Viscosity, Crystallization, and Inherent Reactivity of Copper Slag in Cementitious Systems: FeO/SiO₂ Ratio and CaO Content

The valorization of copper smelting slag as a supplementary cementitious material (SCMs) improves raw material efficiency in copper smelting and reduces CO₂ emissions from the cement industry. A critical factor for SCM performance is the amorphous content, which is influenced by the cooling method, cooling rate, and composition. This study investigated the FeO/SiO₂ ratio (1.1 and 1.3 mol%/mol%) and CaO contents (1.3 and 12 mol%) influence on the crystallization, viscosity, and inherent reactivity within the FeO-SiO₂-Al₂O₃-CaO-MgO system. A hot-stage confocal laser scanning microscope was used to examine the crystallization behavior under continuous cooling conditions. In addition, the viscosity regarding crystallization tendencies was measured and evaluated. The findings demonstrated that increasing the FeO/SiO₂ ratio and CaO content reduced melt viscosity, promoting faster crystallization and imposing stricter demands on the cooling rate to maintain the amorphous structure in the material. Moreover, reactivity tests on water-granulated samples revealed that a higher FeO/SiO₂ ratio and CaO content decreased the reactivity in the evaluated intervals.