DOI: 10.14457/tu.the.2018.1676
title: Geotechnical properties of rice husk ash-lime-soil mixtures and its performance evaluation as subgrade material

description: Soils possessing poor engineering properties are a common troublesome issue to construction engineers. Unlike other projects in which engineers are supposed to cope with poor soils just during the substructure construction period, the whole work in road construction would be a challenge once road engineers encounter soils with weak engineering properties since the work is exclusively relevant to this type of earth materials. In order to solve this problem, two available options are normally opted for. The natural poor soils either need to be replaced by other better materials in strength or to be stabilized. This practice will permanently eliminate the troublesome soil. However, the transported problematic soil would retain its poor engineering properties regardless of where it is placed. Chemical treatment, which can be said as one of soil stabilization techniques, is one of the best choices in terms of problem-solving and process cost. At the same time, environmental concerns are currently main issues catching the attention of scientists and researchers the most. To comply with both engineering and environmental concerns, rice husk ash which is considered as a waste material has been utilized in this study to stabilize Bangkok clay (BKK clay), a common soil found in Thailand which has poor engineering properties, in the presence of activator lime.Soil stabilization can be said to be a soil improvement method adapting physical and chemical property modification concept. Conventional stabilizers such as cement, lime, and fly ash have been simply used in the soil stabilization to enhance natural workability and engineering properties of poor existing soil. In an attempt to use waste materials in soil stabilization, waste materials originated from homes, farms, factories such as rice husk ash, quarry materials, bottom ash, palm kernel shell ash, sugarcane ash, waste ceramics, waste plastics, waste glasses, wood ash, and so on have been utilized in order to improve engineering properties of soil such as compaction characteristics, consistency limits, volume change characteristics, and strengths. On the part of rice husk ash, the ash material has been used in silica gel manufacture, lithium-ion batteries production, portland cement production, metal production, amorphous silica and silicon manufacture, and so on beside its application in soil stabilization.In this experimental study, the soil was replaced by 10%, 20%, 30%, and 50% RHA based on dry soil mass and was added 4%, 8%, and 12% lime. Compaction tests were performed on mixtures in order to obtain optimum moisture contents and maximum dry densities which were used in preparing different mix designs for unconfined compressive strength (UCS) and California bearing ratio (CBR) test. Samples were sealed by plastic wrap then left to cure in ambient temperatures 30±2°C. From the results of unconfined compressive strength test of 28-days-cured samples, mix designs with significant improvement were selected to be studied for shorter and longer curing periods, i.e. 1, 7, 56 days. Scanning electron microscopy (SEM) was performed to explore materials’ morphology. X-ray fluorescence (XRF) was also performed to determine chemical compositions of materials enable explanation of strength gain. In terms of unconfined compressive strength, mix design with 20% of RHA and 12% of lime is the best with 4-fold improvement in strength. On the other hand, mix design with 50% of RHA and 12% of lime is the optimum mix design regarding California bearing ratio.