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34 that is similar to the way RAP and binders mix in HMA pro- gyrations to 92-percent relative density is determined. A tenta- duction and compaction at higher temperatures. The mixing tive limit of 125 percent of the value at the planned field com- depends on the time at elevated temperature and probably the paction temperature was included based on the limited testing stiffness of the RAP binder. In the preliminary mixture design performed during the Phase I workability study. and analysis procedure for WMA, it was envisioned that the amount of RAP that could be added to WMA would be limited 3.3 Phase II Findings by the planned WMA production temperature and the com- patibility of the new and RAP binders. Since the Phase I RAP Phase II of NCHRP Project 09-43 was directed at evaluating study showed that substantial mixing of the RAP and new and validating the revised preliminary WMA mixture design binders does occur at WMA process temperatures, the limi- procedure. Phase II included three studies: (1) a laboratory tations on RAP usage included in the preliminary procedure mixture design study, (2) a field validation study, and (3) a were removed. The appendix describing compatibility testing fatigue study. Findings from each of these studies are presented for blended binders was also removed because the compatibil- in the following sections. Detailed analysis of the Phase II ity tests completed during Phase I showed blends of RAP and studies is included in Appendix E. new binders had compatibility values within the range of typ- ical unmodified binders. A requirement that the planned field 3.3.1 Laboratory Mixture Design Study compaction temperature for WMA incorporating RAP should exceed the temperature where the recovered RAP binder has a In the laboratory mixture design study, the revised pre- G*/sin value of 2.2 kPa was added. A note indicating that the liminary WMA mixture design procedure was successfully effectiveness of the RAP in a mixture will depend on the total applied to several WMA mixtures. For the mixtures tested, the time that the mixture is exposed to elevated temperatures was volumetric properties were not sensitive to the WMA process added. This note also recommends that dynamic modulus tests type or the WMA process temperature. Mixture compactabil- should be conducted on samples of plant mix if the mix will be ity, moisture sensitivity, and rutting resistance were sensitive exposed to temperatures above the compaction temperature to the WMA process type and the WMA process temperature. used in design for less than 2 h. Specific findings are presented and discussed below. Details of The workability study found that it was possible to measure the analysis leading to these findings are presented in Section E7 differences in the workability and compactability of WMA as of Appendix E. compared to HMA. The differences, however, were only signif- icant at temperatures that are below typical WMA production 3.3.1.1 Volumetric Properties temperatures. This indicated that it is not necessary to evaluate workability at the planned production temperature. The eval- For a specific combination of aggregates and binder, the uation of coating at the planned production temperature is suf- paired difference statistical analysis presented in Section E7 ficient. Workability and compactability can be evaluated by of Appendix E found little difference in the volumetric prop- using the gyratory compactor to determine the gyrations to erties of properly designed WMA and HMA when the binder 92-percent relative density at the planned field compaction absorption for the HMA was 1.0 percent or less. These find- temperature and a second temperature that is approximately ings are shown graphically in Figures 18 through 21. 54F (30C) lower than the planned field compaction temper- Figure 18 shows the difference in binder absorption for ature. This will permit an assessment of the effect of tempera- WMA compared to HMA for the mixtures included in the mix- ture on the workability and compactability of the mixture. The ture design study. The absorption in the WMA mixtures was on preliminary mixture design and analysis procedure for WMA average 0.1 percent less than the absorption in the HMA mix- was modified accordingly. Evaluation of workability and com- tures. This difference in binder absorption was statistically sig- pactability at the planned production temperature was elim- nificant. It resulted in an average increase in the design VMA for inated from the "design aggregate structure" and "design the WMA of approximately 0.2 percent as shown in Figure 19, binder content" sections of the procedure. The measure of which was also statistically significant. However, it had little gyrations to 92-percent relative density was used to assess the effect on the design binder content and the effective volume of compactability of the mixture. This is evaluated in the "design binder (VBE) for the mixtures as shown in Figures 20 and 21. binder content" section of the procedure. A tentative limit of The average design binder content for the WMA was less than 35 percent of the design gyrations was included based on 0.1 percent lower than the average design binder content for the research reported by NCAT (21). To evaluate workability and HMA while the average design VBE was 0.1 percent higher for compactability, two additional specimens at the optimum WMA as compared to HMA. Neither of these was statistically binder content are compacted at 54F (30C) below the significant. The design VBE for the Advera mixtures was signif- planned field compaction temperature and the number of icantly higher than the design VBE for the HMA.

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35 0.40 Average Difference in Binder Absorption, wt % 0.30 0.20 0.10 0.00 Advera Evotherm Sasobit All WMA -0.10 -0.20 -0.30 -0.40 Mixture Figure 18. Average difference in binder absorption (WMA-HMA) from the mix design study (error bars are 95-percent one-sided confidence intervals). 1.00 0.80 Average Difference in Design VMA, vol % 0.60 0.40 0.20 0.00 Advera Evotherm Sasobit All WMA -0.20 -0.40 -0.60 -0.80 -1.00 Mixture Figure 19. Average difference in design VMA (WMA-HMA) from the mix design study (error bars are 95-percent one-sided confidence intervals).

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36 0.40 Average Difference in Design Binder Content, wt % 0.30 0.20 0.10 0.00 Advera Evotherm Sasobit All WMA -0.10 -0.20 -0.30 -0.40 Mixture Figure 20. Average difference in design binder content (WMA-HMA) from the mix design study (error bars are 95-percent one-sided confidence intervals). 0.60 0.50 Average Difference in Design VBE, vol % 0.40 0.30 0.20 0.10 0.00 Advera Evotherm Sasobit All WMA -0.10 -0.20 -0.30 -0.40 Mixture Figure 21. Average difference in design VBE (WMA-HMA) for the mix design study (error bars are 95-percent one-sided confidence intervals).

