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OCR for page 53
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Interaction Plot (fitted means) for %Gmm
B M 0 15
94.1 Temp
110
130
93.3 150
Temp 170
92.5
94.1 Binder
B
M
93.3
Binder
92.5
RAP
Figure 33. Interaction plot of RAP, binder, and temperature on %Gmm.
temperature also shows that the effect of the RAP was greater and analysis was to determine whether the low temperature
at higher compaction temperatures. mix properties were affected by the compaction tempera-
ture. If an effect was detected, then the results would be
analyzed to assess the potential that the change was due to
Indirect Tensile Creep Compliance and Strength
binder degradation.
Gyratory specimens compacted at the four compaction Creep compliance results are summarized in Table 30.
temperatures were tested to determine indirect tensile creep Since compliance values are greatly affected by test temper-
compliance in accordance with AASHTO T 322. Creep com- ature, separate analyses were performed at each temperature.
pliance is the inverse of stiffness. Therefore, at very low tem- Figure 34 through Figure 36 show the change in compliance
peratures, a mixture with lower compliance is able to strain values for the modified binders at test temperatures -20°C,
more and avoid thermal fracture. The goal of this testing -10°C, and 0°C, respectively. Similarly, Figure 37 through
Table 30. Summary of creep compliance results (Dt 90 1 x 10-6 1/kPa) for different compaction
temperatures.
Test Temp. °C -20 -10 0
Comp. Temp. °C 110 130 150 170 110 130 150 170 110 130 150 170
Comp. Temp. °F 230 266 302 338 230 266 302 338 230 266 302 338
M 85.5 -19.5 0.0770 0.0716 0.0717 0.0661 0.1244 0.1111 0.1340 0.1088 0.3090 0.3001 0.2177 0.1997
N 84.3 -25.5 0.1416 0.1284 0.1077 0.1088 0.3447 0.2106 0.2106 0.1895 0.9503 0.7135 0.4367 0.4355
G 82.5 -24.2 0.1049 0.0834 0.0704 0.0688 0.1595 0.1302 0.1332 0.1006 0.4937 0.3711 0.3191 0.2160
H 78.3 -26.1 0.0851 0.0929 0.0792 0.0706 0.1702 0.1450 0.1678 0.1401 0.5753 0.5835 0.4825 0.2819
C 75.1 -38.7 0.1383 0.1394 0.1682 0.1509 0.3424 0.3527 0.4028 0.3221 1.3254 1.1280 1.1655 0.8607
I 71.8 -29.2 0.2295 0.1712 0.1792 0.1324 0.3237 0.3525 0.3516 0.1324 0.8144 1.0476 0.7209 0.4414
B 69.3 -37.3 0.1847 0.1808 0.1937 0.1926 0.4525 0.2987 0.4698 0.3873 1.6037 1.2855 1.4417 1.0198
F 67.8 -21.3 0.0728 0.0725 0.0527 0.0723 0.1978 0.1881 0.1598 0.1221 0.4417 0.3788 0.3420 0.2619
O 65.6 -29.7 0.1136 0.0737 0.0934 0.0869 0.2123 0.2077 0.1615 0.1493 0.8818 0.5780 0.4572 0.4249
K 65.3 -13.0 0.0580 0.0445 0.0439 0.0407 0.0668 0.0588 0.0551 0.0478 0.1755 0.1288 0.2243 0.1473
J 64.3 -20.7 0.0584 0.0529 0.0509 0.0581 0.0955 0.0795 0.0693 0.0738 0.2154 0.1886 0.1546 0.1691
E 60.9 -33.1 0.1678 0.1341 0.1237 0.1257 0.4213 0.1034 0.4169 0.3110 1.4816 1.2073 1.2343 0.6301
D 60.3 -31.7 0.1130 0.1001 0.0970 0.1034 0.2527 0.2488 0.2022 0.2209 1.1238 0.7832 0.6618 0.6020
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0.25
Dt (90 sec) x 10-6 1/kPa
0.2
B
0.15 C
G
H
0.1 M
N
0.05
0
100 110 120 130 140 150 160 170 180
Compaction Temperature C
Figure 34. Creep compliance results for modified binders tested at 20°C.
Figure 39 show the change in compliance for the set of un- low PG true grade of -19.5. This observation confirms
modified binders. The compliance results generally follow that a binder's low PG number controls thermal cracking
the expected trends: performance.
· Lower test temperatures yield lower creep compliance From Figure 34 [the lowest test temperature (-20°C)], the
results (higher stiffness), which means that the mixes modified binders are so stiff that compaction temperature
lose their ability to relax thermal strains as the tempera- appears to have a negligible effect. However, for the unmodi-
ture decreases. fied binders, shown in Figure 37, most have a slight trend indi-
· Higher compliance values are generally observed for mixes cating that lower compaction temperatures resulted in slightly
having binders with lower low-temperature grades. higher creep compliance values.
