One of the challenges in designing recycled asphalt mixtures with a high amount of reclaimed asphalt pavement (RAP) is estimating the blending degree between RAP binder and added virgin bitumen. The extent of blending is crucial because asphalt concrete response is influenced by the final binder properties. This paper focuses on the evaluation of interaction and extent of blending between RAP binder and virgin bitumen by studying the microstructures of the blending zone with atomic force microscopy (AFM). AFM is used to probe the change of microstructural properties from a RAP binder and virgin bitumen to the blending zone of these two. Averaged microstructural properties have been observed in thin-film blends of RAP binder and pure bitumen. The morphology of the blending zone (spatial extent of about 50 μm) exhibits domains of a wide range of microstructure sizes (160 nm to 2.07 μm) and can be considered to be a completely blended new material that has been observed directly for the first time. The fully blended binder properties are found to be between those of the two individual binders, as could be inferred from the averaged microstructural properties derived from AFM images of the blending zone. This finding is also consistent with the results of mechanical tests by dynamic shear rheometer on the same materials. Finally, a design formula is proposed that relates the spatial dimensions of the blending zone to temperature and mixing time, which will eventually allow the results of this study to be extended from small-length scales up to the engineering level.

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Coal tar bearing emulsions were used in the Netherlands as binder in anti-skid surfaces for runways because of their perfect adhesion and fuel resistance properties. They are however toxic and will not be allowed anymore after 2010. Therefore alternatives need to be developed. As one of the alternatives, two types of two-component epoxy modified bitumen have been investigated by means of direct tensile tests (DTT), relaxation tests (RT) and dynamic shear rheometer (DSR) tests. The effect of the curing temperature on the strength development of the epoxy modified bitumen was tested. The results show that the tensile strength increases with increasing curing time and temperature. DTT and RT results indicate that this new epoxy modified bitumen has a much higher tensile strength, cures faster than a bitumen emulsion as a binder. Furthermore, it shows a good stress relaxation even at lower temperatures. The curing speed and the ultimate tensile strength after full curing can be easily adjusted. The DSR results show that the complex modulus of this epoxy modified binder is less susceptible to changes in temperature. The results also suggest that this epoxy modified bitumen has better anti-crack properties at lower temperature and less permanent deformation than bituminous binders at higher temperatures. All these results shows that this type of two-component epoxy modified bitumen can be promising as a binder in anti-skid layers.

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The chemical irreversible hardening of epoxy modified bitumen is affected by various physical factors and the successful application of this technology is directly linked with full understanding of chemo-rheological material characteristics. This study proposes a model to describe the material viscosity evolution during hardening of epoxy modified bitumen. The findings from numerical analyses performed to assess the mechanical response of epoxy modified bituminous binders are presented. Information of the chemical interaction of epoxy within a bituminous matrix was collected and all the influential factors have been determined. The proposed chemo-rheological model accounting for the polymerization of the epoxy in the bitumen was formulated and the sensitivity of material parameters, such as activation energy, reaction order and extent of hardening reaction until the gel point of epoxy modified binders, was demonstrated. Results of the analyses suggest that lower levels of activation energy increase the degree of hardening and the rate of viscosity development. By decreasing the hardening reaction until the gel point the achieved viscosity of epoxy modified bitumen was increased showing the importance of gel reaction extent on material viscosity evolution. The numerical studies have shown also that the polymerization rate in the epoxy modified bitumen is highly dependent on the temperature under various (non-) isothermal conditions. Also, the polymerization rate should be considered through all the material curing processes to avoid unwanted variations in the mechanical properties.

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