Fundamental Evaluation of the Interaction Between RAS/RAP and Virgin Asphalt Binders
Fundamental Evaluation of the Interaction Between RAS/RAP and Virgin Asphalt Binders

Author: Munir D. Nazzal

Publisher:

Published: 2017

Total Pages:

ISBN-13:

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A comprehensive laboratory testing program was conducted in this research project to examine the blending between reclaimed asphalt pavement (RAP)/recycled asphalt shingles (RAS) and virgin asphalt binders and to evaluate the factors that may affect fatigue and low-temperature cracking as well as moisture-induced damage in asphalt mixtures prepared using these materials. This project included two parts: a binder study and a mixture study. In the binder study, atomic force microscopy (AFM) was utilized to characterize the micromechanical properties of the interfacial zone that develops between the RAP/RAS binders and the virgin asphalt binders. Three virgin asphalt binders with different performance grades (PG 58-28, PG 64-28, and PG 64-22), three RAP sources, as well as manufacturing waste and tear-off RAS were used in this project. A new sample-preparation procedure was developed to simulate the blending between the RAS/RAP and the virgin asphalt binders that occurs during asphalt mixture production. The micro-structure, stiffness and the adhesive properties along the blending zone were evaluated for different combinations of RAP/RAS binders and virgin binders. In the mixture study, several asphalt mixtures were used to evaluate the effect of the incorporation of RAP and/or RAS on the mix performance, including a control mixture (no RAP or RAS), a mixture containing 30% RAP, a mixture containing 5% tear-off RAS, and a mixture containing 20% RAP and 3% tear-off RAS. All mixtures were designed to meet ODOT specifications for Item 442 (Superpave) Type A for heavy traffic intermediate course asphalt mixes. The resistance of the asphalt mixtures to fatigue cracking was evaluated using the semi-circular bend (SCB) and the indirect tensile strength (IDT) tests. The SCB test was performed using the Illinois Method and the Louisiana Method. In addition the potential for low-temperature cracking was evaluated using the asphalt concrete cracking device (ACCD), and the susceptibility of the asphalt mixtures to moisture-induced damage was evaluated using the AASHTO T 283 (modified Lottman) test. The AFM test results indicated that blending occurred to a varying degree between the RAP binders and the virgin binders for all RAP-virgin binder combinations. The average modulus of the blending zone depended on the properties of the RAP and the virgin binders. For all binders, a reduction in the adhesive bonding energy was also observed in the blending zone due to the presence of RAP. However, the adhesive properties of the blending zone were significantly higher than those in the RAP binders. Statistical analysis also indicated that the stiffness of the interface blending zone is affected by the properties of the RAP and virgin asphalt binders, while the adhesive properties of the interface blending zone is primarily affected by those of virgin binder used. A linear regression model was developed to predict the modulus and adhesive bonding energy of the blending zone in terms of RAP and virgin binder properties. The validation of the regression models suggested that these models can serve as a viable tool in selecting the virgin binder to be used in a RAP mixture based on the properties of the RAP binder. Finally, the AFM imaging and force spectroscopy experiments revealed very limited to no blending between manufacturing waste or tear-off RAS materials and the virgin binders considered. The asphalt mixture test results also showed that the use of tear-off RAS in intermediate asphalt mixes significantly reduced their resistance to low-temperature and fatigue cracking as well as moisture damage, which can be attributed to the limited blending observed in the AFM experiments between the RAS and the virgin asphalt binders.

Interaction Between New and Age-hardened Binders in Asphalt Mixes Containing High Quantities of Reclaimed Asphalt Pavement and Reclaimed Asphalt Shingles
Interaction Between New and Age-hardened Binders in Asphalt Mixes Containing High Quantities of Reclaimed Asphalt Pavement and Reclaimed Asphalt Shingles

Author: Yuan He

Publisher:

Published: 2016

Total Pages:

