@article{yang_li_castorena_shane underwood_cui_2024, title={A framework to identify fatigue failure of asphalt binders under multiple aging levels using linear amplitude and time sweep testing}, volume={25}, ISSN={["1477-268X"]}, DOI={10.1080/10298436.2024.2328132}, abstractNote={The identification of fatigue failure can significantly affect the determination and prediction of fatigue life for a given asphalt binder. In this work, different approaches for identifying the fatigue failure on linear amplitude sweep (LAS) and time sweep (TS) are compared, especially for highly-aged asphalt binders. The candidate methods include traditional 50% or 80% reduction in pseudo-stiffness parameter (denoted as C0.5 and C0.2), peak stored pseudo-strain energy (PSE), peak C × N and peak phase angle. For asphalt binder at multiple aging levels, peak C × N is found to be effective in defining fatigue failure of TS testing. Meanwhile, peak stored PSE is suitable as the failure definition of LAS because it can capture the benefit of polymer modification and has a high accuracy for fatigue life prediction. Nf in strain-control TS test determined by different failure definitions shows that aging can increase the fatigue resistance at early-aged levels and then decrease the fatigue resistance at highly-aged levels. In general, the selected failure definitions have little influence on the trend of Nf with age levels. The purpose of this work is to select the logical failure definitions of asphalt binder under multiple aging levels.}, number={1}, journal={INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING}, author={Yang, Kai and Li, Rui and Castorena, Cassie and Shane Underwood, B. and Cui, Hongjun}, year={2024}, month={Dec} }
 @article{costa_castorena_2024, title={Assessing Recycled Binder Availability, Activity, and Contribution at Different Temperatures}, volume={4}, ISSN={["2169-4052"]}, url={https://doi.org/10.1177/03611981241239966}, DOI={10.1177/03611981241239966}, abstractNote={Recycled binder availability (RBA), degree of activity (DoA), and recycled binder contribution (RBC) are distinct properties often used interchangeably in the literature. This study aims to clarify the distinctions among these terms and assess how they vary with temperature, as well as their interrelationships. To achieve this, a reclaimed asphalt pavement (RAP) sieve analysis approach, indirect tensile strength testing of 100% RAP specimens, and tracer-based microscopy are employed to measure RBA, DoA, and RBC, respectively. Three RAP sources are evaluated, and each property is measured at multiple temperatures. Sieve analysis and microscopy measurements indicate that only partial RBA and RBC, respectively, are achieved, and that these properties display minimal susceptibility to changes in temperature. In contrast, DoA significantly increased as the temperature rose from 100°C to 140°C, reaching 100%, and then plateaued from 140°C to 155°C. In most of the cases, the laboratory-mixed asphalt mixture samples evaluated exhibited RBC values comparable to the RBA measurements for the respective RAP source, suggesting that RBC becomes equivalent to RBA when the DoA reaches 100%.}, journal={TRANSPORTATION RESEARCH RECORD}, author={Costa, Rafaella and Castorena, Cassie}, year={2024}, month={Apr} }
 @article{mocelin_isied_costa_castorena_2024, title={Availability adjusted mix design method as a tool to mitigate the adverse effects of RAP on the performance of asphalt mixtures}, volume={422}, ISSN={["1879-0526"]}, url={https://doi.org/10.1016/j.conbuildmat.2024.135813}, DOI={10.1016/j.conbuildmat.2024.135813}, abstractNote={The use of high percentages of reclaimed asphalt pavement (RAP) in asphalt mixtures offers economic and environmental advantages. However, state agencies place limits on RAP usage to avoid its indiscriminate use without a full understanding of its long-term performance implications. To achieve a more informed and rational use of higher RAP contents, it is essential to quantify recycled binder availability (RBA) and incorporate it into asphalt mixture design. The current design methods often assume complete RBA, leading to less durable mixtures. Standardized mixture design methods fail to rigorously account for the effects of RBA on the volumetric composition of asphalt mixture. Recently, the availability adjusted mixture design (AAMD) method was developed to address these issues by explicitly considering partial RBA in the interpretation of mixture volumetric properties and accounting for the role of RAP agglomerations on aggregate structure. This study tests the hypothesis that the AAMD method can mitigate the adverse performance consequences of RAP through the control of 'available' volumetric and effective binder properties. This was achieved by comparing virgin and RAP mixtures designed with similar 'available' volumetric properties according to the AAMD method. Additionally, control mixtures with RAP contents ranging from 20 to 35 percent were compared to AAMD mixtures with similar 'available' volumetric properties designed with the same RAP content and with 50 percent RAP. The collective results demonstrate that the AAMD method effectively mitigates negative performance consequences of RAP by controlling the 'available' volumetric and effective binder properties.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Mocelin, Douglas Martins and Isied, Mayzan Maher and Costa, Rafaella Fonseca da and Castorena, Cassie}, year={2024}, month={Apr} }
 @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{xue_gulzar_castorena_2024, title={Linear viscoelastic, viscoplastic, and damage characterization of recycled asphalt binders and mixtures containing recycling agents with long-term aging}, volume={6}, ISSN={["1573-2738"]}, url={https://doi.org/10.1007/s11043-024-09721-4}, DOI={10.1007/s11043-024-09721-4}, journal={MECHANICS OF TIME-DEPENDENT MATERIALS}, author={Xue, Lei Gabriel and Gulzar, Saqib and Castorena, Cassie}, year={2024}, month={Jun} }
 @article{isied_mocelin_preciado_vestena_underwood_kim_castorena_2024, title={Mechanical Properties and Performance of Mixtures Containing a High Level of Recycled Materials That Are Designed Using Alternative Approaches}, volume={4}, ISSN={["2169-4052"]}, url={https://doi.org/10.1177/03611981241238228}, DOI={10.1177/03611981241238228}, abstractNote={ Using recycled asphalt material (RAM) in asphalt mixtures is very common among transportation agencies. With the recent development of balanced mix design methods, it is becoming more important to understand how to optimize mixture performance by offsetting the adverse effects of RAM. In this paper, mixtures from three different sources were adjusted according to the availability adjusted mix design (AAMD) and corrected optimum asphalt content (COAC) methods. Three control mixtures containing RAM, three mixtures containing no RAM, five mixtures designed according to the AAMD method (two of which had 50% reclaimed asphalt pavement content), and two mixtures adjusted using the COAC-based approach were evaluated. Both asphalt mixture performance tester experiments and index tests were used in this study to evaluate material-level indicators of cracking and rutting resistance. Additionally, pavement performance simulations were carried out using AASHTOWare Pavement ME and FlexPAVETM to assess how the observed material-level differences led to differences in structural-level pavement performance. Both the AAMD and COAC methods improved cracking measures. However, the results suggest that the additional virgin binder added through the COAC method without any adjustments to the aggregate structure can have negative consequences for the rutting performance measures. In addition, the mixture and pavement performance results suggest that the AAMD method is a rational approach for including recycled binder availability in mix design procedures to promote improvements in the cracking performance of mixtures by controlling the volumetric properties and the aggregate structure of the mix without having a detrimental effect on rutting resistance. }, journal={TRANSPORTATION RESEARCH RECORD}, author={Isied, Mayzan and Mocelin, Douglas Martins and Preciado, Jaime and Vestena, Pablo and Underwood, B. Shane and Kim, Y. Richard and Castorena, Cassie}, year={2024}, month={Apr} }
 @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{gulzar_xue_preciado_fried_castorena_underwood_habbouche_boz_2024, title={Phenomenological modeling of aging and rejuvenation on asphalt binder fatigue characteristics}, volume={425}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2024.135929}, abstractNote={Recycling agents (RAs) have been explored as additives to enhance the properties of recycled asphalt binders. Despite extensive research on RAs, a critical knowledge gap exists regarding their impact on fatigue cracking of asphalt binders, especially considering the aging processes. This study aims to comprehensively investigate the effects of recycling agents on the fatigue properties of asphalt binders, with a specific focus on the influence of aging and rejuvenation. The current Linear Amplitude Sweep (LAS) test analysis procedure is utilized to assess the fatigue properties, and the efficacy of existing LAS test-based indices is evaluated. Furthermore, a novel index based on the simplified viscoelastic continuum damage (S-VECD) theory framework is proposed to monitor changes in fatigue properties with aging and rejuvenation. A total of 26 recycled binder blends are studied and the results demonstrate that the proposed index consistently tracks the effects of aging and rejuvenation in recycled binder blends containing recycling agents. Additionally, cross-scale assessments are conducted by correlating the proposed index with mixture performance, specifically the Indirect Tensile-Cracking Test parameter (CTindex). The findings indicate that the proposed index exhibits a correlation with the CTindex after 1-day Long Term Aging testing and effectively captures the aging sensitivity across different scales.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Gulzar, Saqib and Xue, Lei and Preciado, Jaime and Fried, Andrew and Castorena, Cassie and Underwood, Benjamin Shane and Habbouche, Jhony and Boz, Ilker}, year={2024}, month={Apr} }
 @article{duarte_yadav_castorena_2024, title={Using Color Measurements to Quantify Aggregate and Asphalt Emulsion Compatibility}, volume={5}, ISSN={["2169-4052"]}, url={https://doi.org/10.1177/03611981241242754}, DOI={10.1177/03611981241242754}, abstractNote={The compatibility of asphalt emulsion and aggregate plays a significant role in the aggregate retention performance of chip seals. There are several, similar standardized test methods available for assessing the compatibility of emulsion–aggregate blends, including AASHTO T 59, ASTM D244, and North Carolina Department of Transportation (NCDOT) A-24. In all methods, a sample of aggregate and emulsion is mixed and rinsed. Subsequently, the compatibility of the rinsed sample is reported as “good,”“fair,” or “poor” based on visual inspection of asphalt coating the aggregate surface area. These visual inferences are subjective, making them susceptible to potential operator bias. The aim of this study is to develop an objective means to quantify emulsion–aggregate compatibility by using the Asphalt Compatibility Tester to obtain color-based measures in lieu of the visual assessment procedures. Multiple aggregate sources (granite, limestone, and lightweight), emulsion types (CRS-2L, CRS-2, and SS-1h), and sources were evaluated. In total, 25 emulsion–aggregate blends were analyzed. The results were used to establish color index thresholds to capture good- versus fair- or poor-performance emulsions. Additionally, chip seal samples from five construction projects were subjected to the Vialit test to measure aggregate retention performance. The Vialit test results were compared with the compatibility test results as a preliminary evaluation of the color-based criteria proposed here. The results indicated that the NCDOT A-24 procedure coupled with color measurements is effective at capturing the compatibility of emulsion–aggregate blends, providing a potential means to remove the subjectivity of the current visual rating procedures.}, journal={TRANSPORTATION RESEARCH RECORD}, author={Duarte, Gabriel Macedo and Yadav, Shivpal and Castorena, Cassie}, year={2024}, month={May} }
