@article{alvis_pape_xue_castorena_2023, title={Effects of Asphalt Mixture Constituents on the Recycled Binder Contribution}, volume={4}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.1177/03611981231165021}, DOI={10.1177/03611981231165021}, abstractNote={Reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) are incorporated into some asphalt mixtures produced today. The use of recycled asphalt materials (RAM) in asphalt mixtures encompasses engineering challenges pertaining to uncertainty in the proportion of the recycled binder that is in contact with and blends with the virgin binder in the asphalt mixture, termed recycled binder contribution (RBC) here. Recent research shows that agglomerations of RAM particles are the main cause of partial RBC. These agglomerations prevent recycled binder from interacting with the virgin binder. However, current practices generally assume complete RBC and a detailed understanding of the role of asphalt mixture constituents on RBC does not at present exist. The use of softer binders, extenders, and recycling agents has been proposed in high-RAM-content mixtures to restore recycled binder stiffness and embrittlement. However, the effects of asphalt binder variables as well as RAM type, source, and content on RBC is at present poorly understood. This paper aims to investigate the effects of asphalt mixture constituents on the RBC in asphalt mixtures using energy-dispersive x-ray spectroscopy (EDS) tracer-based microscopy analysis. It is found that the virgin binder, RAM type, and source significantly influence RBC in asphalt mixtures. However, RAP age level and content as well as additives are found to have only marginal impacts on RBC.}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Alvis, Maria Aparicio and Pape, Sonja and Xue, Lei Gabriel and Castorena, Cassie}, year={2023}, month={Apr}, pages={036119812311650} }
 @article{pape_castorena_2022, title={Analysis of the Role of Recycled Material Agglomerations on the Location of Fracture in Asphalt Mixtures}, volume={148}, ISSN={["2573-5438"]}, url={https://doi.org/10.1061/JPEODX.0000382}, DOI={10.1061/JPEODX.0000382}, abstractNote={Studies have demonstrated that recycled material agglomerations are a primary inhibitor of recycled binder availability in asphalt mixtures containing reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS). The literature also suggests that the dispersion of available recycled binder within the virgin binder matrix is variable. This study integrated precedent from portland cement concrete petrography by analyzing the distribution of recycled and virgin binder along the fracture surface of five asphalt mixtures to better understand the implications of recycled material agglomerations and heterogeneous blending on performance using tracer-based energy dispersive X-ray spectroscopy (EDS) analysis. Inspection of sawn asphalt mixture surfaces indicated the presence of recycled material agglomerations in all mixtures evaluated. Fatigue fracture surfaces were obtained using Asphalt Mixture Performance Tester (AMPT) cyclic fatigue testing and preserved via embedment in epoxy. EDS analysis of the fracture surface of asphalt mixture fatigue test specimens revealed that failure occurs within the virgin binder matrix and around recycled material agglomerations, suggesting that the agglomerations act as black rocks. Quantitative EDS analysis demonstrated recycled binder availabilities ranging from approximately 40% to 90% for the five mixtures evaluated in this study, suggesting that considerable variation can exist among recycled material sources. The degree of blending was comparable for all mixtures evaluated. EDS analysis of bulk specimens conducted in areas without agglomerations generally yielded availability and degree of blending results that were in close agreement with those obtained from fatigue fracture surfaces.}, number={2}, journal={JOURNAL OF TRANSPORTATION ENGINEERING PART B-PAVEMENTS}, publisher={American Society of Civil Engineers (ASCE)}, author={Pape, Sonja and Castorena, Cassie}, year={2022}, month={Jun} }
