Improving the strength performance of cemented phosphogypsum backfill with sulfate-resistant binders

Abstract

Utilizing phosphogypsum (PG) as an aggregate for cemented backfill offers an effective waste management approach for phosphorus industry. Nevertheless, the supersulfate property of PG significantly hindered the strength development of cemented PG backfill. This study aims to enhance the strength performance of hardened backfill through the optimization of binder types. Silicate-based cements (P·O 42.5 ordinary Portland cement (OPC) and P·I 62.5 Portland cement (PC)) and (sulpho)aluminate-based cements (62.5 sulphoaluminate cement (CSA) and CA50-II calcium aluminate cement (CAC)) were selected as binders. In this study, backfill samples were prepared by PG, water and different types of binders. The strength development, porosity and hydration characteristics of hardened backfill were studied. The results show that OPC and PC exhibited susceptibility to sulfate, resulting in backfill samples with slow hydration and low strength. In contrast, backfill samples applying CSA and CAC as binders exhibited rapid hardening and significant strength enhancement, particularly in the early age. The active interaction between gypsum and the main components of CSA and CAC, such as ye’elimite (C4A3S¯) and monocalcium aluminate (CA), led to the accelerated hydration process and the generation of abundant ettringite and aluminum hydroxide (AH3). Consequently, the hydration process of CSA and CAC appeared to be exempted from the negative effects of supersulfate environment, maximizing the binding performance. This study emphasizes the favorable binding performance of (sulpho)aluminate-based cements in cemented PG backfill, contributing to the utilization of PG.