Water-Based Epoxy Composite Coating Systems for Reinforcing Steel in Marine Concrete Structures: From Curing Agent Design to the Combined Effects of Multi-Layer Functional Fillers

In this study, a water-based epoxy curing agent was prepared using polyamines (mixed amines), and epoxy coatings were formulated by blending this with a polyurethane-toughened water-based epoxy curing agent in specific proportions. By testing the tensile properties of the water-based epoxy coatings, the curing agent ratio was adjusted and the curing process optimised. A layer of water-based epoxy coating was applied to both the rebar electrodes and the rebar surfaces. Through electrochemical testing, coating thickness measurement, and coating continuity testing, the effects of filler type, particle size, and content on coating performance were investigated. On this basis, steel bars coated with a water-based epoxy coating containing 0.3% graphene–polyaniline composite nanomaterials were used as the control group, whilst a water-based epoxy coating incorporating a silane solution served as the primer. Based on the results of the preliminary screening, a water-based epoxy coating containing 1% silane coupling agent and 10% zinc phosphate was selected as the intermediate coat, whilst a water-based epoxy coating containing fly ash microspheres and polystyrene microspheres was selected as the top coat. Through cold bending tests and tensile strain tests on the coated reinforcing bars, the study investigated the effects of zinc phosphate, fly ash microspheres, and polystyrene microspheres on the cold bending performance and deformation combination performance of the water-based epoxy-coated reinforcing bars. By optimising the curing process, the tensile strength of the coating reached 40.11 MPa, with an elongation at break of 19.94%; the corrosion resistance of the zinc phosphate composite coating (corrosion current density: 0.00589 μA/cm2) was comparable to that of the 0.3% graphene/polyaniline coating; and the fly ash microsphere top coat significantly improved the deformation compatibility between the reinforcing bars and the coating. The high-performance, cost-competitive water-based epoxy coating system developed in this study offers a new technical approach to the durability protection of reinforced concrete structures in marine environments.