Morphology-sensitive rheological responses and phase-separation tendency in physically blended SBS-modified asphalt binders

The morphology of SBS-rich phases in SBS-modified asphalt binder systems is related to viscoelastic behaviour and tendency for phase separation. Physically blended binders without stabilisers or crosslinkers with SBS content ranging from 3–8 wt% have been studied using quantitative fluorescence microscopy along with rheological measurements and hot-storage tests. The key aspect is the simultaneous study of morphology, temperature dependence of Han plots and phase separation after storage in the same SBS-content series. With an increase in SBS content, the morphology of the SBS-rich phase changes from particle-dominated morphology through elongation-dominated transitional morphologies to locally near-network morphology. The largest connected component fraction increased from 1.27% ± 0.05% in SMB-3 to 12.71% ± 0.33% in SMB-8. The Han curve-separation index values dropped from 0.1064 in SMB-3 to 0.0302 and 0.0285 in SMB-6 and SMB-8, respectively. The hot-storage separation index values after ASTM D7173 conditioning showed the same trend, decreasing from 0.3155 ± 0.0043 to 0.1170 ± 0.0029. It was shown that with changing morphology, there is a systematic change in bulk rheological properties and phase separation behaviour. While temperature dependence of Han plots serves as complementary rheological evidence, it does not substitute for standardised storage tests.