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The process of reclaimed asphalt pavement (RAP) recycling may occur multiple times during the life of the pavement. This study investigates the effect of multiple recycling on binder properties by employing a virgin 3045 PEN grade binder that was aged in the laboratory intended to simulate aging of binders in RAP. The aged binder was rejuvenated using two bio-oils and one softer binder. The doses of the bio-oils and softer binder were determined by matching the continuous high-temperature performance grade (PGH) of the rejuvenated RAP binder to that of the virgin binder. This aging and rejuvenation cycle was repeated three times. Finally, fatigue and rutting performance of the binder was evaluated for the three reuse levels. Results indicate that the material can be reused up to three cycles keeping good performance on fatigue or rutting. However, care should be taken regarding the cumulative effect of bio-oils causing an over-softening effect on the of the RAP. [ABSTRACT FROM AUTHOR]

The use of high amounts of reclaimed asphalt pavement (RAP) in asphalt pavements has many economic and environmental benefits; however, there are concerns about brittleness and potential cracking of asphalt mixtures. One of the solutions to address this concern is through the inclusion of recycling agents (rejuvenators). The purpose of this study was to explore the effect of different types of recycling agents (biooils, vegetable oils, tall oil, aromatic extract, and paraffinic oil) on the rheological, microstructural, nanomechanical, and chemical properties of asphalt binder blends with high RAP content. Rheological properties were assessed using a dynamic shear rheometer. Atomic force microscopy was used to determine the microstructural characteristics and nanomechanical properties of the asphalt binder blends. A wavelet packet transform approach was proposed to quantify surface roughness characteristics. Fourier transform infrared spectroscopy was used to evaluate the chemical properties based on carbonyl and sulfoxide indices. Results indicated a correlation between the phases observed in the microstructure and rheological performance. Biooil recycling agents were the most effective in improving the microscopic distribution and rheological properties of binder blends, followed by vegetable oils. However, chemical analysis suggested that the addition of recycling agents did not reverse oxidative aging. Finally, the study recommended a rejuvenation index (RI) that quantified the effectiveness of recycling agents in improving blending and reducing stiffness and aging susceptibility. The RI signified that tall oil was the most susceptible to aging, followed by aromatic extract and paraffinic oil, whereas biooils and vegetable oils were the least susceptible to aging. [ABSTRACT FROM AUTHOR]

Highlights • Summary of current knowledge on recycling agents (rejuvenators) and their application. • Identification of current and future challenges that prevent utilization of recycling agents. • Evaluation of recycling agents effectiveness in binder blends and asphalt mixtures. • Characterization of rejuvenated binder blends and rejuvenated asphalt mixtures. • Cost-effectiveness associated with the use of recycling agents. Abstract Recycling agents, or rejuvenators, are products with chemical and physical characteristics designed to restore the rheological properties of aged asphalt binders to improve the performance of recycled asphalt mixtures with large quantities of reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) that promote economic and environmental benefits. This paper summarizes current knowledge related to the use of recycling agents in the asphalt pavement industry, including properties of recycled and rejuvenated asphalt mixtures. This information is further used to identify current and future challenges that could prevent utilization of recycling agents and production of rejuvenated asphalt mixtures with adequate performance. [ABSTRACT FROM AUTHOR]

Drainability is one of the main characteristics of permeable friction course (PFC) mixtures and is the primary reason for using these mixtures as the surface course in asphalt pavements in the United States. Current approaches suggested for PFC mix design to evaluate drainability (using gyratory-compacted specimens) include: (1) achieving a target total air void (AV) content as an indirect indication of permeability and (2) direct measurement of permeability in the laboratory. The assessment conducted in this study suggested that these approaches are not effective in ensuring adequate drainability in field-compacted mixtures. Thus, different alternatives were evaluated to improve this assessment. Corresponding analysis suggested that: (1) the water-accessible AV content can be used as a surrogate of the total AV content to indirectly assess permeability and (2) the water flow value (outflow time) can be applied to evaluate the field drainability of PFC mixtures. The expected value of permeability, determined using a modified version of the Kozeny-Carman equation, was recommended to analytically predict permeability for mix design and evaluation purposes. [ABSTRACT FROM AUTHOR]

