Extension of the application limits of the W-Cl maintenance principle

• Applicants: Professor Dr.-Ing. Wolfgang Breit; Professor Dr. Christoph Dauberschmidt
• Subject Area: Construction Material Sciences, Chemistry, Building Physics ; Structural Engineering, Building Informatics and Construction Operation
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 453141969

Ensuring the durability of reinforced concrete components is a technically demanding task and is of central importance for society to maintain mobility and secure the real estate stock. The chloride effect on reinforced concrete plays a central role here. The repair of the damage caused by chlorides causes considerable economic damage. In the W-Cl repair concept, the surface of the concrete structure (e.g. a parking deck or an underground car park floor plate) is provided with a coating that prevents the penetration of further chlorides and water, but allows the component to dry out. Due to the dehydration of the concrete, the velocity of the corrosion processes is significantly reduced, so that the further damage process comes to a standstill at best. Repairs of chloride-contaminated components according to the W-Cl principle are much more cost-effective than with the usually conventional repair methods. As part of a DFG research project "Fundamental studies on the mechanisms of repair principle W-Cl and to ensure durability ", basic studies on the limits of application have now been carried out. The research project, which was successfully completed in 2019 and received broad approval in the evaluation, shows that the boundary conditions that enable a guaranteed repair success have a highly restrictive effect: high chloride content at the rebar or water vapour diffusion-inhibiting coatings inhibit that corrosion rates are not reduced to a harmless level. Thus, the application limits of this repair principle are also very limited in the future. In order to extend the application limits of these repair procedures, further investigations are to be carried out within the framework of a follow-up project and new solutions are to be examined. For this purpose, further coating systems will be examined and the test specimens from the initial research project will be further examined. A novel solution approach for RC-components with high chloride contents consists in the targeted drying down of chloride-contaminated and initially uncoated components (e.g. by heat treatment). For this purpose, the proof of the long-term success of the repair by outside storage in an underground car park is to be provided on the basis of practical test specimens. Finally, the findings on the interpretation of measurement results of corrosion current measuring devices in the case of very dry concretes from the WIPANO research project will be used to clarify the results obtained from the previous DFG research project. In particular, limit values are to be determined from which a harmless "passive current density" can be assumed.

• DFG Programme: Research Grants