@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={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{zeng_kim_underwood_guddati_2023, title={Asphalt mixture fatigue damage and failure predictions using the simplified viscoelastic continuum damage (S-VECD) model}, volume={174}, ISSN={["1879-3452"]}, url={https://doi.org/10.1016/j.ijfatigue.2023.107736}, DOI={10.1016/j.ijfatigue.2023.107736}, abstractNote={Fatigue cracking is a primary asphalt pavement distress and various models have been developed to predict the fatigue life of asphalt mixtures using laboratory tests. One such model is the simplified viscoelastic continuum damage (S-VECD) model, which has been implemented in the pavement performance prediction program, FlexPAVETM. The S-VECD model test protocols (AASHTO TP 133 and AASHTO T 400) and data processing tool (FlexMATTM) are widely used around the world. Over the past three decades, this model has been continuously improved and refined. However, questions remain on the model’s ability to predict the material response when stress or strain are used as the model input. Also, different fitting procedures for the model calibration were found to affect the model’s prediction accuracy. In this study, analysis was conducted using data for four typical North Carolina mixes based on single replicate tests and multiple replicate tests to compare the model’s prediction accuracy based on stress versus strain as the model input and by considering fitting errors in the different calculations. The results show that using strain as the model input, which automatically incorporates portions of permanent strain, yields more accurate predictions compared to using stress as the input, regardless of the fitting algorithm. Additionally, in the analysis of individual test data, which is not affected by replicate specimen variability, the model’s predictions match the measured data well, as long as the fitting errors of the damage characteristic curve are controlled. When the data from replicate tests are analyzed together, although specimen variability compromises the S-VECD model’s prediction accuracy, failure can still be reasonably determined when strain is used as the model input.}, journal={INTERNATIONAL JOURNAL OF FATIGUE}, author={Zeng, Zhe and Kim, Y. Richard and Underwood, B. Shane and Guddati, Murthy}, year={2023}, month={Sep} }
 @article{rocha_aragao_nascimento_underwood_2023, title={Balanced Mixture Design Framework for Asphalt Mixtures Based on Index- and Performance-Volumetrics Relationships}, ISSN={["2169-4052"]}, DOI={10.1177/03611981231161063}, abstractNote={Asphalt mixture design methods range from approaches that rely on the volumetric properties of the mix to those that are based on the pavement performance. More advanced mixture analysis procedures allow a comprehensive evaluation that attempts to predict pavement distress based on factors such as traffic, climate, and mixture properties. Among them, balanced mix design (BMD) has been a frequently used approach; its purpose is to achieve an optimum balance between stability and durability. The objective of this work is to bridge the gap between the volumetric properties and performance of asphalt mixtures with respect to pavement fatigue cracking and rutting. In the study, an asphalt mixture was initially designed and then variations in voids in mineral aggregate (VMA) and voids filled with asphalt (VFA) were evaluated based on specified volumetric limits to create a broad volumetric space. Then, dynamic modulus, cyclic fatigue, and stress sweep rutting (SSR) tests were performed at each volumetric condition. Index-volumetrics and performance-volumetrics relationships were calibrated and the optimum mixture design was identified. In addition, a BMD framework was developed, which allows the mixture performance evaluation at multiple volumetric conditions and the selection of an optimized mixture based on the predicted pavement performance and on indexes for all possible combinations of the given set of component materials.}, journal={TRANSPORTATION RESEARCH RECORD}, author={Rocha, Marcos Lamha and Aragao, Francisco Thiago Sacramento and Nascimento, Luis Alberto Herrmann and Underwood, Benjamin Shane}, year={2023}, month={Apr} }
 @article{preciado_gulzar_fried_castorena_underwood_habbouche_boz_2023, title={Benchmarking Recycled Binder Blends Using Statistical Analysis: A Case Study of Virginia and North Carolina}, volume={7}, ISSN={["2169-4052"]}, url={https://doi.org/10.1177/03611981231178812}, DOI={10.1177/03611981231178812}, abstractNote={Recycling agents (RAs) are added to asphalt binder blends containing recycled materials to mitigate the negative effects of adding oxidized material to asphalt mixtures. Several methods exist to select a particular RA dosage to restore a specific Superpave performance parameter. However, the rheological similarities between the RA-modified systems and typical virgin binders across the complete range of temperatures remain to be ascertained. In this study, two RA dosage selection procedures, one aiming to restore high-temperature performance grade and the other aiming to restore low-temperature performance grade were statistically compared. Quality assurance datasets from Virginia and North Carolina were used to benchmark the typical virgin binder properties, and 17 recycled binder blends using constituent materials from the two states were studied with respect to Superpave binder properties. Both univariate and bivariate statistical analyses were applied to compare and contrast the rheological properties of these blends with the benchmarked virgin binder properties for the two states. Then, a statistical similarity analysis was done using the Mahalanobis distance to evaluate the rheological properties of these blends with those of the reference binders. The study found that both dosage selection procedures were successful in achieving rheological similarity at target-specific temperatures and for specific binder properties but might not necessarily yield similar properties at other temperatures. Finally, an example application is presented using statistical analysis to select an RA dosage that yields a rheological fingerprint more similar to that of virgin binder systems.}, 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{saleh_decarlo_underwood_pine_huber_tran_west_kim_2023, title={Case Studies of Asphalt Pavement Quality Assurance Specifications, Performance-Related Specifications, and Performance-Based Specifications}, volume={5}, ISSN={["2169-4052"]}, DOI={10.1177/03611981231166685}, abstractNote={Quality assurance (QA) specifications for asphalt pavement construction measure quality characteristics to adjust payments. The measured quality characteristics are assumed to empirically relate to performance. The validity of this assumption, however, has been questioned in recent years; thus, there has been increased interest in finding ways to more directly evaluate the performance of the as-constructed materials. One proposed method to meet this need involves using the Asphalt Mixture Performance Tester (AMPT) and its associated test methods, which measure fundamental material properties that are then used to calculate the fatigue cracking performance index, S app , and a rutting strain index (RSI). These indices can be used in performance-related specification (PRS) or performance-based specification (PBS) frameworks to determine the pay adjustments during the construction of asphalt pavement. While PBS requires measured indices, PRS uses index-volumetrics relationships (IVRs) to predict S app and RSI based on conventional acceptance quality. Payment can then be based on a percent within limits (PWL) approach. This paper demonstrates how pay adjustments can be made for a paving project in Indiana following three different QA specification frameworks: the current QA specifications framework in the Indiana Department of Transportation, a PRS framework using IVRs, and a PBS framework that employs measured S app and RSI. For each framework, the main elements of the specification were identified and determined. The specification limits for S app and RSI and weight factors in composite pay factor equations were determined such that the resulting pay factors are comparable to pay factors obtained from the current QA practices.}, journal={TRANSPORTATION RESEARCH RECORD}, author={Saleh, Nooralhuda F. and DeCarlo, Katie and Underwood, B. Shane and Pine, William J. and Huber, Gerry and Tran, Nam and West, Randy C. and Kim, Y. Richard}, year={2023}, month={May} }
 @article{souza_enriquez-leon_rocha_osmari_sacramento aragao_brabo pereira_underwood_2023, title={Criterion to Select the Maximum Aggregate Size of Fine-Aggregate Asphalt Matrices}, ISSN={["2169-4052"]}, DOI={10.1177/03611981231159891}, abstractNote={Fine-aggregate matrices (FAMs) are a relevant constituent of asphalt mixtures. Several FAM mix design, fabrication, and characterization protocols have been recently developed to investigate the behavior of such materials. However, there is a lack of experimental evidence on how to define the most appropriate maximum aggregate size (MAS) to fabricate FAM specimens. The focus of this paper is to develop such experimental evidence. Three asphalt concretes (ACs) and their corresponding FAMs with different MASs were tested to determine their stiffness and fatigue properties in uniaxial cyclic tests. In addition, the AC microstructures were scanned using X-ray micro-computed tomography (micro-CT) and analyzed using image analysis techniques. The combination of the AC microstructure assessed by micro-CT with the mechanical characteristics of the mixtures allowed the determination of the most representative MASs for the fabrication of isolated FAM samples. The key conclusion from this study was that ACs with nominal maximum aggregate sizes of 19.0, 12.5, and 9.5 mm are better characterized by FAMs with a MAS of 2.36 mm.}, journal={TRANSPORTATION RESEARCH RECORD}, author={Souza, Thiago Delgado and Enriquez-Leon, Alexis Jair and Rocha, Marcos Lamha and Osmari, Patricia Hennig and Sacramento Aragao, Francisco Thiago and Brabo Pereira, Andre Maues and Underwood, Benjamin Shane}, year={2023}, month={Mar} }
 @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{goenaga_underwood_tirkolaei_neithalath_2023, title={Effect of soil amendments on the compaction characteristics, hydraulic conductivity, and tire sinkage potential of roadside soils}, volume={41}, ISSN={["2214-3912"]}, DOI={10.1016/j.trgeo.2023.101019}, abstractNote={State highway agencies (SHAs) are required to comply with the National Pollution Discharge Elimination Permit (NPDES), which requires that the majority stormwater runoff from highways infiltrate into the roadside and that agencies implement soil based best management practices (BMPs). Per this new permit, SHAs are to install soil based BMPs that can absorb the 85th percentile of a 24-hour stormwater event. The area used for this purpose is typically the road embankments/slopes located adjacent to the roadside, best known as Clear Recovery Zone (CRZ). The CRZ must be traversable and recoverable to meet roadside traffic safety standards. A major concern for SHAs is the uncertainty on how these BMPs will affect the safety of a vehicle should that vehicle leave the roadway and interact with the soft soils. Considering this concern, the study described in this paper has assessed the impact of soil amendments on the compaction characteristics, hydraulic conductivity, and sinkage potential of six native soils of the state of California. These six soils were amended with four of the most used BMPs by the California State of Transportation (Caltrans). The results showed the hydraulic conductivity drops when the percentage of organic matter increases in the soil. They also showed that soils with a soaked surface had much larger sinkage than soils with an intact surface, this sinkage potential increase at the soak condition is proportional to the soil’s clay content.}, journal={TRANSPORTATION GEOTECHNICS}, author={Goenaga, Boris and Underwood, B. Shane and Tirkolaei, Hamed and Neithalath, Narayanan}, year={2023}, month={Jul} }
 @misc{jia_sheng_guo_underwood_chen_kim_li_ma_2023, title={Effect of synthetic fibers on the mechanical performance of asphalt mixture: A review}, volume={10}, ISSN={["2095-7564"]}, DOI={10.1016/j.jtte.2023.02.002}, abstractNote={Numerous studies showed that synthetic fibers are effective for reinforcing the mechanical performance of the asphalt mixture due to their high strength properties, ductility, and durability characteristics. In this paper, the objective is to present a review of the reinforcement effect of synthetic fiber on the mechanical performance of the asphalt mixture. This paper reviews the relevant literature on the characterizations and applications of synthetic fibers to improve different mechanical properties of asphalt mixes, which can provide a reference for the applications and development of synthetic fibers in asphalt pavement. The characteristics of common synthetic fibers are introduced and the utilization of synthetic fibers in asphalt mixture is discussed. Different surface treatment methods for fiber are reviewed and it is found that surface treatment can improve the performance of the synthetic fibers in asphalt mixtures, especially the chemical surface treatment method. The influence of synthetic fiber addition on the mechanical properties of the asphalt concrete such as rutting resistance, tensile strength, water stability performance, and cracking resistance are then discussed. The research results show that aramid, glass, and polyester fibers improve the fatigue cracking resistance of asphalt mixture. Polyester fibers, polyamide fibers, and carbon fibers are used to improve resistance to the permanent deformation of asphalt pavement.}, number={3}, journal={JOURNAL OF TRAFFIC AND TRANSPORTATION ENGINEERING-ENGLISH EDITION}, author={Jia, Haichuan and Sheng, Yanping and Guo, Ping and Underwood, Shane and Chen, Huaxin and Kim, Y. Richard and Li, Yan and Ma, Qingwei}, year={2023}, month={Jun}, pages={331–348} }
 @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"]}, 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{yousefi_haghshenas_underwood_harvey_blankenship_2023, title={Performance of warm asphalt mixtures containing reclaimed asphalt pavement, an anti-stripping agent, and recycling agents: A study using a balanced mix design approach}, volume={363}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2022.129633}, abstractNote={This research aims to use a balanced mix design (BMD) approach to investigate the effect of recycling agents (RAs) and an anti-stripping agent on the mechanical properties of warm-mix asphalt (WMA) containing different levels of reclaimed asphalt pavement (RAP). The BMD used three RAs (aromatic extract, triglycerides and fatty acids, and tall oil), an amidoamine WMA additive (PAWMA®), and an anti-stripping agent (Zycotherm®). The Dynamic Creep (DC), Indirect Tensile Strength (ITS), and Semi-Circular Bending (SCB) fracture tests were respectively used to evaluate the rutting, moisture susceptibility, and cracking resistance of mixtures. In addition, two-dimensional and three-dimensional (2-D and 3-D) performance interaction diagrams were developed as typical approaches for the BMD of asphalt mixtures. For mixtures with RAP, the results indicated that the aromatic extract and tall oil RAs decreased the moisture susceptibility, while triglycerides and fatty acids increased the moisture susceptibility. In addition, the RAs generally decreased the rutting resistance of mixtures while they increased the cracking resistance. This effect was more noticeable in the mixtures treated with triglycerides and fatty acids. The results also showed that introducing PAWMA® and Zycotherm® to the mixtures improved their resistance to moisture damage, cracking, and rutting.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Yousefi, Afshar A. and Haghshenas, Hamzeh F. and Underwood, Benjamin Shane and Harvey, John and Blankenship, Phillip}, year={2023}, month={Jan} }
