STABILIZATION OF EXPANSIVE WEAK SUBGRADE SOIL USING FLY ASH MIXED WITH AND WITHOUT CEMENT KILN DUST: A CASE STUDY IN JIMMA TOWN

Abstract

Expansive Soils are soils that have the ability to shrink and/or swell, and thus change in volume, in relation to changes in their moisture content. Because of this swelling and shrinking behaviors, expansive soils cause structural damage to lightweight structures such as pavement, sidewalks, and driveways. The aim of this study is stabilization of expansive weak subgrade soil using fly ash mixed with and without cement kiln dust. The research conducted through the experimental or laboratory test by using purposive sampling of one representative expansive soil sample based on observation of color and soil texture. The soil sample was disturbed soil sample toked from 2m depth and brought the fly ash and cement kiln dust from coal fired power generation station of Dongfeng textile PLC and Mugher cement enterprise factory respectively. The soil stabilized by fly ash in the proportion of 10%, 15%, 20%, 25% & 30% by dry weight to get the optimum percentage and then activate the mixture by cement kiln dust in the proportion of 5%, 10%, 15%, 20% & 25% by dry weight. To analyze the effect of the stabilizer, the following test was conducted: Atterberg limit, specific gravity, Free swell test, Compaction, UCS, CBR and Percent of CBR swell. The stabilized soil sample tested for compaction, UCS and CBR were cured for 4, 7& 14 days. According to AASHTO and USCS, the soil categorized into A-7-5 and CH soil category respectively. The soil under this category has poor engineering property, which is high plastic index, high free swell index, low UCS, low CBR and high percent of CBR swell. All the engineering properties of virgin soil is improved when blended with non-self-cementing fly ash. However, the analysis result shown that fly ash cannot standalone as stabilizer and its optimum dosage of fly ash was 25% but with addition of cement kiln dust activator, the engineering property of soil was improved as a CKD content increased with respect to curing time. Curing of the sample has a significant effect on the performance of the weak subgrade soil. Stabilization of expansive soil using fly ash mixed with cement kiln dust within respect to curing is an effective option for the improvement of engineering properties of expansive soil.