Influence of granulated blast furnace slag and functionalized multi-walled carbon nanotubes on the mechanical properties and microstructural mechanisms of lithium slag-based geopolymers

This study investigated the effects of functionalized multi-walled carbon nanotubes (MWCNTs(F)) and granulated blast furnace slag (GBFS) on the mechanical properties and microstructural mechanisms of lithium slag-based geopolymer (LSG). LSG specimens were designed with GBFS substitution levels (0 %, 10 %, 20 %, 30 %, 40 %) for fly ash and MWCNTs(F) additions (0, 0.05, 0.1, 0.15 wt% of binder). Experimental results revealed that the LSG specimen containing 30 % GBFS and 0.1 wt% MWCNTs(F) exhibited optimal mechanical properties after 28-day curing, achieving bending and compressive strengths of 8.542 MPa and 88.324 MPa, respectively. Fluidity and setting time tests demonstrated significant improvements in workability and accelerated setting through GBFS and MWCNTs(F) incorporation. Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) analyses indicated that the addition of appropriate GBFS and MWCNTs (F) promoted the formation of Si-O-Al and Al-O-Si bonds, with enhanced diffraction intensities between 18 ° and 30 ° and peak broadening, suggesting accelerated hydration reactions and increased hydration product formation. Scanning electron microscopy (FESEM) observations revealed that MWCNTs(F) functioned as fillers, bridges, and crack-pinning reinforcements, while GBFS optimized the geopolymer microstructure through enhanced structural densification. Thermogravimetric analysis confirmed robust thermal stability for all specimens, with total mass losses below 23 % across the temperature range of room temperature to 1000°C, regardless of additive incorporation. These findings collectively demonstrate that optimized GBFS substitution and MWCNTs(F) addition significantly enhance both mechanical performance and microstructural development in LSG systems.