Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios (2020)

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127 Chapter 5 presents the practical tools developed in this study to evaluate the effectiveness of a recycling agent initially and with aging for mixtures with high RBRs. These proposed tools are also included in the draft AASHTO standard practice in Appendix I. 5.1 Component Materials Selection Guidelines Based on the results presented in Chapter 3 and Chapter 4 from Phase 2 and Phase 3, com- ponent materials selection and proportioning guidelines are proposed in Table 32. These guide- lines are meant to be used as a system, with suggested thresholds to assist in selecting component materials for a high RBR mixture with a recycling agent. For comparison, DTc and PGH values are provided in Table 33 for the base and recycled binders in this study. The PGH thresholds after short-term aging by RTFO are based on the wide variety of materials (and climates) evaluated in this study, as shown in Table 1. The PGH limit for RAP precludes the use of TX RAP, and the PGH limit for RAS precludes the use of TOAS sources based on binder/binder blend and corresponding mixture results gathered throughout this study and highlighted in Chapter 4. The DTc thresholds after both short- and long-term aging by RTFO and 20-h PAV were selected to include the WI PG 58–28 base binder and WI RAP but preclude the TX PG 64–22 base binder and TX RAP due to consistent results across binder and mixture tests that highlighted good and poor performance from these materials, respectively. The NV PG 64–28P base binder was not considered since it is polymer modified and may require additional parameters to capture the corresponding adequate performance. Figure 91 provides further evidence of the relatively poor quality of the TX PG 64–22 base binder (DTc of −4.6) compared to the IN PG 64–22 base binder (DTc of −1.2) of the same PG grade. The DOT control binder blend (without recycling agent) was graded as a PG 82.3–13.3 and PG 77.9–21.3 for the TX and IN base binders, respectively. The selected doses in Figure 91 restored the PG of these blends to a target PG 64–22, and the blends with the IN PG 64–22 base binder required significantly lower recycling agent doses and exhibited much less negative DTc values than the same blends with the TX PG 64–22 base binder. Figure 92 again highlights the effect of a poor-quality base binder by comparing binder blends with these same two base binders (TX PG 64–22 and IN PG 64–22) in Black space, illus- trating similar |G*| values but increased δ values (and thus lower G-R values) for the blends with IN PG 64–22 base binder even at lower recycling-agent doses. Figure 93 illustrates the ultimate impact of a poor-quality base binder on mixture cracking performance, with the IN mixtures at lower recycling-agent doses exhibiting better performance (higher FI values) after LTOA, although similar FI values were realized for some recycling-agent types (V1) after STOA at the selected dose. C H A P T E R 5 Practical Tools for Evaluation of High RBR Binder Blends and Mixtures

128 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios Test Parameter Component Material Base (Virgin) Binder Recycled Material (RAP) Recycled Material (RAS) Recycling Agent High-Temperature, Short-Term Aginga DSR PGH < 64°C < 100°C < 150°C — Low-Temperature, Short- and Long-Term Agingb BBR ΔTc > −3.5°C > −7.5°C — — Proportioning RBR — < 0.5 RBR (RAPBR+RASBR) < 0.15 RASBR — Dose — — — < maximumc without sacrificing rutting resistance NOTE: — = not applicable. aOriginal binder and RTFO aged by AASHTO T 240. b20-h PAV aging at 100°C by AASHTO R 28. cPercentage of total binder in the blend/mixture. Table 32. Component materials selection and proportioning guidelines. Material Source PG Continuous PGH (°C) Continuous PGL (°C) ΔTc (°C) Virgin/Base Binders TX 64-22 68.2 −24.6 −4.6 NH 64-28 66.9 −28.0 +1.2 NV 64-28Pa 65.6 −30.7 −3.6 IN 64-22 66.2 −25.3 −1.2 IN 58-28 59.9 −28.2 −8.0 MN 58-28 58.6 −28.0 +0.1 WI 58-28 59.4 −28.6 −3.4 WI 52-34 52.3 −34.2 +0.4 DE 64-28 66.5 −29.0 +0.1 Recycled Materials RAP TX — 106.6 −2.4 −9.8 IN 88-10 90.4 −13.7 −6.2 NV 82-16 84.4 −20.4 −3.4 NH 88-16 90.2 −20.6 −2.1 WI 82-10 83.5 −10.9 −7.3 DE 82-10 86.2 −13.8 −4.4 MWAS TX — 130.7 — — IN — 123.3 — — DE — 146.0 — — TOAS TX — 178.0 — — CA — 166.0 — — NOTE: — = not available because RAS binders were very stiff and did not meet the m-value criteria (>0.3), even at high testing temperatures. aPolymer-modified binder. Table 33. Characteristics of the base binders and recycled binders.

