Initiation of chloride‐induced corrosion of steel in concrete: role of the interfacial zone

Abstract

This paper provides a brief review of research aimed at characterising the steelconcrete interfacial zone (SCIZ) and its influence on the susceptibility of the metal to pitting corrosion when concrete is exposed to environments that cause ingress of chloride ions accompanied by leaching of hydroxyl ions. For reinforced concrete made from Portland cements, exposed to aqueous solutions of sodium chloride, the buffering effect of solid calcium hydroxide (portlandite) at pH $12.6 has been shown to restrain the gradual decline in the hydroxyl ion concentration of the concrete pore solution phase at depths corresponding to the embedded steel. When the concrete is produced under laboratory conditions that are carefully controlled to exclude macroscopic defects from the SCIZ and the steel is cleaned before being embedded, this can lead to observed chloride threshold levels being consistently greater than 1% chloride by mass of cement. The buffering action of cement hydration products formed in the SCIZ is believed to be partly responsible for this high tolerance to chloride-induced corrosion because it counters the generation of 'anodic acidity' that is a necessary condition for stable growth of pits to occur. Translating this behaviour of laboratory specimens to the performance of full-scale reinforced concrete structures has often proved difficult in the past and there is a need for further research in this area, particularly in relation to the role of non-traditional cements.

Corrosion resistance of low‐nickel duplex stainless steel rebars

“…Nevertheless, even the results of the slower potentiostatic polarisation tests cannot be considered representative of the actual behaviour of steel in concrete, since they cannot replicate the conditions that are present at the concrete-steel interface (i.e. porosity, buffer effect on pH of the hydration product) [25].…”

“…In addition, it has to be considered that the pitting corrosion initiation is a stochastic [1] phenomenon that is influenced by a great number of parameters (chloride threshold should be properly defined only through probability distributions). Another important concern is the absence, even for traditional carbon steel rebars, of a standardised or a generally accepted method for the evaluation of the chloride threshold both on real structures or in laboratory specimens [23][24][25][26][27]. Since there are no standardised methods for the evaluation of the chloride threshold, as well as for the detection of depassivation, a large variety of techniques have been used by different researchers.…”

“…However, they do not allow the definition of a chloride threshold level in concrete, since chloride concentrations in solutions cannot be directly converted in chloride contents in concrete, and, moreover, they may not be representative of the real conditions of a reinforcing bar in concrete (oxygen content at the steel surface, steel/concrete interface, etc.). Tests in concrete are more time consuming, nevertheless they are indeed more representative of real conditions, in particular in considering the role of the steel-concrete interface [25]. This paper is aimed at the evaluation of the corrosion resistance of rebars made of two duplex stainless steels, designated as 1.4162 and 1.4362 according to European standards.…”

Depassivation of steel reinforcement in case of pitting corrosion: detection techniques for laboratory studies

“…To this regard, it should be noted that chloride thresholds found in real structures are usually lower than those found in well-compacted laboratory specimens with similar materials [9]. Another contribution in this special issue will address the role of the interfacial zone on the initiation of chloride-induced corrosion in concrete [10].…”

Effects of Different Environments on Reinforcement Concrete Corrosion

“…The reinforcing steel is depassivated when the pH falls below 10 for any reason, then, the corrosion may occur (Paul, 2000). Thereafter, carbonation or chloride ions can penetrate through the concrete pores to the oxide layer on the rebar, breaking down the passive layer and leaving the steel bar vulnerable against aggressive agents (Page, 2009); corrosion occurs in the presence of moisture and oxygen (Corrosion Guidelines, 2003). Most problems associated with the corrosion of steel in concrete are not due to the loss of steel, but are as a result of the growth of the oxide, that has a volume of about twice to six times that of the steel it replaces, when fully dense (Bertolini et al, 2004;Bertolini and Polder, 1997 ).…”