Abstract
Asphalt concrete is a bonded granular material composed of aggregates and asphalt binder. The chemical, physical, and mechanical properties of these constituents are different. Under typical repeated tire loads, the aggregates do not deform but instead rigidly translate and rotate within the binder. Rutting is the surface manifestation of the internal-structure evolution in asphalt concrete under repeated wheel loading. A procedure to quantify the permanent strain field of asphalt concrete underlying the rutted zone produced by an accelerated wheel testing device is described. This new, noninvasive procedure has been automatically implemented in a computer program named MATCH, which was developed to compare the locations of particles before and after testing and therefore to permit the displacement of individual particles to be tracked. Pattern recognition based on each particle’s cross-sectional area, perimeter, and aspect ratio was used to match the particles. Application of the new procedure to measure the permanent strain field of an asphalt concrete specimen in a Georgia loaded wheel tester is described. The reliability of the procedure for automatically matching the particles in successive images was confirmed by manual procedures. It was found that the permanent strain and the mastic/solid area ratio evolution measured in this application demonstrated strong localism. Dilatancy and contraction were quite significant locally but insignificant globally. The strains in the mastic were much larger than the global or macrostrain. The proposed procedure has significance in the future study of micro-macro properties of bonded granular materials and how factors such as aggregate size, shape, and distribution affect the global response.
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