Influence of K+ and CO32− in activator on high-temperature performance of alkali-activated slag-ceramic powder binary blends

Blast furnace slag (BFS) is an industrial by-product of iron and steel plants that is widely used in alkali-activated materials. Tiles collected during building destruction can be recycled and used as environmentally friendly construction materials. The addition of waste ceramic powder (WCP) to alkali-activated materials relieves pressure on landfills and protects the environment. This study investigated the properties of WCP and BFS mixed pastes activated using different composite activators when heated to 400, 600, and 800 °C for 2 h. Macroscopic dimensional change, residual compressive strength, and ultrasonic pulse velocity (UPV) at high temperatures were measured. Microstructural studies, such as thermogravimetric analysis (TGA), X-ray diffraction(XRD), and Fourier-transform infrared spectroscopy (FTIR), were performed. The main findings can be summarized as follows. After adding K+, the high-temperature resistance of the mixed slurry was improved. After simultaneously adding K+ and CO32-, and after exposure to 800 °C, the NH-Kc sample exhibited the least shrinkage compared to the NH-NS and KH-NS samples, and the residual coefficient of compressive strength was the highest. In conclusion, the introduction of K+ and CO32- into the composite activator is an effective approach to improve the high-temperature resistance of alkali-activated materials exposed to 800 °C.