Thermal degradation of copper-modified geopolymer containing graphene oxide under cyclic heating

This study examines the thermal behaviour of one-part fly ash/slag alkali-activated paste incorporating electrolytic copper powder (ECP) and graphene oxide (GO) under cyclic heat exposure at 400 °C for 10 cycles. To investigate thermal degradation mechanisms, their thermal-mechanical properties, microstructure and pore structure were characterised including ²⁹Si, ²⁷Al, ¹H NMR, nitrogen adsorption-desorption (NAD), XRD, FTIR and SEM/EDS. Results show that heat accelerates geopolymerisation, increasing the Si/Al ratio while inducing a transition from a cross-linked silicate network to shorter-chain C-(N)-A-S-H units, leading to reduced thermal conductivity and specific heat capacity. Despite an increase in total nano-scale porosity (< 100 nm) after heat exposure, continued geopolymerisation and gel network rearrangement led to pore refinement with more gel pore (< 10 nm) and improved mechanical strength. Compared to the plain mix, the incorporation of ECP and GO further enhanced mechanical and thermal stability under cyclic heat exposure. These findings provide the understanding on the role of ECP and GO in mitigating thermal degradation, supporting their potential in high-temperature applications such as thermal energy storage systems.