|Abstract:||Extensive research has been done on rubber-modified asphalt due to its distinct performance benefits, resulting in advancements in the existing rubber modifier technologies. This study focuses on two such new rubber-modifier technologies- an Engineered Crumb Rubber (ECR), and a terminal-blend Rubber Modified Asphalt (RMA) product containing ground tire rubber (GTR) and a common elastomeric polymer, tested alongside a mature terminal-blend GTR product commonly used in Chicago and surrounding areas. The study investigates the low-temperature performance of the mixtures and their durability in terms of permanent deformation. Further, the study examined the effect of softer virgin binder and an increased amount of recycled asphalt shingles (RAS) on mix performance. The products were incorporated into Illinois Tollway’s approved Stone Matrix Asphalt (SMA) Surface Friction Warm Mix Asphalt designs using a base binder (PG 58-28), a softer binder (PG 46-34), and softer binder with increased asphalt binder replacement (ABR) percentage (PG 46-34 with high ABR).
A suite of tests was conducted on plant-compacted gyratories and field cores, namely, Disk-Shaped Compact Tension (DC(T)) test, DC(T) Creep Compliance test, Acoustic Emission (AE) test, and Hamburg Wheel Tracking Test. Further, DC(T)-Hamburg results were plotted on Performance-Space Diagram to obtain a holistic view of mixture performance. Finally, the mixtures were modeled in Illi-TC, a thermal cracking simulation tool developed at UIUC. The key findings suggested that the mixtures would perform well in cold climates, owing to high fracture energy and high compliance. Rutting resistance of the mixtures was also observed to be very high. Performance-Space diagram plots suggest that higher amounts of recycled content can be successfully used if a suitably soft base binder was employed. In addition, the alignment of the data on a relatively straight line on the Hamburg-DC(T) plot demonstrated a significant advantage of pairing the Hamburg with the DC(T) as bookend performance tests. The master curves from the DC(T) Creep Compliance test was very smooth, and the expected trends were observed, namely, change to a softer binder led to more compliant mixes and the addition of more recycled content to the softer binder led to the stiffer mixture. The embrittlement temperatures, obtained from AE tests, supported the findings from DC(T) fracture energy tests in most cases. Finally, Illi-TC modeling showed zero number of critical thermal events for all the mixtures.