Assessment of lithium slag as a supplementary cementitious material: Hydration characteristics, pozzolanic reactivity, and strength development

This study investigates the feasibility of using lithium slag powder (LSP) as a supplementary cementitious material (SCM) in ordinary Portland cement (OPC) systems. Fly ash (FA) and ground-granulated blast furnace slag (GGBS) were used as reference SCMs to compare setting behavior, hydration heat evolution, and mechanical and pozzolanic performance in blended mortars. The effects of SCM type and replacement ratio (10–50 vol. %) on setting time, calorimetric properties, compressive strength, and calcium hydroxide consumption were systematically examined. LSP exhibited delayed setting behavior comparable to that of FA, attributable to its lower CaO content and relatively high sulfate concentration. However, it showed more pronounced secondary aluminate reactions. Isothermal calorimetry revealed that the hydration of LSP-containing systems exhibited a distinct third heat-evolution peak associated with sulfate–aluminate reactions, indicating the active participation of LSP in the hydration process. Although LSP mortars exhibited lower early-age compressive strength than the plain mortar, strength development accelerated beyond 7 days due to progressive pozzolanic reaction between amorphous aluminosilicates in LSP and Ca(OH) 2 . These results indicate that LSP possesses latent pozzolanic reactivity. However, when LSP is used as a SCM, its relatively high SO₃ content necessitates an assessment of volume stability, and an appropriate replacement level should be determined with this consideration in mind.