Comparison of the Zero Shear Viscosity of Bitumen-Filler Mastics Using Different Measurement Techniques

Abstract

Zero shear viscosity (ZSV) or the viscosity at zero shear rate is an intrinsic property of a bituminous binder that has been proved to have a good correlation to the rutting potential of most binders, particularly modified binders. Various techniques and procedures exist to calculate or estimate ZSV. These include creep flow with or without creep recovery, viscosity measurements at low shear rates, sinusoidal oscillation at low frequencies and repeated creep (pulsed creep). Most of these techniques are performed on a dynamic shear rheometer with the ZSV being determined directly from the plotted data or, particularly in the case of the oscillation test, extrapolated to zero frequency using an appropriate mathematical model. This paper investigates the effect of modifying a bituminous binder through the addition of filler to produce bitumen-filler mastic similar to that found within an actual asphalt mixture. The ZSVs of bitumen-filler mastics with different filler types and bitumenfiller ratios have been tested. Three types of filler have been included in the testing programme including inert fillers (limestone and gritstone) as well as an active filler (cement) at various filler-bitumen ratios ranging from 15% to 65%. The ZSV results show varying degrees of modification (increases) of ZSV as a function not only of filler content but also of filler type. In addition, the ZSVs determined by means of the different procedures gave statistically different values, again as a function of both filler content and filler type.