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37 3.3.1.2 Compactability temperature of 215F (102C). Figure 24 shows that different WMA processes have different effects on compactability when The revised preliminary procedure uses the gyratory com- the compaction temperature decreases. The Evotherm WMA pactor to evaluate the compactability of the mixture by mea- with RAP was more sensitive to reductions in the compaction suring the number of gyrations required to reach 92-percent temperature compared to the other processes. It should be relative density at the planned field compaction temperature noted that because the Evotherm was blended in the binder at and again at 54F (30C) below the planned field compaction the terminal, the Evotherm concentration as a percentage of temperature. The paired difference statistical analysis pre- the total binder in the mixture was reduced for the RAP mix- sented in Section E7 of Appendix E found that the com- tures, and this may have affected the compactability of the pactability of WMA mixtures (as measured by the increase in Evotherm WMA with RAP mixtures. the gyrations to 92-percent relative density when the com- paction temperature is decreased 54F [30C]) was sensitive to 3.3.1.3 Moisture Sensitivity the process temperature, presence of RAP in the mixture, and the WMA process. Figure 22 shows the effects of temperature Moisture sensitivity is evaluated in both the revised pre- and RAP on the number of gyrations to reach 92-percent rela- liminary WMA mixture design procedure and AASHTO R 35, tive density at the planned field compaction temperature. Fig- Standard Practice for Superpave Volumetric Design for Hot ure 22 shows that the compactability of the WMA at 260F and Mix Asphalt (HMA), using AASHTO T 283, Resistance of 215F (126C and 102C) was no different than that for HMA Compacted Hot Mix Asphalt (HMA) to Moisture-Induced at 310F (154C) indicating that the WMA processes are effec- Damage. The test is performed on samples that have been tive even with 25-percent RAP added. short-term conditioned for 2 h at the compaction temperature. Figures 23 and 24 show the effects of temperature, WMA The paired difference statistical analysis presented in Section process, and RAP on the increase in the gyrations to reach E7 of Appendix E found the dry tensile strength, conditioned 92-percent relative density when the compaction temperature tensile strength, and tensile strength ratio to be significantly is decreased 54F (30C). Figure 23 shows that the combination lower for WMA as compared to HMA. The analysis also found of low process temperature and RAP significantly decreases the that the WMA process affected the tensile strength ratio. Fig- compactability of WMA. The proposed limit in the revised ure 25 shows the effect of the WMA process on dry tensile preliminary mixture design procedure was 25 percent, and this strength. The dry tensile strengths of the WMA mixtures was exceeded by the RAP mixtures at the lower compaction averaged 25 psi (172 kPa) less than the strength of the HMA Without RAP 25-Percent RAP All Mixtures 5.0 4.0 Average Difference in Gyrations to 92-Percent 3.0 2.0 Relative Density 1.0 0.0 260 215 -1.0 -2.0 -3.0 -4.0 -5.0 o Compaction Temperature, F Figure 22. Average difference in gyrations to 92-percent relative density at the compaction temperature (WMA-HMA) for the mix design study (error bars are 95-percent one-sided confidence intervals).

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38 Without RAP 25-Percent RAP All Mixtures 60.0 92-Percent Relative Density for a 54 F Decrease Average Difference in Increase in Gyrations to 40.0 in Compaction Temperature, % o 20.0 0.0 260 215 -20.0 -40.0 -60.0 o Compaction Temperature, F Figure 23. Effect of temperature on the average difference in increase in gyrations to 92-percent relative density for a 54F decrease in compaction temperature (WMA-HMA) for the mix design study (error bars are 95-percent one-sided confidence intervals). Without RAP 25-Percent RAP All Mixtures 80.0 92-Percent Relative Density for a 54 F Decrease Average Difference in Increase in Gyrations to 60.0 40.0 in Compaction Temperature, % o 20.0 0.0 Advera Evotherm Sasobit All WMA -20.0 -40.0 -60.0 -80.0 Process Figure 24. Effect of WMA process on the average difference in increase in gyrations to 92-percent relative density for a 54F decrease in compaction temperature (WMA-HMA) for the mix design study (error bars are 95-percent one-sided confidence intervals).

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39 0.0 Advera Evotherm Sasobit All WMA Average Difference in Dry Tensile Strength, psi -5.0 -10.0 -15.0 -20.0 -25.0 -30.0 -35.0 -40.0 Mixture Figure 25. Effect of WMA process on the average difference in dry tensile strength at 25C (WMA-HMA) for the mix design study (error bars are 95-percent one-sided confidence intervals). mixtures. This reduction was consistent for all WMA processes tive, even though the tensile strength was reduced significantly and similar for the 260F and 215F (127C and 102C) com- due to the reduced aging of the WMA mixture. paction temperatures. Table 24 summarizes the tensile strength ratios for all of the Figure 26 shows the effect of the WMA process on the tensile mixtures included in the study. Most of the WMA mixtures strength ratio. There was no reduction in the tensile strength had tensile strength ratios below the AASHTO M 323 mini- ratio for the Evotherm process, which uses an anti-strip addi- mum of 80 percent. Only mixtures produced with Evotherm 10.0 Average Difference in Tensile Strength Ratio, % 0.0 Advera Evotherm Sasobit All WMA -10.0 -20.0 -30.0 -40.0 -50.0 Mixture Figure 26. Effect of WMA process on the average difference in tensile strength ratio (WMA-HMA) for the mix design study (error bars are 95-percent one-sided confidence intervals).