 @article{gulzar_castorena_underwood_2023, title={An investigation into the nonlinear rheological behavior of modified asphalt binders using large amplitude oscillatory shear rheology}, volume={24}, ISSN={["1477-268X"]}, url={https://doi.org/10.1080/10298436.2023.2211211}, DOI={10.1080/10298436.2023.2211211}, abstractNote={ABSTRACT Asphalt binders have been studied extensively with respect to their linear viscoelastic properties. From these properties, performance metrics have been derived and used for specification purposes. However, these materials are used in asphalt concrete pavements where they may experience time-dependent loads in the nonlinear regime. In the past, the vast majority of asphalt binders exhibited strong correlations between their linear and nonlinear properties and so despite this mismatch in characterization and the actual use phase domains, a system based on linear properties could be reliably deployed. More recently though, novel binders and additives have been introduced with differing relationships between linear and nonlinear behaviors. As such there is a need to characterize the asphalt binder response under large strains and use specifications that more explicitly account for the binder nonlinearity. Here, an attempt has been made to characterize the nonlinear rheological properties of asphalt binder using large amplitude oscillatory shear. The response of a single terminal blend, crumb rubber modified binder under large strains is analyzed using Lissajous-Bowditch plots while the contribution of higher harmonics is evaluated using Fourier-transform rheology. Finally, the elastic and viscous contributions are obtained using stress decomposition to an orthogonal set of Chebyshev polynomials. It is found that the relative nonlinearity increases with increasing strain and frequency under the tested conditions. The asphalt binder evaluated in this study predominantly exhibits shear thinning and either strain stiffening or softening behavior depending upon the test conditions. The applicability of time-temperature superposition in the nonlinear regime for asphalt binders is also evaluated.}, number={1}, journal={INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING}, author={Gulzar, Saqib and Castorena, Cassie and Underwood, Shane}, year={2023}, month={Dec} }
 @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} }
 @article{goenaga_underwood_castorena_rogers_2023, title={Early Friction and Texture Evolution After an Asphalt Overlay}, volume={1}, ISSN={["2169-4052"]}, url={https://doi.org/10.1177/03611981221149436}, DOI={10.1177/03611981221149436}, abstractNote={ Recent studies have shown that friction and, more notably, macrotexture reduce markedly when pavements are newly overlaid. However, past studies have not identified whether these effects are temporary and, if so, how long they may last. These effects must be quantified to inform strategies for best monitoring and managing friction and the surface characteristics of a pavement network. This paper uses a group of sites that received a surface overlay at some point between the end of 2019 and the end of 2021. At each site, friction and texture were measured sequentially after construction in the center of the lane (CL) and in the right-wheel path (RWP). These observations were used to evaluate the early friction and texture evolution after an asphalt overlay. First, seasonal effects were evaluated using the CL measurements, presumed to be unaffected by traffic, which indicated friction is affected by seasonality, whereas texture is not. A friction seasonal effect model was calibrated and then used to remove the seasonal variation from the RWP observations. The results showed that friction initially increases after an overlay but then, after reaching a maximum, starts to decrease. The average traffic volume needed to reach the point of maximum friction was 15.5 million repetitions. Four parameters, computed from the texture profile, were used to represent macrotexture. The macrotexture was found to generally increase after overlay construction, but in some sites the magnitude and number of peaks decayed with time. }, journal={TRANSPORTATION RESEARCH RECORD}, author={Goenaga, Boris and Underwood, B. Shane and Castorena, Cassie and Rogers, Paul}, year={2023}, month={Jan} }
 @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{mocelin_isied_castorena_2023, title={Influence of reclaimed asphalt pavement (RAP) and recycled asphalt shingle (RAS) binder availability on the composition of asphalt mixtures}, volume={426}, ISSN={["1879-1786"]}, url={https://doi.org/10.1016/j.jclepro.2023.139156}, DOI={10.1016/j.jclepro.2023.139156}, abstractNote={Reclaimed asphalt pavements (RAP) and recycled asphalt shingles (RAS) are incorporated in the production of new asphalt mixtures to reduce cost, waste, and the consumption of virgin materials. The use of recycled asphalt materials (RAM) is limited by controlling agencies due to the uncertainties regarding their impacts on the volumetric composition and long-term performance of the asphalt mixtures. Recycled binder availability (RBA), which reflects the proportion of the recycled binder that is available to blend with virgin asphalt in an asphalt mixture, is currently neglected by the majority of mix design methods adopted by highway agencies, despite complete RBA being considered an unrealistic scenario. An incorrect assumption of the RBA in mixture design has important consequences on the inferred asphalt mixture volumetric properties, and consequently on the performance. A recently created method, so-called Availability Adjusted Mix Design (AAMD), proposes a revised interpretation of the volumetric properties of asphalt mixtures and design of the aggregate structure on the basis of partial RBA caused by agglomerations of RAM particles. The AAMD method is used in this study to evaluate the impacts of RBA on the volumetric properties of a diverse set of surface asphalt mixtures. The impacts of the RBA on the inferences of asphalt mixture composition are assessed for each mixture and the viability of using fixed RBA values for RAP and RAS sources in the state of North Carolina is assessed by comparing the inferred asphalt mixture composition yielded from the source-specific RBA versus the average RBA of the pool of recycled materials studied. The results show that the volumetric properties change considerably as a function of the assumed RBA, and the use of the AAMD becomes crucial for mixtures containing as little as 15 percent RAP and/or 4 percent or RAS. The use of a fixed RAS RBA value, calibrated as the average of a representative set of RAS stockpiles, versus the source-specific values has negligible impacts on the inferred volumetric properties of mixtures containing permissible RAS contents in North Carolina. Conversely, the use of source-specific RAP RBA values is recommended, which can be quantified through comparative sieve analysis of RAP and recovered RAP aggregate.}, journal={JOURNAL OF CLEANER PRODUCTION}, author={Mocelin, Douglas Martins and Isied, Mayzan Maher and Castorena, Cassie}, year={2023}, month={Nov} }
 @article{mocelin_isied_alvis_kusam_underwood_kim_castorena_2023, title={Laboratory Performance Evaluation of Alternative Approaches to Incorporate Recycled Binder Availability into Mixture Design Procedures}, volume={4}, ISSN={["2169-4052"]}, url={https://doi.org/10.1177/03611981231161601}, DOI={10.1177/03611981231161601}, abstractNote={ There is currently uncertainty in how to properly account for partial recycled binder availability within asphalt mixture design procedures so that content of recycled asphalt materials (RAM) can be maximized while still achieving good performance. This study evaluates and compares two alternative approaches to consider partial availability in mixture design: availability adjusted mix design (AAMD) and corrected optimum asphalt content (COAC). The AAMD method revises the calculation of volumetric properties by considering unavailable binder as part of the bulk aggregate volume and uses the RAM gradation to design the aggregate structure. In the COAC method, a mixture is first designed following the conventional Superpave procedures and then a specified increase to the virgin asphalt content is made. Two “control” mixtures containing RAM are evaluated that were originally designed according to the standard Superpave method. Alternative designs were prepared according to the COAC and AAMD methods while maintaining the RAM content in the respective control mixture. Baseline virgin mixtures and one mixture designed following the AAMD method with higher reclaimed asphalt pavement (RAP) content were also prepared. The cracking and rutting performance of the resultant mixtures was evaluated. The results show that the AAMD and COAC approaches lead to an improved cracking performance compared with the control mixtures even for the mixture designed with AAMD at a higher RAP content. However, the mixture designs prepared according to the COAC method presented increased rutting whereas the AAMD mixtures remained at the same level as their respective control mixture. }, journal={TRANSPORTATION RESEARCH RECORD}, author={Mocelin, Douglas Martins and Isied, Mayzan Maher and Alvis, Maria Carolina Aparicio and Kusam, Abhilash and Underwood, B. Shane and Kim, Y. Richard and Castorena, Cassie}, year={2023}, month={Apr} }
 @article{fried_castorena_2023, title={Practical Methods to Construct Asphalt Binder Master Curves and Calculate Christensen-Anderson Model Parameters}, volume={4}, ISSN={["2169-4052"]}, url={https://doi.org/10.1177/03611981231169274}, DOI={10.1177/03611981231169274}, abstractNote={ Asphalt binder master curves are applied to describe the rheological behavior of asphalt binders. A standard for constructing asphalt binder master curves and fitting a model to the results does not presently exist. In this study, a pairwise interpolation is established for free shifting of isotherms. The pairwise interpolation method yields time–temperature shift factors that are in good agreement with the Gordon and Shaw method and can be more easily implemented without sophisticated software. Subsequently, practical methods to calculate the Christensen–Anderson (CA) model crossover frequency and R parameters are compared. The relationship between reduced frequency and the tangent of the phase angle in logarithmic space is generally linear over the tangent of phase angle values spanning from 0.2 to 0.5 and can be used to determine the crossover frequency. Two approaches that generally yielded acceptable model accuracy were identified for calculating the CA model R value: (1) least squares optimization to minimize the sum of squared errors for storage and loss moduli; and (2) fitting a line to log (log dynamic shear modulus) versus the tangent of the phase angle over the tangent of the phase angle values spanning between 0.5 and 2. Based on the asphalt binders evaluated in this study, the CA model can accurately reflect asphalt binder rheological behavior when the dynamic shear modulus exceeds 105 Pa and the phase angle is less than 70° for unmodified asphalts or less than 60° for polymer-modified asphalts. }, journal={TRANSPORTATION RESEARCH RECORD}, author={Fried, Andrew and Castorena, Cassie}, year={2023}, month={Apr} }
