Investigations of Sulfuric Acid Corrosion of Concrete. II: Electrochemical and Visual Observations

Degradation of a mortar specimen exposed to an acidic sulfate solution was studied using iron pins set within the sample with their ends close to the surface. Electrochemical impedance spectroscopy and the open circuit potential of the pins were used to monitor corrosion behavior. An experiment in which the pH of the test solution was maintained in the range of 4-5 for 8 days and 2-3 for 73 days was performed. The experimental data were used to investigate the efficacy of a diffusion-reaction based model with a moving boundary for the corrosion process. The open circuit potential of the pins indicated initiation of active corrosion of the pins closest to the surface of the mortar after 36 days in the second experiment. Visual observation of the cross section of the mortar sample at the end of the experiment indicated that 0.82 mm of the mortar was corroded. The data established the validity of the moving boundary paradigm for sulfide corrosion of concrete. Electrochemical impedance spectroscopy and open circuit potential were found to be valuable tools for monitoring corrosion of the iron pins in the specimen.