Ten lectures on impact-echo

During the last seven years various aspects of the impact-echo method for non-destructive testing of concrete structures were studied in great detail by the authors. This work was performed within the framework of the German collaborative research initiative FOR 384, "Non-destructive evaluation of concrete structures using acoustic and electromagnetic methods", and was supported by the German National Science Foundation (Deutsche Forschungsgemeinschaft, DFG). During this period significant new and important results were obtained and well known facts were re-discussed from a different angle of view. It is the belief of the authors that most of the new and even some of the old facts are not well-established in the impact-echo community. The main aim of the present paper therefore is to summarize these important aspects of impact-echo in terms of ten short lectures. In doing so, we will not only present results of our own work but will also include contributions from other groups with significant relevance for the practical use of impact-echo in field tests.