Mechanical and microstructural characteristics of cemented paste tailings modified with nano-calcium carbonate and cured under various thermal conditions

ABSTRACT This paper focuses on the evaluation of the strength development and microstructure of nano-calcium carbonate (CaCO3) cemented paste backfill experimentally cured under isothermal conditions at room temperature and non-isothermal conditions in the field. A series of mechanical (uniaxial compressive strength, UCS) and microstructural (thermogravimetric, mercury intrusion porosimetry, scanning electron microscope) tests as well as monitoring experiments are experimentally conducted on cemented paste backfill (CPB) specimens with and without nano-calcium carbonate and cured at different times and under isothermal or non-isothermal conditions. The results show that the addition of nano-CaCO3 particles to CPB significantly improves its mechanical strength, irrespective of the thermal curing conditions (isothermal, field non-isothermal conditions). However, the impact of nano-CaCO3 particles on the increase in strength of CPB is only effective or significant at the early ages (curing time≤7 days). It is also found that the higher temperatures improve the accelerating effect of nano-CaCO3 much more than they accelerate the PCI hydration reactions in the first 3 days. Moreover, it is also found the sulphate ions present in the natural gold tailings negatively affect the mechanical performance of nano-CPB and reduced the accelerating effect of nano-CaCO3 due to sulphate attacks.