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40 Table 24. Summary of tensile strength ratios. Design HMA Advera Evotherm Sasobit Gyration Traffic Compaction Compaction Compaction Compaction Mixture Level MESAL RAP TSR, % Temp., F TSR, % Temp., F TSR, % Temp., F TSR, % Temp., F 1 50 < 0.3 Yes 88.3 310 74.5 215 83.0 215 81.7 260 2 50 <0.3 No 92.3 310 95.2 260 93.9 260 94.9 215 3 75 <3 Yes 81.4 310 34.5 260 89.8 260 68.4 260 4 75 <3 No 91.8 310 66.7 215 83.6 260 71.5 215 5 100 <10 Yes 94.7 310 70.6 260 83.7 260 74.0 215 6 100 <10 No 69.8 310 17.9 215 81.5 215 57.8 260 consistently had tensile strength ratios exceeding 80 percent. Nf - Nf HMA ND = WMA 100 (3) Mixture 2, made with Virginia limestone and having a very Nf HMA high binder content, was highly resistant to moisture damage with tensile strength ratios exceeding 92 percent for HMA and where all WMA processes. ND = normalized difference, NfWMA = flow number for the WMA mixture, and 3.3.1.4 Rutting Resistance NfHMA = flow number for the HMA mixture. Rutting resistance in the revised preliminary mixture design The paired difference statistical analysis presented in Sec- procedure is evaluated using the flow number, AASHTO TP 79, tion E7 of Appendix E for the flow number showed the flow Determining the Dynamic Modulus and Flow Number for numbers to be significantly lower for the WMA in compari- Hot Mix Asphalt (HMA) Using the Asphalt Mixture Perfor- son to the HMA. Figure 27 shows the effect of WMA process mance Tester (AMPT). The flow number has also been pro- on the flow number. The average difference was approxi- posed for evaluating the rutting resistance of HMA in NCHRP mately 40 percent and it was similar for all WMA processes. It Project 09-33 (6). Because the flow number is significantly was also similar at both compaction temperatures, as shown different for different gyration levels, the paired difference in Figure 28. The rutting resistance was similar for all WMA statistical analysis used normalized differences defined by processes and both temperatures because the high-temperature Equation 3. Normalized differences were used so that the mix- binder grade for the non-RAP Advera and Evotherm mixtures tures with the higher flow numbers would not dominate the was increased one grade level for the 215F (102C) com- analysis. paction temperature based on the findings from the Phase I 0.0 Advera Evotherm Sasobit All WMA -10.0 Average Difference in Flow Number, % -20.0 -30.0 -40.0 -50.0 -60.0 -70.0 -80.0 Mixture Figure 27. Average normalized difference in flow number (WMA-HMA)/HMA for the mix design study (error bars are 95-percent one-sided confidence intervals).

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41 0.0 260 215 ALL WMA Average Difference in Flow Number, % -10.0 -20.0 -30.0 -40.0 -50.0 -60.0 -70.0 o Compaction Temperature, F Figure 28. Effect of compaction temperature on the average normalized difference in flow number (WMA-HMA)/HMA for the mix design study (error bars are 95-percent one-sided confidence intervals). binder grade study. Increasing the binder stiffness for these used aggregates that far exceeded the angularity requirements conditions increased the measured flow numbers, making the in AASHTO M 323 for this traffic level. The rutting resistance measured flow number difference smaller. of the HMA design for Mixture 4 is slightly less than the design In NCHRP Project 09-33, the following relationship be- traffic level, while the rutting resistance for Mixture 6 is only tween the flow number and the allowable traffic to a rut depth one-half of the design traffic level. The rutting resistance of of 0.5 in. (12.5 mm) was developed (6): the mixtures with RAP is significantly higher than the rutting 0.873 resistance of the mixtures without RAP. Analysis of the data in Fn MESAL = (4) Table 25 suggests that it will be difficult for WMA mixtures 6.222 designed for 10 MESAL or greater to meet the flow number rutting resistance criteria developed in NCHRP Project 09-33. where MESAL = estimated traffic to 12 mm rutting, million equiv- alent single axle loads (MESAL); and 3.3.2 Field Validation Study Fn = flow number per NCHRP 09-33 test conditions, The field validation study addressed several parts of the cycles. revised preliminary mixture design procedure including Table 25 summarizes the allowable traffic from Equation 4 (1) binder grade selection, (2) RAP, (3) short-term oven for all of the mixtures included in the study. Based on the HMA conditioning, (4) specimen fabrication, (5) coating and com- data, the rutting resistance of the two 50 gyration mixtures is sig- pactability, (6) moisture sensitivity, and (7) rutting resistance. nificantly higher than required because both of these mixtures Specific findings for each of these parts are presented and Table 25. Summary of NCHRP 09-33 rutting resistance from flow number testing. Design HMA Advera Evotherm Sasobit Gyration Traffic Compaction Compaction Compaction Compaction Mixture Level MESAL RAP MESAL Temp., F MESAL Temp., F MESAL Temp., F MESAL Temp., F 1 50 < 0.3 Yes 6.1 310 2.4 215 2.0 215 3.5 260 2 50 <0.3 No 2.2 310 1.0 260 1.8 260 1.6 215 3 75 <3 Yes 13.5 310 4.7 260 5.9 260 9.5 260 4 75 <3 No 2.8 310 2.6 215 2.2 260 1.6 215 5 100 <10 Yes 12.3 310 3.5 260 5.0 260 4.1 215 6 100 <10 No 4.9 310 3.9 215 3.9 215 5.9 260

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42 Table 26. Summary of continuous grading of recovered binders. Production Continuous Grade Temperature Project Process Temperature (C) (F) High Intermediate Low Specified NA 58.0 19.0 28.0 Control 280 59.3 14.2 30.6 Colorado I-70 Advera 250 60.0 13.7 31.6 Evotherm 250 61.3 14.1 31.1 Sasobit 250 63.9 15.1 29.9 Specified NA 58.0 16.0 34.0 Yellowstone Control 325 60.0 11.1 34.1 National Park Advera 275 56.3 8.9 36.2 Sasobit 275 60.7 10.1 35.6 New York Specified NA 64.0 22.0 28.0 Route 11 LEA 210 60.5 14.0 31.1 Specified NA 64.0 25.0 22.0 Pennsylvania Control 320 67.7 22.0 24.6 SR2007 Evotherm 250 67.2 22.0 24.9 Specified NA 64.0 25.0 22.0 Control 310 66.6 24.1 22.5 Pennsylvania Advera 250 67.0 22.9 24.1 SR2006 Gencor 250 67.5 21.7 25.7 LEA 210 63.2 21.6 25.4 Sasobit 250 72.9 23.3 22.5 Monroe, North Specified NA 70.0 28.0 22.0 Carolina Astec 275 71.5 23.7 23.9 discussed below. Details of the analysis leading to these find- Advera for the Yellowstone National Park project was 1.7C ings are presented in Section E8 of Appendix E. lower, LEA for the NY Route 11 project was 3.5C lower, and LEA for the Pennsylvania SR2006 project was 0.8C lower. Table 27 summarizes the average difference in continuous 3.3.2.1 Binder Grade Selection grade temperatures for WMA as compared to HMA. The high- Recovered binder grading and estimates of rutting using temperature grade changes are significantly less than estimated dynamic modulus test data from plant mixtures and the from the RTFOT experiment. From the RTFOT experiment, MEPDG rutting model were used to validate the high- the estimated reduction in high-temperature grade for 50F temperature grade bumping table developed from the RTFOT and 100F (28C and 56C) reductions in production temper- experiment (1). Table 26 summarizes the continuous grades ature for a typical asphalt binder having an aging index of 2.4 for the recovered binders from each of the validation mixtures. are 2.8C and 5.6C, respectively. For the field data--excluding Table 26 includes the specified binder grade as well as the Sasobit, which increases the high-temperature grade of the recovered grade. In all cases, the low and intermediate temper- binder--an approximately 50F (28C) reduction in pro- ature properties for the WMA processes comply with the duction temperature resulted in less than a 1C decrease in binder grade specified for the project. There are three cases high-temperature grade, while an approximately 100F (56C) where the high-temperature grade was lower than specified: reduction in production temperature resulted in approximately Table 27. Summary of average difference in continuous grade temperatures for WMA compared to HMA. Average Average Difference in Continuous Grade Difference in Temperature Process Number Production (C) Temperature High Intermediate Low (F) Advera 3 46.7 0.9 1.3 1.6 Evotherm 2 50.0 0.8 0.0 0.4 LEA 1 100.0 3.4 2.5 2.9 Plant Foaming 1 60.0 0.9 2.4 3.2 Sasobit 3 46.7 3.9 0.3 0.3

