Asphalt Rheology to Define the Properties of Asphalt Concrete Mixtures and the Performance of Pavements

The behavior of asphalt concrete paving mixtures at low temperatures is primarily dependent upon the rheological properties of the asphalt binder. The Schweyer Constant Stress Rheometer was used to define the low-temperature rheological properties of asphalts recovered from laboratory-compacted mixtures and field cores. Asphalt viscosity relationships with resilient modulus, mix viscosity, static modulus, stiffness, fractures strain, fracture energy, and fracture stress of the mix were established using dynamic, static, and constant stress indirect tension testing procedures. Resilient moduli predicted from the viscosity of asphalts recovered from pavements were used in elastic layer analyses to define deflection and strain basins produced by Dynaflect or plate tests. These deflection and strain basins compared favorably with those measured on a test pit pavement and on selected in-service pavements. Relationships between asphalt viscosity and mix parameters are presented to illustrate the importance of asphalt viscosity and to suggest their potential use in the modeling of the thermal behavior of flexible pavements. It is shown that there is no appreciable difference between resilient and status moduli when asphalt viscosity exceeds about 400 MPa·s. The importance of shear susceptibility for both asphalt and mix viscosity determinations is discussed with recommendations for use of constant power viscosity to minimize errors induced by extrapolation of viscosity at shear rates outside those obtained in the test. Parameters for thermal and load induced fracture include stress, strain, and energy. Laboratory test results were used to develop relationships between these parameters and the constant power viscosity of the asphalt binder. Tests on pavement cores produced fracture corresponding to that obtained in the laboratory tests. Comments are provided on the reliability of these parameters in defining fracture.