Characteristics of carbide-slag-activated GGBS-fly ash materials: Strength, hydration mechanism, microstructure, and sustainability

To improve the reuse of industrial solid wastes, this study investigates alkali-activated material (AAM) consisting of ground granulated blast-furnace slag (GGBS) and fly ash (FA) activated by carbide slag (CS). A separation treatment process was introduced to obtain reactive ultrafine GGBS and FA (RUGGBS and RUFA). The compressive strength is used to differentiate between representative specimens for exploring the hydration mechanism in terms of hydration process, hydrate types, and pore-structure characteristics. Finally, the environmental and economic benefits of these materials are calculated and analyzed based on the material sustainability indicators (MSIs). The results show that the separation of GGBS and FA reduces their particle size and enhances their hydration activity. Although using RUGGBS and RUFA delays the setting time of AAM, it results in lower hydration heat release and increases compressive strength after aging for 3 days. RUGGBS and RUFA synergistically promote polymerization reactions in CS-activated GGBS-FA systems, which results in more hydrates, including C-S-H gel, C-A-S-H gel, and hydrotalcite-like hydrates, helping to optimize the pore structure and strengthen the material. These findings suggest that separating industrial solid wastes can promote the use of AAMs in construction engineering by significantly reducing their environmental impact.