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43 a one-half grade decrease in the high-temperature grade for 1. The predicted rut depths for the control mixtures are rea- one LEA project. The low-temperature grade changes, on the sonable for the design traffic levels. The design traffic level other hand, are greater than estimated from the RTFOT exper- of the Colorado project was 10 million equivalent single iment. From the RTFOT experiment, the estimated improve- axle loads (MESAL), and the estimated rut depth is 0.11 in. ment in the low-temperature grade for 50F and 100F (28C (2.8 mm). The design traffic level of the Yellowstone and 56C) reductions in production temperature are 0.5C National Park and New York projects was 3 MESAL, and and 1.0C, respectively. For the field data--excluding Sasobit, the estimated rut depth was 0.09 in. (2.3 mm) in both which increases the low-temperature grade of the binder-- cases. an approximately 50F (28C) reduction in production 2. For the Colorado I-70 project, the predicted rutting for temperature resulted in an average improvement in the low- the Advera and Evotherm mixtures was slightly greater temperature grade of the binder of 1.5C, while an approxi- than the control while the predicted rutting for the Saso- mately 100F (56C) reduction in production temperature bit mixture was slightly less than the control. The pre- resulted in a 2.9C improvement in the low-temperature grade dicted rutting for the Advera and Evotherm mixtures was for one LEA project. Based on the recovered binder testing, it only 0.13 in. (3.3 mm). does not appear that the binder grade should be changed when 3. For the Yellowstone National Park project, the predicted using WMA as long as the production temperature is not rutting of the Sasobit and Advera mixtures was essentially decreased by more than 100F (56C). the same as the control at the design traffic level. Rutting for the Colorado I-70, Yellowstone National Park, 4. For the New York project, the predicted rutting for the and New York Route 11 projects was predicted using the PG 64-28 LEA mixture was 0.11 in (2.8 mm), while the Excel spreadsheet, E*Rutting.xls, developed by Arizona State predicted rutting for the PG 70-22 LEA mixture is 0.05 in. University for the dynamic modulus simple performance test (1.3 mm). (22). This spreadsheet rapidly performs asphalt layer rutting predictions using the calibrated rutting model contained in The differences in estimated rutting resistance from field- the MEPDG (1). The mixture dynamic modulus master curve mixed WMA do not support the binder grade bumping rec- is the required material property for this analysis. Master ommendations developed from the RTFOT experiment. For curves were developed for plant mixtures in accordance with production temperature decreases as large as 100F (56C), AASHTO PP 61. The rutting estimates for these three proj- the estimated rutting for a mixture produced as WMA is only ects are shown in Figures 29, 30, and 31. These figures show approximately 25 percent greater than that for the same mix- the following: ture produced as HMA. Control Sasobit Advera Evotherm 0.60 0.50 Predicted Rut Depth, in 0.40 0.30 0.20 0.10 0.00 0.1 1 10 100 Traffic, Million ESALs Figure 29. Predicted rutting for the Colorado I-70 project.

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44 Control Sasobit Advera 0.60 0.50 Predicted Rut Depth, in 0.40 0.30 0.20 0.10 0.00 0.1 1 10 100 Traffic, Million ESALs Figure 30. Predicted rutting for the Yellowstone National Park project. PG 64-28 PG 64-28 LEA PG 70-22 LEA 0.60 0.50 Predicted Rut Depth, in 0.40 0.30 0.20 0.10 0.00 0.1 1 10 100 Traffic, Million ESALs Figure 31. Predicted rutting for the New York project.

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45 Table 28. Measured and estimated fully blended dynamic modulus for the Monroe, North Carolina, mixture produced with the Astec Double Barrel Green process and 30-percent RAP. Recovered Hirsch Measured Ratio of Temperature Frequency Binder G* Estimated E* E* Measured to (F) (Hz) (psi) (ksi) (ksi) Estimated 39.2 10.0 15,681 2,145 2,344 1.09 39.2 1.0 7,339 1,755 1,785 1.02 39.2 0.1 2,839 1,281 1,216 0.95 68.0 10.0 2,014 1,123 1,083 0.96 68.0 1.0 596 663 626 0.94 68.0 0.1 145 328 316 0.96 104.0 10.0 100 270 201 0.74 104.0 1.0 19 114 80 0.70 104.0 0.1 3 51 38 0.74 3.3.2.2 RAP the averages of the measured data fall within the prediction intervals for the Hirsch model, the plant-mixed modulus is Only one of the validation mixtures--the Monroe, North not significantly different from the fully blended modulus, Carolina, mixture--included RAP. This mixture used PG 64-22 indicating that the mixing of the RAP and new binders is binder with 30-percent RAP to produce a mixture meeting acceptable. the requirements for PG 70-22 binder. The mixture was pro- duced at 275F using the Astec Double Barrel Green process. For this mixture, the mixing analysis--based on dynamic 3.3.2.3 Short-Term Oven Conditioning modulus testing of the plant mixture described earlier in the laboratory RAP study (see Section 3.1.4)--was conducted to For WMA and HMA, short-term oven conditioning of 2 h validate that RAP and new binder mix in field-produced WMA. at the compaction temperature was determined by comparing The results of this analysis are summarized in Table 28 and properties of field-mixed, laboratory-compacted specimens shown in Figure 32. The error bars in Figure 32 are 95-percent with properties of laboratory-mixed, laboratory-compacted confidence intervals for the measured data and 95-percent specimens for the mixtures from the Colorado I-70 project. prediction intervals for the Hirsch model predictions. Since The properties that were compared were maximum specific Measured Estimated for Complete Mixing 10000 Dynamic Modulus, ksi 1000 100 10 1 39.2F, 10 Hz 39.2F, 1 Hz 39.2F, 0.1 Hz 104F, 0.1 Hz 68F, 10 Hz 68F, 0.1 Hz 104F, 10 Hz 104F, 1 Hz 68F, 1 Hz Testing Condition Figure 32. Comparison of measured and estimated fully blended dynamic modulus for the Monroe, North Carolina, mixture produced with the Astec Double Barrel Green process and 30-percent RAP.

