AFM-Based Approach to Study Blending between RAP and Virgin Asphalt Binders

Abstract

In this paper, atomic force microscopy (AFM) is used to evaluate micromechanical properties of the interfacial blending zone between reclaimed asphalt pavement (RAP) and virgin asphalt binders. Three virgin asphalt binders with different performance grades (PG 58-28, PG 64-28, and PG 64-22) and two sources of RAP binder are used to evaluate the effects of the different RAP and virgin asphalt binder properties on the stiffness and adhesive properties of the blending zone between these binders. A new procedure is developed to simulate the interaction between RAP and virgin asphalt binders that occurs in the drum in an asphalt plant. The AFM tests indicate that blending occurred between RAP and virgin binder for all six tested RAP-virgin asphalt binder combinations. The reduced modulus for the blending zone depended generally on the virgin binder grade and RAP source. The highest stiffness was achieved from the combination of RAP and PG 64-22, whereas the lowest stiffness was obtained from the combination of RAP and PG 58-28. The bonding energy results indicate that adhesive properties of the blending zone were adversely affected by the presence of RAP within the zone. However, the adhesive properties of the blending zone were significantly better than those for the RAP binders. The variation in the blending zone between both RAP binders and PG 58-28/PG 64-28 indicate that the blending zone might not be homogenous. Further analysis of the concentration of RAP binder within the blending zone revealed dependence on RAP stiffness characteristics. However, the adhesive properties of the blending zone were primarily controlled by the virgin binder properties.