The modulus of asphalt mixture is traditionally measured from the laboratory dynamic modulus test. However, different laboratory test methods often lead to obviously different test results. To evaluate the moduli of asphalt mixtures as constructed in field pavements, this study back-calculated the moduli of the pavement layers, based on measured strain data in Accelerated Pavement Testing (APT). Field tests were conducted to measure strains at different locations of the built pavement section at different temperatures and wheel motion speed. The loading frequencies of the asphalt layer subject to different motion speeds were calculated based on the duration of measured strain pulses. Subsequently, the relationship between the motion speed and the loading frequency was established. An finite element (FE) model of the pavement section was created, which was used to back-calculate the moduli of asphalt pavement layers using the measured strain data. Based on the back-calculation results at different loading conditions, the master curve of the field asphalt layer was determined. This master curve was further used to compare with that obtained from laboratory uniaxial compressive test. The relationship between the field and laboratory moduli was determined to be E_Laboratory= 1.298E_Field.

The modulus of an asphalt layer subjected to repeated loadings was measured to reasonably analyze the damage development therein. The ratio of the reduction in the modulus to the modulus of the undamaged asphalt layer is used to reflect the damage of the asphalt layer; the evolution of the damage with the number of the loadings was analyzed. Full-scale accelerated pavement testing was conducted to simulate the repeated vehicle loadings on the asphalt layer. Falling-weight deflectometer, pavement seismic property analyzer (PSPA), and uniaxial compression dynamic modulus tests were conducted to obtain the modulus of the undamaged asphalt layer in the unloaded area. PSPA was used to obtain the moduli of the damaged asphalt layers in the loading area; the ratios of the reduction in these moduli to the modulus of the undamaged asphalt layer were calculated. The damage development in the asphalt layer was analyzed, and a nonlinear damage-evolution model was established, which assisted in obtaining the speed of the damage development in the asphalt layers at different depths. It is found that the S-type master curve can be used to unify the undamaged moduli derived from the three tests. The results of the field-detection method are in accordance with the predictions obtained from the laboratory master curves. In addition, the regression parameter in the damage-evolution model assists in judging the speed of the damage development in the asphalt layer. The normalization result shows that the lateral asphalt layer at the outer edge of the wheel paths and that at the center of the wheel gap experience slower damage as the depth increases. The mid-depth asphalt layers at the other positions and directions experience faster damage. In conclusion, the nonlinear damage-evolution model can provide the basis for damage development judgment and lay foundation for optimizing the maintenance timing and strategy.

The asphalt-based pavement performance evaluation includes the derivation of the dynamic moduli and loading frequencies of pavement layers under various traffic- and climatic-induced loading conditions. The traffic-induced strain pulses and loading frequencies of commonly used (semi-rigid, flexible, and steel deck) asphalt pavements were experimentally determined by vehicular loading field tests with embedded strain gauges for different axle loads, motion speeds, and temperatures. It was found that the axle load values had no noticeable effect on the pavement loading frequency, which was mainly controlled by the vehicular motion speed. The transverse frequencies were found to be higher than longitudinal ones, while the distributions of loading frequencies by pavement depth differed for three pavements under study. The frequency values at temperatures over 35 °C exceeded those at lower temperatures, while in the temperature range from 4 to 31 °C, the motion speed vs. loading frequency relations for three pavements were nearly identical. The loading frequency f increased approximately linearly with the motion speed V, according to the unified fitting equation for three types of pavements under study, namely f = 0.127 × V. This unified equation was further proved valid to predict the dynamic modulus properties of field asphalt pavement layers. Moreover, several previous prediction models for loading frequency, including the Brown model, Ullidtz model, MEPDG procedure and Ulloa model, were compared to the results in this study. These previous models were found to overestimate the loading frequencies within the asphalt layer. The prediction errors of the Brown model and the Ullidtz model were pronounced. The loading frequencies calculated by the MEPDG procedure and the Ulloa model need to be modified by dividing 2.8 and 1.7, respectively.