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40 Table 3-19. Estimated SAFT operational parameters to reproduce RTFOT aging. Binder RTFOT G*/sin, kPa Estimated Impeller Speed, Estimated Conditioning for 52.5-Min Conditioning, Time for 1,050 rpm rpm Impeller Speed, Min AAD-2 2.65 962 40 AAM-1 6.00 935 47 ABM-2 3.14 857 38 Average 918 42 1,000 rpm impeller speed, 1. To enable a comparison of the rheological properties of 50-minute aging time, material conditioned in the SAFT, MGRF, and RTFOT, and 250-g sample mass, and 2. To allow a comparison of the master curves measured for Vacuum degassing per AASHTO R28 after short-term the binders with master curves back-calculated from mix- aging in the SAFT. ture properties. Figure 3-30 illustrates the sequence of operations for the In the oven-aged mixtures experiment, hot mix asphalt commercial SAFT determined from the SAFT optimization using the binders from the RTFOT verification experiment study. This sequence was used in the verification study. were prepared and aged in accordance with AASHTO R30. Dynamic modulus master curve tests were performed on the mixture samples. From the mixture modulus master curves, 3.6 Verification Study the binder stiffness was estimated using the Hirsch Model (6) The objectives of the verification study were to (1) confirm and compared to the measured stiffnesses obtained from the that the commercial versions of the SAFT and MGRF repro- SAFT, MGRF and RTFOT. duce the degree of aging obtained in the RTFOT for a wide The verification study used six neat MRL binders and six range of neat binders and (2) compare the aging from the SAFT, polymer-modified binders in both experiments. A single MGRF, and RTFOT with that from mixture samples aged in a limestone mixture was used in the oven-aged mixture exper- forced-draft oven in accordance with the performance testing iment. Detailed information for the binders and the mixture protocol contained in AASHTO R30. Initially, the verification was presented earlier in Chapter 2. study only included the SAFT, but it was expanded at the The sections that follow present key findings from the veri- request of the project panel to include the MGRF. fication study. Full details of the study are included in the ver- The verification study consisted of two main components-- ification study report in Appendix E (see the project webpage the RTFOT verification experiment and the oven-aged mix- on the TRB website). The verification study was the last study tures experiment. The RTFOT verification experiment, which in NCHRP 9-36 and provided the basis for making the final included DSR and BBR measurements, was designed to pro- recommendation with respect to a replacement for the RTFOT. vide master curves for the binders in the tank condition and after SAFT, MGRF, and RTFOT conditioning. These binder 3.6.1 RTFOT Verification Experiment master curves served the following two purposes: The RTFOT verification experiment included compar- isons of the short-term conditioned specification parameter, Table 3-20. Rheological properties from VCS-II G*/sin, mass change, master curves, and aging indices for development study. binders conditioned in the RTFOT, SAFT, and MGRF. It was not possible to obtain good quality data for the EVA modified Aging Citgo Property Condition 58-28 ABM-2 AAM-1 AAD-2 Table 3-21. Rheological properties for the Citgo G*, kPa Original 1.18 1.89 2.95 0.88 After SAFT 2.44 3.17 4.94 2.19 PG 58-28 for SAFT aging times of 45 and 50 minutes After RTFOT 2.48 3.15 5.41 2.60 compared to RTFOT. Original 87.3 89.7 85.6 85.8 Phase After SAFT 83.7 89.2 82.7 79.7 RTFOT SAFT SAFT Angle, deg After RTFOT 84.1 89.5 80.3 79.0 Property 45-Min Aging 50-Min Aging Original 1.18 1.89 2.96 0.88 G*, kPa 2.48 2.44 2.65 After SAFT 2.45 3.17 4.98 2.23 Phase Angle, deg 84.1 83.7 83.9 G*/sin After RTFOT 2.49 3.15 5.49 2.65 G*/sin, kPa 2.49 2.45 2.66

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41 SAFT oven heated to 176C Process controller adjusts Oven maintained oven temperature as at 176C needed to bring binder to 163C Heat-up phase Note: 1,000 rpm impeller Binder speed and 250 g sample Temperature = 163C End of conditioning Binder period Temperature = 160C Vessel placed in oven, Binder Temperature < 10 120C min < 20 min Conditioning period , 50 min N2 flowing at Air flowing at 2,000 mL/min 2,000 mL/min Figure 3-30. Sequence of operations used in final SAFT configuration. binder because the polymer tended to separate during testing; the other below the specification criterion. The continuous- therefore, this binder was not included in the comparisons grading temperatures are summarized in Table 3-22. This described below. table includes the average and standard deviation from two separate runs for each device. Figure 3-31 compares the average continuous-grading tem- 3.6.1.1 Specification Parameter G*/sin peratures from SAFT and MGRF conditioning to RTFOT The continuous-grading temperatures for RTFOT-, SAFT-, conditioning. Figure 3-31 includes trend lines for the SAFT and and MGRF-conditioned binders were calculated by inter- MGRF data. This plot clearly shows the better agreement for polating between the logarithm of two measurements, one the MGRF compared to the SAFT. The trend line for the MGRF obtained above the specification criterion of 2.20 kPa and data coincides with the line of equality, while that for the SAFT Table 3-22. Continuous-grade temperatures for RTFOT, SAFT, and MGRF conditioning. Binder Continuous-Grade Temperature, C RTFOT MGRF SAFT Average Standard Average Standard Average Standard Deviation Deviation Deviation AAC-1 56.3 0.21 58.1 0.35 57.2 0.07 AAD-2 59.7 0.49 59.5 0.14 58.0 0.00 ABM-2 60.7 0.35 61.1 0.21 60.5 0.35 AAF-1 67.0 0.44 68.4 2.90 65.5 0.28 AAM-1 68.0 0.35 68.6 1.27 65.0 0.28 ABL-1 69.5 0.35 68.0 0.21 65.3 0.57 Elvaloy 69.9 1.13 68.9 0.14 61.6 0.35 ALF 75.4 0.00 75.2 0.49 69.2 0.21 Novophalt 78.9 0.57 80.0 0.28 73.9 0.14 Airblown 80.2 0.92 79.9 2.05 76.5 0.57 Citgoflex 85.3 0.21 85.9 0.14 82.2 0.21

