Chloride-induced corrosion on reinforcing steel: from the fundamentals to the monitoring techniques

Abstract

One of the most important causes for reinforcing steel corrosion is the presence of chloride ions. They cause localised breakdown of the passive film that initially forms on steel as a result of the alkaline nature of the pore solution in concrete. The harmful chloride ions can be originated from the use of contaminated mix constituents or from the surrounding environment. The determination of a critical level, above which serious problems can occur, has been one of the main goals of investigation. Unfortunately, it is difficult to establish such a value since the chloride level is influenced by several factors. Thus, after concrete contamination, it is of fundamental importance to follow the activity of chlorides and the state of the reinforcing rebars. In this respect, the use of electrochemical techniques such as polarisation resistance, electrochemical impedance, galvanostatic pulse and potential measurements have shown to be powerful tools. Nevertheless, the interpretation of the results becomes sometimes a difficult task. A large number of authors have dedicated several studies to the interpretation of such measurements and a highly dispersed number of interpretations can be found in literature. The aim of this paper is to present an overview on the state-of-the-art of the most important aspects of the corrosion process initiated by chlorides, its development and monitoring techniques.

Phosphate ions as corrosion inhibitors for reinforcement steel in chloride-rich environments

“…The two most common causes of rebar corrosion are (i) localized breakdown of the passive film on the steel due to penetration of chloride ions [5,6] and (ii) generalized corrosion by acidification of the concrete after reaction with atmospheric carbon dioxide [7][8][9]. Even worse is the combination of these two factors.…”

Monitoreo mediante EIS del acero embebido en un concreto de escoria activada alcalinamente expuesto a carbonatación

“…Such effect explains why stationary stage cannot be found by means of conventional techniques such as direct current, linear polarization resistance and Tafel polarization curves. They also explain observed time constants of impedance spectrums at low frequencies and the need to exceed polarization resistivity values (Montemor et al, 2003). Montemor proved that such time constant could be related with concrete humidity.…”

Effect of Red Mud on the Corrosion of Reinforced Concrete Studied by Electrochemical Impedance Spectroscopy

“…However, interpreting the results may be difficult and the use of an equivalent circuit, which can change according to the conditions of the steel, makes the technique more suitable for laboratory studies [11]. The main advantages of EIS are [12] (i) it provides information about the corrosion kinetics, (ii) it is an accurate and reproducible technique suitable for highly resistive environments such as concrete, (iii) it provides data about the electrochemical control mechanism, indicating if corrosion occurs by activation, concentration or diffusion, (iv) it characterizes the state of the rebar and the morphology of the corrosion, (v) it is a nondestructive and nonperturbative technique, since the signals applied are of small amplitude, so the corrosion potential is not changed, (vi) it allows for monitoring of the evolution of the passive or active state over time.…”

“…Electrochemical impedance spectroscopy (EIS) is a powerful technique for characterizing a wide variety of electrochemical systems and for determining the contribution of electrode or electrolytic processes in these systems. According to MONTENOR [11], the impedance of an electrical circuit is the measure of its opposition to an electrical signal (potential or current). It is a combination of passive elements of an electrical circuit: resistance, capacitance, and inductance.…”