Evaluation of short-term strength development of cemented backfill with varying sulphide contents and the use of additives.

The disposal of sulphide tailings and control of strength deterioration of sulphide cemented backfills are of both environmental and financial interest. The uniaxial compressive strength (UCS) of samples with varying sulphide contents (6-25 wt%) was evaluated over a short-term period. A severe strength loss occurred after 14 days on those with low sulphide and the sulphide-rich samples keep increasing over 28 days. With SEM and XRD, it was inferred that the expansive phases were presumably responsible for the strength failure and the mechanical performance is closely in relation to the microstructure. They are deemed to present a positive to negative turn of effects on the strength. Initially, the precipitation in voids and micropores contributes to strength development until the already hardened structure cannot bear the inner pressure, microcracks begin to occur. For sulphide-rich cemented backfills, two kinds of additives, set retarder and accelerator, were adopted to measure their effects on the mechanical strength and setting time as the hardening process of cemented backfills was varied, and the results show that the accelerator gave rise to a rapid gain of strength while followed by a sharp deterioration after 14 days. In contrast, the retarder contributes to the continuous strength growth. From the economic perspective, the use of set retarder or accelerator involves 6.25% and 9.5% of binder cost respectively.