Detecting Unbounded Interface with Non Destructive Techniques

Abstract

The French road network has been built more than 30 years ago, and consists mainly of bituminous pavements. Some of them have also been maintained several times by thin overlays. On these pavements, a lot of damage such as potholes and alligator cracking has been observed, in particular after periods of heavy rain or freeze/thaw. Frequently, this type of damage is assumed to be linked with interface debonding between these overlays and the old pavement, associated with moisture effects. To detect such damages, some non destructive techniques (NDT), as electromagnetic techniques (GPR, step-frequency radar or infra-red) or as mechanical techniques (from static deflection measurements to seismic wave propagation methods), appear as promising approaches. This paper compares two differents NDT to detect debonding during an experiment carried out on the large pavement fatigue carrousel of IFSTTAR in Nantes.

The tests presented in this paper are performed on a 15m long pavement section, consisting of 3 bituminous layers over a granular subbase. Several types of defects have been included at the interface between the two base layers or at the interface between the base layer and the wearing course. Debonded areas of different size and form have been created artificially, using different techniques (sand, Teflon or kraft paper). The construction has been done by a road construction company, using standard road works equipment.

At the start of the experiment, different NDT techniques (Colibri, step frequency radar) are used to detect the different geometrical characteristics of artificial defects. This allows comparing the capability of each technique to detect such damages.