No abstract

No abstract

No abstract

Concrete structural elements of bridges or tunnels may be in contact with water containing chloride during the winter. Furthermore, marine structures are permanently exposed to seawater containing chlorides. In all these cases, penetration of chlorides through the covercrete is a major risk and the service life of structures may be reduced considerably if permeability is too high. Early repair measures are both an economical and an ecological problem nowadays. By adding appropriate admixtures to the fresh concrete, it is possible to produce an internally water repellent material. It is shown that it is possible to substantially reduce chloride penetration through ECC (Engineered Cementitious Composites) in this way, thereby considerably extending the service life of new structures and of repair layers. The properties of the modified ECC are described in detail.

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.