Towards sustainable pavement construction: A review of the degree of blending in hot recycled asphalt mixture

The use of hot recycled asphalt mixture (HRAM) allows for a reduction in the depletion of non-renewable resources and presents environmental benefits. However, concerns arise regarding the performance of HRAM due to the lower degree of blending (DOB) of virgin and aged asphalt (V&A asphalt). This paper aims to provide an up-to-date review on the DOB of V&A asphalt in HRAM. Initially, the paper introduces the DOB of V&A asphalt, followed by an analysis of the blending theory, evaluation methods, and influencing factors of DOB. Subsequently, the effect of DOB on the performance of HRAM is investigated, and molecular dynamic simulation is utilized to analyze the blend of V&A asphalt. Finally, methods for improving DOB are summarized. It was found that the use of high-resolution microscopy with tracer methods such as SEM/EDS was an effective way to characterize DOB. Furthermore, the chemical composition and colloid structure between virgin and aged asphalt are crucial to DOB. Additionally, improving DOB by utilizing the coupling effect of time and temperature during transportation, paving, and compaction stages is promising. Future research should focus on standardizing test methods, refining field simulation models, and developing intelligent construction technologies to achieve more efficient and durable blending. This review provides theoretical guidance and practical references for improving the DOB of V&A asphalt and promoting sustainable pavement construction.