ABSTRACT
In most of the design methods for pavement structures, bituminous layers are considered either fully unbonded or perfectly bonded. However, the actual bonding between interfaces is likely to decrease progressively during service life of pavements. As for bituminous mixtures this results from several factors (traffic, climate, aging of materials, etc…). The design of sustainable pavements requires characterization of the behavior of interfaces both in undamaged conditions (Linear Viscoelasticity) and in the fatigue domain. A specially conceived testing apparatus was developed at University of Lyon/ENTPE in order to study the thermomechanical behaviour of interfaces between bituminous layers. The device can apply quasi-homogenous axial and shear (torsion) stresses on hollow cylindrical samples, under cyclic or monotonic loading. In this study, samples composed of two layers of different bituminous materials are tested by applying a sinusoidal torsion load. Digital Image Correlation (DIC) technology is used to obtain the strain field in the sample and to determine locally the relative displacements at the interface. Tests are conducted in strain control, by applying a small number of loading cycles in a wide range of temperatures and frequencies. The combinations of temperature, loading frequency, strain amplitude and number of loading cycles were adapted in order to investigate the behavior of the interface in its undamaged condition.
