Durability of alkali-activated materials in cementitious leaching environments

• The long-term durability of alkali-activated materials (AAMs) is investigated under water leaching conditions. • Sodium-based geopolymers, potassium-based geopolymers, and alkali-activated blast furnace slags are considered. • Exposure conditions included cement pore solution, limewater, carbonated water, and endogenous curing in sealed environments, until 180 days. • XRD and MAS NMR demonstrate the structural stability of these systems. • The materials also maintain high compressive strengths. This study investigates the long-term durability of alkali-activated materials (AAM) under exposure to different cement leachates, with a particular focus on their potential use in radioactive waste containment applications. Three different binders were considered: sodium-based geopolymers (Na-geo), potassium-based geopolymers (K-geo), and alkali-activated blast furnace slags (BFS). Since these materials may be incorporated into cement-based host structures in deep radioactive waste repositories, their interaction with leachates enriched in cementitious phases was simulated. Exposure conditions included cement pore solution, limewater, carbonated water, as well as endogenous curing in sealed environments. The evolution of porosity was monitored up to 180 days using thermoporometry and nitrogen adsorption–desorption (PSD). Phase changes were identified by X-ray diffraction, 29 Si and 27 Al MAS NMR, while compressive tests assessed mechanical performance. Porosity analyses confirmed the mesoporous nature of AAM, with geopolymers showing only slight variations under alkaline curing, while BFS exhibited a decrease in porosity over time, consistent with strength development. XRD and MAS NMR further demonstrated the structural stability of these systems, with no significant changes in crystalline or amorphous phases. Overall, the materials maintained high compressive strengths, confirming their chemical, physical, and mechanical durability across different cementitious leachate environments.