Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios (2020) / Chapter Skim
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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
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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)
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Figure 92. DTc threshold: binder blend Black space.
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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.
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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)
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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.
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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.
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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.
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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.
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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 Chapter 4 are proposed as developed by Romero (2016) based on field performance of seven field projects in Utah.
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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.
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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: [ ]
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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.
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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.
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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 challenge since the representative PAV aging durations are not only climate specific but also binder specific (i.e., function of binder chemical properties and kinetics)
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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)
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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.
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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.
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