Thermally treated residues and by-products as components of waste-based alkali-activated materials

Despite dwindling supplies of traditional SCMs like granulated blast-furnace slag (GBFS), a plethora of industrial mineral residues and by-products are currently not utilised in ordinary Portland cement (OPC) or alkali-activated material (AAM) binder systems. In many cases, this is due to unfavourable properties of these materials, such as low reactivity or high contents of harmful substances. This contribution demonstrates how various residues and by-products can be utilised as binder components by a thermal treatment at temperatures >1400 ℃ followed by wet granulation. Through chemical and mineralogical characterisation, it could be shown that resulting materials (“up-slags”) are similar to GBFS, consisting mainly of CaO, SiO ₂, Al ₂O ₃ and MgO with high amorphous contents. Subsequent R ³ and activity index tests and fabrication of AAM mortar and paste with a combination of up-slag and non-treated material proved the reactivity of the up-slags in OPC and AAM systems, respectively. The results demonstrate that mineral residues can be valorised as reactive binder components through thermal treatment, supporting a pathway towards a climate-friendly, energy-efficient circular building materials economy while mitigating shortages of traditional SCMs. Through carbothermal reduction, potentially valuable metals (e.g. Fe, Mn, Cr) can be reclaimed during the upcycling process. Further research has also been identified as necessary to improve our understanding of chemical and mineralogical boundary conditions for using upcycled slags as AAM binder components.