• Survey conducted on the state of practice to account for recycled binder activity. • Two recycled binder activity quantification methods were compared. • Recycled binder activity depended on RAP source, conditioning, and mixing temperatures. • Using 100% RAP sources to estimate recycled binder activity is a promising approach. Many environmental and economic benefits can be achieved by employing reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) in asphalt mixtures. However, due to the high stiffness and brittleness of recycled materials, cracking issues may arise when utilizing them at high contents. Recycled binder activity is one of the primary factors that influences the performance of recycled asphalt pavements. Recycled binder activity represents the amount of RAP or RAS binder that becomes active at production temperatures for mixing with the virgin binder. Previous studies have indicated that recycled binders are only partially active; however, the majority of state department of transportation's assume full activity. Designing recycled asphalt mixtures under the assumption of full recycled binder activity may result in mixtures with insufficient binder content and thus increasing the susceptibility for cracking and moisture damage. This paper compares two recycled binder activity quantification methods; the first method quantifies activity using recycled asphalt mixtures of virgin and RAP materials, while the second method uses 100 percent recycled materials. The two methods showed to produce relatively similar recycled binder activity values; however, the use of 100 percent RAP materials showed to be a more promising approach due to its practicality. [ABSTRACT FROM AUTHOR]

Since the 1960s, a uniform circular vertical contact stress has been used to model the tire/pavement interface in asphalt pavements. Recent experimental measurements show that this assumption cannot be used to model the actual interaction. This study investigated the influence of nonuniform contact stress distribution on the stress distribution and permanent deformation profile in asphalt pavements. A previous study measured the tire contact stresses between the pavement surface and moving pneumatic tires. Material properties of a hot mix asphalt mixture used at WesTrack were obtained from compressive strength tests within the framework of an elastic-viscoplastic constitutive model. A three-dimensional finite element (FE) analysis was performed based on boundary conditions and measured vertical stresses at WesTrack. The tire pressure distribution was dependent on the tire load and significantly influenced the pavement response. The FE analysis based on the elastic-viscoplastic model was able to simulate the measured permanent deformation profiles. [ABSTRACT FROM AUTHOR]

The majority of U.S. departments of transportation (DOT) maintain quality assurance (QA) programs that require asphalt binder testing to verify grade compliance according to Superpave performance grade (PG) specifications. In Texas the binder is tested immediately after binder production, although the goal of QA is to ensure that the binder specified is used during construction. Between production and construction, the material is stored and transferred multiple times before it reaches the construction site or hot mix asphalt (HMA) plant. During this journey, binder properties may change due to many factors and these changes may have a negative impact on performance. To evaluate which factors are detrimental, a laboratory testing program was conducted to simulate the effects of storage time, storage temperature, contamination, and modification on the dynamic shear rheometer (DSR) performance parameter G*/sin δ after rolling thin film oven (RTFO) aging. A statistical analysis was performed, and the results indicated that all factors included in the simulation were significant. Results, conclusions, and general recommendations are provided to improve the current TxDOT QA program. [ABSTRACT FROM AUTHOR]

State highway agencies strongly desire to develop and use performance-related specifications (PRS) for highway construction. A PRS for hot mix asphalt (HMA) construction, titled HMA Spec, was recently developed as part of the WesTrack project. The beta version of HMA Spec was applied to compare pay factors and actual rutting performance to predicted performance for four Nevada Department of Transportation (NDOT) test sections on Interstate 80 (I-80) east of Reno, Nevada. Some of these sections were similar in terms of materials and construction techniques to coarse-graded sections constructed at WesTrack, so a comparison to performance at WesTrack was also made. NDOT placed the test sections on I-80 in an effort to assess the applicability of the Superpave mix design process and HMA Spec for Nevada’s conditions. Sections were designed using both Hveem and Superpave mix design methods. Several interesting observations were made while evaluating the HMA Spec output. These observations and field performance data are described in this paper. [ABSTRACT FROM AUTHOR]

