Laboratory performance of zinc anodes for impressed current cathodic protection of reinforced concrete: Fid-Bau Portal

Laboratory performance of zinc anodes for impressed current cathodic protection of reinforced concrete

Brousseau, R. / Arnott, M. / Baldock, B.

Cathodic protection (CP) is used increasingly to mitigate steel reinforcement corrosion in concrete. The performance of zinc materials as impressed current anodes was evaluated. The anode materials investigated included rolled zinc sheets, metallized zinc, and 85 % Zn-15 % Al. The circuit resistance and the adhesion of the anodes was monitored with polarization time. Overall performance of arc-sprayed zinc was good. However, its adhesion to the concrete surface slowly decreased as the current density, or the polarization period, inceased. Penny blank sheets and metallized 85 % Zn-15 % Al were found unsuitable as impressed current anodes. Metallized zinc performed well as impressed current anode over a 900-day test period. There was a loss of adhesion for coating anodes with higher anodic current densities and longer polarization times. Since this also applied to metallized zinc, the application procedure must produce the best adhesion possible to the concrete substrate. Metallized 85 % Zn-15 % Al should not be used as an impressed current anode based on the severe disbondment and blistering observed. Zinc sheets encapsulated in mortar performed poorly and, therefore, are not recommended for use as impressed current anodes. There was an increase in the effective circuit resistance as metallized zinc was oxidized (i.e. the driving voltage for the metallized samples increased with the applied current density and polarization time). The zinc oxidation products did not diffuse in the porous matrix of concrete. Some of the oxidation products chemically reacted to form zinc chloride compounds at the concrete interface. These frequently diffused out through surface defects of the metallized coating.