Blending Efficiency and Effective Styrene Butadiene Rubber Concentration of Micro-Surfacing Mixtures with Reclaimed Asphalt Pavement

Reclaimed asphalt pavement (RAP) has been used in micro-surfacing mixtures with good promise and improved sustainability. However, no systematic study has been conducted to analyze the chemical components of the RAP micro-surfacing mixture when blending virgin binder with RAP binder, and to confirm the reasonableness of using RAP micro-surfacing mixtures. Based on a gap-graded method, this paper explored the chemical properties of RAP micro-surfacing mixtures using attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR) and fluorescence microscopy, and explained the blending mechanism between the RAP and the cold mixture. The blending efficiency and effective styrene butadiene rubber (SBR) concentration were quantified based on various chemical component parameters. The results showed that partial blending existed for RAP micro-surfacing mixtures. It was found that the diffusion happened from the outer layer of the RAP mixture as a result of the coating of emulsion, and could continuously and gradually happen for the RAP mixture, giving higher blending efficiency for a high RAP content mixture. The addition of RAP makes SBR particles more dispersible. Including rejuvenators and increasing curing time could improve the blending efficiency and the effective modifier concentration.