ABSTRACT
Many testing tasks for concrete elements to be solved with elastic waves are related to multilayer systems. Especially this is important for the investigation of tendon ducts. Much effort was invested and success was achieved in the last decade by applying ultrasonic imaging techniques in this field. When the ultrasonic waves transmit a prestressed concrete element, several interfaces appear: Concrete/steel sheet of tendon duct; steel sheet/grouting mortar; grouting mortar/steel wires (strands) and so forth. The scatter and reflection depend of the thickness and form of the steel sheets and the form of the steel wires. Additionally to the grouting faults of interest sometimes air pores strongly appear in the surrounding of the interfaces and influence the wave propagation.