Figure 92. DTc threshold: binder blend Black space. Figure 91. DTc threshold: recycling-agent dose.

130 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios 20.0 Figure 93. DTc threshold: mixture cracking resistance.

Practical Tools for Evaluation of High RBR Binder Blends and Mixtures 131 Finally, Figure 94 and Figure 95 show the combined effect of using a softer base binder (WI PG 52–34 with a lower PGH) that is also of higher quality (DTc = +0.4) compared to the WI PG 58–28 (DTc = −3.4) used in the other binder blends and corresponding mixtures. This combination of a higher-quality and softer base binder effect facilitates the use of a relatively high RBR (0.31) without recycling agent with respect to the binder blend Black space diagram, DTc of the binder blend, and mixture cracking resistance in terms of FI. The blend and mixture Figure 95. DTc threshold: mixture cracking resistance with lower PGH. Figure 94. DTc threshold: binder blend Black space with lower PGH.

132 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios with the softer base binder (WI PG 52–34) surpassed the rejuvenated binder blend and mixture with the WI PG 58–28 base binder and the field recycling agent dose of 1.2% with respect to these evaluation methods that include the effects of aging. 5.2 Recycling-Agent Dose Selection Method As detailed in Chapter 2, the recycling-agent dose to restore the continuous PGH of the recycled binder blend to match PGHTarget yielded the best performance for rejuvenated binders and corresponding mixtures (Arámbula-Mercado et al. 2018b; Kaseer et al. 2017b; Garcia Cucalon et al. 2018) and also yielded blends that met the −22 and −28 PGL requirements. The simplified recycling-agent dose selection method based on DSR testing of unaged material can be summarized in the following three steps: 1. Determine PGH of the base and recycled binders per AASHTO M 320. 2. Select the base binder, RBR, and RAP/RAS combination and calculate PGH of the recycled binder blend as follows: ( ) ( ) ( )= × + × + ×PGH RAP PGH RAS PGH B PGHBlend BR RAP BR RAS BR Base where PGHBlend = continuous PGH of the recycled binder blend (°C), RAPBR = RAP binder ratio (RAP binder percent by weight with respect to the total binder), PGHRAP = continuous PGH of the RAP binder (°C), RASBR = RAS binder ratio (RAS binder percent by weight with respect to the total binder), PGHRAS = continuous PGH of the RAS binder (°C), BBR = base binder ratio (base binder percent by weight with respect to the total binder), and PGHBase = continuous PGH of the base binder (°C). 3. Estimate selected recycling agent dose as follows for a target PG climate: %Recycling Agent PGH PGH Slope RateBlend Target( )( ) = − where PGHBlend = continuous PGH of the recycled binder blend (°C) calculated from previous equa- tion and PGHTarget = continuous PGH of target climate. For tall oils (T), vegetable oils (V), or reacted bio-based oils (B), a recommended slope rate or rate of reduction in PGH of 1.82 can be used based on the materials included in this study as shown in Chapter 2. For aromatic extracts (A), a lower slope rate of 1.38 is recommended based on the materials evaluated in this study as shown in Chapter 2. Blending charts shown in Chapter 2 of recycling agent dose (0%, 2%, 5%, and 10%) versus PGH can also be utilized to determine slope rate. These recycling agents are added to the binder blends or corresponding mixtures at the selected doses according to the following guidelines, as detailed in Chapter 1: • For mixtures with only RAP and all binder blends, the recycling agent is added as 100% replacement for the base binder.