 @article{ding_jeong_lee_underwood_kim_castorena_2023, title={Repeatability and Reproducibility Analysis for Functional Test Results from Asphalt Mixture Performance Tester Cyclic Fatigue Test}, volume={4}, ISSN={["2169-4052"]}, url={https://doi.org/10.1177/03611981231159409}, DOI={10.1177/03611981231159409}, abstractNote={ The standards for asphalt mixture performance tester (AMPT) cyclic fatigue testing (AASHTO T 400-22 and AASHTO TP 133-21) enable pavement engineers to predict asphalt mixture performance over a wide range of loading and climate conditions. To enable widespread implementation of AMPT cyclic fatigue testing, precision statements that define the repeatability and reproducibility of the tests are needed. ASTM E691-20 and ASTM C670-15 provide guidance for conducting an interlaboratory study to determine the precision of a test method. However, the standards are written for test methods that yield a single numerical figure as the test result, whereas the cyclic fatigue test yields the damage characteristic curve—a functional relationship—as a primary test result. In this study, a vnorm index was established to quantify variation in the entire damage characteristic curve. Repeatability and reproducibility analysis was conducted using vnorm, six single-point measures of damage characteristic curve variation, and one single-point measure for the fatigue test failure criterion ( D R). The major findings are: (1) the outcomes of repeatability and reproducibility analysis using single-point measures of the damage characteristic curve vary with the chosen point of reference; (2) vnorm demonstrates clear increases in within- and between-laboratory variations with increasing mixture nominal maximum aggregate size (NMAS) values; (3) within-laboratory variation of D R results increases with increasing NMAS for a given specimen geometry while the reproducibility of D R does not depend on the NMAS. Correspondingly, precision limits for both vnorm and D R were recommended and evaluated using a broad set of test results. }, journal={TRANSPORTATION RESEARCH RECORD}, author={Ding, Jing and Jeong, Jaehoon and Lee, Kangjin Caleb and Underwood, B. Shane and Kim, Youngsoo Richard and Castorena, Cassie}, year={2023}, month={Apr} }
 @article{kuchiishi_castorena_kim_underwood_2023, title={Ruggedness Evaluation of Dynamic Modulus Test Using Small-Scale Test Specimens for Asphalt Mixture Performance Tester}, volume={4}, ISSN={["2169-4052"]}, url={https://doi.org/10.1177/03611981231165780}, DOI={10.1177/03611981231165780}, abstractNote={ The small specimen dynamic modulus test (AASHTO TP 132-19) is of paramount importance for the asphalt community since it can be used to characterize and compare asphalt mixtures and the test outcomes can be used as input for pavement performance predictions. Even though the small specimen dynamic modulus test is broadly used, acceptable limits for controlling critical experimental factors still need to be developed. This paper presents the method and outcomes of a ruggedness evaluation of the Asphalt Mixture Performance Tester (AMPT) dynamic modulus test using small-scale test specimens. Three mixtures were evaluated and seven experimental factors were selected: strain peak-to-peak magnitude, specimen perpendicularity, platen-to-specimen diameter difference, specimen height, temperature, compensation springs, and end friction reducers. The analysis identified the statistically significant factors and it was found that the strain peak-to-peak magnitude and temperature were the most statistically significant factors. The specimen height and the type of end friction reducer were not found to be statistically significant factors. Also, higher strain levels and the use of compensation springs resulted in the overestimation of modulus at higher temperatures. Finally, tolerance limits were determined for each ruggedness factor and modifications to the small specimen dynamic modulus test and related standards were proposed. }, journal={TRANSPORTATION RESEARCH RECORD}, author={Kuchiishi, Andre Kazuo and Castorena, Cassie and Kim, Youngsoo Richard and Underwood, Benjamin Shane}, year={2023}, month={Apr} }
 @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{goenaga_underwood_castorena_cantillo_arellana_2023, title={Using continuous traffic counts extracted from smartphone data to evaluate traffic reductions during COVID-19 pandemic in North Carolina}, url={https://doi.org/10.1016/j.latran.2023.100005}, DOI={10.1016/j.latran.2023.100005}, abstractNote={Lockdowns to deal with the COVID-19 outbreak affected peoples' life in different dimensions. In particular, we are interested in evaluating the effects on traffic flows. For this purpose, it is necessary to accurately estimate the temporal variation of traffic flows during the pandemic period. New data collection techniques, including information from smartphones, can be used to collect this information at multiple locations of a road network. A key step in using this new data collection is the validation against more traditional measures to ensure consistency in traffic volume interpretation. This paper presents a case study whose main goals are to compare the smartphone-based traffic count predictions from the StreetLight data source against the values reported by traditional methods of traffic quantification and estimate reductions and recovery rates on traffic volumes in North Carolina during the COVID-19 pandemic. The results show that the largest reductions in traffic flows occurred mainly during the first three months of lockdown.}, journal={Latin American Transport Studies}, author={Goenaga, Boris and Underwood, B. Shane and Castorena, Cassie and Cantillo, Victor and Arellana, Julian}, year={2023}, month={Dec} }
 @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{yang_li_castorena_underwood_2022, title={Correlation of asphalt binder linear viscoelasticity (LVE) parameters and the ranking consistency related to fatigue cracking resistance}, volume={322}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2022.126450}, abstractNote={Fatigue cracking is a common distress in asphalt pavements. Different cracking parameters obtained from asphalt binder testing have been proposed to measure cracking resistance. In this work, binder tests were conducted on both polymer-modified and unmodified binders, spanning a wide range of binder grades and sources. Linear viscoelastic parameters (i.e., stiffness- or relaxation-based) and binder fatigue damaged-based parameters were both assessed. Test methods included the dynamic shear rheometer (DSR) consisted of temperature-frequency sweep and linear amplitude sweep (LAS) testing, bending beam rheometer (BBR). Parameters selected in this work include |G*|·sinδ (G* is the dynamic shear modulus, δ is the phase angle), Glover-Rowe parameter (GRP), R-value, ΔTc, and number of cycles to failure (Nf) from viscoelastic continuum damage (VECD) analysis. Some calculations, thresholds and fatigue testing temperatures of these parameters are based on the recommendations of the National Cooperative Highway Research Program (NCHRP) Project 9–59. The purpose of this work is to compare different binder parameters that have been proposed as indicators of cracking resistance. The potential changes of intermediate temperature definition are also evaluated. The results show that generally the different stiffness-based binder parameters from the DSR correlate well with each other. A correlation is observed between binder GRP and LAS damage parameters from VECD analysis.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Yang, Kai and Li, Rui and Castorena, Cassie and Underwood, B. Shane}, year={2022}, month={Mar} }
 @article{yang_li_underwood_castorena_2022, title={Effect of laboratory oxidative aging on dynamic shear rheometer measures of asphalt binder fatigue cracking resistance}, volume={337}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2022.127566}, abstractNote={Long-term aging can significantly affect the fatigue property of asphalt pavements. The influence of aging on fatigue resistance of asphalt binder has not been fully understood and unified conclusions are lacking. In this work, the effect of laboratory oxidative aging on fatigue damage resistance and linear viscoelastic (LVE) parameters of asphalt binder is studied. Tests included the temperature-frequency sweep, linear amplitude sweep (LAS) testing and time sweep from the output of dynamic shear rheometer (DSR). Different undamaged parameters (e.g., Glover-Rowe parameter (GRP), dynamic shear modulus |G*| at 64 °C, |G*|·sinδ (δ is the phase angle)) have been proposed as the indicators of aging sensitivity of the asphalt binder and are discussed. The fatigue test results are interpreted under different aging levels by using Simplified viscoelastic continuum damage (S-VECD) analysis. The trends of LVE parameters with increasing aging levels are very intuitive and show a tendency to increase in value with aging. The number of cycles to failure (Nf) shows a less intuitive trend than the LVE parameters. The existing failure criteria GR works well for the Nf prediction for highly aged materials. From the results of measured and predicted Nf from time sweep and LAS tests, fatigue damage resistance appears to increase with long-term aging at low strain levels (less than 7% strain levels in this work). When the aging level continues increasing, the fatigue resistance eventually declined in most cases evaluated. The objective of this study is to evaluate the fatigue resistance of asphalt binder under different aging levels by using various parameters and failure criteria.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Yang, Kai and Li, Rui and Underwood, B. Shane and Castorena, Cassie}, year={2022}, month={Jun} }
 @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{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{matini_gulzar_underwood_castorena_2022, title={Evaluation of Structural Performance of Pavements under Extreme Events: Flooding and Heatwave Case Studies}, volume={3}, ISSN={["2169-4052"]}, url={https://doi.org/10.1177/03611981221077984}, DOI={10.1177/03611981221077984}, abstractNote={ The recent increase in the frequency of extreme weather events has raised awareness and interest in the need for transportation infrastructure resilience. In this paper, the issue of pavement resilience is discussed with the goal of refining the idea for its use in pavement design. It is argued that one critical knowledge gap to advancing the state of the art in this area is distinguishing between functional and structural resiliency. The arguments here are framed using floods and heatwaves to demonstrate the importance of structural resilience. Under extreme event disruptions, structural damage is inevitable. The case study simulations in this paper suggest, depending on the pavement structure, intensity, and frequency of flooding events over the analysis period, that pavement rutting performance can decrease by 15.5% in the case of a structure with sand subgrade and 18.8% in the case of a structure with clay subgrade. In the case of heatwaves, the increase in rutting was found to be 2.9% in a structure with sand subgrade. To move toward more resilient pavement infrastructure, it is important to continuously monitor pavements after extreme events, develop methodologies to predict their performance, incorporate the findings in the current pavement management systems, and adapt design and management strategies accordingly. Future design and management of pavement systems should consider both structural and functional resiliency. This study shows that pavement performance simulations predict a long-term decrease in structural performance as a result of extreme events. }, number={7}, journal={TRANSPORTATION RESEARCH RECORD}, publisher={SAGE Publications}, author={Matini, Narges and Gulzar, Saqib and Underwood, Shane and Castorena, Cassie}, year={2022}, month={Mar} }
