Using Atomic Force Microscopy to Evaluate the Nanostructure and Nanomechanics of Warm Mix Asphalt

Abstract

In this paper, various Atomic Force Microscopy (AFM) techniques are utilized to study the effects of different warm mix asphalt (WMA) additives on the nanostructure and microstructure as well as the adhesive and cohesive properties of an asphalt binder. To achieve this objective, a control asphalt binder was modified with three different types of WMA additives, which included: Advera (a synthetic zeolite), Evotherm, and Sasobit (a commercial wax). The AFM tapping-mode imaging technique was used to examine the nanostructure and microstructure of the different asphalt material considered. In addition, AFM force spectroscopy experiments were conducted using chemically functionalized AFM tips to measure the nanoscale level adhesive and cohesive forces for the control and WMA asphalt binders before and after moisture conditioning. The results of the AFM imaging showed that while the Sasobit additive has reduced the width of the so-called “bee-like” structures within the asphalt binder, the other WMA additives did not have any significant effect on these structures. In addition, the results of the force spectroscopy experiments indicated that the inclusion of the WMA additives significantly increased the adhesive forces of the asphalt binder prior to moisture conditioning. However, all WMA additives except the Sasobit did not have any significant effect on the adhesive forces after moisture conditioning. Finally, Sasobit and Advera were found to reduce the nanoscale cohesive forces within the considered asphalt binders upon moisture conditioning, indicating that these might adversely affect the cohesive bonds within the asphalt binder.