Accuracy and reliability of radar results on bridge decks

The inspection of bridge decks is a routine application of the GPR method. Pavement thickness, depth of reinforcement, concrete damage and the position of tendons are some of the issues that are addressed with GPR. However, in most cases a verification of radar results is either not possible or restricted to a few points. A detailed comparison between radar results and reality for bridge decks is not only of scientific interest but could also improve the acceptance of GPR in this field of work. In an ongoing research project sponsored by the Swiss Federal Roads Authority, bridges designated for demolition are inspected with EMPA´s mobile GPR unit. Radar results are reported before the bridge is taken down. After demolition radar results are verified through a comparison with actual bridge parts. The project aims at the evaluation of the accuracy of radar results on bridge decks, the identification of possible pitfalls and a possible improvement of the method and the way it is applied. Work on four bridges of different types and sizes has been completed by now. It is planned to investigate one or two further bridges during the project. The comparison between radar results and reality proves that GPR inspections provide results with an accuracy and reliability that is sufficient for many applications in civil engineering.