The long-term ageing trends of asphalt binders in highway pavements

The majority of highways around the world are surfaced with asphalt pavements. Improving the durability of highway pavements will enhance sustainability at multiple dimensions. A key factor that affects the durability of asphalt pavements is the oxidative ageing of asphalt binders in hot-mix asphalt (HMA) materials. Upon ageing, the chemical property changes of asphalt binders transfer to its physical property changes, and the physical property changes transfer to the behavioral and performance changes of HMA materials. Understanding asphalt pavement ageing is critically important for rational pavement design and possible development of more durable HMA materials. Both simulated ageing analysis and test data from 21 roads in different climate conditions were used in this study to examine asphalt pavement ageing. From the actual roads, it was found that the severity of asphalt binder ageing does not necessarily decrease with pavement depth. Data from different climate conditions even shows opposite trends. Therefore, the use of one uniform empirical equation, which is the current practice, may be inadequate to characterize the realistic ageing evolution in actual pavements. It is recommended that a mechanistic-based asphalt ageing model be developed by considering the following fundamental influencing factors: ageing susceptibility of the asphalt binder, temperature, and the oxygen exposure of asphalt binder in asphalt mixture.