Advancing circular economy in road construction: Mechanical performance of second-cycle reclaimed asphalt pavement (R²AP)

This study evaluates the performance of recycled asphalt pavement (RAP) and second recycled RAP (R²AP) mixtures to promote sustainability in road construction. The study examined 20 %, 40 %, and 60 % RAP in the first cycle, while the second cycle tested 20 %, 40 %, 60 %, and 80 % R²AP. Various tests, including dynamic creep, four-point beam fatigue, resilient modulus, and indirect tensile strength, were conducted to assess mechanical performance. Mixtures containing 40 % RAP with 80–100 PEN (B1) bitumen and 60 % RAP with 60–70 PEN (B2) bitumen exhibited the best overall performance, achieving high tensile strength (1587 kPa and 1838.5 kPa, respectively), improved stiffness (resilient modulus of 7810.5 MPa and 8000 MPa at 25°C), and enhanced rutting resistance (lowest permanent strain of 3060 µε and 3500 µε). In the second cycle, 40 % R²AP was found optimal for both binders, maintaining satisfactory crack resistance while achieving a resilient modulus of 6000 MPa (B1) and 12,000 MPa (B2) at 25°C. However, fatigue resistance dropped significantly, with an 80 % reduction in fatigue life compared to fresh mixtures, primarily due to increased stiffness from aged bitumen. These findings confirm that optimal RAP and R²AP content can improve mechanical performance and reduce reliance on virgin materials, aligning with circular economy principles by minimizing waste, conserving resources, and lowering environmental impact. To address the limitations of the current study, enhance the understanding of R²AP and advance its application in road construction, future research will focus on evaluating higher R²AP content with rejuvenators, assess its low-temperature performance and moisture resistance, and optimizing mixture design for improved durability and sustainability.