Interlayer Shear Testing under Combined State of Stress

This research aims to investigate the influence of the normal load on the shear behavior of double-layer asphalt specimens. The LCB shear test device proposed by Miro has been chosen as model for the design and the development of two new shear tests in the laboratories of the Sapienza University of Rome; under both shear tests, it possible to apply a normal load so as to reproduce the composed state of stress carried out by the vehicular loading. Several compression levels are investigated, paying attention especially to the load application modes and to the effect of the normal stress on the interlocking properties. The study parameters chosen for the analysis are the maximum shear stress and the slope of the final branch of the response curve or the residual shear stress, in relation to the failure behavior due to the devices. The results of tests performed on the first machine, when the normal load is applied, show a direct proportionality with the normal load and the slope of the response curves after the peak remain constant because it is related to the friction features. With the second machine, which was adjusted to evaluate the shear behaviour for high interface displacements, the peak shear stress and the residual one were also evaluated, showing the increasing in relation to the compression applied during the test. The two machines provide different but comparable results. © (2013) Trans Tech Publications, Switzerland.