Research progress on multi-scale evaluation method for loose defects of asphalt pavement in airports

Airport asphalt pavements were susceptible to loose particle removal under high tire pressures, severe impact, intense torsional shear, and water-temperature-loading coupling. However, the existing evaluation methods were predominantly derived from the highway sector, with insufficient applicability to airports. In response to these issues, the research progress on multi-scale evaluation methods for asphalt pavement loose defects was systematically reviewed. Based on the differences in service conditions between airports and highways, the mechanisms of interfacial adhesion failure, cohesion failure within the transition zone, and cohesion failure within the asphalt mastic associated with loose defects were analyzed. At the macroscale, evaluation methods were summarized, including static-water moisture-stability testing, dynamic-water scouring, and simulations of torsional-shear and impact loading for asphalt mixtures. At the mesoscale, the bonding performance of asphalt-aggregate interfaces characterized by adhesive mechanical tests and surface free energy theory was reviewed. At the micro- and molecular scales, the application of atomic force microscope and molecular dynamics simulations in analyses of interfacial morphology, nanomechanics, and microscale surface energy was summarized. At the full scale, the roles of field evaluation techniques, such as ground penetrating radar and in situ pull-off testing, as well as accelerated loading devices, in investigating the overall loose defect of pavements were assessed. The analysis results indicate that loose defect is a multi-scale coupled deterioration process resulting from the combined effects of intrinsic material properties and multiple external factors. Although macroscale tests facilitate engineering-level screening, it is difficult to reproduce the distinctive service conditions of airports. Meso-, micro-, and molecular-scale methods help elucidate interfacial failure mechanisms, but quantitative correlations with macroscale material loss and field defects remain insufficient. Full-scale evaluation is closer to actual service conditions but is constrained by cost, efficiency, and environmental interference. Future research should develop multifactor coupled simulation devices specifically for airport pavements and establish cross-scale correlation models linking microscopic interfacial energy, mesoscale bonding strength, macroscale material-loss severity, and full-scale in-service behavior.