Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios (2020) / Chapter Skim
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From page 79... ...
79 Chapter 4 presents expanded laboratory performance results for binder blends and mixtures with high RBRs to explore the impact of higher recycling-agent doses than those used in the field projects with respect to the following issues: • Binder blend rheology with aging, • Binder blend aging prediction, • Recycling-agent characterization, • Mixture performance, and • Recycled binder availability. Appendix F provides additional data on binder blend aging prediction, and Appendix G provides additional data on recycling-agent characterization.
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Figure 47. Illustration of |G*
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Expanded Laboratory Performance of High RBR Binder Blends and Mixtures 81 Blend/Mixture DOT Control (0.15 RBR) Rejuvenated (0.3 RBR)
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82 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios These blends were regarded as the reference blends and compared to other blends of similar or higher RBR with recycling agent to evaluate the effectiveness of the recycling agents at the selected doses in improving the performance of the DOT control blend, and in facilitating the use of higher RBR than currently allowed by the DOTs. In Table 27, the rejuvenated binder blends (and asphalt mixtures)
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Expanded Laboratory Performance of High RBR Binder Blends and Mixtures 83 Figure 49.
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84 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios This behavior indicated improved performance, with use of the recycling agent at the selected dose facilitating higher recycled materials contents compared to that of the DOT control. Considering DTc, all blends had poor DTc values, with the blend with recycling agent at close to the field dose showing a higher (less negative)
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Expanded Laboratory Performance of High RBR Binder Blends and Mixtures 85 use of higher recycled materials contents compared to the DOT control. Considering DTc, all blends had good DTc values (higher than those in the TX, IN, and WI blends)
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86 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios combination with the prediction of both oxidation and rheological characteristics in service. The oxidation rate along this path was measured in terms of CA growth (CAg)
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Expanded Laboratory Performance of High RBR Binder Blends and Mixtures 87 (NH PG 64–28, NV PG 64–28P, WI PG 58–28, and WI PG 52–34)
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88 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios where G-R = Glover-Row parameter (kPa)
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Expanded Laboratory Performance of High RBR Binder Blends and Mixtures 89 rates or G-R/CAg HS were observed between blends with only recycling agent added and rejuvenated blends (with recycling agent and recycled materials) for the TX PG 64–22, NH PG 64–28, and NV PG 64–28P base binders.
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90 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios As an example, a summary of CAg predictions for the TX PG 64–22 binder blends over the analysis period at 0.01 m below the surface at the TX field project location is provided in Figure 55. Using the CAg predictions from all the selected base binder blends resulted in the estimated time to reach the G-R thresholds as a function of in-service time at the TX and WI field projects.
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Expanded Laboratory Performance of High RBR Binder Blends and Mixtures 91 (i.e., 600 kPa)
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92 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios Consideration of the NV PG 64–28P binder blends shown in Figure 57 resulted in similar findings for the respective influences of the various components. The exception noted with this polymer-modified blend was found with the cracking onset threshold of 180 kPa for the rejuvenated blend, which was observed at a time similar to that for the NV PG 64–28P base binder, while the significant cracking threshold of 600 kPa was predicted to occur substantially after that for the base binder.
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Expanded Laboratory Performance of High RBR Binder Blends and Mixtures 93 for the oxidation model relative to the TX field project location. After a 20-year simulation, none of the recycled blends with recycled materials (and either base binder)
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94 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios durations among these base binders. For the WI binder blends, different environmental conditions yielded longer durations despite the similarities in kc rates when compared with the other blends.
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Expanded Laboratory Performance of High RBR Binder Blends and Mixtures 95 The basic rejuvenation mechanism by the selected recycling agents is the addition of strongly polar compounds that help to polarize asphaltene clusters in recycled binders and compatibilize them with maltenes, thus breaking up the large asphaltene clusters. Recycling agents with these strongly polar compounds are classified as rejuvenators, and their addition reduces stiffness (|G*
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96 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios ranging from 42 kPa to 45 kPa, whereas the aromatic extract A1 was slightly higher at 55 kPa, and the tall oil exhibited more sensitivity to aging with a G-R value of 84 kPa. A Glover-Rowe long-term aging index was also calculated as the logarithm of the ratio of the G-R parameter for the blend after 40-h PAV to that after RTFO.
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Expanded Laboratory Performance of High RBR Binder Blends and Mixtures 97 be difficult to differentiate and quantify the overlapping peaks, especially for those blends with bio-based recycling agents (including T, V, and B types in this study)
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98 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios by CAg, but the blend experienced substantial increases in G-R due to a rapid deterioration in compatibility between a saturate-rich maltene phase and increasingly larger and more polar asphaltenes. This parameter would likely show the same deficiencies for REOB modified binders, given previous reports from Reinke (2015)
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Expanded Laboratory Performance of High RBR Binder Blends and Mixtures 99 aging. A third experiment was completed to compare the conditioning sequence for rejuvenation and aging for the following two separate options in terms of Black space analysis and calculated G-R parameter: • Conditioning sequence #1: The rejuvenated binder blend was prepared by combining DE base binder (PG 64–28)
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100 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios their G-R parameter values were much higher (typically double) than the G-R parameter values of their counterpart blends in which the recycling agents were aged as part of the conditioning.
