Self-healing of bitumen is a property that positively contributes to the sustainability, maintenance requirements and cost effectiveness of asphalt pavements. Ideally one would like to design an asphalt mix with a well-defined healing potential. Although substantial research efforts have been dedicated to the healing mechanism in bitumen, complete understanding of the fundamental mechanisms that govern the property of healing is still lacking. Here we investigate the manifestation of damage and healing of bitumen at the microstructural level. Three distinct bitumen grades are subjected to mechanical loading conditions, and the damage is investigated at the microstructural level by atomic force microscopy combined with finite element simulations. One of the bituminous phases appears to display visible signs of cracks, which are found to (partly) disappear at moderate temperature changes. Simulations of mechanical loading of experimentally derived finite element meshes are corresponding well with these experimental observations. Moreover, the simulations provide a measure of mechanical response, i.e. stiffness, of the material as a function of strain level. From this it is found that the microstructural cracks lead to diminished structural response properties, whereas after healing these properties are partly recovered. The experimental observations, together with the simulations, support earlier ideas that relate the phenomenon of self-healing in bitumen to their rheological property of thixotropy. Moreover, the work presented hints that the property of self-healing is governed by processes at the microstructural length scale.@en

Trace elements and their concentrations play an important role in both chemical and physical properties of bitumen. Instrumental Neutron Activation Analysis (INAA) has been applied to determine the concentration of trace elements in bitumen. This method requires irradiation of the material with neutrons that transform the elements into radioactive isotopes. By analyzing the activity of the individual nuclides, the concentration of each detectable trace element can be determined with high precision. In this work, we perform trace elemental analyses of 13 distinct bitumens, including 2 modified and 3 bitumens from the material library of Strategic Highway Research Program (SHRP. Three elements, vanadium, nickel and cobalt are found to be present in all bitumens. Vanadium and nickel are found to be the most abundant among all the elements detected. Next to vanadium and nickel, significant concentrations of iron are found in 11 bitumens. The total number of trace elements identified varied from 17 to 28 for the bitumens studied. For modified bitumens, the concentration of trace elements is used as a parameter to measure the extent of modification. The sum of most abundant trace elements (vanadium and nickel) correlates well with the sulphur and asphaltene contents of the same bitumen. Moreover, the concentration of the latter metals are known to be an indicator for the aging characteristics of bitumen. Thus, INAA provides the content of trace elements in bitumen, where the concentrations vary (ppm to ppb) depending on the crude origin of the material. Thus, INAA can be used to trace back the crude origin of the material, which may have applications in the field of asphalt recycling (RAP and RAS).@en

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.

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