For example, Mix B, which has a low PG true grade of From Figure 36 and Figure 39, which are plots of the creep
-37.3°C, is more compliant than Mix M, which has a compliance results at 0°C for the modified and unmodified
0.5
Dt (90 sec) x 10-6 1/kPa
0.4
B
0.3 C
G
H
0.2 M
N
0.1
0
100 110 120 130 140 150 160 170 180
Compaction Temperature C
Figure 35. Creep compliance results for modified binders tested at 10°C.
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1.75
1.5
Dt( 90 sec) x 10-6 1/Kpa
1.25 B
C
1
G
H
0.75
M
0.5 N
0.25
0
100 110 120 130 140 150 160 170 180
Compaction Temperature C
Figure 36. Creep compliance results for modified binders tested at 0°C.
binders respectively, it can be seen that the compliance drops tistically significant factors on compliance results. This analy-
substantially for some binders, including Binders B, C, and N sis is shown in Table 31. As the data in Table 32 and Table 33
of the modified binder set, and Binders E, D, O, and I for the show, the same is true at the other creep compliance tempera-
unmodified binders. These binders are the ones with the low- tures. However, the magnitude of the F-statistic for com-
est low temperature grades. This indicates that the binders with paction temperature relative to the F-statistic for Binder ID is
the lowest low temperature PG grades are more susceptible to much greater for the test results at 0°C, which indicates that the
a loss of compliance due to overheating. creep compliance test at this temperature is more sensitive to
An ANOVA of creep compliance at -20°C with all binders the compaction temperature. Therefore, compaction temper-
confirmed that compaction temperature and binder ID are sta- ature does have a significant effect on low temperature prop-
0.25
Dt (90 sec) x10-6 1/kPa
0.2
D
E
0.15 F
I
0.1 J
K
O
0.05
0
100 110 120 130 140 150 160 170 180
Compaction Temperature C
Figure 37. Creep compliance results for unmodified binders tested at 20°C.
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0.5
0.4
Dt (90 sec) x10-6 1/kPa D
E
0.3 F
I
0.2 J
K
O
0.1
0
100 110 120 130 140 150 160 170 180
Compaction Temperature C
Figure 38. Creep compliance results for unmodified binders tested at 10°C.
erties of the mixtures. Increasing the mixing and compaction the original low critical temperature of the binder and how hot
temperatures can reduce the ability of a mixture to dissipate the mix was heated.
thermal stresses. Following the indirect tensile creep tests, the specimens
Figure 40 illustrates a relationship between the creep were tested to determine tensile strengths. Tensile strength
compliance results at 0°C and binder low PG grade and com- tests were initially conducted at -20°C. However, a few spec-
paction temperature. This graph shows the strong relation- imens reached the maximum load cell capacity of the IDT
ship between the low PG grade and creep compliance, but system, so the remaining tests were conducted at -10°C. The
also shows the influence of compaction temperature on this tensile strength results are summarized in Table 34.
relationship. The main point of this figure is that mixing and An ANOVA on this data, shown in Table 35, indicates that
compaction temperatures influence the potential for low tem- the binder ID, compaction temperature, and their inter-
perature cracking, but the magnitude of the effect depends on action have significant effects on the tensile strengths. The
1.75
1.5
Dt (90 sec) x10-6 1/kPa D
1.25
E
1 F
I
0.75 J
K
0.5
O
0.25
0
100 110 120 130 140 150 160 170 180
Compaction Temperature C
Figure 39. Creep compliance results for unmodified binders tested at 0°C.
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Table 31. ANOVA for creep compliance at 20°C.
Factor Type Levels Values
Binder fixed 13 B,C,D,E,F,G,H,I,J,K,M,N,O
CompT fixed 4 110,130,150,170
Analysis of Variance for Creep -20, using Adjusted SS for Tests
Source DF Seq SS Adj SS Adj MS F P
Binder 12 0.1006398 0.1006398 0.0083866 42.98 0.000
CompT 3 0.0031606 0.0031606 0.0010535 5.40 0.004
Error 36 0.0070239 0.0070239 0.0001951
Total 51 0.1108243
Table 32. ANOVA for creep compliance at 10°C.
Factor Type Levels Values
Binder fixed 13 B,C,D,E,F,G,H,I,J,K,M,N,O
CompT fixed 4 110,130,150,170
Analysis of Variance for Creep -10, using Adjusted SS for Tests
Source DF Seq SS Adj SS Adj MS F P
Binder 12 0.570865 0.570865 0.047572 18.66 0.000
CompT 3 0.028798 0.028798 0.009599 3.77 0.019
Error 36 0.091769 0.091769 0.002549
Total 51 0.691432
Table 33. ANOVA for creep compliance at 0°C.
