Nanoscale viscoelastic characterization of asphalt binders using the AFM-nDMA test
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ORIGINAL ARTICLE
Nanoscale viscoelastic characterization of asphalt binders using the AFM-nDMA test Mohammad Fuad Aljarrah
. Eyad Masad
Received: 17 April 2020 / Accepted: 28 July 2020 Ó RILEM 2020
Abstract 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
M. F. Aljarrah (&) Zachry Department of Civil and Environmental Engineering, Texas A&M University, College Station, TX, USA e-mail: [email protected] E. Masad Mechanical Engineering Program, Texas A&M University at Qatar, Doha, Qatar e-mail: [email protected]
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. Keywords nDMA AFM Viscoelasticity Nanoscale Asphalt binder LDPE
1 Introduction This paper describes and summarizes the first set of measurements of the nanoscale linear viscoelastic (VE) properties of asphalt binders using the novel Nanoscale Dynamic Mechanical Analysis (nDMA) testing mode by the Atomic Force Microscope (AFM) machine. This state-of-the-art method was developed to overcome the limitations of the previous nanoscale VE tests carried out using various Nano indenters and AFM devices [1, 2]. The following sections
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summarize the progression of nanoscale viscoelastic characterization leading to the introduction of the AFM-nDMA mode. Within the past two decades, several studies have been carried out to understand and predict materials’ behavior by characterizing their properties at
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