Enhancing Tensile Performance of Lithium Slag Geopolymers Using Hybrid Fibers and Modified Multi-Walled Carbon Nanotubes

This study investigates the synergistic effects of hybrid fibers and functionalized multi-walled carbon nanotubes (MWCNTs) on the mechanical and microstructural properties of lithium slag–based geopolymers (FL-EGC). Unlike conventional studies that focus on single reinforcement strategies, this work combines nanoscale modification with macroscale fiber reinforcement to overcome the inherent brittleness of geopolymers. Results show that while hybrid fibers and MWCNTs reduce flowability, the incorporation of 2.5% PVA, 1.0% steel fibers, and 0.15% MWCNTs yielded the best balance of performance, improving ultimate tensile stress by 12.7%, strain by 69.2%, and specific fracture energy by 78.2%. Microstructural analysis confirmed that MWCNTs enhanced crack-bridging and matrix densification, while hybrid fibers improved strength and ductility. These findings demonstrate a novel reinforcement pathway for developing sustainable, high-performance geopolymers from industrial by-products, providing both theoretical insights and practical guidance for green construction materials.