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

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36 Chapter 2 provides key results obtained in Phase 2 that were not expanded in Phase 3, including development of a recycling-agent dose selection method used throughout the study; fundamental evaluations toward engineering balanced binder blends that include chemical compatibility, rheological balance, and representative blending; investigation of mixture cracking resistance by S-VECD; and comparison of specimen types. 2.1 Development of Recycling-Agent Dose Selection Method For a specific combination of base binder, recycled binder from RAP/RAS, and recycling- agent, selection of a recycling-agent dose that balances performance in terms of cracking and rutting resistance based on binder blend testing must be completed prior to mixture validation testing. Low recycling-agent doses will fail to provide the mixture with sufficient fatigue and low-temperature cracking resistance. Conversely, high recycling-agent doses will be costly and potentially detrimental to the rutting performance of the mixture, especially during its early life. In the literature, many approaches are used to select a recycling-agent dose. These approaches include using binder blending charts based on viscosity and/or penetration or employing the PG system by evaluating the changes in binder PG grade due to the addition of a recycling agent. However, no standard method is currently available for recycling-agent dose selection. A preliminary recycling-agent dose selection approach was formulated in Phase 2A for a spe- cific combination of materials including the TX PG 64–22 base binder (DTc of −4.6), 0.28 RBR (0.1 TX RAP and 0.18 TX MWAS), and two recycling-agent types (T1 and A1) at multiple recycling-agent doses (0%, 2%, and 10%). These results verified a linear relationship between recycling-agent dose and the PGH and PGL of the recycled binder blends. The combination of materials was expanded in Phase 2B as shown in Table 15, and two additional recycling- agent dose selection approaches were also explored in an effort to develop a standard recycling- agent dose selection method. All three approaches are summarized in this section, followed by a description of a simplified method for the selected approach. Table 15 and Table 16 provide the recycling-agent doses, DTc values, and resulting PG grades for more than 45 materials com- binations prepared in Phase 2A and Phase 2B including six types of base binders, eight types of recycled materials, four combinations of RBRs, and seven types of recycling agents. Additional data and details are included in Arámbula-Mercado and Kaseer et al. (2018b). 2.1.1 Restore PGL (and Verify PGH) In the first approach originally formulated in Phase 2A, the selected recycling-agent dose was the one that restores the PG grade of the recycled binder blend to that of the target binder needed C H A P T E R 2 Key Results from Phase 2

Key Results from Phase 2 37 to satisfy climate and traffic requirements (i.e., PG 70–22 for TX). The PGL of the target binder was used to set the recycling-agent dose for the recycled binder blend. Then the resulting PGH of the binder blend at the selected dose was verified against the PGH of the target binder and adjusted (increased) if needed, while still maintaining the PGL of the target binder. The recycling-agent doses from this approach were evaluated to assess the rejuvenating effec- tiveness via changes in Black space (log |G*| versus δ) with aging (after RTFO, 20 h PAV, and 40 h PAV). The Black space results for the recycled blends with 0.28 RBR; T1, A1, V1, and B1 at the selected dose; and the TX PG 64–22 base binder (DTc = −4.6) are shown in Figure 9. at 15°C and 0.005 rad/s. For each blend in Figure 9, the three markers from right to left represent RTFO, RTFO plus 20-h PAV, and RTFO plus 40-h PAV, respectively. The results after RTFO (0-h PAV) aging indi- cated improved cracking resistance for the recycled binder blends with the selected recycling- agent dose compared to the DOT control blend. However, after 40-h PAV aging, the recycled Field Project Target PG Binder Source and PG Binder ΔTc RBR RAPBR and Source RASBR and Source Recycling Agent % Recycling-Agent Dose (ΔTc#) [PG] Restore PGL, Verify PGH Achieve ΔTc = −5.0 Restore PGH TX 70-22 TX 64-22 −4.6 0.28 0.1 TX 0.18 TXMWAS T1 4.5 (−10) [72-22] 12.5 [58-32] 6 (−9) [70-23] A1 5.5 (−8) [71-22] 9.5 [66-27] 6.5 (−8) [70-23] 0.4 0.4 TX — T1 7.5 (−8) [69-22] 13.0 [57-30] 7.5 (−8) [69-22] A1 10.0 (−6) [73-22] 11.0 [71-23] 12.0 (−5) [70-24] 0.5 0.25 TX 0.25 TXMWAS T1 8.0 (−9) [72-22] 11.5 [65-28] 9.0 (−8) [70-24] 0.25 TX 0.25 TX TOAS T1 11.5 (−9) [74-25] 14.5 [65-32] 13.5 (−6) [70-30] NH 64-28 +1.2 0.4 0.4 TX — A1 6.0 (−5) [75-23] 6.0 [75-23] 9.5 (−3) [70-26] 0.5 0.25 TX 0.25 TX TOAS T1 12.5 (−5) [75-27] 12.5 [75-27] 15.5 (−4) [70-30] NV 64-28P −3.6 0.5 0.25 TX 0.25 TX TOAS T1 13.5 (−5) [75-30] 13.5 [75-30] 16.0 (−4) [70-33] NV 64-28P NV 64-28P −3.6 0.3 0.3 NV — T2 1.5 (−4) [68-28] — 3.0 (−2) [64-31] A2 2.0 (−2) [69-29] — 5.5 (+3) [64-33] IN 64- 22 IN 58-28 −8.0 0.42 0.14 IN 0.28 IN MWAS T2 3.5 (−8) [69-24] 6.5 [63-29] 6.0 (−5) [64-29] NOTE:— = not applicable. Table 15. Binder blends test plan and recycling-agent doses for Phase 2A.

38 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios Field Project Target PG Base Binder Source & PG Binder ΔTc R BR RAPBR and Source RASBR and Source Recycling Agent % Recycling-Agent Dose (ΔTc#) [PG] Restore PGL, Verify PGH Achieve ΔTc = −5.0 Restore PGH TX 70- 22 TX 64-22 −4.6 0.28 0.1 TX 0.18 TX MWAS T1 4.5 (−10) [72-22] 12.5 [58-32] 6 (−9) [70-23] A1 5.5 (−8) [71-22] 9.5 [66-27] 6.5 (−8) [70-23] V1 4.0 (−10) [74-22] 8.5 [64-32] 5.5 (−8) [70-26] B1 4.0 (−8) [74-22] 7.0 [69-28] 6.5 (−8) [70-27] IN 64- 22 −1.2 0.28 0.1 TX 0.18 TX MWAS — — — — T1 2.0 (−4) [74-22] — 5.0 (−3) [70-25] A1 2.0 (−5) [75-22] 2.0 [75-22] 6.5 (−4) [70-25] V1 1.0 (−5) [75-22] 1.0 [75-22] 3.5 (−5) [70-25] B1 1.0 (−5) [75-22] 1.0 [75-22] 4.0 (−3) [70-26] NH 64-28 +1.2 0.5 0.25 TX 0.25 TX TOAS T1 12.5 (−5) [75-27] 12.5 [75-27] 15.5 (−4) [70-30] A1 >20.0 >20.0 >20.0 V1 15.0 (−4) [75-37] 11 [82-30] 17.5 (−3) [70-41] B1 17 (−1) [75-37] 8.0 [89-24] 20.0 (+1) [70-40] IN 64- 22 NH 64-28 +1.2 0.5 0.4 NH 0.1 CA TOAS T1 10.5 N/A 13 V2 11.5 N/A 13 0.7 0.7 NH — B1 9 (−1) [69-29] 0 11.5 (−1) [64-32] 0.28 0.1 TX 0.18 TX MWAS — — — — T1 0.0 (−3) [71-23] — 0.5 (−3) [70-24] A1 0.0 (−4) [71-23] — 0.5 (−3) [70-24] V1 0.0 (−2) [70-24] — — B1 0 (−4) [70-23] — — NOTE: — = not applicable. TX 70-22 MN 58-28 0.0 Table 16. Binder blends test plan and recycling-agent doses for Phase 2B.

