Ultrasonic velocity tomography for inspecting the condition of a bridge pylon

A two-phase ultrasonic velocity tomography technique was introduced to inspect the concrete quality of bridge pylons in Taiwan. In phase I, the modified cross-hole sonic logging method was applied to rapidly identify the aberrant sections of pylon shafts and horizontal beams. Most of the concrete quality was classified as good (G), ie the apparent P-wave velocity ranged from 3600 m/s to 4300 m/s. In phase II, the cross-sectional velocity image method examined the sections with possible anomalies and, in contrast, the uniform sections of the pylon shafts. The cross-sectional velocity image approach effectively demonstrated the spatial position and range of anomalies in the pylon shaft cross-sections. It was suggested that the relatively low-velocity zones, confirmed with surface concrete spalling, be listed as future repair targets for the bridge agency.