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.