Influence of biomass fly ash on durability of self-consolidating cement-tailings grout: Resistance to freeze-thaw cycles and sulfate attack

The durability of backfills is a crucial factor in maintaining the long-term stability of the mine backfill area. Partial replacement of cement by biomass fly ash (BFA) is a cost-effective and sustainable way for viscosity control of self-consolidating cement-tailings grouts (CTG), however, the unfavorable changes of pore structure may affect the durability during the service life. This study investigates the resistance of self-consolidating CTGs to 90 freeze-thaw cycles and 180 days sulfate attack, with and without BFA addition. The mechanical properties and relative dynamic modulus of CTGs were measured and analyzed during the exposure to freeze-thaw cycles and sulfate attack. The changes in pore structure, solid phase, and microstructure were also studied. The results demonstrate that the role of 30 % BFA addition on resistance to freeze-thaw cycles and sulfate highly depends on the water-to-binder ratios of hardened CTGs. At a low water-to-binder ratio of 0.6, the addition of BFA can enhance the performance of concrete in terms of its resistance to freeze-thaw cycles and sulfate attacks. At the water-to-binder ratios of 0.8 and 1.0, BFA can increase the resistance to sulfate attack but degrades the performance after freeze-thaw cycles. At a high water-to-binder ratio of 1.2, the addition of BFA reduces resistance to freeze-thaw cycles and sulfate attack. The varying effects of BFA with different water-to-binder ratios are attributed to the pore structures. When the water-to-binder ratio is 0.6, the CTG containing BFA exhibits the best resistance to freeze-thaw cycles and sulfate attack. This provides insights into the design and application of novel self-consolidating CTGs in engineering sites.