Modulus and Permanent Deformation Characterization of Asphalt Mixtures and Pavements

Rutting refers to the permanent deformation of the asphalt surface. Rutting accumulates in the wheel-paths and is caused primarily by densification and shear flow from repetitive traffic loading. Rutting can cause serviceability problems, such as vehicle hydroplaning and water spray when ruts are filled with water. Thus, the permanent deformation characterization of asphalt concrete pavements is critically important.;The main goal of material-level testing in the laboratory is to predict the behavior of the material in the field. Therefore, rutting should be predicted not only at the material testing level but also at the structural level within a pavement. The Layered ViscoElastic Pavement Analysis for Critical Distresses (LVECD) program can be used to predict rutting behavior in a structural pavement (Eslaminia 2012). This layered viscoelastic structural model is used to calculate the stress and strain levels. These responses are then used in a viscoplastic model, the shift model (Choi 2012), to predict the rut depths of the pavements. Therefore, both the viscoelastic characterization and viscoplastic characterization of asphalt mixtures are important in predicting and evaluating the rutting potential of asphalt mixtures in structural level analysis.;The dynamic modulus test has been used extensively to characterize linear viscoelastic behavior of asphalt and is widely accepted by the asphalt pavement industry. However, the dynamic modulus test is somewhat complex and time-consuming, which limits its practical use. The impact resonance (IR) test is a promising alternative methodology to conventional dynamic modulus testing because the set-up of the IR test is simpler, more efficient, and much less expensive.;For permanent deformation characterization, the triaxial stress sweep (TSS) test has been used to calibrate the shift model. The main advantage of the shift model is that it can account for the effects of temperature, loading time, and deviatoric stress on the permanent deformation of asphalt concrete. However, the TSS test requires eight specimens, and the total testing time including temperature conditioning is two days for a single mixture. Therefore, a simpler method is needed to calibrate the shift model.;The work presented in this dissertation focuses on developing simple performance test methods for both the modulus and rutting of asphalt mixtures. The main objectives are to (1) develop an IR test procedure to determine the dynamic modulus and phase angle of asphalt concrete using a thin disk geometry, (2) predict the rut depth growth of selected pavements using TSS test results and the LVECD program, (3) compare the LVECD predictions to the rut depths measured from field sections, and (4) develop a simplified TSS test protocol to characterize permanent deformation.;For the simple modulus testing, a methodology has been developed in this study to evaluate thin disk-shaped specimens using IR testing to determine the dynamic modulus values of asphalt mixtures. The results demonstrate that the dynamic modulus values of the thin disk-shaped specimens determined from the IR tests are similar to the dynamic modulus values of long cylindrical samples determined from conventional dynamic modulus tests (AASHTO T 342-11) and from IR tests.;A new simplified TSS test, referred to in this study as the S-TSS test, is proposed. The newly developed S-TSS test incorporates a reverse loading block concept and eliminates the intermediate test temperature in order to reduce the testing requirements for the shift model calibration. The proposed S-TSS test requires 4.1 hours of testing time and four specimens in total for a single mixture. The S-TSS test, including temperature conditioning and pressurizing, can be completed within a day. The simulation results support that the proposed S-TSS test allows for a shorter testing time and fewer replicates than conventional testing, but nonetheless is able to produce accurate predictions of permanent deformation.