Electrothermally activated mineral-impregnated carbon-fiber reinforcements for accelerated curing of geopolymer composites

This study investigates geopolymer-impregnated mineral carbon-fiber reinforcements (G-MCFs) as embedded Joule-heating elements for accelerated curing of metakaolin-based geopolymer composites, using epoxy-impregnated CFRP yarns as a reference. Both systems operated as controllable low-voltage DC heaters; however, under the same nominal yarn-temperature regimes, G-MCF produced a stronger matrix-level thermal response than CFRP, as reflected by higher matrix temperatures and faster matrix-temperature development. Penetration testing, calorimetry and FT-IR spectroscopy confirmed accelerated geopolymerisation and earlier development of a load-bearing gel network under targeted Joule heating. Multiscale characterization by MIP, and ESEM revealed a curing–damage trade-off, whereby aggressive thermal activation promoted connected porosity, interfacial void formation and ITZ degradation despite accelerating matrix stiffening. Pull-out testing further demonstrated that moderate electrothermal curing enhanced bond development, whereas prolonged exposure to elevated temperatures reduced interfacial stability. Overall, the results demonstrate that reinforcement-integrated electrothermal curing depends on the combined effects of electrical input, matrix-level thermal response and interfacial integrity, rather than on electrical input or reinforcement temperature alone. Reinforcement–matrix thermophysical coupling is proposed as a possible mechanism contributing to the observed differences between the two reinforcement systems.