Synthesis, application and unique effects of RGOEP on properties of alkali-activated slag binders

•3% RGOEP improved the fracture toughness of water glass activated AAS by more than 42.3 times.•7% RGOEP saw the highest bonding tensile strength, much higher than the control AAS binder.•RGOEP resulted in the formation of a peony flower-like hydration product.•RGOEP is more effective than EP in enhancing AAS binders. A highly-dispersed reduced graphene oxide/epoxy resin (RGOEP) composite was synthesized and used to improve related properties of alkali-activated slag (AAS) binders. This study scrutinizes the effects of epoxy resin and RGOEP composite on the hydration products, microstructure and mechanical properties (especially fracture toughness) of the AAS binders activated by water glass or NaOH solutions. The experimental results showed that RGOEP (3 wt%) is able to significantly improve the fracture toughness of the AAS mortars activated by water glass and NaOH, with more than 42.3 and 13.3 times greater, respectively, compared to the pure AAS counterpart. A peony flower-like hydration product was detected when RGOEP was used which is believed to result from the modification of AAS binding matrix by RGOEP at a nanoscale level. Besides, bonding tensile strength was also improved remarkably when 7 wt% GROEP was added into the BFS binders activated by water glass, almost up to 4.8 and 2.9 times as that of the control mortar and the one enhanced by 5 wt% EP, respectively. Thus, a unique advantage of reduced graphene oxide over epoxy resin in enhancing AAS binders was discovered. Considering a very low content of reduced graphene in epoxy resin (only 0.3 wt%), this research indicates great potential for wider industrial applications of this type of RGOEP in the AAS binders.