 @article{saleh_braswell_elwardany_rad_castorena_kim_2022, place={OXON, ENGLAND}, title={Field Calibration and Validation of a Pavement Aging Model}, volume={2}, ISSN={1477-268X}, url={https://doi.org/10.1080/10298436.2022.2027416}, DOI={10.1080/10298436.2022.2027416}, abstractNote={ABSTRACT A pavement aging model (PAM) is established by calibrating and validating the NCHRP 09–54 kinetics model's predictions against field core measurements. Field cores, laboratory-mixed loose mixtures, and binders from a wide range of pavement sections are used, including both conventional hot mix asphalt (HMA) mixtures and modern materials (i.e. reclaimed asphalt pavement (RAP), warm mix asphalt (WMA), and polymer modified asphalt (PMA)). Field aging levels are measured at different depths from binder extracted and recovered from in-service field cores. The original component materials of these pavement sections are aged in the laboratory and used to calibrate the kinetics model. The measured field aging levels are compared against those predicted from the kinetics model to inform a depth and time dependent field calibration function for the PAM. The validation of PAM using an independent set of field sections shows that, within the limited data used in this study, the calibrated PAM may be able to predict the aging of the conventional HMA, RAP, WMA, and PMA mixtures. The PAM predictions are lastly found to outmatch the predictions by the Global Aging System (GAS) model.}, journal={International Journal of Pavement Engineering}, publisher={TAYLOR & FRANCIS LTD}, author={Saleh, N.F. and Braswell, E. and Elwardany, M. and Rad, F.Y. and Castorena, C. and Kim, Y.R.}, year={2022}, month={Feb} }
 @article{mocelin_castorena_2022, title={Impacts of recycled binder availability on volumetric mixture design and performance}, volume={3}, ISSN={["1477-268X"]}, url={https://doi.org/10.1080/10298436.2022.2046276}, DOI={10.1080/10298436.2022.2046276}, abstractNote={ABSTRACT The use of reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) in asphalt mixtures is a routine process. Recycled binder availability reflects the proportion of the total recycled binder in a given recycled asphalt material (RAM) that is available to blend with the virgin binder. Studies show that agglomerations of adhered RAM particles preclude complete availability. However, the Superpave volumetric mixture design methods adopted by the majority of state agencies assume complete availability. This study makes use of a sieve analysis method and tracer-based microscopy analysis to quantify recycled binder availability. Revisions to asphalt mix design procedures to account for partial availability are proposed, including consideration of the unavailable binder as part of the bulk aggregate volume and the use of the RAM gradation (i.e. black curve) rather than the recovered aggregate gradation (i.e. white curve) to design the mixture’s aggregate structure. Three high RAM content ‘control’ mixtures that were originally designed under the assumption of complete recycled binder availability are redesigned according to the proposed approach. The redesigned mixtures had notably higher virgin binder content than the control mixtures. The redesigned mixtures also had significantly better cracking resistance than the control mixtures while still meeting permanent deformation requirements.}, journal={INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING}, author={Mocelin, Douglas M. and Castorena, Cassie}, year={2022}, month={Mar} }
 @article{zeng_underwood_castorena_2022, title={Low-temperature performance grade characterisation of asphalt binder using the dynamic shear rheometer}, volume={23}, ISSN={["1477-268X"]}, url={https://doi.org/10.1080/10298436.2020.1774766}, DOI={10.1080/10298436.2020.1774766}, abstractNote={ABSTRACT Currently, the bending beam rheometer (BBR) test is the standard method for evaluating the low-temperature performance grade (PG) of asphalt binders. Despite its use, there are limitations with the BBR test with respect to the amount of asphalt binder needed for test specimens, the relative difficulty in preparing specimens, and the overall testing efficiency. On the contrary, the dynamic shear rheometer (DSR) is an efficient test method that is widely used to determine the PG at intermediate and high temperatures. In this study, DSR temperature-frequency sweep tests using the 8-mm parallel plate is proposed as an alternative to the BBR. The method takes advantage of the time-temperature superposition principle and linear viscoelastic interconversion to predict the BBR creep stiffness and m-values at 60 s from the modulus and phase angle measured by the DSR at intermediate temperatures. Two conversion methods were used to verify the ability to predict BBR properties using DSR testing based on 45 binders of diverse PG. The DSR-based method yields good agreement with measured BBR data. On average, the continuous low-temperature PG predicted using the DSR method is within 2.7°C of that measured using the BBR.}, number={3}, journal={INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING}, author={Zeng, Zhe 'Alan' and Underwood, B. Shane and Castorena, Cassie}, year={2022}, month={Feb}, pages={811–823} }
 @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={Abstract}, journal={JOURNAL OF MICROSCOPY}, author={Pape, Sonja Ellen and Castorena, C. A.}, year={2021}, month={Jun} }
 @article{gulzar_richard kim_castorena_shane underwood_2021, title={COVID-19, Uncertainty, and the Need for Resilience-Based Thinking in Pavement Engineering}, volume={147}, ISSN={["2573-5438"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85094102919&partnerID=MN8TOARS}, DOI={10.1061/JPEODX.0000235}, abstractNote={Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal © 2020 American Society of Civil Engineers}, number={1}, journal={JOURNAL OF TRANSPORTATION ENGINEERING PART B-PAVEMENTS}, author={Gulzar, Saqib and Richard Kim, Y. and Castorena, Cassie and Shane Underwood, B.}, year={2021}, month={Mar} }
 @article{ravichandran_castorena_2021, title={Critical Evaluation of Dynamic Shear Rheometer (DSR)-Based Methods to Measure Asphalt Binder Diffusion}, volume={49}, ISSN={["1945-7553"]}, url={https://doi.org/10.1520/JTE20200432}, DOI={10.1520/JTE20200432}, abstractNote={Abstract}, number={6}, journal={JOURNAL OF TESTING AND EVALUATION}, author={Ravichandran, Mukesh and Castorena, Cassie}, year={2021}, month={Nov}, pages={4014–4031} }
 @article{braswell_saleh_elwardany_yousefi rad_castorena_underwood_kim_2021, title={Refinement of Climate-, Depth-, and Time-Based Laboratory Aging Procedure for Asphalt Mixtures}, volume={2675}, ISSN={["2169-4052"]}, DOI={10.1177/0361198120957316}, abstractNote={This paper refines the oxidation kinetics-based approach originally proposed in the NCHRP 09-54 project to determine the laboratory aging durations at 95°C that best reflect the effects of time, climate, and depth on loose asphalt mixtures. Aging durations that match the field aging at various pavement depths were determined in this study for asphalt mixtures, including warm-mix asphalt (WMA), polymer-modified asphalt (PMA), and reclaimed asphalt pavement (RAP). Here, the laboratory aging durations were used to calibrate a climatic aging index to prescribe the laboratory aging duration, given hourly pavement temperature history obtained from Enhanced Integrated Climatic Model analysis of the Modern Era Retrospective-Analysis for Research and Applications, Version 2 weather data. The recalibrated procedure determines the required laboratory aging durations with reasonable accuracy for virgin hot-mix asphalt (HMA) and WMA mixtures. From the recalibrated results, no variations were found with regard to the laboratory aging durations for WMA materials compared with HMA materials, but there were differences between the RAP and non-RAP mixtures. In some instances, the short-term aged RAP mixtures that were prepared according to AASHTO R 30 exceeded the aging level of 4-year-old field cores, suggesting that refinement of this standard short-term aging procedure may be necessary. Approximately half of the PMA sections evaluated exhibited outlier behavior that could have been caused by the unrealistically harsh thermal history of the field projects from which the cores were acquired.}, number={2}, journal={TRANSPORTATION RESEARCH RECORD}, author={Braswell, Elizabeth and Saleh, Nooralhuda F. and Elwardany, Michael and Yousefi Rad, Farhad and Castorena, Cassie and Underwood, B. Shane and Kim, Y. Richard}, year={2021}, month={Feb}, pages={207–218} }
 @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} }
 @article{ding_lee_castorena_kim_underwood_2021, title={Use of Resampling Method to Construct Variance Index and Repeatability Limit of Damage Characteristic Curve}, volume={2}, ISSN={["2169-4052"]}, DOI={10.1177/0361198121994850}, abstractNote={ The simplified viscoelastic continuum damage model has been widely accepted as a tool to predict fatigue performance of asphalt concrete. One key component in the model is the damage characteristic curve that results from a cyclic fatigue test. This curve characterizes the relationship between material integrity (stiffness) and the level of damage in the material. As with any experimental measurement, it is important to know and quantify the variability of the damage curve, but traditional statistical methods are ill-suited for experiments that yield functional data as opposed to univariate data. In this study, a variance index of the damage characteristic curve is first proposed and compared with the expert judgment of the variance of a set of nine different asphalt mixtures. Then, an example analysis for establishing the repeatability limit of a specific mixture as the application of the variance index is presented using the resampling method and hypothesis test. The major findings are as follows: 1) the proposed variance index can match the expert judgment of variability; 2) the shape of the damage characteristic curve can affect the performance of the variance index; 3) the resampling method and hypothesis test can be applied to flag inconsistent data in multi-user or multi-laboratory results; and 4) the resampling method can also be used to construct the repeatability limit of the variance index. }, journal={TRANSPORTATION RESEARCH RECORD}, author={Ding, Jing and Lee, Kangjin Caleb and Castorena, Cassie and Kim, Youngsoo Richard and Underwood, B. Shane}, year={2021}, month={Feb} }
 @article{saleh_keshavarzi_rad_mocelin_elwardany_castorena_underwood_kim_2020, title={Effects of aging on asphalt mixture and pavement performance}, volume={258}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2020.120309}, abstractNote={This study investigates the effects of long-term aging on pavement performance under realistic traffic and thermal conditions. Using the NCHRP 09-54 aging procedure, a systematic study of the effects of aging on asphalt mixture linear viscoelastic and fatigue properties was conducted. The computational engine of FlexPAVE™ V1.1was modified to run more realistic pavement performance simulations. Results suggest that the effect of aging on pavement performance is evident only when simulations employ more realistic traffic and climatic conditions. In the absence of thermal conditions, the effect of changes in mixture properties on pavement performance is not significant.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Saleh, Nooralhuda F. and Keshavarzi, Behrooz and Rad, Farhad Yousefi and Mocelin, Douglas and Elwardany, Michael and Castorena, Cassie and Underwood, B. Shane and Kim, Y. Richard}, year={2020}, month={Oct} }
