Quantifying the thermomechanical response of bitumen from microphase properties

The macroscopic mechanical response properties of bituminous materials originate from the mechanical properties at the microstructural level. From atomic force microscopy (AFM) investigations, it is evident that mainly two material phases are present in bitumen; these phases can be loosely associated with bitumen's chemical composition (i.e., crude oil origin). However, little is known about the mechanical properties of the constituent phases of bitumen. In this research, an AFM technique was used to obtain mechanical property maps of two bitumens. This technique can distinguish between phases and provide quantitative results. The mechanical properties at the nano-to micrometer-length scale govern the overall properties of bitumen when considered as a microscale composite material. A mechanics approach is followed to derive the composite modulus from the individual phase properties. Furthermore, the temperature dependence of mechanical properties is determined on heating the bitumens from ambient conditions. With an increase in temperature, the moduli of both phases decrease, whereas the phases become more adhesive. The results demonstrate a successful quantitative characterization of the mechanical properties of bitumen microphases and the subsequent coarse graining of these properties into composite mechanical response properties. These mechanical properties (i.e., stiffness and adhesion potential) are important input parameters for material design and modeling and will allow one to predict the macroscopic behavior of asphalt concrete according to fundamental quantities. Finally, a better understanding of the temperature dependence of microstructural mechanical properties can contribute to the understanding of the thermorheological properties of bitumen for optimal processing conditions and best performance.