Key Results from Phase 2 39 Field Project Target PG Base Binder Source & PG Binder ΔTc R BR RAPBR and Source RASBR and Source Recycling Agent % Recycling-Agent Dose (ΔTc#) [PG] Restore PGL, Verify PGH Achieve ΔTc = −5.0 Restore PGH TX 70-22 MN 58-28 0.0 0.5 0.25 TX 0.25 TX TOAS — — — — 0.25 TX 0.25 TX TOAS T1 13.5 (−5) [70-24] 13.5 [70-24] 16.5 (−5) [70-26] 0.25 TX 0.25 TX TOAS A1 16.5 (−8) [75-22] >20.0 20.0 (−8) [70-24] 0.25 TX 0.25 TX TOAS V1 13.5 (−10) [75-30] >20.0 16.5 (−10) [70-34] 0.25 TX 0.25 TX TOAS B1 13.0 (−6) [75-30] 16.0 [70-34] 16.0 (−5) [70-34] IN 64-22 IN 58-28 −8.0 0.32 0.25 IN 0.07 IN MWAS — — — — 0.42 0.14 IN 0.28 IN MWAS T2 3.5 (−8) [69-24] 6 [64-29] 6 (−5) [64-29] 0.42 0.28 IN 0.14 IN MWAS T2 N/A N/A 8 0.5 0.36 IN 0.14 IN MWAS T2 N/A N/A 9.5 0.7 0.7 IN — T2 N/A N/A 10 NOTE: — = not applicable. Table 16. (Continued). Figure 9. Black space results for 0.28 RBR recycled blends with TX PG 64–22 and recycling agent at the selected dose to restore PGL.

40 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios binder blends at the selected recycling agent dose were comparable to the corresponding DOT control blend in terms of stiffness and phase angle and were all within the cracking zone. The no- cracking, transition, and cracking zones in Black space were used to evaluate the results, despite the fact that an adjustment to account for the target PG 70–22 climate versus the PG 58–28 used to generate these thresholds should probably be considered. Nevertheless, these example results showed that the selected recycling-agent doses by the first approach to restore the PG grade to that of the target PG were insufficient to maintain effectiveness with aging. 2.1.2 Achieve DTc = -5.0 Recent work by Anderson et al. (2011) suggested a maximum DTc threshold of −5.0 after 40-h PAV aging to minimize the risk of age-related cracking. However, using this DTc threshold would result in excessively high recycling-agent doses that would be costly and likely result in poor mixture rutting resistance. Thus, the dose to achieve a DTc value of −5.0 after the standard 20-h PAV aging was selected in the second approach to increase the recycling-agent dose and possibly increase its effectiveness with aging. Compared to the first approach, the recycling- agent doses increased for the recycled binder blends with the TX PG 64–22 base binder but did not change for the recycled binder blends with the IN PG 64–22 base binder since the doses from the first approach also yielded DTc values of at least −5.0 (or less negative) after 20-h PAV aging. The Black space results for the recycled binder blends with the TX PG 64–22 base binder shown in Figure 10 were promising, demonstrating lower |G*| and higher δ for the recycled binder blends, especially compared to the DOT control blend. In addition, all recycled blends were on or below the transition zone significant cracking threshold after 40-h PAV aging. However, the recycling-agent dose determined with this second approach resulted in recycled blends with low PGH values (i.e., 58°C to 69°C, as shown in Table 16), which could indicate rutting issues at the mixture level. This was confirmed by the Black space results after RTFO, which indicated that the binder blends were likely oversoftened and would possibly result in rut- ting of corresponding mixtures. Therefore, HWTT testing was performed on the mixture with the highest recycling-agent dose (12.5% T1 shown in the bottom right corner in Black space in Figure 10. Black space results for 0.28 RBR recycled blends with TX PG 64–22 and recycling agent at the selected dose to achieve DTc = -5.0.

Key Results from Phase 2 41 Figure 11), and the mixture failed by reaching a rut depth of 12.5 mm (at 50°C) after 2,300 load cycles. These example results showed that for the TX PG 64–22 base binder, the selected recycling-agent doses by the second approach to achieve a DTc value of −5.0 were excessive. In the case of the IN PG 64–22 base binder, the Black space results shown in Figure 11 dem- onstrated different trends compared to those for the TX PG 64–22 base binder, most likely because of the difference in quality, as indicated by DTc (i.e., −4.6 versus −1.2, respectively). This higher quality IN PG 64–22 required less recycling agent to restore PGL and simultane- ously meet the DTc = −5.0 threshold. The Black space results after 20-h PAV aging were within the transition zone, and the results after 40-h PAV aging were in the cracking zone for all recycled blends. Still, there was a clear distinction between the Black space results for the DOT control blend versus the recycled blends (especially with respect to phase angle) despite the low recycling-agent dose used in the recycled blends between 1.0% and 2.0%. These results indicate that even though the use of a higher-quality base binder (with a less negative DTc value) yielded lower recycling-agent doses and partially restored the phase angle of the recycled blend, the second approach to achieve DTc = −5.0 was still inadequate in terms of determining a recycling- agent dose with prolonged effectiveness on aging. 2.1.3 Restore PGH (Match Continuous PGH) The third approach for selecting a recycling-agent dose provided values between those of the first and second approaches and followed a methodology similar to that used in mix design where as much binder (or in this case, recycling agent) as possible is included for durability and cracking resistance as long as rutting resistance is maintained. For the first approach (restore PG to that of the target binder, which for TX was a PG 70–22), the resulting continuous PGH was checked and reduced if necessary to just meet a PG 70 grade with a PGH close to 75°C. The third approach was to further increase the recycling-agent dose to a PGH of 70°C in the hopes of improving the effectiveness with aging. Compared to the other two approaches, this third approach was based only on DSR results and accounted for the combined effects of the aging state of the recycled materials (RAP and RAS) and the recycled material combination (RAPBR Figure 11. Black space results for 0.28 RBR recycled blends with IN PG 64–22 and recycling agent at the selected dose to achieve DTc = -5.0.

42 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios and RASBR). In addition, with this approach, the PGL was restored to that of the target binder or improved further (more negative) for all binder blends, as shown in Table 15. The Black space results for the third approach for the recycled binder blends with the TX PG 64–22 base binder shown in Figure 12 seemed promising, demonstrating low G* and high δ for the recycled binder blends with different recycling-agent types at all aging levels. Blends with T1, A1, and V1 barely reached the transition zone cracking onset threshold after 20-h PAV aging and showed much better performance compared to the DOT control blend. In addition, the RTFO results were not as close to the bottom right corner in Black space as those from the second approach. To verify rutting resistance, HWTT testing was performed on the mixtures with the TX PG 64–22 and IN PG 64–22 base binders, 0.28 RBR (0.1 TX RAP and 0.18 TX MWAS), and A1 that yielded the highest recycling-agent dose by this approach (i.e., 6.5%). The mixture with the TX PG 64–22 base binder reached 10,300 load cycles before exhibiting 12.5-mm rut depth, while the mixture with the IN PG 64–22 base binder reached the same threshold after 5,000 load cycles. Usually, mixtures with a target PG 70-XX are required to sustain at least 15,000 load cycles before achieving 12.5-mm rut depth at 50°C. Thus, although both of these mixtures would fail this criterion, a significant improvement was observed with respect to the performance of the TX PG 64–22 mixture with 12.5% T1 (which failed at 2,300 load cycles). In addition, based on the results and an alternate analysis proposed by Yin et al. (2014b), the rutting resistance could not be separated from moisture susceptibility. The third approach was also used for the blends with 0.5 RBR (0.25 TX RAP and 0.25 TX TOAS) for both the NH PG 64–28 (with DTc = +1.2) and the MN PG 58–28 (with DTc = 0.0) base binders. For the blends with the NH PG 64–28 base binder, the recycling-agent doses to match continuous PGH were high but reasonable for the binder blends with T1, V1, and B1; but the recycling-agent dose was excessive with A1 (> 20%). This may be an indication of incom- patibility or an unbalanced recycled materials combination. For the binder blends with the MN PG 58–28 base binder, the recycling-agent doses to match continuous PGH were reason- able for all recycling-agent types. However, the DTc values for these binder blends were still more negative compared to those with the NH PG 64–28 base binder, probably due to the better qual- ity based on DTc of the NH PG 64–28 base binder. Figure 12. Black space results for 0.28 RBR recycled blends with TX PG 64–22 base binder and recycling agent at the selected dose to restore PGH.

