Geotechnical and environmental responses of paste tailings systems to coupled thermo-chemical loadings

Abstract

Geotechnical and environmental responses of paste tailings systems to coupled thermo chemical loadings. Cement paste tailings (CPT) and tailings shotcrete (TS) are investigated for thermo-chemo coupled effects on mechanical strength, durability and reactivity. CPT are made from Portland cement type I (PCI) and PCI-slag with 0 ppm, 5000 ppm, 15000 ppm and 25000 ppm of sulphate, cured at 2°C, 20°C, 35°C and 50°C and tested for UCS at 28, 90, and 150 days respectively. The mechanical strength depends upon both sulphate and temperature. Sulphate concentration, up to 15000 ppm, contributes positively to the strength whereas 25000 ppm reduces the strength at 50°C. Sulphate adsorption by calcium silicate hydrate (C-S-H) at 35°C and 50°C is also noticed. CPT used in cold mines is also found less durable than CPT used in hot mines (20°C-35°C). The reactivity of the CPT system depends upon pyrite content and type of binder as well as curing time. Reactivity increases with increase of pyrite content and decreases with increase of curing time. The reactivity also increases with increase of curing temperature. TS samples made from PCI, PCI-slag and PCI-fibre with 0 ppm, 2500 ppm and 5000 ppm of sulphate, are prepared and cured at 2°C, 20°C, 35°C and 50°C and tested for UCS at 1, 7, 28 and 120 days respectively, to study the thermochemical effect on mechanical strength, durability and reactivity. The results show that sulphate and temperature significantly affect the mechanical strength, durability and reactivity of TS. Sulphate content up to 2500 ppm is found to contribute positively to the strength whereas 5000 ppm at higher temperatures shows deterioration in strength due to sulphate attack (adsorption of sulphate by C-S-H gel). PCI-slag performs better than PCI in sulphate and non-sulphate environments at 20°C and 35°C, but PCI-slag show poor performance at 2°C and 50°C. Fibre does not contribute any additional gain in strength to the TS. PCI performs very well at 50°C in sulphate as well as non-sulphate environments. The TS with PCI-Slag shows the lowest fluid transport ability. The reactivity of TS also depends upon percentage of pyrites and types of binder.