Activation of ultra-fine steel slag and ground granulated blast furnace slag in alkaline waste solutions via phosphogypsum and calcium carbide slag

This study expands the ways of utilizing multiple solid wastes. The pH value of SRL (soda residue liquid) closely matches that of the cement pore solution, making it a viable substitute for tap water in mixing. Purified PG (phosphogypsum) can serve as an alternative to traditional sulfate activators. CS (calcium carbide slag), currently serves as a widely utilized alkaline activator. PG and CS synergistically activate GGBFS (ground granulated blast furnace slag) in the presence of SS (steel slag) within the SRL environment. A synergistic effect is observed between SS and GGBFS. The test results demonstrate that the composite system achieves a 28-day strength of up to 60 MPa. The effect of SS content on the hydration kinetics, setting time, compressive strength was investigated. To elucidate the role of SS and PG in the reaction, the hydration products were characterized with TGA, XRD and SEM-EDS. The results suggest that the Cl- in SRL undergoes effective immobilization within the system, thereby filling the gel pores as Friedel's salt (Fs) and facilitating the formation of a dense structure. Q-XRD coupled with TGA was utilized to analyze the changes in crystalline and non-crystalline phases within the system, revealing the hydration mechanism of steel slag activated by physical, chemical, and mineral factors in an alkaline waste solution environment.