Adhesion Evaluation of Duplex Paint System for Sustainable Infrastructure

Steel structures such as highway bridges, walkway railings are painted with organic coatings to provide aesthetic appeal and corrosion resistance. In a duplex system organic paints are applied to galvanized or metalized steel surfaces. The duplex system is potentially more sustainable than the zinc-rich primer/steel system due to its longer lasting corrosion resistance. A perceived weakness of the duplex system is that the paint adhesion on the metallic zinc is harder to achieve. In order to understand factors influencing the paint adhesion on galvanized or metalized steel, a series of experimental tests were performed for adhesion strengths of 4 different paints and 3 different types of roughened zinc surfaces on 84 test panels. The contact angles were also measured for freshly formulated liquid paints on the roughened zinc surfaces to test if there is a correlation between the paint wetting property and the adhesive strength. By comparing duplex system and zinc-rich primer/steel qualified by Northeast Protective Coating Committee (NEPCOAT), it was found the paint adhesion of duplex system is as strong as the zinc primer/steel panels based on test results with the ASTM D4541 procedure. It was also found that adhesive strengths depend on the match between the paint and type of roughened zinc surfaces. The measurement of liquid paint wetting properties indicates potential correlation between contact angle and the pull-off adhesive strength. It has been suggested that contact angle/strength correlation could be useful as a tool for optimizing the match between paints and the profiled zinc surfaces.