Today's and future slags ‐ Potentials and Challenges

The steel industry produces the most widely used metal on earth. The main challenge of the industry for the next decade is the steel production transformation process. The CO₂ intensive blast furnace/basic oxygen furnace (BOF) route will be substituted by a combination of a Direct Reduced Iron plant (based on natural gas, at later stage on “green” hydrogen) with an Electric Arc Furnace (EAF) or a Submerged Arc Furnace (SAF), heated with renewable energy. Thus, the well‐known latent hydraulic granulated blast furnace slag (GBS) being successfully used in cement and concrete for more than 140 years will vanish step by step. GBS is used as a supplementary cementitious material (SCM) not only, but in particular, due to its clinker reduction and from there its CO₂ reduction potential for the cement and concrete production. Whereas the DRI process itself does not generate any slag, EAF and SAF will do. These slags will be very different. Moreover, the new EAF slags will be also different compared to today's scrap based EAF slag. However, specific slag/metal ratios, resulting slag volumes, chemical and mineralogical compositions and physical properties of the new slags are yet unknown. Thus, also their cementitious and environmental properties are still unknown. Different running projects aim mainly to create slags being similar to GBS. The main objective is to provide the cement and concrete industry furthermore with a (latent) hydraulic SCM.