A numerical study of polarization tests applied to corrosion in reinforced concrete

摘要

The evaluation of steel corrosion in reinforced concrete is commonly carried out using techniques like half-cell potential (HCP) and linear polarization resistance (LPR) measurements. The latter is however the subject of interrogations concerning the relevance of the method and the actual steel area polarized by the external current I_(ce) applied from a surface counter-electrode. To control the path of the polarizing current I_(ce) towards a specific steel area, a current-confining device (guard-ring) is used in some LPR instruments, which imposes an additional current I_(gr) around the counter-electrode. The impact of this guard-ring on LPR measurements is deduced from the uniform corrosion assumption. However, previous works have shown that the polarizing current spreading in macrocell corrosion systems is more complex and does not verify the uniform corrosion hypothesis. This paper presents the results of a 2D numerical study providing new insights on the theoretical impact of a guard-ring in case of galvanostatic pulse measurements performed on a macrocell corrosion system. The polarizing and confining currents are spread in a similar way over the macrocell system. In the case of an anodic polarization, both I_(ce) and I_(gr) are collected by the active steel area. In the cathodic direction, both I_(ce) and I_(gr) are spread over the passive areas. Consequently, numerical results show that the assumed confining effect cannot be achieved in presence of corrosion macrocells and it is actually impossible to define a specific polarized area. Moreover, since polarizing and confining currents have similar distributions, the confining current fully contributes to the system polarization, while it is not considered in LPR measurement analyses.