Abstract
This report presents the development and verification of non-destructive testing (NDT) methods for detecting voids in tendon ducts of post-tensioned concrete structures. The work is based on laboratory testing using purpose-built mock-up specimens with documented internal conditions, allowing objective evaluation of NDT performance under controlled conditions. Ground-penetrating radar was verified as a reliable method for locating tendon ducts and defining geometry, forming the basis for targeted ultrasonic inspection. Ultrasonic methods showed clear sensitivity to entirely ungrouted duct sections, with detectability decreasing for greater duct depth, dense reinforcement, and multi-layer configurations. The results confirm that NDT is effective for identifying empty ducts, while interpretation uncertainty remains and is influenced by inspection strategy and operator competence. The mock-up program establishes a repeatable verification framework that supports method comparison and training, and provides a foundation for structured inspection workflows.