Balanced Mix Design for Enhanced Performance of Stone Matrix Asphalt with Recycled Asphalt Shingles in Oklahoma

Abstract: Sustainable pavement design continues to attract growing interest as different transportation agencies seek to balance performance, cost, and environmental responsibility. Recycled Asphalt Shingles (RAS) have become one of the most promising recycled materials in this effort due to their asphalt binder content and potential economic benefits derived from incorporating them into asphalt mixtures. However, concerns about increased mix stiffness, cracking, and long-term durability have limited their broader use, especially in surface mixtures where flexibility and fatigue resistance are critical. This study explores how RAS can be integrated into Stone Matrix Asphalt (SMA) using the Balanced Mix Design (BMD) framework while ensuring adequate performance. Three SMA mixtures were prepared at 0%, 3%, and 5% RAS contents using Oklahoma Department of Transportation (ODOT)–approved designs. Two post-consumer RAS sources with different gradations were evaluated to capture material variability and the specimens were subjected to short-term and long-term oven aging to examine how durability evolved over time. Performance was assessed through the Hamburg Wheel Tracking Test (HWTT) and the Indirect Tensile Asphalt Cracking Test (IDEAL-CT), representing rutting and cracking resistance, respectively.

All mixtures satisfied BMD performance thresholds, demonstrating balanced rutting and cracking resistance across RAS contents. Rutting resistance generally improved with increasing RAS content, while cracking tolerance showed a moderate decline but remained above acceptable limits. Statistical analysis confirmed that significant performance differences occurred only at the 5% RAS level, suggesting that SMA can safely accommodate up to 3% RAS without compromising cracking resistance. Furthermore, no meaningful differences were observed between RAS sources, indicating consistent performance despite material variability. Overall, these results show that RAS can be successfully integrated into SMA when guided by performance-based mix design principles, providing a practical and sustainable pathway for surface mixtures in Oklahoma.