Determining Intrinsic Healing Properties of Asphalt Binders: Role of Dynamic Shear Rheometer

A self-healing material has the inherent ability to partially reverse damage. There is consensus that the healing of damage has a substantial effect on the performance of asphalt pavements. It is important to understand the mechanisms responsible for healing in asphalt binders, to develop a model to predict healing on the basis of these mechanisms, and to develop test methods to determine the properties required for use with such a model. A healing model for asphalt materials comprises a convolution of wetting and intrinsic healing processes that occur across a crack interface. According to the proposed convolution process, intrinsic healing or strength gain across a crack surface occurs in two steps: an instantaneous strength gain resulting from the interfacial cohesion between the crack faces, and a time-dependent strength gain resulting from intermolecular diffusion and randomization across the crack interface. A modified form of the Avrami equation, which includes a parameter for instantaneous strength gain, is used to describe the intrinsic healing in asphalt binders. A test method is described that is based on the use of a dynamic shear rheometer for estimating the parameters of the intrinsic healing function. Five asphalt binders with considerably different compositions were studied. Limited validation of this test method and the intrinsic healing model are presented by comparing the parameter related to instantaneous healing with the thermodynamic work of cohesion for the selected binders.