Evaluating Asphalt Binders Prepared with Different Processes to Meet the Same Performance Grade: Use of Atomic Force Microscope

Abstract

This paper summarizes the results of a laboratory testing program conducted to evaluate the microstructure, adhesion, and other mechanical properties of asphalt binders meeting the same performance grade (PG) but produced by using different processes and modifiers. To that end, atomic force microscope (AFM) tapping mode imaging and force spectroscopy experiments were conducted on different straight-run and modified asphalt binders meeting the same PG. In addition, bitumen bond strength and semicircular beam (SCB) tests were conducted on the different binders evaluated and on the mixes prepared by using those binders, respectively, for comparison. The AFM images indicated that the microstructure of the modified binders was different from those of the straight-run binders. The AFM force spectroscopy test results showed that binders with the same PG could have significantly different adhesion properties. The results of the SCB tests indicated that the fatigue performance was affected by the adhesion properties of the binders evaluated. The AFM bonding energy had a very good correlation with the flexibility index parameter obtained from SCB test results. The results of this paper suggest that the adhesion properties of asphalt binders should be included in their evaluation process and specifications.