Study on the Salt-Freezing Damage of Concrete with All-Solid-Waste Cementitious Material Based on Red Mud, Circulating Fluidized Bed Combustion Fly Ash, Calcium Carbide Slag, and Ground Granulated Blast Furnace Slag

This study aims to clarify the damage evolution mechanism of red mud-based all-solid-waste cementitious concrete under salt-freezing conditions. A quaternary solid-waste cementitious system was developed using red mud (RM), circulating fluidized bed combustion fly ash (CFBFA), calcium carbide slag (CS), and ground granulated blast furnace slag (GGBFS). Concrete specimens with water-to-binder ratios of 0.4 / 0.5 and with/without air-entraining agents were prepared. Salt-freeze cycle tests combined with multiple characterization methods were conducted to systematically analyze the changes in physical-mechanical properties, pore structure, and material composition of the specimens. Results show that after 30 cycles, the 0.4 ratio group exhibited a strength loss rate of 17.55% and mass loss rate of 0.3%, significantly lower than the 37.34% strength loss of the 0.5 ratio group. Air-entraining agents optimized pore structure by reducing macropores, thereby lowering the strength loss rate to 11.90%. Salt-freezing cycles increased porosity from 1.25% to 1.61%, with small pores ( < 0.1 mm 3 ) surging by 183.50% as the primary damage cause. The cementitious material reacted with salt solution to form glauberite, which temporarily filled pores but lacked long-term stability.