Yield stress and strength of saline cemented tailings in sub-zero environments: Portland cement paste backfill

The objective of this study is to investigate the time-dependent evolution of the yield stress, strength and deformation behaviour of cemented paste backfill (CPB) that contains Portland cement as the binder with different saline concentrations in a sub-zero environment (− 6 °C). Yield stress measurement with the vane method, uniaxial compressive testing and microstructure analysis have been conducted on various CPB samples with different sodium chloride (salt; NaCl) concentrations and cured in a sub-zero temperature for different times (0, 0.25, 1, 2 and 4 h for yield stress measurement; 7, 28 and 90 days for compressive strength testing). The results show that the yield stress decreases with an increase in salinity. The strength of CPB under freezing conditions decreases as the concentration of NaCl is increased. A shift from the strain-softening behaviour of CPB that has no salinity to the strain-hardening behaviour of CPB with high salinity is observed. Additionally, it is also noticed that with curing time, the deformation behaviour of the studied CPB becomes gradually less ductile. The microstructural analysis results show that the binder hydration products are affected by the salinity. There is strong indication that the absorption of the Na + ions by calcium-silicate-hydrate leads to the decrease of the strength of CPB with different saline concentrations. The results of this investigation provide technical information for the designing of cost-effective, safe and durable CPB structures in sub-zero mining environments.