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42 MGRF SAFT Line of Equality 88 .0 MGR F MGRF or SAFT High Temperature Grade, C 82 .0 76 .0 SAF T 70 .0 64 .0 58 .0 52 .0 52.0 58.0 64.0 70.0 76.0 82.0 88.0 RTFOT High Temperature Grade, C Figure 3-31. Comparison of SAFT and MGRF continuous-grading temperatures to RTFOT continuous-grading temperature. indicates less stiffening, particularly for high-stiffness binders. 1.8C and does not appear to depend on the stiffness of Figure 3-32 shows the difference between the continuous- the binder. grading temperatures for the SAFT- and MGRF-conditioned Paired difference t-testing was used to assess the signifi- binders compared to the RTFOT-conditioned binders. The cance of the differences shown in Figures 3-31 and 3-32. The difference for the SAFT appears to depend on the stiffness of analysis was conducted for three groups: (1) neat binders, the binder, and for stiffer binders the difference can reach as (2) modified binders, and (3) all binders. The results of this much as a full grade. The difference for the MGRF is within analysis are summarized in Tables 3-23, 3-24, and 3-25 for MGRF SAFT 6.0 Difference in High Temperature Grade (MGRF or 3.0 SAFT minus RTFOT), C 0.0 -3.0 -6.0 -9.0 -12.0 52.0 58.0 64.0 70.0 76.0 82.0 88.0 RTFOT High Temperature Grade, C Figure 3-32. Difference in continuous-grading temperature for SAFT and MGRF residue compared to RTFOT residue.

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43 Table 3-23. Summary of paired t-test Table 3-25. Summary of paired t-test for neat binders. for all binders. Continuous-Grading Differences (MGRF or Continuous-Grading Differences (MGRF or Binder Temperature, C SAFT minus RTFOT), C Binder Temperature, C SAFT minus RTFOT), C RTFOT MGRF SAFT MGRF SAFT RTFOT MGRF SAFT MGRF SAFT AAC-1 56.3 58.1 57.2 1.8 0.9 AAC-1 56.3 58.1 57.2 1.8 0.9 AAD-2 59.7 59.5 58.0 -0.2 -1.7 AAD-2 59.7 59.5 58.0 -0.2 -1.7 ABM-2 60.7 61.1 60.5 0.4 -0.2 ABM-2 60.7 61.1 60.5 0.4 -0.2 AAF-1 67.0 68.4 65.5 1.4 -1.5 AAF-1 67.0 68.4 65.5 1.4 -1.5 AAM-1 68.0 68.6 65.0 0.6 -3.0 AAM-1 68.0 68.6 65.0 0.6 -3.0 ABL-1 69.5 68.0 65.3 -1.5 -4.2 ABL-1 69.5 68.0 65.3 -1.5 -4.2 Average Difference, C 0.42 -1.62 Elvaloy 69.9 68.9 61.6 -1.0 -8.3 Standard Deviation of Differences, C 1.18 1.84 ALF 75.4 75.2 69.2 -0.2 -6.2 Calculated t 1.034 -2.151 Novophalt 78.9 80.0 73.9 1.1 -5.0 tcritical (0.05, 5 degrees of freedom) 2.015 2.015 Airblown 80.2 79.9 76.5 -0.3 -3.7 SAFT Citgoflex 85.3 85.9 82.2 0.6 -3.1 Conclusion No Difference Lower Average Difference, C 0.27 -3.24 Standard Deviation of Differences, C 1.00 2.65 Calculated t 0.882 -4.054 tcritical (0.05, 10 degrees of freedom) 1.812 1.812 the three groups. Details of the analysis are presented in No SAFT Appendix E. This analysis shows that the continuous grade Conclusion Difference Lower is the same for RTFOT and MGRF conditioning. The high- temperature grade is lower for SAFT conditioning. This finding holds for both neat and modified binders. that as technicians gain more experience with the MGRF, its Since the testing included replicate samples of each variability should become similar to that for the RTFOT. binder conditioned in the three short-term conditioning devices, an initial evaluation of the variability of the SAFT 3.6.1.2 Mass Change and MGRF relative to the RTFOT was made. This evalua- tion was done using an F-test on the pooled variance com- The MGRF test includes a mass change measurement that puted from the variances of the duplicate tests for the 11 is determined in the same manner as the RTFOT: the change binders. This analysis is summarized in Table 3-26 and in mass is calculated from the mass of the flask measured shows that the test variability is somewhat greater for the before and after aging. As discussed in Section 3.4, the SAFT MGRF compared the RTFOT. Variability for the SAFT is uses a VCS to collect and then weigh the mass of volatiles similar to the RTFOT. Details of this analysis are presented exiting the vessel during aging. The performance of the VCS in Appendix E. was discussed earlier in Section 3.4.3, so only the compari- The MGRF variability was high for 2 of the 11 binders son of the mass change in the MGRF and RTFOT will be pre- tested: AAF-1 and Airblown. The variability for the other sented here. binders was similar to that from the RTFOT. It is expected Mass change data from the MGRF and RTFOT are sum- marized in Table 3-27 and compared in Figure 3-33. Fig- ure 3-33 shows that there is a good relationship between the Table 3-24. Summary of paired t-test mass change measured in the MGRF and that measured in for modified binders. the RTFOT. The MGRF values are approximately 40 percent of the RTFOT values. This is in agreement with the data col- Continuous-Grading Differences (MGRF or lected in the Western Research Institute study of the MGRF Binder Temperature, C SAFT minus RTFOT), C (2) that was discussed earlier in Section 3.2.2.1. RTFOT MGRF SAFT MGRF SAFT AAC-1 56.3 58.1 57.2 1.8 0.9 AAD-2 59.7 59.5 58.0 -0.2 -1.7 ABM-2 60.7 61.1 60.5 0.4 -0.2 3.6.1.3 Christensen-Anderson Master AAF-1 67.0 68.4 65.5 1.4 -1.5 Curve Parameters AAM-1 68.0 68.6 65.0 0.6 -3.0 ABL-1 69.5 68.0 65.3 -1.5 -4.2 Binder master curves were developed from the combined Average Difference, C 0.42 -1.62 DSR and BBR data using the Christensen-Anderson Model Standard Deviation of Differences, C 1.18 1.84 (33). The Christensen-Anderson Model was used because the Calculated t 1.034 -2.151 parameters in the model are useful in interpreting changes in tcritical (0.05, 5 degrees of freedom) 2.015 2.015 SAFT rheology that occur during laboratory conditioning or in- Conclusion No Difference Lower service aging. Equation 2 presents the Christensen-Anderson

