Technical Papers and Presentations

Field aging of asphalt pavement plays a vital role in limiting the pavements’ service life, and it is one of the major reasons for road maintenance. A long-term field aging results from the oxidation of asphalt mixtures when exposed to the ambient environmental conditions for extended periods. Models have been established to represent the multiple physics that contribute to the ageing of asphalt pavement, including: (1) heat transfer to determine pavement temperature profile, (2) diffusion of oxygen from the air into the connected air voids of the asphalt pavement, (3) diffusion of oxygen from the air void channels to the inside of the asphalt binder coating films, and (4) the growth of oxidation products in the asphalt binders. These four aging-related physics were mathematically modeled and experimentally validated individually in the literature, however, they were not effectively integrated into a comprehensive model and predict the aging of asphalt pavements in the field. The challenge lies in that the aging-related physics are circularly dependent and time-dependent. Another challenge results from the complexity in numerical modeling of the high nonlinearity caused by the circular dependence between the four physics. As a result, to accurately predict the aging of asphalt pavements, a comprehensive, time-dependent model is needed to address the circular dependency of the aging multiphysics.

This study investigates the circular dependence between the aforementioned aging-related physics and uses the weak-form differential equation based the finite element program COMSOL Multiphysics^® software to efficiently couple them into one integrated model, by using the Heat Transfer in Solids and the Coefficient Form PDE physics interfaces. The model inputs include the available site-specific hourly weather data, binder oxidation kinetics which can be obtained from the accelerated laboratory binder aging tests, the mixture design properties, and the pavement structure properties and materials thermal and diffusive characteristics. The model was validated using the available pavement temperature profiles at The Federal Highway Administration (FHWA) Long-Term Pavement Performance (LTPP) program for road sections at different climate regions, as well as the field measurements of the oxidation products using the FHWA extensive reports. Simulation results show that the model can effectively address the circular dependence between the aging-related multiphysics and accurately predict the annual profiles of temperatures and oxidation products along pavement depth for asphalt pavement sections in different climate zones. Oxidation grows quickly in summer than that in winter. More oxidation occurs on top layers than that in the middle and bottom layers, leading to an aging gradient at the pavement depth. Additionally, there is an aging gradient at the bitumen film thickness surrounding the interconnected air voids channel.