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Expanded Laboratory Performance of High RBR Binder Blends and Mixtures 101 when a recycling agent is added to a recycled binder. If dissolved oxygen in the asphalt really can be diverted to other reactions, rather than forming the highly damaging benzylic carbonyl, there could be additional benefits from recycling agents beyond the initial impact on rheology.
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102 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios The aromatic extract A1 has historically been the gold standard for petroleum-based recycling agents. Often promoted as replacing the aromatics and resins lost to oxidation, these recycling agents can maintain compatibility with oxidized asphaltenes under much more rigorous aging conditions than their paraffinic counterparts.
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Expanded Laboratory Performance of High RBR Binder Blends and Mixtures 103 used to restore rheology by different types of recycling agents that may be listed on a qualified products list. Mixture characterization tests including I-FIT and HWTT were also conducted for comparison to the corresponding binder blends.
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104 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios selected doses in improving the performance of the DOT control mixtures, and in facilitating the use of higher RBR than currently allowed by the DOTs. Results presented in this section are for LMLC specimens after STOA and LTOA.
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Figure 68. MR test results.
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106 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios rejuvenation, mixtures are expected to move toward the lower right corner, which indicates a reduction in stiffness with a corresponding increase in phase angle. The magnitude and slope between two points in mixture Black space were also determined to quantitatively evaluate the change in rheological properties with aging, as defined in Equation 21 and Equation 22, respectively: ( )
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Expanded Laboratory Performance of High RBR Binder Blends and Mixtures 107 brittle (higher phase angle) with longer aging paths (larger magnitude)
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108 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios control mixture with similar RBR (TX) , or producing high RBR asphalt mixtures with statistically similar or higher FI to that of the DOT control mixtures with lower RBR (IN, NV, WI, and DE)
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Expanded Laboratory Performance of High RBR Binder Blends and Mixtures 109 4.4.3 Low-Temperature Cracking Resistance (Low-Temperature Mixture Black Space with Sm and m-valuem, CRIEnv) The BBRm test and the UTSST were used to explore low-temperature mixture cracking resistance as data were available for different materials combinations from the five field projects.
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Figure 75. FI results.
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Figure 76. CRI results.
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Figure 77. BBRm test results (unfilled symbols represent STOA specimens while filled symbols represent LTOA specimens)
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Expanded Laboratory Performance of High RBR Binder Blends and Mixtures 113 UTSST modulus and CRIEnv results for NV LMLC mixtures at different levels of aging are presented in Figure 78 and Figure 79, respectively. The moduli variation with decreasing temperature shows the low-temperature behavior of the mixture with a focus on viscous softening, crack initiation, and fracture for this study, while the CRIEnv provides an overall index that simultaneously takes these different aspects of behavior into account.
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114 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios effect after LTOA. These results were confirmed by CRIEnv values, although all three mixtures at high 0.3 RBR (both the recycled mixture and both rejuvenated mixtures)
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Expanded Laboratory Performance of High RBR Binder Blends and Mixtures 115 a more pronounced effect after LTOA. These results were confirmed by CRIEnv values, although the higher recycling-agent dose provided sufficient low-temperature cracking resistance even after LTOA.
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116 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios (with PG 64–28 base binder) , all with the recycling agent at the selected dose, passed the minimum rutting requirements.
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Expanded Laboratory Performance of High RBR Binder Blends and Mixtures 117 In a similar manner, the following methodology was developed and demonstrated in Phase 2 to estimate the RAP binder availability based on an evaluation of mixtures with specific sizes of virgin aggregate and RAP: 1. Prepare the virgin mixture using: a.
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118 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios (a)
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Expanded Laboratory Performance of High RBR Binder Blends and Mixtures 119 The coated RAP particles in the RAP mixture have the same binder content as the coated virgin aggregate particles on the No. 4 sieve in the virgin mixture.
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120 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios equals 4.0% in this example, which represents 100% availability, and Scenario 2 when RAP′ Pb equals 7.3% in this example, which represents 0% availability. From this relationship, a binder availability factor (BAF)
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Expanded Laboratory Performance of High RBR Binder Blends and Mixtures 121 4.5.3 Factors Affecting RAP BAF The proposed methodology was also used to estimate the RAP BAF of actual RAP materials from seven different sources in the United States: TX, Florida (FL) , IN, New Hampshire (NH)
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122 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios temperature, the higher the BAF. This is expected since higher mixing temperatures help soften the RAP binder, making it more fluid and facilitating its blending with the base binder.
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Expanded Laboratory Performance of High RBR Binder Blends and Mixtures 123 RAP binder will be active and available in the mixture, compared to 80% for the WI RAP. However, if the mixing temperature is increased to 150°C, the availability of the RAP binder from TX and WI will increase to about 70% and 95%, respectively.
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124 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios (a)
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Expanded Laboratory Performance of High RBR Binder Blends and Mixtures 125 Figure 89b shows, however, that adding the recycling agent slightly increased the RAP BAF at 150°C mixing temperature but did not show any statistical difference except for the TX and FL RAP sources. This would indicate that the recycling agent helps increase the RAP BAF only at low mixing temperatures and that increasing the mixing temperature has an equivalent effect to adding a recycling agent.
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126 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios • Use of high-quality base binders improves performance of high RBR binder blends and mixtures with recycling agents. • Rejuvenation mechanisms differ by recycling-agent type.
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