Air-coupled Impact-echo Actuation Applied on Concrete Sleepers for Crack Detection

Abstract Worldwide, about one billion prestressed concrete sleepers degenerate due to loads, chemical reactions, moisture or climatic conditions. Corrosion of the reinforcement or damage to the material structure can occur in the sleeper without any visible external signs. Therefore, non-destructive testing methods are required to reliably assess the condition. In this work, six prestressed concrete sleepers of type B70 are examined using the impact-echo method. Three different actuation methods are applied: a manually operated impact-hammer, an electromechanically mounted impact-cylinder and an air-coupled supersonic jet flow. All three actuation types show similar and consistent spectrograms. In intact rail sleepers, a dominant frequency above 10 kHz is always visible. In contrast, damaged sleepers show a dominant frequency significantly below 10 kHz. This simple threshold analysis can already be used for a condition assessment of the sleepers. Since the supersonic jet flow is continuous, an air-coupled inspection during travel at up to 80 km/h is theoretically possible. Since the nozzles are inexpensive, robust and virtually maintenance-free, a multi-channel actuation could be realised with little effort. In the future, the entire sleeper could be inspected non-destructively in a single high-speed pass, including a real-time condition assessment.