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S. Nahar, M. Mohajeri, A. Schmets, A. Scarpas, M. F. C. Martin, G. Schitter:
"First observation of the blending zone morphology at the interface of reclaimed asphalt binder and virgin bitumen";
Transportation Research Record, 2370 (2013), 1; 1 - 9.

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.

http://dx.doi.org/10.3141/2370-01