Determining the optimum dosage of a rejuvenator is essential to fulfilling its restoration mission on aged bitumen. Inadequate rejuvenator dosage will lead to insufficient rheological property restoration, whereas excessive rejuvenator content will oversoften the binder blend, leading to impaired rutting resistance. Two different methods, namely, blending chart and response surface modeling, are used in this study to optimize the rejuvenator dosage of binder blends with a high reclaimed asphalt pavement (RAP) binder ratio. Recycled binder blends were prepared using 25 %, 50 %, and 75 % recovered RAP binder and the corresponding virgin binder proportions, with added rejuvenator contents ranging from 0 to 10 % by weight of the binder blend. Rheological tests were performed under a wide temperature range to obtain different indexes as optimization criteria. Indexes include rotational viscosity at binder mixing and compaction temperatures, critical performance grading (PG) temperatures, nonrecoverable compliance, and crossover temperature. The results indicate that indexes obtained at a higher-temperature range required more rejuvenator content to restore the properties of the recycled binder blend to reach a target value. Some indexes only reflected the decrease in stiffness without revealing the changes in the viscous behavior and relaxation capacity. In addition, the selection of optimization criteria should consider the dominant distress type for the specific region. The difference in rejuvenator dosage determined by the blending chart and response surface modeling methods was found to be marginal.

Hot center plant recycling (HCPR) technology has been prioritized as a sustainable and cost-effective solution for asphalt pavement rehabilitation and maintenance due to its environmental and economic benefits. A critical component of HCPR is the preheating of reclaimed asphalt pavement (RAP), which aims at increasing RAP utilization rates and improving the performance of recycled asphalt mixtures. However, either insufficient or excessive preheating temperatures can negatively impact production efficiency and the mechanical properties of hot recycled mixtures containing RAP. This review systematically evaluates current RAP preheating strategies, analyzing their advantages, limitations, and practical implications. Furthermore, it reveals the influences of preheating temperature on the agglomeration and dispersion phenomena of RAP as well as the blending and fusion efficiency between aged and virgin asphalt binders, which are essential for achieving homogeneous recycled mixtures. Additionally, the study identifies relevant performance indicators for RAP and how to establish suitable preheating temperatures based on these indicators. By synthesizing existing research, this article highlights critical knowledge gaps and provides recommendations for future studies, particularly in refining the RAP preheating strategy and determining the optimal preheating temperature range.

The reuse of reclaimed asphalt pavement (RAP) offers economic and environmental benefits in road construction. However, its inconsistent quality—stemming from material complexity and poor management—limits its efficient and high-value application. A key factor contributing to RAP variability is particle agglomeration, where aged asphalt mortar binds aggregate together, leading to inaccurate aggregate gradation measurements and unpredictable contributions of aged binder. These inconsistencies reduce the uniformity and mechanical performance of recycled asphalt mixes. This paper provides a critical review of refined RAP separation treatments recently developed as supplementary RAP processing techniques to reduce variability and enhance performance consistency. Among these methods, rotary centrifugal decomposition has emerged as a promising technique for disaggregating RAP agglomerates and recovering coarse aggregates with minimal residual aged asphalt. Large-scale applications have demonstrated its efficiency in producing well-graded RAP fractions, typically separating recycled coarse aggregates (5–20 mm) from bitumen-rich fine RAP (0–5 mm). Despite its potential to improve RAP recycling rates and high-RAP-content mix performance, challenges remain in preserving coarse aggregate integrity, controlling gradation refinement, and managing the bitumen-rich fine fractions. Therefore, further research is needed to optimize the separation process to minimize material degradation and excessive fine fractions and assess long-term practicality and cost effectiveness through life-cycle analysis.