100 years durability for bridge and tunnel constructions The variable 3-stage concept

After a relatively short period of use (about 20 years), very high levels of chloride were detected in the components of traffic structures (tunnel walls, emergency walkways, bridge piers, abutments, bridge caps) exposed to chloride impact. On some components, the resulting reinforcement corrosion had already progressed to such an extent that an exchange/demolition of the corresponding components had to be made. In order to be able to plan and execute more durable structures in the future, the so-called 3-step-concept was developed in which a total of three approaches to increase the durability are available and can be assigned individually to the different components. In the derivation of the variable 3-step concept, various durability-related damages of traffic structures were first analyzed in order to identify the areas that are still not adequately protected by the normative durability requirements. At the same time, the factors influencing the durability (salt, traffic intensity, removal of the chloride source from the component, component orientation) were worked out, so that a meaningful classification of the components could be made with knowledge of damages and impacts. Based on the factors influencing the resistance side (concrete cover, material resistance concrete and steel, surface protection system), three solution strategies were developed with which the durability of components exposed to chlorides can be improved. Essentially, this is a slowdown in chloride transport through concrete-technological measures, an increase in critical corrosion-inducing chloride content by using reinforcing steel with increased corrosion resistance, and inhibiting chloride entry into the structural concrete by applying hydrophobic treatment. In the last step, it was possible to assign the measures necessary to the respective component categories to achieve a durability that is sufficient over the entire service life.