Effects of differential oxygen access on the corrosion behavior of zinc relevant to mechanically stabilized earth walls

In the past years the performance of Mechanically Stabilized Earth walls (MSE walls) have raised some controversy due to early failure at some locations. This has been attributed to aggressive environments. The purpose of this paper is to study the effect of differential oxygen access on the corrosion performance of zinc, the most common material used as protection system on MSE walls. Uneven soil compaction creates differential oxygen access, which is expected to promote corrosion macrocells that will compromise the performance of the structure. High purity zinc (99.6 wt%) was immersed in solutions with varied concentration of Na₂SO₄ to simulate the conditions found in soils and ground water, while the concentration of NaCl was kept at 3.5 wt%. Corrosion rates were measured using potentiodynamic polarization testing in different concentrations of oxygen, and Scanning Electron Microscope (SEM), and X-Ray Diffraction (XRD) were used to characterize the corroded samples. Results indicate an increase on the corrosion rate with increasing amount of Na₂SO₄, as well as a potential difference between samples in oxygen saturated, aerated and de-aerated conditions indicating the possibility for macrocell formation under the studied conditions.