ISBN-13: 9781339825762

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As virgin pavement material sources become scarcer and costlier the use of higher quantities of reclaimed asphalt pavement (RAP) and reclaimed asphalt shingles (RAS) in the production of new asphalt mixes becomes increasingly desirable. RAP/RAS binder in the mix has different levels of aging. Through oxidation, the binder becomes stiffer and more rigid than virgin binder, and thus results in a pavement material that is more brittle and susceptible to fatigue and thermal cracking. The purpose of this dissertation study was to investigate the interactions between new and age binders and evaluate asphalt mixes performance. A major concern associated with the use of high percentages of RAP and/or RAS is the level of blending between virgin and age-hardened binders, because the performance of the mix can be highly influenced by the properties of the composite binder. The blending between new binder and age-hardened RAP binder can be explained through diffusion mechanisms. This research used asphalt binder testing and diffusion and aging theory to investigate the evolution of blending between virgin and RAP binders during asphalt mix production, storage, and placement. The rheological properties of a two-layer asphalt binder sample composed of virgin and simulated RAP binder were measured using a dynamic shear rheometer (DSR) after conditioning following hot mix asphalt (HMA) and warm mix asphalt (WMA) time-temperature paths during mixing and placement. The diffusion and aging coefficients for the composite binder were estimated by comparing measured shear stiffness values with those predicted using a diffusion model and considering asphalt binder aging over time. The diffusion model is solved numerically based on the finite control volume approach. Results show that the HMA results in nearly full blending of the new and aged binders following the time-temperature paths used in this study; while the WMA results in only partial blending. Traditionally, the properties of blended binders in asphalt mixes containing RAP and RAS are evaluated through rheological testing of the binder extracted and recovered from a mix. However, this approach has long been criticized for being labor intensive, for potentially altering the chemistry of the binder and consequently changing the binder rheology, for forcing blending of binders that may not have been present in the mix, and for creating hazardous material disposal issues. The research presented in this dissertation proposes an alternative approach for characterizing blended binders by testing the linear viscoelastic properties of a fine aggregate matrix (FAM) asphalt mix using a torsion bar fixture in a DSR. A procedure has been developed for preparation and testing of small FAM cylindrical FAM specimens. The results demonstrated that this testing is sensitive to FAM mixes made of different virgin binders, RAP/RAS contents, with and without rejuvenating agent. More importantly, FAM mix testing shows similar results as that from DSR binder testing and full mix testing in terms of rankings of master curves and Black diagrams. Statistical analysis (ANOVA) on stiffness values from FAM testing also provides the same conclusion to that at binder and mix levels. Therefore, FAM approach has the potential to be used as a substitute to stiffness testing for mix comparison purposes. It is also a less expensive and more efficient testing approach than the full mix testing.The combined effect of RAP, RAS, and different virgin binder sources and grades on performance of the blended binders and asphalt mixes was also investigated. Previous studies have indicated that RAP, RAS, and virgin binder grades each has certain effects on performance of the mix. The addition of RAP/RAS undermines fatigue and thermal performance and improves rutting resistance. The virgin binder grade should be carefully chosen based on the percentages of RAP/RAS in the mix. Results from unconfined RLT appears to show that reducing the binder grade when using more than 25 percent RAP results in rutting performance similar to the original grade. Therefore, it is likely safe for high temperatures if the binder grade is reduced to meet the low and intermediate temperature requirements. Asphalt binders contain different organic molecules, and thus their chemical compositions vary according to the source of the oil used in their production. Virgin binders from different sources blend differently with the age-harden oxidized binder in RAP/RAS. Therefore, depending on the level of blending between virgin and oxidized binders, the performance of the mixes could vary substantially. Findings from this work indicated that virgin binder source had some effect on the blended materials. Additional research that came from the testing approaches to complete the investigation of RAP/RAS with this dissertation were also investigated. All the asphalt mixes used in this study were designed following Caltrans modified Superpave mix design procedure and tested using an Asphalt Mixture Performance Tester (AMPT). The effects of specimen preparation variables in terms of compaction method, compaction level, test temperature, stress state, and deformation measurement location when using the AMPT to predict mix stiffness and permanent deformation were evaluated. The best approach using Superpave testing equipment that appears to best characterize expected rutting performance as defined by previous calibrated RSCH results were also investigated.

Functional Pavement Design
Functional Pavement Design

Author: Sandra Erkens

Publisher: CRC Press

Published: 2016-10-14

Total Pages: 212

ISBN-13: 1317285522

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Functional Pavement Design is a collections of 186 papers from 27 different countries, which were presented at the 4th Chinese-European Workshops (CEW) on Functional Pavement Design (Delft, the Netherlands, 29 June-1 July 2016). The focus of the CEW series is on field tests, laboratory test methods and advanced analysis techniques, and cover analysis, material development and production, experimental characterization, design and construction of pavements. The main areas covered by the book include: - Flexible pavements - Pavement and bitumen - Pavement performance and LCCA - Pavement structures - Pavements and environment - Pavements and innovation - Rigid pavements - Safety - Traffic engineering Functional Pavement Design is for contributing to the establishment of a new generation of pavement design methodologies in which rational mechanics principles, advanced constitutive models and advanced material characterization techniques shall constitute the backbone of the design process. The book will be much of interest to professionals and academics in pavement engineering and related disciplines.

