Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios (2020) / Chapter Skim
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4 More than 90% of highways and roads in the United States are built using HMA or WMA mixtures. In the early 1990s, the Federal Highway Administration (FHWA)
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Introduction 5 PRAS = percentage of RAS by weight of mixture, and Pbtotal = binder content of the combined mixture. In spite of the symbiotic benefits, state DOTs limit the use of RAP and/or RAS in asphalt mixtures for reasons that include variability of the recycled materials and concerns about long-term mixture performance.
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Figure 1. NCHRP 09–58 overview.
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Introduction 7 field projects in Texas (TX) , Nevada (NV)
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TX 70-22 P (ΔTc -4.9) -- -- -- Base Binder -- -- -- -- -- -- -- -- -- -- -- 2.7% T1 (field)
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Materials Combinations Binder Testing Mortar Testing (PG) Mixture Testing Base Binder Recycled Materials Recycling Agent Dose and Type (Dose Selection Methodc)
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NOTE: Gray shading indicates IN field project material combinations; -- = not applicable. aAt RTFO, 20 PAV, and 40 PAV aging.
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NOTE: Gray shading indicates WI and DE field project material combinations; -- = not applicable. aAt RTFO, 20 PAV, and 40 PAV aging.
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Introduction 13 – SAR-AD -- saturates, aromatics, resins–asphaltene determinator fractions. – CII -- colloidal instability index.
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14 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios • Predominant Use of RAP at High RBRs: Despite the widespread acceptance across state DOTs of the use of recycled materials in HMA and WMA mixtures, survey results reported in the first interim report indicated that most DOTs do not commonly use a high percentage of RAP (60% use 11%–20%, or approximately 0.1–0.2 RAPBR, and 23% use 21%–30%, or approximately 0.2–0.3 RAPBR) and do not commonly use a high percentage of RAS (65% use 0%–3%, or approximately 0–0.13 RASBR, and 29% use 4%–6%, or approximately 0.17–0.26 RASBR)
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Introduction 15 semicircular bend (SCB) test recommended by NCHRP Project 9–57, "Experimental Design for Field Validation of Laboratory Tests to Access Cracking Resistance of Asphalt Mixtures" (Zhou and Newcomb 2015)
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16 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios Author(s) and Year Laboratory Test(s)
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Author(s) and Year Laboratory Test(s)
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Table 6. Previous research on the effect of recycling agents on rutting resistance and moisture susceptibility of recycled asphalt mixtures.
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Introduction 19 Chapter 3 presents a summary of field performance of high RBR mixtures in the field projects and a comparison of field and corresponding laboratory performance toward development of thresholds for cracking resistance. Chapter 4 provides more detailed laboratory performance results of high RBR binder blends and associated mixtures in terms of the following challenges associated with the evaluation of the effectiveness of recycling agents in high RBR binder blends initially and with aging: • Binder blend rheology with aging, • Binder blend aging prediction, • Recycling-agent characterization, • Mixture performance, and • Recycled binder availability.
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20 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios • Kaseer, F., L Garcia Cucalon, E
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Introduction 21 1.5.1 Field Projects and Materials In selecting field projects for use in the Phase 2 laboratory experiments and the Phase 3 field experiments, consideration was given to obtaining a range in each of the following factors to make the conclusions of this study as comprehensive as possible: • Recycling agents by category, as defined in Table 7, for comparison of types; • RAPBR and RASBR; • Environmental zone, as defined by the SHRP Long-Term Pavement Performance Program (SHRP-LTPP) and shown in Figure 2; and • Traffic volume.
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22 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios Table 8 through Table 12 provide details for the test sections in the field projects constructed in TX, NV, IN, WI, and DE (Figure 2) , respectively, which include those used in Phase 2 from TX, NV, and IN and in Phase 3 from WI and DE.
