Multiphysics measurements of in-service asphalt pavements for the analysis of their long-term aging behaviors: systems, methods, and key insights

The long-term aging of in-service asphalt pavements is affected by coupled Multiphysics factors, including temperature, oxygen exposure, and moisture content. Although pavement temperature is routinely monitored, in-situ measurement of oxygen and moisture within asphalt pavements remains largely unexplored, resulting in limited accuracy in aging analysis and prediction. To address such a critical gap, this study developed an integrated system for the simultaneous measurement and monitoring of temperature, oxygen, and moisture within asphalt pavements, enabling the characterization of their spatiotemporal variations. In laboratory investigation, the system was employed to investigate oxygen distribution characteristics for different asphalt mixture types. In field investigation, the system was deployed in a full-scale test section for year-long monitoring, providing first-hand information on in-situ oxygen and moisture distributions within asphalt pavements. The lab test demonstrated that oxygen distribution in asphalt mixtures is predominantly governed by the rate of oxygen transport, which is strongly influenced by the characteristics of air voids. The field investigation revealed a distinct arc-shaped distribution profile of oxygen content with pavement depth, challenging the traditional assumption of monotonic variation of oxygen distribution in pavements. A bidirectional oxygen diffusion model was proposed to capture this finding. Additionally, moisture was found to play a substantial role in modulating the distributions of both oxygen and temperature. Overall, these findings enhance the understanding of asphalt aging mechanisms in pavements and establish a foundation for more accurate aging predictions and the development of targeted anti-aging strategies.