Effects of Joule heating and graphene oxide on mechanical property and microstructure of fly ash-granulated blast furnace slag-steel slag geopolymer

Joule heat curing (JHC) is a promising technique to improve curing efficiency of concrete, presenting higher applicability in the curing of geopolymer owning high ionic mobility and electrical conductivity. To further improve the conductivity and JHC curing efficacy, graphene oxide (GO) was added to the fly ash - granulated blast furnace slag - steel slag based geopolymer. The effect of JHC voltages (10–30 V), heating periods (2–8 h) and GO content (0–0.03 wt%) on the ternary geopolymer were investigated, and the underlying mechanisms were explored. JHC and GO both showed positive effects on the performance of geopolymer. The geopolymer containing 0.01 wt% GO and cured by JHC at 15 V for 8 h exhibited the most significant performance enhancement, achieving a 28-day compressive strength of 50.47 MPa, comparable to that of specimens oven cured at 80 °C, while the flexural strength reached 4.66 MPa, significantly higher than the oven cured counterpart. In addition, the drying shrinkage was reduced by 91.54 % compared with the ambient cured specimens. According to the porosity, micro-morphology and molecular bonding characterization, the microstructural compactness and production of Na(Ca)-Al-Si-OH (N(C)-A-S-H) gels were promoted by JHC, and GO can provide more nucleation sites for the formation of N(C)-A-S-H gels and fill extra pores besides improving the electrical conductivity and JHC efficacy. Although the JHC was enhanced by the relatively high ionic conductivity of geopolymer, the electron conductivity should be further improved for a stable and uniform retaining of elevated curing temperature after hardening. • Optimal electrical regime and GO content significantly improve curing efficiency. • Joule heating enhances matrix strength and density by promoting gel formation. • Variations in heat dissipation across the matrix lead to differences in polymerization degree.