Investigation of Rheological and Nano-Rheological Properties of Asphalt Binders
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The study of asphalt emulsion needs a fundamental knowledge of the physical and chemical properties of emulsion. This work investigate different evaporative residue recovery methods as they relate not only to macro scale properties but also to the asphalt microstructure and nano-rheology. Furthermore, this study demonstrates the application of dynamic shear rheometer for macro scale and the application of atomic force microscopy imaging for nano-scale. Extraction of nano-scale engineering properties, i.e. dissipated energy, elastic modulus, adhesion force provide information for prediction of performance related characteristics. This work implements the framework of mechanics by investigating two different solution, elastic and viscoelastic as they relate not only to macro-scale properties of the binder but also to the binder microstructure. It was revealed that different evaporative recovery methods induces substantial microstructural changes in residual binder, i.e. phase distribution, phase percentage, phase structure. It has also been shown that mechanical behavior of asphalt microstructure correlates with bulk behavior of the binder through experimental measurements and finite element modeling techniques. The rheological properties of binders are now commonly used in materials specifications and are used as input to the Mechanistic-Empirical Pavement Design Guide (MEPDG). Therefore, an approach of using predictive models to estimate the rheological properties of the bituminous materials accurately would be useful for the pavement design. In this study, a modeling approach is proposed which is based on fundamental viscoelastic principles. To establish the models, a large data set that was obtained from multiple existing national efforts across the United States was used. The database consists of measured modulus values from mixtures with modified and unmodified binders, and mixtures having various amounts of reclaimed asphalt pavement (RAP). As a result, two predictive models were developed to estimate the binder shear modulus and phase angle given the desired physical and mechanical properties of asphalt mixtures. These models can be used for a wide range of temperatures (covering -10? up to 54.4?C) that are recommended in the American Association of State Highway and Transportation Officials (AASHTO) TP62-03 test protocol. It is believed that the aforementioned findings of this study can lead to enhance the knowledge of rheological properties of binders in RAP mixtures at intermediate and high temperatures without the need to extract binder from mixture.