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33
CHAPTER 3
Findings and Applications
Experimental Results High Shear Rate Viscosity Method
Binder Testing Table 9 shows the mixing and compaction temperature
results from the high shear rate viscosity tests performed
This section summarizes the results from all of the binder
using Yildirim's approach. The table also shows the mixing
tests including Superpave performance grading of the binders,
and compaction temperatures from the equiviscous method
mixing temperatures from the equiviscous method and the
for comparison. It can be seen from these data that the tem-
three candidate methods, SEP tests, multi-stress creep recov-
peratures from the high shear rate viscosity method are very
ery tests, and analyses of binder degradation following the SEP
similar to the equiviscous method for most of the binders.
test.
Mixing temperatures for all of the modified binders are
greater than 350°F, with most above 360°F. Since modified
Binder Grading binder results from the high shear viscosity method are exces-
sive and the method provides essentially no improvement
Table 8 lists the Superpave performance grades of the compared with the equiviscous method, further analysis of the
binders as reported by the supplier/producer and the results high shear rate viscosity method is not included in this report.
of the grading conducted by NCAT. In this table and in all
subsequent tables showing the study binders, the binders are
sorted by their high temperature true grade as a simple way Steady Shear Flow Method
of putting the binders in a rational order. Modified binders Table 10 shows the results from the Steady Shear Flow
are identified by shaded rows. method. These mixing and compaction temperatures are
Binder L, which contained ground tire rubber as a modifier, substantially lower than the equiviscous mixing and com-
was not able to be graded or tested in DSR equipment due to paction temperatures. The differences between the two meth-
apparent incompatibility of the rubber particles and the ods are greater for modified binders, which indicates that
asphalt. Therefore, binder L was not included in the results or many of these binders exhibit shear thinning (i.e., lower
analysis. viscosity at higher shear rates) behavior. The steady shear flow
Based on NCAT's binder grading results, nearly half of method also yields lower mixing and compaction tempera-
the binders did not meet the requirements for the Super- tures for the unmodified binders: in most cases, the mixing
pave binder grade as reported by the supplier. The discrep- temperatures are more than 10°F lower than the equiviscous
ancies between the producer's grades and the results from mixing temperatures.
NCAT were mostly due to low temperature properties. Binder
G actually met a higher grade than the supplier reported.
However, the differences between the reported grade and Phase Angle Method
NCAT results are generally fairly small and probably not signif- Mixing and compaction temperatures determined using
icant considering lab variability of the tests. The NCAT results the Phase Angle method are shown in Table 11. For the
are used throughout the analysis to sort the binders and to modified binders, the mixing and compaction temperatures
serve as a baseline for evaluating changes due to heating the using the Phase Angle method are substantially lower than
binders to elevated temperatures. from the equiviscous method. For the unmodified binders,
