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OCR for page 68
68
SSF Mix T = - 12.57 + 1.010 Phase Angle Mix T
350 Regression
95% CI
G
340 N
S 12.2325
H R-Sq 65.6%
330 R-Sq(adj) 62.5%
B
C
320 I
SSF Mix T
F O
310
300 M
E
J D
290
K
280
270
300 310 320 330 340
Phase Angle Mix T
(a)
SSF Mix T = - 79.22 + 1.228 Phase Angle Mix T_1
350 Regression
95% CI
G
340 N
S 6.40025
H
R-Sq 91.0%
330 R-Sq(adj) 90.1%
B
C
320 I
SSF Mix T
F O
310
300
E
J D
290
K
280
270
300 310 320 330 340
Phase Angle Mix T_1
(b)
Figure 52. Correlation of mixing temperatures from the SSF Method
and the Phase Angle method: (a) all binders, (b) excludes Binder M.
methods, the methods will give equivalent results at 318°F as shown in Table 37. Since the SSF method and the Phase
(159°C), which should be the upper end of the range of com- Angle method had similar correlations with the mix tests and
paction temperatures. At the lower end of the compaction tem- both appear to be viable options for determining mixing and
perature range for typical paving-grade binders, the results of compaction temperatures, both methods were carried for-
the SSF method will be about 18°F (10°C) lower than the com- ward in the validation experiment.
paction temperature from the Phase Angle method. A summary of the mixing and compaction temperatures
determined from the SSF and Phase Angle methods for the
validation binders is shown in Table 37. The true grades of
Validation Experiment Results and Analysis
each of the validation binders determined by NCAT differed
A set of four independent binders were selected at the from the grades reported by the producers. Also included in
beginning of the study for a small validation experiment to the table are the midpoints of the mixing and compaction
verify the recommended method. This set of binders included temperatures recommended by the respective binder suppli-
a variety of crude sources, PG grades, and modification types, ers. Another point of reference is the equiviscous mixing and
OCR for page 69
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SSF Comp = - 68.99 + 1.194 Phase Angle Comp
320 Regression
G 95% CI
N
310 S 10.1739
H R-Sq 72.2%
R-Sq(adj) 69.6%
300
B
SSF Comp C
I
290
F O
280
M
E
270
J D
260 K
250
275 280 285 290 295 300 305 310 315
Phase Angle Comp
(a)
SSF Comp = - 131.8 + 1.414 Phase Angle Comp_1
320 Regression
G 95% CI
N
310 S 5.60787
H R-Sq 92.2%
R-Sq(adj) 91.4%
300
B
C
SSF Comp
I
290
F O
280
E
270
J D
260 K
250
275 280 285 290 295 300 305 310 315
Phase Angle Comp_1
(b)
Figure 53. Correlation of Compaction Temperatures from the SSF Method
and the Phase Angle Method: (a) all binders and (b) excludes Binder M.
compaction temperatures for the unmodified Binder Y, which under predicted the mixing and compaction temperatures for
were 333°F and 308°F, respectively. three of the four validation binders. The Phase Angle method
Overall, the temperatures from the Phase Angle method are also under predicted the mixing and compaction temperatures
lower than for the SSF method, but the differences are not con- relative to the equiviscous method for the unmodified binder.
sistent for this set of binders. For Binder Z, the results for the The SSF method over predicted mixing temperatures for three
methods were very similar, but for Binder W, the difference of the four binders and over predicted compaction tempera-
between the results of the two methods was 20°F for the mix- tures in just two cases. Both candidate methods over predict
ing temperature. Compared with the producers' recommended mixing and compaction temperatures for Binder X and under
mixing and compaction temperatures, the Phase Angle method predict mixing and compaction temperatures for Binder Z.
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Table 37. SSF and Phase Angle method results for
validation binders.
Midpoint of
SSF Method Phase Angle Method Producer's
Recommendation
Binder Mixing Comp. Mixing Comp. Mixing Comp.
Binder True Temp. Temp. Temp. Temp. Temp. Temp.
I.D. Grade (ºF) (ºF) (ºF) (ºF) (ºF) (ºF)
W 90.0 -17.8 358 329 338 311 345 325
X 74.2 -27.9 345 315 338 310 312 282
Y 73.0 -21.4 325 295 314 291 321 298
Z 81.9 -20.1 327 300 325 300 350 320
The suppliers' recommendations for binders are typically based with the pugmill mixer are reasonable for each of the binders,
on field experience using aggregate types, gradations, or other ranging from 291°F for the unmodified Binder Y to 341°F
variables that may be substantially different than the materials for the SBS modified Binder W. However, the temperatures
and conditions used in this experiment. for achieving the baseline coating percentage with the bucket
Mixture tests with the validation binders were conducted mixer are excessive and are extrapolated outside of the
in the same manner and with the same materials as for the temperature range of the experiment for the three modified
main mixture experiments. Mixture tests with the validation binders.
binders included coating tests with both mixer types, worka- Table 40 summarizes the results of the workability tests for
bility tests, and compaction tests. the validation binders. Only one sample was tested for each
Data from the mix coating tests using the bucket and pug- binder. As with the main workability experiment, the regres-
mill mixers for each of the validation binders are shown in sions from these workability tests were used to estimate the
Table 38. Following the same approach used for the main temperature at which the torque was equal to 10 N m for each
coating test experiment, these data were used to predict the binder. These results appear to be reasonable and follow the
mixing temperatures needed to achieve the baseline coating expected trend that higher PG binders will require a higher
percentages for both mixer types. The results of the coating temperature to achieve the same workability.
test experiments with the validation binders are shown in Mix compaction tests with the validation binders followed
Table 39. It can be seen that the results of the coating tests the same protocol as with the main compaction experiment
Table 38. Results of coating tests with validation binders.
