Thermal, microscopic, and rheological characterization of rejuvenated asphalt binders

Transportation agencies are increasingly incorporating reclaimed asphalt pavement (RAP) in asphalt mixtures due to the scarcity and increased costs of virgin resources. The usage of RAP brings both economic as well as environmental benefits. Nonetheless, because RAP is an aged, stiff, and brittle material, utilizing it in large quantities can make the pavement more prone to cracking and reduce its service life. Recycling agents (rejuvenators) are additives typically applied to partially restore the properties of aged asphalt binders and facilitate using higher RAP contents. While considerable effort has been made on evaluating the influences of recycling agents on asphalt binders’ performance, the rejuvenation mechanisms of recycling agents have not yet been thoroughly examined. This study's objective was to evaluate the influence of various types of recycling agents on the properties of asphalt binder blends containing 50% RAP binder. The oxidative stability of the recycling agents and rejuvenated binder blends was evaluated utilizing thermogravimetric analysis (TGA). The glass transition region and the compatibility of the binder blends were assessed using differential scanning calorimetry (DSC). Finally, atomic force microscopy (AFM) experiments were conducted to study the mechanisms of the recycling agents at the nanoscale level. The results revealed a relationship between the phases detected in the microstructure and the physical characteristics of the binder blends. DSC analysis showed that after the inclusion of recycling agents, the breadth and temperature of the glass transition region were reduced, indicating the formation of a less brittle material. AFM observations showed that the dispersion of the polar molecular associations in the RAP binder correlated with the changes in the glass transition region as measured using the DSC. The study's findings were used to characterize the effectiveness of recycling agents based on the thermal, microstructural, and rheological properties of rejuvenated binder blends to help explain the mechanisms of recycling agents.