Correlation of processing parameters and ageing with the phase morphology of styrene-butadiene-styrene block co-polymer modified bitumen

The morphology development of styrene-butadiene-styrene (SBS) block copolymer modified bitumen as a function of processing parameters was investigated using a combination of optical (OM) and confocal laser scanning microscopy (CLSM). The homogeneity of blends of SBS and bitumen increased with increasing mixing time, where the application of higher shear rates enhances the dispersion and distribution of the SBS phase in the bitumen matrix. For higher shear rates, SBS was swollen between 6 and 8 times that of its initial volume and shear rate is more influential than mixing time in achieving a highly dispersed SBS phase in bitumen. The bitumen components having fluorescence properties (i.e. saturates and aromatics) were homogenously dispersed in the bitumen phase, confirmed by highly uniform fluorescence intensity 3D colour maps (CLSM). The fluorescence intensity of the SBS modified bitumen samples was much more variable with regions of high and low intensity due to inhomogeneous dispersion of the polymer in the bitumen and, the absorption of the fluorescence components of the bitumen by the PS and PB phases of SBS. For longer mixing times the SBS modified bitumen aged, observed from a decrease in fluorescence intensity. Long term in-service aging of the SBS modified bitumen blends, simulated using a pressure aging vessel, resulted in a decrease in fluorescence intensity. Only the sample prepared at the lowest shear rate (1000 rpm) and shortest mixing time (15 min) displayed variable intensity in the 3D colour maps as the SBS copolymer was poorly mixed in the bitumen phase.