@article{fried_boz_preciado_gulzar_underwood_castorena_habbouche_2024, title={Evaluation of Alternative Approaches to Restore the Rheology of Recycled Asphalt Binders}, volume={3}, ISSN={["2169-4052"]}, url={https://doi.org/10.1177/03611981241235179}, DOI={10.1177/03611981241235179}, abstractNote={This study evaluates the ability of softer virgin binders, recycling agents (RAs), and extenders to restore the rheology of reclaimed asphalt pavement (RAP) binders to that of control binders. Control binders are those binders that would be specified for use with virgin mixtures. Two procedures for RA dosage selection are examined: 1) dose to restore the intended high-temperature grade; and 2) dose to restore the intended low-temperature grade. A broad range of point parameters and rheological parameters that measure the balance of relaxation and stiffness characteristics are examined at two long-term age levels. The results of recycled binder blends are compared with the control virgin binders statistically. Using softer virgin binders generally resulted in blended binder performance-graded properties that were similar to or better than the control. However, these softer binder systems often exhibited other rheological properties that were inferior to the control. The rheological characteristics of the RA blends varied with the RA type and dosage. Blends with dosages that restored the intended high-temperature grade generally yielded the most favorable comparisons to the control binders. RAs derived from triglycerides and fatty acids and from tall oils generally yield more favorable rheological characteristics than those derived from aromatic extracts. In addition, a vacuum gas oil extender achieved similar blend rheological characteristics to RAs but extenders containing re-refined engine oil bottoms generally yielded a poor balance of stiffness and relaxation characteristics. Rheological balance parameters are generally weakly correlated, suggesting they provide unique insight into the rheological behavior of binders.}, journal={TRANSPORTATION RESEARCH RECORD}, author={Fried, Andrew and Boz, Ilker and Preciado, Jaime and Gulzar, Saqib and Underwood, Benjamin Shane and Castorena, Cassie and Habbouche, Jhony}, year={2024}, month={Mar} }
 @article{preciado_gulzar_castorena_underwood_habbouche_boz_2024, title={Performance Assessment of High Reclaimed Asphalt Pavement Asphalt Mixtures with Recycling Agents}, volume={4}, ISSN={["2169-4052"]}, url={https://doi.org/10.1177/03611981241236483}, DOI={10.1177/03611981241236483}, abstractNote={The increased use of reclaimed asphalt pavement (RAP) in asphalt mixtures has promoted the use of recycling agents (RAs) to mitigate the effect of oxidized materials on the performance of asphalt mixtures. This laboratory-based study assesses the linear viscoelastic (LVE), cracking resistance, and permanent deformation properties of recycled asphalt mixtures containing RAs. The dosage levels used for this study were determined based on the manufacturer’s recommendation to restore the blended binder system’s low-temperature performance grade (PGL) to −22°C. The study found that blending a performance grade (PG) 64-22 virgin binder with RAs in high RAP mixtures can yield a comparable LVE response to high RAP mixtures designed using a softer binder (PG 58-28). Moreover, the study revealed that the cracking performance of high RAP mixtures could be improved without jeopardizing the rutting potential of the material by using RAs at dosage levels selected to yield a blended binder PGL of −22°C.}, journal={TRANSPORTATION RESEARCH RECORD}, author={Preciado, Jaime and Gulzar, Saqib and Castorena, Cassie and Underwood, Benjamin Shane and Habbouche, Jhony and Boz, Ilker}, year={2024}, month={Apr} }
 @article{preciado_gulzar_fried_castorena_underwood_habbouche_boz_2023, title={Benchmarking Recycled Binder Blends Using Statistical Analysis: A Case Study of Virginia and North Carolina}, volume={7}, ISSN={["2169-4052"]}, url={https://doi.org/10.1177/03611981231178812}, DOI={10.1177/03611981231178812}, abstractNote={Recycling agents (RAs) are added to asphalt binder blends containing recycled materials to mitigate the negative effects of adding oxidized material to asphalt mixtures. Several methods exist to select a particular RA dosage to restore a specific Superpave performance parameter. However, the rheological similarities between the RA-modified systems and typical virgin binders across the complete range of temperatures remain to