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

Author: Amy Epps Martin

Publisher:

Published: 2020

Total Pages: 284

ISBN-13: 9780309481045

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"More than 90 percent of highways and roads in the United States are built using hot-mix asphalt (HMA) or warm-mix asphalt (WMA) mixtures, and these mixtures now recycle more than 99 percent of some 76.2 million tons of reclaimed asphalt pavement (RAP) and about 1 million tons of recycled asphalt shingles (RAS) each year. Cost savings in 2017 totaled approximately $2.2 billion with these recycled materials replacing virgin materials. The TRB National Cooperative Highway Research Program's NCHRP Research Report 927: Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios presents an evaluation of how commercially available recycling agents affect the performance of asphalt mixtures incorporating RAP and RAS at high recycled binder ratios."--

Engineered Frameworks for Evaluating the Use of Recycling Agents in Surface Asphalt Mixtures for Virginia
Engineered Frameworks for Evaluating the Use of Recycling Agents in Surface Asphalt Mixtures for Virginia

Author: Jhony Habbouche

Publisher:

Published: 2023

Total Pages: 0

ISBN-13:

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In recent years, several state highway agencies have introduced special provisions and specifications to allow the use of higher contents of reclaimed asphalt pavement (RAP) in asphalt surface mixtures. The challenges associated with high RAP mixtures can be addressed through the use of additives such as recycling agents (RAs) and/or softer binders. Currently, there are no specific guidelines or specifications available to evaluate the acceptability of RAs in Virginia. The purpose of this study was to evaluate the short- and long-term effectiveness of RAs in improving the performance of asphalt mixtures, particularly those with high RAP contents. Another objective of the study was to establish a performance-based framework to determine the acceptability of a specific RA product for inclusion in the Virginia Department of Transportation’s Approved Product List. Both objectives were achieved by benchmarking recycled binder blends (Phase I) and mixtures (Phase II). These were then compared in terms of laboratory performance to commonly used virgin asphalt binders and mixtures in Virginia. Moreover, a comprehensive review of the literature and information from state departments of transportation and RA suppliers on the current state of the practice regarding the use of recycled materials and RAs in asphalt mixtures was summarized. Component materials, including three virgin asphalt binders, RAP and aggregate materials from three different sources, and six RAs, were collected and tested. Phase I involved testing virgin and RAP binders; combinations of virgin binder and RAP binder; and combination of virgin binder, RAP binder, and RAs. A total of 26 binder blends were evaluated at various aging conditions through numerous rheology- and chemistry-based tests. In Phase II, 10 asphalt mixtures were designed and evaluated for durability, resistance to rutting, and resistance to cracking at various aging conditions. Cross-scale evaluation of asphalt binder and mixture testing data was established. Finally, preliminary verification was performed using data collected from various field trials constructed in Virginia. Based on the binders and mixtures tested in this study, the effectiveness of RAs in improving the properties of asphalt binder blends is specific to the product being used and to the targeted temperatures or conditions. Moreover, RAs can enhance the performance and increase the use of recycled materials in asphalt mixtures provided that the correct and suitable dosage of RA product is determined through a performance-based testing framework. The study recommends the following: (1) adopting the streamlined frameworks presented in this study to determine the acceptability of a given RA; (2) further validating the presented framework using different component materials; (3) employing balanced mix design tests to assess the performance characteristics of surface mixtures (with A and D designations) with RAs and drafting a roadmap; (4) collecting and further evaluating the field performance of all trials involving high RAP, RAs, and/or softer binders; (5) investigating the availability and activity of binders, especially with RAs, in RAP materials; (6) evaluating and establishing a protocol to assess the consistency of RAP materials; and (7) quantifying the environmental and economic impacts of using surface mixtures with high RAP contents and/or RAs.

Infrared Spectroscopy Analysis of the Blending of Virgin and RAP Binders in Hot Recycled Asphalt Mixture with CTBN as Tracer
Infrared Spectroscopy Analysis of the Blending of Virgin and RAP Binders in Hot Recycled Asphalt Mixture with CTBN as Tracer

Author: Zhen Yang

Publisher:

Published: 2018

Total Pages: 13

ISBN-13:

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This study conducted an infrared analysis of a recycled asphalt mixture that contains a high percentage of reclaimed asphalt pavement (RAP) and uses carboxyl-terminated butadiene acrylonitrile (CTBN), which has an absorption peak at 2,238 cm-1, as a tracer in the virgin asphalt. The infrared spectroscopy results of the asphalt test specimens containing 1-15 wt. % of CTBN indicated that 5 wt. % virgin asphalt is most appropriate. Infrared spectroscopy was performed on specimens of recycled asphalt mixture that contained 45 % RAP, and a statistical analysis was performed on the results. The results indicated that the virgin and RAP asphalt binders were not completely mixed, as is typically assumed. The blending degree of the virgin binder and RAP binder in the outer layer of the RAP aggregate particles was higher than that in the inner layer. The blending degree is inhomogeneous and has a three-dimensional hierarchy that depends on the depth and location of the asphalt mastic membrane over the aggregate.