Practical Tools for Evaluation of High RBR Binder Blends and Mixtures 133 • For mixtures with RAP and RAS and doses greater than 5.0%, the recycling agent is added as 100% addition to the base binder with a mandatory requirement to ensure adequate mixture rutting resistance. As detailed in Chapter 4, this recycling-agent dose selection method was verified in recycled and rejuvenated binder blends and mixtures using materials combinations from field projects in TX, NV, IN, WI, and DE. 5.3 Materials Proportioning Guidance Recommended limits in Table 32 for RASBR of 0.15 (or approximately 3.5% by total weight of mixture) stem from current state DOT limits of 3–5% (Epps Martin et al. 2015) and com- parisons of balanced (0.4 RAPBR + 0.1 RASBR) recycled materials combinations and equivalent but unbalanced (0.25 RASBR + 0.25 RAPBR) materials combinations as shown in Figure 96 and highlighted in Arámbula-Mercado et al. (2018a). While neither binder blend enters the block cracking zone with extended aging, the unbalanced mixture exhibited inadequate rutting resistance by HWTT with N12.5 of 4,800 load cycles compared to the corresponding balanced mixture with N12.5 of 16,500 load cycles. This poor mixture performance stems from the lack of RAS binder availability at normal mixing temperatures of 150°C–175°C (300°F–350°F), which likely results in the recycling agent oversoftening the base binder. A maximum limit for total RBR (RAPBR + RASBR) of 0.5 is also suggested based on the scope of materials combinations evaluated in this study, as shown in Table 1. Finally, the proportioning threshold provided in Table 32 for recycling-agent dose is generic and based on the recycling-agent dose selection method proposed to restore the continuous PGH of the recycled binder blend to match PGHTarget. For the component materials and materials combinations evaluated in this study that followed the recommended component materials Figure 96. RBR thresholds: binder blend Black space and mixture rutting resistance.

134 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios guidelines in Table 32, this maximum was approximately 8%–10% to ensure adequate mixture rutting resistance. This suggested maximum range based on performance considerations was also similar to ranges provided by the following two efforts that examined current economic considerations for the recycling agents evaluated in this study: • Discussions with recycling-agent manufacturers that recommended 6%–8% based on economics. • An economic analysis that indicated that using recycling agents at doses of 10%–15% is rea- sonable to double the RAP content from 20% to 40% and save from $6 to $8 per ton of mix- ture when virgin material costs are relatively high (Epps Martin et al. 2017). Ultimately, the recycling-agent dose should be selected to satisfy binder blend and correspond- ing mixture performance requirements and be feasible economically. By utilizing the suggested maximum recycling-agent dose range based on performance considerations and Equation 2 to estimate recycling-agent dose, materials combinations can also be screened to determine reasonable and balanced recycled materials content (RAPBR, RASBR) for specific base binders. Table 34 provides a series of examples for 0.5 RBR com- binations formulated to a PGHTarget of 70. The first materials combination has unbalanced RAPBR/RASBR with a relatively poor-quality TX PG 64–22 base binder (DTc = −4.6), highly aged TX RAP (PGH = 106.6°C), and TX TOAS (PGH = 178.0°C) that results in a very high recycling-agent dose that is likely uneconomical and would likely result in inadequate rutting resistance in a corresponding mixture. This unbalanced RAPBR/RASBR combination stems from the lack of binder availability from highly aged recycled materials at normal mixing tem- peratures of 150°C –175°C (300°F –350°F) and likely oversoftening of the base binder by the recycling agent. These highly aged TX recycled materials may be useful at lower RBRs, with a more balanced RAPBR/RASBR, or with a different base binder. The second materials combi- nation uses the same materials but balances the RAPBR/RASBR to 0.4/0.1 with a significant reduction in recycling agent dose. However, its absolute value remains beyond the suggested range. By changing the RAS type to the less-aged TX MWAS (PGH = 130.7°C) in the third materials combination, the recycling agent dose can be further reduced, but it is still beyond the suggested range. By changing the RAP type to the less-aged NH RAP (PGH = 90.2°C) in the fourth materials combination, the recycling agent dose is again reduced, but this combina- tion is not effective unless RAP with a lower PGH is available locally. Finally, the fifth materials combination illustrates that changing the base (virgin) binder to a softer PG grade (both PGH and PGL) of higher quality (DTc = 0.0) can further reduce the recycling-agent dose to an acceptable and likely economical value. Base (Virgin) Binder RAP RAS Recycling- Agent Dose (%) Comments TX PG 64-22 ΔTc = −4.6 0.25 TX RAP 0.25 TX TOAS 19.4 Unbalanced, Very High Dose 0.4 TX RAP 0.1 TX TOAS 13.5 Δ RAP/RAS, High Dose 0.4 TX RAP 0.1 TX MWAS 10.9 Δ RAS Type, High Dose 0.4 NH RAP 0.1 TX MWAS 7.3 Δ RAP Type, Marginal Dose MN PG 58-28 ΔTc = 0.0 0.4 NH RAP 0.1 TX MWAS 5.0 Δ Base Binder, Acceptable Dose Table 34. Materials proportioning examples at 0.5 RBR and PGHTarget of 70.

