Corrosion of steel in porous media–role of the interfacial zone

The mechanism of corrosion of metals embedded in porous media is fundamentally different from corrosion of metals in bulk electrolytes. This difference is related to various aspects, including the heterogeneity found at the interfacial zone where the metal meets the porous medium, in particular the co-existence of different solid, liquid and gas phases at the metal surface. The local conditions of the interfacial zone are thus important to understand and predict corrosion of steel in porous media. This contribution reviews recent advances in the understanding of steel corrosion in porous media commonly found in the engineering context. The focus lies on steel corrosion in concrete, both with respect to localized (chloride-induced) corrosion and corrosion in near-neutral pH conditions that can be found in carbonated concrete. Recent results show that the corrosion process is governed not only by the chemistry of the liquid at the steel surface, but also by chemico-physical processes such as the interrelation of the pore structure and the exposure moisture conditions, determining the amount of liquid retained in the pores at the interfacial zone, and the transport of various species involved in the electrochemical reactions. These findings have implications for the conceptual understanding and for ensuring the durability and the sustainability of civil infrastructures in corrosive environments.