 @article{pape_castorena_2022, title={Application of Sieve Analysis to Estimate Recycled Binder Availability}, volume={2}, ISSN={["2169-4052"]}, url={https://doi.org/10.1177/03611981211073324}, DOI={10.1177/03611981211073324}, abstractNote={One of the challenges of engineering asphalt mixtures containing reclaimed asphalt pavement (RAP) is uncertainty in the proportion of the total recycled asphalt binder that is available to interact and blend with the virgin asphalt, referred to as the recycled binder availability. The industry presently lacks a practical method to quantify RAP binder availability. Research has shown that the primary source of unavailable recycled binder is agglomerations of adhered RAP particles. The binder bound within the agglomerations is unavailable to contact and therefore blend with virgin asphalt. Building on this knowledge, this study establishes a practical method to quantify the extent of RAP agglomeration and, in turn, RAP binder availability by comparing the gradation of recovered RAP aggregates with that of the RAP itself. A size-exclusion method and corresponding predictive equation to estimate RAP binder availability from the high-temperature performance grade of recovered RAP binder and mixing temperature were also assessed. Four RAP sources were evaluated. Each RAP stockpile was paired with virgin aggregates from the same plant that the RAP was sourced at to produce eight mixtures. Tracer-based microscopy measurements within the eight mixtures were generally in good agreement with the estimations of recycled binder availability using sieve analysis. Implementing the size-exclusion method was challenging with local aggregate, and estimates using the predictive equation yielded in some cases good but overall poorer agreement with the measurements of recycled binder availability from tracer-based microscopy compared with the sieve analysis approach.}, journal={TRANSPORTATION RESEARCH RECORD}, author={Pape, Sonja and Castorena, Cassie}, year={2022}, month={Feb} }
 @article{pape_castorena_2022, title={Effects of laboratory preheating procedures on recycled binder contribution in asphalt mixtures}, volume={375}, ISSN={["1879-1786"]}, url={https://doi.org/10.1016/j.jclepro.2022.134207}, DOI={10.1016/j.jclepro.2022.134207}, abstractNote={Recycled asphalt material (RAM) preheating procedures for fabricating laboratory-mixed asphalt mixture samples vary considerably, which may impact the recycled binder contribution. That is, the percentage of the recycled binder that is mobilized and incorporated into the virgin binder within the asphalt mixture. Three different preheating procedures were used to fabricate samples of four asphalt mixtures from different sources in the laboratory. In one procedure, both the virgin aggregate and RAM were conditioned to slightly above the mixing temperature. In another, the RAM was heated to 110 °C and combined with RAM preheated slightly above the mixing temperature. In the third method, the virgin aggregate was superheated and mixed with recycled material at room temperature. Three of the study mixtures contained reclaimed asphalt pavement (RAP) with contents spanning 21 to 40 percent and the fourth contained 25 percent RAP and 4 percent recycled asphalt shingles (RAS). Recycled binder contribution in the fabricated mixtures was quantified using tracer-based microscopy. Complete recycled binder contribution was not achieved in any of the laboratory-mixed samples. The two preheating methods that did not utilize superheating yielded statistically equivalent recycled binder contribution results for the three RAP mixtures. The superheating procedure yielded significantly higher recycled binder contribution compared to the other methods in some cases. The mixture with RAS demonstrated greater sensitivity in recycled binder contribution to the preheating procedure compared to the RAP only mixtures. The results of this study suggest preheating procedures should be specified to minimize variability in laboratory-fabricated asphalt mixture samples.}, journal={JOURNAL OF CLEANER PRODUCTION}, author={Pape, Sonja Ellen and Castorena, Cassie}, year={2022}, month={Nov} }
