Portland cement stabilisation of Canadian mature fine oil sands tailings

Mature fine tailings (MFT) are waste suspended in large on-site ponds after bitumen extraction from oil sands. This study investigated the effectiveness of Portland cement binders on the stabilisation of MFT. Laboratory tests were performed to investigate the effects of the curing period (7, 14 and 28 d) and cement dosages (1, 5, 10 and 15 wt%) on the geotechnical properties of MFT, including solid contents (water contents), undrained shear strength and Atterberg limits. The results indicate an increase in all these properties of MFT with cement dosages. The increase in the solid content of MFT is mainly attributed to cement hydration. The undrained shear strength of MFT mixed with 10 and 15% Portland cement increased to 7·65 and 15·5 kPa at 28 d curing, respectively, from virtually 0 kPa. The strength gain of the stabilised MFT is due to the internal formation of reticulate and fibrous structures, mainly calcium silicate hydrate gels, which is confirmed by scanning electron microscopy (SEM) images and X-ray diffractograms. SEM analysis also indicates that the aggregated nature of the MFT fabric is more significant with more cement addition. The results of this study provide much needed insights for potential applications of Portland cement in MFT stabilisation.