ABSTRACT
The encasement of anchor rods in cement paste reduces the contact of metal materials with aggressive environments in guyed power transmission line towers, however, many cases of premature failure due to corrosion of the anchorage systems are still reported. Chloride ions are considered to be one of the main factors responsible for the initiation and propagation of corrosion, however, there are many differences regarding the critical concentration of chloride in the soil and cement paste and their influence on the formation of corrosion products. In this study carbon steel 1040 was exposed in the laboratory to environments with different concentrations of chloride ions, 764 and 1764 mg/kg in the soil, 2.0% and 3.5% in the cement paste, based on the analytical results obtained in samples of rods and their surroundings, taken from the field. The investigation of the corrosion state of the metal in the laboratory was evaluated, over time, by the measurement of open circuit potential (OCP), electrochemical impedance spectroscopy (EIS). The corrosion products were characterized by scanning electron microscopy with elemental chemical analysis (SEM/EDS) and X-ray diffraction (XRD). By means of the EIS analysis, it was possible to detect the evolution of the corrosive process of the metal in the soil and cement paste, even though different forms of corrosion were observed: general in the soil and localized in the cement paste. Moreover, the evaluation of the corrosion products, by SEM and XRD, indicated the presence of goethite and calcite on the steel surface exposed to the soil, and in the steel encapsulated in cement paste it was possible to visualize the pits formed and the compositions of their surface surroundings. These results suggest to need to use corrosion resistant metals in environments with chloride ions, in order to increase the durability of the anchorage system.
Keywords
anchor rods; corrosion; chloride; soil; cement paste
