Evaluation of bio-binder modified asphalt's adhesion behavior using sessile drop device and atomic force microscopy

Bio-binder is a renewable material which can be derived from natural resources. Applications of bio-binder in enhancing asphalt's properties have gained profound progresses in past several years. However, limitation still exists in our knowledge on adhesion property of asphalt blended with bio-binder. This study aims to characterize adhesion behavior of bio-binder modified asphalt using sessile drop device (SDD) and atomic force microscopy (AFM). Relationship between the two test results is also investigated. It is shown that addition of bio-binder would introduce different impacts on surface properties for different base asphalts (Pen30 and Pen70 asphalts in this paper), which may be attributed to distinct compatibilities between bio-binder and different asphalts. And the work of adhesion data demonstrates that the bio-binder enhances the interaction between basalt and bio-binder modified Pen70 asphalt binders while depress the interaction between basalt and bio-binder modified Pen30 asphalt binders. It is also found that AFM adhesive force is tip-dependent which may be interpreted using different contact mechanics. In this paper, the high coefficient of variation in soft tip's data may result from the capillary force and contamination during scanning. Interestingly, dispersive surface free energy and AFM results show some reasonable agreements for modified Pen70 asphalts, though there is still a gap between these two methods' results. It is speculated that the variations between surface free energy method and AFM measurement can be attributed to the differences in probe substance, test scale and measured components. Findings in this paper not only promote the development of bio-binder modified asphalt, but also shed lights of the application of AFM in characterization of asphalt's adhesion property.