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44 Table 3-26. Analysis of variability of MGRF and SAFT relative to RTFOT. Standard Deviation, C Variance, (C)2 Binder RTFOT MGRF SAFT RTFOT MGRF SAFT AAC-1 0.21 0.35 0.07 0.043 0.125 0.005 AAD-2 0.49 0.14 0.00 0.243 0.020 0.000 ABM-2 0.35 0.21 0.35 0.120 0.045 0.125 AAF-1 0.44 2.90 0.28 0.190 8.405 0.080 AAM-1 0.35 1.27 0.28 0.123 1.620 0.080 ABL-1 0.35 0.21 0.57 0.120 0.045 0.320 Elvaloy 1.13 0.14 0.35 1.280 0.020 0.125 ALF 0.00 0.49 0.21 0.000 0.245 0.045 Novophalt 0.57 0.28 0.14 0.320 0.080 0.020 Airblown 0.92 2.05 0.57 0.845 4.205 0.320 Citgoflex 0.21 0.14 0.21 0.045 0.020 0.045 Number of Replicates 2 2 2 Pooled Variance 0.3027 1.3482 0.1059 Computed F NA 4.45 2.86 Critical F (0.05, 10, 10) NA 2.98 2.98 MGRF No Conclusion NA Higher Difference Model for the frequency dependency of the binder shear -19 (T - Td ) log a (T ) = (3) modulus. 92 + T - Td -R 1 1 log 2 log 2 log a (T ) = 13016.07 - (4) T Td G ( ) = G g 1 + R c (2) r where a(T) = shift factor where T = temperature, K G() = complex shear modulus Td = defining temperature, K Gg = glass modulus, approximately equal to 1GPa r = reduced frequency at the reference temperature, Above Td the Williams-Landel-Ferry (WLF) equation is valid, rad/s but below Td it is no longer valid and the Arrhenius equation c = cross over frequency at the reference temperature, must be used. This is because the asphalt binder is not in an rad/s equilibrium condition as a result of physical hardening. The R = rheological index four unknown parameters: Gg, c, R, and Td, were obtained through non-linear least squares fitting of Equations 2, 3, and The shift factors relative to the defining temperature are 4 using the data from the testing program. The parameter, c, given by Equations 3 and 4 for temperatures above and below changes with temperature and therefore is always given at the the defining temperature, respectively (33). reference temperature, selected as 22C for direct comparison with the data back-calculated from the mixture master curves. Table 3-27. Mass change To construct the complete master curve, the bending beam data for RTFOT and MGRF. rheometer creep stiffness was converted to shear modulus using the following approximate interconversions. Mass Change, % Binder S (t ) RTFOT MGRF AAC-1 -0.058 -0.232 G ( ) (5) ABL-1 -0.654 -0.345 3 AAM-1 0.122 0.113 Citgoflex -0.196 -0.103 1 Airblown 0.031 0.033 ( ) (6) Novophalt -0.132 -0.045 t AAF-1 -0.008 -0.063 ABM-2 -0.349 -0.100 where AAD-2 -1.058 -0.362 Elvaloy -0.173 -0.060 G() = shear modulus ALF 64-40 -0.207 -0.073 S(t) = creep stiffness

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45 0.20 0.00 y = 0.3978x MGRF Mass Change, % -0.20 R2 = 0.6971 -0.40 Line of Equality -0.60 -0.80 -1.00 -1.20 -1.20 -1.00 -0.80 -0.60 -0.40 -0.20 0.00 0.20 RTFOT Mass Change, % Figure 3-33. Comparison of mass change for MGRF and RTFOT. = frequency in rad/s is the frequency where the phase angle is 45 degrees and is t = time in seconds typically close to the point where the viscous asymptote inter- sects the glassy modulus. The crossover frequency, c, is an Figure 3-34 presents an example of the fitted master curve indicator of the hardness of the binder. Finally, the rheologi- and the nomenclature used with the Christensen-Anderson cal index, R, is the difference between the log of the glassy Model. A major advantage of the Christensen-Anderson modulus and the log of the dynamic modulus at the crossover Model is that the model parameters have physical significance. frequency. It is an indicator of the rheological type. The glassy modulus is the limiting maximum modulus and is Table 3-28 summarizes the Christensen-Anderson Model approximately equal to 1 GPa, reflective of the stiffness of parameters for tank, RTFOT, SAFT, and MGRF condition- carboncarbon bonds that predominate in asphalt binders. ing. The effect of conditioning on the rheology of the binder The viscous asymptote is the 45 line that the master curve is best represented by changes in the model parameters from approaches at low frequencies and is an indicator of the tank condition to short-term aged condition. Figures 3-35 steady-state viscosity of the binder. The crossover frequency through 3-37 compare changes for SAFT and MGRF condi- Glassy Modulus 1 GPa 1.0E+09 1.0E+08 Rheological Index, R 1.0E+07 -28 C BBR Viscous -22 C BBR 1.0E+06 Asymptote -16 C BBR -10 C BBR 1.0E+05 G*, Pa 10 C DSR 22 C DSR 1.0E+04 34 C DSR 46 C DSR 58 C DSR 1.0E+03 70 C DSR FIT 1.0E+02 Cross-Over Frequency, c 1.0E+01 1.0E+00 1.0E-06 1.0E-04 1.0E-02 1.0E+00 1.0E+02 1.0E+04 1.0E+06 1.0E+08 1.0E+10 Reduced Frequency at 25 C, rad/sec Figure 3-34. Christensen-Anderson Model master curve.