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46 Field Mix Compaction Temp 2 h 2.600 2.550 Maximum Specific Gravity 2.500 2.450 2.400 2.350 2.300 Mixture/Process Figure 33. Comparison of maximum specific gravity for all validation mixtures. gravity, indirect tensile strength, and dynamic modulus. To mum specific gravity of the laboratory and field mixtures is the validate this short-term conditioning, maximum specific grav- same, indicating that the binder absorption is the same for the ity and indirect tensile strength measurements were made on laboratory and field mixtures. The aggregate water absorption all of the validation sections. ranged from 0.5 percent for the Pennsylvania SR2007 mixtures Figures 33 and 34 compare the maximum specific gravity to 2.5 percent for the Yellowstone National Park mixtures. and tensile strength data for all of the validation mixtures. The Figure 34 shows differences in indirect tensile strength for error bars shown in Figure 33 are the single operator d2s pre- the field mixtures minus the laboratory mixtures. The error cision from AASHTO T 209. These data show that the maxi- bars for the average difference in this figure are 95-percent con- 45 35 IDT Strength Differences, psi 25 15 5 YNP Control YNP Sasobit Average PA SR2006 Gencor PA SR2007 Evotherm CO I-70 Evotherm CO I-70 Advera PA SR2007 Control PA SR2006 Control PA SR2006 Sasobit PA SR2006 LEA CO I-70 Control CO I-70 Sasobit YNP Advera Monroe NC Astec PA SR2006 Advera -5 -15 -25 Mixture/Process Figure 34. Differences in indirect tensile strength between field mixes and laboratory mixes short-term conditioned for 2 h at the compaction temperature.

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47 fidence intervals for a paired t-test comparison. Since the error bars capture zero, this indicates that the WMA mixtures are bars for the average difference do not capture zero, the tensile very similar to the HMA that they were based on. These find- strength of the field-mixed specimens is statistically higher ings confirm the findings of the mixture design study that the than the tensile strength of the laboratory-mixed specimens. volumetric properties of properly designed WMA and HMA This indicates that short-term conditioning of 2 h at the com- mixtures are very similar. paction temperature provides less aging on average than the The WMA mixture design procedure uses process-specific, field mixtures. The findings from this analysis appear to have specimen-fabrication procedures to simulate the WMA process. been biased by the data from the Pennsylvania SR2006 project. For plant foaming systems this requires the production of This project provided one-third of the data for the analysis, foamed asphalt in the laboratory. At the time NCHRP Project and the field mixtures for this project had consistently higher 09-43 was completed, the Wirtgen WLB-10 laboratory foaming tensile strength than the laboratory-prepared mixtures. The machine was the only commercially available laboratory foam- average difference for all projects was 9 psi (48 kPa); not con- ing equipment. An evaluation of the feasibility and practicality sidering the Pennsylvania SR2006 project, the average differ- of designing foamed asphalt WMA mixtures in the laboratory ence was only 1.4 psi (9.8 kPa). Considering the bias from this using the Wirtgen WLB-10 was conducted at the University of project, the recommended short-term oven conditioning in Wisconsin-Madison. The evaluation was conducted for the the final WMA mixture design procedure was kept at 2 h at the Gencor WMA process from the Pennsylvania SR2006 project compaction temperature. and for the Astec WMA process from the Monroe, North Carolina, project. The following describes the process used to fabricate foamed asphalt using this equipment. 3.3.2.4 Specimen Fabrication Operation of the Wirtgen WLB-10 foaming machine In the validation study, the WMA specimen-fabrication requires asphalt binder temperatures above 320F (160C), procedures were used to fabricate specimens for several WMA thus the mixing temperature of the foamed asphalt mixture is processes including Advera, Astec Double Barrel Green, controlled by the temperature of the aggregates. It is assumed Evotherm DAT, Gencor Ultrafoam, LEA, and Sasobit. Fig- that the asphalt binder will quickly revert to the mixing tem- ure 35 shows the difference in air voids at Ndesign between the perature when it comes in contact with the aggregate. The mass WMA mixture and either the HMA job mix formula or the cor- of foamed asphalt that is required is calculated based on the responding HMA control mixture. The average difference over weight of the aggregates. The aggregate and mixing bucket are all projects is less than 0.03 percent. The error bars shown for placed under the foaming head, and the foamed asphalt is shot the average are 95-percent confidence levels. Since the error into the bucket as shown in Figure 36. The flow of foamed 1.5 1.0 Air Void Difference (WMA-HMA), % 0.5 0.0 YNP Sasobit CO I-70 Sasobit CO I-70 Evotherm PA SR2006 LEA CO I-70 Advera PA SR2006 Sasobit PA SR2007 Evotherm PA SR2006 Gencor YNP Advera NC Astec Average PA SR2006 Advera -0.5 -1.0 -1.5 -2.0 Project/Mixture Figure 35. Differences in air voids at Ndesign between WMA and corresponding HMA mixtures.

