Evaluation of Concrete Distributed Cracks by Ultrasonic Travel Time Shift Under an External Mechanical Perturbation: Study of Indirect and Semi-direct Transmission Configurations

摘要

Techniques based on non-linear acoustics have been proven sensitive to micro-defects in heterogeneous materials, such as concrete, but their implementation on-site is very restrictive. Ultrasonic travel time shift, a technique where a high frequency ultrasonic wave probes the medium while a low frequency elastic wave disturbs it to create a "time delay", is a new promising technique that may be used efficiently on-site. This technique is based on nonlinear behaviour of concrete. Moreover, this technique offers the possibility of evaluating linear parameter, such as ultrasonic pulse velocity of direct waves. The scope of this paper is to study the applicability of the technique at different level of concrete damage and define its advantages, limitations in order to optimize its use.