The residual cross section factor as a key parameter for the static evaluation of corroding reinforced concrete structures

Abstract

In this paper the development of a key parameter for the static evaluation of corroding steel reinforced concrete members is presented. Based on an extensive test series under defined laboratory conditions as well as outdoor exposure the time dependent morphology and thus the development of the residual cross section of reinforcement steel embedded in uncracked concrete with high chloride contents has been investigated. In order to reach that goal a cutting edge sensor system using the principle of optical triangulation has been applied. Based on the obtained results a so called Residual Cross Section Factor has been developed. Its value and time dependency is discussed linking it to further morphological key parameters such as the corroding surface area as well as the maximum pitting depth on the corroded steel probe. The applicability of the introduced factor in comparison to the well known pitting factor is presented and discussed.

A discussion on the order of magnitude of corrosion current density in reinforcements of concrete structures and its link with cross-section loss of reinforcement

“…Probably, but this remains an open question, the fraction of the corrosion current density leading to the reduction in the reinforcement cross-section is very small compared to that corresponding to the extension of the anode areas. This is also highlighted in [25] by Harnisch and Raupach, who explain that the reduction of pitting factor with time could be due to more lateral corrosion damage at corrosion spots. Results from Robuschi et al [46] also support the laterally extension of anodic area.…”

“…Others approaches have been done to link the pitting depth to the chloride-induced corrosion activity (namely I corr the corrosion current or i corr the corrosion current density by considering the anodic area A a ). A pitting factor  pit was introduced by Gonzales et al [16] and Ullig et al [67], but the applicability of the factor is questionable as it is poorly related to the residual steel cross-section as quoted by Harnisch and Raupach [25]. Val and Melchers [68] try to give a less conservative calculation of the residual cross-section based on the pitting depth, using a dome shaped corrosion pit.…”

“…Harnisch and Raupach [25] introduced a residual cross section factor A s (t) which is time dependent and represent the ratio between the corrosion depth calculated from the minimum residual cross-section and the general corrosion depth calculated from I corr .…”

“…They find a ratio between maximum and average corrosion ranging between 2.4 and 16.1. Because local loss of cross-section is not necessarily related to the pit depth, Harnisch and Raupach [25] introduce a residual cross section factor. Nevertheless, pitting factor measurement could only be destructive and would frequently correspond to measurements made after the appearance of corrosion-induced cracks.…”

“…To be able to predict the service life of existing or new structures, it is necessary to have reliable values of corrosion current density. This would allow the actual local reduction in cross-section to be calculated, which is the key parameter for re-evaluation of corroded reinforced concrete structures [25].…”