Effects of ladle slag on Class F fly ash geopolymer: reaction mechanism and high temperature behavior

Due to its low hydraulic reactivity, ladle slag is currently underutilized with nearly 80% of annual generation is either landfilled or dumped. This work investigates the joint activation of LS with Class F fly ash, and the impact of ladle slag on fly ash geopolymer with the focus on activation, hydrates assemblage, conversion process, and thermal behavior. Results reveal that the unique reaction process of ladle slag in alkali activation system shows a positive influence on fly ash geopolymers. Within an alkaline system rich in soluble Si, the initially hydrated CAH phases transform into C-A-S-H, which not only hinders the conversion and enhances the mechanical strength but also retains the geopolymerization. The hybrid geopolymer system exhibits superior thermal performance to pure fly ash geopolymers, especially under high temperature exposure. With increasing ladle slag substitution, more stable crystalline phases are formed at high temperatures. After 800 °C exposure, a high residual compressive strength of 64.7 MPa is achieved with 25 wt% ladle slag addition compared to 55.2 MPa in pure fly ash geopolymers.