Synergistic activation mechanism and long-term properties of a solid waste cementitious materials based on red mud and calcium carbide slag

A new type of ecological cementitious material was developed by using various solid waste materials to prepare low-cost and low-carbon eco-friendly materials. By incorporating circulating fluidized bed fly ash (CFBFA), red mud (RM), calcium carbide slag (CS), and ground granulated blast furnace slag (GGBS), the mechanical properties of the cementitious material were first studied. Then, the hydration products were characterized by XRD, TG-DTG, FT-IR, and SEM. Finally, the synergistic activation mechanism of RM and CS was elucidated by conductivity, pH measurement, and ICP ion concentration determination. The results showed that in the early stage, RM solidificated quickly, a large amount of AFt was generated by the hydration of CFBFA and GGBS mainly played a nucleation effect, the 3 days compressive strength of the paste could reach 6.0 MPa. During the hydration process, Na+ in RM was replaced by Ca2+ in CS, transforming from a stable compound state to a free state and forming a strong alkaline environment with OH-, which can accelerate the hydration reaction rate of the system. In the later stage of hydration, GGBS participated in the hydration reaction, consuming calcium hydroxide and generating C-(A)-S-H gel to fill the paste pores.