Effectiveness of two stage stabilization of Laterite soil using sand and cement for road base and subbase course: the case of Ngunja hill

The effectiveness of blending weak and marginal laterite soils with sand and subsequent stabilization of the resulting mix with cement was investigated. This is with a view to reducing initial construction cost by making use of locally available sand in coastal areas of Tanzania as a partial replacement of cement needed for stabilization purposes. Laboratory tests were performed on natural laterite soils and its mixes with sand and/or cement to determine engineering properties. Laterite soil was mixed with sand in the proportions of 30%, 40%, 50% and 60% sand content. Samples of laterite soil and laterite soil mixed with sand were treated with cement at 3%, 4% and 5% cement contents. Results indicate that addition of sand improves engineering properties of the Ngunja hill laterite soil, with a 50% laterite to 50% sand giving the optimum mix proportion. The major findings revealed that mechanically stabilized laterite soil samples possess improved gradation characteristics but inadequate bearing strength. Cement stabilization of laterite soil with cement alone can produce mixes with adequate strength for subbase and base course construction at cement contents considered uneconomical. Two stage stabilization technique is therefore considered to be economically, technically and environmentally attractive as it employs mostly local materials and minimizes materials to be disposed of.