Quarry dust is a by-product of rubble crusher units and is a commonly available material, due to the vast usage of crusher metal in the construction industry. This product can be used to improve engineering properties of high plasticity silty (MH) soils, in order to develop a cost effective method for highway sub-grade construction. As such, research reported in this paper illustrates the effect of using of quarry dust' as an admixture to improve the engineering properties of high plasticity silty soils with combination of cement. High plasticity silty soils which were rejected by one of the main road construction projects in Sri Lanka, were selected as the test samples. These high plasticity silty soils were mixed in the laboratory with different percentages of quarry dust and 2% of cement, on the weight and left to harden for a period of seven days. Further, shear strength behavior of soil-quarry dust mixes were presented in this paper. The results of the subsequent tests revealed that even mixing with only quarry dust, caused appreciable improvement in engineering characteristics of poor quality soils. It was found that this improvement can be significantly enhanced with the addition of 2% of cement. Therefore, problems associated in the construction of highways over clayey sub grade, can be reduced significantly by mixing with quarry dust and cement.

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