Mechanism of Cathodic Prevention of Carbon Steel in Concrete

In this work, I aim to clarify the mechanism that allows steel to attain higher chloride threshold as it is cathodically polarized. Specifically, I seek to provide empirical information on whether an intrinsic (predominantly interfacial effects of polarization) or an extrinsic (predominantly concentration changes due to polarization) mechanism may be dominant in the beneficial effect of polarization. I carried out this experiment with 12 identical concrete specimens, each with a cast-in steel plate, constantly exposed them to high-chloride environment. The specimens were divided into 4 triplicates and polarized at 4 different level from OCP, -200, -300 to -400 mVSCE The specimens were closely monitored for signs of corrosion. When corrosion was detected in a specimen, it was demolished to gain access to steel-concrete interface. Measurements of pH using a novel procedure and chloride ion concentration were done on the interface using an adapted in-situ pH measurement and a Florida Department of Transportation procedure respectively. The pH and chloride ion concentrations obtained in this study favor to some extent a dominant intrinsic mechanism interpretation, while the evidence in support of a dominant extrinsic mechanism interpretation remains elusive