Recycling lithium slag into eco-friendly ultra-high performance concrete: Hydration process, microstructure development, and environmental benefits

To ascertain the viability of utilizing lithium slag (LS) in the development of eco-friendly ultrahigh performance concrete (UHPC), this paper provides a detailed analysis of the effects of LS on UHPC. Specifically, the hydration and microstructural changes in UHPC containing LS (LS-UHPC) were comprehensively examined. Based on the results of isothermal calorimetry, X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP), LS primarily acts as a filler, promotes nucleation, provides internal curing, and participates in the pozzolanic reaction. Significantly, the internal curing effect and the pozzolanic reaction enhanced the strength development of LS-UHPC. UHPC with 20 % LS exhibited the highest 28 d compressive strength at 134.48 MPa and presented the densest microstructure. However, approximately 4 % of the calcium hydroxide in LS-UHPC would not be involved in the pozzolanic reaction. The presence of gypsum in LS led to increased ettringite formation in LS-UHPC. Although LS extended the induction period of UHPC, it intensifi ed the hydration degree of cement. In LS-UHPC, the molar ratio of Ca/Si of C-(A)-S-H decreased, whereas the molar ratio of Al/Si increased, implying that the dissolved aluminum from LS was incorporated into the C-S-H chains. The integration of LS not only considerably reduced the carbon emissions and energy consumption of UHPC but also optimized LS recycling. Overall, the development of a sustainable UHPC by incorporating LS is both practicable and advantageous for environmentally conscious construction practices.