Morphology, thermal analysis and rheology of Sasobit modified warm mix asphalt binders

The microstructure–property relationship of Sasobit modified Warm Mix Asphalts (WMA) is investigated in terms of thermal, rheological and morphological studies. Four asphalt binders with different types and grades and two Sasobit concentrations (1% and 3% by weight) are included in this study. A 3-D network structure or pseudo-solid like behavior of 3% Sasobit modified WMA is demonstrated. The network structure contributes to blend stiffening at high temperatures resulting in the high limiting temperature being expanded by 5–16 °C, and the breakdown of time–temperature superposition at temperatures above 30 °C. The network microstructure is developed not only on the asphalt surface as depicted by Atomic Force Microscopy (AFM) images, but also in the bulk as implied by rheology. Considering the unchanged glass transition temperatures of asphalts after blending with Sasobit, the network formation is presumably due to the interactions among Sasobit crystals, which act as the physical crosslinks in the viscous asphalt liquid. For 1% Sasobit blends, dendrites rather than typical “bee structure” are observed, which is at least partially due to the high molecular weight of Sasobit and its relatively large concentration compared with naturally occurring wax inside asphalts. The network or dendritic microstructure appears only dependent on the Sasobit concentration, regardless of asphalt types and grades investigated. In addition, Sasobit is not expected to exhibit an undue negative effect on low temperature performance as suggested by 2 °C upshift of the limiting low temperatures.