Key Results from Phase 2 43 The Black space results for these blends with T1 and V1 shown in Figure 13 were promising, demonstrating low |G*| and high δ for the recycled binder blends at all aging levels. The recycled blends with T1 reached or were on the threshold of the cracking zone after 40-h PAV aging. The other recycled blends with V1 did not reach the transition zone cracking onset threshold after 40-h PAV aging. Based on these results, the third approach to match continuous PGH is recom- mended for recycling-agent dose selection. 2.1.4 Simplified Recycling-Agent Dose Selection Method The recycling-agent doses from the selected method to match continuous PGH of the binder blends with 0.5 RBR (0.25 TX RAP and 0.25 TX TOAS) were high (15.5 to 17.5 percent). In addi- tion to the fact that these mixtures may have inadequate rutting resistance, these high recycling- agent doses may not be cost effective based on the economic analysis provided in Appendix G; in addition, they likely indicate incompatibility or an unbalanced materials combination because of insufficient availability and blending of the recycled binder, particularly from the RAS, that is exacerbated in corresponding mixtures. In recycled mixtures, part of the recycled binder is not available during mixing, particularly for stiffer materials such as those containing MWAS; in some cases, like in TOAS, the recycled binder is likely a black rock. For example, the PGH of TX TOAS is 178°C, and it is expected that most of the TOAS binder will not be blended with the base binder when preparing mixtures at common mixing temperatures that range from 132°C to 162°C (270°F to 325°F), or even lower for mixtures with WMA additives. With less avail- able recycled binder and incomplete blending, a high recycling-agent dose determined based on completely blended binder testing may oversoften the base binder and result in mixture rutting. Therefore, maximum RBR should be controlled, particularly maximum RASBR from TOAS, to ensure adequate performance at reasonable recycling-agent doses up to approxi- mately 10%–15% based on the economic analysis in Appendix G. This analysis indicates that the use of recycling agent at these doses is reasonable to double the RAP content from 20% to 40% and save from $6 to $8 per ton HMA/WMA or from $0.30 to $0.40 per 1% RAP when virgin material costs are relatively high. This represents approximately 7% to 10% of in-place prices for HMA/WMA. Figure 13. Black space results for 0.5 RBR recycled blends with NH PG 64–28 and MN PG 58–28 base binders and recycling agent at the selected dose to restore PGH.

44 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios To limit the RBR and thus recycling-agent dose, the PGH of the blend of base and recycled binders can be controlled through the use of blending charts. Figure 14 presents example blend- ing charts for recycled binder blends with 0.31 RBR and 0.5 RBR (0.31 and 0.5 WI RAP) with the WI PG 58–28 base binder that are verified by the measured data shown. The following linear relationship can be used to establish the blending chart and calculate the PGH of a binder blend (Equation 13): [ ]( )( ) ( )= × + × + × Equation 13PGH RAPBR PGH RASBR PGH BaseBR PGHBlend RAP RAS Base binder where RAPBR = RAP binder ratio, RASBR = RAS binder ratio, and BaseBR = base binder ratio. To validate the blending chart based on Equation 13, the measured PGH of the binder blends without recycling agent in Table 15 and Table 16 were compared to the corresponding calculated PGH as shown in Figure 15. A strong correlation was observed, with only the binder blends with TX MWAS having slightly lower measured PGH than calculated values. There- fore, the blending charts based on Equation 13 can be used to estimate PGH of the recycled binder blends without testing. The PGHs of recycled binder blends in Table 15 and Table 16 (including multiple base binders, recycled materials, and RBRs) were then plotted versus the recycling-agent dose (for multiple recycling-agent types) required to match continuous PGH to that of the target binder. These plots contain many different material combinations that are categorized by the groups shown in the legends. Figure 16 illustrates the recycling-agent dose required to restore the PGH to 70°C and 64°C for each of four types of recycling agent (T1/T2, A1/A2, V1/V2, and B1). Since the slopes of the relationships (for T1, V1, and B1) shown in Figure 16 are similar, they were com- bined in Figure 17 to match the continuous PGH of different binder blends to targets of 70°C Figure 14. Binder blending chart for 0.31 and 0.5 RAP RBR recycled blends with WI PG 58–28.

Key Results from Phase 2 45 Figure 16. Recycling-agent dose to restore the PGH of the recycled blend to 70çC and 64çC for four recycling-agent types. Figure 15. Calculated versus measured PGH of the recycled blends without recycling agent.

46 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios and 64°C to provide a more universal recycling-agent dose estimation method. The petroleum products (A1/A2) were excluded since these recycling agents exhibited a flatter slope (1.38) com- pared to other recycling agents (1.89, 1.77, and 1.77 for T1/T2, V1/V2, and B1, respectively), as illustrated in Figure 16. Therefore, removing A1/A2 reduced the variability in Figure 17 and will minimize the risk of oversoftening the binder blends since A1/A2 requires the highest doses to match continuous PGH. Specific recycling-agent dose blending charts from recycling-agent sup- pliers such as those shown in Figure 16 should be used if available. Additional data and details are included in Kaseer and Garcia Cucalon et al. (2018b). The results shown in Figure 17 are promising and show a strong relationship between the PGH of the blend of base and recycled binders (which can be estimated with Equation 13 with- out testing) and the recycling-agent dose to restore to the target PGH, regardless of the base binder, recycled materials, RBR, or recycling-agent type. Results also illustrate the recycling- agent rejuvenation capacity of the seven types of recycling agents evaluated, with an approximate average of 1% recycling agent to reduce the PGH by 1.8°C. Equation 14 can be used to estimate the recycling-agent dose to restore the continuous PGH of the recycled blend with a recom- mended slope rate or rate of reduction in PGH of 1.82 for tall oils (T), vegetable oils (V), and reacted bio-based oils (B) evaluated in this study. For aromatic extracts (A), a lower slope rate of 1.38 is recommended based on the materials evaluated in this study. [ ]( )= −% Equation 14Recycling Agent PGH PGH Slope RateBlend Target where %Recycling Agent = estimated recycling-agent dose to match continuous PGH. The slope rate can be determined (or the estimated recycling-agent dose can be verified) by preparing recycled blends with 0%, 2% or 5%, and 10% recycling agent and measuring PGH and PGL using the DSR and BBR, respectively, if component materials are available. An example of determining recycling-agent dose (and slope rate or rate of reduction in PGH) using these data is illustrated in Figure 18. Figure 17. Recycling-agent dose to match the continuous PGH of the recycled blend to 70çC and 64çC.

