The Effect of Lithium Slag on the Physicomechanical Properties and Hydration Characteristics of Ferroaluminate Cement

Abstract To explore the resource utilization potential of industrial waste lithium slag (LS) in the ferroaluminate cement (FAC) system, this study conducted tests on the workability, mechanical strength, hydration, and microstructure of LS-FAC composite cement pastes, revealing the influence mechanism of LS on the physical-mechanical properties and hydration process of FAC. The results show that the electrical resistivity at 24 h initially decreased and then increased, whereas the fluidity, setting time, and cumulative exothermic at 72 h decreased with the increase in LS from 0% to 30%. In addition, LS had a promoting effect on the early hydration of the FAC, which could accelerate the hydration exothermic rate, shorten the hydration induction period, and accelerate the hydration process; this effect was due to the active mineral gypsum ( CaSO 4 · 2 H 2 O ) in LS, which could directly participate in the early hydration of FAC and preferentially react with C 4 A 3 S ¯ to form ettringite (AFt), greatly promoting its nucleation and growth. An interesting phenomenon could also be seen: although the incorporation of LS significantly increased the early formation rate and number of AFt, it was hardly helpful for the early strength development of the sample. According to SEM and MIP tests, the addition of LS changed the crystal morphology of AFt. The AFt crystals formed in the early stage were not only short and slender but also mostly disorderly stacked on the surface of cement particles, which cannot be effectively lapped to form a network structure. Although the excessive and rapidly generated AFt filled and refined the large pore size to a certain extent, it led to an increase in porosity and total pore volume and a loose paste structure. This may not be conducive to the development of early strength. However, the compressive strength of mortar samples with 5% and 10% LS at 90 d exceeded that of the control sample, which increased by 6.9% and 3.8%, respectively, mainly because that the volcanic ash activity of LS was sufficiently exerted in the later stage, and an appropriate amount of LS ( ≤ 10 % ) could effectively improve the pore structure of FAC and enhance the later strength. This study demonstrated the feasibility of LS mixed with FAC, which provided a new solution for the high-value utilization of bulk industrial solid waste and the low-carbon development of the building materials industry.