Practical Tools for Evaluation of High RBR Binder Blends and Mixtures 135 5.4 Binder Blend Rheological Evaluation Tools Table 35 provides binder blend evaluation tools for use with high RBRs and recycling agents. These tools are meant to be used as a system, with requirements recommended for at least one high-temperature and one intermediate- or low-temperature test where data are available for a specific combination of materials in a high RBR blend with a recycling agent. For recycled or rejuvenated binder blends with high RBRs, the continuous PGH of the target climate should be matched using either a softer base binder or a recycling agent with a recycling-agent dose selected based on the method detailed in Chapter 2 and summarized previously. Some of the other recommended thresholds are adopted from existing research, including the intermediate-temperature G-R parameter criteria (Glover et al. 2015; Rowe 2011) and the low-temperature DTc criteria (Anderson et al. 2011), with the recommended aging conditions developed based on this extensive study and the materials combinations in Table 1 and laboratory tests in Table 13. In this study, DTc values after 20-h PAV aging were utilized for practicality, but extended aging after 40-h PAV is recommended for the G-R parameter because the standard 20-h PAV aging by AASHTO R 28 is not always sufficient to evaluate the evolution of recycling agent effectiveness. The Tδ = 45° thresholds are provided as an alternate intermediate-temperature parameter based on their correlation to the G-R parameter (Garcia Cucalon et al. 2018). A comparison of binder blends in Black space in Chapter 4 that includes the G-R parameter thresholds illustrates the effects of increased recycling agent doses to ensure long-term durability with high RBRs. 5.5 Mixture Performance Evaluation Tools Table 36 provides comprehensive mixture evaluation tools for use with high RBRs and recy- cling agents that balance mixture cracking resistance at both intermediate and low temperatures and rutting resistance at high temperatures. Evaluation of rejuvenated mixtures is imperative since these mixture properties control performance and allow for consideration of incomplete blending between base and recycled binders and recycling agent. These tools are meant to be utilized as a system, with requirements recommended for at least one high-temperature and one intermediate- or low-temperature test where data are available for a specific materials combination in a high RBR mixture with a recycling agent. Some of these recommended thresholds are adopted from existing specifications, including the low-temperature BBRm criteria and the high-temperature N12.5 rutting criteria. Thresholds Test Parameter Suggested Performance Threshold High-Temperature, Original and Short-Term Aging DSR PGH Target Climate Intermediate-Temperature, Track with Aging DSR G-R < 180 kPa after 20-h PAV < 600 kPa after 40-h PAV DSR Tδ = 45° < 32°C after 20-h PAV < 45°C after 40-h PAV Low-Temperature, Short- and Long-Term Aging BBR ΔTc > −5.0 after 20-h PAV Table 35. Binder blend evaluation tools for use with High RBRs and recycling agents.