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Introduction 23 Mixture Type/Test Section Virgin DOT Control (0.28 RBR) +0.5% WMA Rejuvenated (0.28 RBR)
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24 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios For the laboratory experiments, materials were selected from those used in the field projects and expanded with additional base binders from NH and MN; RAP from NH; TOAS from TX and CA; and A1, V1, V3, B1, B2, and P recycling agents as shown in Table 1 and summarized as follows: • Phase 2A: – High 0.3 to 0.5 RBRs with all RAP and RAP/RAS combinations with equivalent RAPBR and RASBR. – Traditional aromatic (A1, A2)
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Introduction 25 – NV field project materials: NV PG 64–28P base binder, NV RAP, and T2 and A2. – IN field project materials: IN PG 64–22 and IN PG 58–28 base binders, IN RAP and IN MWAS, and T2.
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26 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios Performance Issue Binder Parameter and Test Mortar Parameter and Test Mixture Parameter and Test Recycling-agent dose selection PGH after S Aging, PGL after L Aging per AASHTO T 315, T 313, and M 320 -- -- Rheological balance and effectiveness evolution with aging PGH after S Aging per AASHTO T 315 & M 320 ∆Tc @ Tlow after L Aging per AASHTO PP 78 G-R & Tδ=45° @ Tint with Aging by DSR Master Curve per AASHTO T 315 CA Growth by FT-IR with Aging Oxidation Kinetics and G-R/CAg HS by FT-IR and DSR Master Curve ∆Tc @ Tlow after L Aging per AASHTO PP 78 MR @ Tint after S, L Aging per ASTM D7369 Externally across Diameter |E* |, φ@ Thigh, Tint and Tlow after S, L Aging per AASHTO T 342 G-Rm @ 20°C, 5 Hz Rutting resistance and balanced mixture PGH after S Aging per AASHTO T 315 and M 320 PGH after S Aging per Draft AASHTO N12.5 by HWTT^ & APA Jr^ @ Thigh after S Aging per AASHTO T 324 Fatigue cracking resistance G-R @ Tint with Aging by DSR Master Curve per AASHTO T 315 PGI after L Aging per Draft AASHTO FI & CRI by I-FIT @ Tint after S and L Aging per AASHTO TP 124 DR & Nf@GR = 100 by S-VECD and |E*
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Introduction 27 (a)
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28 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios Table 14 provides a summary of the specimen fabrication aging protocols and guidelines for recycling-agent blending by addition or replacement. As an example, for a mixture with 30% RAP (PbRAP = 5.0%)
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Introduction 29 1.5.2.2 Aging Protocols Critical or representative aging protocols were used for specimen fabrication for each laboratory test across the pavement temperature spectrum, with short-term aged binders (after RTFO) or mixtures (short-term oven aging [STOA]
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30 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios scattering (ELS) detector and a variable wavelength absorbance detector set at 500 nm.
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Introduction 31 Since some of the selected recycling agents contain large amounts of carbonyl, CAg was monitored during aging to define oxidative changes, rather than the more traditional CA, which represents the total carbonyl peak area. For mortars, laboratory testing followed the latest draft of test method AASHTO T XXX-12 Estimating Effect of RAP and RAS on Blended Binder Performance Grade without Binder Extraction (www.arc.unr.edu/Outreach.html)
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32 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios ∫ [ ]
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Introduction 33 Additional characterization resulting from the UTSST measurements was also developed to summarize mixture low-temperature cracking resistance and combine specific aspects of the thermal stress and thermal strain relationships with those of the thermos-viscoelastic property regions and recognize the benefits of certain mixture characteristics. A cracking resistance index (CRIEnv)
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34 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios (a)
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Introduction 35 where CRIEnv = UTSST cracking resistance index including the environmental adjustment factor; Av = area of viscous behavior, i.e., area of stress–strain up to viscous softening; Ai = area of crack initiation, i.e., area of stress–strain from viscous softening up to crack initiation; Ap = area of crack propagation, i.e., area of stress–strain from crack initiation up to ultimate fracture; svgt = thermal stress at viscous–glassy transition; sf = thermal stress at fracture; Avgt-F = area under the thermal stress–strain plot between the viscous–glassy transition temperature and the fracture temperature of the restrained UTSST specimen; and Avgt-crit = area under the thermal stress–strain plot between the viscous–glassy transition temperature and the required environmental temperature at a given location. In this configuration, increased levels of low-temperature cracking resistance are indicated by larger values of the CRIEnv.
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