Key Results from Phase 2 47 2.2 Chemical Compatibility of Binder Blends Recycling heavily aged RAP/RAS into new asphalt pavements while maintaining sufficient durability is challenging because recycled binders have a larger asphaltene content (and larger size asphaltene agglomerations) compared to base binders and are therefore significantly stiffer and more brittle. Depending on the RBR and resulting PGH of the binder blend, the target PG for a specific field project can be met by blending with a softer (substitute) base binder and/or by incorporating a recycling agent. Rejuvenation by inclusion of a recycling agent is generally attributed to a combination of the following mechanisms: • Softening from blending with a recycling agent, • Reduction of the size of asphaltene agglomerations, given that the recycling agent may break apart strong polar bonds or aromatic pi-pi interactions, and • Improvement in the dispersive power of the continuous maltene phase by inclusion of a recycling agent. The challenge becomes further complicated considering that aging of rejuvenated binder blends could result from a combination of the following mechanisms that are not necessarily common to base binders: • Formation of pericondensed asphaltenes and related changes in compatibility with maltenes, • Reagglomeration of asphaltene agglomerates that may have initially been dispersed during blending with the recycling agent, and • Chemical changes in the recycling agent with aging that may result in reduced dispersive power of the maltene phase. Chemical compatibility of binder blends was evaluated to do the following: • Provide fundamental insight into the mechanisms of rejuvenation when recycling agents are included, with specific interest on the impact of recycling agents on asphaltene agglomera- tions; and Figure 18. Example of optimum recycling-agent dose verification.

48 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios • Assess rheological and physicochemical changes upon rejuvenation and aging of binder blends considering the materials combinations presented in Table 17. Rheological characterization was conducted using the DSR and BBR to determine PGH and PGL and the G-R parameter with aging. Physicochemical aspects of recycling and rejuvenation were evaluated by MDSC and SAR-AD. Tracking of oxidation products was performed using FT-IR. Additional data and details are included in Garcia Cucalon et al. (2017). The materials combinations considered included two different base binders (TX PG 64–22 and NH PG 64–28), three types of recycled materials (RAP, MWAS, and TOAS from TX), and two types of recycling agents (T1 and A1) at different doses by weight of total binder. The DOT control blend used in the field (0.3 control) included RAP with a PGH of 107 and MWAS with a PGH of 133. Alternatives to the blend used in the field included consideration of the effect of recycling agent type (T1 and A1), inclusion of higher RBR (0.5) and a more oxidized TOAS (PGH of 178), and use of a higher-quality base binder (NH PG 64–28). The recycling-agent doses for the blends considered in this experiment were optimized to restore PGL of the target binder (PG 70–22) as previously described, and the resulting PG grades of the binders and binder blends are presented in Table 17. MDSC evaluation was conducted primarily to characterize glass transition temperature (Tg) and the high-end temperature of the glass transition (Tg End) for base binders and binder blends after inclusion of recycled binders and recycling agents. This second parameter changes more significantly with aging (Huang et al. 2015), with an increased Tg End being undesirable because it indicates the glass transition and potentially embrittlement extends to higher temperatures. In this experiment, the inclusion of recycled binders resulted in small changes in Tg but more signif- icant increases in Tg End. Conversely, the inclusion of a recycling agent reduced both Tg and Tg End significantly, with greater improvement at higher recycling-agent doses. These results were expected since softening/rejuvenating additives (including recycling agents) are significantly less Binder/Binder Blend Blend Proportionsa Recycling Agentb Continuous PG Base Binder TX RAPBR TX RASBR Dose PGH PGL TX PG 64-22 PG 64-22 — — — 69.4 −24.6 NH PG 64-28 PG 64-28 — — — 66.9 −28 0.28 Control 0.7 PG 64-22 0.1 0.18 MWAS — 81 −15.6 0.28 + 4.5% T1 0.7 PG 64-22 0.1 0.18 MWAS R4444.5% T1 73 −22.0 0.28 + 5.5% A1 0.7 PG 64-22 0.1 0.18 MWAS 5.5% A1 71 −22.3 0.5 Control MWAS 0.5 PG 64-22 0.25 0.25 MWAS — 88 −10.6 0.5 MWAS + 7.5% T1 0.5 PG 64-22 0.25 0.25 MWAS 7.5% T1 73 −21.7 0.5 Control TOAS 0.5 PG 64-22 0.25 0.25 TOAS — 102 −2.1 0.5 TOAS + 11.5% T1 0.5 PG 64-22 0.25 0.25 TOAS 11.5% T1 74 −25.8 0.5 Control TOAS 64-28 0.5 PG 64-28 0.25 0.25 TOAS — 101 −12.7 0.5 TOAS 64-28 + 12.5% T1 0.5 PG 64-28 0.25 0.25 TOAS 12.5% T1 75 −27.1 NOTE: — = not applicable. aBy weight of total blend. bBy weight of total binder. Table 17. Chemical compatibility materials combinations.

Key Results from Phase 2 49 viscous and can exhibit much lower Tg compared to base binders, and therefore significantly lower Tg and PGL in corresponding binder blends (Lei et al. 2016). The SAR-AD CII and total TPA indices indicated a detrimental effect on compatibility when including recycled materials in a binder blend. The benefit of adding a recycling agent was not clear based on these indices for the recycling-agent doses evaluated, but complete rebalancing of the SAR-AD fractions to proportions comparable to those of base binders is not likely at any dose. The asphaltene determinator from this test was further utilized to investigate the possible recycling-agent rejuvenation mechanism by dissociation of asphaltene agglomerations. Fig- ure 19 presents the asphaltenes observed by the 500-nm detector in terms of fractions soluble in cyclohexane (CyC6), toluene, and methylene chloride:methanol (CH2Cl12:MeOH). Incorpo- ration of recycled materials resulted in increased asphaltene content, as expected. However, SAR-AD only captured a very minor decrease in asphaltene content when A1 was included and even an increased asphaltene content for blends with TOAS, including 11.5% and 12.5% T1. This was unexpected, considering that T1 does not contain any of the polycyclic aromatic mol- ecules thought to create the molecular associations called asphaltenes. On further consideration, the fatty acid group on the tall oil molecule must have enough polarity to bond with other polar molecules in the asphaltenes. A strong fatty acid–asphaltene polar interaction may be the mecha- nism by which the recycling agent provides improved molecular mobility of the large asphaltene agglomerates. Rheological evaluation with aging was also conducted for the base binders, DOT control blend (0.28 control), and rejuvenated binder blends. G-R parameters are presented in Figure 20 with the corresponding cracking onset (180 kPa) and significant cracking (600 kPa) thresholds that define the G-R transition zone in Black space. The DOT control blend (0.28 control) was excessively brittle based on the two damage thresholds after RTFO and PAV aging. Comparing both base binders, the TX PG 64–22 reached the durability thresholds significantly faster than the NH PG 64–28. All the rejuvenated binder blends with short-term aging (RTFO) ranked between both base binders and exhibited improved performance compared to the DOT con- trol blend (0.28 control). After 20-h PAV aging, all the rejuvenated binder blends exceeded the Figure 19. SAR-AD results—asphaltene determinator 500 nm.

50 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios cracking onset threshold and exhibited similar or slightly worse performance compared to the poor-quality TX PG 64–22 base binder. After 40-h PAV aging, all rejuvenated binder blends would be expected to have significant cracking based on G-R thresholds. The aging and associated stiffening and embrittlement of these rejuvenated binder blends may be related to chemical changes different to those common for base binders. In addition to formation of common oxidation products, it is possible that with time, the binder blend loses compatibility due to reagglomeration of asphaltene clusters that may have initially been dis- persed during blending with recycling agents, and/or chemical changes in the recycling agents with aging may affect rheology. Analysis of the FT-IR spectrum with aging showed increases in peaks at 1,743 cm-1, 1,700 cm-1, and 1,032 cm-1, associated with formation of esters, ketones/ carboxylic acids, and sulfoxides, respectively. Changes in the 1,743 cm-1 and 1,700 cm-1 peaks may be associated with changes in recycling agents as well as the common oxidation process of asphalt binders. Further evaluation of chemical changes in recycling agents with aging and their impact on the chemistry and rheology of rejuvenated binder blends was completed in Phase 3 and described subsequently. This experiment provided fundamental insight to the mechanisms of rejuvenation and aging of binder blends with a recycling agent through rheological and physicochemical characteriza- tion. The main findings can be summarized as follows: • Rheological (PG and G-R) and physicochemical (MDSC Tg and Tg End) measurements confirm that there is a rejuvenation effect from inclusion of recycling agents. • With long-term aging, rejuvenation effectiveness is diminished, especially after 40-h PAV aging. Nevertheless, all rejuvenated binder blends continued to show improved performance compared to the DOT control blend without any recycling agent, corroborating the added value of using a recycling agent to increase RBR. • SAR-AD indices may allow evaluation of the evolution of compatibility with aging but may not have equivalent relevance as a tool to evaluate the effectiveness of different recycling agents in partially restoring binder rheology. • Chemical analysis by SAR-AD did not confirm or deny the hypothesis regarding the reduc- tion of asphaltene agglomerates by inclusion of recycling agents but did provide evidence Figure 20. G-R with aging.

