ORIGINAL ARTICLE Signiﬁcance of macrocell corrosion of reinforcing steel in partially carbonated concrete: numerical and experimental investigation M. G. Sohail • S. Laurens • F. Deby • J. P. Balayssac Received: 12 July 2012 / Accepted: 18 September 2013 Ó RILEM 2013 Abstract Concrete carbonation is usually assumed to induce microcell corrosion of reinforcing steel by uniform depassivation. However, the carbonation front evolves continuously as a slow, time-dependent process and concrete carbonation is often non-uniform in real concrete structures. Hence some areas of the steel reinforcement network in concrete are likely to be depassivated before others and, consequently, the theoretical conditions of macrocell corrosion appear to occur quite frequently in real concrete structures. This paper therefore focuses on steel corrosion phenome- nology in partly carbonated concrete structures. The conclusions are supported by an experimental and numerical study based on accelerated macrocell corrosion tests, carried out on partly carbonated concrete specimens with embedded active and passive steel bars. The specimen design allowed for electri- cally connecting one active bar with one or several passive bars in order to form macrocell corrosion systems with various cathode-to-anode (C/A) surface ratios. Despite the high resistivity of the carbonated concrete layer, direct measurements of galvanic current revealed high macrocell corrosion rates, even in cases of low C/A ratio. The signiﬁcance of galvanic coupling in carbonation-induced corrosion was thus conﬁrmed experimentally. In addition to experiments, a synthetic, but comprehensive, theoretical description of macrocell corrosion is proposed and ﬁnite element simulations of experiments are reported. The agree- ment between numerical and experimental results is demonstrated regarding both potential ﬁeld and C/A inﬂuence on macrocell current intensity. This consis- tency highlights the relevance of the modeling and simulation approach. Keywords Macrocell corrosion  Reinforced concrete  Carbonation  Accelerated tests  Numerical simulation 1 Introduction Corrosion of steel in reinforced concrete (RC) is a major cause of structural damage. Today, the repair and rehabilitation of RC structures in industrial countries are as important and costly as new construc- tion. Rebar corrosion in concrete is mainly due to the ingress of chloride ions to the steel surface or carbonation of the concrete cover. The pH of concrete pore solution is normally above 12. In such an alkaline environment, an oxide ﬁlm is formed on the steel surface, which protects it from corrosion (steel passivation). Both carbonation and chloride ingress cause this oxide ﬁlm to break down [9] thus allowing the corrosion process to start. The corrosion of steel in M. G. Sohail  S. Laurens (&)  F. Deby  J. P. Balayssac LMDC, UPS, INSA, Universite´ de Toulouse, 135, Avenue de Rangueil, 31077 Toulouse Cedex 4, France e-mail: stephane.laurens@insa-toulouse.fr Materials and Structures DOI 10.1617/s11527-013-0178-2