ABSTRACT
This study evaluated the improvement of bearing capacity of lateritic soil for pavement subgrade by addition of rock flour stabilized with 0 - 12% rock flour by dry weight of soil at incremental rate of 3% and compacted using British Standard Light (BSL), West Africa Standard (WAS) and British Standard Heavy (BSH) compactive efforts. Results show that the lateritic soil sample used for this study is classified as A-7-6 according to American Association of State Highway and Transportation Officials (AASHTO). The formulated mixtures from the A-7-6 soil and rock flour showed an improvement in the index properties of the mixtures with increasing rock flour. The Liquid limit and Plasticity index reduced from 42 - 32% and 29.30 - 13.48% respectively as rock flour increased from 0 – 12%, while plasticity index of A-7-6 soil with rock flour showed considerable reduction in plasticity indices of mixtures with increasing content rock flour content. 1.802, 1.820 and 1.870g/cm³ were obtained as MDD values and 12.40, 11.90 and 11.60% as OMC values for the natural soil using BSL, WAS and BSH compaction efforts respectively. Highest set of values were obtained at 9% addition of rock flour. BSH gave the highest UCS value of 250.89kN/m², while BSL and WAS gave 180.8 and 218.12kN/m² respectively. Generally, a progressive improvement in soaked and unsoaked CBR values were observed for the stabilized specimen with increasing rock flour content. The least CBR value for soaked and unsoaked conditions were observed at 3 % addition of rock flour. For soaked condition at 3% addition of rock flour, the soaked CBR values obtained for BSL, WAS and BSH were 21.15, 25.93 and 28.21% respectively, while 37.88, 41.74 and 42.73% were obtained for unsoaked CBR in the same other of energy level adopted. In terms of consistency limits, the mixtures did not achieve the required threshold values for subgrade specified as LL < 35 and PI < 12% in local codes suggesting the use of higher rock flour contents to enhance these parameters. As regards to soaked and unsoaked CBR, results from the three energy levels adopted that is; BSL, WAS and BSH, meets the minimum requirements of 10% for flexible pavement subgrade according to NGS, (1997). To optimize their structural strength for subgrade application, the mixtures should be compacted to 100% of the relative densities.
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