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OCR for page 57

57
SAFT RTFOT
10 10
8 8
Change in Td for RTFOT Aging, °C
Change in Td for SAFT Aging, °C
6 6
4 4
2 2
0 0
-2 -2
-2 -1 0 1 2 3 4 5 6 7 8 9 10
Change in Td for R30 Aging, °C
Figure 3-46. Comparison of change in defining temperature for short-term
mixture and binder aging.
The Spearman's rank correlation coefficient for the SAFT test. Table 3-39 summarizes average aging indices for
rankings is only 0.60 and the correlation is not significant at the neat and modified binders for 10 kPa unaged binder
the 95 percent level. stiffness. Data are presented for four aging procedures
(AASHTO R30 mixture aging and binder aging using the
RTFOT, MGRF, and SAFT). In computing the averages
3.7 Short-Term Aging of Modified
and standard deviations given in Table 3-38, the data
Binders
for the EVA binder were eliminated due to the testing dif-
One of the purported issues with the RTFOT is that the ficulties caused by phase separation that were discussed
aging of modified binders is less because the higher viscos- previously.
ity modified binders do not maintain a thin film during the The average aging indices for neat and modified binders
are compared in Figure 3-48 for the four short-term aging
Table 3-36. Aging indices for AASHTO R30 procedures. The error bars shown in Figure 3-48 are 95 per-
conditioning based on back-calculated binder cent confidence intervals for the average. These comparisons
modulus values. show that there is little difference in the average aging index
for the neat and modified binders included in NCHRP Pro-
Aging Indices from AASHTO R30 for Various
Unaged Binder Modulus Values
ject 9-36.
1 10 100 1,000 10,000 100,000 Table 3-39 also summarizes the results of hypothesis test-
Binder kPa kPa kPa kPa kPa kPa ing for the average of the mean 10-kPa aging index between
AAC-1 4.78 3.50 2.34 1.43 0.84 0.55
AAD-2 6.46 4.53 3.01 1.91 1.19 0.77 neat and modified binders for the four short-term aging
AAF-1 5.26 4.49 3.61 2.68 1.83 1.17 procedures. This testing shows that the average aging index
AAM-1 2.95 2.62 2.23 1.80 1.40 1.00 is the same for neat and modified binders for short-term
ABL-1 3.43 2.89 2.32 1.77 1.30 0.97
ABM-2 1.70 1.79 1.87 1.89 1.73 1.32 mixture aging in accordance with AASHTO R30 and short-
Airblown 6.66 4.34 2.71 1.65 1.02 0.72 term binder aging in the RTFOT and the MGRF. For the
ALF 3.33 2.74 2.24 1.82 1.48 1.19
SAFT, the hypothesis testing shows that the average aging
Citgoflex 0.85 1.20 1.72 2.40 3.09 2.79
Elvaloy 6.13 4.34 2.94 1.93 1.26 0.86 index for the neat binder is greater than that for the modi-
Novophalt 2.61 2.66 2.58 2.34 1.94 1.43 fied binder.

OCR for page 57

58
SAFT RTFOT MGRF Equality
5.0
4.5
RTFOT, SAFT, or MGRF Aging Index
4.0
3.5
RTFOT
R2 = 0.87
3.0
MGRF
2.5 R2 = 0.67
2.0
SAFT
R2 = 0.26
1.5
1.0
0.5
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
R30 Aging Index
Figure 3-47. Comparison of 10 kPa aging indices for mixture and
binder testing.
Table 3-37. Regression analysis of Table 3-38. Comparison of ranking of
aging indices from AASHTO R30, binder aging indices.
RTFOT, SAFT, and MGRF.
Binder Rank
Model Measure Value R30 RTFOT SAFT MGRF
R2 0.87 AAC-1 5 7 1 1
Slope 0.41 AAD-2 1 2 3 3
AAF-1 2 1 2 2
RTFOT vs R30 p-value for slope 0.0002
AAM-1 9 6 7 10
Intercept 1.04
ABL-1 6 5 6 8
p-value for intercept >0.0001
ABM-2 10 10 5 9
R2 0.26 Airblown 3 3 4 6
Slope 0.25 ALF 7 9 8 7
SAFT vs R30 p-value for slope 0.0639 Citgoflex 11 11 11 11
Intercept 0.88 Elvaloy 4 4 10 4
p-value for intercept 0.0563 Novophalt 8 8 9 5
R2 0.67 Spearman Rank 0.91 0.60 0.80
Slope 0.30 Correlation Coefficient p-value 0.0001 0.0510 0.0031
MGRF vs R30 p-value for slope 0.0012
Intercept 1.42
p-value for intercept 0.0010
Table 3-39. Average 10 kPa aging indices for neat and modified
binders.
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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59
Neat Modified
5.0
4.5
4.0
3.5
Aging Index 3.0
2.5
2.0
1.5
1.0
0.5
0.0
R30 RTFOT MGRF SAFT
Aging Procedure
Figure 3-48. Comparison of average 10-kPa aging indices for neat and
modified binders.