Structural transitions and physical networks in wax-modified bitumens

This research focuses on the characterisation and evaluation of wax-modified bitumens for use in warm mix asphalt (WMA). Wax-modified bitumens were produced by addition of different types of wax to a 50/70 unmodified bitumen. Five different waxes were used, including synthetic hydrocarbons Fischer–Tropsch wax, Montan waxes and amidic-functionalised waxes. A basic structural picture of wax-modified bitumens was initially derived from the analysis of the thermal properties and morphological arrangements. The mechanical properties of the binders were then evaluated by rheometry, which indicated that bitumen modification with synthetic and functionalised waxes provides significant alteration in the overall colloidal structure. A comprehensive analysis of linear viscoelastic spectra depicted the existence of a sequence of structural transitions and relative behavioural processes, which deeply alter the behaviour of the original binder at in-service temperatures. All the rheological dynamics were interpreted in the light of the concept of residual crystallinity. The presence of physical networks generated by contiguous microcrystalline segments was finally hypothesised to explain the gel-like behaviour of the materials.