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46 Table 3-28. Christensen-Anderson Model parameters. Log10 Binder Glassy Rheological Parameter, R, log10 Pa log10 Crossover Frequency, , rad/s Defining Temperature, Td, C Source Modulus, Pa Tank SAFT RTFOT MGRF Tank SAFT RTFOT MGRF Tank SAFT RTFOT MGRF AAC-1 8.6 1.21 1.62 1.50 1.55 3.42 2.41 2.68 2.42 -9.8 -0.7 -3.6 -1.5 AAD-2 9.2 1.92 2.17 2.16 2.14 4.11 3.18 3.28 3.31 -18.1 -15.6 -15.1 -14.7 AAF-1 8.6 1.39 1.63 1.65 1.85 2.39 1.56 1.41 1.24 -1.3 3.7 3.8 4.0 AAM-1 8.6 1.49 1.67 1.86 1.91 2.39 1.92 1.41 1.40 -3.1 0.3 2.7 3.7 ABL-1 8.7 1.55 1.65 1.77 1.75 2.97 2.62 2.15 2.27 -14.9 -13.1 -10.7 -11.0 ABM-2 8.7 0.90 0.91 0.90 1.02 2.97 2.74 2.69 2.59 -4.1 -4.1 -3.1 -2.9 Airblown 8.8 2.31 2.42 2.41 2.29 0.88 0.35 0.12 0.38 3.7 5.0 4.2 3.8 ALF 10.9 4.69 5.13 5.36 5.47 2.71 1.48 0.81 0.70 -15.2 -12.6 -12.8 -10.4 Citgoflex 9.8 2.95 3.06 3.33 3.18 1.82 1.35 0.63 0.92 -7.5 -6.2 -2.6 -2.1 Elvaloy 9.2 2.06 2.18 2.44 2.41 3.29 2.77 1.99 2.32 -13.4 -11.1 -9.5 -10.8 Novophalt 8.8 1.60 1.63 1.83 1.87 2.20 1.80 1.14 1.26 -9.7 -9.4 -5.1 -4.2 tioning to RTFOT conditioning for R, c, and Td, respectively. equality. As shown, there is significant scatter in the data The general trends shown in these figures are reasonable. The because the master curve parameters are somewhat inter- rheological index increases with short-term conditioning, indi- related and depend on the quality of the data. Trend lines are cating that the master curve is becoming flatter. The crossover shown for the SAFT and the MGRF data in Figures 3-35 and frequency decreases, indicating that the binder is becoming 3-36 to make it easier to interpret these plots. The trend lines harder with short-term conditioning. Finally, the defining for the MGRF data are much closer to the line of equality than temperature increases on short-term aging, indicating greater those for the SAFT data. temperature dependency. The results of regression analyses for the change in the If the changes in model parameters are the same for Christensen-Anderson Model parameters are summarized in SAFT- and MGRF-conditioned binders compared to RTFOT- Table 3-29. Details of this statistical analysis are presented conditioned binders, the data should plot along the line of in Appendix E (see the project webpage on the TRB website). SAFT MGRF 0.9 0.9 0.8 0.8 0.7 MGRF 0.7 Change in R for MGRF Aging Change in R for SAFT Aging 0.6 0.6 0.5 0.5 0.4 0.4 SAFT 0.3 0.3 0.2 0.2 0.1 0.1 0.0 0.0 -0.1 -0.1 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Change in R for RTFOT Aging Figure 3-35. Comparison of change in rheological index for RTFOT, SAFT, and MGRF aging.

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SAFT MGRF 0. 0 0.0 -0 .2 -0.2 -0 .4 -0.4 for MGRF Aging for SAFT Aging -0 .6 -0.6 -0 .8 -0.8 -1 .0 -1.0 c) c) Change in log10 ( -1 .2 -1.2 Change in log10 ( -1 .4 -1.4 -1 .6 -1.6 -1 .8 -1.8 -2 .0 -2.0 -2 .2 -2.2 -2.2 -2.0 -1.8 -1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 Change in log ( c) for RTFOT Aging Figure 3-36. Comparison of change in crossover frequency for RTFOT, SAFT, and MGRF aging. SAFT MGRF 10 10 9 9 8 8 Change in Td for MGRF Aging, C Change in Td for SAFT Aging, C MGRF 7 7 6 6 5 5 4 SAFT 4 3 3 2 2 1 1 0 0 0 1 2 3 4 5 6 7 8 9 10 Change in Td for RTFOT Aging, C Figure 3-37. Comparison of change in defining temperature for RTFOT, SAFT, and MGRF aging. Table 3-29. Regression analysis of change in Christensen- Anderson Model parameters. Hypothesis Test of Equality of Average Neat Modified Aging Index for Neat and Modified Binders Method Standard Standard Pooled Average Average t tcritical Conclusion Deviation Deviation s R30 3.30 1.08 3.05 1.32 1.19 0.43 2.26 No difference RTFOT 2.44 0.46 2.26 0.58 0.52 0.55 2.26 No difference MGRF 2.44 0.47 2.30 0.35 0.42 0.54 2.26 No difference SAFT 1.97 0.48 1.34 0.27 0.40 2.60 2.26 Neat > Modified

