Characterization of the corrosion products of one of the pedestrian paths of the bridge "Punto Cero" in the city of Medellin, Colombia

In this work, we present the structural and magnetic characterization of the rust products formed on one of the pedestrian paths of the bridge “Punto Cero” of the city of Medellín, Colombia. The rust products were obtained by scraping three zones of the surface of the pedestrian path, namely: a surface that faces the sky, a surface that faces the floor of the path and a surface with a crack, where a high corrosion state was observed. The rusts were characterized by X-ray Diffraction, Fourier Transform Infrared Spectroscopy, room temperature Mössbauer Spectroscopy and Vibrating Sample Magnetometry. The analyses made by these techniques show that the rust products formed on the surfaces facing the sky and floor are composed mainly by goethite, lepidocrocite and maghemite, in percentages of 74%, 24% and 2% respectively, while the rust taken from the more corroded substrate presented 55% of goethite, 28% of lepidocrocite and 17% maghemite. Mössbauer and X-ray measurements were highly consistent with the percentages of each phase found in all rusts. The results suggest that in addition to the type of steel and the atmospheric conditions which the structure is exposed, the specific location of some surfaces plays an important role in the type and percentage of phase formed on them, being higher the presence of spinel phase in the zones more prone to moisture accumulation. On the other hand, the formation of maghemite could be an indication of an important state of corrosion of some surfaces, which could serve as a guide to start preventive maintenance actions on the structure.