 @article{safaei_castorena_2020, title={Improved interpretation of asphalt binder parallel plate dynamic shear rheometer fatigue tests}, volume={21}, ISSN={["1477-268X"]}, DOI={10.1080/10298436.2018.1438611}, abstractNote={Abstract The time sweep test, consisting of cyclic, torsional loading in the dynamic shear rheometer (DSR), has been employed for the fatigue characterisation of asphalt binders. The parallel plate geometry imposes radially inhomogeneous strain field, which results in a radial inhomogeneous stress field. Past efforts have inferred fatigue damage in DSR tests based on monitoring the apparent edge stress, which is calculated using linear radial mapping to the total torque. The assumption of linear variation in the shear stress response with radial distance from the specimen centre is erroneous of material or geometric nonlinearities such as cracking. To improve the interpretation of parallel plate fatigue tests, a means to account for the non-linear radial gradient in stress response is derived using simplified viscoelastic continuum damage (S-VECD) modelling. The developed methodology is validated through comparison to cone and plate results where the stress state is uniform. The results demonstrate that the developed methodology allows for accurate determination of S-VECD model coefficients using parallel plate testing alone.}, number={1}, journal={INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING}, author={Safaei, Farinaz and Castorena, Cassie}, year={2020}, month={Jan}, pages={74–87} }
 @article{saleh_mocelin_yousefi rad_castorena_underwood_kim_2020, title={Predictive Framework for Modeling Changes in Asphalt Mixture Moduli with Oxidative Aging}, volume={2674}, ISSN={["2169-4052"]}, DOI={10.1177/0361198120938775}, abstractNote={This paper presents a predictive framework for asphalt mixture moduli as a function of aging time with two levels of sophistication. This work is built on the method currently implemented in Pavement mechanistic-empirical (ME) that uses an effective time/frequency concept based on time-aging superposition to model the effect of aging on a mixture’s modulus. Time-aging superposition implies that an asphalt mixture’s modulus mastercurves, corresponding to different aging levels, coincide when they are shifted horizontally on the log-frequency axis. This study improves the accuracy of the existing model by decoupling the time-temperature and time-aging shifts. The new framework also uses the binder dynamic shear modulus | G*| as an aging index instead of the viscosity, which is used in Pavement ME. The | G*| aging index is used to calculate an effective frequency at short-term aging (STA), which is then used in the asphalt mixture sigmoidal model to calculate the corresponding asphalt mixture modulus with aging. The pavement aging model introduced by NCHRP 09-54 predicts log | G*| at 64°C and 10 rad/s for a specific field-aged condition and pavement depth. The proposed framework can use the predicted log | G*| to predict the mixture’s corresponding dynamic modulus (| E*|) at that aging level and pavement depth. Level 1 of this framework requires characterizing the | G*| at STA and calibrating the NCHRP 09-54 pavement aging model as well as measuring the mixture | E*| at STA. Level 2 does not require any binder testing, providing relatively less accurate predictions but relieving some testing requirements.}, number={10}, journal={TRANSPORTATION RESEARCH RECORD}, author={Saleh, Nooralhuda F. and Mocelin, Douglas and Yousefi Rad, Farhad and Castorena, Cassie and Underwood, B. Shane and Kim, Y. Richard}, year={2020}, month={Oct}, pages={79–93} }
 @article{adams_castorena_kim_2019, title={Construction quality acceptance performance-related specifications for chip seals}, volume={6}, ISSN={["2095-7564"]}, DOI={10.1016/j.jtte.2019.05.003}, abstractNote={The research described herein details the establishment of a framework for construction quality acceptance performance-related specifications (PRS) for chip seal surface treatments. This paper establishes acceptance quality characteristics (AQCs) and relationships between the AQCs and related chip seal performance measures. This work is a critical step in developing PRS for constructed chip seal treatments and establishing suitable guidelines for the PRS. The main objective of this paper is to determine appropriate test methods to evaluate each defined AQC. The relationships that are established between the AQCs and chip seal performance are used to define performance ranges and threshold values for a particular performance measure. These performance ranges and threshold values then can be used to define pay factors for the constructed chip seal section. The threshold values and pay factors for each AQC described herein are preliminary recommendations and require further validation prior to implementation. However, this research demonstrates how these PRS would be utilized to ensure acceptable chip seal construction quality in the field. The developed construction quality acceptance PRS framework uses the percent within limits (PWL) concept to determine whether a chip seal lot passes the PRS threshold values and whether the contractor receives full pay, is subject to a pay penalty, or fails the construction PRS and must correct the chip seal within the first year in service, which constitutes the typical warranty period for contracted chip seal work. Finally, recommendations are made as to the next steps in the development and validation of these construction quality acceptance PRS that are needed for implementation by contractors and state roadway maintenance agencies.}, number={4}, journal={JOURNAL OF TRAFFIC AND TRANSPORTATION ENGINEERING-ENGLISH EDITION}, author={Adams, Javon and Castorena, Cassie and Kim, Y. Richard}, year={2019}, month={Aug}, pages={337–348} }
 @article{malladi_castorena_2019, title={Field measurements of emulsion application rates and pavement emulsion absorption in tack coats and chip seals}, volume={218}, ISSN={["1879-0526"]}, url={https://doi.org/10.1016/j.conbuildmat.2019.05.105}, DOI={10.1016/j.conbuildmat.2019.05.105}, abstractNote={Simple and practical test frameworks for field measurements of Emulsion Application Rates (EARs) in chip seal and tack coat applications are identified. The methods identified allow for local in situ measurements of the EAR that can be obtained during construction. For both tack coats and chip seals, the test methods identified allow for determining the EAR from residual binder application rate measurements combined with the emulsion water content. Implementation of the test frameworks established in this study could be used as part of a quality assurance/quality control program.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, publisher={Elsevier BV}, author={Malladi, Haritha and Castorena, Cassie}, year={2019}, month={Sep}, pages={701–711} }
 @article{fried_malladi_castorena_2019, title={Impact of Crack Sealant on Pavement Skid Resistance}, volume={2673}, ISSN={["2169-4052"]}, DOI={10.1177/0361198119849590}, abstractNote={ Crack sealing is often a cost-effective preventive maintenance strategy for prolonging pavement service life when applied to pavements in relatively good condition. Crack sealing is generally ineffective for extending the life of heavily cracked pavements. However, crack sealing is often applied to pavements with extensive cracking. The application of crack sealing to pavements with extensive cracking can pose a skid resistance hazard. This study investigates the relationship between the amount and distribution of crack sealant application and pavement skid resistance. Locked-Wheel Skid Tester (LWST) testing was conducted on several pavement projects in North Carolina, United States, with varying amounts and patterns of crack sealant. Images of the locations of LWST testing were obtained and processed to determine the percentage of the pavement surface area covered by crack sealant. A relationship between the percentage of the wheel path covered by crack sealant and LWST results was established that demonstrates the application of high amounts of crack sealant to the wheel path can pose safety hazards. The effect of crack sealant on pavement skid resistance is a function of the existing pavement’s frictional characteristics. The results of this study highlight the need for the development of crack sealant specification provisions to avoid the loss of skid resistance. }, number={7}, journal={TRANSPORTATION RESEARCH RECORD}, author={Fried, Andrew and Malladi, Haritha and Castorena, Cassie}, year={2019}, month={Jul}, pages={362–370} }
 @article{rawls_castorena_2019, title={In situ measurements of emulsion application rates}, volume={20}, ISBN={1477-268X}, DOI={10.1080/10298436.2017.1347438}, abstractNote={ABSTRACT The emulsion application rate (EAR) is critical to the performance of tack coats and surface treatments. Current quality assurance and quality control measures for EARs are limited and fail to consider in situ measurements. This study evaluates in situ measures to address transverse and longitudinal variability in applied EARs and pavement emulsion absorption using field experiments. Results demonstrate that the Tack Lifter can be used effectively to measure pavement emulsion absorption rates and to capture longitudinal variability in the applied EAR. The Tack Lifter is a simple, weighted device that is placed on a super-absorbent sheet which absorbs emulsion applied to a pavement or plate. When applied directly to a pavement, the device measures the effective EAR on the pavement, neglecting emulsions absorbed into the paving surface. When applied to a plate placed on the pavement prior to emulsion application, the device measures the total applied EAR. Results indicate emulsion absorption should be quantified prior to construction to guide appropriate adjustment of the target EAR. Applied EARs can vary significantly along the length of paving. Limited results indicate transverse variability is relatively consistent along the length of paving and therefore, should be remedied prior to construction rather than using in situ measurements.}, number={7}, journal={INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING}, author={Rawls, Mary and Castorena, Cassie}, year={2019}, pages={811–819} }
 @article{bozorgi_fried_montoya_castorena_2019, title={The effect of laboratory compaction method on the resilient behaviour and fabric of aggregate base course materials}, volume={21}, ISSN={1468-0629 2164-7402}, url={http://dx.doi.org/10.1080/14680629.2019.1580606}, DOI={10.1080/14680629.2019.1580606}, abstractNote={Aggregate base course (ABC) layer is a key structural component of most pavements. The compaction of ABC is a crucial procedure affecting its mechanical performance. There are two different methods commonly used in the lab to compact ABC specimens: impact and vibratory. Past studies have demonstrated that the compaction method can affect the resilient deformation behaviour of ABC. However, the reasons for these differences in terms of the constituent ABC particle properties and the resultant compacted aggregate fabric remains unclear. This study evaluates the influence of the laboratory compaction method on the resilient behaviour and fabric of two ABC materials with differing mineralogies. Resilient modulus tests performed on the specimens compacted with the two methods result in different behaviours. A series of subsequent laboratory tests were performed to explain the observed resilient behaviour by assessing changes in aggregate morphology and fabric. The study presented herein incorporates digital imaging analyses using a novel specimen preparation technique. The results demonstrate that impact compaction can degrade ABC materials that are susceptible to crushing. This, in turn, increases the resilient modulus of the ABC by increasing the number of contact points between particles. It is recommended that the compaction method used in the laboratory match the compaction processes in the field as best as possible to obtain the most representative resilient modulus test results.}, number={7}, journal={Road Materials and Pavement Design}, publisher={Informa UK Limited}, author={Bozorgi, Arash and Fried, Andrew and Montoya, Brina M. and Castorena, Cassie}, year={2019}, month={Feb}, pages={1–13} }
