An additional layer of concrete is often cast on an existing bridge deck for retrofit purposes. The condition of the interface between the concrete layers is crucial for the bearing capacity of the new deck and different surface preparations are investigated. The test specimen are designed to fit the in situ situations and are tested in the laboratory. The bearing capacity of the composite deck is tested under cyclic loading in order to detect fatigue failure under high static loads. The tests are accompanied by a detailed numerical investigation of the problem employing a nonlinear finite elements analysis. The scope of the numerical analysis is the verification of the analytical results and the investigation of the influence due to creep and shrinkage. The experimental results and the numerical results have been in agreement until now.