Percentage of Coated Aggregate Particles by ASTM D2489
Mixer Type Pugmill Bucket
Mixing Temp. °C 120 140 160 180 120 140 160 180
Mixing Temp. °F 248 284 320 356 248 284 320 356
W 90.0 -17.8 17.7 62.2 76.4 86.1 43.9 66.5 81.7 88.6
X 74.2 -27.9 36.7 70.7 80.3 93.3 35.0 26.4 97.4 99.8
Y 73.0 -21.4 73.7 92.9 92.4 91.0 75.3 83.6 98.7 95.2
Z 81.9 -20.1 36.8 79.4 85.3 92.1 27.6 44.5 73.6 98.5
Table 39. Predicted mixing temperatures for good coating
for the validation binders.
Pugmill Mixer Bucket Mixer
True
ID T for 89% T for 97%
Grade a b A b
Coating Coating
W 90.0 -17.8 4508.4 0.0609 341 174.784 0.0413 406
X 74.2 -27.9 1614.4 0.0570 331 30484.3 0.0744 365
Y 73.0 -21.4 27.68 0.0373 291 57.00 0.04256 349
Z 81.9 -20.1 6693.6 0.0699 311 9506.3 0.0682 365
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Table 40. Summary of workability test results for achieve a density level of 92.0% of Gmm. The compaction
the validation binders. temperatures based on this approach seems reasonable for
three of the four binders. The predicted compaction temper-
ID Workability Regression Equation R2 ºC ºF
2
ature for Binder W is outside of the experimental range and
W y = -0.0024x - 0.3432x + 20.098 0.94 155 311
appears to be too high.
X y = 0.0021x2 - 0.9269x + 108.17 0.79 150 302 Table 42 summarizes the differences between results of the
Y y = 0.0059x2 - 1.8786x + 165.73 0.57 139 282 mixture tests and the results from candidate methods for each
Z y = 0.0048x2 - 1.5287x + 136.05 0.86 153 308 of the validation binders. Since the coating test results with the
bucket mixer were so far outside of the experimental range
except that for the validation binders, compaction tests were and outside of reasonable limits, they were not included in this
only performed at the three temperatures: 130°C, 150°C, and analysis. Comparing the absolute differences for the two can-
170°C. Table 41 shows the results of the compaction tests for didate methods, it can be seen that results with the Phase
the validation binders. It can be seen from these data that Angle method agree more closely with the mix tests than the
none of the mixes reached the baseline density of 92.9% of SSF method. However, it also can be seen that many of the dif-
Gmm established in the main compaction experiment. This ferences are substantial for both of the candidate methods.
is probably due to a slight adjustment to the SGC internal Although these large differences may be considered to be an
angle during routine calibration of the machine that took indication that neither of the candidate methods provides
place in the time lag between the main compaction experi- accurate mixing and compaction temperatures, it is even
ment and the validation tests. Therefore, the temperature- more likely that the results of the mix tests are less reliable than
density regression was used to estimate the temperature to the candidate binder tests.
Table 41. Results of compaction tests with validation binders.
%Gmm at 25 Gyrations Compaction
Temperature
Regression Equation
Binder 266ºF 302ºF 338ºF for 92.0%
(T is temperature, °C)
Binder True (130ºC) (150ºC) (170ºC) Gmm,°F
I.D. Grade (°C)
%Gmm =
W 90.0 -17.8 91.5 91.8 92.1 344 (173)
0.0135T+89.756
X 74.2 -27.9 91.7 91.5 92.8 %Gmm = 0.028T+87.926 294 (146)
Y 73.0 -21.4 91.8 92.4 92.4 %Gmm = 0.014T+90.053 282 (139)
Z 81.9 -20.1 91.8 92.3 92.3 %Gmm = 0.125T+90.213 301 (149)
Table 42. Summary of differences (°F) between mix test results
and candidate methods results for the validation binders.
Phase
Angle Phase Angle
SSF Mixing Mixing SSF Mix & Mix & Phase
Temp. Temp - Comp. Comp. SSF Angle
Temp. for Temp. for Midpoint Midpoint Compaction Compaction
89% 89% Temp. - Temp. - Temp. - Temp. -
Coating in Coating in Temp. for Temp. for Temp. for Temp. for
Binder Pugmill Pugmill Equal Equal 92.0% 92.0%
I.D. Mixer Mixer Workability Workability Gmm Gmm
W +17 -3 +33 -15 -15 -33
X +14 +7 +28 +21 +21 +16
Y +34 +23 +28 +13 +13 +9
Z +16 +14 +6 -1 -1 -1
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