Non-linear viscoelastic and micromorphological properties of SBS-modified asphalt binder

• Significant phase separation was observed in modified binder under large strain. • 3.0 % is the threshold polymer content at which the most unstable system formed. • Stable system formed in modified binder below or above the threshold content. Contrary to the conventional linear viscoelastic analysis, asphalt binder’s response in the non-linear viscoelastic (NLVE) domain can potentially reveal more complex aspects of its micromorphology. This research aimed at investigating the evolution of the NLVE and micromorphological properties of styrene–butadiene–styrene (SBS)-modified asphalt binder depending on their polymer content. For this purpose, the high-temperature NLVE response of asphalt binders was evaluated by shear strain amplitude and time sweeps. Moreover, their microstructure was obtained by confocal fluorescence microscopy and segmented into three phases for the quantitative analysis which included global morphological features, as well as those of discrete and continuous phases. The NLVE rheological response and the morphology of modified binders experienced a significant transition as the polymer content increased. A notable threshold in this transition was observed at 3.0 % of SBS, between which two mechanically and morphologically stable configurations were formed. Below this threshold (at 1.5 % of SBS), the binder with small and highly dispersed SBS particles behaved like a continuum and its NLVE response was dominated by the asphalt phase. Above the threshold (from 4.5 to 6.0 % of SBS), large and irregularly shaped porous SBS particles boosted the resistance to large deformation and led to high non-linearity.