Zero Shear Viscosity of Bitumen-Filler Mastics

There has been an increasing awareness of the role of zero shear viscosity (ZSV) of bituminous binders as performance indicators of resistance to permanent deformation of asphalt mixtures because in some cases the conventional criteria for binders do not get reflected in asphalt pavement rutting performance. The aim of this paper is to analyze the zero shear viscosities of bitumen and bitumen-filler mastics with three different levels of limestone filler concentrations on the basis of two viscosity measurement techniques by using a dynamic shear rheometer (DSR). The empirical Cox-Merz rule is used to examine the viscosity correlation between dynamic oscillatory and rotational viscometry measurements. The straight-run 40/60 penetration grade bitumen and limestone bitumen-filler mastics containing low (15%) and intermediate (35%) filler content by mass obey the Cox-Merz rule, whereas the high filler content (65%) mastic shows a divergence in two types of viscosity measurements. The ZSVs of the bitumen and bitumen-filler mastics at 40°C and 60°C are determined by estimating from the two types of viscosity measurements at zero shear conditions on the basis of the Cross model calculation. In the ZSV stiffening ratios, the 65% limestone bitumen-filler mastic shows a considerable increase in stiffening effect compared with both the base bitumen and the other two mastics. With regard to the comparison with the rutting indicators, a significantly greater ZSV stiffening ratio shows that the two conventional rutting criteria G* at 0.4 Hz and G*= sin δ at 1.6 Hz are underestimated.