Impact of high-temperature exposure on the thermal and physio-mechanical performance of graphene-reinforced geopolymer composites

Geopolymer composites are emerging as sustainable materials with significant potential in the construction industry. While geopolymers are known for their inherent thermal resistance properties, their mechanical stability at elevated temperatures remains a key challenge due to microstructural degradation and moisture-induced damage. This study investigates the reinforcing effect of graphene oxide (GO) on fly ash-based geopolymer composites under ambient and high-temperature (900°C) conditions. Low-cost, industrial-grade GO with iron impurities was combined into the geopolymer matrix at varying dosages (0.1–0.4 wt% of binder). The mechanical properties and microstructural characteristics of graphene-reinforced geopolymer composites (GRGC) were then compared with plain geopolymer composites (without GO)- control. Results indicated that the addition of 0.2 wt. (%) GO in GRGC composites enhanced the compressive strength by 16.59 (%) and 18.48 (%) at 7 and 28 days of curing, respectively, compared to the control specimens. The strength enhancement in GRGC was more significant at a high-temperature exposure, as reflected by a 104 (%) increase in compressive strength compared with the control specimens. The physio-mechanical behaviour was analysed through microstructural investigations, such as Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and Thermogravimetric Analysis (TGA). Microstructural analyses revealed that GO did not contribute to any new phase formation, acting as a nanofiller, refining the pore structure and enhancing matrix densification without altering the primary amorphous gel phase, while also improving thermal stability and reducing mass loss at elevated temperatures. The results suggest that GO enhanced thermal stability by reducing dehydration rates and transforming the amorphous gel matrix into a uniform crystalline structure after high-temperature exposure. These findings demonstrate the potential of GO-reinforced geopolymer composites as thermally stable and mechanically resilient materials for high-temperature structural applications.