 @article{karanam_goenaga_underwood_2023, title={Quantifying Uncertainty with Pavement Performance Models: Comparing Bayesian and Non-Parametric Methods}, volume={3}, ISSN={["2169-4052"]}, DOI={10.1177/03611981231155188}, abstractNote={An important part of pavement management systems is accurately estimating the performance-time-degradation relationship. One common approach to establishing this relationship is to use performance family curves. These curves are developed by collecting performance data at specific points in time and collectively shifting pavements of various ages to identify the probable underlying function. This paper compares two alternative methods for characterizing such a family curve function. First, a Bayesian method (Method-A) is used, which fits both the family curve and the shift factor function in parallel by assuming a Beta distribution for pavement performance condition rating (PCR). Second, a non-parametric method (Method-B) is developed, which fits the model in two steps; (1) by fitting the family; and (2) by horizontal shift to minimize the error. PCR values from flexible pavements in North Carolina (NC-PCR) are used for this comparison. These data include a total of 30,988 pavement sections segregated according to surface type and traffic level. Data from 2013 to 2015 are used for model calibration, and data from 2016 are used for model validation. The root means square error and k-fold cross-validation test are used to conduct the comparison, and Method-A is found to be preferred. The uncertainty in both models is quantified and compared. On the basis of this uncertainty, the Bayesian method is preferred, but in cases with large data sets, a non-parametric method does result in lower uncertainty.}, journal={TRANSPORTATION RESEARCH RECORD}, author={Karanam, Gnana Deepika and Goenaga, Boris and Underwood, Benjamin Shane}, year={2023}, month={Mar} }
 @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"]}, 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 v norm index was established to quantify variation in the entire damage characteristic curve. Repeatability and reproducibility analysis was conducted using v norm , 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) v norm 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 v norm 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} }
 @article{fabrizio_underwood_lucia_orazio_ezio_2023, title={Self-healing master curves of bituminous binders: a non-linear viscoelastic continuum damage framework}, ISSN={["2164-7402"]}, DOI={10.1080/14680629.2023.2180295}, abstractNote={In this paper the viscoelastic continuum damage theory was used to investigate the damage and self-healing potential of bituminous binders, considering the effects of rest temperature, thixotropy, and non-linearity. Experimental testing was carried out by using a procedure in which continuous oscillatory shear loading was imparted to the specimens with the inclusion of a single rest period under multiple temperature conditions. Quantification of self-healing included the determination of material integrity gained and damage parameter recovered after the rest period. Such parameters were calculated by excluding time-dependent and non-linear biasing effects, which were directly evaluated by means of a distinct set of experiments. Results were modelled by using the so-called self-healing master curves, constructed by applying the linear viscoelastic time-temperature shift factors. These self-healing master curves are intended to be used as straightforward tools for the prediction of the self-healing response of neat and polymer modified binders in various time-temperature combinations.}, journal={ROAD MATERIALS AND PAVEMENT DESIGN}, author={Fabrizio, Miglietta and Underwood, B. Shane and Lucia, Tsantilis and Orazio, Baglieri and Ezio, Santagata}, year={2023}, month={Feb} }
 @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{barros_nascimento_sacramento aragao_underwood_pivetta_2022, title={Characterization of the permanent deformation of asphalt mixtures based on indexes and on pavement structural performance}, volume={326}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2022.126555}, abstractNote={This paper evaluates the resistance to rutting of asphalt mixtures based on the pass-fail Flow Number (FN) index and on Stress Sweep Rutting (SSR) testing results. SSR provides information to assess the rutting evolution, either by the Rutting Strain Index (RSI) or by pavement simulations performed in FlexPAVETM. The results indicate that FN is a competent index for preliminary analyses of the mixture performance, but it does not provide accurate estimations if the temperature and traffic level are taken into account. Thus, more robust analyses such as those based on SSR parameters and FlexPAVETM simulations are required.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Barros, Larissa Montagner and Nascimento, Luis Alberto and Sacramento Aragao, Francisco Thiago and Underwood, Benjamin Shane and Pivetta, Felipe do Canto}, year={2022}, month={Apr} }
 @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{jeong_underwood_kim_2022, title={Cracking performance predictions using index-volumetrics relationships with direct tension cyclic fatigue test and Illinois Flexibility Index Test (I-FIT)}, volume={315}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2021.125631}, abstractNote={This paper introduces a methodology to predict fatigue cracking indices from asphalt mixture volumetric conditions using the index-volumetrics relationship (IVR). Two different tests, the Illinois Flexibility Index Test (I-FIT) and the direct tension cyclic fatigue test, were conducted using two North Carolina plant-mixed lab-compacted (PMLC) mixtures, RS9.5C and RI19.0C, obtained from field projects. Several mixture samples were collected from different truck loads for each mixture. The research team determined three sets of fatigue index values from the I-FIT, i.e., flexibility index (FI), cracking resistance index (CRI), and balanced cracking index (BCI) values, and determined another set of fatigue index values, Sapp index values, from the direct tension cyclic fatigue tests. IVRs for the individual mixtures and test indices were developed and then used to predict the fatigue index values at the volumetric properties that were not used in the IVR development. A good agreement was found between the predicted and measured index values. Except for the BCI values of the RS9.5C mixture, most of the I-FIT cracking test results showed counterintuitive trends with regard to air void content; however, the Sapp index showed more intuitive trends in both mixtures. The effect of binder content on the index values was not included in this study due to an inherent limitation of PMLC mixtures, which is the narrow range of binder content for the collected mixture samples compared to air void content.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Jeong, Jaehoon and Underwood, Shane and Kim, Y. Richard}, year={2022}, month={Jan} }
 @article{wang_underwood_kim_2022, title={Development of a fatigue index parameter, S-app, for asphalt mixes using viscoelastic continuum damage theory}, volume={23}, ISSN={["1477-268X"]}, DOI={10.1080/10298436.2020.1751844}, abstractNote={Fatigue cracking is one of the major distresses in asphalt pavements. Engineers have used many methods, from sophisticated numerical simulations to experience-based knowledge, to address fatigue cr...}, number={2}, journal={INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING}, author={Wang, Yizhuang David and Underwood, Benjamin Shane and Kim, Youngsoo Richard}, year={2022}, month={Jan}, pages={438–452} }
 @article{noorvand_mobasher_underwood_kaloush_2022, title={Development of an analytical framework for evaluation of critical fiber length in asphalt concrete with a fiber pullout test}, volume={360}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2022.129561}, abstractNote={The interfacial shear bond strength (τ) between fibers and matrix is typically measured by fiber pullout test to determine the critical fiber length (Lc) in fiber reinforced composites. In fiber reinforced asphalt concrete (FRAC), the τ is a time-dependent property and it is affected by asphalt modulus. The main objective of this study was to establish a relationship between the τ and modulus of asphalt mastic and asphalt concrete (AC), from which the Lc in AC was determined. Results from direct tension test, performed to validate the analytical framework, suggested that the use of longer fibers (38-mm vs 19-mm) showed higher reinforcement efficiency in FRAC.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Noorvand, Hossein and Mobasher, Barzin and Underwood, Shane and Kaloush, Kamil}, year={2022}, month={Dec} }
 @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{noorvand_castro_underwood_kaloush_2022, title={Evaluating interaction of fibre reinforcement mechanism with mesostructure of asphalt concrete}, volume={23}, ISSN={["1477-268X"]}, DOI={10.1080/10298436.2020.1813286}, abstractNote={Published studies generally demonstrate positive benefits from using Mechanically Fibre-Reinforced Asphalt Concrete (M-FRAC). However, improvements vary with the particular asphalt mixture used in ...}, number={5}, journal={INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING}, author={Noorvand, Hossein and Castro, Samuel and Underwood, Benjamin S. and Kaloush, Kamil E.}, year={2022}, month={Apr}, pages={1594–1611} }
 @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.}, journal={TRANSPORTATION RESEARCH RECORD}, publisher={SAGE Publications}, author={Matini, Narges and Gulzar, Saqib and Underwood, Shane 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={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{goenaga_karanam_underwood_2022, title={Method to Reduce Uncertainty in the Prediction of Pavement Condition With a Lower Sample Frequency}, volume={4}, ISSN={["2169-4052"]}, DOI={10.1177/03611981221086636}, abstractNote={In this paper, the effect of missing pavement condition observations in the predictions of the future state of a road network was evaluated. Real data from North Carolina were used for this purpose. First, the auto-regression method was compared against the most common “family-curve” modeling approach. It was found that the auto-regression method improves the predictive accuracy of predictions, at both project and network levels. By using the auto-regression method over the “family-curve” approach it is possible to reduce, on average, the Mean Absolute Percent Error of the predictions by 40%. Second, this paper evaluates the case in which a reduced survey frequency is unavoidable, and state highway agencies might need to plan the network maintenance based on historical observations and the subsample of the current condition. Observations of the Pavement Condition Rating for years 2013–2019 were used to define four different scenarios of reduced survey frequency: Scenario 1—“business-as-usual,” where the entire network is surveyed every year; Scenario 2—“reduced-sampling,” analyzed the case where the entire network is surveyed every other year; Scenario 3—“halfway-sampling,” evaluates the case where only half of the network is surveyed every year; and Scenario 4—“least-sampling,” considers the case where only a third of the network is monitored every year. Scenario 1 was used as the baseline of comparison, and as expected it was found that whenever possible the network should be monitored annually; however, if that is not feasible the best option, from the ones evaluated in the paper, should be Scenario 3.}, journal={TRANSPORTATION RESEARCH RECORD}, author={Goenaga, Boris and Karanam, Deepika and Underwood, Benjamin Shane}, year={2022}, month={Apr} }
 @article{liu_shan_li_underwood_qi_2022, title={Molecular-based asphalt oxidation reaction mechanism and aging resistance optimization strategies based on quantum chemistry}, volume={223}, ISSN={["1873-4197"]}, DOI={10.1016/j.matdes.2022.111225}, abstractNote={Understanding the oxidation reaction mechanism of asphalt is critical to improving its aging resistance. Here, quantum chemistry (QC) was used to study the oxidation reaction mechanism of 12 typical asphalt molecules. On this basis, the molecular models of aged asphalt were established, and the aging resistance optimization strategies of asphalt were proposed. The results show that the oxidation sites for oxygen-containing or heteroatoms-free molecules are on aromatic carbons (I molecules). Reducing hydrogen and hydroxyl radicals can improve its aging resistance. The oxidation sites for sulfur- or nitrogen-containing molecules are on heteroatoms (II molecules). Reducing oxygen free radicals content can improve its aging resistance. The molecules containing sulfur and cata-condensed polycyclic aromatic hydrocarbons (PAHs) (such as R5) have the strongest oxidation reactivity. Reducing its content can improve asphalt aging resistance. Combining the QC and experiment results, LH90 contains more I molecules, while UP70 and MM70 contain more II molecules (especially As3 and R5). The aging resistance of UP70 and MM70 is poor than LH90. Reducing the content of As3 or R5 molecules or the content of oxygen radicals can improve the aging resistance of UP70 and MM70. These findings lay a foundation for designing and preparing asphalt with excellent aging resistance.}, journal={MATERIALS & DESIGN}, author={Liu, Shuang and Shan, Liyan and Li, Guannan and Underwood, B. Shane and Qi, Cong}, year={2022}, month={Nov} }
 @article{gulzar_goenaga_underwood_2022, title={Novel Index for Vulnerability Assessment of Flexible Pavement Infrastructure to Temperature Rise: Case Study of Developing Countries}, volume={28}, ISSN={["1943-555X"]}, url={https://doi.org/10.1061/(ASCE)IS.1943-555X.0000669}, DOI={10.1061/(ASCE)IS.1943-555X.0000669}, abstractNote={Road infrastructure is engineered to perform through constant exposure to climatological stressors. Due to climate change in particular, expected rises in the average ambient and extreme temperatures, pavement performance might deviate from what was originally predicted at the design stage. This poses serious risks to the long-term performance of this infrastructure because the capacity of a transportation network to provide an acceptable level of service over the period that it was intended for is also seriously affected. However, identifying where potential risks are greatest and where more involved planning and prioritizing is needed is hampered by the lack of vulnerability assessment methods that appropriately integrate failure pathways and engineering decisions. In this study, a new vulnerability index is proposed—extent of pavement grade reliability loss (EPGRL), which has the capacity to capture both flexible pavement performance and transportation serviceability. The index is based on two assumptions. First, flexible pavement performance is directly related to the inherent rheological properties of the asphalt binder, which can be estimated from the performance binder grade requirements for a locale. Second, the level of service of a road network can be represented by its connectivity, expressed here by a network centrality measure, the betweenness score. Two developing countries, Colombia and India, were selected to analyze the capabilities of the EPGRL. The results obtained indicate the EPGRL captures the available performance capability of pavement infrastructure together with the importance of transportation network elements. Hence, it can be used as a tool to evaluate and quantify the vulnerability of transportation infrastructure to future climate change.}, number={1}, journal={JOURNAL OF INFRASTRUCTURE SYSTEMS}, author={Gulzar, Saqib and Goenaga, Boris and Underwood, B. Shane}, year={2022}, month={Mar} }
