The durability of carbon steel reinforced concrete infrastructure is often limited by rate of corrosion damage progression. Over the past couple of decades, corrosion-resistant alloys, such as stainless steels (SS), have garnered attention as a potential way to address the durability of reinforced concrete exposed to aggressive marine environments. However, there are currently no models available to accurately forecast corrosion of stainless-steel reinforced infrastructure and durability projections for carbon steel may not consider the necessary mechanistic steps.

Traditional corrosion durability projections adopt the classic two stage model considering the time prior to and following corrosion initiation often distinguished by the point in time where enough chlorides have accumulated at the steel surface to exceed the chloride concentration required to initiate corrosion.[1] Such models do not consider the evolution of pitting or crevice corrosion and the potential for progression to more widespread corrosion. Therefore, research is required to first identify the expected corrosion damage morphology of stainless steels in concrete and then to formulate a theoretical framework that can be used to describe accurately its progression provided expected exposure conditions. This work attempts to develop an efficient yet informative method to study pitting corrosion evolution of steel in concrete with the objective of identifying the role of the cement pore structure on damage evolution and pit or crevice stability.

Recently, bipolar electrochemistry has been used to identify potential-kinetic-corrosion damage mode relationships from single measurements on ferritic [2] and duplex stainless steels.[3] Bi-polar electrochemistry (BPE) comprises indirect dc polarization of a conductive element usually immersed in an electrolyte in cases where direct contact to the elements need to be avoided. In application to pitting corrosion studies, BPE followed by post exposure 3D surface metrology can provide pitting characteristics as a function of applied potential from a single experiment. In this work various BPE configurations including single and split electrodes are used to assess the feasible in applying a suitable potential distribution on steel plate specimens that have a thin cement overlay. A finite element model was developed to simulate the applied potential distribution considering the cell geometry and interfacial kinetics. The corrosion damage morphology and the pitting characteristics obtained will be compared to that of chloride-ponded SS reinforced concrete beams to uncover mechanistic insight on SS corrosion damage evolution.

1. Tuutti, K: Corrosion of steel in concrete. 1982, Stockholm. Swedish Cement and Concrete Research Institute, ISSN 0346-6906. Royal Institute of Technology, Stockholm. Department of Building Materials
2. Zhou, Yiqi, and Dirk Lars Engelberg. "On the application of bipolar electrochemistry to characterise the localised corrosion behaviour of type 420 ferritic stainless steel." Metals10, no. 6 (2020): 794.
3. Zhou, Yiqi, and Dirk Lars Engelberg. "Fast testing of ambient temperature pitting corrosion in type 2205 duplex stainless steel by bipolar electrochemistry experiments." Electrochemistry Communications117 (2020): 106779.