Mineral Residues and By-Products Upcycled into Reactive Binder Components for Cementitious Materials

In contrast to granulated blast-furnace slag (GBFS), many other industrial residues and by-products such as steel slags are currently not utilised to produce hydraulic or alkali-activated binders. Simultaneously, the building materials industry is confronted with steadily growing demands for increased CO₂ and resource efficiency, as well as dwindling supplies of traditional supplementary cementitious materials. This contribution covers the characterisation of slag-like compounds prior to and after carbothermal treatment, with respect to their utilisation potential as binder components. The treated materials were highly amorphous with a favourable chemical composition - particularly high contents of CaO, SiO₂, Al₂O₃ and MgO, high (CaO+MgO)/SiO₂-ratios (>1.0, ideally > 1.2) and low amounts of unwanted impurities like Fe- and Mn-containing compounds. Subsequent characterisation of the reactivity of the processed materials revealed high hydraulic activity (activity index up to >100% after 28 days) and suitability for alkali-activation. In contrast, the untreated materials showed only insufficient hydraulic activity but could successfully be used as binder components in alkali-activated materials. Chemical indices based on the amorphous content and the content of CaO, MgO, Al₂O₃, SiO₂, FeO and MnO were identified as suitable control parameters for estimating the potential hydraulic activity of slag-like materials.