Tensile properties and microstructure of lightweight engineered geopolymer composites containing PVA fibers and multi-walled carbon nanotubes (MWCNTs) after high-temperature exposure

This study investigates the effects of elevated temperatures on the properties of lightweight engineered geopolymer composites (LW-EGC). The LW-EGC was reinforced with 2.5 % polyvinyl alcohol (PVA) fibers and 0.15 % multi-walled carbon nanotubes (MWCNTs) and subjected to temperatures ranging from 20 °C to 800 °C. Performance evaluations included measurements of mass loss, tensile strength , crack formation , and microstructural evolution using thermogravimetric analysis (TG), tensile tests , scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FT-IR). Results revealed that LW-EGC exhibited progressively greater mass loss as temperature increased, though the mass-loss rate gradually decreased due to the evaporation of water and decomposition of calcium-rich phases. Tensile strength reached a maximum at 200 °C but decreased significantly beyond 400 °C, mainly due to the melting of PVA fibers and increased matrix porosity . SEM analyses showed extensive decomposition of PVA fibers and progressive degradation of the geopolymer matrix at higher temperatures, weakening the overall composite structure. XRD and FT-IR analyses confirmed calcite decomposition and highlighted the excellent thermal stability of N(C)-A-S-H gel. • High-temperature tensile properties of LW-EGC with PVA fibers and MWCNTs were investigated. • Mass loss, tensile strength , and crack development were evaluated at temperatures up to 800 °C. • PVA fiber melting and matrix decomposition significantly reduced mechanical performance above 400 °C. • LW-EGC exhibited excellent thermal stability and energy absorption.