Evaluation of mineral waste streams for alkali-activated materials: Reactivity and utilization potential

Mineral wastes constitute one of the largest waste streams worldwide, and their recycling in alkali-activated materials (AAMs) offers a promising pathway towards resource efficiency and CO2 reduction. This study investigates the suitability of 39 Austrian mineral by-products, wastes, and secondary raw materials (WSRM) as precursors for AAM production. Comprehensive chemical and mineralogical analyses were used to derive reactivity variables, which were linked to the performance of standardized AAM paste systems prepared at fixed Si/Al ratios ranging from 1.5 to 2.5. Seven-day compressive strengths between 20 and 63 MPa with WSRM shares of 30–85 wt.-% were obtained. The combination of reactivity data with strength properties allowed the identification of four distinct groups of WSRM exhibiting strongly diverse reactivity behavior: Calcium-rich WSRM, such as basic oxygen furnace slag and wood combustion fly ash, exhibited high chemical reactivity, whereas electric arc furnace slag, open-hearth furnace slag, and stone wool displayed strength development strongly dependent on the reactive Si/Al ratio, with an optimum between 1.7 and 1.8. Construction and demolition waste and clay-based wastes primarily contributed through filler effects, though partial chemical reactivity was evident. In contrast, silica-rich WSRM, including waste glass, glass wool, and fluidized bed ashes, showed negligible reactivity. By linking extensive chemical and mineralogical analyses with fundamental binder properties, this study provides a framework for tailoring WSRM-based alkali-activated binders and advancing circular economy strategies in construction materials.