A comparative analysis of the corrosion characteristics of electro-galvanized steel coated with epoxy zinc-free and zinc-rich coatings in 5% NaCl

Anchor elements and pad hooks are used to attach large or small parts made of Glass Fiber Reinforced Concrete (GFRC) panels to the main structure of a building. The protection of these metallic parts is important to avoid corrosion. This work aims to compare the protection ability of normal epoxy and zinc-rich coatings (96% Zn) against chloride-induced corrosion of GFRC electrogalvanized pad hooks. The ASTM B117 salt spray test methods supported by SEM and EDAX surface analysis were adopted. The influence of surface treatment on coating thickness and performance was also considered. The results obtained show that the normal epoxy coatings are unsuitable for the studied pad hooks. Corrosion progressed under the coatings. Surface pre-treatment has a significant effect on the thickness of coatings. The average thickness of a two-coats untreated, sandblasted, and wire brushed pad hook zinc-rich coated layer is 39.27 µm, 117.8 µm, and 228.2 µm. The sandblasted pad hooks coated with zinc-rich coatings exhibit high corrosion resistance after the salt spray test. The EDAX results reveal that the surface products on the sandblasted zinc-rich coatings were devoid of the main substrate components, namely Fe, Si, and Mn but consisted of 2.43 wt.% O, 0.53 wt.% Cl, and 96.49 wt.% Zn. The absence of these elements implies no corrosion and effective corrosion prevention by zinc-rich coatings. Visual observation and SEM images corroborate the EDAX results. However, the thickness of the sand-blasted zinc-rich coated surface increased from 117.8 µm to 306.2 µm due to the formation of ZnO. Zinc-rich coatings are recommended for the protection of GFRC electrogalvanized hooks and elements.