Laboratory performance evaluation of RAP/RAS mixtures designed with virgin and blended binders

When developing blending charts for RAP/RAS mixtures, it is presumed that laboratory testing of blended and virgin binders match the performance characterization of the plant-produced mixtures with the recycled materials. However, the thoroughgoing blend of the virgin binder into the RAP/RAS material is not guaranteed in an asphalt mix plant. In some cases, blending charts results in a virgin binder which is two performance grades softer than the target binder. Kentucky Transportation Cabinet was interested in determining if using a two-grades-softer binder would have a deleterious effect on pavement performance. In this study, four RAP/RAS field mixtures were collected from highway projects in Kentucky. The mixtures were subjected to beam fatigue, IDT creep/strength, and DC(t) fracture tests at the Asphalt Institute laboratory. Furthermore, a laboratory standard mixture was utilized as a control for the expected performance from the mixtures in central Kentucky. The results showed that using virgin binders, which were two grades softer than the target performance grade, resulted in drastically softer mixtures, as compared to the control mixture. This finding suggests the rutting potential of the pavement could escalate by using such a soft virgin binder. Nonetheless, the fracture energy of the mixtures did not improve by using a twogrades- softer binder. In summary, the mixture with one-grade-softer virgin binder exhibited a closer performance to the control mixture.