136 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios for Sm and m-valuem parameters in low-temperature mixture Black space as shown in Chap- ter 4 are proposed as developed by Romero (2016) based on field performance of seven field projects in Utah. Thresholds for N12.5 from HWTT specifications from IL for PG 58-XX and PG 64-XX target climates and from TX for PG 64-XX and PG 70-XX climates are also sug- gested. These two states (IL and TX) provide examples of cold and warm climates, respec- tively, based on recommended separation at 40° north latitude, as suggested in NCHRP 09–52. These cold and warm climates are specified in Table 36 for mixture rutting resistance with different thresholds depending on climate for the results of HWTT or APA tests conducted at a single temperature (50°C). This effect of climate was illustrated throughout this study and requires further research to tie laboratory and field aging, which is especially critical for high RBR mixtures. Results from this study were utilized to set thresholds for intermediate- and low-temperature cracking resistance and a combined intermediate-temperature rheological property for mix- tures. For intermediate-temperature mixture cracking resistance, the comparison in Chapter 3 of laboratory and field performance led to the proposed threshold of 7 for FI for available data from LMLC specimens after STOA (Figure 46). For low-temperature mixture cracking resis- tance, however, the comparison in Chapter 3 led to the proposed threshold of 38 for CRIEnv for RPMLC specimens after LTOA (Figure 45), so G-Rm was utilized as a limiting combined rheological property for both RPMLC and LMLC specimens to transform the CRIEnv threshold to an adjusted value for LMLC specimens after LTOA, as shown in Figure 97 and Figure 98. The threshold of 38 developed in Chapter 3 for RPMLC specimens was utilized with the relationship in Figure 97 to find a limiting combined rheological property of 19,000 MPa. This value was then used with the relationship in Figure 98 to determine a threshold of 17 for CRIEnv for LMLC specimens after LTOA. Finally, correlations between cracking resistance parameters (FI and CRIEnv) and G-Rm for LMLC specimens, as shown in Figure 98 and Figure 99, provided evidence that a maximum threshold of 19,000 MPa appears reasonable after LTOA, with cracking likely for mixtures with G-Rm values of 8,000 MPa after STOA based on proposed thresholds for CRIEnv and FI, respectively. Table 36. Mixture evaluation tools for use with High RBRs and recycling agents. Test Parameter Suggested Performance Threshold High-Temperature, Short-Term Aging HWTT or APA N12.5 > 5,000 for PG 58-XX > 7,500 for PG 64-XX in cold climate > 10,000 for PG 64-XX in warm climate > 15,000 for PG 70-XX Intermediate-Temperature, Track with Aging |E*| G-Rm < 8,000 MPa after STOA < 19,000 MPa after LTOA Intermediate-Temperature, Short-Term Aging I-FIT FI > 7 after STOA Low-Temperature, Short- and Long-Term Aging BBRm Sm and m-valuem < Utah threshold on m-valuem vs. Sm after STOA (Figure 77) UTSST CRIEnv > 17 after LTOA

Practical Tools for Evaluation of High RBR Binder Blends and Mixtures 137 Figure 97. G-Rm versus CRIEnv for RPMLC specimens after LTOA to find limiting combined rheological property. Figure 98. G-Rm versus CRIEnv for LMLC specimens after LTOA to develop CRIEnv threshold.

138 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios 5.6 RAP Recycled Binder Availability Factor Based on the strong correlation between RAP BAF and RAP PGH shown in Figure 88, the RAP BAF can be estimated using Equation 24 and Equation 25 for mixing temperatures of 140°C and 150°C, respectively: [ ]( )= − + °0.014 1.898 140 Equation 24RAP BAF RAP PGH for C [ ]( )= − + °0.010 1.771 150 Equation 25RAP BAF RAP PGH for C This value is suggested for use in reducing the recycled binder from the RAP to the RBR in a mixture to ensure that sufficient base binder is included in a mix design. 5.7 Laboratory Aging and Climate Effects Results from this study repeatedly illustrate that initial rheological quality and how rheol- ogy changes due to aging are important, and both depend somewhat on field project location, with the first based on component material availability and economics and the second based on climate. This section presents evaluations of standard laboratory aging protocols that are inde- pendent of location and the effects on predicted binder performance in terms of the G-R param- eter and measured mixture performance in terms of MR and FI. 5.7.1 Binder Climate Effects A preliminary comparison between laboratory and predicted field oxidative aging of select base binders was conducted using the following two analyses: • Analysis A—Different Climate: prediction of the evolution of CA for one base binder (NH PG 64–28) in three different climates––Durham, NH; Reno, NV; and Tyler, TX. Figure 99. G-Rm versus CRIEnv for LMLC specimens after STOA to develop G-Rm threshold.