 @misc{zeiada_liu_ezzat_al-khateeb_underwood_shanableh_samarai_2022, title={Review of the Superpave performance grading system and recent developments in the performance-based test methods for asphalt binder characterization}, volume={319}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2021.126063}, abstractNote={Asphalt binder plays an important role in the overall resistance of an asphalt mixture to pavement distresses. The rheological properties should be fully characterized before it is put into field use. Usually, a grading system is employed to evaluate and select the appropriate asphalt binder. The Superpave performance grading (PG) system made the first attempt to directly relate the measured physical properties of asphalt binders to field performance with due consideration of pavement conditions. Conceptually, this approach represents a significant substantial advancement over the traditional penetration and viscosity grading systems. Novel tests and specifications were devised in the Superpave PG system to address the performance requirements. This paper provides a review of the Superpave PG system with respect to workability, rutting resistance, fatigue cracking resistance, and thermal cracking resistance. Although the Superpave PG system is purported to be superior to the traditional grading systems, some deficiencies have been reported regarding the test methods and corresponding evaluation indicators. The Superpave PG system can be further refined if these deficiencies can be addressed effectively. Therefore, the second objective of this paper is to summarize the recent developments in performance-based test methods for asphalt binder characterization. Potential specification tests can be selected from those performance-based test methods in order to refine the Superpave PG system.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Zeiada, Waleed and Liu, Hanqi and Ezzat, Helal and Al-Khateeb, Ghazi G. and Underwood, Shane and Shanableh, Abdallah and Samarai, Mufid}, year={2022}, month={Feb} }
 @article{fraser_chester_underwood_2022, title={Wildfire risk, post-fire debris flows, and transportation infrastructure vulnerability}, volume={7}, ISSN={["2378-9697"]}, DOI={10.1080/23789689.2020.1737785}, abstractNote={Wildfires have grown in number, size and intensity in the American West and forecasts predict worsening trends. Evidence mounts that post-fire debris flows pose a major hazard to infrastructure, pa...}, number={3}, journal={SUSTAINABLE AND RESILIENT INFRASTRUCTURE}, author={Fraser, Andrew M. and Chester, Mikhail V and Underwood, B. Shane}, year={2022}, month={May}, pages={188–200} }
 @article{tsantilis_underwood_miglietta_riviera_baglieri_santagata_2021, title={Ageing effects on the linear and nonlinear viscoelasticity of bituminous binders}, volume={22}, ISSN={["2164-7402"]}, DOI={10.1080/14680629.2021.1908406}, abstractNote={The paper investigates the effects of ageing on the linear and nonlinear viscoelastic properties of bituminous binders for paving applications. Four neat binders were analysed in their unaged state...}, journal={ROAD MATERIALS AND PAVEMENT DESIGN}, author={Tsantilis, Lucia and Underwood, Shane B. and Miglietta, Fabrizio and Riviera, Pier Paolo and Baglieri, Orazio and Santagata, Ezio}, year={2021}, month={Jun}, pages={S37–S50} }
 @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"]}, 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.}, 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{daryaee_habibpour_gulzar_underwood_2021, title={Combined effect of waste polymer and rejuvenator on performance properties of reclaimed asphalt binder}, volume={268}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2020.121059}, abstractNote={In hot asphalt recycling, use of reclaimed asphalt binder has resulted in stiffer binders. To counter this phenomenon, rejuvenators are utilized. Further, research has shown that polymers can improve the performance properties of the aged bitumen. The study of the combined effect of both (rejuvenator and polymer) on the rheological properties of reclaimed asphalt binder can provide useful insights about the performance of the binder in hot asphalt recycling projects. In the current study, the combined effect of a rejuvenator and polymer derived from a waste source on the mechanical properties of bitumen containing varying percentages of reclaimed asphalt binder (RAB) is evaluated for the first time. The fatigue behavior was evaluated using linear amplitude sweep (LAS), and time sweep (TS) tests while rutting resistance was assessed using multiple stress creep recovery (MSCR) test. Moreover, bending beam rheometer (BBR) test is also performed to compare the sample’s low-temperature cracking. Results indicate that the synergistic use of waste polymer along with rejuvenator substantially improves the high, intermediate, and low-temperature properties of the blends with 50% RAB content compared to that of the control bitumen. Therefore, the use of waste PBR in hot asphalt recycling (HIR) projects, in addition to improving the performance of recycled bitumen can also be introduced as an environmental-friendly option.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Daryaee, Daryoosh and Habibpour, Mahdi and Gulzar, Saqib and Underwood, Benjamin Shane}, year={2021}, month={Jan} }
 @article{wang_ghanbari_underwood_kim_2021, title={Development of framework of the predictive performance-engineered mix design procedure for asphalt mixtures}, volume={6}, ISSN={["1477-268X"]}, url={https://doi.org/10.1080/10298436.2021.1938044}, DOI={10.1080/10298436.2021.1938044}, abstractNote={This paper presents a new asphalt mixture design framework for predictive performance-engineered mix design (PEMD) and the theory and procedures that underlie the proposed design method. This method allows pavement engineers to determine an optimized mix design based on the predicted pavement/mixture performance for all possible combinations of a given set of component materials (i.e. aggregate and binder) in the design space. The proposed PEMD process is based on the ‘performance-volumetrics relationship’ (PVR) concept. The calibration of the PVR is based on the mixture performance predicted from FlexPAVETM, a three-dimensional finite element program that performs viscoelastic analysis under moving loads, using the material properties of the asphalt mixture in question at widely spaced volumetric conditions. Three mixtures of different nominal maximum aggregate sizes and binder types are used to demonstrate the proposed PEMD process. Finally, the predicted performance results obtained from different design approaches are compared.}, journal={INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING}, author={Wang, Yizhuang David and Ghanbari, Amir and Underwood, Benjamin Shane and Kim, Youngsoo Richard}, year={2021}, month={Jun} }
 @article{wang_ghanbari_underwood_kim_2021, title={Development of preliminary transfer functions for performance predictions in FIexPAVE (TM)}, volume={266}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2020.121182}, abstractNote={Mechanistic-empirical design and performance-related specifications are state-of-the-art tools for designing pavements and determining incentives/disincentives for paving contracts. These methods require the reliable prediction of pavement performance throughout the pavement’s design life. One such prediction program is FlexPAVE™, which applies three-dimensional viscoelastic finite element analysis with moving loads to calculate the pavement’s mechanical responses under traffic loading and given climate data. The simplified viscoelastic continuum damage model and shift model are used to calculate the fatigue damage in the pavement’s cross-section and the rut depths, respectively. With regard to fatigue damage, a fatigue transfer function is needed to convert the computed cross-sectional damaged area (i.e., the damage level) to the cracked area on the pavement surface. With regard to rut depth, a rutting transfer function is needed to calibrate the predicted rut depths. In this study, preliminary transfer functions for the predicted fatigue damage and rut depths were developed using four sets of field measurement data obtained from test sections in the United States, Canada, and South Korea that include interstate highways and an accelerated testing facility. Good agreement between the predicted performance and field observations was found after calibration of FlexPAVE™.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Wang, Yizhuang David and Ghanbari, Amir and Underwood, Benjamin Shane and Kim, Youngsoo Richard}, year={2021}, month={Jan} }
 @article{goenaga_matini_karanam_underwood_2021, title={Disruption and Recovery: Initial Assessment of COVID-19 Traffic Impacts in North Carolina and Virginia}, volume={147}, ISSN={["2473-2893"]}, DOI={10.1061/JTEPBS.0000518}, abstractNote={The coronavirus disease of 2019 (COVID-19) pandemic has affected every aspect of peoples’ lives, including their mobility. In this study, the impact of closures related to the pandemic on traffic patterns is assessed for the state of North Carolina and the Commonwealth of Virginia. The results of the initial assessments indicated that the average reduction in traffic volume was 27% across North Carolina and Virginia. Findings suggest that a slight increase in traffic at the beginning of the stay-at-home orders was followed by at most a 40% reduction after closures. The changes in traffic volumes in terms of road and vehicle classification are most substantial in Interstate routes and for passenger cars and buses. The average recovery rate of traffic volume after the occurrence of the maximum reductions was between 2.3% and 3.4% per week.}, number={4}, journal={JOURNAL OF TRANSPORTATION ENGINEERING PART A-SYSTEMS}, author={Goenaga, Boris and Matini, Narges and Karanam, Deepika and Underwood, B. Shane}, year={2021}, month={Apr} }
 @article{hernandez-fernandez_harvey_underwood_ossa-lopez_2021, title={Pavement Fatigue Damage Simulations Using Second-Generation Mechanistic-Empirical Approaches}, ISSN={["2169-4052"]}, DOI={10.1177/03611981211027152}, abstractNote={This article aims to demonstrate the advanced features of two second-generation mechanistic-empirical (ME) pavement analysis engines by focusing on their ability to conduct fatigue performance analysis. First, a comprehensive review is presented of both mechanistic and empirical damage models, underlining the additional features of CalME and FlexPAVE™ over AASHTOWare Pavement ME Design. Then, the capabilities of these methodologies are demonstrated by simulating the fatigue damage performance of an example study section. For these simulations the mechanical properties of four asphalt concrete mixtures, assembled in the laboratory with similar mix design attributes but diverse fatigue characteristics, were utilized. The empirical transfer functions were initially calibrated against field cracking for the unmodified mixture cracking predictions. After that, fatigue damage simulations for the other three mixtures were performed. The results showed a similar ranking in fatigue cracking performance for both software simulations. Polymer-modified mixtures exhibited higher fatigue cracking resistance, whereas the unmodified mixture showed the worst cracking resistance. However, significant differences in cracking initiation and progression rates were observed for all mixture simulations before and after calibration. This discrepancy was related to the different approaches to considering traffic loads in each software system, single axle in FlexPAVE™ and axle spectrum in CalME. Finally, current, and future enhancements for both analysis engines are briefly discussed.}, journal={TRANSPORTATION RESEARCH RECORD}, author={Hernandez-Fernandez, Noe and Harvey, John T. and Underwood, Benjamin Shane and Ossa-Lopez, Alexandra}, year={2021}, month={Jul} }
 @article{zhang_kaloush_underwood_hu_2021, title={Preparation and performances of SBS compound modified asphalt mixture by acidification and vulcanization}, volume={296}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2021.123693}, abstractNote={Polyphosphoric acid (PPA) was used to improve the performances of styrene–butadienestyrene (SBS) modified (SM) asphalt mixture further and decline the SBS content, however the negative effect of PPA on the performances of SM asphalt mixture is still unclear. The major purpose of this paper is to indicate the negative effect and provide an efficient way to solve the problem. In this paper, SM asphalt, SBS/PPA-modified asphalt (SPMA), SBS/PPA/sulfur-modified asphalt (SPSMA) were prepared, the physical properties were studied and the morphology was investigated by using scanning electron microscope (SEM). The mixtures of base asphalt (BA), SM asphalt, SPMA, SPSMA were designed and prepared in the light of Superpave mixing design method and Phoenix specifications. Universal testing machine (UTM) system was used to investigate the effect of SBS, PPA, sulfur on the properties of BA mixture. It was found that PPA declined the crack, fatigue resistance and moisture susceptibility of SM asphalt mixture and the problem can be solved well by vulcanization, the morphology change of SBS from coarse particle to threadlike one after vulcanization prompted the swelling of SBS in asphalt. Therefore SBS compound modified asphalt pavement material with better performances and lower cost can be prepared by taking advantage of acidification and vulcanization.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Zhang, Feng and Kaloush, Kamil and Underwood, Shane and Hu, Changbin}, year={2021}, month={Aug} }
 @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{jeong_underwood_kim_2021, title={Rutting performance prediction using index-volumetrics relationships with stress sweep rutting test and Hamburg wheel-track test}, volume={295}, ISSN={["1879-0526"]}, url={https://doi.org/10.1016/j.conbuildmat.2021.123664}, DOI={10.1016/j.conbuildmat.2021.123664}, abstractNote={This paper describes a methodology to develop index-volumetrics relationships (IVRs) for rutting of asphalt mixtures. These relationships are developed from rutting performance test results and the volumetric properties (In-place VMA and In-place VFA) of the mixture at so-called ‘four corners’ of the volumetric space. Two rutting tests, the stress sweep rutting (SSR) test and Hamburg wheel-track (HWT) test, were employed to characterize the rutting performance of two mixtures acquired from two field projects. The IVRs for the individual mixtures and test methods were developed and used to predict the mixtures’ rutting performance as a function of the two volumetric properties.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, publisher={Elsevier BV}, author={Jeong, Jaehoon and Underwood, B. Shane and Kim, Y. Richard}, year={2021}, month={Aug} }
 @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{underwood_caro_varveri_2020, title={Advancements in the characterisation and design of asphalt materials}, volume={21}, ISSN={["1477-268X"]}, DOI={10.1080/10298436.2019.1650928}, abstractNote={"Advancements in the characterisation and design of asphalt materials." International Journal of Pavement Engineering, 21(8), p. 955}, number={8}, journal={INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING}, author={Underwood, Shane and Caro, Silvia and Varveri, Aikaterini}, year={2020}, month={Jul}, pages={955–955} }
 @article{mansourkhaki_ameri_habibpour_underwood_2020, title={Chemical Composition and Rheological Characteristics of Binders Containing RAP and Rejuvenator}, volume={32}, ISSN={["1943-5533"]}, DOI={10.1061/(ASCE)MT.1943-5533.0003016}, abstractNote={AbstractOne of the most important concerns in using different additives for improving fatigue and low-temperature cracking resistance is the diminishing rutting resistance of pavement. In this rese...}, number={4}, journal={Journal of Materials in Civil Engineering}, author={Mansourkhaki, A. and Ameri, M. and Habibpour, M. and Underwood, B.S.}, year={2020}, month={Apr}, pages={04020026} }
