Refined Separation Treatment for Reclaimed Asphalt Pavement (RAP) Processing: A Review

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.