Defect detection in concrete members

A rock pocket is a deficient volume within hardened concrete consisting of coarse aggregate and voids that reduce the overall stiffness of the concrete members. The leakage of wet concrete from the form, segregation, or insufficient consolidation during concrete placement may leave rock pockets in concrete construction. This study is concerned with the detection, location and quantification of internal defects, particularly rock pockets, in reinforced concrete members. This is achieved by coupling in situ vibration testing with finite element analysis through Bayesian inference. First, the importance of providing sufficient physical evidence while calibrating the finite element models is illustrated using simulated experiments. With simulated experiments, model calibration successfully detected not only the locations but also the severity of rock pocket defects. Then, the results of impact hammer tests, completed on a concrete beam defected with rock pockets are presented. The finite element model of the test beam is segmented, and the stiffness properties of these segments are independently calibrated with the help of Bayesian calibration techniques using varying amounts of experimental information. The success in detecting defects obtained using simulated experiments, was not observed when the procedure is applied to the scaled concrete beams tested under laboratory conditions. However, the cause(s) of the poor performance with real experiments can be attributed to several factors, each of which requires further evaluation. (Publication approved for unlimited, public release on November-4-2009, Unclassified.)