Reclaimed Asphalt Pavement (RAP) in Cold Recycled Bituminous Mixtures: A Systematic Review

Cold asphalt recycling has been gaining increasing research interest despite the technical challenges hindering its wider application. This systematic review analyses research trends in cold recycled mixtures, including stabilisation with both bitumen emulsion and foamed bitumen, with an emphasis on the incorporation of Reclaimed Asphalt Pavement (RAP). The findings highlight the influence of RAP properties, both aggregate and aged bitumen, on the performance of the mixtures. The aggregate strongly influences gradation and packing, which in turn determine the mechanical properties of the mixture. Meanwhile, the aged bitumen contributes to the mixture performance as a physical layer between RAP aggregates and fresh bitumen, reducing stress concentration at the mixture interface. Although the materials show promising mechanical properties and have been successfully utilised in the field, research gaps remain in quantitatively correlating RAP properties with mixture performance, which would inform a better mix design approach and improve the reliability of this technology.