Comparison of novel imaging sensor and gamma ray tomography imaging of grout deficiencies in external post-tensioned structural tendons

Abstract A relatively simple and economical novel NDT method (Tendon Imaging Unit, TIU) for imaging grout anomalies in external post-tensioned structural tendons combines magnetic and impedance measurements. Validation comparison was conducted against a well-established but more resource intensive NDT technology, gamma-ray tomography (GRT), on test tendons with steel strands and grout voids, unhydrated grout, and excess water. GRT could resolve individual strands but TIU still provided viable strand envelope data. Both TIU and GRT detected full voids, outer voids, and unhydrated grout but neither adequately sensed a small inner void. TIU provided only limited detection of a water filled void compared with better GRT identification. Results support TIU deployment for wide range screening inspections that would otherwise be prohibitively costly, reserving advanced techniques like GRT for more focused targets.