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S. Nahar, A. Schmets, G. Schitter, A. Scarpas:
"Quantifying the Thermomechanical Response of Bitumen from Microphase Properties";
Transportation Research Record, 2574 (2016), 1 - 17.

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, which can loosely be associated with its chemical composition (i.e. crude 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 is able to distinguish between different phases and provides quantitative results. The mechanical properties at the nano to micrometer length scale govern the overall properties of bitumen, when considered as a micro-scale composite material. A mechanics approach is followed to derive the composite modulus from the individual phase properties. Furthermore, the temperature dependence of mechanical properties are determined upon 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 micro-phases, and the subsequent coarse graining of these properties into composite mechanical response properties. These mechanical properties (i.e. stiffness, adhesion potential) are important input parameters for material design and modeling, and will allow to predict the macroscopic behavior of asphalt concrete based on fundamental quantities. Finally, better understanding of the temperature dependence of microstructural mechanical properties can contribute to the understanding of the thermo-rheological properties of bitumen for optimal processing conditions and best performance.

http://dx.doi.org/10.3141/2574-11