Mechanical properties and chemical synergistic mechanism of lithium slag concrete under mechanical-chemical activation conditions

This study systematically examines the mechanical performance and microstructural evolution of concrete incorporating alkali-mechanically activated lithium slag (LS). Unconfined compressive strength (UCS) tests were conducted at 7 and 28 days of curing to assess the influence of LS content on early and later-age strength development. Multiscale characterization techniques, including scanning electron microscopy (SEM), X-ray Fluorescence (XRF), X-ray Diffraction (XRD) nuclear magnetic resonance (NMR), and Fourier-transform infrared spectroscopy (FTIR), were used to reveal the dual mechanism of chemical activation and physical pore refinement. The results show a non-monotonic trend in compressive strength with increasing LS content, with an optimum at 20% replacement, where the UCS reached 103% and 105% of that of the control mix at 7 and 28 days, respectively. NMR analyses reveal that activated LS contributes to refinement of the pore structure, resulting in reduced pore size and enhanced matrix densification. SEM, energy dispersive spectroscopy (EDS), and thermogravimetric (TG) analyses indicate that the improved strength is primarily attributed to the pozzolanic reaction between activated LS and cement hydration products, forming additional calcium silicate hydrate (C-S-H) and other binding phases. These findings highlight the dual role of alkali-mechanically activated LS in enhancing concrete performance through coupled microstructural refinement and chemical reactivity, offering a sustainable approach for valorizing lithium slag in cementitious materials.