Factor Type Levels Values
Binder fixed 13 B,C,D,E,F,G,H,I,J,K,M,N,O
CompT fixed 4 110,130,150,170
Analysis of Variance for Creep 0, using Adjusted SS for Tests
Source DF Seq SS Adj SS Adj MS F P
Binder 12 7.08764 7.08764 0.59064 35.14 0.000
CompT 3 0.88120 0.88120 0.29373 17.48 0.000
Error 36 0.60509 0.60509 0.01681
Total 51 8.57393
2
y = 0.0615e-0.0882x
1.8 R2 = 0.8207
110
1.6 y = 0.0517e-0.0881x 130
Creep Compliance x10-6 1/kPa
R2 = 0.8108 150
1.4
y = 0.0493e-0.0855x 170
1.2
R2 = 0.8206
1
y = 0.0456e-0.078x
0.8 R2 = 0.871
0.6
0.4
0.2
0
-50 -45 -40 -35 -30 -25 -20 -15 -10
PG Low True Grade
Figure 40. Graph of relationships between low PG grade, compaction
temperature, and IDT creep compliance at 0°C.
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Table 34. Summary of indirect tensile strengths (MPa).
Test Temp. °C -20 -10
Comp. Temp. °C 110 130 150 170 110 130 150 170
Comp. Temp. °F 230 266 302 388 230 266 302 388
Avg. 3.57 3.44 3.81 3.46
M 85.5 -19.5
St. Dev. 0.10 0.23 0.22 0.54
Avg. 2.67 3.20 3.04 3.12
N 84.3 -25.5
St. Dev. 0.25 0.29 0.10 0.19
Avg. 2.95 3.56 4.05 3.51
G 82.5 -24.2
St. Dev. 0.55 0.51 0.10 0.52
Avg. 3.89 3.62 3.74 3.09
H 78.3 -26.1
St. Dev. 0.15 0.34 0.39 0.82
Avg. 2.82 2.78 2.96 3.08
C 75.1 -38.7
St. Dev. 0.09 0.39 0.11 0.16
Avg. 2.71 2.63 2.64 2.84
I 71.8 -29.2
St. Dev. 0.27 0.23 0.21 0.20
Avg. 2.99 4.08 3.81 3.39
B 69.3 -37.3
St. Dev. 0.72 0.11 0.18 0.74
Avg. 3.26 3.54 3.68 3.82
F 67.8 -21.3
St. Dev. 0.21 0.43 0.35 0.17
Avg. 2.83 3.14 3.97 3.73
O 65.6 -29.7
St. Dev. 0.20 0.39 0.17 0.60
Avg. 3.14 3.83 3.74 3.79
K 65.3 -13.0
St. Dev. * 0.07 0.23 **
Avg. 3.52 3.31 3.74 3.76
J 64.3 -20.7
St. Dev. 0.35 0.28 0.27 0.07
Avg. 2.78 2.75 2.75 2.95
E 60.9 -33.1
St. Dev. 0.15 0.28 0.29 0.28
Avg. 3.43 3.48 3.64 3.49
D 60.3 -31.7
St. Dev. 0.57 0.43 0.29 0.25
* only one tensile strength result, ** only two tensile strength results
interaction plot (Figure 41) shows that there were no consis- have compaction temperature as a significant effect on
tent trends. Compaction temperature seems to have different tensile strength. For Binder K, a Tukey's multiple comparison
effects on tensile strengths for the different binders. For exam- ( = 0.05) of tensile strengths at the four temperatures showed
ple, a few binders show a peak in tensile strength at 130°C or that the tensile strength at 110°C was significantly lower than
150°C, others show lower tensile strengths in the middle of for the other temperatures. However, this data set had a very
the temperature range, and others show tensile strengths limited number of samples. For Binder O, the tensile strengths
increasing throughout the compaction temperature range. at 110°C were significantly lower than the other temperatures,
The data were further analyzed for each binder separately and the tensile strength at 130°C was significantly lower than
to evaluate the significance of compaction temperature. In 150°C, but not significantly different than 170°C. Overall, the
these separate analyses, only Binders K and O were found to tensile strength results varied from binder to binder such that
Table 35. ANOVA for indirect tensile strength at 10°C.
Factor Type Levels Values
Binder fixed 11 C,D,E,F,H,I,J,K,M,N,O
Temp fixed 4 110,130,150,170
Analysis of Variance for TS, using Adjusted SS for Tests
Source DF Seq SS Adj SS Adj MS F P
Binder 10 17.87942 16.67716 1.66772 17.74 0.000
Temp 3 1.77062 1.84765 0.61588 6.55 0.000
Mix*Temp 30 6.20140 6.20140 0.20671 2.20 0.002
Error 100 9.40024 9.40024 0.09400
Total 143 35.25169
S = 0.306598 R-Sq = 73.33% R-Sq (adj) = 61.87%
