Abstract:
This paper presents an experimental study on the strength and suction evolution of cemented paste backfill (CPB) and CPB that contains blast furnace Slag (Slag-CPB) with different content of sulphate at early ages. CPB and Slag-CPB with 0, 5,000, 15,000 and 25,000 ppm sulphate content were prepared and cured at room temperature (20°C) for 1, 3, 7 and 28 days. Mechanical, hydraulic conductivity test and microstructural analyses were performed on the studied samples, suction and electrical conductivity of the samples were monitored. The results show that sulphate has a significant negatively effect on the early age strength and suction evolution of CPB and can lead to a positive or negative effect on Slag-CPB i.e., cause an increase or decrease in strength and acceleration or reduction in the amount and rate of self-desiccation. Inhibition of cement hydration and pozzolanic reaction, ettringite induced coarseness of pore structure and sulphate absorption by C-S-H are found as main reasons that affect CPB strength and suction evolution. This study has demonstrated that the effect of sulphate on the early strength and self-desiccation of CPB is an important factor for consideration in the designing of cost-effective, safe and durable CPB structures as well as using slag for reducing the mining cycle time in sulphide mines.
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