The potential of copper slag as a precursor for partially substituting blast furnace slag to prepare alkali-activated materials

The safe and efficient treatment of copper slag (CS) is an important aspect of the circular economy and green development. In order to reduce the negative environmental impact, CS is used as a precursor to substitute different contents of ground granulated blast furnace slag (GGBS) in the manufacturing of alkali-activated materials (AAM)) in this study. The feasibility of AAM incorporated with CS as a precursor is evaluated through the macroscopic performances including setting time, water requirement of normal consistency (WRNC), fluidity, compressive strength and flexural strength. Additionally, the microstructure is characterized using nuclear magnetic resonance (NMR), X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), scanning electron microscope (SEM) and thermogravimetric analysis (TGA), respectively. The results show that the optimal substitution rate of CS for GGBS in AAM mortar is 30 wt%. The compressive strength and flexural strength of AAM incorporated with 30 wt% CS at 28 days reach 71.7 MPa and 9.3 MPa, respectively, which are equivalent to the control group. The microstructure analyses reveal that the substitution of GGBS with CS reduces the formation of C-A-S-H due to the relatively low pozzolanic activity of CS. However, the micro-aggregates effect of CS and the filling effect of its hydration products (ferric hydroxide/ferrous hydroxide, and ferrosialate gels) can enhance the compactness of hardened paste and improve its mechanical performance.