Page 46 - Mechanics of Asphalt Microstructure and Micromechanics

Mechanical Proper ties of Constituents 39

Arm viscometer placed in a thermostatically controlled oil bath at constant temperature.
A slight vacuum is applied to the small opening of the viscometer to induce the flow of
asphalt binder over the siphon section. As for the dynamic viscosity, the kinematic vis-
cosity is determined (in centistokes) by multiplying the time (in seconds) the asphalt
flows between two timing marks by the calibration factor provided with the viscometer.
This method was proposed by the FHWA and AASHTO and is covered under ASTM
D2170.

2.1.9.3 Zero Shear Viscosity (ZSV)
Zero shear viscosity of asphalt binder was first studied by Puzinauskas (1967, 1979) as
he extrapolated the calculated apparent coefficients of viscosity to a zero strain rate. It
was also assumed that the steady-state strain rate was reached at a series of shear stress
levels. Zero shear viscosity has been also studied by various researchers (Anderson, et
al., 2000, 2002; Shenoy 2001b, 2004; Bahia et al., 2001) since the inception of the Strategic
Highway Research Program (SHRP) as an alternative to the high-temperature specifica-
tion parameter for evaluating rutting resistance G*/sin δ. In his work, Shenoy (2001a,
2004) has developed a performance-based specification parameter, |G*|/(1 - (1/tanδ
sinδ)) that describes the unrecovered strain in the binders more accurately as it is more
sensitive to the variations in the phase angle (δ) than the original Superpave specifica-
tion parameter (|G*|/sinδ).
Dongre and D’Angelo (2003) proposed the following steady-state viscosity equa-
tion, based on the Carreau model, which can be used to calculate the zero shear viscos-
ity from data obtained using the dynamic shear rheometer:
η
η 0
1+ { [( dt 2 } [( 1− )/n 2] (2-13)
λγ / )]d
where h = steady state viscosity
h 0 = zero-shear viscosity
dg/dt = shear rate at steady state
l, n = constants

The cross model is based on four parameters to describe the flow curves of pseudo-
plastic fluids:
η* − η* ∞ 1 (2-14)
η * − η * 1 + (K ω) m
0 ∞
*
where h = complex viscosity
*
h 0 = complex zero shear viscosity
h = limiting viscosity in the second Newtonian region
*
w = angular frequency (rad/s)
K, m = constants
For dynamic shear rheometer (DSR) frequency sweep performed in the 0.1 rad/s
and 100 rad/s interval it can be assumed that h >> h , thus the above equation be-
*
*
comes:
η *
η = 0 (2-15)
*
1 + (K ω) m