Enhancing Adhesion and Corrosion Resistance of Epoxy Coatings on Steel Reinforcing Bars Through the Incorporation of Functional Interface Layers

To enhance the stability of epoxy (EP) coatings on steel bars while improving their active and passive corrosion protection properties, the functional composite coatings were designed and prepared. Intercalated zirconium phosphate nanofillers (LCZrP) loaded with corrosion inhibitors were firstly synthesized and designed, and then were integrated into silane coatings (SC), which were preapplied to the bar substrate to enhance the integrity and interfacial adhesion properties. Lastly, an epoxy layer was applied, resulting in the functional composite coatings (LCZrP/SC/EP). The chemical composition and surface morphology were performed using scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM-EDS). The corrosion resistance of the coatings was evaluated using electrochemical impedance spectroscopy (EIS), complemented by adhesion tests to analyze the service stability of the coatings. The findings revealed that the silane interlayer notably improved the interfacial bonding at the junction where the epoxy resin interacts with the steel bar, thereby enhancing the corrosion resistance. Notably, the coating presented the optimal corrosion resistance when the nanofiller content was 0.04 wt.%. The impedance modulus at 0.01 Hz (|Z| 0.01Hz ) for the LCZrP/SC/EP coated coating was 5.05 × 10 10 Ω·cm 2 , which was two orders of magnitude greater than that of the EP coatings and the EP coating with silane interlayer (SC/EP) by one order of magnitude. Following 30 days of immersion, its |Z| 0 . 01Hz remained higher than the EP coating as well as the SC/EP coatings. The integral LCZrP/SC/EP coatings exhibit excellent long-lasting corrosion protection, owing to the self-responsive characteristics of LCZrP, the interfacial adhesion of the LCZrP/SC interlayer, and the enhanced barrier effect of the EP coatings. This combination effectively integrates active and passive protection strategies, thereby preventing metal corrosion. The above solution ensures that the coatings provide durable and reliable protection against corrosion over extended periods.