Coupled effects of sulphate and temperature on the strength development of cemented tailings backfills: Portland cement-paste backfill

Cemented paste backfill (CPB), which is a mix of tailings, water and cement, is subjected to the combined actions of temperature and sulphate during its service life. There is a need to acquire solid knowledge on the coupled effects of temperature and sulphate on the strength of CPBs for a safe, durable and cost-effective design of CPB structures. Hence, the main objective of this paper is to use an experimental approach to study the combined effect of temperature and sulphate on the strength development and microstructure (mineralogical composition of the hardened cement paste) of CPBs. About 200 CPB specimens with various initial sulphate contents (0, 5000, 15,000, and 25,000 ppm) and cured at different temperatures (0 °C, 25 °C, 20 °C, 35 °C, and 50 °C) are tested at different curing times (28, 90, and 150 days). The results show that the coupled effect of temperature and sulphate has a significant impact on the strength and mineralogical composition of the CPB. Depending on the curing time, temperature and initial sulphate content, the sulphate can have a positive or negative impact, i.e., leads to an increase or decrease of CPB strength. The obtained results show a strong indication that the absorption of sulphate by calcium–silicate–hydrate (C–S–H) could lead to the formation of lower quality C–S–H, thereby decreasing the strength of the CPB. This study has demonstrated that the coupled effect of sulphate and temperature on CPBs is an important factor for consideration in the designing of cost-effective, safe and durable CPB structures.