Electrochimica Acta 46 (2001) 3905 – 3912 Electrochemical behaviour of steel rebars in concrete: influence of environmental factors and cement chemistry C. Andrade a , M. Keddam b , X.R. No ´ voa c, *, M.C. Pe ´rez c , C.M. Rangel d , H. Takenouti b a Institute of Construction Sciences ‘‘Eduardo Torroja’’, CSIC, Apdo 19002, Madrid, Spain b UPR15 du CNRS, Uniersite ´P. et M. Curie, 75252 Paris Cedex 05, France c Departamento de Enxen ˜erı ´a Quı ´mica, ETSEI, Uniersidade de Vigo, 36200 Vigo, Spain d INETI, Estrada do Pac ¸o do Lumiar, 1699 Lisbon Codex, Portugal Received 31 May 2000; received in revised form 12 January 2001 Abstract Four series of reinforced concrete specimens have been studied over 3 years exposure in a 100% relative humidity atmosphere. Addition of CaCl 2 , NaNO 2 , and a mixture of CaCl 2 and NaNO 2 changed the cement chemistry with respect to an ordinary portland cement series of samples used as reference series. The study, based on low-scan rate cyclic voltammetry and electrochemical impedance spectroscopy, confirms previous results obtained in alkaline medium, i.e. the redox activity in the rebar’s oxides layer greatly influences the electrochemical behaviour of rebars in the passivity potential domain. Different redox processes also influence the active and cathodic protection domains that make corrosion rate estimations very difficult. The possibilities of estimating corrosion rate are discussed in terms of cement chemistry and corrosion potential of the system. © 2001 Elsevier Science Ltd. All rights reserved. Keywords: Steel in concrete; Corrosion inhibitors; Oxides layer; Passivation; Nitrites www.elsevier.com/locate/electacta 1. Introduction The enormous economic costs related to the mainte- nance, restoration and replacement of concrete struc- tures have encouraged the rapid development of non-destructive inspection techniques. Descriptions of the various methods currently in use for in situ evalua- tion of concrete structures are given in the literature [1]. The most widely used methods for controlling steel reinforcements are [2]: visual observation, gravimetric tests, potential mapping (PM), linear polarisation (po- larisation resistance method, R p ), transient techniques (coulostatic, galvanostatic, potentiostatic), electrochem- ical noise analysis (ENA), and electrochemical impedance spectroscopy (EIS). Most of them are based on the electrochemical nature of steel corrosion. Although PM according to ASTM C876 standard is the most commonly used electrochemical technique to assess reinforcing bar (rebar) corrosion [3], some doubts arise about the real meaning of the measured electrode potential due to the many different phenomena present in the concrete bulk that can influence the measured potential. Diffusion potentials, membrane potentials, and streaming potentials can be cited among such factors [4]. Moreover, factors inherent to the electro- chemical behaviour of iron in this medium are also important for correlating corrosion potential and cor- rosion risk. These factors will be discussed in the present paper. * Corresponding author. Tel.: +34-986-8122-13; fax: +34- 986-8122-01. E-mail address: rnovoa@uvigo.es (X.R. No ´ voa). 0013-4686/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII:S0013-4686(01)00678-8