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temperatures were about 40°C below the equiviscous tem- 400
peratures. They recommended that the equiviscous method 350
be used to determine mixing and compaction temperatures
Viscosity (PaS)
300
for Newtonian binders and the ZSV method be used for 250
modified binders. 200
150 76°C
Extrapolated High Shear Rate Viscosity 100
82°C
50 88°C
Yildirim et al. (43) presented an approach that estimates 0 92°C
high shear rate binder viscosity from rotational viscosity 0 100 200 300 400 500 600
measurements for the determination of mixing and com- Shear Stress, Pa
paction temperatures. The shear rate of 490 1/s was selected
Figure 6. Steady shear viscosity over a range of
from experimental work with mixtures compacted in a SGC.
shear stresses.
The same mixtures were prepared with four different binders
and then compacted in the SGC over a range of relatively low
temperatures (between 50°C and 95°C) to amplify the effect
of temperature on mix density. It was hypothesized that tures ranging from 76°C to 94°C (169°F to 201°F). At high
equivalent mix densities would occur when the viscosities of shear stresses, around 500 Pa, the viscosities of modified
binders were the same. To find the point where binder vis- binders approach a steady state (i.e., very small change in vis-
cosities were the same, the binders were tested in a Brookfield cosity with increasing shear stress). This is illustrated in Fig-
viscometer at shear rates ranging from 0.1 1/s to 93 1/s. These ure 6. Using a log-log temperature-viscosity chart, the viscosi-
viscosity data were extrapolated to find the shear rate where ties from the 500-Pa shear flow tests are extrapolated out to
the unmodified asphalt and the modified asphalts had the 180°C (356°F). As with unmodified binder using the equivis-
same viscosity. The hypothesis was that the shear rate at which cous principle, the recommended mixing temperature is
the viscosities of binders intersect is equivalent to the shear based on a viscosity of 0.17 ± 0.02 Pa s. The recommended
rate that the mix experiences in the gyratory mold during compaction temperature from the steady shear flow tech-
compaction. The average equiviscous shear rate for the eight nique is 0.35 ± 0.03 Pa s, which is higher than the equiviscous
pairs of mixtures was 487 1/s, which was rounded to 490 1/s. compaction range of 0.28 ± 0.03 Pa s. Reinke indicated that the
The extrapolated viscosity of binders at 490 1/s was referred mixing and compaction temperatures derived from the steady
to as the high shear rate viscosity. Using a shear rate of 490 1/s, shear flow method for the few polymer-modified binders eval-
the traditional viscosity criteria of 0.17 ± 0.02 Pa s for mix- uated matched well to the temperature ranges successfully
ing, and 0.28 ± 0.03 Pa s for compaction, they determined used in practice.
mixing and compaction temperatures for the four modified
binders to be 10°C to 40°C (18°F to 72°F) below the respec- Shear Rate Dependency
tive temperatures from AASHTO T 312.
This method was criticized on several points (44). One As noted previously, Shenoy (36) proposed a technique of
issue with this approach was the use of unrealistically low selecting mixing temperatures based on shear rate dependency
compaction temperatures and then using viscosity measure- and other factors. The study included only two polymer-
ments at those temperatures to extrapolate viscosity-shear modified asphalts, Styrelf® and Novophalt®. The binders and
rate data. The accuracy of the estimates for viscosities at the a diabase filler were mixed at four temperatures ranging from
recommended shear rate of 490 1/s was questioned. At higher 150 to 200°C (302 to 392°F) and tested in the Brookfield vis-
temperatures typical of the range normally used in the labo- cometer with three spindles to generate viscosities over a range
ratory, the binders would have exhibited less shear thinning of shear rates. The ratio of viscosities for the filled binder
behavior and thus the extrapolations would be different. divided by the unfilled binder showed a pessimum point for
the Novophalt® around 180°C (356°F). For the Styrelf®, the
viscosity ratio was at an apparent minimum around 163°C.
Steady Shear Flow
Shenoy selected the mixing temperature range for the binders
Reinke (45) presented another concept, which he called the based on a table of pass/fail criteria for shear-rate dependency,
steady shear flow test, to determine mixing and compaction fluidity, Arrhenius plot smoothness, degradation, aging, and
temperatures. This approach uses a DSR with a 500-micron viscosity ratio. This yielded mixing temperatures of 180°C
gap and a 25-mm-diameter plate geometry. The viscosities of (356°F) for the Novophalt® binder and a range of 163°C to
binders are tested over a range of shear stresses at tempera- 180°C (325°F to 356°F) for the Styrelf® binder.
