Multiconstituent Nonlinear Viscoelastic Framework for Modeling Asphalt Binders and Mixtures

The mechanical response of asphaltic material is complex and usually nonlinear depending on the applied stresses and strains. The material exhibits nonlinearity in several ways, such as non-proportional responses to external loading, shear-thinning/thickening, and generation of normal force when sheared. Moreover, asphalt mixtures have several constituents and are sensitive to factors like time, temperature, and confinement pressure, among others. The importance of accounting for nonlinearity in the response of asphaltic materials has been well documented in the literature. However, most available models only account for specific nonlinear aspects of materials (usually the non-proportional response to external loading) and have several inherent shortcomings. For example, the model proposed by Schapery \cite{schapery1969characterization} was to violate conservation of angular momentum for large deformation \cite{rajagopal2005note} and the integral models developed by Cheung and Cebon \cite{cheung1997experimental} cannot account for the normal force generated when the material is sheared \cite{srinivasa2013model}. This research aims to develop a framework to account for the nonlinear behavior of asphalt binders and mixtures. For this reason, thermodynamics-based constitutive models were developed. First, this framework is used to understand and account for the contribution of the individual constituents of asphalt mixtures to overall nonlinear behavior. This allows one to understand and better design the material constituents so mixtures can last longer in the field. The model is corroborated with experimental data obtained from subjecting asphalt mixtures to various experimental protocols. Second, the model is further developed to represent the behavior of blended asphalt mixtures containing reclaimed (recycled) asphalt and virgin binder. Lastly, the model is modified to account for confinement and temperature effects on asphalt mixture behavior. The outcome of this research is the development of a comprehensive nonlinear viscoelastic framework that analyzes asphaltic materials and accounts for the effects of their constituents. The findings of this research highlight the importance of using appropriate testing protocols and choosing the correct model to analyze asphaltic material response. This research will pave the way for developing a fundamental understanding of the responses of asphalt mixtures subjected to different confinement conditions, while accounting for the densification and implicit response of the material. Consequently, the outcome of this study can be used to predict material responses in the field with greate