Zero Shear Viscosity evaluation of PMB bituminous binders with different levels of polymer modifications

The characterization of bituminous binders may be carried out through determination of ZSV (Zero Shear Viscosity). The ZSV is the material viscosity measured for static stresses, low shear stress and longtime of application, to achieve a steady-state flow. The viscosity determined under these conditions may be regarded as an intrinsic property of the material, which is independent to the applied stress state, thus from a theoretical point of view it is a unique parameter to correlate with the viscous sliding damage and accumulation of plastics deformation (rutting). In this paper the Authors show the results of an experimentation, with the dual objective of assessing the effectiveness of the different ZSV measuring procedures and the reliability in the bituminous binders performance characterization. The study was conducted using a virgin bituminous binder (70/100 penetration class) modified with different percentage by weight of SBS radial polymer (3%, 4% and 5). The bituminous binder, virgin as well as modified (PMBs), was subjected to ageing treatments (RTFOT and PAV), prior to the repetition of the tests. The research has revealed the influence of significant parameters on ZSV and on the measures repeatability, such as the temperature variation (40, 50 and 60°C), the test duration, the level of shear stress (10÷50Pa), the distance between DSR plates (1÷2mm) and the binders’ ageing.