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48 This analysis shows that there is a significant relationship in compared to the SAFT. However, the slope for the MGRF the change in the model parameters between the SAFT and data is close to 1, and the 95 percent confidence interval for RTFOT and the MGRF and RTFOT. The strength of the rela- the slope captures 1. The slope for the SAFT data is 0.74 and tionships, as indicated by the R2 values, is better for the MGRF the 95 percent confidence interval for the slope does not compared to the SAFT. Additionally, the slopes for the MGRF capture 1. The conclusion from this analysis is that the data are close to 1, and the 95 percent confidence intervals for MGRF produces aging indices that are approximately the the slope capture 1 for all three parameters. The slopes for the same as the RTFOT. Aging indices from the SAFT are less SAFT data range from 0.6 to 0.7, and only the 95 percent con- than those from the RTFOT. fidence interval for the slope of the change in Td relationship captures 1. This analysis shows that MGRF aging produces changes in the Christensen-Anderson master curve parameters 3.6.2 Oven-Aged Mixture Experiment that are not significantly different from those for the RTFOT, while the SAFT aging produces different changes in the master In the oven-aged mixture experiment, binder properties curve parameters. back-calculated from mixture dynamic modulus test data were used to assess how well the binder aging procedures simulate the aging that occurs in mixtures during short- 3.6.1.4 Aging Indices term oven conditioning. Dynamic modulus master curve tests were performed on samples prepared from uncondi- Another technique for judging the conditioning that tioned mixture and from mixture conditioned for 4 hours occurs in the SAFT and MGRF relative to the RTFOT is to at 135C as specified in AASHTO R30. From the mixture calculate and compare aging indices for the procedures. dynamic modulus master curves, the binder shear modulus This was done by calculating aging indices at a common master curves were estimated using the Hirsh Model (6). temperature for each aging condition (but different for The back-calculated binder modulus data were then ana- each binder) and at a series of moduli. This approach par- lyzed to assess how well the binder aging procedures simu- allels the aging that occurs in an actual pavement--the late the aging that occurs in mixtures during short-term oven change that occurs in stiffness at temperatures correspon- conditioning. The EVA-modified binder was not included in ding to different unaged moduli. The temperatures where the comparisons due to the difficulties in testing this binder that G* for the unaged binders at 10 rad/s is equal to 1, 10, 100, were discussed earlier. The sections that follow describe the 1,000, 10,000, and 100,000 kPa were calculated using the major findings from the oven-aged mixture experiment. The fitted Christensen-Anderson Model for each binder. These complete analysis is included in the verification study report temperatures are shown in Table 3-30. The fitted Chris- in Appendix E (see the project webpage on the TRB website). tensen-Anderson Model was then used to calculate the complex moduli for the binders for the three aging condi- tions at these temperatures and 10 rad/s. The moduli for 3.6.2.1 Back-Calculated Binder Properties the aged binders were then divided by the moduli for the unaged binders. The resulting aging indices are shown in Binder properties for the mixtures were obtained by Table 3-30. preparing mixtures, developing a dynamic modulus master Figure 3-38 compares aging indices from the SAFT and curve for each mixture, and then back-calculating binder MGRF with those from the RTFOT for the binders used in properties from the mixture modulus data. The dynamic the study. If the aging indices for the SAFT and MGRF are modulus master curve testing was performed in accordance the same as the RTFOT, the data should plot along the line with AASHTO TP79, "Determining the Dynamic Modulus of equality. As shown, there is significant scatter in the data. and Flow Number for Hot Mix Asphalt (HMA) Using the Trend lines are shown for the SAFT and MGRF data in Fig- Asphalt Mixture Performance Tester (AMPT)," and PP61, ure 3-38. The trend line for the MGRF data falls nearly on "Developing Dynamic Modulus Master Curves for Hot Mix the line of equality while the trend line for the SAFT data is Asphalt (HMA) using the Asphalt Mixture Performance much lower. The results of regression analyses for the aging Tester (AMPT)," which were developed in NCHRP Project indices are summarized in Table 3-31. Details of this statis- 9-29 (34). The testing was conducted at three temperatures tical analysis are presented in Appendix E. This analysis and four frequencies as summarized in Table 3-32. The low shows that there are significant relationships between the and middle temperatures were set at 4C and 20C, respec- aging indices from the SAFT and RTFOT, and the MGRF tively. The upper temperature was selected based on the and RTFOT. The strength of the relationship, as indicated binder grade: 34C for the softer binders (AAC-1, AAD-2, by the R2 value, is approximately the same for the MGRF ABL-1, ABM-2, ALF, and Elvaloy) and 40C for AAF-1,