 @article{sheng_wu_yan_jia_qiao_underwood_niu_kim_2020, title={Development of environmentally friendly flame retardant to achieve low flammability for asphalt binder used in tunnel pavements}, volume={257}, ISSN={["1879-1786"]}, DOI={10.1016/j.jclepro.2020.120487}, abstractNote={Abstract This paper reports the development of an environmentally friendly flame retardant, referred to as FRC-Si, to improve the fire resistance of asphalt binder without compromising mixture performance. This flame-retardant composite (FRC) contains four halogen-free flame-retardant components: expandable graphite (EG), magnesium hydroxide (MH), calcium hydroxide (CH), and ammonium polyphosphate (APP). These four components have different ranges of thermal reaction temperature so they can effectively absorb heat throughout the entire process of binder combustion. An orthogonal experiment with six binder properties as the influential factors was designed for this study. Then, a multi-criteria decision analysis method was employed to find the optimal proportion of the combined EG, MH, CH, and APP to be 5:5:4:9, respectively. A silane coupling agent was added to modify the surface properties and improve stability of the asphalt binder, thereby transforming the preliminary FRC to FRC-Si. Based on activation index values and oil absorption of the binder, the optimum content of the silane coupling agent was determined to be 1.2% by mass of FRC. In addition, the rheological properties and flammability of styrene-butadiene-styrene (SBS) binder with various dosages of FRC-Si were obtained and the optimum content of FRC-Si was determined to be 8% by mass of binder. Finally, cone calorimeter tests were performed to evaluate the flame retardancy of asphalt mixtures with SBS, FRC, and FRC-Si binders. Results indicate that FRC-Si not only reduced the amounts of heat and carbon monoxide (CO) released, but also delayed the release of CO, thereby supporting the application of FRC-Si as a flame retardant for asphalt pavements in tunnels.}, journal={JOURNAL OF CLEANER PRODUCTION}, author={Sheng, Yanping and Wu, Yongchang and Yan, Yu and Jia, Haichuan and Qiao, Yunyan and Underwood, B. Shane and Niu, Dongyu and Kim, Y. Richard}, year={2020}, month={Jun} }
 @article{goenaga_underwood_fuentes_2020, title={Effect of Speed Bumps on Pavement Condition}, volume={2674}, ISBN={2169-4052}, DOI={10.1177/0361198120927005}, abstractNote={Speed bumps are efficient traffic calming devices that allow transport authorities to control vehicle speeds and improve safety in specific locations. Though frequently used in residential areas, they have become increasing prevalent in other higher volume roadways (particularly in developing countries), because of their effectiveness, low-cost of implementation, and easy installation process. However, in these countries there is no proper technical guidance for speed bump design and implementation, which is why one can often find these devices placed on an arterial highway or on roads where the proportion of trucks is high. The most important consequence of placing a speed bump on a road with large numbers of trucks is that the pavement deterioration process will accelerate as a result of the induced vibrations and bouncing of a truck’s suspension. In this paper the relationship between the bump geometry—length and height—and the dynamic load transmitted to the pavement is studied. A full truck model has been used to simulate the vehicle dynamics while passing over the bump, to estimate the demand imposed over the pavement. Damage was calculated for each simulation scenario using a combination of linear-elastic analysis and empirical damage functions. The geometry that leads to less damage is the circular, with a minimum length of two meters and a maximum height of ten centimeters.}, number={9}, journal={Transportation Research Record}, author={Goenaga, Boris and Underwood, Shane and Fuentes, Luis}, year={2020}, pages={66–82} }
 @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{medina_salim_underwood_kaloush_2020, title={Experimental Study for Crowdsourced Ride Quality Index Estimation Using Smartphones}, volume={146}, ISSN={["2573-5438"]}, DOI={10.1061/JPEODX.0000225}, abstractNote={The use of smartphones to collect roughness measurements or ride quality has become popular in recent years, owing to the potential for substantial cost savings in data collection. Hurdles to widespread adoption of these techniques include the quality, uncertainty, and variability of the measurements. The objective of this paper is to evaluate the multifactor effects of collecting ride quality measurements from smartphones and how crowdsourcing using measurements from a population of different vehicles can be used to overcome or mitigate the effects of less resolute and more variable measurements. This investigation was carried out using two experiments. First, a full factorial design of experiment (DOE) was developed to evaluate the multifactor effects on ride quality measurements using the average rectified slope (ARS). Second, a custom DOE with the objective of analyzing the ARS from a population of vehicles from different classifications was carried out. The results from the first experiment suggested that individual factors contribute to statistical differences in ARS measurements. However, the second experiment showed that when looking into a population of vehicles with randomly sampled factors, the ARS measurements converge, and the statistical analysis showed no significance. This approach can be successfully implemented using a crowdsourcing approach where the focus is to analyze a population of vehicles instead of individual measurements.}, number={4}, journal={JOURNAL OF TRANSPORTATION ENGINEERING PART B-PAVEMENTS}, author={Medina, Jose R. and Salim, Ramadan and Underwood, B. Shane and Kaloush, Kamil}, year={2020}, month={Dec} }
 @article{gundla_salim_shane underwood_kaloush_2020, title={Implementation of the AASHTO M 332 Specification: A Case Study}, volume={2674}, ISSN={["2169-4052"]}, DOI={10.1177/0361198120933266}, abstractNote={Over the past 20 years, changes in asphalt binders, the widespread adoption of polymer modified asphalts, and the need to bump asphalt binder grades to consider traffic conditions have exposed the gaps in the AASHTO M 320 specification, and subsequently led to the AASHTO M 332 specification. The State of Arizona initiated an experimental study to explore the possibility of adopting AASHTO M 332 into its binder specifications. In this paper, the specific challenges, technical implications of some key differences in the current Arizona standard compared with the AASHTO M 332 standard, and the approach taken to overcome the differences are explored and documented. Some of the key issues include the shortcomings of the J nr difference parameter, uncertainty of the pressurized aging vessel (PAV) temperature to be used, effect on the intermediate temperature parameter, |G*|sin δ, and the prospective distribution of asphalt binder grades if the new specification is adopted. Overall, the AASHTO M 332 specification is promising for the State of Arizona with minor changes recommended to prevent changes in binder formulations and influx of asphalt binders inferior to those currently available.}, number={9}, journal={TRANSPORTATION RESEARCH RECORD}, author={Gundla, Akshay and Salim, Ramadan and Shane Underwood, B. and Kaloush, Kamil E.}, year={2020}, month={Sep}, pages={959–971} }
 @article{gundla_underwood_2020, title={Molecular weight distribution of asphalt binders from Laser Desorption Mass Spectroscopy (LDMS) technique and its relationship to linear viscoelastic relaxation spectra}, volume={262}, ISSN={["1873-7153"]}, DOI={10.1016/j.fuel.2019.116444}, abstractNote={Asphalt binder is a complex viscoelastic hydrocarbon, whose performance depends upon interaction between its physical and chemical properties, both of which are equally important to the successful understanding of the material. In this research effort, a physico-chemical relationship is developed by utilizing the technique of Laser Desorption Mass Spectroscopy (LDMS) to relate the molecular structure of asphalt binders to its viscoelastic properties. The molecular weight distribution (MWD) data obtained from the LDMS technique is used to develop a relationship between number average molecular weight and width of relaxation spectrum of asphalt binders obtained from linear viscoelastic characterization using dynamic shear rheometer. The relationship shows that as the molecular weight of asphalt binders increase, they require more time to relax the developed stresses. Also, the shape descriptors of the molecular weight distribution suggest that asphalt binders possessing greater asymmetry and kurtosis require more time to relax the developed stresses.}, journal={FUEL}, author={Gundla, Akshay and Underwood, B. Shane}, year={2020}, month={Feb} }
 @article{gulzar_underwood_2020, title={Nonlinear Viscoelastic Response of Crumb Rubber Modified Asphalt Binder Under Large Strains}, volume={2674}, ISSN={["2169-4052"]}, DOI={10.1177/0361198120907097}, abstractNote={Agencies have been increasing their use of polymer modified asphalt binders in recent years to address performance issues and lengthen the useful life of their pavements. When deployed these materials likely experience strain levels exceeding their linear viscoelastic (LVE) limits. The same situation exists in non-polymer modified asphalt binders as well, but the effect may be more pronounced in polymer modified systems because of their bi-phasic nature. In this study, terminally blended crumb rubber (CR-TB) modified asphalt is studied to understand and quantify the nonlinear viscoelastic response under large strains. The CR-TB binders are extensively used in pavements subjected to high vehicular loads and extreme climatic conditions; thereby, their response under large strains becomes more critical. The current standard characterization techniques are based on LVE response using small amplitude oscillatory shear rheology only and do not consider the behavior of binders under large strains. In this study, large amplitude oscillatory shear (LAOS) rheology is used as a framework to more thoroughly investigate the complete response of the CR-TB modified asphalt binder under large strains at 30°C, 40°C, 50°C, and 60°C and at the frequencies of 0.5, 1, and 5 Hz. The LAOS response is analyzed using Fourier-transform rheology and the orthogonal stress decomposition method involving Chebyshev polynomial representation. It is found that nonlinearity manifests greatly in this study material as strain levels increase and frequencies decrease. The relative nonlinearity increases with increasing strain amplitude and is more significant towards lower end of the tested temperature range. The CR-TB binder shows strain-stiffening/softening and shear-thinning/thickening behavior depending upon a specific temperature, strain level, and frequency.}, number={3}, journal={TRANSPORTATION RESEARCH RECORD}, author={Gulzar, Saqib and Underwood, B. Shane}, year={2020}, month={Mar}, pages={139–149} }
 @article{underwood_mascaro_chester_fraser_lopez-cantu_samaras_2020, title={Past and Present Design Practices and Uncertainty in Climate Projections are Challenges for Designing Infrastructure to Future Conditions}, volume={26}, ISSN={["1943-555X"]}, DOI={10.1061/(ASCE)IS.1943-555X.0000567}, abstractNote={Designing infrastructure for a changing climate remains a major challenge for engineers. In popular discourse a narrative has emerged that infrastructures are likely underdesigned for the future. Weather-related hazards are directly embedded in the infrastructure design process. Yet the codes and standards that engineers use for this risk analysis have been changing for decades, sometimes increasing and other times decreasing design values. Further complicating the issue is that climate projections show increasing or decreasing intensities depending on the hazard and region. Thus, it is not clear that infrastructure is universally underdesigned. Here, analyses are developed at both regional and national scales using precipitation and roadway drainage systems to answer this question. First, it is shown that modeling uncertainty can pose challenges for using future projections to update region-specific standards. Second, the results show that depending on the historical design conditions and the direction of projections, roadway drainage infrastructures may be designed appropriately in some regions while in others they are possibly underdesigned. Given these uncertainties, the authors believe that there is a need for alternative design paradigms, and these needs are discussed.}, number={3}, journal={JOURNAL OF INFRASTRUCTURE SYSTEMS}, author={Underwood, B. Shane and Mascaro, Giuseppe and Chester, Mikhail V and Fraser, Andrew and Lopez-Cantu, Tania and Samaras, Constantine}, year={2020}, month={Sep} }
 @article{jeong_wang_ghanbari_nash_nener-plante_underwood_kim_2020, title={Pavement performance predictions using performance-volumetric relationship and evaluation of construction variability: Example of MaineDOT shadow project for the development of performance-related specifications}, volume={263}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2020.120150}, abstractNote={This paper describes the process chain for a shadow project of the Federal Highway Administration’s Asphalt Mixture Performance-Related Specifications (PRS) by the MaineDOT. Eleven mixture samples were acquired from a field project selected by MaineDOT and were performance-tested for calibration (a ‘four corners’ procedure) and verification to develop the performance-volumetric relationship (PVR) for the selected mixture. The PVR function for the selected mixture worked reasonably well to predict pavement performance at the volumetric conditions that were not included in the PVR development and reflected reasonable trends with regard to various field densities.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Jeong, Jaehoon and Wang, Yizhuang David and Ghanbari, Amir and Nash, Casey and Nener-Plante, Derek and Underwood, Benjamin Shane and Kim, Y. Richard}, year={2020}, month={Dec} }
 @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{mansourkhaki_ameri_habibpour_underwood_2020, title={Relations between colloidal indices and low-temperature properties of reclaimed binder modified with softer binder, oil-rejuvenator and polybutadiene rubber}, volume={239}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2019.117800}, abstractNote={Asphalt binder properties play an important role in the behavior of asphalt concrete pavements at low temperature and should be studied using laboratory tests. This research investigates the relationship between chemical properties and low-temperature performance of asphalt binders at RAP contents of 15%, 30%, 50 and 100% by weight. The asphalt is also modified with a softer binder, oil rejuvenator and polybutadiene rubber (PBR 1220) modified binder. Binder testing includes penetration test, softening point, bending beam rheometer (BBR) and Fraass breaking point. Moreover, saturate, aromatic, resin, and asphaltene (SARA) fractionation is used to study the induced changes in the chemical composition of binders after adding RAP. The results show that binders modified with oil-rejuvenator have better resistance to low temperature cracking in comparison with softer binder and polymer modified binder (PMB), particularly at high percentages of RAP. Using a softer virgin binder also demonstrates improvements in the low-temperature performance of RAP binder. Moreover, PBR 1220 blended with RAP binder showed poor resistance to low-temperature cracking, it means that having a low Tg (for polymer) would not necessarily lead to a good low temperature cracking of the polymer-modified binder. Finally, some promising statistical correlations are found between colloidal indices and low-temperature performance of samples with RAP content.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Mansourkhaki, Ali and Ameri, Mahmoud and Habibpour, Mandi and Underwood, B. Shane}, year={2020}, month={Apr} }
 @article{hernandez-fernandez_underwood_ossa-lopez_2020, title={Simulation of the asphalt concrete stiffness degradation using simplified viscoelastic continuum damage model}, volume={140}, ISSN={["1879-3452"]}, DOI={10.1016/j.ijfatigue.2020.105850}, abstractNote={Abstract A procedure based on the simplified viscoelastic continuum damage model is developed to simulate asphalt concrete stiffness degradation caused by the application of cyclic loads. Several tests are performed to characterize the linear viscoelastic and fatigue damage properties of four asphalt mixtures. It was found that the piecewise approach proposed to simulate the stiffness evolution successfully describes the damage growth under loads applications. It was also found that the exponential model used to fit the characteristic curves best describes the stiffness evolution for the entire load history. Finally, stiffness evolution simulations showed higher fatigue resistance for polymer-modified mixtures.}, journal={INTERNATIONAL JOURNAL OF FATIGUE}, author={Hernandez-Fernandez, Noe and Underwood, B. Shane and Ossa-Lopez, Alexandra}, year={2020}, month={Nov} }
