No abstract

Concrete resistivity is an important durability related material parameter. It correlates with various properties, e.g., the reinforcement corrosion rate, the water saturation degree and the porosity. The resistivity is typically determined on a structure by using the Wenner probe. Unfortunately the results can strongly be influenced by heterogeneities, e.g., reinforcement bars or inhomogeneous moisture distributions. Neglecting these effects can lead to significant misinterpretations. In order to consider these influences quantitatively the applicability of the electrical resistivity tomography (ERT) on reinforced concrete has been studied. The aim of the method is to determine the distribution of the concrete resistivity perpendicular to the concrete surface. Based on this data the spatial distribution of material properties can be derived and the influence of an inhomogeneous resistivity distribution on the corrosion rate of the reinforcement can be studied. ERT can be applied to determine the resistivity distribution of reinforced concrete within certain resolution limits. Within this work the influence of different electrode configurations and rebar positions as well as the improvement of the resolution by considering prior information are exemplarily shown. Compared to the Wenner configuration the resolution and accuracy can be improved significantly with dipole–dipole measurements.

Besides visual inspections, taking cores or samples and measurements at the concrete surface, the use of embedded sensors can be an effective tool for the assessment of the condition of concrete structures. For new structures sensors can be placed in positions without the possibility of access during use and for existing structures sensors can be used to follow the condition of the structure at relevant selected points. Actually different types of sensor systems are available based on different electrochemical or other methods.

For reinforced concrete structures a localisation of all significant critical areas can only be done by a full surface inspection. The economic advantages are obvious: uncritical areas have not to be repaired expensively [1]. The first step of the assessment should always be a visual inspection [2]. The range of deterioration causes can be limited and the degree of deterioration may be estimated roughly. The inspection program can be adjusted to the requirements. By means of a full surface potential mapping areas with a high risk for chloride induced reinforcement corrosion can be localised, although no deteriorations are visually detectable at the concrete surface. In combination with concrete cover depth and resistivity measurements areas with corrosion promoting exposure conditions can be localised even if the reinforcement is not yet depassivated. The following publication gives an overview about the essential full surface investigation methods to localise critical areas regarding corrosion of steel in concrete. The selection of methods is based on the inspection procedure given in [2]. IVDefects that can, in the foreseeable future, decrease the reliability of the structure. Repair is needed on the short term/immediately Delamination and spalling of concrete cover, corrosion stains and damage at the concrete surface, decrease of rebar cross-section V Defects that present a serious danger for safety of the structure. Intervention is needed immediately Delamination and spalling of larger concrete areas, progressive corrosion processes visible, significant decrease of rebar cross-section