction of forest roads.