A road/airport pavement is a multi-layered structure generally composed of several layers of bituminous materials, cement-bound materials on unbound granular materials. In the design phase, the different bituminous layers are considered perfectly bonded and therefore expected to work as a unique structure throughout the service life of the pavement. However, due to environmental, traffic and/or material-related conditions, the quality of the bond varies in time. The layers in the structure tend to work more and more independently with degrading bonding capacity, which induces a reduction of the pavement life. Therefore, the mechanical behavior of the interface between bituminous layers has been recently studied with original approaches. There were tests developed to focus on the interface study, for example Ancona shear testing research and analysis device at the Marche Polytechnic University, the shear-torque fatigue testing device at the University of Limoges and other tests. Most of the studies on this topic present several limits. One or few loading configurations can be applied to the sample (for example, pure shear of the interface) and studies focus only on the interface strength. Moreover, stress and strain fields within the sample are not homogenous, therefore not allowing investigating the intrinsic mechanical behaviour of the interface. In this study, the 2T3C (“Torsion, Traction/Compression sur Cylindre Creux” in French, Torsion, Traction/Compression on Hollow Cylinder) apparatus developed at ENTPE is used to investigate the behaviour of a bituminous interface under shear loading and small strain cycles.

The device consists of different basic parts: (1) a servo-hydraulic press capable of imposing axial and shear loading (cyclic or monotonic) on a hollow cylindrical specimen, equipped with a thermal chamber controlling the temperature; (2) four cameras gathered by pairs used to perform digital image correlation (DIC) analysis, in order to determine the three-dimensional strain field in upper and lower layers and calculate the relative displacements at the interface between different layers; (3) several displacement sensors around the specimen to control its global deformation: one pair of noncontact sensors to control displacements in the vertical direction, and another pair to control torsional displacement. The sample has a total height of 125 mm, an outer radius of 86 mm and an inner radius of 61 mm. The small thickness of the cylindrical wall of the sample allows considering quasi-homogeneous strain and stress fields.