Ambient effect comparative performance between Zn and Al/Zn/In point anodes in reinforced concrete

This investigation presents the performance of zinc-based point anodes based on laboratory results after a three years evaluation period. Twelve small reinforced concrete beams, six 60 x 10 x 15 cm and six 120 x 20 x 30 cm, were fabricated for this evaluation. Concrete mixtures were prepared with and without chloride contamination. Chloride contamination was achieved adding between 1% and 3.5 wt% chlorides by cement weight during mixing. Beams were exposed to two different relative humidities, either constant 95% RH or outdoor 77 % RH. The commercially available zinc-based point anodes were placed at one end of the beams to determine how polarized the rebars get when interconnection between the anode and the steel was achieved. Half cell potentials, current distribution, and polarization decay due to the anode interconnection with the rebar were measured. On the other hand, aluminium/zinc/indium anodes were evaluated at 77 % RH by using similar beams. This investigation presents the anode polarization efficiency, which depends of the environment humidity and, in turns, to the concrete resistivity. It was determined that these anodes might protect steel in highly humid concrete, like parts of the structures exposed to splash and/or tidal zone.