Key Results from Phase 2 51 of a strong polar interaction between asphaltenes and T1 that may contribute to increased molecular mobility and restoration of rheological properties as observed. • Considering the large number of recycling agents available on the market, it is important to understand the chemical changes typically observed in the different recycling-agent types that may compromise durability of binder blends. A complementary study was conducted in partnership with Texas A&M University at Qatar exploring microstructural and rheological changes upon aging, rejuvenation, and further aging. Menapace et al. (2018b) found that the improved flow properties observed rheologically (by PG and G-R) were detected in atomic force microscopy (AFM) as a reduction in surface rough- ness, smoother borders of dispersed domains, increased matrix area, and better dispersion of domains in the rejuvenated binders. Note that the dispersed domains observed with AFM were on the order of microns, which is orders of magnitude larger than what the literature reports on size of asphaltene aggregates/clusters. Additional data and details are included in Menapace et al. (2018b). 2.3 Rheological Balance of Binder Blends In developing the recycling-agent dose selection method, three approaches were evaluated, and the final recommendation was to increase recycling-agent dose without sacrificing PGH (dose to match PGH). Blending charts investigated limits on recycled materials and the balance between base binders and recycled binders to improve the potential for effective rejuvenation by recycling agents at selected doses. Evaluation of chemical compatibility provided fundamental insight on rejuvenation mechanisms contributing to the observed changes in rheology, changes in temperature transition parameters observed by MDSC, and rejuvenation effectiveness with aging in terms of the intermediate-temperature G-R parameter. Based on limitations of and practicality concerns associated with the physicochemical characterization methods, an addi- tional rheological parameter was explored at intermediate temperatures to capture the solid- to fluid-like transition. Considering early life rutting potential and the effects of rejuvenation and aging in intermediate (solid- to fluid-like transition) and cold temperature (DTc) compatibility, it was possible to engineer or better select rheologically balanced binder blends. Figure 21 illustrates the temperature dependency of binders and binder blends, including two transition parameters, the rheological glass transition (Tg) defined as the maximum G″ and the crossover temperature or solid- to fluid-like transition temperature (Tδ = 45°). Above Tδ = 45°, the binder (or blend) exhibits primarily fluid-like viscous behavior (G″ > G′); there- fore, under load it is more likely to flow and dissipate energy instead of cracking. Below Tδ = 45°, cracking is of concern since the binder (or blend) exhibits primarily solid-like viscoelastic behavior (G′ > G″) and it is thus more likely to store energy instead of relax stress. Typically for unmodified binders, a more solid-like behavior (lower phase angle) is associated with increased brittleness (Ruan et al. 2003). Both of these transition parameters (Tg and Tδ = 45°) are related to molecular motion and are thus frequency-dependent phenomena, but in this experiment, Tδ = 45° was determined at the standard DSR frequency of 10 rad/s. A limited set of materials combinations were characterized using a DSR temperature-sweep conducted at 10 rad/s with a constant cooling rate of 0.5°C/min from 40°C to −40°C to deter- mine Tδ = 45° and highlight its utility. The effect of recycled materials on this parameter is shown by comparing the TX PG 64–22 base binder (Figure 21a) and the recycled PG 88–10 binder blend (Figure 21b). Both have a similar Tg, while Tδ = 45° is significantly shifted (increased) by the inclusion of aged recycled materials. The effect of rejuvenation by recycling agent is presented in Figure 21c, with both Tg and Tδ = 45° decreasing compared to the recycled binder blend shown in Figure 21b. The resulting PG 73–22 rejuvenated binder blend met the climatic requirements

52 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios (a) 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 -40 -30 -20 -10 0 10 20 30 40 D yn am ic S he ar M od ul us (k P a) Temperature (°C) G* G' G" Tg Tδ=45° (b) 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 -40 -30 -20 -10 0 10 20 30 40 D yn am ic S he ar M od ul us (k P a) Temperature (°C) G* G' G" Tg Tδ=45° 0.5 RBR (c) 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 -40 -30 -20 -10 0 10 20 30 40 D yn am ic S he ar M od ul us (k P a) Temperature (°C) G* G' G" Tδ=45°Tg 7.5% RA Figure 21. Temperature dependency of binder and binder blends for (a) TX base (PG 64–22), (b) TX recycled blend (PG 88–10), and (c) TX recycled blend + 7.5% recycling agent (PG 73–22). for TX (PG 70–22), with PGL and Tg decreased due to the low viscosity and low Tg charac- teristic of typical recycling agents. Tδ = 45° was decreased but not restored to that of the base binder (Figure 21a), even though all binders and binder blends met the associated intermediate- temperature PG specification at 25°C and 28°C for PG 64–22 and PG 70–22, respectively. The |G*| sinδ (G″) parameter and specification threshold may not be sufficient to capture the effects of binder embrittlement with recycled materials and rejuvenation by recycling agent since it only considers changes in the viscous component of the complex modulus. Crossover temperature (Tδ = 45°) at 10 rad/s is an alternate intermediate-temperature parameter that can also be obtained from DSR master curves, with the simplest approach shifting the crossover frequency (ωc) to 10 rad/s by applying time-temperature superposition principles, resulting in a robust parameter for tracking the effect of binder aging and rejuvenation. As detailed in Garcia Cucalon et al. (2018), DSR master curve data for calculating Tδ = 45° were available for the materials combinations shown in Table 1 that included four base binders, five recycled materials, five recycling agents, and five aging conditions in different combinations. Thresholds tied to field performance and laboratory failure tests (ductility) are not available for Tδ = 45° as they are for the G-R parameter, but a strong relationship was found between these two intermediate-temperature parameters, as shown in Figure 22, for many binders and binder blends, including those with WMA additives, polymers, and recycling agents, over multiple aging conditions. Considering the G-R thresholds previously introduced, preliminary crossover temperature (Tδ = 45°) durability thresholds were set at 32°C and 45°C for inadequate perfor- mance with aging.

Key Results from Phase 2 53 Figure 23 presents a summary graph highlighting the approach to engineering rheological bal- ance by optimizing PGH and tracking Tδ = 45° with aging. The factors evaluated include two base binders with their corresponding DOT control blends (0.28 RBR), two recycling-agent types/ doses, and a very high RBR. The NH PG 64–28 base binder is of better quality compared to the TX PG 64–22 base binder based on DTc, as discussed previously, PG useful temperature interval (UTI), SAR-AD CII, and G-R with aging. The crossover temperature (Tδ = 45°) results with aging provide the same conclusion. Furthermore, the quality of base binders is reflected in the DOT control blends (with the same RAP/RAS combination), where the control blend with the NH PG 64–28 base binder had better Tδ = 45° before and after aging than that with the TX PG 64–22 base binder. Two recycling-agent types (V1 and T1) at different doses were incorporated in the 0.28 RBR DOT control blend with TX PG 64–22 base binder. Increasing the recycling-agent dose resulted in improved (lower) crossover temperature (Tδ = 45°) with aging, but the PGH was lower than the 70°C requirement for TX. Increased recycling-agent doses were best for long-term y = 0.001x3.535 R² = 0.929 0 10 20 30 40 50 60 70 80 90 G lo ve r- R ow e, 0 .0 05 ra d/ s, 1 5° C ( kP a) Crossover Temperature (°C) Binders and Control Blends WMA Rejuvenated Blends Polymer Modified (PM) PM Rejuvenated Blends PM with Recycling Agent 32 °C -W ar ni ng 45 °C -L im it 180kPa 600kPa 10 5 10 4 10 3 10 2 10 1 10 0 10 -1 10 -2 Figure 22. Defining trial durability thresholds for Tc = 45°. Figure 23. Engineering balanced recycled binder blends.

