Three-Dimensional Real Contact Area at the Tire–Asphalt Interface Revealed by Synchrotron X-Ray CT

Abstract Tire and road wear particles are considered a major source of microplastic pollution globally, necessitating a deeper understanding of friction and wear mechanisms at the tire–road interface. A key parameter governing these phenomena is the real contact area; however, to the best of our knowledge, the direct three-dimensional evaluation of the actual contact state at the tire rubber–asphalt interface remains lacking. Therefore, in this study, synchrotron-based micro-X-ray computed tomography (CT) is utilized to visualize the tire rubber–asphalt pavement interface under vertical loading conditions and evaluate the real contact area in three dimensions at the tread block scale. To this end, semi-manual image segmentation is applied to the CT data to distinguish between the aggregates, asphalt binder, tire rubber, and voids and extract the contact interface through three-dimensional reconstruction. Results reveal that real contact does not occur uniformly over the nominal contact area but is localized and governed by surface roughness. In addition, the real contact area showed an overall increase with increasing vertical load, demonstrating qualitative agreement with contact behavior predicted using the Greenwood–Williamson statistical contact model. Furthermore, X-ray transmission images show that an apparent displacement was observed on the asphalt side under vertical loading, suggesting caution when assuming a rigid pavement in the discussions on tire–road contact behavior. The proposed approach provides fundamental insight into contact mechanics at the tire–road interface, offering a valuable experimental basis for advancing the understanding of friction and wear phenomena beyond conventional two-dimensional contact assumptions.