Lithium slag (LS), a by-product of lithium extraction processes, poses a significant disposal challenge during the rapid development of new energy technologies. In this study, LS was used to replace partially washed sand in the process of mortar production to compensate for the content of stone powder in sand. Five mortar mixes containing varying proportions of LS were prepared, and the macroscopic performance was evaluated. A comprehensive microscopic analysis, including microstructure observations, hydration product identification, and pore structure analysis, was conducted. The impact of LS on the chloride ion permeability of mortar was also investigated in this study. The results indicate that an increase in LS content gradually reduces the workability of the mortar, with a 39.29% decrease in fluidity when 40% of the sand is replaced with LS. Moreover, the compressive and flexural strengths of the mortar initially increase and then decrease with higher LS content. Microscopic tests reveal that 20% LS substitution significantly optimizes the pore structure of the mortar, resulting in a lower chloride ion permeability coefficient. Consequently, 20% LS substitution is recommended as the optimal dosage for use as fine aggregate in mortar.

Investigating the effects of lithium slag (LS) as an admixtures on the properties of different cement pastes can expand its potential applications in construction materials. This study examines the influence of LS content (0%, 10%, 20%, and 30%) on the performance of ordinary Portland cement (OPC), ultra-fine ordinary Portland cement (UPC), and calcium sulfoaluminate cement (CSC) pastes. The underlying mechanisms are explored using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). The results indicate that incorporating LS reduces the fluidity, setting time, and bleeding rate of cement pastes but enhances their compressive strength at 1, 7, and 28 days. Specifically, LS improves the long-term strength of OPC pastes, whereas it primarily enhances the early-age strength of UPC pastes. For CSC pastes, LS significantly promotes both early and later-age strength. SEM, XRD, and FTIR analyses reveal that the effects of LS stem from a filling effect and the activation of hydration reactions, where reactive components and gypsum in LS promote the formation of hydration products such as calcium silicate hydrate (C-S-H) and ettringite. These findings provide a theoretical basis for the application of LS in diverse cementitious systems.