Corrosion Performance of Steel and Zinc-Based Materials in Diverse Unsaturated Soils: Insights From a 2-Year Field Exposure

The corrosion of metals in soils is a major problem for asset managers within the infrastructure and energy sectors. Usually, the soil corrosivity class is defined using standards and field tests. In the context of solar park structures' durability, the present study was conducted for 2 years, in which the corrosion behavior of carbon steel, pure zinc, and hot-dip galvanized steel was investigated through exposure to a variety of global unsaturated soil environments. Test sites included sandy and clay soils with varying pH levels and electrical resistivities. Corrosion was evaluated through visual inspection, mass-loss measurements, and characterization of corrosion products using Raman and Fourier transform infrared spectroscopy. Results highlight the critical influence of soil moisture, oxygen availability, resistivity, and sulfates on corrosion rates. Notably, the Fe/Zn corrosion rate ratio highlighted the material-specific sensitivity to soil chemistry. Severe localized penetration and zinc coating consumption were observed in poorly-drained saline sandy soil, challenging the predictive accuracy of the current DIN 50929 standard.