Rejuvenator content optimization using the semi-circular bend test and balanced mix design

Incorporating reclaimed asphalt pavement (RAP) into asphalt mixes has been a common practice for decades. Within the last decade use of recycled asphalt shingles (RAS) into asphalt mixes has also been gaining momentum. Adding RAS and high contents of RAP into asphalt mixes favors rutting performance of the final mixture, but such mixes are generally prone to cracking because of brittleness of the aged recycled binders. Typically, a softer virgin binder or a rejuvenator is used in such mixes to alleviate the stiffening effect of the recycled binder. To better utilize recycled materials and rejuvenating agents, a balanced mix design has been proposed and implemented in recent studies. A balanced mix is one with satisfactory or optimum performance with respect to both permanent deformation and cracking. This research builds upon those studies and provides a complementary approach to evaluate balanced mix designs for RAP/RAS mixes using binder and mix performance tests. Tested mixtures included virgin mixes with different binder performance grades and various RAP/RAS mixes with multiple dosage rates and three types of rejuvenators. The semi-circular bend (SCB) test and the Hamburg wheel tracking test were employed to evaluate the intermediate temperature fracture performance and high temperature rutting performance of asphalt mixes. Two performance indices from binder tests, i.e., binder shear modulus at intermediate temperature and Glover-Rowe (G-R) parameter were paired with flexibility index from the SCB test. In parallel, the high temperature performance grade and non-recoverable creep compliance (Jm) of binders were compared with the mix rutting obtained from the Hamburg wheel tracking test and the peak load from SCB test. Results showed that adding RAP and RAS severely deteriorates intermediate temperature cracking resistance of asphalt mixes, but such resistance could be recovered to some extent by adding rejuvenators. While increasing the amount of rejuvenator improvedflexibility and cracking resistance, it resulted in a drastic increase in the Hamburg rut depth. High temperature performance indices of binder and asphalt mixes complement each other and agree well in defining the mix performance in terms of rutting resistance. However, the same could not be statedfor intermediate temperature fracture performance indices. While binders with rejuvenator showed superior cracking resistance based on binder performance criteria, the corresponding asphalt mixes, on the other hand, exhibited poor performance in terms of flexibility index.