Mechanical Properties of Corrosion-Damaged Reinforcement by John Cairns, Giovanni A。 Plizzari, Yingang Du, David W。 Law and Chiara Franzoni

Corrosion of embedded reinforcement is the most prevalent form of degradation of reinforced concrete structures, and may impair structural capacity through loss of bar section, loss of bond between reinforcement and concrete as a result of longitudinal crackin , or loss of concrete cross section。 The effect of corrosion attack on mechanical properties of reinforcement is investigated through physical tests on bars with simulated and real corrosion damage and through a simple numerical model。 Bars subjected to local or pitting attack may suffer a relatively modest loss of strength but a significant loss of ductility, and this is related principally to the variability of attack along the length of the bar。 The numerical model supplements experimental work through a parametric study on the influence of steel characteristics。 Finally, guidelines on assessment are suggested that are derived from results reported in the paper and from elsewhere in the published literature。87375

Keywords: corrosion; ductility; reinforcement。

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Corrosion of embedded reinforcement is the principal cause of deterioration of structural concrete and a major economic cost for maintenance of national infrastructures。1 The effect of this deterioration on residual capacity is there-fore a matter of concern to those charged with ensuring safe operation of concrete structures。 It is clear, however, that many reinforced concrete structures remain in service once reinforcement has started to corrode and cover concrete over the bars has begun to spall; there is extensive evidence that modest amounts of corrosion do not pose an appreciable threat to structural stability。 Nonetheless, it is essential that responsible engineers have at their disposal the means to verify that the affected structures retain an acceptable margin of safety。 However, data and methods from which a reliable assessment of residual capacity of corrosion-damaged structures can be made are scarce。

Corrosion may affect residual capacity through several mechanisms, including loss of bar section, loss of concrete section as a result of longitudinal cracking and spalling, and a reduction in the interaction, or bond, between reinforcement and concrete。2,3 This study focuses on the first of these mechanisms, namely the changes to mechanical properties of reinforcement as a consequence of corrosion。

Corrosion attack may be broadly classified as either: 1) uniform; or 2) localized, sometimes referred to as pitting attack。 The consequences of these two forms of attack differ markedly。 Uniform attack can be addressed simply by using the residual cross section of the bar with essentially unchanged mechanical properties; only in the case of substantial loss of section on rein-forcement manufactured through the quenched and tempered process might an adjustment be necessary to account for the variation in material properties through the bar section。

Pitting attack is a more insidious form of attack for two reasons。 First, the localized nature of attack together with a less expansive form of oxidation products from the corrosionreactions means that substantial section loss may occur prior to warning signs of longitudinal cracking becoming visible on the surface of the member。 Local corrosion sites are, however, readily detectable by the half-cell method, where they appear as a zone of strongly negative potential surrounded by a high potential gradient。 Second, pitting attack affects not only strength, but also ductility。 The normal design and assessment rules established in codified procedures are based on an assurance of adequate ductility that may no longer be applicable under pitting attack, and could thus be unsafe。

This paper reports a study into the effects of corrosion on residual mechanical properties of steel reinforcement conducted through numerical modeling, physical tests in which corrosion damage was simulated by machined defects, and physical tests in which corrosion was accelerated by means of anodic polarization。 This report is confined to performance under static loading only。