Influence of lithium slag on the mechanical properties of engineered cementitious composites

Engineered cementitious composites (ECCs) are advanced ductile cementitious materials with superior tensile pseudo-strain-hardening behaviour and multiple microcracking capacity. However, their high cement consumption results in substantial carbon dioxide footprints and elevated production costs, restricting sustainable applications of ECCs. Lithium slag (LS), a voluminous industrial by-product with pronounced pozzolanic activity, has not been systematically investigated in ECC matrices. Therefore, in this study, eco-friendly ECC mixtures, with partial replacement of ordinary Portland cement with LS at mass fractions of 10%, 20% and 30%, were investigated. The workability, mechanical properties and microstructural evolution of the LS-ECCs were systematically characterised. The results showed that LS impaired the flowability of fresh ECC mixtures. However, a 20% LS replacement ratio yielded the most balanced comprehensive performance, achieving a 28-day compressive strength of 71.8 MPa, ultimate tensile strength of 4.2 MPa and tensile strain capacity of 9.0%. Microscopic analyses demonstrated that LS actively participated in the pozzolanic reaction, consuming portlandite and generating dense calcium aluminium silicate hydrate gels, which refined the matrix microstructure and improved fibre–matrix interfacial bonding and fibre bridging efficiency. Excessive LS (30%) resulted in insufficient pozzolanic reaction due to limited portlandite availability, leading to deteriorated mechanical performance. The results of this study validate the technical feasibility of LS-ECCs, with 20% LS identified as the optimal cement replacement level for balancing workability, mechanical properties and environmental benefits. The findings provide a sustainable pathway for industrial solid waste valorisation and the development of low carbon dioxide, high-performance ECCs.