be ascertained. In this study, two RA dosage selection procedures, one aiming to restore high-temperature performance grade and the other aiming to restore low-temperature performance grade were statistically compared. Quality assurance datasets from Virginia and North Carolina were used to benchmark the typical virgin binder properties, and 17 recycled binder blends using constituent materials from the two states were studied with respect to Superpave binder properties. Both univariate and bivariate statistical analyses were applied to compare and contrast the rheological properties of these blends with the benchmarked virgin binder properties for the two states. Then, a statistical similarity analysis was done using the Mahalanobis distance to evaluate the rheological properties of these blends with those of the reference binders. The study found that both dosage selection procedures were successful in achieving rheological similarity at target-specific temperatures and for specific binder properties but might not necessarily yield similar properties at other temperatures. Finally, an example application is presented using statistical analysis to select an RA dosage that yields a rheological fingerprint more similar to that of virgin binder systems.}, number={3}, journal={TRANSPORTATION RESEARCH RECORD}, author={Preciado, Jaime and Gulzar, Saqib and Fried, Andrew and Castorena, Cassie and Underwood, Benjamin Shane and Habbouche, Jhony and Boz, Ilker}, year={2023}, month={Jul} }
 @misc{gulzar_fried_preciado_castorena_underwood_habbouche_boz_2023, title={Towards sustainable roads: A State-of-the-art review on the use of recycling agents in recycled asphalt mixtures}, volume={406}, ISSN={["1879-1786"]}, url={https://doi.org/10.1016/j.jclepro.2023.136994}, DOI={10.1016/j.jclepro.2023.136994}, abstractNote={The use of asphalt mixtures containing previously paved asphalt mixture from milled pavements, so-called reclaimed asphalt pavements or RAP, has been around for more than half a century. Historically, relatively low RAP contents were used, around 15% of the total mix. Recently, the use of high RAP contents has increased and now it is common to design mixtures with 30% or higher RAP contents, especially in the US. At these higher recycled contents, the characteristics of the recycled material begin to significantly affect the behaviors of the asphalt mixtures and alter the pavement performance. The use of recycled materials in asphalt mixtures at these contents may result in diminishing returns in terms of prospective performance at or beyond a certain incorporation dosage level. To overcome this barrier, recycling agents (RA) have been proposed to extend the break-even point and/or provide savings, both in terms of cost-effectiveness as well as environmental impacts. This paper is an examination of the use of RAs in recycled asphalt mixtures. There have been many reviews regarding RAs in the recent past, notably the review compiled as part of the United States National Cooperative Highway Research Program (NCHRP) Project 09–58. However, this field is evolving very quickly and there have been notable advances that require a renewed examination of the state of the art with respect to RA usage. In these intervening years, some specific advances have been made to propose novel methods for understanding the chemical nature of RAs, how RAP interacts with the virgin binder and RA, and how acceptable performance of recycled asphalt binder blends and mixtures can be achieved through dosage selection methods. However, the scientific knowledge on the selection and use of RAs in asphalt pavements is limited, and there is a need to develop robust methodologies that establish threshold criteria and performance metrics to facilitate their use on a regular basis. While there do exist some general trends with respect to RA effectiveness, the specific benefits and limitations found in individual studies vary greatly. Thus, given the current state of knowledge, RAs should be evaluated on a material-by-material basis using asphalt mixtures designed and delivered using local practices.}, journal={JOURNAL OF CLEANER PRODUCTION}, author={Gulzar, Saqib and Fried, Andrew and Preciado, Jaime and Castorena, Cassie and Underwood, Shane and Habbouche, Jhony and Boz, Ilker}, year={2023}, month={Jun} }
