Corrosion of carbon steel in heterogeneous argillite/cement grout environment

The corrosion processes of carbon steel electrodes embedded in a specific cement grout were studied at 25°C (56 days) and at 25°C and 80°C (55 + 57 days). Two situations were addressed, A: steel in contact with cement grout, and B: steel in contact with both cement grout and argillite. The corrosion processes were studied via electrochemical measurements and the corrosion product layer was characterized using µ-Raman spectroscopy, XRD and SEM. For experiment A, the carbon steel electrodes, entirely covered with cement grout, remained passive at 25°C. However, the increase in temperature to 80°C induced a passive to active transition, leading to the formation of a thin corrosion product layer mainly composed of FeS. For experiment B, the part of the carbon steel surface covered with argillite presented a more severe localized degradation. The corrosion mechanisms could be linked to the cement composition and properties. The pH of the considered cement grout proved too low, and its sulfide content too high, for the envisioned application.