Lithium slag-cement composite mortar (LSCCM) was prepared by replacing part of 42.5 Ordinary Portland cement with lithium slag (LS). The effects of LS on the properties of cement mortar and its mechanism of action were analyzed by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), heat of hydration method, nuclear magnetic resonance (NMR) technique and mercury intrusion porosity (MIP). The results showed that LS replacing part of the cement would reduce the fluidity of the system, shorten the setting time, lower the strength in the preperiod, increase the strength in the postperiod, change the pore size distribution, and would not cause changes in the hydration products. In the early stage, LS just plays a filling role, the hydration reaction rate of the LSCCM decreases, and the pores in the system become larger, resulting in a lower compressive strength than the cement mortar at 3d and 7d. In the later stage, the LS undergoes pozzolanic reaction, which makes the LSCCM become denser, and when the replacement amount of lithium slag is 20% of the cement mass, the 28d compressive strength of the LSCCM can reach 50.2 MPa, which is 9.4% higher than that of the cement mortar specimen.

Keywords: Lithium slag, Alkali-silica reaction, Mechanical properties, Porosity, Microstructure.