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In cold regions with sub-zero surface temperatures, the addition of chloride-free antifreeze (Ca(NO2)2, Ca(NO3)2, and CO(NH2)2) 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(NO2)2, Ca(NO3)2, and CO(NH2)2) 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. [ABSTRACT FROM AUTHOR]

• Field cemented paste backfill (CPB) structures are subjected to non-isothermal curing. • Non-isothermal strength, pore structure, and self-desiccation of CPB investigated. • Non-isothermal curing condition significantly increases the CPB strength. • Non-isothermal curing condition enhances CPB self-desiccation and refines its pore structure. • Stope backfilled with Portland cement-CPB has a significant advantage over stope with Slag-CPB. In the field, cemented paste backfill (CPB) structures are subjected to non-isothermal curing conditions. In this study, the non-isothermal strength, pore structure development, and self-desiccation of CPB were investigated. CPB specimens with different types of binders and tailings were prepared and cured under isothermal (room temperature: 20 °C) and field non-isothermal conditions. Unconfined compressive strength (UCS) tests, microstructural tests and analyses as well as monitoring experiments, were conducted on CPB specimens cured over various ages. The obtained results show that the non-isothermal curing condition significantly increases the strength as well as the strength increase rate of the CPB regardless of the type of binder and tailings used. Moreover, the non-isothermal condition leads to more intense self-desiccation of CPB as well as the refinement of the pore structure of CPB due to the generation of more hydration products, such as calcium–silicate–hydrate (C–S–H), in the non-isothermal CPB. It is also found that a mine cavity (stope) backfilled with CPB material made with Portland cement type I (PCI) has a significant advantage over stope backfilled with CPB made with slag/PCI (50%/50%) in terms of strength formation and enhancement of self-desiccation due the difference in the non-isothermal curing conditions. The findings of this study provide insight into the development of the mechanical and microstructure properties as well as self-desiccation of CPB structures when exposed to field thermal curing condtions, thereby contributing to the improvement of mechanical stability and economic performance of future CPB designs. The impact of non-isothermal curing conditions on CPB properties need to be considered in mine backfill design and operations. [ABSTRACT FROM AUTHOR]