The economic and environmental benefits of using recycled asphalt materials continue to motivate agencies to increase their proportion in new pavement construction and maintenance and rehabilitation activities, but the resulting reduced cracking resistance remains an engineering performance challenge. The addition of recycling agents is one of the strategies to mitigate this issue caused by the increased stiffness and brittleness of the recycled mixture. This study explored the mechanism by which different types of recycling agents partially restore flexibility and ductility of asphalt binder and mixtures. A binder blend with 50% reclaimed asphalt pavement (RAP) binder was rejuvenated with seven types of recycling agents. Rheological and chemical tools were used to evaluate the binder blends and compare their performance to a control blend without a rejuvenator to study the rejuvenation mechanism. Corresponding asphalt mixtures were also tested to ensure adequate performance. Based on the results, the recycling agents were divided into three categories: (a) Softeners, (b) Replenishers, and (c) Emulsifiers. The results showed that while some agents act only on a physical level, others interact with the blend at a chemical level that affects the physical properties. A novel parameter was developed to compare the effectiveness of various recycling agents. [ABSTRACT FROM AUTHOR]

Public and private sectors promote increased use of recycled materials in asphalt pavement construction. However, concerns exist about possible premature pavement embrittlement and cracking because of these aged materials. Recycling agents, or rejuvenators, are used to offset these concerns. Rejuvenation mechanisms can be inferred depending on the type of recycling agent, yet there is a lack of supporting experimental evidence, especially related to the recycling agent-asphaltene interaction. This study provides insight on the effects and mechanisms of rejuvenation through extensive rheological and physicochemical characterization by considering experimental variables such as type of recycling agent, type/proportion of recycled materials, and binder type. Rejuvenation was effective based on restoration to PG 70-22, reduction in the Glover-Rowe parameter, and reduction in the glass transition temperature midpoint and end. Chemical characterization was not conclusive, yet the results were interpreted as strong recycling agent-asphaltene polar interaction. Rheological benefits from rejuvenation were gradually lost with long-term aging. [ABSTRACT FROM AUTHOR]

Understanding the performance of rejuvenated asphalt mixtures is critical for cleaner pavement design and construction, as the use of rejuvenators lead to environmental and economic benefits with the ability to increase recycling but promote rutting and moisture susceptibility at a high recycled binder ratio. Existing models have not systematically evaluated rejuvenated asphalt mixtures in terms of rutting performance from a mechanistic approach, and there is a lack of research related to the third stage of rutting induced by high-temperature moisture damage. To overcome these shortcomings, two-stage and three-stage mechanistic-empirical models based on viscoelastic stress-strain response were proposed in this study to predict and evaluate rutting and moisture susceptibility of rejuvenated asphalt mixtures. Wheel tracking tests in wet and dry conditions were performed on a virgin asphalt mixture (without recycled materials) and on rejuvenated asphalt mixtures (with recycled materials and rejuvenator), and the cumulative rutting curves were investigated. In addition, linear viscoelastic properties at a reference temperature were used as input parameters in a finite element model (FEM) to calculate the viscoelastic response of virtual specimens under repeated loading. The FEM results were then substituted into the proposed models to determine the material parameters for wet and dry conditions separately. Two prediction results were combined to determine the proportion of rutting caused by stripping in rejuvenated asphalt mixtures. Four indices were used in the evaluation of rutting in wet conditions. Based on the wheel tracking test results, the rejuvenated asphalt mixtures with the highest recycled material content performed worst in wet conditions and best in dry conditions, which indicates that anti-stripping agent might be necessary for rejuvenated asphalt mixtures. [ABSTRACT FROM AUTHOR]

Abstract: Fatigue cracking due to fracture damage is one of the major structural distresses prevalent in today’s hot-mix asphalt (HMA) pavements. HMA resistance to fracture is governed by two fundamental mechanisms: the number of repetitive load cycles for microcracks to coalesce into macrocracks in a crack initiation process (N i) and the number of repetitive load cycles for macrocrack propagation through the HMA layer thickness in a crack propagation process (N p). To adequately model HMA fracture resistance, the fundamental mechanisms of these two processes must be understood. In this study, mathematical models for computing N i and N p were formulated based on continuum fracture-mechanics, the work potential theory, and pseudo-strain energy and surface energy concepts. Verification and sensitivity analysis of the models based on laboratory test data, with traditional Texas HMA mixes, yielded plausible results. Overall, the formulated models were found to be potentially promising as a fundamental means to quantitatively characterize the fracture and fatigue cracking resistance of HMA mixes. However, validation and calibration of the models with more HMA mixes and field data is strongly recommended. [Copyright &y& Elsevier]