Investigations of sulfuric acid corrosion of concrete. II: Electrochemicaland 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 potent ial of the pins were used to monitor corrosion behavior. An experiment in w hich the pH of the test solution was maintained in the range of 4-5 for 8 d ays and 2-3 for 73 days was performed. The experimental data were used to i nvestigate the efficacy of a diffusion-reaction based model with a moving b oundary for the corrosion process. The open circuit potential of the pins i ndicated 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 indica ted that 0.82 mm of the mortar was corroded. The data established the valid ity of the moving boundary paradigm for sulfide corrosion of concrete. Elec trochemical impedance spectroscopy and open circuit potential were found to be valuable tools for monitoring corrosion of the iron pins in the specime n.