Reaction Kinetics, Microstructural Evolution and Mechanical Performance of LiOH-Activated Slag

Activator chemistry plays an important role in governing reaction kinetics, phase assemblage and structural development in alkali-activated slags. While sodium- and potassium-based activators are widely used, the influence of alternative alkali cations remains insufficiently understood. This study investigated LiOH-GGBS and compared its reaction kinetics, mechanical performance, and microstructural development with NaOH-GGBS and water-OPC. Reaction kinetics were assessed using isothermal calorimetry. Mechanical performance was evaluated through compressive, split tensile, and flexural strength tests up to 90 days. Microstructural and phase evolution were examined using SEM-EDS, XRD, and TGA. LiOH-GGBS exhibited slower early-age reaction kinetics than NaOH-GGBS and OPC, resulting in lower early-age strength. However, sustained strength development enabled LiOH-GGBS to surpass the 90-day compressive strength of OPC by 8% and reach around 85% of that of NaOH-GGBS. SEM-EDS analysis revealed progressive matrix densification and continued gel evolution over time, while XRD and TGA confirmed the formation of a CH-free binder dominated by C(L)-A-S-H type gels and hydrotalcite-like phases, comparable to NaOH-GGBS. Lower gel-related bound water at early ages for LiOH-GGBS (70% of OPC and 65% of NaOH-GGBS at 7 days) corroborates delayed reaction kinetics, while its gradual increase with curing age (92% of OPC and 75% of NaOH-GGBS at 90 days) supports sustained gel formation and long-term strength development. The results highlight the role of cation chemistry in AAS systems. Strong hydration and the reduced early-age catalytic effectiveness of Li+ ions moderate early reaction kinetics, redistributing gel formation over time and enabling sustained microstructural and strength development.