Effect of SBS molecular structure on the rheological properties of ternary nanomodified bituminous binders

The work presented in this paper focused on the rheological properties of ternary composites for paving applications constituted by bitumen, nano-sized additives and polymer modifiers. Non-functionalized multiwall carbon nanotubes and two types of styrene-butadienestyrene polymers, linear and radial, were used to modify a reference neat bitumen with the specific goal of highlighting the effects of polymer structure on the final properties of composites. Binary blends containing a single additive were also investigated for comparative purposes. Materials were characterized by means of dynamic mechanical analysis and their internal structure was assessed with fluorescence microscopy observations. Experimental outcomes indicated that polymer architecture played a crucial role in promoting effective interactions between modifiers and carbon nanotubes. Specifically, in the presence of linear styrenebutadienestyrene, carbon nanotubes acted as compatibility activators, leading to the formation of stable and continuous ternary systems. On the contrary, in the case of radial styrene-butadienestyrene, beneficial effects provided by nano-modification were jeopardized by the increased thermodynamic instability which resulted from the combined use of these two components.