Nanoscale viscoelastic characterization of asphalt binders using the AFM-nDMA test

This paper portrays the first set of results of nanoscale viscoelastic (VE) properties of asphalt binders obtained using the recently developed Atomic Force Microscopy-Nanoscale Dynamic Mechanical Analysis (AFM-nDMA) testing mode. To this end, nanoscale frequency sweeps were carried out on eight different asphalt samples including an unmodified asphalt binder and seven Low-Density Polyethylene (LDPE) modified binders. The nDMA testing mode was successful in obtaining the nanoscale VE properties of asphalt binder and constructing nanoscale master curves. This method was also used successfully to distinguish among the different constituents of heterogeneous binder samples based on their dynamic viscoelastic properties. Furthermore, bulk-scale frequency sweeps tests were performed using a Dynamic Shear Rheometer (DSR) in order to compare the nanoscale properties with the bulk properties. There were major differences between the bulk and nanoscale test results. For example, nanoscale dynamic modulus values were higher than their bulk-scale counterparts and the difference increased with an increase in temperature and/or decrease in frequency. On the other hand, the nanoscale phase angle values were less than their bulk counterparts and the difference increased with an increase in frequency. These findings indicate that asphalt binders exhibit stiffer and more elastic behavior at the nanoscale than at the bulk scale. There are distinct differences in the shapes of the master modulus and phase angle curves obtained from the nano and bulk measurements. This paper includes testing guidelines and procedures that would be useful for future experimental investigations of nano VE properties.