Performance Assessment of Asphalt Mixes Containing Reclaimed Asphalt Pavement and Tire Rubber
Performance Assessment of Asphalt Mixes Containing Reclaimed Asphalt Pavement and Tire Rubber

Author: Shawn Shiangfeng Hung

Publisher:

Published: 2018

Total Pages:

ISBN-13: 9781085585194

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The pavement community, including both agencies and industries, is moving toward more sustainable pavement designs and pavement network management. Increasing amounts of recycled materials, both reclaimed asphalt pavement (RAP) and recycled tire rubber, are expected to be used in new pavement construction projects in the future to reduce the use of virgin binder and aggregates. The main concern of using recycled materials in new asphalt pavement is the potential negative effect on the performance. Thus, the primary objective of this dissertation is to improve the current laboratory testing technologies and performance assessment approaches for characterizing the performance-related properties of asphalt mixes containing recycled materials and to improve understanding of how these properties affect the performance of asphalt pavements so that they can be designed and constructed better. A major challenge regarding the use of high RAP content mixes is the differences in the rheological properties of the virgin binder (mixes without RAP) and the blended binder (mixes with RAP). Traditionally, binder blending charts are used to determine the appropriate RAP content in asphalt mixes and the selection of virgin binder grade as part of the Superpave volumetric mix design procedures when RAP is incorporated in the mix. However, producing mixes based on blending charts that require testing of extracted and recovered RAP binders is expensive and hazardous. An alternative test approach for binder blending charts using fine aggregate matrix (FAM) mix testing is presented in this dissertation. The results demonstrated that the proposed approach could estimate the blended binder intermediate and low performance grading temperatures within ±3°C of the measured blended binder performance grading temperatures. Even though the proposed approach is not as accurate as the blending chart method (within ±2°C), it provides both cost and environmental benefits. Currently, the Superpave Performance Grading (PG) system cannot not be used to evaluate the performance-related properties of asphalt rubber binders produced using larger crumb rubber particles (maximum particle size passing 2.36 mm sieve) due to the limitations of parallel plate geometry. With the consideration of more open-graded or gap-graded rubberized hot mix asphalt (RHMA-O and RHMA-G) projects in the future, it is important to be able to perform Superpave PG testing on asphalt rubber binder and to establish performance-based contract acceptance criteria for the production of asphalt rubber binders. The test results indicated that the concentric cylinder geometry is an appropriate alternative geometry to parallel plates for quantifying the properties of asphalt rubber binders and specifically for assessing the high-temperature performance properties of binders containing crumb rubber particles larger than 250 [mu]m. Concerns have been raised with regard to incorporating reclaimed rubberized asphalt pavement (RRAP) into dense-graded new hot mix asphalt (HMA-DG) and RAP into new RHMA-G since the interactions between the virgin binder, age-hardened binder, and recycled tire rubber could considerably affect the rutting, fatigue cracking, and thermal cracking performances of new HMA-DG and RHMA-G. The fundamental differences between RAP and RRAP were identified and the performance of new mixes that contain these recycled materials were evaluated in this study. The experimental results showed that adding RRAP to HMA-DG mixes is ideal to resist rutting and low-temperature cracking based on the changes in mix stiffness. The HMA-DG mixes containing RRAP are better at resisting high tensile strain loadings than mixes containing RAP. In addition, adding RAP to RHMA-G mixes improves the rutting performance but diminishes the cracking performance, and potentially negating the benefits of selecting RHMA-G as an overlay to retard the rate of reflection cracking. Lastly, the effects of rest periods on asphalt fatigue performance considering asphalt thixotropy, non-linearity, self-heating, self-cooling, and steric hardening were also investigated in this research. The experimental test results showed that asphalt thixotropic softening and other biasing effects control the first 10 to 15 percent decrease in stiffness for unmodified binders and 15 to 35 percent decrease in stiffness for modified binders under cyclic loading, and this decrease in stiffness can be recovered with the introduction of rest periods. This means that most of the repeated loadings applied to test specimens within the thixotropic softening range do not caused any fatigue damage but only softening of the materials. Thus, by providing sufficient rest periods within the thixotropic softening range can effectively improve asphalt fatigue performance. Both the thixotropic softening range and the required time for thixotropic recovery (i.e., rest periods) need to be considered in asphalt fatigue test and mechanistic-empirical (ME) design for better evaluation of the true fatigue performance.