ACIMP

The French road network consists mainly of national roads, most of which being built about 40 years ago. Road surface defects are caused mainly by underground defects (horizontal or vertical cracks which are defects that appear within the pavement, like debondings) that can occur long before visible degradations appear on the surface. For embedded cracks (which are not visible from outside), so-called “surface” cracks (essentially within the first two layers of the pavement), renovation work can be necessary (depending on the crack size and quantity). In contrast, for so-called “structural” cracks (cracks within several layers which are also not visible from outside), renovation work become more important. The structural pavement diagnosis is hence necessary in order to prevent disasters. Thus, pavement structure diagnosis and monitoring are major challenges for the sustainable management of the road network. Detection, localization and characterization of horizontal or vertical embedded cracks are important diagnosis elements which influence the application of maintenance and management policies. These defects are characteristic of the degradation state of the structure. The geometrical characteristics of these defects (their shape, width, length, depth of occurrence etc.) as well as the extent and paths of water induced by these defects is a very important indicator of durability of these structures. This detection makes it possible to locate a potential pathology within the structure, to evaluate its state of health, to predict its evolution and consequently to improve the decision support tools. The major issues are to realize an early detection of these types of defects, to locate them with high accuracy and to characterize them geometrically with microwave non-destructive testing and evaluation methods. In order to do this, two radar tools will be used: the first one, which is more conventional, is the Ground Penetrating Radar (GPR); the second one, an innovative concept for this application, is the Ground Based Synthetic Aperture Radar (GB-SAR). This detection and evaluation is a major challenge which remains ill-resolved. Indeed, nowadays, GPR have insufficient time resolution. Thus, in this project, we propose on the one hand to develop new high-resolution processing methods with GPR and GB-SAR and on the other hand to use higher and wider frequency bands than those currently used in literature. Indeed, we propose for both radars to use narrow frequency bands (about 0.2 to 2 GHz to detect and characterize the structural cracks which are in depth), but also ultra-wide frequency bands (about 5 to 20 GHz, for the surface cracks). The first innovation of this project is to use and to take into account wider frequency bands than those currently used in the literature. Thus, electromagnetic models (rigorous and asymptotic) are extended, adapted and developed in order to better understand the diffusion physical phenomena in a stratified medium composed of cracks. The second innovation is to extend the GB-SAR to this “pavement” application. The third innovation consists in proposing new high-resolution processing methods for GPR and GB-SAR tools. Thus, the project will be structured in five Work Packages (WP): one of them being the project management, another being the electromagnetic modeling of the direct problem, two others being the development of high resolution methods with a low computational complexity and a higher processing speed to estimate the medium parameters (one with GPR, the other one with GB-SAR); the last WP addresses the experimental platform and the related measurements.