A thermodynamic framework for modelling healing of asphalt mixtures

Abstract

Asphalt mixtures exhibit complex stress and strain response. Currently asphalt mixtures are modelled as linear elastic/linear viscoelastic materials. Aging of the binder during service life, development of normal stresses during torsion, densification of the mixture due to repeated traffic loading, healing during rest periods etc., are some instances that clearly underline the need to consider the non-linear response characteristics of this material. Healing of asphalt mixtures during rest periods between load applications is one such response which requires careful consideration from the perspective of modelling. If the material is subjected to several cycles of loading and if it is subjected to rest period of sufficient duration after these loading cycles, it is seen that the response after the rest period is similar to that of a much "stiffer" material when compared with the same response before rest period. In short, the material exhibits "beneficial internal structural change" during the application of rest period. The focus of the investigation is to first record through careful experiments healing of asphalt mixtures in the laboratory and then model the same using a rigorous constitutive modelling framework. Since confinement pressure played a significant role in the development of healing, the constitutive model derived had material functions explicitly depending on pressure. The veracity of the model predictions was corroborated with the experimental results and it was found that the predictions were reasonably good.