The effect of mix design method on performance of asphalt mixtures containing reclaimed asphalt pavement and recycling agents: Superpave versus balanced mix design

The balanced mix design (BMD) is an alternative method to determine the Optimum Binder Content (OBC) of asphalt mixtures that considers both volumetric and performance properties. However, the feasibility of using this method for designing asphalt mixtures with high reclaimed asphalt pavement (RAP) materials (e.g., 25% and 50%) without and with different types of recycling agents (RAs) needs to be further investigated. To this end, the OBC of asphalt mixtures was first determined through Superpave Mix Design (SMD) by considering volumetric properties. Then mixtures using OBC and OBC ± 0.6% were prepared. Three mechanical tests, including Hamburg Wheel Tracking (HWT), Illinois Flexibility Index (I-FIT), and Indirect Tensile Strength (ITS) in dry and wet conditions, were utilized for high-temperature rutting, mid-temperature cracking, and moisture damage resistance characterization, respectively. The results showed that the RAP-blended mixtures with and without RAs prepared with the OBCs could pass rutting and moisture damage resistance criteria while the cracking resistance of these mixtures was lower than the accepted threshold, except control mixture (i.e., C). Although introducing the RAs to the RAP blended mixtures improved their cracking resistance, an increase in OBC is still needed in RAP mixtures in order to meet the cracking resistance requirement. It was concluded that the SMD might not be an appropriate method for designing the mixtures containing high-RAP materials with and without RAs and these mixtures need to be designed using the BMD method. Among the three RAs evaluated in this study, the aromatic extract RA had the most influence on the rutting performance regardless of the RAP content, while mixtures treated by the aromatic extract RA showed the best cracking resistance.