Optimization of the Evaluation Indexes for Asphalt UV Aging Behaviors based on Multi-scale Characterization Methods: from the Evolution of Their Physical-Chemical Properties and Microscope Morphology

Aiming to propose some suitable evaluation indexes to quantitatively characterize the UV aging resistance of asphalt binders, firstly, effects of UV aging on asphalt’s properties were comprehensively explored from the multiple scales, including their physical rheological properties, chemical compositions and microscope morphology. The above properties of asphalt binders before and after UV aging were respectively measured with the conventional physical properties tests, dynamic shear rheometer (DSR) test, thin-layer chromatography test (TLC) test, gel permeation chromatography (GPC) test and atomic force microscopy (AFM) test. Subsequently, based on some principles for establishing evaluation indexes, such as discrimination, regularity and consistency, the optimal evaluation indexes were proposed to quantitatively characterize the UV aging resistance of asphalt binders. Finally, relationships between the physical properties, chemical compositions and micro morphology of asphalt binders were discussed with the Pearson correlation coefficient method. Test results show that UV aging has a significant effect on physical rheological properties of asphalt, and ranking of aging resistances among asphalt binders evaluated by different macro indices are nearly consistent. Among these macro indexes, the G-R parameter aging index are proved to be the evaluation index with the highest discrimination degree, followed by complex shear modulus G* aging index (60 °C, 10 rad/s, 1 %) and zero shearing viscosity ZSV aging index (60 °C). Chemical composition test results demonstrate that with the growth of UV aging degree, resins components in asphalt increase gradually, while aromatics components decrease, which results in the proportion of larger molecular size (LMS) in asphalt gradually increases. And AFM test results show that UV aging will cause the number of the “bee structure” and roughness values of asphalt gradually decrease, thus promoting the transformation of the asphalt micro structure to smooth. Pearson correlation analysis indicates the compared with the roughness Ra, the Gel index Ic and LMS possesses higher correlation with G-R and G*, whose R values both exceed 0.8. Thus, it may be appropriate to adopt some chemical composition evaluation indexes (such as Ic, LMS) to characterize the UV aging degree of asphalt binders from the microscope perspective.