 @article{pape_castorena_2021, title={Assessment of the impacts of sample preparation on the use of EDS for analysing recycled asphalt blending}, volume={6}, ISSN={["1365-2818"]}, DOI={10.1111/jmi.13036}, abstractNote={Several past studies have demonstrated merit to using tracer‐based energy dispersive X‐ray spectroscopy (EDS) analysis to investigate blending between virgin and recycled materials in asphalt mixtures. However, these past studies have focused on proof of concept and did not establish robust fabrication and microscopy procedures. This study rigorously evaluates the ability to form a stable blend between the tracer and virgin asphalt binder, and the potential for tracer smearing during the preparation of EDS specimens. The results demonstrate that a high shear mixer can be used to prepare homogeneous, stable blends of a titanium dioxide tracer and virgin binder. A critical evaluation of an asphalt mixture specimen prepared to contain specific areas with and without the tracer demonstrates no evidence of tracer smearing due to sample preparation. The results demonstrate that tracer‐based EDS analysis of asphalt mixtures can measure local recycled material availability.}, journal={JOURNAL OF MICROSCOPY}, author={Pape, Sonja Ellen and Castorena, C. A.}, year={2021}, month={Jun} }
 @article{lee_pape_castorena_kim_2017, title={Evaluation of Small Specimen Geometries for Asphalt Mixture Performance Testing and Pavement Performance Prediction}, ISSN={["2169-4052"]}, DOI={10.3141/2631-09}, abstractNote={The use of small specimen geometries in asphalt mixture performance testing to enable the testing of as-built pavement layers has been gaining attention in recent years. Small specimens could also improve the testing efficiency of laboratory-fabricated specimens by allowing the extraction of multiple test specimens per gyratory-compacted sample. Rigorous assessment of the small specimen geometries is required before the use of such geometries is standardized. In this study, small specimens were evaluated for dynamic modulus and simplified viscoelastic continuum damage fatigue. Three specimen geometries (100-mm- and 38-mm-diameter cylindrical specimens and 25- × 50-mm prismatic specimens) were compared by using five mixtures with a nominal maximum aggregate size (NMAS) ranging from 9.5 to 25.0 mm. The results show that the dynamic modulus and phase angle master curves agreed at low and intermediate temperatures, regardless of the NMAS values of the mixture. At the high temperature, the small specimen dynamic modulus values were slightly higher and the phase angle values were slightly lower than those of the large specimens. The specimen-to-specimen variability for the large and small specimens was comparable. The fatigue test results for the mixtures evaluated were comparable, except for the 25-mm mixture, which proved problematic in the testing of both small and large specimens. Pavement performance was predicted by the layered viscoelastic analysis for critical distresses program by using the test results for the small and large specimens. These results suggest that specimen geometry had a minimal effect on pavement fatigue damage predictions, which indicates promise for the use of small specimen geometries in practice.}, number={2631}, journal={TRANSPORTATION RESEARCH RECORD}, author={Lee, Kangjin and Pape, Sonja and Castorena, Cassie and Kim, Y. Richard}, year={2017}, pages={74–82} }
 @article{castorena_pape_mooney_2016, title={Blending Measurements in Mixtures with Reclaimed Asphalt Use of Scanning Electron Microscopy with X-Ray Analysis}, ISSN={["2169-4052"]}, DOI={10.3141/2574-06}, abstractNote={ A major impediment to the widespread use of asphalt concrete with a high content of reclaimed asphalt pavement (RAP) is uncertainty in the degree of blending between the RAP and the fresh binder. Furthering knowledge concerning the blending between RAP and fresh binder has been difficult because of the lack of an experimental method to quantify the degree of blending in asphalt concrete. This study introduces energy dispersive X-ray spectroscopy (EDS) scanning electron microscopy (SEM) as a means to analyze the degree of blending between RAP and fresh materials in asphalt concrete. EDS allows for mapping the distribution and relative proportion of elements in a sample, hence, allowing for the detection of the distribution of elements in an asphalt concrete specimen. Fresh and RAP binders will have a similar elemental composition. Therefore, titanium dioxide in a fine powder form (0.15-µm particles) is blended with the fresh binder as a tracer before the production of asphalt concrete to enable delineation of the RAP and fresh binders using EDS SEM. The efficacy of EDS SEM for quantifying the degree of blending between RAP and fresh binders in asphalt concrete is demonstrated with two high RAP content mixtures. }, number={2574}, journal={TRANSPORTATION RESEARCH RECORD}, author={Castorena, Cassie and Pape, Sonja and Mooney, Charles}, year={2016}, pages={57–63} }