Towards understanding corrosion initiation in concrete – Influence of local electrochemical properties of reinforcing steel

Abstract

The ageing of reinforced concrete (RC) structures in the industrialized countries increases the probability of durability issues. The mechanism of chloride-induced corrosion, the most common deterioration process in RC structures, is still not well understood. Improvement in the understanding of localized corrosion initiation is crucially required to allow for cost efficient and durable maintenance of the existing infrastructures and for service life design of new structures. This study reports results from localized electrochemical characterization of reinforcing steel surfaces taken with a local sensor positioned at different locations on the rebars. This permitted “mapping” the local Open Circuit Potentials for different rebars with different surface conditions. Moreover, local cyclic voltammetries on selected spots were also carried out. Subsequently, the samples were exposed to a chloride solution to provoke corrosion initiation. The corrosion initiation sites from visual inspection were correlated with the local electrochemical characterization. Results show a clear difference depending on the surface condition. Furthermore, for non-rusted surfaces, a spatial distribution of the local electrochemical behaviors seems to follow a pattern depending on the geometry of the steel bar and influencing the location of corrosion initiation.

Reinforced concrete structures: A review of corrosion mechanisms and advances in electrical methods for corrosion monitoring

“…It was also shown that the corrosion rate is greater for rebars exposed to natural weathering (pre-rusted rebars) than for the as-received rebars [78]. The initial surface state of the rebar and the distribution of native rust are thus major parameters controlling the corrosion susceptibility, and a non-uniform mill scale layer can create weak points for corrosion initiation [79,80]. Hence, as for cement-based materials, a detailed description of the rebar grade, composition, microstructure and initial surface condition is necessary for a correct interpretation of the data and the development of database for the assessment of corrosion mechanisms.…”

Methods for characterising the steel–concrete interface to enhance understanding of reinforcement corrosion: a critical review by RILEM TC 262-SCI

“…Local information about mill-scale and rust layer properties may be obtained through local electrochemical measurements, either by dedicated techniques applied to rebars [8,126] or steel immersed in simulated solutions such as employing scanning vibrating electrode technique (SVET) or similar methods. CMEA has been used to measure local corrosion rates on rebar surface in mortar [79,127] and shows promise in relating these measurements to heterogeneities in the SCI such as interfacial voids and moisture variations, when coupled with some of the other techniques described in this paper.…”

“…''Spatial & temporal'' refers to the ability to capture changes in properties over space and time on a single specimen distribution. However, other techniques less wellknown in the cement and concrete community may overcome this limitation [8,126]. These include scanning electrochemical microscopy (SECM), localised electrochemical impedance spectroscopy (LEIS) and scanning vibrating electrode technique (SVET).…”

The effect of the steel–concrete interface on chloride-induced corrosion initiation in concrete: a critical review by RILEM TC 262-SCI

“…Moreover, it was noted that for deformed bars, the corrosion started at ribs, whereas for plain bars the trigger for corrosion initiation was always an air void. Michel and Angst [31] found that, on largely rust-free surfaces, corrosion tends to initiate close to or on ribs, whereas on rusty rebars, corrosion does not preferably initiate on ribs (corrosion tests in alkaline solutions). In samples taken from engineering structures, Boschmann et al [32] reported preferential corrosion initiation close to and on ribs for one concrete structure, while this was not observed in two other structures.…”

“…in terms of chemical composition of the different surface components. Local electrochemical studies have revealed the marked diversity in local electrochemical behavior of as-received surfaces as well as their mutual polarization when immersed in an electrolyte [31,130]. Surface inhomogeneities have also been related to a size effect, meaning that larger exposed electrodes exhibit a higher probability of corrosion through a size effect [10,127,131,132].…”