54 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios durability, but rutting susceptibility must also be considered to achieve rheologically balanced blends. Based on these results, B1 was the most effective in rejuvenating the 0.28 RBR blends with TX materials. Finally, B1 was added to a very high RBR blend with 0.7 NH RAP and 0.3 NH PG 64–28 base binder to meet a 70 PGH and was able to maintain a low crossover temperature (Tδ = 45°) after aging, highlighting the importance of appropriate materials selection and their combinations to facilitate the use of high RBR. Garcia Cucalon et al. (2018) provided additional insight on the importance of selection of better-quality base binders (including polymer modified) for recycling applications and opti- mization of components for improved compatibility of recycled and rejuvenated blends. The parameter DTc, an indicator of low-temperature compatibility, was also evaluated for base binders, recycled blends, and rejuvenated blends and correlated linearly to Tδ = 45° with an R 2 of 0.61. An alternative approach toward engineering balanced recycled binder blends was explored with an intermediate-temperature transition parameter, crossover temperature (Tδ = 45°), in combination with more commonly used parameters PGH and DTc. The main findings can be summarized as follows: • In combination with PGH and DTc, Tδ = 45° was useful in evaluating rejuvenation and aging processes with respect to early rutting and long-term durability. This study confirmed the importance of selecting high-quality base binders in recycling construction projects. The type of recycled materials and recycling-agent type/dose can also be optimized for improved rheo- logical balance. • Despite the potential differences in the fundamental aging mechanisms operating within polymer-modified systems, the characteristic behavior and evaluation framework outlined for unmodified binders was demonstrated as applicable to polymer-modified systems. • The correlation presented resulted in guidelines for initial threshold selections for Tδ = 45° that should be adjusted in future studies by considering asphalt mixture properties and climate. Tδ = 45° data were presented in terms of temperature, thus facilitating climate-based adjust- ments and alignment to PG specifications. 2.4 Representative Binder Blending The influence of recycled materials and recycling agents on the continuous PG of the material combinations shown in Table 1 was evaluated using the mortar procedure in the latest draft AASHTO standard test method for Estimating Effect of RAP and RAS on Blended Binder Performance Grade without Binder Extraction (www.arc.unr.edu/Outreach.html). Figure 24 through Figure 27 indicate the high-, intermediate-, and low-temperature continuous PG for the various binder blends and mortars for the TX recycled materials and T1 (Figure 24 through Figure 26) and for the NV recycled materials and A2 and T2 (Figure 27) at the respective RBRs and recycling-agent doses from the corresponding field projects. The results with the TX PG 70–22 target binder in Figure 24 suggest that T1 influenced PGH more than PGL, with a more pronounced effect in restoring the controlling m-value PGL com- pared to the stiffness PGL. For the mortars containing either RAP or MWAS separately, T1 at the selected dose restored the PGL to the target of −22°C. However, it did not fully restore the PGL to the target of −22°C when the recycled materials were added together at the field combination of 0.28 RBR (0.1 RAP + 0.18 MWAS). Figure 25 shows the results for the binder blends and mortars with the TX PG 64–22 softer (substitute) binder. T1 again had a more significant effect in restoring the controlling m-value PGL compared to the stiffness PGL for the materials combinations containing MWAS.

Key Results from Phase 2 55 Figure 24. Effect of recycling and recycling agent on continuous PG for binder blends and mortars with TX PG 70–22 target binder, T1, and TX recycled materials.

56 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios Figure 25. Effect of recycling and recycling agent on continuous PG for binder blends and mortars with TX PG 64–22 softer (substitute) binder, T1, and TX recycled materials.

Key Results from Phase 2 57 Figure 26. Effect of recycling and recycling agent on continuous PG for binder blends and mortars with NH PG 64–28 softer (substitute) binder, T1, and TX recycled materials.

58 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios Figure 27. Effect of recycling and recycling agent on continuous PG for binder blends and mortars with NV PG 64–28P target binder, A2 and T2, and NV recycled materials.

Key Results from Phase 2 59 However, T1 at the selected dose was only able to partially restore the PGL (to the target of −22°C) when either RAP or MWAS was added separately or when the recycled materials were added together at the field combination of 0.28 RBR (0.1 RAP + 0.18 MWAS). These results suggest that a higher recycling-agent dose might be required for these materials combinations. Similar test results are presented in Figure 26 for the NH PG 64–28 softer (substitute) binder. In all cases, the use of an improved base binder (with a less negative or positive DTc) facilitated the addition of RAP, MWAS, or the combination of both recycled materials, with or without the use of T1, with PGL values less than or equal to the target of −22°C. In these cases, when a recycling agent was not needed, the use of T1 at the selected dose was detrimental with a reduc- tion in PGH and an increase in PGL. Two different recycling agents were used with the NV PG 64–28P target binder for the NV recycled materials, as shown in Figure 27. Both binder blends with 0.30 RAPBR and A2 or T2 at the selected doses met the target PGH of 64°C, but T2 reduced PGH more than A2. For the mortars with more representative blending, A2 reduced PGH more than T2 such that the mortar with A2 did not meet the target PGH of 64°C. The NV PG 64–28P binder blend results also showed that the use of A2 or T2 at the selected doses was effective in restoring the PGL to the target of −28°C, with a more pronounced effect in restoring the controlling m-value PGL compared to the stiffness PGL. Again, the mortars with more representative blending indicated different results, with the recycling agent only able to partially restore the m-value PGL. Figure 28 and Figure 29 show a comparison between binder blends with complete blending and mortars with more realistic blending in terms of PGH and PGL for the TX PG 64–22 softer (substitute) binder with TX field project materials and the NV PG 64–28P target binder with NV field project materials, respectively. For the TX PG 64–22 softer (substitute) binder, the PGH from the mortar procedure was significantly lower (6.2°C to 11.0°C colder) than the PGH for the binder blend, resulting in a narrower UTI. The PGL from the mortar procedure also resulted in a narrower UTI (with PGL values 1.1°C to 3.6°C warmer) compared to that for the binder blend. For the NV PG 64–28P target binder, the PGH from the mortar procedure was again lower (2.1°C to 8.2°C colder) than that for the binder blends for all controlling cases. The PGL from the mortar procedure also resulted in a narrower UTI (with PGL values 1.6°C to 5.0°C warmer) for the controlling m-value cases, but a wider UTI was realized (with PGL values 1.0°C to 2.0°C colder) for the stiffness PGL. For both base binders and all mortars and binder blends, the PGL was controlled by m-value. Figure 30 through Figure 33 show DTc values for binder blends and mortars whose results were in general agreement with each other. For the TX PG 70–22 target binder, T1 was effective in increasing the DTc when RAP, MWAS, or the combination of both recycled materials was used at the selected RBR values. For the TX PG 64–22 softer (substitute) binder, T1 was also effective in increasing (or not decreasing) the DTc for the materials combinations containing MWAS. For the NH PG 64–28 softer (substitute) binder, when a recycling agent was not needed per the previous discussion, the use of T1 at the selected dose was detrimental with a decrease in DTc for all materials combinations except that with MWAS only. For the NV PG 64–28P target binder, both A2 and T2 were effective in increasing the DTc. Results for binder blends and mortars indicated that recycling agents reduce both PGH and PGL. In general, complete blending with the binder blends resulted in overestimation of both the PGH (warmer by 3°C–8°C for NV and 6–7°C for TX) and the PGL (colder by 2°C–5°C for NV and 1°C–2°C for TX) and suggests that perhaps an adjustment is needed to binder blend continuous PG results to account for representative incomplete blending. The more representa- tive mortar results also showed increased recycling-agent effectiveness in terms of DTc for both the TX and NV field project materials combinations. Thus, the mortar procedure can be used to provide useful insights for these complex materials combinations.

