Nanoscale and Macroscale Characterization of the Influence of RAP and RAS on Cracking Resistance of Asphalt Mixes

This paper summarizes the results of laboratory tests that were performed to characterize the blending of recycled asphalt binders [recycled asphalt shingles (RAS) and reclaimed asphalt pavement (RAP) binders] and virgin asphalt binders and to examine the effects of RAP and RAS on the fatigue cracking resistance of asphalt mixtures. Atomic force microscopy (AFM) was used to characterize the interfacial zone that develops between RAP and a virgin asphalt binder and compare it to the interfacial zone that develops between tear-off RAS and the same virgin asphalt binder. Several asphalt mixtures with RAS, RAP, and combinations of the two were also evaluated, including a control mixture (with no RAP or RAS), a mixture containing 30% RAP, a mixture containing 5% tear-off RAS, and a mixture containing 20% RAP and 3% tear-off RAS. A semicircular bend (SCB) test was used to examine the resistance of the asphalt mixtures to fatigue cracking. The AFM test results indicated that blending occurred between the considered RAP and virgin asphalt binders. A reduction in adhesive bonding energy was observed in the blending zone due to the presence of RAP. However, the adhesive bonding energy of the blending zone was significantly higher than the adhesive bonding energy in the RAP binder. The AFM imaging and force spectroscopy experiments revealed no blending between the considered tear-off RAS material and the virgin asphalt binder. The SCB test results showed that the inclusion of the tear-off RAS in the asphalt mixtures considered in this study significantly reduced their fatigue cracking resistance.