 @article{medina_noorvand_underwood_kaloush_2020, title={Statistical Validation of Crowdsourced Pavement Ride Quality Measurements from Smartphones}, volume={34}, ISSN={["1943-5487"]}, DOI={10.1061/(ASCE)CP.1943-5487.0000891}, abstractNote={Advances in computing capabilities, image processing, and sensing technologies have permitted the development of specialized vehicles equipped with the capability to assess pavement condition at normal operating speeds. This has greatly improved engineers’ ability to assess and manage pavements, but the equipment is costly, and not all agencies can afford to purchase it. Recently, researchers have developed smartphone applications to address this data collection problem, but most of this work focused on a restricted setup, or calibration. This paper presented a methodology to estimate a ride quality index (RQI) from crowdsourced smartphone measurements and validated this approach with the use of statistical methods. This investigation was divided into three phases. First, a mechanical model to assess ride quality was developed. Second, the Monte Carlo method and the probabilistic point estimate were adopted to simulate RQI measurement responses to different longitudinal profiles from different vehicle traffic spectra. Third, the effects of wander and multilane effects in estimating the minimum required sample size for RQI measurements to converge were evaluated. Once the mechanical model was developed, the results from the Monte Carlos simulations showed that in 83% of cases, the RQI measurements showed no statistical significance. The results from the effect of multilane and wandering effects showed that the sample size for RQI measurements to converge adopting a coefficient of variation of 2% is 400 samples considering a single lane and wander, and 435 samples considering two lanes and wander. The use of the Monte Carlo method successfully validated the crowdsourced smartphone-based RQI measurements as an alternative method to evaluate pavement condition. This approach has the potential to save transportation agencies millions of dollars in pavement condition surveys and to give a better sense of pavement condition in real time.}, number={3}, journal={JOURNAL OF COMPUTING IN CIVIL ENGINEERING}, author={Medina, Jose R. and Noorvand, Hossein and Underwood, B. Shane and Kaloush, Kamil}, year={2020}, month={May} }
 @article{nafisi_mocelin_montoya_underwood_2020, title={Tensile strength of sands treated with microbially induced carbonate precipitation}, volume={57}, ISSN={["1208-6010"]}, DOI={10.1139/cgj-2019-0230}, abstractNote={During large earthquake events where bending moments within soil cements are induced, the tensile strength of cemented soil may govern the deformational behavior of improved ground. Several studies have been conducted to assess the tensile strength of artificially cemented sands that use Portland cement or gypsum; however, the tensile strength of microbially induced carbonate precipitation (MICP)-treated sands with various particle sizes measured through direct tension tests has not been evaluated. MICP is a biomediated improvement technique that binds soil particles through carbonate precipitation. In this study, the tensile strength of nine specimens were measured by conducting direct tension tests. Three types of sand (coarse, medium, and fine) were cemented to reach a heavy level of cementation (e.g., shear wave velocity of ∼900 m/s or higher). The results show that the tensile strength varies between 210 and 710 kPa depending on sand type and mass of carbonate. Unconfined compressive strength (UCS) tests were performed for each sand type to assess the ratio between tensile strength and UCS in MICP-treated sands. Scanning electron microscopy (SEM) images and surface energy measurements were used to determine the predominant failure mode at particle contacts under tensile loading condition.}, number={10}, journal={CANADIAN GEOTECHNICAL JOURNAL}, author={Nafisi, Ashkan and Mocelin, Douglas and Montoya, Brina M. and Underwood, Shane}, year={2020}, month={Oct}, pages={1611–1616} }
 @article{ding_wang_gulzar_kim_underwood_2020, title={Uncertainty Quantification of Simplified Viscoelastic Continuum Damage Fatigue Model using the Bayesian Inference-Based Markov Chain Monte Carlo Method}, volume={2674}, ISSN={["2169-4052"]}, DOI={10.1177/0361198120910149}, abstractNote={The simplified viscoelastic continuum damage model (S-VECD) has been widely accepted as a computationally efficient and a rigorous mechanistic model to predict the fatigue resistance of asphalt concrete. It operates in a deterministic framework, but in actual practice, there are multiple sources of uncertainty such as specimen preparation errors and measurement errors which need to be probabilistically characterized. In this study, a Bayesian inference-based Markov Chain Monte Carlo method is used to quantify the uncertainty in the S-VECD model. The dynamic modulus and cyclic fatigue test data from 32 specimens are used for parameter estimation and predictive envelope calculation of the dynamic modulus, damage characterization and failure criterion model. These parameter distributions are then propagated to quantify the uncertainty in fatigue prediction. The predictive envelope for each model is further used to analyze the decrease in variance with the increase in the number of replicates. Finally, the proposed methodology is implemented to compare three asphalt concrete mixtures from standard testing. The major findings of this study are: (1) the parameters in the dynamic modulus and damage characterization model have relatively strong correlation which indicates the necessity of Bayesian techniques; (2) the uncertainty of the damage characteristic curve for a single specimen propagated from parameter uncertainties of the dynamic modulus model is negligible compared to the difference in the replicates; (3) four replicates of the cyclic fatigue test are recommended considering the balance between the uncertainty of fatigue prediction and the testing efficiency; and (4) more replicates are needed to confidently detect the difference between different mixtures if their fatigue performance is close.}, number={4}, journal={TRANSPORTATION RESEARCH RECORD}, author={Ding, Jing and Wang, Yizhuang David and Gulzar, Saqib and Kim, Youngsoo Richard and Underwood, B. Shane}, year={2020}, month={Apr}, pages={247–260} }
 @article{underwood_2019, title={A method to select general circulation models for pavement performance evaluation}, volume={22}, ISSN={1029-8436 1477-268X}, url={http://dx.doi.org/10.1080/10298436.2019.1580365}, DOI={10.1080/10298436.2019.1580365}, abstractNote={Studies to understand the role of future climate on transportation infrastructure may use climate multiple models and interpret the results based on the statistical variation in simulated outcomes. Unfortunately, specific guidance on the models to choose that ensure results span the breadth of possible outcomes is limited, and the solution involves running simulations using as many models as possible. The objective of this study is to provide guidance on which models from the Coupled Intercomparison Project 5 (CMIP5) dataset to use for pavement studies in the United States and in so doing provide a framework for selecting models from other datasets and locations. Effective temperature functions are derived and used to select individual models from the CMIP5 dataset that represent the maximum, median, and minimum outcomes of the whole ensemble. The results are clustered based on region and represent relatively hot, cold, and median future assumptions. The model selection process is verified using detailed pavement analyses with all models at individual pavement sites in four states. The models chosen using the effective temperature approach are found to align with the extremes and the median, with further improvements to median estimates obtained by averaging all three (maximum, minimum, and median) models.}, number={2}, journal={International Journal of Pavement Engineering}, publisher={Informa UK Limited}, author={Underwood, B. Shane}, year={2019}, month={Feb}, pages={1–13} }
 @article{wang_ghanbari_underwood_kim_2019, title={Development of a Performance-Volumetric Relationship for Asphalt Mixtures}, volume={2673}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.1177/0361198119845364}, DOI={10.1177/0361198119845364}, abstractNote={This paper aims to establish the relationship between the volumetric performance of asphalt mixtures and their performance in relation to pavement fatigue cracking and rutting. A good performance-volumetric relationship (PVR) can dramatically improve the working efficiency of mixtures and can be used in future performance-engineered mixture design and performance-related specifications. For this study, three asphalt mixtures were first designed to incorporate systematic changes in volumetric conditions, then fatigue cracking and rutting performance tests were conducted at each condition. Statistical analyses of the results suggest that a first-order (linear) model and power model would be an appropriate form of the PVR function. The number of volumetric conditions required to calibrate the PVR function is also investigated. Finally, a rule of thumb for selecting the volumetric conditions for the model calibrations is provided. The verification results show that the proposed PVR function is able to capture the response of mixture performance to changes in volumetric conditions.}, number={6}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Wang, Yizhuang David and Ghanbari, Amir and Underwood, Benjamin Shane and Kim, Youngsoo Richard}, year={2019}, month={May}, pages={416–430} }
 @article{salim_gundla_underwood_kaloush_2019, title={Effect of MSCR Percent Recovery on Performance of Polymer Modified Asphalt Mixtures}, volume={2673}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.1177/0361198119841283}, DOI={10.1177/0361198119841283}, abstractNote={The AASHTO M332 specification includes a relationship between the non-recoverable creep compliance at 3.2 kPa ( J nr 3.2 ) and the percent of elastic recovery ( R 3.2 ) from the multiple stress creep and recovery (MSCR) test. Justification for the exact position of this curve based on binder performance is largely undocumented in the technical literature as is the singular effect of higher or lower R 3.2 values on mixture performance. In this study, nine binders were tested to evaluate the effect of R 3.2 on the performance of asphalt mixtures. Binders with similar J nr 3.2 and varying MSCR R 3.2 were divided into four groups based on their J nr 3.2 value. Comparisons were made based on results obtained from the dynamic modulus test, Hamburg wheel tracking test, and axial fatigue test. Based on these tests, it was shown that R 3.2 had a strong relationship to the dynamic modulus of asphalt mixtures especially at intermediate and high temperatures. Binders with lower R 3.2 had a higher dynamic modulus but showed no correlation to phase angle. Both modulus and phase angle of the mixture correlated to the binder shear modulus and phase angle. Binders with high R 3.2 had a greater fatigue resistance and the effect is quite noticeable. However, R 3.2 was shown to have little to no effect on the rutting resistance of the asphalt mixtures for the temperatures tested in this study. Finally, an alternative J nr 3.2 versus R 3.2 relationship based on the results of this study is also presented.}, number={5}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Salim, Ramadan and Gundla, Akshay and Underwood, B. Shane and Kaloush, Kamil E.}, year={2019}, month={Apr}, pages={308–319} }
 @book{underwood_braham_2019, title={Fatigue or Not Fatigue, That is the Question}, url={http://rgdoi.net/10.13140/RG.2.2.13898.41921/1}, DOI={10.13140/RG.2.2.13898.41921/1}, author={Underwood, Shane and Braham, Andrew}, year={2019}, month={May} }
 @article{salim_gundla_zalghout_underwood_kaloush_2019, title={Relationship between Asphalt Binder Parameters and Asphalt Mixture Rutting}, volume={2673}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.1177/0361198119842129}, DOI={10.1177/0361198119842129}, abstractNote={The selection and specification of asphalt binder is one of the factors that ultimately affect the long-term performance of asphalt pavements. Many agencies currently follow AASHTO M320 for their binder specifications, where the ratio of dynamic modulus to the sine of the phase angle, | G*|/sin δ, is the binder rutting parameter. However, an alternative now exists, AASHTO M332, which uses the non-recovered creep compliance, J nr , for this purpose. In this paper, the relative merits of these two parameters are compared using experimental results from 21 different asphalt mixtures from Arizona. The rutting parameters according to AASHTO M332 and M320 were determined for each of the binders in these mixtures and, for each mixture, two rutting performance tests were conducted: Hamburg wheel tracking test and repeated load permanent deformation test. The two binder rutting parameters demonstrated very high correlation to one another for non-polymer modified asphalts, but inconsistent correlation for polymer modified asphalts. Both Hamburg wheel tracking tests and repeated load permanent deformation tests showed positive correlations to both | G*|/sin δ and J nr . It was concluded that, while both parameters showed good correlation, the J nr of the binder relates better to mixture rutting than does | G*|/sin δ. Considering the results in this study, it is believed that J nr is a slightly better rutting parameter for binder specifications.}, number={6}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Salim, Ramadan and Gundla, Akshay and Zalghout, Ali and Underwood, B. Shane and Kaloush, Kamil E.}, year={2019}, month={Jun}, pages={431–446} }
 @article{lee_pape_castorena_underwood_kim_2019, title={Strain-Level Determination Procedure for Small-Specimen Cyclic Fatigue Testing in the Asphalt Mixture Performance Tester}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.1177/0361198119845357}, DOI={10.1177/0361198119845357}, abstractNote={With an increase in small-specimen cyclic fatigue testing using the Asphalt Mixture Performance Tester (AMPT), researchers have observed that the strain-selection guidelines in AASHTO TP 107-14 that are intended for large AMPT cyclic fatigue tests are inadequate for testing small specimens. The machine compliance factor is significantly different for testing small specimens compared with large specimens because of different required load levels, resulting in a significant offset in the relationship between the input strain and the number of cycles to failure. To this end, this paper presents the development and verification of a phenomenological model that relates strain levels to dynamic modulus and number of cycles to failure for small-specimen AMPT cyclic fatigue tests, as well as the development of a corresponding stepped strain-level determination procedure that takes into account cases when the initially selected strain-level results in an unexpected number of cycles to failure. The final procedure includes a table with input strain levels and step strain increments for a wide range of dynamic modulus values as well as a flow chart to guide the use of the step strain adjustment procedure.}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Lee, Kangjin “Caleb” and Pape, Sonja and Castorena, Cassie and Underwood, B. Shane and Kim, Y. Richard}, year={2019}, month={Jun}, pages={036119811984535} }
