Characterization of metallurgical slags towards the formulation of alternative binders

The large CO₂ emissions which come from limestone calcination, one of the raw materials to produce Portland cement, pose an urgent global issue that requires industrially sustainable alternative options to replace this material. This work is about the characterization of three types of metallurgical slags from Italian companies, two of them are from steel mills (with an EAF production process) and the other one from foundry process. We try to find if we can take advantage of these waste materials as supplementary cementitious materials, encouraging the use of local products to produce eco-sustainable binders. The analyses done give us information about the elementary chemical composition, by the X-ray fluorescence, the mineralogic composition, by X-ray powder diffraction, and the particle size distribution by laser granulometry. Calorimetric data are important to assess the behaviour and the reactivity of the different slags in the cementitious formulations. Mechanical compressive and splitting test determine the mechanical strength of the formulations. The two slags from steel mills are reactive, show quick setting (due to their abundance in mayenite), and thus they need the addition of GBBS and gypsum to slow down their reactivity. The slag from the foundry process is not much reactive, it does not have problems of quick setting and expansive reactions and it can be mixed to the cement as it is, without the addition of GBBS. By choosing the correct quantity of slag, GBBS and gypsum mixed together in different formulations, these materials can reach mechanical strength classes of 32.5 MPa and 42.5 MPa.