Multi-scale evaluation of the effect of rejuvenators on the performance of high RAP content mixtures

• Adhesive bonding energy of RAP–virgin binder interfacial blending zone was measured using AFM.
• The investigated rejuvenators increased the adhesive bonding energy of RAP–virgin binder interfacial.
• The RAP–virgin binder interfacial blending zone moduli are different than those of the blends prepared by manually mixing of the RAP and virgin binders.
• The interfacial blending zone adhesive properties might be one of the factors dictating fatigue performance of high RAP mixtures.

Atomic Force Microscopy (AFM) techniques were used to study the effects of rejuvenators on the nano-mechanical properties of the interfacial blending zone that forms between RAP and virgin asphalt binders in a high RAP content mixture. In addition, examined links between the nano-scale properties and the macro-scale performance were evaluated. This was done by evaluating the macro-scale properties and performance of RAP and the virgin asphalt binders’ blends as well as the mixtures with high RAP content. The results of the AFM indentations tests indicated that the rejuvenators did not have a significant effect on the modulus of the virgin binder. However, the indentation modulus of the interface blending zones was significantly decreased. Furthermore, the AFM force spectroscopy results showed that the rejuvenators increased the interfacial blending zone adhesive bonding energy. The comparison between the Dynamic Shear Rheometer (DSR) and AFM results indicated that the interfacial blending zone properties are different than those of the blends prepared by manually mixing RAP and virgin binders. This might suggest that the 100 percent blending is not attainable and an alternative method such as the one presented in this paper could be a better tool to evaluate the composite asphalt binder in mixtures with high RAP content. The AFM indentation modulus of interfacial blending zone correlated well with the Hamburg Wheel Tracking test of the high RAP content mixtures. Finally, the results the beam fatigue test suggested that the interfacial blending zone bonding energy might be one of the factors dictating fatigue performance of high RAP mixtures.