Investigation of immobilized RAP binder on asphalt-asphalt/aggregate interaction under multiple temperatures

The traditional blending process includes blending recycled asphalt pavement (RAP) aggregates and virgin aggregates first and then adding the virgin binder. In the first blending process, the mobilized RAP binder coated virgin aggregates, and the immobilized RAP binder remained RAP aggregates. The objective of this study was to investigate the role of the immobilized RAP binder in the mixing process. The contact angle test and binder bond strength (BBS) test were utilized under multiple temperature conditions to discuss the interaction behavior between immobilized RAP binder and virgin binder/aggregate. Results showed that at 90–170 °C, the spreading degree and rate of contact angle between virgin binder and immobilized RAP binder was bigger and higher than that between virgin binder and virgin aggregate, which indicated that the contact behavior between virgin binder and RAP aggregate was stronger than that between virgin binder and virgin aggregate. But at 50–90 °C, the changes in contact behaviors were unstable and irregular. In BBS test, at 20–60 °C, the bonding strength between virgin binder and slate coated by immobilized RAP binder was higher than that between virgin binder and clean slate. At 0–20 °C, the BBS of former was slightly smaller than that of latter. It was believed that the immobilized RAP binder on the surface of RAP aggregate could promote more effective wetting effect between RAP aggregates and virgin binder during mixing, which was better than that between virgin binder and virgin aggregate. •The effect of immobilized RAP binder in the mixing process was studied and revealed.•The interaction of Asphalt and asphalt/aggregate under different temperature was evaluated.•The contact behaviors between asphalt and asphalt/aggregate under medium and high temperature were analyzed by contact angle test.•The bonding strengths between asphalt and asphalt/aggregate under medium and low temperature were analyzed by pull off test.•The influence of immobilized RAP binder film at different thickness on binder bonding strength was studied.