Investigation of the influence of crack width on healing properties of asphalt binders at multi-scale levels

- The healing evolution of asphalt binder is directly monitored under FESEM image analysis.
- The healing rate of asphalt binder is found to be nonlinear based on direct image analysis.
- Temperature and aging have important effect on the healing of asphalt binder under FESEM monitoring.
- Healing is triggered by the diffusion mechanism of asphalt molecules based on MD simulation.
- Crack width directly influences asphalt healing; asphalt heals faster with smaller width.

Crack width, a practical measurement of the damage severity in the field, is conceptually believed to have important influence on the healing properties of asphalt materials. Understanding the relationship between crack widths and healing capacity of asphalt pavement provides practical linkage between the microscopic healing phenomena and the macroscopic pavement performance. The objective of this paper is to characterize the healing behavior of asphalt binders with different crack width at multi-scale levels. A Field Emission Scanning Electron Microscopy (FESEM) was used to directly monitor the effect of crack width on healing at macroscale level. Small scale molecular dynamics (MD) simulation models with different crack widths were built to investigate the micromechanical healing mechanism of asphalt binder and characterize the influence of crack width on healing. The MD modeling was conducted using an open-source code software LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator). Healing was found to be triggered by the diffusion mechanism of asphalt molecules. Higher temperature would result in higher diffusivity of molecules and thus higher healing rate. Degree of aging would also have important impact on healing. Both the macroscopic and microscopic investigation indicated that crack width had important influence on the healing of asphalt. For the same crack length asphalt heals faster when the width of crack is smaller.