Nowadays concrete is the building material par excellence and worldwide more and more precast concrete-elements are used. Façade ele- ments, pipes, noise-protection walls next to streets but also tubbings used in tunnels are prefabricated. But such precast concrete elements are very demanding for production. To reduce the weight and/or improve the esthetic appeal such elements have to become thinner and thin- ner. Therefore sometime it happens that the steel reinforcement is not sufficiently covered any more by concrete which leads to corrosion of the steel and at the end to rust stain at the surface and to spalling.