 @article{rad_elwardany_castorena_kim_2018, title={Evaluation of Chemical and Rheological Aging Indices to Track Oxidative Aging of Asphalt Mixtures}, volume={2672}, ISSN={["2169-4052"]}, DOI={10.1177/0361198118784138}, abstractNote={ Oxidative age hardening in asphalt binder leads to embrittlement. Embrittled asphalt is prone to fatigue and thermal cracking. Therefore, the ability to predict asphalt binder oxidative age hardening within a pavement throughout its service life could inform improved pavement material selection, design, and maintenance practices. Studying the evolution of oxidative aging requires the use of key properties to track oxidation levels, termed aging index properties (AIPs) here. The objective of this study is to identify suitable rheological and chemical AIPs to track oxidation levels in asphalt materials. A wide range of laboratory and field aged materials were evaluated in this study. A range of chemical AIPs determined by Fourier transform infrared spectroscopy (FTIR) absorbance peaks and areas were evaluated based on their correlation with laboratory aging duration. Rheological AIPs were evaluated based on the strength of their relationship to the chemical changes induced by oxidation. The rheological AIPs evaluated included the dynamic shear modulus, zero shear viscosity, Glover-Rowe parameter, and crossover modulus. The chemical AIP evaluation that most strongly correlated with laboratory aging duration is the carbonyl plus the sulfoxide absorbance peaks. The results indicate that both the dynamic shear modulus and Glover-Rowe parameter constitute rheological AIPs that relate directly to the chemical changes induced by oxidation. }, number={28}, journal={TRANSPORTATION RESEARCH RECORD}, author={Rad, Farhad Yousefi and Elwardany, Michael D. and Castorena, Cassie and Kim, Y. Richard}, year={2018}, month={Dec}, pages={349–358} }
 @article{castorena_ilias_adams_kim_2018, title={Low-Temperature Emulsion Performance-Graded Specification for Chip Seals}, volume={2672}, ISSN={["2169-4052"]}, DOI={10.1177/0361198118790133}, abstractNote={ Chip seals are applied to existing roadways to slow deterioration and improve pavement surface conditions without increasing the pavement’s structural capacity. Chip seals typically are comprised of asphalt emulsion and aggregate. Although it is well known that the properties of asphalt emulsion are critical to chip seal performance, the current specifications for these binders are empirical in nature and are not based on the properties that relate directly to chip seal performance. This study proposes emulsion performance-graded specifications that are designed to mitigate aggregate loss at low temperatures. To develop the proposed specifications, the research team executed an experimental plan to identify the residual binder properties that relate to chip seal aggregate loss at low temperatures. This research considered both fracture mechanics and rheology-based binder properties. Dynamic shear moduli, evaluated at critical phase angle values, demonstrated the strongest correlation to chip seal aggregate loss at low temperatures. Critical phase angle values were varied as a function of the low-temperature climatic emulsion performance grade of interest. This study also established preliminary specification limits for the dynamic shear modulus values based on critical chip seal performance thresholds. }, number={28}, journal={TRANSPORTATION RESEARCH RECORD}, author={Castorena, Cassie and Ilias, Mohammad and Adams, Javon and Kim, Y. Richard}, year={2018}, month={Dec}, pages={266–276} }
 @article{malladi_asnake_lacroix_castorena_2018, title={Low-Temperature Vacuum Drying Procedure for Rapid Asphalt Emulsion Residue Recovery}, volume={2672}, ISSN={["2169-4052"]}, DOI={10.1177/0361198118791913}, abstractNote={ Asphalt emulsions are used extensively in tack coats and preservation surface treatments. The current specifications for asphalt emulsion residue recovery in AASHTO PP 72 are based on low-temperature evaporative drying. The shortest residue recovery procedure included in AASHTO PP 72 requires 6 h of conditioning in an oven to dry an emulsion. The ability to recover emulsion residues efficiently is of great interest given the ongoing efforts to develop emulsion performance-graded specifications based on residual binder properties. In this study, a rapid, vacuum drying technology was evaluated for asphalt emulsion residue recovery. The procedure enables the recovery of sufficient residual binder for dynamic shear rheometer (DSR) testing within 20–40 min. Five emulsions of different classifications were evaluated using both the vacuum drying procedure and the AASHTO PP 72 procedures. The vacuum drying procedure leads to similar water loss to the AASHTO PP 72 procedures. Based on the temperature-frequency sweep and multiple stress creep and recovery (MSCR) test results, the vacuum-dried residues are softer and more viscous than residues recovered using the AASHTO PP 72 procedures. Fourier transform infrared spectroscopy (FTIR) was performed to identify if oxidation levels could explain the observed in rheological trends. However, the results suggest no clear trend in the oxidation levels of residues recovered using AASHTO PP 72 compared with the rapid vacuum procedure. Future work is necessary to infer which method best reflects residual binders placed in the field. }, number={28}, journal={TRANSPORTATION RESEARCH RECORD}, author={Malladi, Haritha and Asnake, Meron and LaCroix, Andrew and Castorena, Cassie}, year={2018}, month={Dec}, pages={256–265} }
 @article{adams_ilias_castorena_kim_2018, title={Performance-Graded Specifications for Asphalt Emulsions Used in Chip Seal Preservation Treatments}, volume={2672}, ISSN={["2169-4052"]}, DOI={10.1177/0361198118770169}, abstractNote={ This paper details the development of a framework for emulsion performance-grade (EPG) specifications for chip seal treatments. Chip seals are preservation surface treatments that are designed to improve the condition of the pavement surface while mitigating deterioration of the overall pavement structure. Asphalt emulsions used in chip seals often are selected based on factors that are not necessarily related to performance. Aggregate loss and bleeding have been identified as the most critical chip seal distresses that are related to binder performance. Storage stability, sprayability, and drain-out have been determined to be the most critical constructability concerns. For this study, binder and mixture test methods were identified to reflect the failure mechanisms for each critical distress type. The emulsion residue test methods that were identified to capture chip seal performance are the multiple stress creep and recovery test for bleeding and the dynamic shear rheometer frequency sweep test for low-temperature aggregate loss. The fresh emulsion test methods that were identified to capture chip seal constructability are the three-step shear test and storage stability test. The proposed EPG specifications for the fresh emulsion properties that are related to constructability were developed using statistical analysis of the binder test results. The proposed EPG specifications for the residual binder properties were developed by defining the temperature-independent relationships between the emulsion residue properties and mixture performance that correspond to each critical distress. Preliminary specification limits were then established based on the values of the binder properties that correspond to the critical mixture performance thresholds. }, number={12}, journal={TRANSPORTATION RESEARCH RECORD}, author={Adams, Javon and Ilias, Mohammad and Castorena, Cassie and Kim, Y. Richard}, year={2018}, month={Dec}, pages={20–31} }
 @article{xie_castorena_wang_kim_2017, title={A framework to characterize the healing potential of asphalt binder using the linear amplitude sweep test}, volume={154}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2017.08.021}, abstractNote={The healing characteristics of asphalt binders affect the fatigue performance of asphalt mixtures and field pavements. The objective of this paper is to quantify the healing potential of asphalt binders using the linear amplitude sweep (LAS) test under various damage level and rest period durations. A healing protocol based on the LAS test is successfully established to measure the healing behaviour of asphalt binder by applying the rest periods before and after cohesive failure. Based on the simplified-viscoelastic continuum damage (S-VECD) model, the percent healing (%HS) is quantified from the healing recovery of the accumulated damage growths. The neat asphalt binder exhibits better %HS results than the SBS modified binder in the pre-failure conditions. However, the SBS modified binder exhibits a higher healing potential in the post-failure case. The rest-damage superposition principle (RDSP) is further investigated in the pre-failure cases to remove and unify the effects of damage level and rest period by constructing a %HS mastercurve at a given reference damage level. The developed healing mastercurve and related damage shift factor can be used to represent the intrinsic healing potential of a given asphalt binder. A series of healing indices are proposed and discussed based on the healing mastercurve to numerically compare the healing performance of asphalt binders.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Xie, Wei and Castorena, Cassie and Wang, Chao and Kim, Y. Richard}, year={2017}, month={Nov}, pages={771–779} }
 @article{adams_castorena_im_ilias_kim_2017, title={Addressing Raveling Resistance in Chip Seal Specifications}, ISSN={["2169-4052"]}, DOI={10.3141/2612-05}, abstractNote={ Chip seals are applied to existing roadways to slow deterioration and improve pavement surface conditions without increasing the pavement’s structural capacity. The raveling of chip seals can cause damage to vehicles and thus is a safety concern. Raveling resistance is related to both material application rates and material properties. The current chip seal specifications fail to adequately address the material-related aspects of raveling resistance. This study seeks to develop recommendations to address raveling resistance in future chip seal specifications. Strain sweep binder tests, binder bond strength (BBS) tests, and Vialit chip seal mixture tests were conducted to assess early raveling, late raveling, and wet raveling at two intermediate temperatures. The results demonstrate that the bond that develops between the residual binder and the aggregate is highly dependent on the interaction between the emulsion and the aggregate during curing. The importance of emulsion–aggregate compatibility in raveling resistance indicates that raveling resistance cannot be addressed in binder specifications alone. Rather, it is recommended that intermediate temperature raveling resistance should be addressed during chip seal mixture design. Vialit and BBS tests, in which emulsion is cured on rock, can both be used to effectively quantify the aggregate loss potential of a chip seal. These two tests are able to capture the benefits of polymer modification and produce results that correlate. However, the Vialit tests are easier to implement than the BBS tests and require no expensive equipment. Therefore, Vialit tests are recommended to address early, late, and wet raveling resistance in future chip seal specifications. }, number={2612}, journal={TRANSPORTATION RESEARCH RECORD}, author={Adams, Javon and Castorena, Cassie and Im, Jeong Hyuk and Ilias, Mohammad and Kim, Y. Richard}, year={2017}, pages={39–46} }
