Dear Colleagues,

Corrosion of steel in reinforced or prestressed concrete structures is one of the main processes contributing to early deterioration and reducing the service life of buildings and civil infrastructure. The process starts with the depassivation of steel, usually triggered by carbonation or chloride contamination of concrete. Afterwards, the steel corrosion rate depends on the environmental conditions, mainly on the humidity of concrete and the temperature. The consequences of corrosion of the steel rebar are cracking of the concrete cover due to expansion caused by oxide formation, spalling and/or delamination of the cover, loss of bond between concrete and steel, loss of steel ductility, and loss of the cross-sectional area of steel.

Despite having received preferential attention from the scientific–technical community, the complex physical–chemical mechanisms involved in the process of steel reinforcement corrosion are still the focus of intense research and sometimes subject to erroneous interpretations. One of the active fields is related to the possibility of making predictions, through model calculations, about the onset of the corrosion process and the eventual reaching of the so-called durability limit-state. Many difficulties are encountered when attempting to apply rigorous modelizations of the ingress and transport mechanisms of deleterious species, such as chloride ions, through the porous network of concrete. This is especially true under conditions of concurrency of several transport mechanisms, such as those present in the wet–dry cycling conditions of concrete structures.

Another key area of research is the prevention of steel reinforcement corrosion and the rehabilitation or reparation of structures affected by this process. For instance, there is active research assessing the protective effect of substituting classical Portland cement concrete with other cementitious binders, using different admixtures or selected surface treatments such as cast-in or surface applied corrosion inhibitors. The so-called electrochemical techniques for controlling the corrosion process, such as electrochemical chloride extraction and re-alkalization of concrete, and cathodic protection of steel in concrete, deserve a special mention.

Finally, remarkably interesting research is also active on the development of non-destructive techniques for the early detection of steel corrosion and of the subsequent damage inflicted to the cementitious matrix. It is widely accepted that the costs of rehabilitation are greatly reduced if decisions on prevention can be made promptly. Classical electrochemical techniques able to evaluate damaged areas and the activity of the corrosion process, such as half-cell potential mapping, determining the electrical resistivity of concrete and measuring the corrosion rate of steel through several techniques such as linear polarization, electrochemical impedance, or analysis of electrochemical noise are of particular interest, as is the emerging field on the use of different physical techniques, mainly related to the interaction of mechanical waves with concrete for detecting damage caused to the cementitious matrix, i.e., early detection of the concrete cover’s microcracking. In this regard, techniques of interest include acoustic emission, impact echo, nonlinear ultrasonic techniques, etc. 

Prof. Dr. Miguel-Ángel Climent
Prof. Dr. Carmen Andrade
Guest Editors

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