 @article{markolf_hoehne_fraser_chester_underwood_2019, title={Transportation resilience to climate change and extreme weather events – Beyond risk and robustness}, volume={74}, ISSN={0967-070X}, url={http://dx.doi.org/10.1016/j.tranpol.2018.11.003}, DOI={10.1016/j.tranpol.2018.11.003}, abstractNote={Abstract The long-term reliability and functioning of transportation systems will increasingly need to consider and plan for climate change and extreme weather events. Transportation systems have largely been designed and operated for historical climate conditions that are now often exceeded. Emerging knowledge of how to plan for climate change largely embraces risk-based thinking favoring more robust infrastructure designs. However, there remain questions about whether this approach is sufficient given the uncertainty and non-stationarity of the climate, and many other driving factors affecting transportation systems (e.g., funding, rapid technological change, population and utilization shifts, etc.). This paper examines existing research and knowledge related to the vulnerability of the transportation system to climate change and extreme weather events and finds that there are both direct and indirect “pathways of disruption.” Direct pathways of disruption consist of both abrupt impacts to physical infrastructure and impacts via non-physical factors such as human health, behavior, and decision making. Similarly, indirect pathways of disruption result from interconnections with other critical infrastructure and social systems. Currently, the direct pathways appear to receive much of the focus in vulnerability and risk assessments, and the predominant approach for addressing these pathways of disruption emphasizes strengthening and armoring infrastructure (robustness) guided by risk analysis. However, our analysis reveals that indirect pathways of disruption can have meaningful impacts, while also being less amenable to robustness-based approaches. As a result, we posit that concepts like flexibility and agility appear to be well suited to complement the status quo of robustness by addressing the indirect and non-physical pathways of disruption that often prove challenging - thereby improving the resilience of transportation systems.}, journal={Transport Policy}, publisher={Elsevier BV}, author={Markolf, Samuel A. and Hoehne, Christopher and Fraser, Andrew and Chester, Mikhail V. and Underwood, B. Shane}, year={2019}, month={Feb}, pages={174–186} }
 @article{zeiada_gudipudi_underwood_souliman_2018, title={Effect of Loading Waveform Pattern and Rest Period on Fatigue Life of Asphalt Concrete Using Viscoelastic Continuum Damage Model}, volume={2672}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.1177/0361198118773892}, DOI={10.1177/0361198118773892}, abstractNote={Fatigue cracking is one of the most critical types of distress in asphalt pavements and is due to actions of repetitive traffic loading over time. The fatigue life of asphalt concrete is often estimated from laboratory experiments where the performance depends directly on the test method, loading conditions, temperature, rest period, and aging in addition to the composition and properties of the mixture itself. The uniaxial fatigue test has become a popular method for developing constitutive models that describe the fatigue behavior of asphalt concrete mixture owing to the uniform states of stress across the specimen section. This study investigates the effect of the loading waveform (sinusoidal versus haversine) and rest period (continuous versus intermittent) on the laboratory fatigue life of asphalt concrete mixtures. The fatigue analysis was performed using the simplified viscoelastic continuum damage (S-VECD) approach where the damage characteristic (C-S) curves were established for all the cases, and then used to estimate the fatigue laws through simulated predictions. The proposed uniaxial fatigue test and analysis method were able to determine the fatigue life relationships of asphalt concrete mixture at different waveform and rest period conditions with a reduced testing time compared to other traditional testing and analysis methods. Overall, both rest period and waveform pattern were found to affect the laboratory fatigue life of asphalt concrete mixture. Model predictions show that pulse-rest loading yields an equivalent fatigue life to continuous loading at strain values that are approximately four times greater.}, number={28}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Zeiada, Waleed Abdelaziz and Gudipudi, Padmini P. and Underwood, B. Shane and Souliman, Mena I.}, year={2018}, month={May}, pages={451–461} }
 @article{noorvand_salim_medina_stempihar_underwood_2018, title={Effect of Synthetic Fiber State on Mechanical Performance of Fiber Reinforced Asphalt Concrete}, volume={2672}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.1177/0361198118787975}, DOI={10.1177/0361198118787975}, abstractNote={It has been recognized that there exists a potential benefit from using synthetic fibers to reinforce asphalt mixtures. In these mixtures, the state of the fibers may play an essential role in their reinforcement function. This study aims to quantify the state of synthetic fiber distribution for two different aramid fiber–based asphalt mixtures and then show the impacts of fiber dispersion on modulus, rutting, and fatigue performance of each asphalt mixture in comparison with one another and with respect to an equivalent non-reinforced asphalt mixture. Both a quantitative and qualitative assessment of aramid fibers distribution as well as state of fiber are investigated using a fiber extraction procedure and microscopy imaging, respectively. The results suggested that a higher level of micro-fibrillation as well as high distribution of aramid fibers improved the rutting resistance of asphalt mixtures, while the distribution level of aramid fibers and fibers state did not affect the modulus and fatigue. These results are specific to the mixture studied but provide the first objective and detailed study describing fiber state, fiber dispersion, and performance.}, number={28}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Noorvand, Hossein and Salim, Ramadan and Medina, Jose and Stempihar, Jeffrey and Underwood, B. Shane}, year={2018}, month={Jul}, pages={42–51} }
 @article{mamlouk_vinayakamurthy_underwood_kaloush_2018, title={Effects of the International Roughness Index and Rut Depth on Crash Rates}, volume={2672}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.1177/0361198118781137}, DOI={10.1177/0361198118781137}, abstractNote={Pavement distresses directly affect ride quality, and indirectly contribute to driver distraction, vehicle operation, and accidents. In this study, analysis was performed on highways in the states of Arizona, North Carolina, and Maryland to investigate the relationship between accident rate and pavement ride quality (roughness) and rut depth. Two main types of data were collected: crash data from the accident records and International Roughness Index (IRI) and rut depth data from the pavement management system database in each state. Crash rates were calculated using the U.S. Department of Transportation method, which is the number of accidents per 100 million vehicle-miles of travel. Sigmoidal function regression analysis was performed to study the relationship between crash rate and both IRI and rut depth. In all cases, the crash rate did not show substantial increases until an IRI value of 210 inches/mile or a critical rut depth of 0.4 inches. When the IRI or rut depth increased above these values the crash rate increased. This is a key conclusion that provides empirically derived thresholds for IRI and rut depth to reducing the accident rate.}, number={40}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Mamlouk, Michael and Vinayakamurthy, Mounica and Underwood, B. Shane and Kaloush, Kamil E.}, year={2018}, month={Jun}, pages={418–429} }
 @article{medina_underwood_mamlouk_2018, title={Estimation of Asphalt Concrete Modulus Using the Ultrasonic Pulse Velocity Test}, volume={144}, ISSN={2573-5438 2573-5438}, url={http://dx.doi.org/10.1061/JPEODX.0000036}, DOI={10.1061/JPEODX.0000036}, abstractNote={The mechanical dynamic modulus test was used to determine the dynamic moduli of hot-mix asphalt (HMA) with and without different types of fibers, and master curves were developed. The ultrasonic pulse velocity (UPV) test was then conducted on the same specimens to estimate the dynamic moduli across multiple temperatures, and master curves were developed. The Poisson’s ratios required for UPV modulus prediction were estimated for different reduced frequencies, and a sensitivity analysis on their effect on the modulus values was performed. The master curves developed using the UPV moduli were superimposed on the mechanical test master curves and matched closely. Witczak’s predictive equation and the Hirsch model were also used to predict the dynamic modulus master curves. The UPV moduli closely matched the mechanical dynamic moduli better than those predicted from the Witczak or Hirsch models at intermediate and high reduced frequencies. An attempt was made to combine the UPV modulus prediction with the Witczak and Hirsch models to improve moduli estimation at low reduced frequencies. Typical mechanical test methods are time consuming and require an expensive load frame and instrumentation setup. The UPV test requires less time, and the equipment needed is relatively inexpensive. Using the UPV test in combination with either the Witczak or Hirsch model is recommended as a lower-cost alternative to develop the master curves of the HMA dynamic moduli.}, number={2}, journal={Journal of Transportation Engineering, Part B: Pavements}, publisher={American Society of Civil Engineers (ASCE)}, author={Medina, Jose Roberto and Underwood, B. Shane and Mamlouk, Michael}, year={2018}, month={Jun}, pages={04018008} }
 @article{mensching_daniel_underwood_2018, title={Exploring indicators for fatigue cracking in hot mix asphalt pavements using simplified-viscoelastic continuum damage theory}, volume={19}, ISSN={1468-0629 2164-7402}, url={http://dx.doi.org/10.1080/14680629.2018.1418713}, DOI={10.1080/14680629.2018.1418713}, abstractNote={Fatigue cracking in asphalt pavements results in decreased ride quality, decreased fuel economy, and provides an avenue for intrusion of water. Since the current asphalt mixture design relies prima...}, number={3}, journal={Road Materials and Pavement Design}, publisher={Informa UK Limited}, author={Mensching, David J. and Daniel, Jo Sias and Underwood, B. Shane}, year={2018}, month={Jan}, pages={536–545} }
 @article{miglietta_underwood_tsantilis_baglieri_kaloush_santagata_2018, title={Fatigue Properties of Nano-Reinforced Bituminous Mixtures: A Viscoelastic Continuum Damage Approach}, volume={11}, ISSN={1996-6814}, DOI={10.1016/j.ijprt.2018.04.004}, abstractNote={Abstract The experimental investigation described in this paper focused on the effects of nanoclays on the fatigue behaviour of bituminous mixtures. Damage characteristics of a bituminous mixture produced by making use of a nano-reinforced binder were compared to those of a reference mixture obtained by employing the same neat bitumen used as a base in the preparation of the nanoclay–bitumen blend. Dynamic modulus tests and direct tension cyclic fatigue tests were carried out to determine the linear viscoelastic properties and the damage evolution characteristics of materials. Corresponding results were modelled by means of a viscoelastic continuum damage approach and by making use of a more empirical evaluation based on the classical Wohler representation. It was found that the use of nanoclays produced a reinforcement of bituminous mixtures, the benefits of which were observed both in the progression of damage and in the occurrence of ultimate failure conditions.}, number={7}, journal={International Journal of Pavement Research and Technology}, author={Miglietta, F. and Underwood, B.S. and Tsantilis, L. and Baglieri, O. and Kaloush, K.E. and Santagata, E.}, year={2018}, month={May}, pages={766–773} }
 @article{wang_xie_underwood_2018, title={Fatigue and Healing Performance Assessment of Asphalt Binder from Rheological and Chemical Characteristics}, volume={51}, ISSN={["1871-6873"]}, DOI={10.1617/s11527-018-1300-2}, number={6}, journal={Materials and Structures}, author={Wang, C. and Xie, W. and Underwood, B.S.}, year={2018}, month={Dec}, pages={171–182} }
 @article{stempihar_gundla_underwood_2018, title={Interpreting Stress Sensitivity in the Multiple Stress Creep and Recovery Test}, volume={30}, ISSN={0899-1561 1943-5533}, url={http://dx.doi.org/10.1061/(ASCE)MT.1943-5533.0002153}, DOI={10.1061/(ASCE)MT.1943-5533.0002153}, abstractNote={The original intent of the Jnrdiff limit applied to multiple stress creep and recovery test results was to ensure that an asphalt binder does not fail if, under real-world application, it experienced higher stresses or temperatures than what was considered in the laboratory. In recent years, challenges meeting the Jnrdiff specification for asphalt binders with low Jnr3.2 (mainly less than 0.5 kPa−1) have been documented, with reported Jnrdiff values greater than 400% in some cases. This paper presents an argument that Jnrdiff is an inaccurate representation of stress sensitivity, unfairly penalizes asphalt binders with low Jnr3.2, and lacks correlation with expected changes in field rutting performance. A new parameter that more appropriately describes stress sensitivity, Jnrslope, is presented. Jnrslope shows a better performance-based relationship to expected changes in rutting and more accurately ranks the study asphalt binders than Jnrdiff. Jnrslope also demonstrates the ability to capture changes in Jnr3.2 with respect to increases in test temperature. Finally, a conceptual, performance-based Jnrslope specification limit is presented. Overall, Jnrslope provides an alternate parameter to accurately interpret and describe stress and temperature sensitivity and demonstrates potential as a performance-based parameter.}, number={2}, journal={Journal of Materials in Civil Engineering}, publisher={American Society of Civil Engineers (ASCE)}, author={Stempihar, Jeffrey and Gundla, Akshay and Underwood, B. Shane}, year={2018}, month={Feb}, pages={04017283} }
 @inproceedings{stempihar_gundla_underwood_2017, title={Alternate interpretation of stress sensitivity in AASHTO T350}, booktitle={96th Annual Meeting of the Transportation Research Board}, author={Stempihar, J. and Gundla, A. and Underwood, B.S.}, year={2017} }
 @article{noorvand_karnati_underwood_2017, title={Autonomous Vehicles}, volume={2640}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.3141/2640-03}, DOI={10.3141/2640-03}, abstractNote={With ongoing technological improvements and research in the field of autonomous vehicles, it is becoming evident that the technology has the potential to substantially affect the transportation sector. Although the potential benefits with respect to productivity increases, cost decreases, and safety are evident, the potential for these vehicles to negatively or positively affect the transportation infrastructure is unclear. In this study, the influence of truck loadings positioning on the long-term performance of transportation infrastructure was estimated by carrying out performance simulations of pavement structures. Scenarios considering both full and partial use by autonomous trucks were considered. In all cases, performance was estimated with respect to rutting, fatigue cracking, and overall pavement smoothness, and the results were compiled in terms of reduced pavement thickness. It was found that if controlled appropriately, autonomous trucks could be highly beneficial for the pavement infrastructure design, and they would be most effective when they represented more than 50% of the total truck traffic. It was also found that in the absence of appropriate control, specifically by repeatedly positioning trucks in the same location, the amount of damage could be highly detrimental, and noticeable influences may occur at autonomous truck volumes as low as 10%.}, number={1}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Noorvand, Hossein and Karnati, Guru and Underwood, B. Shane}, year={2017}, month={Jan}, pages={21–28} }
 @article{noorvand_sai_underwood_2017, title={Autonomous vehicles: Assessment of the implications of truck positioning on flexible pavement performance and design}, journal={Transportation Research Record}, author={Noorvand, H. and Sai, G. and Underwood, B.S.}, year={2017}, pages={21–28} }
 @article{gudipudi_underwood_2017, title={Development of modulus and fatigue test protocol for fine aggregate matrix for axial direction of loading}, volume={45}, number={2}, journal={Journal of Testing and Evaluation}, author={Gudipudi, P. and Underwood, B.S.}, year={2017}, pages={497–508} }