Practical Tools for Evaluation of High RBR Binder Blends and Mixtures 139 • Analysis B—Different Base Binder: prediction of the evolution of CA for each of three base binders (TX PG 64–22, NH PG 64–28, and NV PG 64–28P) in one climate in Reno, NV. TEMPS was used to predict hourly pavement temperatures at selected depths in the HMA layer for each of the three climates. The G-R/CAg HS for the evaluated binders was used in con- junction with the predicted evolution of CA (and calculated CAg) to estimate the in-service time to reach the cracking onset threshold (i.e., G-R = 180 kPa). Table 37 summarizes the predicted number of years for Analysis A and Analysis B with the following observations provided based on these results: • Analysis A: The NH PG 64–28 base binder had the highest predicted number of in-service years to reach cracking onset when used in the NH climate. The lowest number of years to reach cracking onset was observed in the TX climate, as demonstrated by a 50% reduction in the predicted in-service time compared to the NH climate. The results indicated that the NH PG 64–28 base binder will age much faster in the TX climate when compared to NV and NH climates and thus reach cracking onset earlier in the pavement service life. • Analysis B: The NV PG 64–28P base binder had a predicted in-service time to reach cracking onset that was more than twice the number of years predicted for the other two base binders in the same NV climate. The results indicated that the NV PG 64–28P base binder outper- forms the other two base binders in the NV climate, which both showed similar performance. These three base binders were also long-term aged for 20-, 40-, and 60-h PAV aging. The PAV-aged binders were tested to determine the G-R parameter, and the results are summarized in Table 38. The equivalent PAV duration to reach a G-R parameter value of 180 kPa was then estimated based on the evolution of the G-R parameter as a function of predicted in-service time as sum- marized in Table 37. Consequently, the following observations were made: • Analysis A: The NH PG 64–28 base binder required 52, 55, and 58 hours in the PAV to reach the same level of G-R parameter (180 kPa) in the three different climates of NH, NV, and TX, respectively. Thus, a longer PAV duration is needed for the NH PG 64–28 base binder when used in the TX climate to reach cracking onset. • Analysis B: An equivalent PAV duration to reach cracking onset in the NV climate of 13, 55, and 59 hours was estimated for the TX PG 64–22, NH PG 64–28, and NV PG 64–28P base Base Binder Climate Predicted In-Service Time to Reach G-R = 180 kPa (years) Equivalent PAV Duration to Reach G-R = 180 kPa (h) TX PG 64-22 Reno, NV 5.0 13 NH PG 64-28 Durham, NH 6.1 52 Reno, NV 4.6 55 Tyler, TX 4.1 58 NV 64-28P Reno, NV 11.9 59 Table 37. Predicted field in-service times and equivalent PAV durations to reach cracking onset for different base binders and climates. Table 38. Measured G-R parameter after PAV aging for different base binders. PAV Aging Duration (hours) G-R at 15°C and 0.005 rad/s (kPa) TX PG 64-22 Base Binder NH 64-28 Base Binder NV 64-28P Base Binder 20 218.4 22.7 17.8 40 523.5 85.4 50.2 60 772.5 249.6 218.4

