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Table 319. Estimated SAFT operational parameters to reproduce
RTFOT aging.
Binder RTFOT G*/sin, kPa Estimated Impeller Speed, Estimated Conditioning
for 52.5Min Conditioning, Time for 1,050 rpm
rpm Impeller Speed, Min
AAD2 2.65 962 40
AAM1 6.00 935 47
ABM2 3.14 857 38
Average 918 42
· 1,000 rpm impeller speed, 1. To enable a comparison of the rheological properties of
· 50minute aging time, material conditioned in the SAFT, MGRF, and RTFOT, and
· 250g sample mass, and 2. To allow a comparison of the master curves measured for
· Vacuum degassing per AASHTO R28 after shortterm the binders with master curves backcalculated from mix
aging in the SAFT. ture properties.
Figure 330 illustrates the sequence of operations for the In the ovenaged 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, polymermodified binders in both experiments. A single
MGRF, and RTFOT with that from mixture samples aged in a limestone mixture was used in the ovenaged mixture exper
forceddraft 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 ovenaged mix on the TRB website). The verification study was the last study
tures experiment. The RTFOT verification experiment, which in NCHRP 936 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 shortterm conditioned specification parameter,
Table 320. Rheological properties from VCSII 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 5828 ABM2 AAM1 AAD2 Table 321. 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 5828 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 45Min Aging 50Min 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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SAFT oven
heated to 176°C
Process controller adjusts
Oven maintained oven temperature as
at 176°C needed to bring binder to
163°C
Heatup phase
Note: 1,000 rpm impeller
Binder
speed and 250 g sample
Temperature
= 163°C End of
conditioning
Binder period
Temperature
= 160°C
Vessel placed in oven,
Binder Temperature < 10
120°C min
< 20 min Conditioning period , 50 min
N2 flowing at Air flowing at 2,000 mL/min
2,000 mL/min
Figure 330. 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 322. This
described below. table includes the average and standard deviation from two
separate runs for each device.
Figure 331 compares the average continuousgrading tem
3.6.1.1 Specification Parameter G*/sin
peratures from SAFT and MGRF conditioning to RTFOT
The continuousgrading temperatures for RTFOT, SAFT, conditioning. Figure 331 includes trend lines for the SAFT and
and MGRFconditioned 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 322. Continuousgrade temperatures for RTFOT,
SAFT, and MGRF conditioning.
Binder ContinuousGrade Temperature, °C
RTFOT MGRF SAFT
Average Standard Average Standard Average Standard
Deviation Deviation Deviation
AAC1 56.3 0.21 58.1 0.35 57.2 0.07
AAD2 59.7 0.49 59.5 0.14 58.0 0.00
ABM2 60.7 0.35 61.1 0.21 60.5 0.35
AAF1 67.0 0.44 68.4 2.90 65.5 0.28
AAM1 68.0 0.35 68.6 1.27 65.0 0.28
ABL1 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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MGRF SAFT Line of Equality
88 .0
MGR F
MGRF or SAFT High Temperature Grade, ºC
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, ºC
Figure 331. Comparison of SAFT and MGRF continuousgrading
temperatures to RTFOT continuousgrading temperature.
indicates less stiffening, particularly for highstiffness binders. ±1.8°C and does not appear to depend on the stiffness of
Figure 332 shows the difference between the continuous the binder.
grading temperatures for the SAFT and MGRFconditioned Paired difference ttesting was used to assess the signifi
binders compared to the RTFOTconditioned binders. The cance of the differences shown in Figures 331 and 332. 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 323, 324, and 325 for
MGRF SAFT
6.0
Difference in High Temperature Grade (MGRF or
3.0
SAFT minus RTFOT), ºC
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 332. Difference in continuousgrading temperature for
SAFT and MGRF residue compared to RTFOT residue.
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Table 323. Summary of paired ttest Table 325. Summary of paired ttest
for neat binders. for all binders.