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49 Table 3-30. Complex moduli and temperatures used to calculate aging indices. G*, T, Aging Index G*, Aging Index Binder Binder T, C kPa C kPa SAFT RTFOT MGRF SAFT RTFOT MGRF 1 56.9 2.35 2.11 2.70 1 77.1 1.86 3.17 2.56 10 43.0 2.56 2.21 2.92 10 59.5 1.76 2.81 2.40 100 30.8 2.59 2.19 2.94 100 44.0 1.64 2.42 2.20 AAC-1 Airblown 1,000 19.7 2.35 2.00 2.66 1,000 29.8 1.49 2.00 1.95 10,000 8.6 1.86 1.63 2.06 10,000 15.5 1.31 1.59 1.65 100,000 -5.2 1.16 1.16 1.27 100,000 -2.5 1.09 1.20 1.30 1 57.1 2.51 3.08 2.87 1 70.1 1.52 2.51 2.58 10 40.6 2.32 2.85 2.73 10 46.6 1.41 2.12 2.25 100 26.2 2.08 2.55 2.51 100 27.2 1.32 1.78 1.96 AAD-2 1,000 13.1 1.80 2.18 2.20 ALF 64-40 1,000 10.7 1.23 1.49 1.72 10,000 0.5 1.49 1.77 1.82 10,000 -4.0 1.15 1.26 1.51 - 100,000 1.20 1.36 1.42 100,000 -17.6 1.03 1.03 1.18 13.2 1 64.5 2.29 2.99 3.18 1 87.1 1.05 1.43 1.68 10 50.4 2.32 2.97 2.90 10 64.4 1.04 1.39 1.73 100 38.0 2.24 2.78 2.46 100 45.3 1.03 1.35 1.76 AAF-1 Citgoflex 1,000 26.5 2.01 2.39 1.93 1,000 28.6 1.02 1.30 1.76 10,000 14.9 1.65 1.85 1.40 10,000 13.2 1.01 1.24 1.71 100,000 0.3 1.14 1.19 0.92 100,000 -2.0 1.00 1.17 1.59 1 65.6 1.42 2.29 1.92 1 66.0 1.21 3.10 3.05 10 50.8 1.44 2.23 1.90 10 48.3 1.22 2.78 2.67 100 37.7 1.42 2.05 1.79 100 32.9 1.22 2.40 2.25 AAM-1 Elvaloy 1,000 25.6 1.35 1.77 1.58 1,000 19.1 1.20 1.98 1.82 10,000 13.5 1.22 1.41 1.30 10,000 5.7 1.16 1.57 1.43 100,000 -1.9 1.03 0.98 0.92 100,000 -8.7 1.10 1.22 1.11 1 67.7 1.55 2.71 2.27 1 78.0 1.32 2.23 2.49 10 50.3 1.53 2.63 2.23 10 59.6 1.30 2.20 2.46 100 35.2 1.48 2.43 2.10 100 43.7 1.26 2.09 2.33 ABL-1 Novophalt 1,000 21.4 1.39 2.12 1.88 1,000 29.3 1.22 1.88 2.07 10,000 7.8 1.26 1.70 1.57 10,000 15.2 1.15 1.59 1.71 100,000 -8.5 1.10 1.25 1.21 100,000 -1.1 1.06 1.24 1.29 1 61.5 1.70 1.69 1.96 10 48.3 1.68 1.73 1.96 100 36.8 1.65 1.76 1.89 ABM-2 1,000 26.6 1.58 1.74 1.74 10,000 16.8 1.44 1.64 1.48 100,000 5.4 1.21 1.36 1.14 AAM-1, Air Blown, Citgoflex, Novophalt, and EVA. This 7 and 8 present the form of the master curve that was fitted to testing protocol produces 10 dynamic modulus and phase the data. Equation 7 is the form of the dynamic modulus mas- angle measurements for each specimen. Three replicate ter curve recommended in the Mechanistic-Empirical Pave- specimens were tested in this project. ment Design Guide (MEPDG) for use in pavement structural Dynamic modulus master curves were fitted to the meas- design (35). This sigmoidal function describes the frequency ured data using the procedure in AASHTO PP61. Equations dependency of the modulus at the reference temperature,

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50 3.5 MGRF 3.0 SAFT or MGRF Aging Index 2.5 SAFT 2.0 SAFT MGRF Equality 1.5 1.0 0.5 0.5 1.0 1.5 2.0 2.5 3.0 3.5 RTFOT Aging Index Figure 3-38. Comparison of aging indices for RTFOT, SAFT, and MGRF. which for this testing was selected to be 22C to coincide with The final form of the dynamic modulus master curve equa- that used in the binder testing. The shift factors describe the tion is obtained by substituting Equation 8 into Equation 7. temperature dependency of the modulus. Equation 8 provides ( log E max - log E min ) the form of the Arrhenius equation used for the shift factors. log E = log E min + Ea 1 1 (9) + log + - 19.14714 ( log E max - log E min ) 1+ e T Tr log ( E ) = log E min + (7) 1+ e + r The limiting maximum modulus of the mixture E*min was where estimated using the Hirsch Model (6) and a limiting maxi- E = dynamic modulus mum binder shear modulus of 1 GPa (145,000 psi) (32). Emax = limiting maximum modulus Equation 10 presents the Hirsch Model. As shown, the limit- Emin = limiting minimum modulus ing maximum modulus of the mixture is a function of VMA r = frequency of loading at the reference temperature and VFA. It ranges from about 3,100 to 3,800 ksi for typical , = parameters describing the shape of the sigmoidal ranges of VMA and VFA. function VMA VFA xVMA E mix = Pc 4, 200, 000 1 - + 3 G binder E a 1 1 100 10, 000 log a (T ) = - (8) 19.14714 T Tr 1 - Pc + (10) where VMA 1 - a(T) = shift factor as a function of temperature 100 VMA + T = temperature, Kelvin 4, 200, 000 3VFA G binder Tr = reference temperature, Kelvin Ea = activation energy Table 3-32. Temperatures and Table 3-31. Regression frequencies used in analysis of aging indices. the dynamic modulus master curve testing. Measure SAFT MGRF Slope 0.64 1.00 Temperature, C Frequency, Hz Lower 95% CI 0.70 0.96 4.0 10, 1, and 0.1 Upper 95% CI 0.79 1.03 20.0 10, 1, and 0.1 R2 0.93 0.96 34.0 or 40.0 10, 1, 0.1, and 0.01

