Reactivity of cemented paste backfill containing polycarboxylate-based superplasticizer

Abstract

Superplasticizers are used in the preparation of cemented paste backfill (CPB) to improve its rheological properties. CPB produced from sulphide-bearing tailings can generate acid mine drainage (AMD), which has negative environmental impact. The AMD potential can be assessed based on the reactivity of the CPB when exposed to the atmosphere. However, the effect of superplasticizers on the reactivity of CPB is unknown. This paper presents findings from experimental investigations on the effects of polycarboxylate superplasticizers (PCSP) on the reactivity of CPB containing pyrite. The reactivity of cured CPB specimens was determined by monitoring the rate of oxygen consumption in an enclosed chamber. Microstructural tests, namely mercury intrusion porosimetry, X-ray diffraction, and thermogravimetric analyses were also carried out to have a better understanding of the reactive mechanisms. The results obtained show that the addition of PCSP leads to a proportionate reduction of reactivity. The admixture causes the refinement of the pore structure of the CPB by mainly improving binder hydration and self-consolidation. It was also observed that less pyrite crystals were present in the CPB containing the superplasticizer. High curing temperature was also found to improve binder hydration, leading to a decrease in reactivity of CPB with PCSP. Due to the micro-filer effects on the CPB pore structure, partial replacement of cement with fly ash and blast furnace slag also decreases the reactivity of CPB. These research findings will be valuable for the design of cost-effective, more environmentally friendly and sustainable CPB structures.