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48 Figure 36. Introducing foamed asphalt to mixing bucket. Figure 38. Foamed asphalt mixture after 90 s mixing asphalt into the mixing bucket is metered using a flow con- time. troller. Based on a known flow rate, the user prescribes the time required to obtain the appropriate quantity of asphalt binder. The mixing bucket, with the foamed asphalt sitting on top from 1.0 to 3.0 percent. To accommodate this difference, of the aggregate, is immediately transferred to the laboratory the existing flow controller was replaced with one that was mixer, mixed for 90 s, and transferred to a shallow pan. Illus- smaller and more precise. Operation of the machine for trations of the foamed asphalt mixture before and after the WMA applications was possible; however, due to the low 90 s mixing time are provided in Figures 37 and 38, respec- percentage of water required for WMA, the operation of the tively. After mixing, the foamed mix is short-term aged at the flow controller was approaching its minimum control tol- compaction temperature for 2 h and compacted. erance. The more precise flow controller was selected with The operation of the foaming machine presents some the intent of delivering a more consistent foam at the water practical concerns for WMA laboratory mixture design. content used in the WMA field production. The machine is designed to produce large quantities of The machine is intended for preparation of samples of foam- material. This was an issue especially in trying to prepare stabilized asphalt base course and cold in-place recycling. samples for evaluation of the maximum specific gravity. The These applications require foamed asphalt with water con- sample size to conduct the maximum specific gravity test for tents above 10 percent by weight of the asphalt binder. In 9.5-mm mixtures is 1,000 g. A timer is used to control the contrast, the water content for WMA applications ranges amount of foamed asphalt shot into the bucket. Because of the flow rate of the foaming head, the machine provides the required 50 to 60 g of foamed asphalt in a fraction of a sec- ond. This amount of time is insufficient for the machine to produce a consistent asphalt foam, introducing potential reproducibility issues into the results. Use of this machine for small batches of aggregate is not recommended; instead, large batch sizes should be produced and then split for the various tests required. At times the air line in the machine becomes clogged, so instead of foamed asphalt, an asphalt/water mix is produced. This problem has been encountered with both the neat PG 64-22 binders from the Pennsylvania and North Car- olina projects and Styrene-Butadiene-Styrene (SBS) mod- ified PG 76-22 binder used in another project. The valve that controls the flow of the air at the foaming head becomes clogged regularly, requiring disassembly and cleaning of the head. This issue occurred on three separate occasions while Figure 37. Foamed asphalt before mixing. preparing samples for this project, each time resulting in a

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49 delay of 2 to 3 h. The regularity with which this problem The compactability data in Table 29 indicate that the occurs suggests that redesign of the foaming head of the Colorado I-70, Pennsylvania SR2007, and Monroe, North machine may be needed for continuous use as a mix design Carolina, mixtures were easy to compact. National Center for tool. The problem was more severe with the SBS modified Asphalt Technology (NCAT) reported average gyrations to binder. After production of approximately 20 samples, the 92-percent relative density of 35 and 20 percent of Ndesign for machine clogged and had to be taken apart and fully cleaned dense graded HMA mixtures with coarse and fine grada- before further use. tions (21). At the compaction temperature, the gyrations to Finally, the preparation of the foamed mixes requires a sig- 92-percent relative density for these three projects ranged nificant amount of technician time and expertise. Each mix from 20 to 40 percent of Ndesign. For the other two projects, design evaluated for this project required three separate Yellowstone National Park and Pennsylvania SR2006, the days for foamed mix production. mixtures were less compactable. The Yellowstone National Park mixtures were designed using the Hveem method and therefore had much lower binder content than they would 3.3.2.5 Coating and Compactability have if they had been designed using AASHTO R 35 or the As required by the revised preliminary WMA mixture revised preliminary WMA mixture design procedure. The air design procedure, coating and compactability were measured void content at 75 gyrations for the HMA control mixture for on all of the WMA mixtures in the field validation study. this project was 6.8 percent. The Pennsylvania SR2006 con- Coating was evaluated using AASHTO T 194, which counts trol HMA mixture could not be verified by the research team. the number of fully coated coarse aggregate particles in the mix- At the optimum binder content from the approved mix design, ture. Compactability was evaluated on the basis of the number the air void content at 75 gyrations was 6.2 percent, well above of gyrations necessary to achieve 92-percent relative den- the design value of 4.0 percent. sity at the planned field compaction temperature and again at The effect of temperature on the compactability of the mix- 54F (30C) below the planned field compaction temperature. tures is quantified by the percent increase in the number of Table 29 summarizes the results of the evaluation of coating gyrations to 92-percent relative density. The revised prelimi- and compactability. nary WMA mixture design procedure limits this increase to Coating was 100 percent for all of the mixtures that were 25 percent. All of the WMA mixtures included in the field val- mixed using a planetary mixer with a wire whip. The percent- idation study met this criterion. There were no reported work- age of coating was lower for the two mixtures mixed with a ability issues for any of the field mixtures. bucket mixer and particularly low for the North Carolina mix- ture, which had about 16 percent of its total binder content con- 3.3.2.6 Moisture Sensitivity tributed by the RAP. All of the mixtures were prepared using 90 s of mixing. Apparently, the bucket mixer is less efficient and Moisture sensitivity was evaluated for all of the validation requires longer mixing times for equivalent coating. There were mixtures using AASHTO T 283. Specimens were compacted no reported coating issues for any of the field mixtures. to a target air void content of 7.0 percent 0.5 percent using Table 29. Coating and compactability of field validation mixtures. Temperature, F Gyrations to 92% of Gmm At At Gyration Project Process Coating Mix Compact Compact Compact Increase, Temp Temp 54F % Advera 250 230 1001 15 18 20 Colorado I-70 Evotherm DAT 250 230 1001 20 23 15 Sasobit 250 230 1001 19 22 16 Yellowstone Advera 275 250 1001 69 -- -- National Park Sasobit 275 245 1001 > 75 -- -- PA SR2007 Evotherm DAT 250 230 1001 20 24 20 Advera 250 230 1001 47 48 2 Gencor PA SR2006 and 250 230 812 35 38 9 Ultrafoam GX PA SR2012 LEA 210 195 1001 50 52 4 Sasobit 250 230 1001 51 59 16 Monroe, North Astec Double 275 260 652 16 16 0 Carolina Barrel Green 1 Mixed with Blakeslee planetary mixer with wire whip. 2 Mixed with bucket mixer.