ContinuousGrading Differences (MGRF or ContinuousGrading 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
AAC1 56.3 58.1 57.2 1.8 0.9 AAC1 56.3 58.1 57.2 1.8 0.9
AAD2 59.7 59.5 58.0 0.2 1.7 AAD2 59.7 59.5 58.0 0.2 1.7
ABM2 60.7 61.1 60.5 0.4 0.2 ABM2 60.7 61.1 60.5 0.4 0.2
AAF1 67.0 68.4 65.5 1.4 1.5 AAF1 67.0 68.4 65.5 1.4 1.5
AAM1 68.0 68.6 65.0 0.6 3.0 AAM1 68.0 68.6 65.0 0.6 3.0
ABL1 69.5 68.0 65.3 1.5 4.2 ABL1 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 shortterm 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 Ftest 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 326 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: AAF1 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 327 and compared in Figure 333. Fig
ure 333 shows that there is a good relationship between the
Table 324. Summary of paired ttest 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
ContinuousGrading 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
AAC1 56.3 58.1 57.2 1.8 0.9
AAD2 59.7 59.5 58.0 0.2 1.7
ABM2 60.7 61.1 60.5 0.4 0.2
3.6.1.3 ChristensenAnderson Master
AAF1 67.0 68.4 65.5 1.4 1.5 Curve Parameters
AAM1 68.0 68.6 65.0 0.6 3.0
ABL1 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 ChristensenAnderson Model
Standard Deviation of Differences, °C 1.18 1.84 (33). The ChristensenAnderson 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 ChristensenAnderson
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Table 326. Analysis of variability of MGRF and
SAFT relative to RTFOT.
Standard Deviation, °C Variance, (°C)2
Binder
RTFOT MGRF SAFT RTFOT MGRF SAFT
AAC1 0.21 0.35 0.07 0.043 0.125 0.005
AAD2 0.49 0.14 0.00 0.243 0.020 0.000
ABM2 0.35 0.21 0.35 0.120 0.045 0.125
AAF1 0.44 2.90 0.28 0.190 8.405 0.080
AAM1 0.35 1.27 0.28 0.123 1.620 0.080
ABL1 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 WilliamsLandelFerry (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 nonlinear 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 22°C for direct comparison
with the data backcalculated from the mixture master curves.
Table 327. 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
AAC1 0.058 0.232 G ( ) (5)
ABL1 0.654 0.345 3
AAM1 0.122 0.113
Citgoflex 0.196 0.103 1
Airblown 0.031 0.033 ( ) (6)
Novophalt 0.132 0.045 t
AAF1 0.008 0.063
ABM2 0.349 0.100 where
AAD2 1.058 0.362
Elvaloy 0.173 0.060 G() = shear modulus
ALF 6440 0.207 0.073 S(t) = creep stiffness
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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 333. 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 334 presents an example of the fitted master curve indicator of the hardness of the binder. Finally, the rheologi
and the nomenclature used with the ChristensenAnderson cal index, R, is the difference between the log of the glassy
Model. A major advantage of the ChristensenAnderson 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 328 summarizes the ChristensenAnderson 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 shortterm aged condition. Figures 335
steadystate viscosity of the binder. The crossover frequency through 337 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
CrossOver
Frequency, c
1.0E+01
1.0E+00
1.0E06 1.0E04 1.0E02 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 334. ChristensenAnderson Model master curve.
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Table 328. ChristensenAnderson 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
AAC1 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
AAD2 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
AAF1 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
AAM1 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
ABL1 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
ABM2 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 shortterm 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 335 and
frequency decreases, indicating that the binder is becoming 336 to make it easier to interpret these plots. The trend lines
harder with shortterm conditioning. Finally, the defining for the MGRF data are much closer to the line of equality than
temperature increases on shortterm 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 ChristensenAnderson Model parameters are summarized in
SAFT and MGRFconditioned binders compared to RTFOT Table 329. 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 335. 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 336. 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 337. Comparison of change in defining temperature for RTFOT,
SAFT, and MGRF aging.
Table 329. 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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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 ChristensenAnderson master curve parameters 3.6.2 OvenAged Mixture Experiment
that are not significantly different from those for the RTFOT,
while the SAFT aging produces different changes in the master In the ovenaged mixture experiment, binder properties
curve parameters. backcalculated 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 135°C 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 backcalculated 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 pavementthe late the aging that occurs in mixtures during shortterm oven
change that occurs in stiffness at temperatures correspon conditioning. The EVAmodified 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 ovenaged mixture experiment. The
fitted ChristensenAnderson Model for each binder. These complete analysis is included in the verification study report
temperatures are shown in Table 330. The fitted Chris in Appendix E (see the project webpage on the TRB website).
