Relationship Between the Crossover Temperature and Asphalt Chemistry Through Validation of the Rheo+ Method Using Eight Binders from the United States, Canada, Mexico, and Spain

Fatigue is one of the most common failures of asphalt pavements and is strongly influenced by the properties of the asphalt binder. The relationship between the resistance to fatigue and the aging of asphalt cement has been a subject of discussion and with many conclusions to be unified. That said, this research work validates a new tool called RHEO-PLUS (RHEO+), which allows correlating the viscoelastic mechanical properties measured in a dynamic shear rheometer (DSR), with respect to the changes in the chemical composition of the asphalt at different degrees of oxidation. As asphalt oxidizes, its chemical composition changes, affecting its rheology and increasing the polarity of the molecules. This, in turn, causes the appearance of more rigid molecular structures that directly affect the elastic response, crack resistance, and durability of the asphalt. The oxidation products with the greatest contribution to asphalt hardening are sulfoxides and carbonyls. Therefore, their determination and quantification are performed by Fourier transform infrared (FTIR) spectroscopy using the attenuated total reflectance (ATR) technique. Additionally, it is complemented with a temperature sweep, at constant speed and controlled deformation using a dynamic shear rheometer (DSR) to determine the crossover temperature (Tcross) at different degrees of oxidation. Both parameters together make it possible to recognize whether the binder is in optimal, aged, or oxidized condition.