The investigation into the mechanical performance and microstructure evolution of cemented paste backfill disposal in...

The closed open pit provides tailings storage with a good placement site, it not only alleviates environmental pollution but also ensures the pit slope safety. Compared with traditional surface tailings disposal, surface cemented paste disposal (SPD) has the advantages of good mechanical strength and low permeability, making it more suitable for backfilling in closed open pits. However, the SPD method is vulnerable to environmental temperature. This research presents the tentative results of internal temperature, mechanical performance, and microstructure evolution of SPD specimens subjected to frost attack. The controlled tests were conducted by considering the freezing temperature, freezing duration, and freezing onset time. Meanwhile, the applicability of silica fume (SF) as a partial cement substitute in cold regions was evaluated. The results illuminate that the freezing process of early-age SPD specimens can be divided into cooling and ice nucleation phase, speedy ice crystallization phase, and ice crystallization end phase. Compared with the compressive strength of SPD specimens without frost damage, the compressive strengths of SPD specimens are severely damaged by sub-zero freezing temperatures. The UCS of the SPD samples pre-cured at -1 °C, -6 °C and -12 °C for 1 day decreased to 93%, 65%, and 56% compared with the non-frozen SPD specimens. The degradation of compressive strength is exacerbated by increases in freezing duration and decreases in freezing temperature. As the temperature decreased from -1 °C to -12 °C, the strength loss of the pre-freezing SPD specimens exceeded 60%. A later freezing onset time is required for SPD specimens to acquire sufficient strength to resist frost damage. In addition, silica fume has a positive effect on the compressive strength evolution of SPD specimens under low temperatures. The UCS growth rate of SPD specimens with 5% silica fume was 25.3%. The research offers a series of valuable and reliable references for the SPD, which holds significant importance for exposing the frost damage mechanism in SPD.