60 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios (a) (b) Figure 28. Comparison between binder blends and mortars for TX PG 64–22 softer (substitute) binder, T1, and TX recycled materials: (a) PGH, and (b) PGL.

Key Results from Phase 2 61 (a) (b) Figure 29. Comparison between binder blends and mortars for NV PG 64–28P target binder, A2 and T2, and NV recycled materials: (a) PGH, and (b) PGL.

62 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios Figure 30. Effect of recycling and recycling agent on DTc for binders and mortars with TX PG 70–22 target binder, T1, and TX recycled materials. Figure 31. Effect of recycling and recycling agent on DTc for binder blends and mortars with TX PG 64–22 softer (substitute) binder, T1, and TX recycled materials.

Key Results from Phase 2 63 Figure 33. Effect of recycling and recycling agent on DTc for binder blends and mortars with NV PG 64–28P target binder, A2 and T2, and NV recycled materials. Figure 32. Effect of recycling and recycling agent on DTc for binder blends and mortars with NH PG 64–28 softer (substitute) binder, T1, and TX recycled materials.

64 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios 2.5 Mixture Cracking Resistance by S-VECD To assess the possibility of utilizing S-VECD testing and analysis per AASHTO TP 107 with the AMPT to evaluate the evolution of recycling agent effectiveness in improving intermediate- temperature fatigue cracking resistance of mixtures with high RBRs, LMLC and RPMLC speci- mens were tested. Per AASHTO TP 107, fatigue testing is conducted at temperatures determined by Equation 15: [ ]= + −  2 3 Equation 15Test Temperature PGH PGL Two failure criteria were employed: • The rate of pseudo strain energy release (GR) and • The average reduction in pseudo stiffness up to failure (DR). GR characterizes the rate of damage accumulation during load application, with higher values indicating faster damage accumulation and therefore less time before the material is expected to fail (Zhang et al. 2013). Sabouri and Kim (2014) found that the correlation between GR and the traditional fatigue parameter number of cycles to failure (Nf) is given in Equation 16: [ ]= γ δ Equation 16G NR f where γ and δ are considered material properties. For simplicity, the number of cycles (Nf) corresponding to G R of 100 was adopted for ranking mixtures. DR is given in Equation 17 (Wang and Kim 2017): ∫ [ ] ( ) = −1 Equation 170D C dN N R N f f where C = the pseudo stiffness, which ranges from 1 (undamaged state) to 0 (damaged state). Whereas the GR criterion requires a minimum of three test replicates, the DR parameter can be evaluated using individual test replicates. A higher value of both parameters suggests better mixture cracking resistance. Generally, there are three possible types of failures encountered during S-VECD fatigue testing, and each type determines the appropriateness of the data for further analysis: • Brittle failure: This type occurs when the material is too stiff, causing it to fracture abruptly, and there are insufficient data to evaluate both failure criteria. • End failure: This type is defined as cracking outside the LVDT gauge length as shown in Figure 34, and there are uncertainties surrounding evaluation of both failure criteria. • Middle failure: This desired type of failure is defined as cracking within the LVDT gauge length as shown in Figure 34, and data obtained facilitate determination of both failure criteria. Testing information for TX LMLC specimens and RPMLC specimens from the IN, NV, and WI field projects is summarized in Table 18, Table 19, Table 20, and Table 21, respectively, with the appropriateness of the resulting fatigue data indicated by the following three status colors: • Green = middle failure, • Yellow = end failure, and • Red = brittle failure.

Key Results from Phase 2 65 End Failure Middle Failure Figure 34. Crack location in specimen. Mixtures Rep. No. Actual Temp (PG-Based Temp) Microstrain Initial Modulus (Mpa) Initial Phase Angle (°) Nf (approx.) Crack Location Status Final Phase Angle (°) Virgin (70-22) 1 21 (21) 300 6,520 16 48,000 Middle OK 49 2 350 6,000 17 6,500 Middle OK 43.5 DOT Control 0.28 RBR 1 18 (18) 300 8,281 5.0 — Edge Fracture — 2 21 (18) 250 8,850 11.1 230 Edge Fracture 16 DOT Control 0.28 RBR (WMA) 1 21 (18) 175 6,007 13.3 55,000 Edge End Fail 25 2 225 7,984 12.5 260 Edge End Fail 21 Rejuvenated 0.28 RBR (2.7%) T1 1 21 (18) 150 6,703 11.8 1,200 Edge End Fail 16 2 23 (18) 150 7,556 12.4 4,000 Edge End Fail 17.4 Rejuvenated 0.28 RBR (2.7%) T2 (PG 64-28) 1 23 (15) 200 7,250 16.2 100,000 Middle OK 32.5 3 275 7,300 16.3 2,000 Edge End Fail 27.5 Rejuvenated 0.28 RBR (3.5%) T1 1 23 (18) 150 6,500 12.4 140,000 Middle OK 25.4 2 21 (18) 200 7,890 11.6 800 Edge End Fail 16 4 150 8,000 11.5 8,000 Edge End Fail 23.7 Rejuvenated 0.28 RBR (5.5%) A1 20 23 (18) 175 6,450 15.2 62,000 Middle OK 41.5 21 225 6,500 15.8 11,000 Middle OK 42 Rejuvenated 0.5 RBR (12.5%) T1 (PG 64-28) 1 21 (18) 200 9,600 10.1 5,500 Edge End Fail 22.5 2 150 9,800 11.3 26,000 Middle OK 26.5 3 130 10,700 10.3 140,000 Middle OK 21.2 NOTE: — = not applicable. Table 18. S-VECD testing information for TX LMLC mixtures.