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50 Table 30. Summary of AASHTO T 283 results. Conditioned Tensile Production Compaction Dry Tensile Tensile Strength Project Process Temperature Temperature Strength Strength Ratio (F) (F) (psi) (psi) (%) Control 280 260 88.3 80.4 91 Advera 250 230 80.3 0.0 0 Colorado I-70 Evotherm 250 230 71.9 32.4 45 Sasobit 250 230 82.8 58.8 71 Control 325 315 110.2 87.1 79 Yellowstone Advera 275 250 86.4 65.7 76 National Park Sasobit 275 245 95.4 72.5 76 Pennsylvania Control 320 300 102.3 92.1 90 SR2007 Evotherm 250 230 86.0 79.1 92 Control 310 275 104.6 65.6 63 Advera 250 230 98.3 34.8 35 Pennsylvania Gencor 250 230 97.3 42.1 43 SR2006 LEA 210 195 103.7 86.1 83 Sasobit 250 230 97.1 51.8 53 Monroe, North Astec 275 260 164.0 127.7 78 Carolina the binder content from the job mix formula or the binder 2 h at the compaction temperature. The flow number test was content determined from the mix design verification. Per the conducted at the 50-percent reliability high pavement temper- preliminary WMA mixture design procedure the mixture was ature from LTPPBind 3.1 for the project location. As recom- conditioned 2 h at the compaction temperature. Table 30 mended in NCHRP 09-33, the flow number testing used summarizes the results. unconfined specimens with repeated deviator stress of 87 psi Nine of the 11 WMA mixtures and 2 of the 4 HMA control (600 kPa) and contact deviator stress of 4.4 psi (30 kPa). mixtures have tensile strength ratios less than 80 percent. The Table 31 summarizes the results. effect of the WMA process on moisture sensitivity is mixture The allowable traffic in Table 31 was calculated using the and process specific. For the Colorado I-70 project, the tensile relationship between flow number and allowable traffic to an strength ratio was reduced by all of the WMA processes. For estimated rut depth of 0.5 in. (12.5 mm) developed in NCHRP this project, the Advera specimens failed during the condition- Project 09-33 (see Equation 4) and discussed earlier in the mix- ing processes. The WMA processes had no effect on the tensile ture design study (see Section 3.3.1.4). Three of the mixtures strength ratio for the Yellowstone National Park and Pennsyl- do not meet the rutting resistance criteria: the Advera and LEA vania SR2007 projects. For the Pennsylvania SR2006 project, mixtures for the Pennsylvania SR2006 project and the Monroe, the Advera, Gencor, and Sasobit WMA processes reduced the North Carolina, mixture. The North Carolina mixture has a tensile strength ratio, while the LEA process increased it. The very high design VMA of 17.6 percent, indicating that the rut- LEA process includes an anti-strip that is added to the binder ting resistance of this mixture could be improved by decreas- at the plant. For the plant foaming processes, the AASHTO ing the design VMA. In NCHRP Project 09-33, a maximum T 283 results may have been adversely affected by the poorer VMA of 17 percent has been recommended for 9.5-mm mix- coating obtained with the bucket mixer when simulating these tures to limit the effective binder content of the mixture and processes. provide adequate rutting resistance. The rutting resistance of the Hveem designed mixtures from the Yellowstone project is very high. Also, the rutting resistance of the 50-gyration mix- 3.3.2.7 Rutting Resistance tures from the Pennsylvania SR2007 project is high consider- Rutting resistance was evaluated for all of the field validation ing the design traffic level. These mixtures were produced with mixtures using the flow number test, AASHTO TP 79. Speci- highly angular manufactured sand and crushed stone. mens were compacted to a target air void content of 7.0 per- Table 32 compares the rutting resistance of the WMA mix- cent 0.5 percent using the job mix formula binder content or tures to that of the HMA control mixtures. The Gencor mix- the binder content determined from the mix design verifica- ture from the Pennsylvania SR2006 project was not included tion. All of the specimens were within this tolerance except for in this analysis because the air void content of the specimens the Gencor mixture for the Pennsylvania SR2006 project, for this mixture was much lower than the air void content of which was compacted to 4.5 percent. Per the preliminary all of the others. The rutting resistance for all WMA processes WMA mixture design procedure, the mixture was conditioned except Sasobit is less than the HMA control due to the lower

