Abstract
Black cotton soil also known as expansive soil poses severe challenges to engineering projects. The seasonal volume change of black cotton soil result to shrinking and swelling of the soil thereby making the geotechnical properties of the soil undesirable for construction. In this study, black cotton soil was stabilized with different proportion of Terrasil and Zycobond (ratio 1:2) with a constant 10% Rice Husk Ash in order to improve the soil properties. Terrasil is a commercially available chemical product which has stabilizing properties was mixed with RHA which is an important by product of rice husk burning composing high silica. Samples of BCS were investigated with the mixture of terrasil, zycobond and rice husk ash in different proportion; 0, 0.5, 1, 2. 4, 6, and 8%. Geotechnical test such as Atterberg limit, compaction and California bearing ratio test were conducted to access the improvement in soil properties. The atterberg limit test revealed a continuous increase in LL and a fluctuating increase in PL compared to a lower value of LL and PL in control sample. The highest MDD from different mix ratio was for 0%T-0%B+10%RHA test, however, comparing this highest with the control, the control seems to be higher. For the CBR, the highest value is mix ratio 0.5%T-1%B+10%RHA which is higher than the control. OMC of 23% was observed in mix ratio 2%T-4%+10%. The shrinkage limit reduced in a progressive manner from the control mix to the last mixture 8%T-16%B+10%RHA, More so, the CBR result was 25% in mix ratio 0.5%T-1%B+10%RHA which represented a more reliable stabilizer mixture in this study. In conclusion, shrinkage limit reduced which is a very important remedy for black cotton soil that swells largely. This particular test helps to reduce the swelling properties and increase the CBR value of BCS.

Key words: Atterberg Limit, Black cotton, California bearing ratio, Compaction, Rice Husk ash, Terrasil, Zycobond.