140 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios binders, respectively. Thus, the TX PG 64–22 base binder exhibited a large G-R value and required a much shorter PAV duration to reach cracking onset. Figure 100 shows the measured G-R parameter for all three base binders after PAV aging as a function of PAV aging duration. The data clearly show that the TX PG 64–22 base binder had a significantly higher G-R parameter (> 180 kPa) when compared to the other two base bind- ers, both having comparable G-R parameter values. However, the TX PG 64–22 base binder had a lower susceptibility to PAV aging, as demonstrated with a lower slope compared to the NH PG 64–28 and NV PG 64–28P base binders. Thus, for a given location and associated climate, a mixture with the TX PG 64–22 base binder will likely exhibit cracking early in the pavement’s life, while mixtures with the NH PG 64–28 and NV PG 64–28P base binders are expected to perform similarly and not exhibit cracking until much later. Figure 101 shows the measured G-R parameter for all three base binders after PAV aging as a function of the predicted in-service years in the NV climate. The data in Figure 101 show a dif- ferent behavior for each of the three base binders. While NH PG 64–28 and NV PG 64–28P had similar G-R parameter values, they exhibited different in-service times to reach the measured G-R threshold. This is due to the fact that both binders have different chemical properties in terms of binder kinetics that led to a difference in the predictions of binder oxidative aging as a function of time. The rate of change in G-R parameter as a function of in-service time was higher for the TX PG 64–22 when compared to the NH PG 64–28 and the NV PG 64–28P base binders, both having relatively comparable rates. These results contradict the observed behavior of the base binders as a function of PAV aging duration (Figure 100). Overall, the data in Figure 101 show that the NV PG 64–28P outperformed both the TX PG 64–22 and NH PG 64–28 base binders in the NV climate, as demonstrated with lower G-R parameter values and longer in-service time to reach cracking onset (i.e., G-R = 180 kPa). These results suggest the need for a threshold value for both the magnitude of the G-R param- eter and the rate of change in the G-R parameter as a function of in-service time. This requires testing of binders at multiple PAV aging durations (preferably three). However, a reliable use Figure 100. PAV-based G-R parameter versus PAV aging duration for TX PG 64–22, NH PG 64–28, and NV PG 64–28P base binders.

Practical Tools for Evaluation of High RBR Binder Blends and Mixtures 141 of the threshold value on the rate of change in the G-R parameter necessitates the adjustment of the PAV aging durations to properly simulate in-service oxidative aging. This will be a chal- lenge since the representative PAV aging durations are not only climate specific but also binder specific (i.e., function of binder chemical properties and kinetics). A possible solution is direct measurement of CA on PAV-aged binders after multiple durations using FT-IR and develop- ment of a threshold value for G-R/CAg HS. 5.7.2 Mixture Climate Effects Cumulative degree days (CDDs; 32°F base) based on daily average temperatures since construction were gathered for each field project location (TX, IN, NV, WI, and DE) to provide a quantitative basis for field aging that accounts for differences in construction dates and environments at different field project locations, as utilized previously in NCHRP 09–52 (Newcomb et al. 2015a). CDD curves for the field projects in this study are presented in Figure 102 with coring dates indicated by a black point. Similar to the field projects from NCHRP 09–52, the TX field project (in a warmer climate) showed a constant steeper CDD slope. For the WI and DE field projects, which were constructed in the fall and are located in milder climates, flat initial CDD slopes were evident. The IN and NV field projects also demonstrated a flat CDD slope during the fall/ winter seasons. Figure 103 shows the CDD values for postconstruction cores of 18 mixtures over a wide range of mixture components and production parameters versus their associated average MR ratios (aged/unaged) and a power trendline with a high coefficient of determination (R2). Fig- ure 103 also shows the corresponding average MR ratio of 1.88 for all LMLC specimens with an STOA protocol of 2 h at 135°C (275°F) plus LTOA of 5 days at 85°C (185°F) plotted as a circle where the value crosses the power trendline for the MR ratio versus CDD relationship. The vertical and horizontal error bars represent one standard deviation from the average MR Figure 101. PAV-based G-R parameter versus predicted in-service time for TX PG 64–22, NH PG 64–28, and NV PG 64–28P base binders.

142 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios ratio value and corresponding CDD values, respectively. A laboratory STOA protocol of 2 h at 135°C (275°F) plus LTOA of 5 days at 85°C (185°F) was able to produce mixture aging equiva- lent to an average of 17,000 CDDs in the field, which is close to the 16,000 CDDs reported in NCHRP 09–52. Based on the CDD curves shown in Figure 102, the in-service time for each field project corresponding to 17,000 CDDs was determined and is summarized in Table 39. As shown, the laboratory STOA protocol of 2 h at 135°C (275°F) plus LTOA of 5 days at 85°C Figure 102. Cumulative degree days for NCHRP 09–58 field projects. Figure 103. MR ratio versus CDD for postconstruction cores and correlation of LTOA with field aging.

