Multi-fractal morphology of un-aged and aged SBS polymer-modified bitumen

Polymer-modified bitumen (PmBs) has been characterised by fluorescence microscopy, conventional performance tests and by the rheological measurements, before and after the Rolling Thin Film Oven Test (RTFOT), and by multi-fractal analysis. The addition of 2-7 wt-% of linear styrene-butadiene-styrene block copolymer (SBS-L) or radial block copolymer (SBS-R) increased viscosity, softening point and complex modulus of PmBs. Hardening of PmBs occurred and the elastic response decreased after RTFOT aging. SBS-L PmBs are more susceptible to RTFOT aging. Digital fluorescence micrographs of sections of PmBs qualitatively exhibit different morphological structures which can be quantitatively probed by multi-fractal analysis: differences are reflected in the f (alpha) spectrum. The PmBs which appear less multi-fractal have the best rheological properties. In another approach, the focal fractal dimensions' distributions for the SBS-modified bitumen have peak around 2.35 (which corresponds to the bitumen-rich phase) and around 2.7 (which corresponds to the noncontinuous SBS-rich phase).