The long-term corrosion of mild steel in depassivated concrete: Localizing the oxygen reduction sites in corrosion produ
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Judith Monnier Institut de Chimie et des Matériaux Paris-Est, Université Paris-Est Créteil, UMR 7182, F-94320 Thiais, France
Pascal Berger CEA, SIS2M, LEEL, CEA Saclay F-91191 Gif-sur-Yvette, France
Delphine Neff CEA, SIS2M, LAPA, CNRS UMR3299, F-91191 Gif Sur Yvette, France
Valérie L’Hostis and Stéphanie Perrin CEA, DEN, DPC, SCCME, F-91191 Gif Sur Yvette, France
Philippe Dillmann CEA, SIS2M, LAPA, CNRS UMR3299, F-91191 Gif Sur Yvette, France LMC IRAMAT CNRS UMR5060 CNRS, France (Received 27 July 2011; accepted 6 October 2011)
Over a long period (.10 years), the prediction of iron/mild steel corrosion in concrete requires the use of a mechanistic approach. For that purpose, a key point of the mechanisms involved is the localization of the oxygen reduction sites within the thick corrosion layers, which may greatly influence the nature of the rate-limiting step. In this context, iron rebars (originally covered with concrete) were sampled from a 50-year-old historical building and submitted to isotopic tracers methods (18O) combined with structural Raman microspectroscopy analyses on transverse sections. By this method, the authors demonstrate that the oxygen reduction sites are strongly impacted by the presence of a conductive phase (magnetite) in contact with the metallic substrate. I. INTRODUCTION
The need to predict the corrosion of iron/mild steel rebars embedded in carbonated concrete over a long period (.10 years) has become a full-fledged scientific challenge for various emerging applications: reinforced containers for interim storage facilities of intermediate-level wastes,1,2 civil engineering,3,4 and conservation of heritage artifacts.5 Because of the great thickness and the complex nature of the corrosion product layer (CPL),6–10 the empirical approach is not sufficient. A mechanistic approach is needed for the prediction of long-term.11–13 This approach requires an accurate description of the physicochemical at micrometer scale. For that purpose, we propose a methodology based on the recorrosion of ferrous artifacts, previously naturally corroded for several decades in depassivated concrete, in specific short-term in-lab experimentations. Most of published long-term corrosion mechanisms show that after an initial period, concrete becomes completely carbonated, decreasing the pH of pore-filling solution. This a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.391 J. Mater. Res., Vol. 26, No. 24, Dec 28, 2011
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scenario implies that the initial passivating CPLs that form on steel progressively evolve toward a depassivated system, containing thick and porous corrosion products.8,10,13 Then, corrosion processes are assumed to be ruled by the oxygen transport through a porous multilayer system (successively the concrete and the CPL, as illustrated in Fig. 1), followed by its consumption at the cathodic sites.13,14 As the CPL is generally considered as the most compact barrier, the corrosion kinetics is assum
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