Study of simulated disbonded polymer film on Zn-Al alloy coated reinforcing steel rebars

Highlights: A passivation mechanism is proposed for the disbonding of polymer coating applied on galvanized steel rebar inside concrete. In concrete, when coating applied on galvanized steel rebar is disbonded, crevice corrosion most likely will not occur. The closer the disbondment of polymer coating to the galvanized rebar, the better chance for passivation inside concrete. - Abstract: A cell was made to model disbonded regions of a polymeric coating on 98Zn/2Al alloy used to protect rebar of reinforced concrete. A crevice electrode was designed to make a tight crevice with a gap thickness less than 0.03 mm. Experiments were conducted with the crevice facing downward in 1 M sodium hydroxide. The results for thinner crevices indicated a general trend of a larger potential rise of around 1 V. A dissolution/passivation mechanism was proposed to occur inside the crevice. A general pseudo-passivation was concluded to occur inside the crevice that protects the 98Zn/2Al alloy from corrosion.