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 36... ...
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 recyclingagent, 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.
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Key Results from Phase 2 37 to satisfy climate and traffic requirements (i.e., PG 70–22 for TX)
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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#)
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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#)
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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 nocracking, 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.
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Key Results from Phase 2 41 Figure 11) , and the mixture failed by reaching a rut depth of 12.5 mm (at 50°C)
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42 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios and RASBR)
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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.
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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 blending charts for recycled binder blends with 0.31 RBR and 0.5 RBR (0.31 and 0.5 WI RAP)
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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.
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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)
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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.
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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.
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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.
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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.
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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.
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52 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios (a)
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Key Results from Phase 2 53 Figure 23 presents a summary graph highlighting the approach to engineering rheological balance 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)
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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.
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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.
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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)
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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)
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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.
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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)
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60 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios (a)
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Key Results from Phase 2 61 (a)
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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.
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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.
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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 intermediatetemperature fatigue cracking resistance of mixtures with high RBRs, LMLC and RPMLC specimens were tested. Per AASHTO TP 107, fatigue testing is conducted at temperatures determined by Equation 15: [ ]
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Key Results from Phase 2 65 End Failure Middle Failure Figure 34. Crack location in specimen.
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66 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios Mixtures Rep.
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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)
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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)
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Key Results from Phase 2 69 Figure 37. MR test results for WI mixtures of different specimen types.
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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.
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