2T3C apparatus and DIC technology to investigate the thermomechanical behaviour of the interface between bituminous layers

Abstract

The bonding at the interface is seen in most road structure design methods as perfectly bonded and this ideal condition is supposed to last during the whole service life. However, the real working capacity at the interface is complex and gradually degrades because of repeated traffic load and weather conditions. A new apparatus called 2T3C (“Torsion, Traction, Compression sur Cylindre Creux” in French, or “Torsion, Tension, Compression on Hollow Cylinder” in English) was developed at the ENTPE/University of Lyon to investigate the thermomechanical behaviour of the interface between bituminous layers. The sample has two layers of similar or different materials. It has a total height of 125 mm and a wall thickness of the 25mm. The thickness was chosen small enough in order to validate the assumption of quasihomogenous stress and strain fields between inner and outer surface. The DIC technology is performed considering the three listed elements: (1) two couple of cameras are situated on two opposite sides of the sample (4 cameras in total) to take 3D images; (2) a software is employed to calculate the displacements in 3 dimensions of all points in the area of interest; and (3) the strain fields in the 2 layers and the displacement gap at the interface are computed using a method developed at the University of Lyon/ENTPE. In this paper, a focus is proposed on the viscoelastic and fatigue behaviours of the two bituminous layers and of the interface. Small and large numbers of loading cycles are successively considered in the small strain domain.