tensenAnderson 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 BackCalculated 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 330. preparing mixtures, developing a dynamic modulus master
Figure 338 compares aging indices from the SAFT and curve for each mixture, and then backcalculating 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 338. 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 331. Details of this statis 929 (34). The testing was conducted at three temperatures
tical analysis are presented in Appendix E. This analysis and four frequencies as summarized in Table 332. The low
shows that there are significant relationships between the and middle temperatures were set at 4°C and 20°C, 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: 34°C for the softer binders (AAC1, AAD2,
by the R2 value, is approximately the same for the MGRF ABL1, ABM2, ALF, and Elvaloy) and 40°C for AAF1,
OCR for page 40
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Table 330. 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
AAC1 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
AAD2 1,000 13.1 1.80 2.18 2.20 ALF 6440 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
AAF1 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
AAM1 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
ABL1 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
ABM2
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
AAM1, 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 MechanisticEmpirical 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 338. Comparison of aging indices for RTFOT, SAFT, and MGRF.
which for this testing was selected to be 22°C 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 332.
Temperatures and
Table 331. 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 333 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 339 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 ABL1. 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 333. 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 AAC1 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 AAD2 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 AAF1 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 AAM1 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 ABL1 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 ABM2 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.E06 1.E05 1.E04 1.E03 1.E02 1.E01 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 339. Mixture dynamic modulus master curves for ABL1.
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. Backcalculated binder
shortterm 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 340 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 135°C in accordance with AASHTO R30. The effect of the
the binder can be estimated from the mixture dynamic mod shortterm 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 backcalculated binder
and the VMA and VFA of the test specimens, Equation 10 can modulus data by fitting the ChristensenAnderson 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 340 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
1.0E03 1.0E02 1.0E01 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 340. Backcalculated binder modulus master curves for ABL1.
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53
Table 334. ChristensenAnderson Model parameters for
backcalculated 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
AAC1 8.6 1.16 1.85 3.69 2.57 6.4 5.5
AAD2 9.2 1.90 2.47 4.33 2.98 14.4 15.6
AAF1 8.6 1.32 1.46 2.64 1.85 3.5 4.2
AAM1 8.6 1.83 2.07 2.51 1.66 0.4 2.3
ABL1 8.7 1.72 2.01 2.92 2.07 13.3 12.4
ABM2 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 ChristensenAnderson able agreement in the master curve parameters for unaged
master curve parameters are summarized in Table 334 for the conditions. Table 335 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 bestfit regression line for each of the three
parameters captures 1, the line of equality, indicating that the
The purpose of the ovenaged mixture experiment was to
backcalculated master curves vary in a similar manner as
compare the degree of aging from the shortterm binder
the tank master curves for the range of binders tested.
aging procedures with that from mixtures conditioned at
Figures 345 through 346 compare changes in the mas
135°C for 4 hours in accordance with AASHTO R30. The first
ter curve parameters for AASHTO R30 mixture aging with
approach for comparing the shortterm binder and mixture
RTFOT and SAFT aging for the binders. Comparisons were
aging procedures was to compare the ChristensenAnderson
not made for MGRF aging because analysis of the binder
master curve parameters obtained from the shortterm
aging data showed RTFOT and MGRF aging were essen
binder aging procedures with those obtained from the back
tially the same. Figures 344 and 346 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 shortterm
the crossover frequency, c, and the defining temperature, Td.
mixture and binder aging. The trend lines in Figure 345
Recall, the physical significance of the ChristensenAnderson show that there is a weak relationship for the crossover
master curve parameters are as follows: frequency between the shortterm 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 shortterm 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 backcalculated binder modulus
transition of the binder. data using the method previously described for the binder
testing. Table 336 presents aging indices computed in this
Figures 341 through 343 compare the Christensen manner for each of the binders for various unaged binder
Anderson master curve parameters backcalculated 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
OCR for page 40
54
5
4
R for Tank Binder
3
2
1
0
0 1 2 3 4 5
R for Backcalculated from Unaged Mixture
Figure 341. 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 342. 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 343. 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 337.
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 347 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 347 shows a reasonable relationships indicate that the aging index from the shortterm
correlation between the AASHTO R30 mixture aging and the binder aging tests is less than that obtained from shortterm
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 shortterm binder aging procedures to AASHTO R30.
Table 335. Regression Table 338 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 338 also presents the Spearman's rank correlation
Anderson Model coefficient and its significance level (pvalue) for the three
parameters. shortterm 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 pvalues 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 338
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.
OCR for page 40
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 344. Comparison of change in rheological index for shortterm 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 345. Comparison of change in crossover frequency for shortterm mixture
and binder aging.