 @article{wang_castrorena_zhang_kim_2017, title={Application of Time-Temperature Superposition Principle on Fatigue Failure Analysis of Asphalt Binder}, volume={29}, ISSN={["1943-5533"]}, DOI={10.1061/(asce)mt.1943-5533.0001730}, abstractNote={AbstractThe linear amplitude sweep (LAS) test has been proposed for fatigue specifications of asphalt binders. Recently, a newly developed fatigue failure definition and energy-based failure criterion have been proposed for improving the LAS procedure and data interpreting; however, these improvements only affect LAS data conducted at a constant temperature. This paper, therefore, discusses the loading temperature effects on LAS-based binder fatigue, damage evolution, and final fatigue failure occurrence. Experimental results indicate that both damage characteristic curves (DCCs) and the failure criterion derived from the simplified-viscoelastic continuum damage (S-VECD) model are strongly affected by the testing temperature. However, the temperature shift factors determined from the dynamic shear modulus testing within the linear viscoelastic domain have been proven to be effective in eliminating the temperature influence for both fatigue DCCs and the failure criterion. The validation on binder phase dem...}, number={1}, journal={JOURNAL OF MATERIALS IN CIVIL ENGINEERING}, author={Wang, Chao and Castrorena, Cassie and Zhang, Jinxi and Kim, Y. Richard}, year={2017}, month={Jan} }
 @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{rad_elwardany_castorena_kim_2017, title={Investigation of proper long-term laboratory aging temperature for performance testing of asphalt concrete}, volume={147}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2017.04.197}, abstractNote={The performance implications of laboratory asphalt loose mixture aging at 135 °C were evaluated by comparing the performance of mixtures subjected to long-term aging at 95 °C and 135 °C to yield the same rheology. Although the rheology of the mixtures aged at 135 °C and 95 °C matched, their chemistry differed. Performance test results suggest that the chemical changes induced by aging at 135 °C can negatively impact performance. The relationship between binder chemistry and rheology was unaffected by aging temperatures at or below 95 °C. The rate of oxidation increased with an increase in temperature, and thus, the optimal loose mixture aging temperature is 95 °C.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Rad, Farhad Yousefi and Elwardany, Michael D. and Castorena, Cassie and Kim, Y. Richard}, year={2017}, month={Aug}, pages={616–629} }
 @article{safaei_castorena_2017, title={Material nonlinearity in asphalt binder fatigue testing and analysis}, volume={133}, ISSN={["1873-4197"]}, url={https://doi.org/10.1016/j.matdes.2017.08.010}, DOI={10.1016/j.matdes.2017.08.010}, abstractNote={Fatigue cracking is a primary distress in asphalt pavements caused by the accumulation of damage under repeated traffic loading. Asphalt binder is the weakest constituent of asphalt mixture. Therefore, the inherent fatigue resistance of the asphalt binder contained within the pavement is anticipated to influence pavement performance. The simplified viscoelastic continuum damage (S-VECD) model has been applied to predict fatigue life of asphalt binders under varying loading and thermal conditions using time sweep and linear amplitude sweep (LAS) test results. The majority of past efforts using S-VECD analysis protocol have neglected the effects of material nonlinearity and attributed all material integrity loss to damage for the sake of simplicity. Herein, experimental and analytical methods are evaluated for delineating damage and nonlinearity in fatigue testing of asphalt binder. None of the experimental methods evaluated enabled accurate separation of damage and nonlinearity at the high strain amplitudes included in LAS tests. Therefore, an analytical method using S-VECD modeling was proposed to back calculate nonlinear dynamic shear moduli from LAS test results. Results can be used to generate a nonlinear S-VECD model which allows for improved fatigue life predictions.}, journal={MATERIALS & DESIGN}, author={Safaei, Farinaz and Castorena, Cassie}, year={2017}, month={Nov}, pages={376–389} }
 @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} }
 @article{elwardany_yousefi rad_castorena_kim_2016, title={Evaluation of asphalt mixture laboratory long-term ageing methods for performance testing and prediction}, volume={18}, ISSN={1468-0629 2164-7402}, url={http://dx.doi.org/10.1080/14680629.2016.1266740}, DOI={10.1080/14680629.2016.1266740}, abstractNote={Ageing has long been recognised as a major distress mechanism for asphalt concrete and, by extension, asphalt pavements. Ageing causes the material to stiffen and embrittle, which leads to a high potential for cracking. Although a significant amount of effort has been placed on understanding the ageing process of asphalt binder, less effort has been put forth to develop laboratory ageing procedures for producing aged mixture specimens for performance testing. An optimal laboratory conditioning procedure to simulate long-term ageing for performance testing and prediction is required in order to integrate the effects of long-term ageing in pavement prediction models and other mechanistic design and analysis methods. In this study, oven ageing and pressure ageing vessel ageing are applied to both loose mix and compacted specimens in order to evaluate and select an ageing method to simulate long-term ageing for performance testing and prediction. The selected method must be able to maintain specimen integrity in order to be used for performance testing and prediction. Efficiency, practicality, and versatility also are considered in evaluating the ageing methods. The results demonstrate that loose mix ageing in an oven is the most promising ageing method to produce mixture specimens for performance testing in terms of efficiency, specimen integrity, versatility, and cost.}, number={sup1}, journal={Road Materials and Pavement Design}, publisher={Informa UK Limited}, author={Elwardany, Michael D. and Yousefi Rad, Farhad and Castorena, Cassie and Kim, Y. Richard}, year={2016}, month={Dec}, pages={28–61} }
 @article{wang_zhang_castorena_zhang_kim_2016, title={Identifying fatigue failure in asphalt binder time sweep tests}, volume={121}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2016.06.020}, abstractNote={Identification of fatigue failure of asphalt binder in time sweep test results remains a question crucial to asphalt binder fatigue performance evaluation and prediction. This paper presents a comparison of different analysis approaches for defining the occurrence of fatigue failure during time sweep fatigue tests conducted in both control-displacement and control-stress loading modes. The candidate failure definitions evaluated include the traditional 50% reduction in stiffness parameter (S0.5), dissipated energy indicators including the dissipated energy ratio (DER) and the ratio of dissipated energy change (RDEC), as well as two phenomenological parameters corresponding to the peak in S × N and peak in phase angle. Both phenomenological parameters and dissipated energy based indicators were found to be effective in defining fatigue failure. Statistical analysis results further indicate that maximum S × N, maximum phase angle and RDEC approach provide equivalent fatigue life results, however, peak in S × N is strongly recommended for detecting fatigue failure of asphalt binder in time sweep tests because it is easy to calculate and well defined.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Wang, Chao and Zhang, Han and Castorena, Cassie and Zhang, Jinxi and Kim, Y. Richard}, year={2016}, month={Sep}, pages={535–546} }
 @article{safaei_castorena_kim_2016, title={Linking asphalt binder fatigue to asphalt mixture fatigue performance using viscoelastic continuum damage modeling}, volume={20}, ISSN={["1573-2738"]}, DOI={10.1007/s11043-016-9304-1}, number={3}, journal={MECHANICS OF TIME-DEPENDENT MATERIALS}, author={Safaei, Farinaz and Castorena, Cassie and Kim, Y. Richard}, year={2016}, month={Aug}, pages={299–323} }
 @article{veytskin_bobko_castorena_2016, title={Nanoindentation and Atomic Force Microscopy Investigations of Asphalt Binder and Mastic}, volume={28}, ISSN={["1943-5533"]}, DOI={10.1061/(asce)mt.1943-5533.0001532}, abstractNote={AbstractNanoindentation techniques were implemented to calculate and interpret linear viscoelastic properties of asphalt binder and mastic through low-load spheroconical (blunt) nanoindentation. Experiments on three rolling thin-film oven (RTFO)–aged binders (two neat and one polymer modified) and 24 RTFO-aged mastics were implemented for reproducible creep indentations at ultra low loads. Creep compliance model parameters were extracted and used to determine dynamic modulus values for each material. Dynamic modulus values from nanoindentation were validated by using macroscopic dynamic shear rheometer (DSR) testing for two binders and two mastics (RTFO-aged). Atomic force microscopy (AFM) images of binder and mastic microstructure were obtained to shed insight on how microstructural phenomena relate to mechanical properties. The new results were combined with previously determined work of cohesion values for three binders and 30 mastics (RTFO-aged) made with the same materials to link microstructural phe...}, number={6}, journal={JOURNAL OF MATERIALS IN CIVIL ENGINEERING}, author={Veytskin, Yuriy and Bobko, Christopher and Castorena, Cassie}, year={2016}, month={Jun} }
 @article{veytskin_bobko_castorena_2016, title={Nanoindentation investigation of asphalt binder and mastic viscoelasticity}, volume={17}, ISSN={["1477-268X"]}, DOI={10.1080/10298436.2014.993393}, abstractNote={An exploratory nanoindentation technique for creep testing of two neat asphalt binders and one mastic at room temperature is developed, tested and verified. This work presents a new approach to obtain viscoelastic properties from low-load spherical (blunt) nanoindentation. Interconverted shear relaxation modulus mastercurves are determined from nanoindentation data. The magnitudes and trends of these mastercurves are found to be in reasonable agreement with Dynamic Shear Rheometer (DSR) results in a stiffness range associated with the range of time and temperature used in nanoindentation testing. Nanoindentation creep data is transformed to develop a mastercurve of dynamic modulus. The portion of this mastercurve corresponding to the frequency and temperature range included in nanoindentation testing demonstrates reasonable agreement with DSR results. These initial results suggest the potential to expand nanoindentation testing to forensic investigations involving testing of preserved asphalt binder and mastic components within field-extracted asphalt concrete composites.}, number={4}, journal={INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING}, author={Veytskin, Yuriy and Bobko, Christopher and Castorena, Cassie}, year={2016}, month={Apr}, pages={363–376} }
 @article{rawls_im_castorena_2016, title={Tack Lifter for In Situ Measurement of Effective Emulsion Application Rates}, ISSN={["2169-4052"]}, DOI={10.3141/2550-11}, abstractNote={ Emulsion application rates are critically important to the performance of pavement surface treatments and tack coats. In this study, the tack lifter was introduced as a means to measure in situ effective emulsion application rates at specific locations along the length of paving. The tack lifter is a simple, weighted device that is placed on top of a superabsorbent foam sheet applied to a paving surface. The absorbent sheet soaks up emulsion from the roadway surface to get a spot check of the amount of emulsion on the surface. The device measures the effective emulsion application rate on the paving surface, neglecting emulsions absorbed into the paving surface. Laboratory studies of emulsion application onto chip seal and hot-mix asphalt concrete surfaces demonstrate the ability of the tack lifter to capture the sensitivity of emulsion absorption to pavement surface texture. In addition, preliminary tack lifter field trial results are presented to demonstrate its use as a quality control field test. }, number={2550}, journal={TRANSPORTATION RESEARCH RECORD}, author={Rawls, Mary and Im, Jeong Hyuk and Castorena, Cassie}, year={2016}, pages={80–88} }
