Sulphate-temperature-time interactions and their influence on rheological characteristics of cemented paste backfill

Abstract

Cement paste backfill (CPB) can provide social and economic benefits such as treating mine waste, preventing surface settlement, providing a safe working platform in underground mines and improving ore recovery. Rheological properties (including yield stress and viscosity) are key factors influencing the ability of CPB to be successfully transported into specified mine stopes. However, no study has been carried out to comprehensively examine the rheological properties of CPB under the combined effects of sulfate, temperature and time. This study was therefore carried out to evaluate the yield stress and viscosity of CPB samples with different sulfate contents (0 ppm, 5000 ppm, 15,000 ppm and 25,000 ppm), exposed to different temperatures (2 °C, 20 °C and 35 °C) and subjected to different curing or transport times (0, 20 min., 1 h and 2 h). Additional measurements, such as TG/DTG, pH, zeta potential and EC monitoring, were also carried out. It was found that CPB viscosity increased significantly with the simultaneous increase in sulfate, time and temperature, and that yield stress also increased, but at a relatively limited rate. There was competition between the yield stress-reducing factor (e.g. sulfate) and the increasing factors (temperature, time). Higher temperatures had a compensatory or counterbalancing effect on the reduction in CPB yield stress caused by the addition of sulfate. It was also found that the significant increase in viscosity was due to the combined effect of a greater number of ettringite crystals generated by the addition of sulfate and a greater number of hydration products produced by higher temperature and/or longer time. The results of this research will be useful for the efficient design of a long-distance transport system for CPB in mines located in permafrost and/or warm regions, in deep mines as well as for CPB containing sulfate.