Residual capacity of corroded reinforcing bars

Abstract

This paper presents an experimental investigation into the residual capacity of corroded reinforcing bars. By performing both accelerated and simulated corrosion tests on bare bars and on bars embedded in concrete, the mechanism of the reduction of the capacity of corroded reinforcement was investigated. The influence of type and diameter of reinforcement on its residual capacity is discussed. The experimental results show that, due to local attack penetration, the residual cross-section of a corroded bar is no longer round and varies considerably along its circumference and its length. Although the force-extension curves of corroded bars are similar to those of noncorroded bars for up to 16% corrosion, their residual yield and ultimate forces decrease more rapidly than their average cross-sectional area and, therefore, their residual strength decreases significantly. Even though the residual capacity of corroded small diameter and/or plain bars reduces more than that of large diameter or ribbed ones, differences are not significant and can be neglected. Finally, a simple equation is proposed to predict the residual capacity of corroded reinforcing bars in practice.

Effect of corrosion on ductility of reinforcing bars

“…In the following analysis, bar stress and strain were calculated, respectively, by dividing force by average cross-sectional area, 4 and extension by the gauge length of either the extensometer or the LVDT, as appropriate. The elongation of a reinforcing bar was taken as the ratio, expressed as a percentage of the increase in the distance between the two marks on the bar surface after its rupture to their initial distance of 200 mm.…”

“…In addition to 21 non-corroded control specimens, 84 specimens were subjected to accelerated corrosion with a direct current impressed and the three remaining specimens were subjected to simulated corrosion with bare bars mechanically machined in the workshop, before they were tensioned until rupture to measure their residual strength 4 as well as their ductility.…”

“…A proof stress was not used because corrosion was found not to change the shape of the stress-strain curve. 4 External surface and residual section of corroded reinforcement A visual examination of the corroded reinforcement showed that the conditioning corrosion did indeed change the external surface of a steel bar. Compared with the non-corroded reinforcement, as corrosion time increased from 7 days to 28 days under an impressed direct current, the corrosion pits on the reinforcement surface developed in different ways: They increased in number and expanded in size, while some of them joined up with each other to give an appearance between that of the reasonably uniform corrosion due to concrete carbonation and the localised corrosion due to chloride penetration.…”

“…Hence, when corrosion reduces bar section, the yield and ultimate strengths are reduced by similar amounts and the strength ratio is largely unaffected. 4 Furthermore, the hardening strain and elastic modulus of a reinforcing bar are dependent on their chemical composition and manufacturing process. Corrosion removes iron ions T08 R16 T08 T16 T32 R08 R16 T08 T16 R08 R16 T08 T16 T32 R08 R16 T08 T16 only from the bar surface and does not change the nature and composition of the remaining steel bar.…”

“…On the other hand, corrosion in the presence of chloride ions usually results in a much more localised and pitting type of corrosion. The latter type of corrosion not only decreases the actual load-bearing capacity of the reinforcement, 4 but also affects its ductility. For a larger number of earthquake-resistant and momentredistributed structures, although careful consideration would have been given to their design and detailing to ensure that they would have a significant amount of ductility at the construction stage, once steel starts to corrode substantially, their actual ductile capacity may deteriorate and possibly become much less ductile than had been anticipated.…”