Influence of sand impurities in cement-treated clays

Cement stabilisation is a well-established technique used in conventional onshore soil improvement works where a large quantity of cement is added to increase the soil's shear strength. However, the application to land reclamation often requires only a low cement dosage and at much higher water content, far exceeding the liquid limit of the soil. In addition, reclamation fill is becoming more heterogeneous with varying amounts of granular material in clayey soils. In this study, a higher unconfined compressive strength of cement-treated clayey soils is attained at a lower water to cement (w/c) ratio. This is persistent for clayey soils with sand impurities. The soil to cement (s/c) ratio produces differing strength development in cement-treated clayey soils, owing to counteracting mechanisms between the degree of bonding and size of pore volume, arising from different amounts of cement and water content, respectively. The normalised strength development of cement-treated clayey soils with curing time follows a logarithmic relationship across different w/c, s/c and sand content. Strong linear correlations between early-age and later-age curing specimens are also observed, which permits early strength prediction of cement-treated clayey soils. In order to account for the variation in microfabric characteristics and pore spaces induced by sand, the free water to cement ratio, (w/w_L)/c, is shown to be more appropriate in assessing strength development of cement-treated soils than conventional water to cement ratio (w/c). This is demonstrated with matching strength predictions and measured values for both Singapore marine clay and kaolin clay.