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51 Table 31. Summary of flow number and rutting resistance results. NCHRP Design Production Compaction Test 09-33 Traffic Flow Project Process Temperature Temperature Temperature Allowable Level Number (F) (F) (F) Traffic (MESAL) (MESAL) Control 280 260 321 24.8 Advera 250 230 165 13.9 Colorado I-70 < 10 101 Evotherm 250 230 154 13.0 Sasobit 250 230 409 30.7 Control 325 315 687 48.2 Yellowstone <3 Advera 275 250 106 459 33.9 National Park (estimated) Sasobit 275 245 1089 72.2 Pennsylvania Control 320 300 124 10.8 < 0.3 126 SR2007 Evotherm 250 230 93 8.4 Control 310 275 42 4.2 Advera 250 230 27 2.8 Pennsylvania <3 Gencor 250 230 121 1041 9.31 SR2006 LEA 210 195 21 2.3 Sasobit 250 230 54 5.2 Monroe, North < 10 Astec 275 260 136 38 3.9 Carolina 1 Specimens compacted to 4.5-percent air voids instead of 7.0 percent. short-term conditioning temperatures. The rutting resis- temperature, which represents the stiffness of WMA mixtures tance decreases approximately 6 percent for every 10F (5.5C) at the time of construction, generally fail criteria that are based reduction in compaction temperature. Sasobit increases the on 4 h of conditioning at 275F (135C). To extend existing high-temperature stiffness of the binder, resulting in improved performance criteria to WMA, a two-step loose mix condition- rutting resistance. ing procedure should be considered. This two-step procedure would include 2 h of conditioning at the compaction temper- ature to simulate the absorption and binder stiffening that 3.3.3 Feasibility of Using a occurs during construction, followed by aging at a representa- Two-Step Aging Process tive high in-service pavement temperature to simulate early for Performance Testing stiffening during the service life of the pavement. The represen- Criteria for evaluating rutting resistance using the flow tative in-service pavement temperature should be in the range number and other tests are generally based on mixtures that of 120F to 150F (50C to 65C) depending on the project have been laboratory conditioned for 4 h at 275F (135C) location and based on the 50-percent reliability high pave- in accordance with AASHTO R 30. Although it is generally ment temperature from LTPPBind 3.1. The conditioning time accepted that this conditioning represents the binder stiffening should be selected such that typical HMA mixtures reach that occurs during construction, it appears from the short- approximately the same stiffness after the two-step condition- term conditioning study that this level of conditioning is more ing procedure as they reach after 4 h of conditioning at 275F representative of the stiffness of the binder after some short (135C). This additional study was beyond the scope of period in service. The findings from the mix design study and NCHRP Project 09-43, but an analysis of the feasibility was the field validation study show that the rutting resistance of performed using loose mix aging data collected under NCHRP WMA mixtures that are conditioned 2 h at the compaction Project 09-13 (23). NCHRP Project 09-13 included data that could be analyzed to investigate the effect of aging at in-service pavement temper- Table 32. Summary of average atures compared to HMA mixing and compaction tempera- difference in allowable traffic tures. With the database reported for NCHRP Project 09-13, WMA compared to HMA. dry tensile strengths were collected on Superpave gyratory- Average Average compacted samples for five mixtures prepared for four loose Difference in Difference in mix aging conditions: Process Number Compaction Allowable Temperature Traffic (F) (%) Unaged, Advera 3 46.7 35 2 h at 275F (135C), Evotherm 2 50.0 35 LEA 1 80.0 45 4 h at 275F (135C), and Sasobit 3 48.3 +32 16 h at 140F (60C).

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52 Dry tensile strengths were measured after two compacted ing at 275F (135C) through loose mix oven conditioning at sample conditioning periods: 0 h and 96 h at room tempera- representative in-service temperatures. Since the suggested ture. The database extracted from this study is presented in two-step procedure would include 2 h of conditioning at the Section E9 of Appendix E. compaction temperature to simulate the absorption and binder In analyzing this data, the data for the two compacted mix stiffening that occurs during construction, the in-service aging aging conditions were combined. Figure 39 shows plots of the step will require less than 16 h of loose mix aging at the repre- ratio of the average strength of the conditioned specimens to sentative in-service temperature. the unaged specimens. From Figure 39, it appears that there is an error in the unaged data for the Maryland mixture because 3.3.4 Fatigue Study the ratios of the conditioned to unaged tensile strengths are always less than one, indicating that the mixture softens upon One of the potential benefits of WMA mixtures is improved loose mix conditioning, which is not rational. Individual spec- fatigue characteristics in comparison to HMA mixtures due to imen air voids were not reported, but the text stated that the air the reduced aging that occurs during plant mixing at the lower void tolerance for specimen fabrication was 7.0 1.0 percent. WMA process temperatures. The fatigue study was designed Because of the questionable unaged data for the Maryland to evaluate the fatigue resistance of WMA in comparison to mixture, the unaged data were eliminated from the analysis. HMA. The study was conducted on the two mixtures summa- Figure 40 shows the average tensile strength for the remaining rized in Table 33. three loose mix aging conditions: 2 h at 275F (135C), 4 h at For each mixture, specimens were prepared as HMA and 275F (135C), and 16 h at 140F (60C). The error bars in Fig- WMA using three processes: Advera, Evotherm G3, and ure 40 are 95-percent confidence intervals based on the mea- Sasobit. The fatigue resistance of the eight mixtures was then sured data for each mixture. Figure 40 shows that the tensile characterized using continuum damage theory. Continuum strengths for 16 h at 140F (60C) are somewhat higher than damage theory is a new, powerful tool for characterizing the the other aging conditions, indicating that this aging condition fatigue behavior of asphalt concrete in a thorough and rational stiffens the mixture somewhat more than the shorter aging way with relatively limited amounts of testing. Continuum times at the higher temperatures. This was confirmed by a two- damage theory has recently been applied to the fatigue response way analysis of variance that is presented in Section E9 of of asphalt concrete mixtures by several researchers (24, 25). Appendix E. Recently a practical approach for using continuum damage This analysis shows that it is possible to reach the level of theory to quickly and accurately characterize the fatigue resis- binder stiffening caused by 4 h of loose mix oven condition- tance of asphalt concrete mixtures was developed (26). In this 1.8 Nevada Alabama Colorado Maryland Texas 1.6 Aged/Unaged Tensile Strength Ratio 1.4 1.2 1.0 0.8 0.6 0.4 2 h at 135C 4 h at 135C 16 h at 60C Aging Condition Figure 39. Effect of loose mix aging on tensile strength (23).

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53 Nevada Alabama Colorado 300 Maryland Texas 250 Dry Tensile Strength, psi 200 150 100 50 0 2 h at 135C 4 h at 135C 16 h at 60C Aging Condition Figure 40. Comparison of tensile strengths for loose mix aging conditions (23). Table 33. Design properties for fatigue study mixtures. Mix Number 4 6 Design Gyrations 75 100 Aggregate Water Absorption, % 1.6 1.3 RAP No No NMAS 9.5 mm 9.5 mm Coarse PA Gravel VA Diabase Aggregate PA Limestone VA Diabase Sources Fine PA Gravel Natural Sand RAP None None Sieve Size, mm 12.5 100 100 9.5 98 98 4.75 63 53 2.36 44 40 Gradation 1.18 32 31 0.6 22 22 0.3 12 12 0.15 5 7 0.075 3.0 4.8 FAA 43.5 48.3 Aggregate CAA 98/95 100/100 Properties Flat & Elongated 7.4 7.6 Sand Equivalent 80.2 76.7 Binder Content, wt % 6.3 5.7 Effective Binder Content, wt % 5.3 4.7 Air Voids, vol % 4.3 3.7 Voids in Mineral Aggregate, vol % 16.3 15.1 Effective Binder Content, vol % 12.0 11.4 Voids Filled With Asphalt, % 73.6 75.5 Dust to Effective Asphalt Ratio 0.6 1.0