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Abstract
The properties of asphalt mixtures containing a high amount of reclaimed asphalt are presumed to be strongly influenced by the degree of blending between old and virgin bitumen. As part of a PhD project, fundamental testing at micro- and nano-levels was undertaken to achieve better understanding of the blending and diffusion phenomenon between rheologically and chemically different bitumens. Three different techniques were used to observe the interface zones of bitumen–bitumen and aggregate–bitumen zones. Nanoindentation, nano-computed tomography (nano-CT) scanning and optical microscopy were done on three different groups of prepared samples. Nanoindentation was conducted to evaluate the difference of surface stiffness of aggregate binder interfaces. Nano-CT scanning techniques were used to observe slight differences in density of the interface in binder zones. Optical microscopy was conducted on thin sections of an asphalt mixture to detect the interface zone between two binders. With nano-CT scanning, it is possible to see the separation zone between the hard- and soft-grade bitumen. Nano-CT scanning images on two different bitumens clearly showed the two bitumen layers due to their varying densities but it was not possible to detect two different binders inside the mixture. Initial results from the nanoindentation study illustrated the benefit of using nanoindentation in detecting two different binders. It was not possible to detect hard and soft bitumens from optical microscopy images on thin sections. Differences in enhanced colours in some points were caused by their difference in thickness. The three-dimensional analysis of bitumen nano-CT images seems to be in reasonable agreement with the assumed bitumen microstructure but further research is needed to confirm this.