Strength and suction development of cemented paste backfill with ternary cement blends

In this paper, the effect of ternary binder containing Portland cement type I (PCI), slag, and limestone (LS) powder in varying proportions on the suction development and the mechanical strength of cemented paste backfill (CPB) was investigated. Mechanical tests, microstructural analyses (thermo-gravimetry analysis (TG/DTG) and mercury intrusion porosimetry), and monitoring (suction, electrical conductivity, and temperature) experiments were conducted on CPB. In the first part of this study, binary binders with two different PCI:slag proportions, 50:50 and 80:20, were examined with no LS, followed by the slag replacement with increasing weight percentages of LS from 0% to 20% by weight of the total binder, with constant cement content. The results indicate that the slow slag hydration kinetics decreased the suction and strength gain rate at a young age in the binary sample with high slag content (50 wt.%); however, its latent hydraulic and pozzolanic properties enhanced the strength gain at a later age, from 28 days. The addition of 5 wt.% and 10 wt.% LS to the ternary binder system improved the early age strength of CPB up to 7 days and 1 day, respectively, compared with the binary control samples, i.e., CPB with slag and without LS. While the addition of up to 10% LS to the ternary binder improved the rate of suction development and increased suction at early ages, beyond 10%, the addition of LS slightly decreased mechanical performance at all ages. Overall, the results obtained reveal that up to 50 wt.% slag with up to 10 wt.% LS with cement could be used as a ternary binder to improve the early age strength and suction development rate of CPB studied without significant loss in compressive strength at advanced ages. The results of this research could be of great benefit to the mining industry through the use of a ternary binder to replace cement, which could improve the overall performance of the CPB system, facilitate a more sustainable CPB design, and improve tailings management practices and overall economics.