Corrosion monitoring at the repair of chloride-containing reinforced concrete structures

Prof. Dr.-Ing. Christoph Dauberschmidt
Department of Civil Engineering

The research project "KoMICS" in cooperation with the Technical University of Munich and the Federal Institute for Materials Research and Testing, as well as four industrial partners and the German Committee for Reinforced Concrete (DAfStb) as the guideline institution, aims in at the development of a corrosion monitoring system for chloride-containing reinforced concrete structures. The project is funded by the Federal Ministry for Economic Affairs and Energy under the WIPANO Directive. In this context, the incorporation of the results developed in the framework of the project into a draft regulation at the end of the project should take place.

Chloride ingress into reinforced concrete components can take place, for example, by de-icing salt or seawater due to convection and diffusion into the pore structure or cracks of the concrete. Normally reinforcing steel forms a passive layer due to the alkalinity of the concrete and is thus protected from corrosion under normal environmental conditions. However, as soon as a critical chloride concentration has reached the reinforcing steel, damaging pitting corrosion can occur, which can lead to high cross-sectional losses on the reinforcing steel in a short period of time. As a result, the load-bearing capacity of the component can be rapidly reduced. There are several possible principles for repairing damaged components. In a conventional repair, the chloride-containing concrete is removed by high-pressure water blasting and replaced with new concrete. For this type of repair, however, usually complex support of the components is required.

An alternative and much more less invasive repair method provides (if the degree of damage of the reinforcement still allows this) to leave the chloride-contaminated concrete in the structure by applying a coating which is open to water vapour diffusion. Like a functional clothing this is to prevent re-entry of water into the concrete, and to allow the drying of the concrete. If the water content of the concrete is decreasing, the corrosion process can be reduced to a harmless level. This repair method is controversially discussed among experts, as it is associated with the current state of knowledge with the high technical risk that a sufficient drying process in the component does not occur. To proof the success of the repair, the regulations order the installation of a monitoring system for measuring the corrosion activity in the structure. Guidelines for the design of such a monitoring system and for the assessment of the measurement data are not given in the regulations.

As part of the research project, the implementation of a corrosion monitoring system and its application limits will be developed. The findings are going to be translated into a draft regulation afterwards.