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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations

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Publication Number:  FHWA-HRT-99-143    Date:  June 2001
Publication Number: FHWA-HRT-99-143
Date: June 2001


Microdamage Healing in Asphalt and Asphalt Concrete, Volume III: A Micromechanics Fracture and Healing Model for Asphalt Concrete

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Volume 3 documents the development of a micromechanics fracture and healing model for asphalt concrete. This model can be used to calculate the density and growth of microcracks during repeated direct tensile controlled-strain loading. The model is based on a relationship among stiffness changes in the mixture as damage occurs, the rate of change in dissipated pseudo strain energy as loading are applied to the samples and as damage occurs and mixture properties including crack length changes upon loading and mixture cohesive surface energies. The report demonstrates that microcrack growth is the dominate mode of distress at temperatures below 25C and that microcrack healing is the dominate mode of recovery of dissipated pseudo strain energy at these test temperatures. However, at temperatures above about 25C, the predominate mode of distress is plastic damage. Cracking rates during fatigue damage are related to de-wetting cohesive surface energy measurements of the bitumen whereas microcracking healing rates are related to wetting cohesive surface energy measurements of the bitumen. Surface energies of five bitumens with widely different chemical compositions were found to correlate strongly with healing properties as defined by viscoelastic fracture and healing theory.



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