ZERO-SHEAR VISCOSITY: PHENOMENONS AT MEASUREMENT, INTERPRETATION AND RELATION TO PERMANENT DEFORMATION

Non-Newtonian behaviour of polymer-bitumen systems is presented and exemplified with dynamic viscosity measurements. Two phenomenons have been shown: non-Newtonian dependence of viscosity on shear rate (stress) and influence of internal structure of a material. A proposed simplified equation enables calculation of zero-shear viscosity of polymer-bitumen system from viscosity measurements conducted under varied stress conditions, using relatively simple laboratory equipment, ie rotational viscometer. Zero-shear viscosity values as independent from testing conditions may be assumed as an objective material property. The main problem is a limitation of testing equipment to achieve as low shear rate (shear stress) as possible to approach zero-shear conditions as close as possible. Rutting resistance of bituminous mixture showed fairly good correlation with zero-shear viscosity of polymer-modified bituminous binder. The main doubt may be whether zero-shear stress conditions are representative for wheel traffic loading. On the other hand it is clear that the most hard loading conditions for bituminous materials are of standing loads or at very low velocities. In this respect zero-shear viscosity gives a proper indication of material resistance to deformation. (A) For the covering abstract see IRRD 885061.