Practical Tools for Evaluation of High RBR Binder Blends and Mixtures 143 (185°F) was equivalent to approximately 12 months in service in warmer climates such as TX and 24 months in service in colder climates such as WI. These results are again in agreement with those from NCHRP 09–52. Similar to the MR ratio versus CDD relationship and the correlation of laboratory LTOA to field aging for the MR ratio, Figure 104 shows the CDD values for the postconstruction cores of 18 mixtures versus their associated average FI ratios (aged/unaged) and a power trendline with a high coefficient of determination (R2). Figure 104 also shows the corresponding average FI ratio of 0.4 for all LMLC specimens with an STOA protocol of 2 h at 135°C (275°F) plus LTOA of 5 days at 85°C (185°F) plotted as a circle where the value crosses the power trendline for the FI ratio versus CDD relationship. The vertical and horizontal error bars represent one standard devia- tion from the average FI ratio value and corresponding CDD values, respectively. A laboratory STOA protocol of 2 h at 135°C (275°F) plus LTOA of 5 days at 85°C (185°F) was able to produce mixture aging equivalent to an average of 12,000 CDDs in the field. Based on the CDD curves shown in Figure 102, the in-service time for each field project corresponding to 12,000 CDDs was determined and is summarized in Table 40. As shown, the laboratory STOA protocol of 2 hours at 135°C (275°F) plus LTOA of 5 days at 85°C (185°F) was equivalent to approximately 8 months in service in warmer climates such as TX and 20 months in service in colder climates such as WI. Table 39. Correlation of field aging in terms of in-service time for MR ratio and laboratory LTOA of 5 days at 85çC (185çF). Field Project In-Service Time for MR Ratio after 2 h at 135°C (275 °F) + 5 days at 85°C (185°F) TX 12 months NV 15 months DE 17 months IN 20 months WI 24 months 0.0 0.2 0.4 0.6 0.8 1.0 0 5000 10000 15000 20000 25000 30000 F I R at io Cumulative Degree Days (°F-days) Predicted Measured 5 days at 85°C R2 = 0.809 Figure 104. FI ratio versus CDD for postconstruction cores and correlation of LTOA protocols with field aging.

144 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios 5.8 Key Findings Key findings from this study presented in this chapter based on the practical tools developed to evaluate the effectiveness of a recycling agent initially and with aging for mixtures with high RBRs include the following: • Recycling-agent effectiveness must be characterized in high RBR binder blends or mixtures initially and with long-term aging to capture initial compatibility and rheological response to oxidation. • Recycling-agent dose to match continuous PGH for the target climate is required for high RBR binder blends and mixtures to maintain durability with long-term aging. • Use of high-quality base binders (DTc ≥ −3.5) improves performance of high RBR binder blends and mixtures with recycling agents. • Recycling agents are more effective in rejuvenating less-aged recycled materials (RAP more than RAS and MWAS more than TOAS) in balanced, limited proportions (< 0.5 RAPBR + RASBR and ≤ 0.15 RASBR). RAS contents should be limited because at typical production temperatures, RAS likely acts as a filler with none of the stiff, brittle recycled binder available for blending. • Adequate performance for high RBR binder blends with recycling agents can be controlled with proposed thresholds for PGH, G-R parameter, and DTc. • Adequate performance for high RBR mixtures with recycling agents can be controlled with proposed thresholds for N12.5, G-Rm, FI, Sm and m-valuem, and CRIEnv. • Recycled binder in RAP and RAS is not 100% available in mixtures, with binder availability dependent on age and climate and proposed maximum limits on PGH of 100°C and 150°C, respectively. • A binder oxidative aging model can be used to evaluate different binders in different climates and explore the tie between field and laboratory aging. • Based on CDD, laboratory STOA of 2 h at 135°C (275°F) plus LTOA of 5 days at 85°C (185°F) was equivalent to approximately 8 or 12 months in service in warmer climates and 20 or 24 months in service in colder climates for mixture cracking resistance and stiffness, respectively. Table 40. Correlation of field aging in terms of in-service time for FI ratio and laboratory LTOA of 5 days at 85çC (185çF). Field Project In-Service Time for FI Ratio after 2 h at 135°C (275 °F) + 5 days at 85°C (185°F) TX 8 months NV 10 months DE 11 months IN 12 months WI 20 months