 @article{gundla_gudipudi_underwood_2017, title={Evaluation of the sensitivity of asphalt concrete modulus to binder oxidation with a multiple length scale study}, volume={152}, ISSN={0950-0618}, url={http://dx.doi.org/10.1016/j.conbuildmat.2017.07.067}, DOI={10.1016/j.conbuildmat.2017.07.067}, abstractNote={Abstract It is well known that the properties of asphalt concrete mixture are affected by the oxidation of asphalt cement. However, the precise relationship between these two length scales remains largely uncharacterized. In the present study, a multiple length scale evaluation approach is applied to study and quantify the sensitivity of the mechanical properties of asphalt concrete mixture to asphalt cement oxidation. The study involves temperature and frequency sweep experiments on unaged and aged asphalt cement (to establish baseline properties), asphalt mastic (to consider physico-chemical aspects), and Fine Aggregate Matrix (FAM – to consider air voids and aggregate interaction effects). The multiscale approach separates effects of aggregate-binder physico-chemical interactions from those caused by air voids and physical aggregate interactions. Also, all asphalt cements were pre-aged to specific aging levels before preparing respective aged mastics or FAM samples. The methodology adopted for assessment of sensitivity was based on the theory of crossover modulus and second order rate kinetics of asphalt binder oxidation. The results from the analysis indicate that the mechanical properties of mastics are more sensitive to binder oxidation than FAM. Also, mechanical properties of mastics and FAM materials prepared with softer binders are more sensitive to oxidation than those with higher modulus asphalt cements. Finally, it is found that if a laboratory aging procedure is found to match the rheological properties of in-service level of asphalt oxidation at a given level of accuracy, then the expected accuracy in matching the resulting modulus of an asphalt mixture tested after being subjected to that laboratory process will be 1.5–3.6 times higher.}, journal={Construction and Building Materials}, publisher={Elsevier BV}, author={Gundla, Akshay and Gudipudi, Padmini and Underwood, B. Shane}, year={2017}, month={Oct}, pages={954–963} }
 @article{kim_eisenberg_bondank_chester_mascaro_underwood_2017, title={Fail-safe and safe-to-fail adaptation: decision-making for urban flooding under climate change}, volume={145}, ISSN={0165-0009 1573-1480}, url={http://dx.doi.org/10.1007/s10584-017-2090-1}, DOI={10.1007/s10584-017-2090-1}, abstractNote={As climate change affects precipitation patterns, urban infrastructure may become more vulnerable to flooding. Flooding mitigation strategies must be developed such that the failure of infrastructure does not compromise people, activities, or other infrastructure. “Safe-to-fail” is an emerging paradigm that broadly describes adaptation scenarios that allow infrastructure to fail but control or minimize the consequences of the failure. Traditionally, infrastructure is designed as “fail-safe” where they provide robust protection when the risks are accurately predicted within a designed safety factor. However, the risks and uncertainties faced by urban infrastructure are becoming so great due to climate change that the “fail-safe” paradigm should be questioned. We propose a framework to assess potential flooding solutions based on multiple infrastructure resilience characteristics using a multi-criteria decision analysis (MCDA) analytic hierarchy process algorithm to prioritize “safe-to-fail” and “fail-safe” strategies depending on stakeholder preferences. Using urban flooding in Phoenix, Arizona, as a case study, we first estimate flooding intensity and evaluate roadway vulnerability using the Storm Water Management Model for a series of downpours that occurred on September 8, 2014. Results show the roadway types and locations that are vulnerable. Next, we identify a suite of adaptation strategies and characteristics of these strategies and attempt to more explicitly categorize flooding solutions as “safe-to-fail” and “fail-safe” with these characteristics. Lastly, we use MCDA to show how adaptation strategy rankings change when stakeholders have different preferences for particular adaptation characteristics.}, number={3-4}, journal={Climatic Change}, publisher={Springer Science and Business Media LLC}, author={Kim, Yeowon and Eisenberg, Daniel A. and Bondank, Emily N. and Chester, Mikhail V. and Mascaro, Giuseppe and Underwood, B. Shane}, year={2017}, month={Oct}, pages={397–412} }
 @article{abkarian_el asmar_underwood_2017, title={Impact of Alternative Project Delivery Systems on the International Roughness Index: Case Studies of Transportation Projects in the Western United States}, volume={2630}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.3141/2630-10}, DOI={10.3141/2630-10}, abstractNote={The impact of alternative project delivery methods (APDM) was compared with that of the traditional method of design–bid–build (DBB) on the long-term performance of transportation projects. The metric used to quantify long-term performance differences between projects is the international roughness index (IRI), which is an indicator of ride quality. Data were collected on four alternative delivery projects on the National Highway System in Arizona and Colorado, along with data on their comparable DBB projects. Two of the projects provided northbound and southbound data and their respective comparisons, so six pairs of projects were investigated. In the study of the IRI time series, five of the six APDM projects were found to perform better than their traditional counterparts. This exploratory study contributes to the body of knowledge by starting to quantify the impact of APDM on the actual long-term performance of transportation projects.}, number={1}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Abkarian, Hoseb and El Asmar, Mounir and Underwood, Shane}, year={2017}, month={Jan}, pages={76–84} }
 @inproceedings{abkarian_asmar_underwood_2017, title={Impact of alternative project deliver systems on the International Roughness Index (IRI) ? Case studies of transportation projects in the Western U.S.}, booktitle={96th Annual Meeting of the Transportation Research Board}, author={Abkarian, H. and Asmar, M. and Underwood, B.S.}, year={2017} }
 @article{abkarian_asmar_underwood_2017, title={Impact of alternative project deliver systems on the International Roughness Index (IRI) ? case studies of transportation projects in the Western U.S.}, volume={2630}, journal={Transportation Research Record}, author={Abkarian, H. and Asmar, M. and Underwood, B.S.}, year={2017}, pages={76–84} }
 @article{gudipudi_underwood_zalghout_2017, title={Impact of climate change on pavement structural performance in the United States}, volume={57}, ISSN={1361-9209}, url={http://dx.doi.org/10.1016/j.trd.2017.09.022}, DOI={10.1016/j.trd.2017.09.022}, abstractNote={This study uses climate projections from multiple models and for different climate regions to investigate how climate change may impact the transportation infrastructure in the United States. Climate data from both an ensemble of 19 different climate models at both RCP8.5 and RCP4.5 as well as three individual prediction models at the same Representative Concentration Pathways (RCP) levels is used. These models are integrated into the AASHTOWare Pavement ME software to predict the pavement performance. Comparisons are made between the predicted performance with respect to typical pavement distresses using both historical climate data as well as climate projection data. Though there is substantial variation for different prediction models in terms of the magnitude of the impact, the consistency in results suggest that projected climate changes are highly likely to result in greater distresses and/or earlier failure of the pavement. This finding is consistent across all the climate zones studied, but varies in magnitude of 2–9% for fatigue cracking and 9–40% for AC rutting at the end of 20 years depending on the climate region of the pavement section and prediction model used. This study also compares the impacts incorporating temperature only projections with temperature and precipitation projections. In this respect, the sections considered in this study do not show any substantial difference in the pavement performance when the precipitation data from the climate predictions are also considered in the climate inputs into AASHTOWare Pavement ME software.}, journal={Transportation Research Part D: Transport and Environment}, publisher={Elsevier BV}, author={Gudipudi, Padmini P. and Underwood, B. Shane and Zalghout, Ali}, year={2017}, month={Dec}, pages={172–184} }
 @inproceedings{gudipudi_underwood_zalghout_2017, title={Impact of climate change on the pavement performance and its sensitivity to various climate prediction models}, booktitle={96th Annual Meeting of the Transportation Research Board}, author={Gudipudi, P. and Underwood, B.S. and Zalghout, A.}, year={2017} }
 @inproceedings{noorvand_sai_underwood_2017, title={Implications of autonomous truck use on flexible pavement performance and design}, booktitle={96th Annual Meeting of the Transportation Research Board}, author={Noorvand, H. and Sai, G. and Underwood, B.S.}, year={2017} }
 @inproceedings{gudipudi_underwood_2017, title={Improvement in reliability of fatigue life prediction of asphalt concrete using fine aggregate matrix (FAM) experimental data and its sensitivity to input parameters}, booktitle={96th Annual Meeting of the Transportation Research Board}, author={Gudipudi, P. and Underwood, B.S.}, year={2017} }
 @article{underwood_guido_gudipudi_feinberg_2017, title={Increased costs to US pavement infrastructure from future temperature rise}, volume={7}, ISSN={1758-678X 1758-6798}, url={http://dx.doi.org/10.1038/nclimate3390}, DOI={10.1038/nclimate3390}, abstractNote={The selection of materials for road construction in the United States is based on assumptions of a stationary climate. With increasing temperatures, upholding these practices could add up to US$26.3 billion in US-wide maintenance costs by 2040 under RCP8.5. Roadway design aims to maximize functionality, safety, and longevity1,2. The materials used for construction, however, are often selected on the assumption of a stationary climate1,3. Anthropogenic climate change may therefore result in rapid infrastructure failure and, consequently, increased maintenance costs, particularly for paved roads where temperature is a key determinant for material selection. Here, we examine the economic costs of projected temperature changes on asphalt roads across the contiguous United States using an ensemble of 19 global climate models forced with RCP 4.5 and 8.5 scenarios. Over the past 20 years, stationary assumptions have resulted in incorrect material selection for 35% of 799 observed locations. With warming temperatures, maintaining the standard practice for material selection is estimated to add approximately US$13.6, US$19.0 and US$21.8 billion to pavement costs by 2010, 2040 and 2070 under RCP4.5, respectively, increasing to US$14.5, US$26.3 and US$35.8 for RCP8.5. These costs will disproportionately affect local municipalities that have fewer resources to mitigate impacts. Failing to update engineering standards of practice in light of climate change therefore significantly threatens pavement infrastructure in the United States.}, number={10}, journal={Nature Climate Change}, publisher={Springer Science and Business Media LLC}, author={Underwood, B. Shane and Guido, Zack and Gudipudi, Padmini and Feinberg, Yarden}, year={2017}, month={Sep}, pages={704–707} }
 @article{zeiada_hamad_omar_underwood_khalil_karzad_2017, title={Investigation and modelling of asphalt pavement performance in cold regions}, volume={20}, ISSN={1029-8436 1477-268X}, url={http://dx.doi.org/10.1080/10298436.2017.1373391}, DOI={10.1080/10298436.2017.1373391}, abstractNote={The performance of asphalt pavement is highly affected by climate factors, such as temperature and precipitation. Different temperature and moisture conditions change the paving material properties, which consequently influence pavement performance. Considerable research has been conducted to study the effect of climate factors on pavement performance; however, there are no focused studies that have investigated the performance of asphalt pavements in cold regions. In this research, the effect of different design factors on asphalt pavement performance in cold regions is investigated utilising data extracted from the Long-Term Pavement Performance database. Only control sections with no historical maintenance or rehabilitation records were considered. The International Roughness Index (IRI) was adopted as the pavement performance measure. The IRI value is expected to increase gradually over time due to pavement deterioration. Initial screening of the data showed that most of the pavement sections experienced remarkable IRI increase followed by an unexpected decrease. An in-depth investigation revealed that frost heave was the main reason of this unexpected IRI trend as it was correlated in most of the cases to sudden monthly freezing index increases, especially for sections with no subsurface drainage and less layers thicknesses. An Artificial Neural Network with a Forward Sequential Feature Selection algorithm and regression analysis were employed to model pavement performance in cold regions and determine the most significant design factors prevailing in cold climate conditions. Moreover, a sensitivity analysis was performed to investigate the interrelation between the considered features and the IRI. As a result, several climate-related factors were found to have a significant impact on the performance of asphalt pavements in cold regions such as average temperature, freezing index, freeze/thaw, wind velocity and relative humidity.}, number={8}, journal={International Journal of Pavement Engineering}, publisher={Informa UK Limited}, author={Zeiada, Waleed and Hamad, Khaled and Omar, Maher and Underwood, B. Shane and Khalil, Mohamad Ali and Karzad, Abdul Saboor}, year={2017}, month={Sep}, pages={986–997} }
 @inproceedings{markolf_hoehne_fraser_underwood_chester_2017, title={Maintaining reliability of transportation systems and interdependent infrastructure under climate change}, booktitle={International Society of Industrial Ecology and International Symposium on Sustainable Systems and Technology Conference}, author={Markolf, S. and Hoehne, C. and Fraser, A. and Underwood, B.S. and Chester, M.}, year={2017} }
 @article{medina_underwood_2017, title={Micromechanical shear modulus modeling of activated crumb rubber modified asphalt cements}, volume={150}, ISSN={0950-0618}, url={http://dx.doi.org/10.1016/j.conbuildmat.2017.05.208}, DOI={10.1016/j.conbuildmat.2017.05.208}, abstractNote={Abstract The rheological properties of three asphalt cements containing reacted and activated rubber (RAR) are evaluated to quantify the relative effects of swelling, splitting, and absorption. Rheological testing and electron microscopy are used to measure the dynamic shear modulus, |G∗|, and rubber particle changes respectively. It is found that |G∗| increased for all RAR and that particles swell 15.8–49.3% with those in softer asphalt showing the greatest swelling. Micromechanical models are used to predict |G∗| of the materials. The Hashin and Christensen models are found to accurately predict the measured moduli after accounting for the swelling, splitting, and absorption.}, journal={Construction and Building Materials}, publisher={Elsevier BV}, author={Medina, Jose R. and Underwood, B. Shane}, year={2017}, month={Sep}, pages={56–65} }
 @article{medina_underwood_kaloush_2017, title={Micromechanical shear modulus modeling of activated crumb rubber modified asphalt cements}, journal={Construction and Building Materials}, author={Medina, J. and Underwood, B.S. and Kaloush, K.E.}, year={2017}, pages={56–65} }
