Geotechnical Study of the Properties of Black Cotton Soil Treated with Cement and Bone Ash as Admixture

Abstract

Black cotton soils are vulnerable to changes in moisture content; they swell when in contact with water and shrink upon drying up of the water. These changes, therefore, affect the properties of the soils. In order to improve these properties the common methods are modification or stabilization or both. In this paper an attempt was made to assess the effectiveness of black cotton soil blended with ordinary Portland cement (OPC) and bone ash (BA) for soil stabilization. The study was therefore about improvement of the properties of black cotton soil with bone ash admixed with ordinary Portland cement and the determination of the optimum quantity that could be used as road construction material at minimal cost. Bone generated waste from slaughter houses (abattoirs) could be effectively utilized for civil engineering construction works, aiming at minimizing the disposal problems and reducing the environmental hazard. The preliminary investigation on the black cotton soil collected along Gombe-Biu road in Yamaltu (Baure village) Yamaltu Deba Local Government Area of Gombe state Nigeria, shows that the soil belongs to A-7-6 (31) in the American Association of State Highway and Transport Officers and CH in the Unified Soil Classification Systems (USCS), respectively. Ordinary Portland cement (OPC) / Bone ash (BA) blend in stepped concentrations of 0, 2, 4, 6 and 8% and 0, 2, 4, 6, 8 and 10% respectively, by dry weight of soil, were used to treat the soil. Compaction was carried out using three energy levels namely: the British Standard Light, West African Standard and the British Standard Heavy. The liquid limit decreased steadily from 65% for the natural soil to 55.5% at 6% OPC / 6% BA content, while the plastic limit increased from 25% for the natural soil to 39% at 6% OPC / 6% BA treatment. Generally, the maximum dry density (MDD) increased while optimum moisture content (OMC) decreased with higher BA treatment. The UCS values of specimens treated with 6% OPC / 6% BA increased from 752, 779 and 827kN/m 2 for the natural soil to 1688, 2250 and 2667kN/m 2 when cured for 7, 14 and 28 days, respectively. There was an increase in the unsoaked CBR values from 6, 9 and 12% for the natural soil compacted with BSL, WAS and BSH energies to 48, 80 and 85% at 6% OPC / 6% BA content. The soaked CBR values of 4, 7 and 9% for the natural soil compacted with BSL, WAS and BSH energies, respectively, increased to peak values of 43, 71 and 74% at 6% OPC / 6% BA content. The durability of specimens was determined by immersion in water. Based on the results obtained the optimum of 6% OPC / 6% BA treatment on the black cotton soil could be used as sub-base material when compacted with BSH.