Monitoring of Crack Propagation in Concrete Using Embedded Piezoelectric Transducers

A concrete structure can be subject to several factors that may damage it during its service life. These factors are either be climatic, chemical or accidental. The security requirements are more and more speci c and severe. To ensure the safety of a structure, it is important to know its state and the properties of the materials that make it up. For this purpose, many tests has been developed. Most of them consist to apply mechanical or chemical tests on specimens of a structure. These tests are called Destructive Tests. The use of this kind of tests to determine properties from a structure in service should be avoided as often as possible. The rst and the most simple test is the visual inspection of the structure, but this can only identify macroscopic damage at accessible locations. As an alternative, many Non-Destructive Tests has been developed during the last thirty years with applications either in civil engineering structures or in aeronautics. Most of them also requires an inspector and, in addition to the high costs, the number of tests and the location of these tests are strongly restricted. The current trend in research is the development of embedded structural health monitoring methods. The main goal is to reduce inspection costs and risks of unexpected failure using real-time online monitoring systems. For this purpose, sensors and inspection devices are miniaturized and some of them are embedded in the structure. The automation of the measurement improve the e ciency, the repeatability of the tests but also has the advantage of a better integration in the overall design of the structure. In the eld of damage detection in concrete, tests using piezoelectric transducers are very common. The principle is very basic, it consists of sending acoustic waves from a transducers and measuring the response on a other transducers. Acoustic waves are produced by the mechanical vibration of the medium. For instance, this method allows of computing the velocity of the propagated waves, which is an important property to evaluate the state of the concrete. Integrate this kind of sensors in the structure improve the e ciency of these tests and add more exibility in the choice of the location. Within this framework, the concept of Smart Aggregates(SMAGs) has been developed by researchers at the University of Houston, Texas.