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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
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69 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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70 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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71 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 | | 81 47 95 50 50 59