Analysis of Microscopic Damage Mechanism of Asphalt Binder Through Atomic Force Microscopy (AFM)

A neat asphalt binder and styrene-butadiene-styrene (SBS) modified asphalt binder were examined through atomic force microscopy (AFM) to evaluate the microscopic damage mechanism of asphalt binders. First, an in-situ tensile loading device for conducting AFM tests was designed. Next, the morphology and mechanical properties of microstructures of the asphalt surfaces were analyzed through in-situ tests. Subsequently, a two-dimensional model of asphalt binders based on the AFM test results was developed using ABAQUS software, and the stress distribution of the asphalt surfaces under tensile loading was analyzed. Finally, the AFM test and finite element simulation results were combined to analyze the microstructural damage mechanism of the asphalt. The results show that three types of microstructures exist on the surface of the neat asphalt binder, i. e., the bee, bee-casing, and interstitial structures. The SBS-modified asphalt binder has no visible bee-casing structure. The interstitial and bee structures have the weakest and strongest anti-deformation abilities, respectively. The addition of the SBS modifier decreases the stress on the asphalt surface and distributes the stress more uniformly. Under tensile loading, phase separation occurs in the interstitial structure, and this separation phenomenon is intensified with the increase in the strain. The phase separation occurs at the location under the maximum stress. The asphalt damage involves the initiation of phase separation in the microstructure under high stress, and then the formation of the phase separation increases with the load until microcracks are formed. © 2020, Editorial Department of China Journal of Highway and Transport. All right reserved.