66 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios Mixtures Rep. No. Actual Temp (PG- Based Temp) Microstrain Initial Modulus (Mpa) Initial Phase Angle (°) Nf (approx.) Crack Location Status Final Phase Angle (°) Virgin (PG 64-22) 1 18 (18) 250 10,000 14.8 21,000 Edge OK 28 2 225 9,920 14.8 50,000 Edge OK 28 3 275 10,000 14.9 9,000 Middle OK 29.5 DOT Control 0.32 RBR 1 15 (12) 225 12,000 11.3 24,000 Edge End Fail 24.6 2 250 10,700 12.5 19,000 Edge End Fail 26.9 3 300 11,580 12.4 140 Edge End Fail 16 4 200 11,030 12.1 200,000 No crack End Fail 25.9 Rejuvenated 0.42 RBR (3%) T2 1 15 (12) — 14,000 — — — Fracture — 2 20 (12) 150 12,000 9 140 Edge Fracture 11 3 25 (12) — — — — — Fracture — 4 27 (12) 150 11,000 10 200 Edge Fracture 12 NOTE: — = not applicable. Table 19. S-VECD testing information for Indiana RPMLC mixtures. Mixtures Rep. No. Actual Temp (PG- Based Temp) Microstrain Initial Modulus (Mpa) Initial Phase Angle (°) Nf (approx.) Crack Location Status Final Phase Angle (°) Virgin 1 15 (15) 300 5,100 22.4 200,000 No Crack End Fail 47.8 2 400 5,550 19.5 4,600 Edge End Fail 41.8 3 350 5,650 20.1 4,000 Edge End Fail 38.2 5 310 5,510 2.1 85,000 Middle OK 51 6 330 5,800 19.5 15,000 Middle OK 47 DOT Control 0.15 RBR 2 18 (15) 250 6,180 19.6 185,000 Middle OK 49 3 275 6,180 19.5 110,000 Middle OK 58 4 300 6,030 20.2 100,000 Middle OK 52.5 5 350 5,880 19.8 23,000 Middle OK 50.8 6 375 5,960 19 13,000 Middle OK 48.5 Recycled 0.3 RBR 1 18 (15) 250 7,700 15.2 145,000 Middle OK 42.7 2 300 7,130 15.4 7,000 Edge End Fail 30 3 275 7,650 15.7 70,000 Middle OK 43 5 300 8,670 14.7 32,000 Middle OK 43 8 325 8,350 14.4 14,500 Middle OK 46 Rejuvenated 0.3 RBR (2%) T2 1 18 (15) 250 7,880 14.9 46,000 Edge End Fail 31.5 2 275 8,420 14.9 6,200 Edge End Fail 30 3 250 7,440 16 18,000 Edge End Fail 33 5 200 7,300 15.5 230,000 Middle OK 36 6 260 7,700 15.2 16,500 Edge End Fail 33 Rejuvenated 0.3 RBR (2%) A2 1 18 (15) 250 7,680 15.9 59,000 Edge OK 43.4 2 300 7,020 16.4 50 Edge Fracture — 3 225 7,080 16.1 75,000 Edge End Fail 34 5 275 7,070 16.4 52,000 Middle OK 45.6 6 290 7,230 15.6 19,000 Edge End Fail 37 7 200 7,370 16.6 160,000 Middle OK 38.5 NOTE: — = not applicable. Table 20. S-VECD testing information for Nevada RPMLC mixtures. Testing stiff and brittle mixtures resulting from high RBRs and aged materials, along with the aging gradient induced by LTOA of compacted specimens, resulted in a significant number of brittle and end failures. To reduce the probability of brittle failures, the testing temperatures were often increased from those calculated using Equation 15, and these test temperatures are also indicated in Table 18, Table 19, Table 20, and Table 21. In spite of the difficulties associated with S-VECD testing, adequate data were obtained for assessing the WI and NV RPMLC mixtures. The failure criteria are presented subsequently in bar graphs with an error bar indicating one standard deviation from the mean value for the

Key Results from Phase 2 67 DR criterion that used more than one replicate and facilitated statistical evaluation. For the WI mixtures, both S-VECD failure criteria (DR and GR) in Figure 35 show an improvement with the addition of the field dose of the recycling agent (1.2%) and with the use of a softer base binder (PG 52–34) compared to the 0.31 RBR recycled control mixture. However, neither strategy for increasing RBR restored the parameters to the level of the DOT control mixture (0.22 RBR). For the NV mixtures with results in Figure 36, the field dose of the recycling agent (2%) pro- vided an increase in the GR value over the mixture with no recycling agent; however, there was no improvement in the DR parameter. Neither parameter was restored to the level of the DOT Mixtures Rep. No. Actual Temp (PG- Based Temp) Microstrain Initial Modulus (Mpa) Initial Phase Angle (°) Nf (approx.) Crack Location Status Final Phase Angle (°) DOT Control 0.22 RBR 1 21 (12) 275 6,970 18 24,000 Middle OK 53 2 300 7,600 17 10,000 Middle OK 49 3 300 7,200 17.6 8,900 Middle OK 54 4 260 7,400 17.4 20,000 Middle OK 54.8 8 315 7,430 16.8 7,200 Middle OK 54 Recycled 0.31 RBR 1 18 (12) 250 10,120 13 14,000 Middle OK 46 2 275 9,820 13.8 5,700 Edge End Fail 34 3 275 9,770 13.6 6,900 Middle OK 43 4 300 8,970 14.4 3,100 Edge End Fail 31 5 21 (12) 315 7,200 17 6,900 Middle OK 43 6 300 8,000 15.8 8,800 Middle OK 42 Recycled 0.31 RBR (PG 52-34) 2 21 (6) 275 6,710 19.4 16,000 Middle OK 57.5 3 300 6,450 20.6 13,000 Middle OK 54 4 330 6,040 21 13,000 Middle OK 57 6 315 7,060 19.2 9,800 Middle OK 53.5 Rejuvenated 0.31 RBR (1.2%) V2 1 21 (12) 275 7,680 16.5 14,000 Middle OK 52.5 2 300 8,150 16.3 3,100 Middle OK 48.5 3 245 7,370 16.8 62,000 Middle OK 50.5 4 260 8,190 16 25,000 Middle OK 54.5 Table 21. S-VECD testing information for Wisconsin RPMLC mixtures. Figure 35. S-VECD criteria for WI RPMLC mixtures.

68 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios control (0.15 RBR), indicating that the field dose did not facilitate the use of higher recycled materials content (0.3 RBR). Because of the limited scope of successful S-VECD results obtained for aged mixtures with high RBRs and the need for additional efforts to determine the best way to use this tool for these types of mixtures, the use of this test and analysis approach is not recommended at this time. 2.6 Comparison of Specimen Types Figure 37 and Figure 38 present the MR and I-FIT results for field cores and for LMLC and RPMLC specimens after STOA and LTOA for the WI field project materials combinations. For each mixture, the darker-shaded stacked column represents the MR and FI after STOA (at construction for the field cores), and the hatched lighter-shaded stacked column represents the MR and FI after LTOA (at 1 year after construction for the field cores). All specimen types, including the field cores, had AV values within 7 ± 0.5%. Based on the error bars (+ one standard deviation) for each specimen type in Figure 37, the LMLC specimens after STOA and field cores at construction showed similar stiffness (green and blue bars), and lower stiffness than the RPMLC specimens (red bars). The higher stiff- ness of the RPMLC specimens was likely due to the reheating of the loose plant mixture, and thus the additional aging introduced in these specimens. Similar trends were also observed after LTOA where both the LMLC specimens and field cores showed similar stiffness, but lower than the RPMLC specimens (except for the DOT control mixture). The I-FIT test results, shown in Figure 38, also indicated that the LMLC specimens and field cores consistently showed similar FI values regardless of aging condition or service time in the field, and both had higher FI values than RPMLC specimens. These results provide justification for selecting LMLC specimens when possible to evaluate the performance of recycled asphalt mixtures with recycling agents since the additional aging Figure 36. S-VECD criteria for NV RPMLC mixtures.

Key Results from Phase 2 69 Figure 37. MR test results for WI mixtures of different specimen types. Figure 38. I-FIT test results for WI mixtures of different specimen types.

70 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios introduced due to reheating the plant loose mixtures significantly affected the laboratory test results for the RPMLC specimens. In some cases, RPMLC data were utilized when available and appropriate. 2.7 Key Findings Key findings from this study presented in this chapter from results obtained in Phase 2 that were not expanded in Phase 3 include the following: • Recycling-agent effectiveness must be characterized in high RBR binder blends initially and with long-term aging to capture initial compatibility and rheological response to oxidation. • A 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, with a lower dose to restore PGL only sufficient with short-term aging. • Chemical analysis of high RBR binder blends with recycling agents is challenging, and addi- tional evaluation tools are needed. • Crossover temperature (Tδ = 45°) can be used as an alternative approach to the G-R parameter to engineer balanced recycled binder blends. • Use of high-quality base binders improves performance of high RBR binder blends and mix- tures with recycling agents. • Rejuvenation mechanisms differ by recycling agent type. • Mortar procedures provide realistic assessment of binder blending and narrow the PG UTI as compared to that of a corresponding binder blend. • Recycling agents are more effective in rejuvenating less-aged recycled materials (RAP more than RAS and MWAS more than TOAS) in balanced, limited proportions. • Modifications are needed for testing high RBR mixtures after long-term aging. • Reheating to produce RPMLC specimens is especially detrimental to high RBR mixtures with recycling agents. • Standard laboratory fabrication protocols with STOA produce specimens that represent cores for high RBR mixtures with and without a recycling agent.