Unveiling the Potential of Civil Briquette Furnace Slag as a Silico–Aluminon Additive in Alkali-Activated Materials

Civil briquette furnace slag (FS), as a type of industrial solid waste, is not currently being recycled as a resource by the building materials industry. This study focuses on the potential of FS in the formulation of alkali-activated materials (AAMs) compared with calcium carbide slag (CS). This study encompasses three distinct AAM systems: alkali-activated fly ash alone (AAFA), fly ash-slag powder blends (AAFB), and slag powder alone (AABS). Electrical conductivity, fluidity, drying shrinkage, and flexural and compressive strengths were also assessed. Advanced characterization techniques, including SEM-EDS, XRD, FTIR, and TG-DSC, were utilized to examine the morphology, mineralogy, and reaction products. Despite the chemical similarity between FS and CS, FS exhibits limited active chemical components (SiO2, Al2O3, CaO, and MgO) and primarily functions as a physical filler, and thus lacks the chemical binding properties of CS. FS has a positive effect on the long-term compressive strength of the AABS system but not on the AAFA and AAFB systems. The NaOH-activated SP mortar sample with 20% FS reaches a compressive strength of 29.8 MPa at 360 days. The binding strength in AAMs incorporating FS is predominantly attributed to the gel formation within the alkali-activated matrix. This research offers valuable insights into the strategic use and substitution of CS, FS, and other silico-aluminon additives within the context of AAMs development.