 @article{fried_xue_gulzar_preciado_underwood_castorena_2022, title={Evaluation of Recycling Agent and Extender Dosage Selection Procedures to Restore the High-Temperature Climatic Performance Grade}, volume={2676}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.1177/03611981221074361}, DOI={10.1177/03611981221074361}, abstractNote={Dosage selection is important for effective use of recycling agents and extenders in asphalt pavements. A standardized protocol for extender and recycling agent dosage selection does not presently exist. NCHRP Project 09-58 established a recycling agent dosage selection procedure that aims to restore the desired high-temperature grade of a blend of recycled binder, virgin binder, and additive. Their simplified procedure relies on the existence of class-specific relationships between the blended system high-temperature grade and additive content. Further, the dosage selection procedure assumes complete recycled binder availability. There is general consensus that complete recycled binder availability is not achieved in practice, which may yield asphalt mixtures with poor rutting performance. This study seeks to evaluate the universality of the slopes proposed in NCHRP Project 09-58 to both extenders and recycling agents and evaluate the rutting resistance of asphalt mixtures prepared using additive dosages selected to restore the high-temperature grade of the blended binder system. This study encompasses one reclaimed asphalt pavement (RAP) and one recycled asphalt shingles (RAS) mixture. Two extender and two recycling agent products were evaluated. The results indicate that different additive types yield different slopes of the blended system high-temperature grade versus additive content. The results also show that uncertainty should be accounted for when establishing a dosage selection procedure to ensure that the blended binder grade does not fall below the desired value. The rutting resistance of mixtures prepared using additive dosages intended to restore the high-temperature grade all passed recommended Hamburg wheel-track criteria.}, number={6}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Fried, Andrew and Xue, Lei Gabriel and Gulzar, Saqib and Preciado, Jaime and Underwood, B. Shane and Castorena, Cassie}, year={2022}, month={Feb}, pages={302–314} }
 @article{habbouche_boz_underwood_castorena_gulzar_fried_preciado_2021, title={Review From Multiple Perspectives for the State of the Practice on the Use of Recycled Asphalt Materials and Recycling Agents in Asphalt Concrete Surface Mixtures}, volume={2676}, ISSN={["2169-4052"]}, url={https://doi.org/10.1177/03611981211061130}, DOI={10.1177/03611981211061130}, abstractNote={The objective of this paper is to provide information from multiple perspectives on the current state of the practice with regard to using recycled materials and recycling agents (RAs) in asphalt concrete mixtures. This information was collected through a survey of U.S. transportation agencies and RA suppliers combined with a search of RA-related specifications and pilot projects previously constructed. Moreover, a case study describing the Virginia Department of Transportation’s experience with RAs provides a tangible example of how at least one agency is approaching the potential implementation of these technologies. This practice review was achieved by documenting the experience, lessons learned, and best practices of multiple asphalt experienced contractors and asphalt binder suppliers in the Virginia area. This paper follows a similar survey conducted in 2014 as part of NCHRP 09-58 and provides a second look at the use of RAs across North America. Not all state departments of transportation have experience with using RAs. Factors preventing the use of RAs included specification limitations, lack of expertise in processing recycled materials, supporting data, and negative prior experiences. Developing a performance-based testing framework is mandatory for the successful use of RAs. In general, good and frequent communication with the RA supplier is critical and necessary during the planning stages, the production of mixtures, and the continuous quality control by the supplier to resolve issues when they arise. Finally, a strong quality control and quality assurance-testing program should be implemented to ensure that materials meet the properties needed to produce a good-performing mixture.}, number={4}, journal={TRANSPORTATION RESEARCH RECORD}, publisher={SAGE Publications}, author={Habbouche, Jhony and Boz, Ilker and Underwood, Benjamin Shane and Castorena, Cassie and Gulzar, Saqib and Fried, Andrew and Preciado, Jaime}, year={2021}, month={Dec} }