Shear Properties as Viable Measures for Characterization of Permanent Deformation of Asphalt Concrete Mixtures

Released in 1994, the Superpave® asphalt mix design system represented the culmination of a $50 million investment by the Strategic Highway Research Program to reduce the overall life-cycle costs of asphalt pavements. At this time, an extensive investigation to recommend a laboratorybased simple performance test for evaluating the resistance of Superpave mixes to permanent deformation is under way through the NCHRP. As a complementary effort, researchers at Carleton University are developing a field simple performance test for asphalt mixes known as the in situ shear stiffness test (InSiSST). InSiSST is unique to the asphalt industry; it measures the shear properties of compacted asphalt layers in the field without the need for coring or specimen preparation. Initial test results at the Superpave specific pavement studies test site (SPS-9) in Petawawa, Ontario, have shown excellent correlation between the in situ shear stiffness and observed permanent deformation. With additional testing and correlation, it is hoped that the InSiSST facility will complement the laboratory Superpave simple performance test to provide the asphalt industry with improved tools for mitigating permanent deformation. Information about the development effort is presented for context purposes, but the main objective is to further establish the benefit of fundamental asphalt shear properties for characterizing resistance to permanent deformation by presenting new and powerful performance models relating asphalt mix properties and shear properties to permanent deformation.