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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,