Effects of modified multi-walled carbon nanotubes and PVA fibers on mechanical properties and microstructure of lithium slag base geopolymer

In this study, the effects of modified multi-walled carbon nanotubes (MWCNTs) and polyvinyl alcohol fibers (PVA fibers) on the mechanical properties of lithium slag base geopolymer were investigated. Firstly, orthogonal tests were conducted by selecting four levels under each of the five factors: modulus, alkali equivalent, waterbinder ratio, lithium slag replacement, and binder-sand ratio. Based on the results of 16 sets of fluidity and setting time experiments in the orthogonal tests, the base ratio of lithium slag base geopolymer was selected. Then, carboxylated multi-wall carbon nanotubes (COOH-MWCNTs) and PVA fibers with different contents were added to the base ratio to conduct flexural and compressive tests. The results showed that adding COOHMWCNTs and PVA fibers improved the mechanical properties of lithium slag base geopolymer. The 28d flexural strength and compressive strength of 0.1 %COOH-MWCNTs were increased by 17.5 % and 14.9 %, respectively, and the 28d flexural strength and compressive strength of 0.1 %COOH-MWCNTs and 0.9 %PVA fibers were increased by 58.1 % and 31.2 %, respectively. Finally, the effects of COOH MWCNTs and PVA fibers on the crystal phase and chemical bonds of lithium slag base geopolymer were analyzed using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Field emission electron microscopy (FESEM) was used to analyze lithium slag base geopolymer at the microscopic level, and the reinforcement mechanism of COOH MWCNTs and PVA fibers on lithium slag base geopolymer was proposed.