The impact of hybrid solvent-borne/waterborne coating applications on the corrosion resistance of coating systems for steel bridge structures

Purpose This study evaluates the effects of hybrid waterborne/solvent-borne coating systems on the corrosion resistance and mechanical properties of protective coatings for bridge steel structures. The purpose of this study is to identify optimal material combinations that balance efficiency with long-term durability. Design/methodology/approach Nine coating systems were formulated using four epoxy primers, two epoxy intermediate coats and two fluorocarbon topcoats. Their performance was assessed through neutral salt spray (NSS) and Xenon lamp aging tests (XAT). Protective mechanisms and interfacial compatibility were analyzed using electrochemical impedance spectroscopy, adhesion testing, gloss retention, color difference measurements and tensile property assessments. Findings Solvent-borne systems, particularly those with epoxy zinc–aluminum primers, demonstrated superior long-term corrosion resistance, achieving low-frequency impedance modulus (|Z|0.01Hz) of approximately 1,010 O·cm2 after 28 days. This resulted from aluminum oxide’s shielding and self-healing effects. Hybrid systems exhibited significant performance degradation: adhesion strength declined from 16 MPa to 2 MPa after 42 days of testing, while barrier properties weakened (|Z|0.01Hz <104 O·cm2). This degradation is attributed to polarity mismatches, curing conflicts and interfacial defects. Originality/value This work provides novel insights into the critical role of material compatibility in coating design, highlighting trade-offs between eco-friendly waterborne components and solvent-borne systems’ durability.