New techniques appear in the domain of non-destructive bridge inspection. Amongst these methods, the Impact Echo was the focus of numerous tests. The results of these tests are encouraging. The Impact Echo method is based on the use of a wave of pressure generated by the impact of a steel marble on the concrete surface. The method is used to detect injection defaults in the sheathing of the prestressing cables, delaminations in the concrete layers, cavities, cracks and thickness of structural elements. The Impact Echo method has passed the level of prototype and is close to being considered a reliable method of inspection. The field of application must be clearly defined as a function of requirements and the capacity to detect a given type of default must be verified independent of local test conditions.
The different elements of the research are
(1) to add value to the results of existing tests,
(2) to conduct in situ and laboratory tests, and
(3) to provide recommendations with the goal of transmitting to engineers the results of this study in the form of a description of the domain of application and of concept of use of the Impact Echo method.
The Impact-Echo method is inappropriate in certain cases. e.g. for checking the grout in prestressing cable duct. On the other hand, the method is very effective for detecting zones or defects with dimensions falling within certain limits (see page 57 of attached document).
Impact-Echo measurements must be carried out by a specialist in order to ensure the correct interpretation of the measurement results. Preparation is very important for all Impact-Echo measurements. Predicting possible defects allows a verification of their detectability and the selection of the correct hammer.
Test should not be undertaken in bad weather and two operators are usualy need for the tests.
Future research should be concerned on improving the practical aspects of the Impact-Echo method. The imactor-accelerometer system could be automated and signal processing software should be improved in order to make results easier to read and implement.
It is also important to disseminate information about the Impact-Echo method among those involved in the evaluation and maintenace of existing structures.