Optimizing recycled asphalt mixtures with zeolite, cottonseed oil, and varied RAP content for enhanced performance and circular economy impact

The pavement industry has been increasingly encouraged to adopt a more circular approach, associating economic development with a more responsible use of natural resources, due to the significant impacts that its activities impose, particularly on the environment and financial resources. One practice aligned with the circular economy trend is the use of Reclaimed Asphalt Pavement (RAP) in asphalt mixtures. Several methods have been adopted to increase the amount of RAP without compromising the mechanical performance of recycled asphalt mixtures, with particular emphasis on warm mix additives and animal and vegetable oils. In this study, the incorporation of zeolite and cottonseed oil in different proportions in these mixtures was evaluated. Blending charts were used to establish the maximum recycling rates based on the critical temperatures of bio-binders formulated with cottonseed oil. For this research, two sets of recycled asphalt mixtures were analyzed: one with 15%, 25%, and 33% RAP, containing 4%, 6%, and 10% cottonseed oil, respectively, and another with 15%, 25%, and 33% RAP, containing 0.3% zeolite. The mixtures were evaluated for both mechanical performance and circularity aspects through an integrated analysis of mechanical properties (tensile strength, resilient modulus, moisture damage, Cantabro abrasion, flow number, fatigue life) and the Mixture Circularity Index (MCIRAM). All recycled mixtures, regardless of the type of additive, demonstrated satisfactory mechanical performance in all tests conducted. The integrated analysis of mechanical and circularity dimensions identified that the recycled asphalt mixture containing 0.3% zeolite and 25% RAP is the most advantageous, as it met the mechanical criteria and exhibited good environmental performance. Among the mixtures with bio-binder, the combination containing 33% RAP and 10% cottonseed oil exhibited superior mechanical performance and demonstrated greater circularity.