Zementgebundene Beschichtungen zum Schutz und zur Instandsetzung von Stahlbetonbauwerken / Protective and repair layers for concrete structures

Cement based layers are frequently used during the repair of reinforced concrete structures nowadays. They restore the protection of the reinforcement against the penetration of aggressive substances. Protective coatings can also be applied to new structures in order to improve their durability. This paper discusses a concept for the improvement of durability of existing and new reinforced concrete structures using protective layers. To offer protection and to prevent the transport of harmful substances inside the reinforced concrete structure these layers have to be free from cracks during the planned service life. Under usual conditions such layers are submitted to different phenomena like thermal, hygral and autogenous shrinkage and swelling. These processes create a complex state of eigenstresses inside the system layer-subbase. The tensile stresses can lead to the formation of cracks and delamination of the protective layer after a few years. This paper suggests an approach for correct design of systems of protective as repair layers. For this purpose a numerical model is used in order to determine the time dependent stress distribution and the crack formation due to different loads and boundary conditions. On this basis the requirements for a layer can be formulated ad hoc as a function of the probabilistic properties of each damaged building and the risk of failure can be minimized.