Characterization of permanent deformation in asphalt concrete using a laboratory prediction method and an elastic-viscoplastic model

This dissertation presents a laboratory prediction method and a mechanistic approach to characterize the permanent deformation of asphalt mixtures. For the laboratory prediction method, two supplemental performance tests (The Asphalt Pavement Analyzer (APA) and Repeated Simple Shear Test at Constant Height (RSST-CH)) were conducted to evaluate the ability to assess resistance of hot mix asphalt (HMA) to permanent deformation. Performance data under full-scale trafficking collected for several replacement sections at WesTrack were compared with test results for mixtures fabricated in the laboratory using WesTrack materials and tested at a critical temperature for permanent deformation. Test results from the APA and the RSST-CH showed good agreement with downward rut depths measured under full-scale trafficking.; For the mechanistic approach, an elastic-viscoplastic continuum model is proposed to simulate the permanent deformation of an asphalt mixture selected from those evaluated with the laboratory method. Uniaxial compressive strength tests were conducted at seven different strain rates to obtain the material parameters of the elastic-viscoplastic constitutive model. In addition, triaxial compressive strength tests were performed at a low strain rate and four different confinement pressures to obtain material parameters for the Drucker-Prager yield function. The test temperature was 60°C based on the critical temperature for permanent deformation of the field section. The model and its calculated parameters were used in a finite element simulation of the Simple Shear Test at Constant Height (SST-CH), and results were compared to experimental measurements at 60°C. Reasonable agreement was found between predicted results and the experimental SST-CH measurements indicating the validity of the model and its parameters. Equivalent single axle loads (ESALs) at a standard temperature were obtained based on temperature distribution data at WesTrack and the test results of repeated load triaxial tests at different temperatures using a temperature conversion approach. A three-dimensional finite element analysis was performed based on geometry conditions and loading conditions at WesTrack. The same trend of rutting profiles was obtained for both the measured and the simulated rutting profiles. A reasonable agreement of permanent deformation was found between the ESALs at a standard temperature and the simulated results.