Passivation of cold-sprayed zinc-coated steel bars in simulated concrete pore solution

Hot-dip galvanized coating is proved to be effective in preventing chloride ion induced corrosion on steel bars, however, highly-toxic substances generated during the plating process seriously pollute the surrounding environment. Cold-sprayed zinc as an environment-friendly technology is an alternative to the hot-dip galvanized technology, but it has not been applied to steel bars in the alkaline environment of concrete. This study first fabricated the cold-sprayed zinc-coated steel bars, and then investigated the influences of Ca2+ concentration and pH on the passivation of zinc-coated steel bars in the simulated concrete pore solutions through electrochemical tests, microstructure examination, and element composition analysis. The experimental results show that passive film can be generated on the surface of cold-sprayed zinc-coated specimens in the simulated concrete pore solutions with pH=12.5 and Ca2+ concentration above 0.8 g/L, but Ca2+ concentration determines the density and quality of the passive film. The passive film can resist the attack of chloride ions up to 0.2 mol/L. Compared with hot-dip galvanized coating, more large-sized and compacted crystals are generated on the surface of cold-sprayed zinc coating. Thus, it is feasible to apply cold-sprayed zinc technology to provide corrosion protection for steel bars in the concrete.