Evaluation of NDT methods for detection of prestressing steel damage at post-tensioned concrete structures

For an assessment of the risk potential of existing structures, where in the case of prestressing steel damage the load‐bearing capacity could be significantly affected, non‐destructive testing techniques which enable reliable evaluation of the condition of the prestressing steels are of utmost importance. During the demolition of a post‐tensioned concrete bridge in Berlin where damage of prestressing wires due to hydrogen‐induced stress corrosion cracking were found in former investigations, parts of the girders of the bridge superstructure could be taken out. After non‐destructive investigations by means of two testing techniques based on magnetic leakage flux measurement and one technique based on electromagnetic resonance measurement, subsequent removal of the concrete cover up to the ducts, opening the ducts and evaluation of the prestressing steels allowed a verification of the results obtained by the NDT methods. From the results it can be concluded that areas with fractures of several wires can be detected by the two techniques based on magnetic leakage flux measurement.