Optimizing Mix Attributes to Increase RAP Proportion in Asphalt Mixtures

Abstract: The steady increase in the use of reclaimed asphalt pavement (RAP) reflects a positive trend towards environmental and economic benefits. The present study investigates the impact of various influential factors, specifically binder content, RAP content, and binder grade on the performance of RAP-inclusive asphalt mixtures. The primary focus is to enhance the understanding of how adjustments in binder content and grade can produce durable high RAP mixtures that exceed current allowable RAP limits (20-30%). To validate the experimental findings, Tukey's pairwise post hoc analysis was employed to assess statistical differences among various RAP mixture combinations. Preliminary results indicate that the performance of RAP mixtures is significantly influenced by binder content, RAP content, and binder grade, with binder content being the most critical factor. Performance tests suggest that strategic adjustments in mix design attributes, particularly binder content and grade can enhance RAP utilization by up to 10%. While Tukey's analysis indicates that further increases in RAP content may not improve cracking resistance, they do enhance rutting tolerance. To achieve a balance between fatigue cracking and rutting resistance, a Balanced Mix Design (BMD) approach was implemented. The BMD findings reveal that a slight increase in binder content (less than 0.5%) or utilizing the same binder content with a one-grade bump can yield performance levels statistically comparable to those of control samples.