Bitumen modification with reactive and non-reactive (virgin and recycled) polymers: A comparative analysis

The main goal of this research was to compare the modification capability of two different types of bitumen modifiers: non-reactive plastomers and elastomers, and reactive polymers. The group of non-reactive polymers included a block copolymer (SBS), recycled thermoplastic polymers (EVA/LDPE blends), and crumb tire rubber, which were mixed at a processing temperature of 180 °C. In the second group, a reactive MDI–PEG prepolymer, a low processing temperature modifier (90 °C), was considered. The study was mainly focused on the characterization of the thermorheological behaviour of selected modified bitumen samples. In addition, the thermal behaviour (by modulated DSC), and morphology (by optical microscopy) of these modified bitumen samples were also evaluated. All of these bitumen modifiers significantly improve the thermomechanical properties of the resulting binder, especially at high in-service temperatures. However, whereas bitumen modified by non-reactive polymers undergo marked oxidation events due to the high processing temperature used (180 °C), MDI–PEG modified bitumen does not experience this phenomenon because of the lower processing temperature involved (90 °C). In general, non-reactive polymers should be added in much larger concentrations than the reactive polymer to obtain similar results, although the latter requires a further period of curing, at room temperature, to induce suitable modification. Finally, only MDI–PEG modified bitumen is stable when stored at high temperature (163 °C), whereas all the non-reactive polymer-modified bitumen studied undergo either phase separation or particle precipitation.