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51 where VFA = voids filled with asphalt, % G binder = shear complex modulus of binder, psi 0.58 VFAx 3 G binder Table 3-33 summarizes the dynamic modulus master curve 20 + VMA parameters obtained by numerical optimization of Equation 9 Pc = 0.58 VFAx 3 G binder after substitution of the limiting maximum modulus obtained 650 + from Equation 10. Figure 3-39 shows a typical comparison of VMA unconditioned and conditioned mixture master curves and temperature shift factors as well as the measured data for Emix = mixture dynamic modulus, psi ABL-1. Similar plots for all of the 12 binders are included in VMA = voids in mineral aggregates, % Appendix E. The error bars shown are 95 percent confidence Table 3-33. Mixture modulus master curve parameters. Parameter Binder Unconditioned Conditioned Binder Unconditioned Conditioned Air Voids, % 4.6 4.4 4.3 4.0 VMA 16.4 16.0 16.4 15.9 VFA 72.3 72.7 73.6 74.6 E*max, ksi AAC-1 3342.2 3366.2 Airblown 3349.1 3381.6 E*min, ksi 7.5 4.1 3.6 2.2 -0.1910 -0.5708 -1.1127 -1.3366 0.6503 0.4924 0.4485 0.3721 Ea, kJ/mole 213344 211294 217602 208852 Air Voids, % 4.2 4.2 4.3 4.3 VMA 16.0 15.5 16.4 15.7 VFA 73.7 73.1 73.6 72.7 E*max, ksi 3371.5 3396.0 3363.9 3382.8 E*min, ksi AAD-2 5.1 5.3 ALF 21.7 21.1 -0.0012 -0.3389 0.5936 0.2370 0.5674 0.4767 0.5903 0.5194 Ea, kJ/mole 180577 182085 169894 173512 Air Voids, % 3.9 4.0 3.7 3.9 VMA 15.6 15.6 15.5 15.5 VFA 75.2 74.2 76.1 76.1 E*max, ksi 3401.2 3396.1 3411.3 3417.9 E*min, ksi AAF-1 5.3 2.6 Citgoflex 18.0 40.0822 -0.8889 -1.3679 -0.6852 -0.8515 0.5905 0.5199 0.5239 0.6811 Ea, kJ/mole 212784 211229 187462 194955 Air Voids, % 4.4 4.2 4.2 4.0 VMA 16.4 16.1 15.9 15.5 VFA 73.1 74.1 73.6 74.0 E*max, ksi 3346.5 3368.1 3376.5 3400.7 E*min, ksi AAM-1 3.6 2.4 Elvaloy 12.5 7.6 -0.6677 -0.9797 -0.1281 -0.6076 0.5018 0.4312 0.5684 0.4448 Ea, kJ/mole 225645 234911 188958 193486 Air Voids, % 4.2 4.0 4.0 4.0 VMA 15.8 15.4 15.9 15.6 VFA 73.3 74.2 75.0 74.1 E*max, ksi 3380.4 3407.3 3383.7 3395.6 E*min, ksi ABL-1 6.2 8.1 EVA 29.0 7.1 -0.4518 -0.6041 -0.7557 -1.1755 0.5407 0.5080 0.5999 0.4138 Ea, kJ/mole 187271 188768 190346 191384 Air Voids, % 4.1 4.2 3.8 3.8 VMA 15.9 15.8 15.3 15.5 VFA 73.9 73.0 75.2 75.4 E*max, ksi 3378.0 3378.8 3385.7 3409.8 E*min, ksi ABM-2 7.4 8.7 Novophalt 9.0 13.8 -0.7397 -0.9640 -0.9371 -1.1633 0.8694 0.8167 0.5481 0.5569 Ea, kJ/mole 195125 200619 183832 190785

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52 10000 UNAGED STOA 1000 E*, ksi 100 3 2 Log Shift Factor 1 0 10 -1 -2 -3 0 10 20 30 40 Temperature, C 1 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 Reduced Frequency, Hz Figure 3-39. Mixture dynamic modulus master curves for ABL-1. intervals based on the pooled standard deviation of the calculated binder shear moduli for the testing conditions dynamic modulus data for all binders. As shown in this figure, used in the dynamic modulus testing. Back-calculated binder short-term oven conditioning in accordance with AASHTO shear modulus data for all of the binders is included in R30 results in significant stiffening of the mixture. Appendix E. Figure 3-40 presents data for both the uncondi- The mixture dynamic modulus is highly sensitive to the tioned mixture and the mixture conditioned for 4 hours at stiffness of the binder in the mixture. The shear modulus of 135C in accordance with AASHTO R30. The effect of the the binder can be estimated from the mixture dynamic mod- short-term oven conditioning is clearly evident. It results in ulus using the Hirsch Model (6) previously presented as significant stiffening, particularly at the higher temperatures. Equation 10. Knowing the dynamic modulus of the mixture Master curves were developed for the back-calculated binder and the VMA and VFA of the test specimens, Equation 10 can modulus data by fitting the Christensen-Anderson Model to the be solved for the binder shear modulus. This is best done by data as described previously for the binder test data. The glassy trial and error. Figure 3-40 presents an example of the back- modulus from the binder testing was used in fitting the back- 100000 10000 Binder G*, kPa 1000 Mix STOA 100 Mix Unaged 10 1 1.0E-03 1.0E-02 1.0E-01 1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 Reduced Frequency at 22 C, rad/s Figure 3-40. Back-calculated binder modulus master curves for ABL-1.

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53 Table 3-34. Christensen-Anderson Model parameters for back-calculated binder moduli. Rheological Defining Log10 Crossover Binder Log10 Glassy Parameter, R, Temperature, Td, Frequency, , rad/s Source Modulus, Pa Log10 Pa C Unaged R30 Unaged R30 Unaged R30 AAC-1 8.6 1.16 1.85 3.69 2.57 -6.4 -5.5 AAD-2 9.2 1.90 2.47 4.33 2.98 -14.4 -15.6 AAF-1 8.6 1.32 1.46 2.64 1.85 -3.5 -4.2 AAM-1 8.6 1.83 2.07 2.51 1.66 0.4 2.3 ABL-1 8.7 1.72 2.01 2.92 2.07 -13.3 -12.4 ABM-2 8.7 0.59 0.68 3.43 3.09 -9.5 -7.3 Airblown 8.8 2.27 2.94 1.14 -0.57 -2.2 -3.1 ALF 10.9 4.49 5.18 3.18 1.32 -18.4 -15.8 Citgoflex 9.8 3.82 3.33 0.15 0.29 -4.2 2.0 Elvaloy 9.2 2.32 3.03 3.02 1.23 -12.1 -10.4 Novophalt 8.8 1.73 2.10 2.03 0.73 -13.5 -4.5 calculated master curves. The resulting Christensen-Anderson able agreement in the master curve parameters for unaged master curve parameters are summarized in Table 3-34 for the conditions. Table 3-35 summarizes the results of regression 11 binders included in the binder evaluation. analyses for each of the parameters. Details of this statistical analysis are presented in Appendix E (see the project webpage on the TRB website). The 95 percent confidence intervals for 3.6.2.2 Comparison of Master Curve Parameters the slope of the best-fit regression line for each of the three parameters captures 1, the line of equality, indicating that the The purpose of the oven-aged mixture experiment was to back-calculated master curves vary in a similar manner as compare the degree of aging from the short-term binder the tank master curves for the range of binders tested. aging procedures with that from mixtures conditioned at Figures 3-45 through 3-46 compare changes in the mas- 135C for 4 hours in accordance with AASHTO R30. The first ter curve parameters for AASHTO R30 mixture aging with approach for comparing the short-term binder and mixture RTFOT and SAFT aging for the binders. Comparisons were aging procedures was to compare the Christensen-Anderson not made for MGRF aging because analysis of the binder master curve parameters obtained from the short-term aging data showed RTFOT and MGRF aging were essen- binder aging procedures with those obtained from the back- tially the same. Figures 3-44 and 3-46 show that there is no calculated binder moduli from the mixture dynamic modu- relationship for the change in the rheological index and the lus testing. The parameters include the rheological index, R, change in the defining temperature between short-term the crossover frequency, c, and the defining temperature, Td. mixture and binder aging. The trend lines in Figure 3-45 Recall, the physical significance of the Christensen-Anderson show that there is a weak relationship for the crossover master curve parameters are as follows: frequency between the short-term mixture and binder aging, with the mixture aging producing somewhat harder The rheological index, R, is the difference between the log binders. of the glassy modulus and the log of the dynamic modu- lus at the crossover frequency. It is an indicator of the rheological type. 3.6.2.3 Aging Indices The crossover frequency, c, is the frequency where the The second approach for comparing the short-term mixture phase angle is close to 45 degrees and is an indicator of the and binder aging procedures was to compare aging indices hardness of the binder. computed from the fitted binder master curves. Aging indices The defining temperature, Td, is an indicator of the glass were computed from the back-calculated binder modulus transition of the binder. data using the method previously described for the binder testing. Table 3-36 presents aging indices computed in this Figures 3-41 through 3-43 compare the Christensen- manner for each of the binders for various unaged binder Anderson master curve parameters back-calculated from the modulus values ranging from 1 to 100,000 kPa. The 1 kPa unaged mixture dynamic modulus tests with those measured values are based on unaged binder modulus values that were for the tank binder. These figures show that there is reason- below the range measured in the dynamic modulus test and

