Study of Alkali-Silica reaction in blast furnace slag mortars activated with NaOH and LiOH

This study investigates the Alkali-Silica Reaction (ASR) behavior in Ground Granulated Blast Furnace Slag (GGBFS) mortars activated with NaOH (GGBFS-NaOH) and LiOH (GGBFS-LiOH). AAS mortars incorporating feldspar-based reactive aggregates were prepared with varying molar concentrations of each activator. Accelerated mortar bar tests (ASTM C1260) showed that GGBFS-NaOH samples showed expansion beyond the threshold limit of 0.1% within four days of exposure at 10 M concentration, whereas GGBFS-LiOH samples showed negligible expansion (≤ 0.02%) throughout the test period. Microstructural analysis confirmed the presence of ASR gel and microcracking in GGBFS-NaOH mortars, particularly near the interfacial transition zone. In contrast, LiOH activation resulted in the formation of dense lithium-silicate layers and stable C–A–S–H gels, effectively mitigating silica dissolution and crack development. Thermodynamic modelling corroborated these findings, showing that GGBFS–LiOH favored stable C–A–S–H and Stratlingite phases that immobilize alkalis and minimize expansion, whereas GGBFS–NaOH formed C–S–H, AFm, and zeolites, indicating greater alkali mobility and ASR risk. Thus, the study offers a characterization-driven mechanistic insight into the enhanced ASR resistance of LiOH-activated systems.