 @article{safaei_castorena_2016, title={Temperature effects of linear amplitude sweep testing and analysis}, number={2574}, journal={Transportation Research Record}, author={Safaei, F. and Castorena, C.}, year={2016}, pages={92–100} }
 @article{davis_castorena_2015, title={Implications of physico-chemical interactions in asphalt mastics on asphalt microstructure}, volume={94}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2015.06.026}, abstractNote={Asphalt binder and filler blend to form asphalt mastic, which constitutes the effective adhesive film in asphalt concrete. Pavement performance can be improved through better engineering of the mastic, which requires a fundamental understanding of the interaction between asphalt and filler. Physico–chemical interactions result in adsorption of polar fractions of the asphalt onto filler surfaces, leading to the formation of an interphase layer on the surface of particles and modifying the asphalt binder matrix. This study seeks to investigate the effects of physico–chemical interaction on binder matrix microstructure using Atomic Force Microscopy (AFM) and qualitatively relate microstructural findings to macroscopic rheology.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Davis, Chelsea and Castorena, Cassie}, year={2015}, month={Sep}, pages={83–89} }
 @article{veytskin_bobko_castorena_kim_2015, title={Nanoindentation investigation of asphalt binder and mastic cohesion}, volume={100}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2015.09.053}, abstractNote={A nanoindentation technique for determining the cohesive properties of neat, modified, and aged asphalt binders and mastics with varying filler volumetric concentrations is developed, tested, and verified. Cohesive properties of binder and mastic are critically important to the fracture resistance of asphalt concrete. A new approach to calculate and interpret important cohesive properties from nanoindentation data through low-load sphero-conical (blunt) nanoindentation is presented. Work of effective cohesion values are determined as the average response over multiple possible microstructures for three asphalt binders and 30 different mastics of varying filler volumetric concentrations. Results point to evidence of a critical filler volume fraction beyond which further addition of filler does not affect work of effective cohesion. This plateau in work of effective cohesion values is speculated to be related to the combined effects of volume-filling, particle interactions, and physicochemical interactions. The critical filler volumetric concentrations corresponding to the plateau in work of effective cohesion range between 0.20 and 0.30, which is within the range from literature of 0.15–0.30. Testing of binder and mastic through nanoindentation is an important step toward in situ testing of mastic within asphalt concrete, which is inaccessible using conventional macroscopic experimental methods.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Veytskin, Yuriy and Bobko, Christopher and Castorena, Cassie and Kim, Y. Richard}, year={2015}, month={Dec}, pages={163–171} }
 @article{wang_castorena_zhang_kim_2015, title={Unified failure criterion for asphalt binder under cyclic fatigue loading}, volume={16}, ISSN={["2164-7402"]}, DOI={10.1080/14680629.2015.1077010}, abstractNote={Defining failure and developing a unified failure criterion for the fatigue testing of asphalt materials remain a challenge. This study seeks to develop a failure criterion for the fatigue testing of asphalt binders under cyclic loading in the dynamic shear rheometer. Newly developed pseudo-strain energy (PSE)-based failure analysis is introduced for both the time sweep fatigue test and the accelerated linear amplitude sweep (LAS) test (AASHTO TP101). The presented methodology builds upon recent advances in the simplified viscoelastic continuum damage (S-VECD) modelling of asphalt mixtures. Trends in stored PSE have been proven to be effective in defining failure for the LAS tests of asphalt binders. This new proposed failure definition is material-dependent and, thus, is effective in capturing the benefits of asphalt modification for binder fatigue resistance. In addition, it is found that a unique relationship that is independent of loading history exists between the PSE release rate and fatigue life. The fatigue life predictions using this relationship and the S-VECD model are in reasonable agreement with the laboratory-measured fatigue life data and also generally relate well with the field fatigue performance measured in the FHWA-ALF (Federal Highway Administration – Accelerated Loading Facility) pooled fund study.}, journal={ROAD MATERIALS AND PAVEMENT DESIGN}, author={Wang, Chao and Castorena, Cassie and Zhang, Jinxi and Kim, Y. Richard}, year={2015}, pages={125–148} }
 @article{safaei_lee_nascimento_hintz_kim_2014, title={Implications of warm-mix asphalt on long-term oxidative ageing and fatigue performance of asphalt binders and mixtures}, volume={15}, ISSN={1468-0629 2164-7402}, url={http://dx.doi.org/10.1080/14680629.2014.927050}, DOI={10.1080/14680629.2014.927050}, abstractNote={The use of warm mix asphalt (WMA) has been increasing in recent years due to its ability to reduce the production temperatures of asphalt concrete. The long-term implications of reduced production temperatures and, hence, reduced short-term ageing on long-term performance remain largely unknown. This study evaluates the effect of age hardening in WMA binders and mixtures compared with hot mix asphalt (HMA) binders and mixtures with respect to fatigue damage. Two WMA technologies are considered: foaming by water injection and Evotherm modification. For this study, the asphalt mixtures were subjected to laboratory conditioning in a forced air convection oven to simulate long-term field ageing according to AASHTO R30. The asphalt mixtures and extracted binders were subjected to linear viscoelastic and fatigue characterisation following ageing. Because oxidative ageing occurs within the asphalt binder phase of asphalt concrete, this paper focuses on the relative performance of WMA and HMA binders at various ageing levels and compares this binder performance to the respective mixture performance. Cyclic direct tension tests were used to measure the fatigue resistance of the asphalt mixtures, and the linear amplitude sweep (LAS) test was used to measure the fatigue resistance of the binders. Simplified viscoelastic continuum damage (S-VECD) analysis was performed to interpret the fatigue test results and predict the fatigue performance of the binders and mixtures using a pavement structural model. The results demonstrate that after substantial long-term ageing, differences between the fatigue performance of WMA and HMA become insignificant. The results also demonstrate good agreement between the binder and mixture results, indicating that the LAS test coupled with S-VECD analysis is able to capture the binder's contribution to mixture fatigue.}, number={sup1}, journal={Road Materials and Pavement Design}, publisher={Informa UK Limited}, author={Safaei, Farinaz and Lee, Jong-sub and Nascimento, Luis Alberto Hermann do and Hintz, Cassie and Kim, Y. Richard}, year={2014}, month={Jun}, pages={45–61} }
 @inproceedings{safaei_hintz_2014, title={Investigation of the effect of temperature on asphalt binder fatigue}, DOI={10.1201/b17219-181}, booktitle={Asphalt Pavements, vols 1 and 2}, author={Safaei, F. and Hintz, C.}, year={2014}, pages={1491–1500} }
 @article{hintz_bahia_2013, title={Simplification of Linear Amplitude Sweep Test and Specification Parameter}, ISSN={["2169-4052"]}, DOI={10.3141/2370-02}, abstractNote={ The linear amplitude sweep (LAS) test has recently been approved by AASHTO as a provisional standard and is currently being considered for specification of asphalt binder fatigue resistance. The LAS test is a cyclic torsion test conducted in the dynamic shear rheometer (DSR) that uses increasing loading amplitudes to accelerate damage. The LAS test has been proposed as a surrogate to the time sweep (TS) test, which is a conventional fatigue test consisting of repeated cyclic loading at constant amplitude. The TS test is considered unsuitable for specification because of the uncertainty in the test duration required to induce and quantify fatigue. Recent ruggedness testing efforts have shown that the LAS test cannot be conducted by all DSRs. This study evaluates a simpler amplitude ramping procedure that resolved the difficulties encountered with some rheometers. Additionally, a simple specification parameter is introduced to offer a practical approach to define damage tolerance. The definition of failure is based on a more recent study to explain the mechanisms of fatigue damage under TS testing in the DSR. On the basis of a comparison between TS and LAS test results, this paper demonstrates that the damage evolution in the two tests differs, thus indicating that the LAS test is very complex and is better referred to as a damage tolerance test rather than a true fatigue test. With the simplified analysis approach for the modified LAS procedure, a critical cracking length signifying the start of rapid crack growth is proposed for specification of binder damage tolerance at intermediate temperature. }, number={2370}, journal={TRANSPORTATION RESEARCH RECORD}, author={Hintz, Cassie and Bahia, Hussain}, year={2013}, pages={10–16} }
 @article{hintz_bahia_2013, title={Understanding Mechanisms Leading to Asphalt Binder Fatigue in the Dynamic Shear Rheometer (DSR)}, volume={82}, ISSN={["0270-2932"]}, DOI={10.1080/14680629.2013.818818}, abstractNote={Asphalt binder fatigue resistance is important in determining overall pavement fatigue performance. One procedure commonly used to characterise asphalt binder fatigue resistance is the time sweep test, which consists of repeated cyclic loading in the dynamic shear rheometer (DSR). Generally, apparent changes in complex modulus and phase angle with respect to number of loading cycles are used to define fatigue performance. Although results from DSR testing have been shown to correlate well with asphalt mixture fatigue performance, the mechanisms responsible for changes in binder properties in the DSR were previously not well understood. Results in this study demonstrate that fracture can explain the changes in loading resistance during fatigue testing in the DSR. Under cyclic torsional loading of cylindrical specimens, fracture manifests as a circumferential crack that starts at the periphery of a sample and propagates inward, reducing the effective sample radius. Digital visualisation of binder specimens following testing allows for determination of the fractured and intact sample radius. Predictions of fracture propagation based on measurements of loading resistance and fracture mechanics concepts agreed favourably with direct measurements based on visualisation. Furthermore, it is shown in this study that fracture morphology and progression of crack growth of asphalt binders under time sweep testing match those observed for other materials under similar loading conditions. Based on these findings, fracture mechanics concepts are used to present an analysis framework that allows for predicting binder fatigue life at any loading amplitude using the results of a single time sweep test.}, journal={ASPHALT PAVING TECHNOLOGY 2013, VOL 82}, author={Hintz, Cassie and Bahia, Hussain}, year={2013}, pages={465–501} }
 @inproceedings{hintz_bahia_2013, title={Understanding mechanisms leading to asphalt binder fatigue in the dynamic shear rheometer (DSR)}, volume={82}, booktitle={Asphalt paving technology 2013, vol 82}, author={Hintz, C. and Bahia, H.}, year={2013}, pages={465–501} }