Mechanical properties of cemented tailings backfill with chloride-free antifreeze.

In cold regions with sub-zero surface temperatures, the addition of chloride-free antifreeze (Ca(NO), Ca(NO), and CO(NH)) is an inexpensive method to prevent pipeline freezing during cemented tailings backfill (CTB) transport. However, the curing temperature of CTB after reaching the mine cavity tends to be above-zero. The mechanical properties of CTB with a chloride-free antifreeze in above-zero environments have not been investigated. Therefore, this study aimed at thoroughly exploring the effect of chloride-free antifreeze on the mechanical properties of CTB in above-zero environments. CTB samples with chloride-free antifreeze (Ca(NO), Ca(NO), and CO(NH)) and different concentrations (0, 5, 15, and 35 g/L) were prepared and cured in different above-zero environments (2, 20, and 35 °C). The unconfined compressive strength tests were performed after 1, 3, 7, and 28 days. In addition, a series of microstructural analyses and monitoring experiments were conducted. The results indicated that the addition of a 15-g/L chloride-free antifreeze decreased the strength of CTB curing at 20 °C after 1, 3, and 7 days and increased the strength after 28 days. Moreover, the CTB strength evolution with the curing time depends on the chloride-free antifreeze concentration and above-zero curing temperature. According to the TG/DTG analyses results, calcium ions had a promoting effect on the carbonation of calcium hydroxide. The findings of this study can provide a guideline for the application of chloride-free antifreeze on the mine backfill in cold regions.