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43 82°C, so the data shown is from the test temperature of 76°C. This graph is shown with the same Jnr scale as for the un- 18 modified binders to illustrate the lower compliance results 16 for the modified binders. As with the unmodified binders, the 14 modified binders show a trend of decreasing Jnr as the SEP 12 temperature was increased. However, there is no evidence of 10 degradation of the binders due to the exposure to the elevated Jnr (1/Pa) temperatures in the SEP test. 8 In summary, the assessment of changes in binder proper- 6 ties due to the conditioning of the samples to elevated tem- 4 peratures in the SEP test indicates that all binders increase in 2 stiffness with higher temperatures. The magnitudes of the 0 property changes differ among the binders in the experiment, H B 0 but with the limited data set there does not appear to be any C 130 consistent trend that binders from particular crude sources Binder ID M 150 N 170 are more temperature susceptible than others. Also, modified G 190 SEP Temp. (C) and unmodified binders generally appear to be affected by high temperatures to similar magnitudes. The results do not Figure 24. MSCR Jnr results at 3200 Pa stress for modified binders. provide any evidence that high temperatures cause degrada- tion of the binders. However, this finding may only indicate that the conditions of the SEP test are not severe enough to binders exhibit more recoverable strain (i.e., are more elastic) cause significant damage to the binders. after exposure to higher temperatures. The unmodified binder that has the greatest change in Jnr with higher SEP temper- atures is Binder I, the air-blown PG 70-28 using an Alaskan Mixture Testing Slope/Canadian crude blend. This binder was consistently This section presents the results of the tests with the binders among the binders with the greatest property changes due to in mixture tests over a range of mixing and compaction tem- the SEP conditioning. It was also the binder with the highest peratures. Results are given for the coating tests, the workabil- opacity and, therefore, it may have lost some volatile compo- ity tests, the compaction tests, and the indirect tensile creep nents that caused a substantial increase in stiffness. compliance and strength tests. Figure 24 shows the effect of SEP temperature on Jnr for modified binders. As with the unmodified binders, the Jnr data Mixture Coating Tests used to evaluate degradation were from the high grade temper- ature, except for the PG 82 binders (M, N, and G). For these Results of the coating tests are summarized in Table 19. three binders, the creep recovery tests were not performed at The table shows the percentage of coated particles determined Table 19. Summary of coating test results. 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 M 85.5 -19.5 52.6 59.0 90.1 89.6 63.0 98.0 99.3 99.3 N 84.3 -25.5 21.5 60.7 68.2 88.3 57.3 70.9 90.4 99.5 G 82.5 -24.2 19.5 65.4 83.3 82.1 79.6 91.4 93.9 97.4 H 78.3 -26.1 37.4 74.8 91.7 83.0 73.0 94.5 88.5 92.9 C 75.1 -38.7 40.8 74.9 85.3 86.4 81.0 88.4 92.5 96.0 I 71.8 -29.2 53.1 72.3 87.1 91.7 83.6 98.2 99.2 100 B 69.3 -37.3 72.4 71.9 82.5 87.2 82.2 95.9 99.4 98.9 F 67.8 -21.3 51.9 89.3 88.0 90.3 77.3 98.2 99.0 99.4 O 65.6 -29.7 57.2 83.9 86.5 92.0 90.1 89.2 99.8 99.7 K 65.3 -13.0 81.0 87.7 90.7 95.5 78.5 96.7 99.9 99.9 J 64.3 -20.7 81.8 83.8 90.3 92.1 75.0 96.4 99.1 99.9 E 60.9 -33.1 91.2 86.7 92.5 95.9 85.6 97.8 98.4 100 D 60.3 -31.7 89.4 91.2 95.0 98.1 91.0 97.3 99.2 99.6
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44 Table 20. ANOVA results for mix coating experiment. Factor Type Levels Values Binder fixed 13 B,C,D,E,F,G,H,I,J,K,M,N,O Temp fixed 4 120,140,160,180 Mixer fixed 2 Bucket,Pugmill Analysis of Variance for %Coating, using Adjusted SS for Tests Source DF Seq SS Adj SS Adj MS F P Binder 12 9507.79 10437.15 869.76 39.04 0.000 Temp 3 23859.07 23195.39 7731.80 347.06 0.000 Mixer 1 10341.81 9827.25 9827.25 441.12 0.000 Binder*Temp 36 5421.71 5917.35 164.37 7.38 0.000 Binder*Mixer 12 2627.86 2565.34 213.78 9.60 0.000 Temp*Mixer 3 1287.80 1159.38 386.46 17.35 0.000 Binder*Temp*Mixer 36 4483.41 4483.41 124.54 5.59 0.000 Error 118 2628.77 2628.77 22.28 Total 221 60158.22 by the Ross count method as mixing temperatures were of increased coating at higher temperatures, but that the increased from 248°F to 356°F (120°C to 180°C). effect is not linear. The results also show that the bucket Analysis of variance (ANOVA) is a common method of mixer provided better coating than the pugmill. This seems analyzing data from a statistical experimental design to assess to conflict with the hypothesis that the bucket mixer would differences associated with experimental treatments. Out- be less efficient than the pugmill due to its lower mixing put from the ANOVA for the coating experiment is shown speed (slower shear rate). However, besides mixing speed, in Table 20. From these results, it can be seen that all three the action of the two mixers is very different. The tumbling of the main factors (binder ID, mixing temperature, and action of the bucket mixer, like that of a drum mix plant, allows mixer type) were highly significant. The interactions of these aggregate particles to stay in contact with the binder and other factors were also statistically significant, however, based on the coated particles. This could be a more efficient coating process F values, not nearly to the same degree as the main factors by than a pugmill, which is a more violent churning action with themselves. aggregate particles tossed into space, especially when the pug- The main effects plots for the coating test experiment are mill is under filled. shown in Figure 25. All of the modified binders, except For each binder, the coating percentages were related to Binder B, plot below the overall mean for percent coating, mixing temperatures using Sigmoid functions of the form: which indicates that aggregates are harder to coat with the modified binders under the same conditions. The tempera- 1 C= (8) ture effect on coating percentage follows the expected trend 1 + ae - b T Main Effects Plot for %Coating Fitted Means Binder Temp 90 80 70 Mean B C D E F G H I J K M N O 120 140 160 180 Mixer 90 Modified binders are shown with triangle symbols 80 70 Bucket Pugmill Figure 25. Effects of binder, temperature, and mixer on coating percentage.