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54 5 4 R for Tank Binder 3 2 1 0 0 1 2 3 4 5 R for Backcalculated from Unaged Mixture Figure 3-41. Comparison of rheological index from unaged mixture and tank binder tests. 5 4 for Tank Binder 3 c 2 log10 1 0 0 1 2 3 4 5 log10 c for Backcalculated from Unaged Mixture Figure 3-42. Comparison of crossover frequency from unaged mixture and tank binder tests.

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55 4 2 0 -2 Td for Tank Binder -4 -6 -8 -10 -12 -14 -16 -18 -20 -20 -18 -16 -14 -12 -10 -8 -6 -4 -2 0 2 4 Td for Backcalculated from Unaged Mixture Figure 3-43. Comparison of defining temperature from mixture and binder tests. the 100,000 kPa values were above the range measured in the poorer. The regression analysis is summarized in Table 3-37. dynamic modulus test. The remaining values were within the Details of this statistical analysis are presented in Appendix E range of the measured data. (see the project webpage on the TRB website). The slope and Figure 3-47 compares aging indices from the mixture testing intercept from the RTFOT and the MGRF regression models with those from the RTFOT, SAFT, and MGRF for an unaged are both significant at the 99 percent level, while those for the binder modulus of 10 kPa, the lowest stiffness included in the SAFT are not significant at the 95 percent level. The slopes of the mixture testing conditions. Figure 3-47 shows a reasonable relationships indicate that the aging index from the short-term correlation between the AASHTO R30 mixture aging and the binder aging tests is less than that obtained from short-term RTFOT and MGRF. The correlation for the SAFT is much aging of mixtures in accordance with AASHTO R30. Rankings for the aging indices can be used to compare the short-term binder aging procedures to AASHTO R30. Table 3-35. Regression Table 3-38 summarizes the rankings for each test, with the analysis of unaged mixture rank of 1 given to the binder with the highest aging index. and tank, Christensen- Table 3-38 also presents the Spearman's rank correlation Anderson Model coefficient and its significance level (p-value) for the three parameters. short-term binder aging procedures. Higher values of the Parameter Measure Value Spearman's rank correlation coefficient indicate greater sim- Slope 0.94 ilarity in the rankings. The p-values for the Spearman's rank Lower 95 % CI 0.85 correlation coefficient indicate the level of statistical signifi- R Upper 95 % CI 1.02 R2 0.88 cance for the rankings. The ranking analysis in Table 3-38 Slope 0.95 shows that the RTFOT provides the closest rankings compared Lower 95 % CI 0.81 to AASHTO R30 with a Spearman's rank correlation coefficient c Upper 95 % CI 1.08 of 0.91 and a significance level exceeding 99.9 percent. The R2 0.86 Slope 0.95 MGRF also provides similar rankings to AASHTO R30 with Lower 95 % CI 0.71 a Spearman's rank correlation coefficient of 0.80 and a sig- Td Upper 95 % CI 1.19 nificance level of 99.7 percent. The SAFT provides rankings R2 0.78 having the greatest difference compared to AASHTO R30.

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56 SAFT RTFOT 1.0 1.0 0.8 0.8 0.6 0.6 Change in R for RTFOT Aging Change in R for SAFT Aging 0.4 0.4 0.2 0.2 0.0 0.0 -0.2 -0.2 -0.4 -0.4 -0.6 -0.6 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 Change in R for R30 Aging Figure 3-44. Comparison of change in rheological index for short-term mixture and binder aging. SAFT RTFOT 0.0 0.0 -0.2 -0.2 -0.4 -0.4 for RTFOT Aging for SAFT Aging -0.6 -0.6 -0.8 SAFT -0.8 -1.0 -1.0 c) c) Change in log10 ( -1.2 -1.2 Change in log10 ( -1.4 -1.4 -1.6 RTFOT -1.6 -1.8 -1.8 -2.0 -2.0 -2.2 -2.2 -2.2 -2.0 -1.8 -1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 Change in log ( c) for R30 Aging Figure 3-45. Comparison of change in crossover frequency for short-term mixture and binder aging.