Dynamic tests on bituminous layers interface

The most common test used to evaluate the interface bond strength of asphalt pavements is the guillotine direct shear test working in monotonic modality. Under this test configuration the specimen reaches failure in a mode very different from those activated in an actual pavement. In fact, the repetitive loading applied by vehicles is considerably lower than the interface resistance measured by a monotonic test. Moreover, the stress paths imposed to the specimen nowhere are experienced on field, in terms of ratio between shear and normal stresses and their variation during loading time. This study regards the dynamic performance of double-layered cylindrical specimens evaluated by a shear tester where the specimen is inclined so as to obtain contemporarily variations of the applied normal and shear stresses. Various inclinations are used to reproduce several combinations of these two stress components as they actually occur on field in those positions where the vehicle wheels generate a shear stress always in the same direction and proportional to the normal stress. As both normal and shear components influence the interface resistance to repetitive stress, a dynamic failure surface is assessed in the three-dimension space, with the two stress components as independent variables and the number of cycles at failure as dependent variable.