 @article{gudipudi_underwood_2017, title={Use of Fine Aggregate Matrix Experimental Data in Improving Reliability of Fatigue Life Prediction of Asphalt Concrete: Sensitivity of This Approach to Variation in Input Parameters}, volume={2631}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.3141/2631-07}, DOI={10.3141/2631-07}, abstractNote={Asphalt concrete (AC) material performance has been assessed by numerous mechanistic models over the years. Often these models are purported to enable more accurate prediction of the pavement service life than existing empirical models. Most of these models use fundamental material properties, which are obtained by performing experiments on the materials, as input variables. However, by introducing more variables, these models create the potential for greater uncertainty because the variables have inherent variability. Variations observed in these input parameters affect the reliability of any resulting performance predictions. In an effort to improve the reliability of fatigue life predictions, experimental data from the fine aggregate matrix (FAM) phase was used in this study for predicting fatigue life. From the comparative assessment, it was observed that the reliability of fatigue life predictions was improved by more than 50% when data from the FAM phase rather than AC data were used. An upscaling procedure was used in predicting the AC material fundamental properties and then in performing a reliability analysis with the predicted data. More reliable fatigue prediction results were also observed when the AC predicted data were used; however, this improvement was not as good as that in the FAM phase. A parametric sensitivity analysis was performed to determine whether variation in any one parameter resulted in a greater impact on the resultant reliability than did variation of other parameters. From the analysis, it was observed that the variation of the modulus parameter affected the reliability predictions more than did the variation of the other input parameters considered in this study, regardless of the model failure criteria used.}, number={1}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Gudipudi, Padmini P. and Underwood, B. Shane}, year={2017}, month={Jan}, pages={65–73} }
 @inproceedings{medeiros_underwood_castorena_rupnow_rawls_2016, title={3D measurement of pavement macrotexture using digital stereoscopic vision}, booktitle={95th Annual Meeting of the Transportation Research Board}, author={Medeiros, M. and Underwood, B.S. and Castorena, C. and Rupnow, T. and Rawls, M.}, year={2016} }
 @article{underwood_2016, title={A continuum damage model for asphalt cement and asphalt mastic fatigue}, volume={82}, ISSN={0142-1123}, url={http://dx.doi.org/10.1016/j.ijfatigue.2015.08.020}, DOI={10.1016/j.ijfatigue.2015.08.020}, abstractNote={Abstract An analytical model is developed for the mechanical degradation of asphalt cement and mastic under repeated loading. The model is derived by applying the strain decomposition principle to consider linear viscoelastic, nonlinear viscoelastic, and damage mechanisms. The experimental processes to isolate the behaviors and the analytical functions used to model each are described. It is found that the Schapery type damage approach is capable of modeling the fatigue process of these materials once appropriate consideration is taken for their nonlinear viscoelastic responses. Fatigue in asphalt mastics is also found to occur due to physical damage occurring in the asphalt cement.}, journal={International Journal of Fatigue}, publisher={Elsevier BV}, author={Underwood, B. Shane}, year={2016}, month={Jan}, pages={387–401} }
 @inproceedings{underwood_2016, title={A nonlinear viscoelastic damage model for asphalt binder and mastics}, booktitle={1st Transportation Research Congress}, author={Underwood, B.S.}, year={2016} }
 @article{yang_braham_underwood_hanz_reinke_2016, title={Correlating field performance to laboratory dynamic modulus from indirect tension and torsion bar}, volume={18}, ISSN={1468-0629 2164-7402}, url={http://dx.doi.org/10.1080/14680629.2016.1267438}, DOI={10.1080/14680629.2016.1267438}, abstractNote={Dynamic modulus has several useful functions in flexible pavements, including stress/strain characterisation, rutting and cracking characterisation, an input into several analytical and numerical models, and a primary input into Pavement ME Design. While the traditional dynamic modulus test is run in the uniaxial configuration, this is not possible for field cores. Therefore, the indirect tension dynamic modulus (IDT |E*|) and torsion bar shear modulus (torsion bar |G*|) have been developed. However, there has been limited research looking at analysing the data from field cores for these two geometries, comparing modulus data from the two geometries, examining in-service ageing of dynamic modulus, and quantifying pavement conditions using dynamic modulus. This research examines 10 field sections in Arkansas, comprising of 4 “good” performing sections, 2 “medium” performing sections, and 4 “poor” performing sections in an attempt to address these four questions. First, this research found that using AASHTO T342 and AASHTO R62 can lead to irrational coefficients but provide rational results. Second, while the IDT |E*| and torsion bar |G*| values were similar at high modulus values, the IDT |E*| values began to increase as the modulus decreased compared to the torsion bar |G*| values, increasing to over a decade of difference. Third, a noticeable difference was observed between the modulus values of the bottom surface layer and top surface layer, with the bottom surface layer showing higher modulus values in all cases. While the upper surface layer showed higher oxidation, other weathering effects such as moisture and traffic appear to have overwhelmed the oxidation effect and pavement deterioration has reduced the integrity of the mix. Finally, both the IDT |E*| and torsion bar |G*| were not able to quantify a noticeable difference between poor and medium performing sections, and medium and good performing sections, but were able to quantify a difference between the poor and good behaving sections. Overall, the IDT |E*| and torsion bar |G*| tests were able to produce consistent master curves, correlate to each other, identify differences between surface course lifts, and quantify differences in field performance.}, number={sup1}, journal={Road Materials and Pavement Design}, publisher={Informa UK Limited}, author={Yang, Shu and Braham, Andrew and Underwood, Shane and Hanz, Andrew and Reinke, Gerald}, year={2016}, month={Dec}, pages={104–127} }
 @inproceedings{mensching_daniel_underwood_2016, title={Developing an indicator for fatigue cracking in hot mix asphalt pavements using viscoelastic continuum damage principles}, booktitle={8th International RILEM Conference on Mechanisms of Cracking and Debonding in Pavements}, author={Mensching, D. and Daniel, J.S. and Underwood, B.S.}, year={2016} }
 @article{gudipudi_underwood_2016, title={Development of Modulus and Fatigue Test Protocol for Fine Aggregate Matrix for Axial Direction of Loading}, volume={45}, ISSN={0090-3973}, url={http://dx.doi.org/10.1520/JTE20150295}, DOI={10.1520/JTE20150295}, abstractNote={The testing of fine aggregate matrix (FAM) is rapidly gaining attention in the pavement research community because of its notable similarities with asphalt concrete (AC) and the increased testing efficiency that it affords. In most of the existing studies, FAM tests are used for characterization of relative material performance in the presence of phenomenon like moisture damage and healing. However, to better understand the fundamental properties of FAM and to establish the mechanistic connection between its properties and those of AC, proper fabrication and testing protocols need to be established. The focus of this research is to develop such standard testing protocols for both dynamic modulus and uniaxial fatigue testing. In the current effort, two FAM materials are prepared with the same gradation but two different asphalt cements (PG 64-22 and PG 76-16). Pilot studies to support the development of sample fabrication protocols are explained. Both FAM materials are tested for modulus and uniaxial fatigue, and during testing both on-specimen and machine actuator displacement are recorded. Material parameters were separately calculated using these two deformation measurements and compared to uncover the errors resulting from machine-based measurements of FAM. The percentage error in measuring dynamic modulus of FAM specimens using actuator strain ranged from 5 % to 79 %. After correcting actuator strain with a constant machine compliance factor, the percentage error changed to 10 %–32 %, which is still high. In addition, variation in time dependency and fatigue damage characterization was observed using the corrected actuator data to on-specimen data. To overcome all of the above issues and measure reliable test data for FAM, it is concluded that protocols must include measurement of on-specimen deformation.}, number={2}, journal={Journal of Testing and Evaluation}, publisher={ASTM International}, author={Gudipudi, P. P. and Underwood, B. S.}, year={2016}, month={Mar}, pages={20150295} }
 @article{zeiada_kaloush_underwood_mamlouk_2016, title={Development of a Test Protocol to Measure Uniaxial Fatigue Damage and Healing}, volume={2576}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.3141/2576-02}, DOI={10.3141/2576-02}, abstractNote={Various laboratory testing methods have been developed to characterize the fatigue response of asphalt concrete mixtures. These test methods attempt to simulate in-service conditions or formulate constitutive models. Experiments such as the four-point beam fatigue test have attempted to simulate in-service conditions. The prediction accuracy of such experiments depends on their effectiveness in simulating actual field conditions such as loading, support, stress state, and environment. Constitutive modeling experiments have aimed at measuring fundamental stress–strain relationships so that rigorous constitutive models can be formulated. The results from these experiments are used as input for field performance prediction algorithms. The uniaxial fatigue test is a promising method in this category because of the constant stress state across the specimen section. A few documents have focused on standard test methods for the uniaxial fatigue test; however, there are no AASHTO or ASTM protocols available that include the healing of asphalt concrete mixtures. The main objective of this study was to report on the development of a uniaxial fatigue test protocol that measures fatigue damage and healing of asphalt concrete mixtures. The documented work includes surrogate studies to identify appropriate sample fabrication procedures, gluing materials and procedures, alignment, machine compliance, type of strain wave shape, and strain-control mode of loading. It was found that the use of a gluing jig and 180-mm compaction height was essential to achieve successful mid-specimen failures. In addition, the sinusoidal strain wave shape and on-specimen strain-controlled mode of loading are appropriate test conditions for fatigue damage and healing characterization of asphalt concrete mixtures.}, number={1}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Zeiada, Waleed Abdelaziz and Kaloush, Kamil E. and Underwood, B. Shane and Mamlouk, Michael}, year={2016}, month={Jan}, pages={10–18} }
 @article{zeiada_kaloush_underwood_m._2016, title={Development of test protocol to measure axial fatigue damage and healing}, journal={Transportation Research Record}, author={Zeiada, W. and Kaloush, K. and Underwood, B.S. and M., Mamlouk}, year={2016}, pages={10–18} }
 @inproceedings{zeiada_kaloush_underwood_mamlouk_2016, title={Development of test protocol to measure axial fatigue damage and healing}, booktitle={95th Annual Meeting of the Transportation Research Board}, author={Zeiada, W. and Kaloush, K. and Underwood, B.S. and Mamlouk, M.}, year={2016} }
 @inproceedings{stempihar_underwood_nazar_kaloush_2016, title={Durable fiber reinforced asphalt concrete friction courses for airfield runways}, booktitle={Proceedings International Society on Asphalt Pavements Symposium}, author={Stempihar, J. and Underwood, B.S. and Nazar, S. and Kaloush, K.}, year={2016} }
 @article{mogawer_austerman_underwood_2016, title={Effect of Binder Modification on the Performance of an Ultra-Thin Overlay Pavement Preservation Strategy}, volume={2550}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.3141/2550-01}, DOI={10.3141/2550-01}, abstractNote={The objective of this study was to determine whether asphalt rubber (AR) binders will provide similar or better performance compared with a polymer modified asphalt (PMA) binder when used in a high-performance, ultra-thin lift overlay pavement preservation strategy. Current specifications for these types of overlays normally require the use of a PMA binder, because it has the ability to make these overlays more elastic under traffic loading and is less sensitive to temperature fluctuations. However, several state agencies are looking into the feasibility of incorporating sustainable and environmentally friendly technologies, such as AR binders and warm mix asphalt (WMA) technologies, into their asphalt mixtures, including those used for high-performance, ultra-thin lift overlays. This study examined the effect of binder modification type (AR or PMA) and the influence of the use of WMA in high-performance, ultra-thin lift overlays. In general, the mixtures that were tested provided comparable rutting, moisture damage, and low-temperature cracking performance in the high-performance, ultra-thin lift overlay. However, the use of the AR binders indicated reduced performance compared with the PMA binder in mixture fatigue cracking via the beam fatigue test, and mixture reflective cracking in the overlay tester. The results from the beam fatigue test were not always supported by the fatigue life predictions from the simplified viscoelastic continuum damage model. The only detriment to mixture performance for mixtures incorporating WMA was a reduction in fatigue cracking performance when used with AR binders.}, number={1}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Mogawer, Walaa S. and Austerman, Alexander J. and Underwood, Shane}, year={2016}, month={Jan}, pages={1–7} }
 @inproceedings{palanievelu_zapata_underwood_2016, title={Effect of as-compacted moisture content and density on pavement performance in different climatic regimes}, DOI={10.1061/9780784479742.109}, abstractNote={While asphalt-concrete layer properties are more sensitive towards temperature variations, the subgrade stiffness have proven to be quite sensitive to moisture content fluctuations. When embankments are needed during the pavement construction, the soil must be compacted at a particular moisture-density condition to reach homogeneous properties. Due to construction variability, the as-compacted conditions might vary from the required specifications. This is of particular interest when dealing with compacted fine grained subgrade materials due to the influence of soil permeability in the seasonal moisture content fluctuation. The main objective of this study is the evaluation of the structural capacity and pavement performance due to the variability associated with the as-compacted moisture and density conditions, for different climatic regions. Three types of materials ranging from silt to clay were used in the analysis. Weather information from three locations was collected to represent different climate regimes. The pavement performance was analyzed using the Mechanistic-Empirical Pavement Design Guide (MEPDG) procedure by using the response of the pavement to three major distresses: fatigue cracking, rutting and thermal cracking. Two different levels of input accuracy were compared: Level 2, which uses simple index material and compaction properties and Level 3, which uses just the simple index material properties to estimate the resilient modulus. Results indicated that the soil compacted to optimum moisture content predicted less amount of distress when compared to the wet or dry optimum conditions for the low plasticity soils; whereas the predicted distresses increase with the increase in the as-compacted moisture content for the high plasticity soils. When compared with ratio of optimum condition, international roughness index (IRI) had a maximum increase of 5% in Chicago and Atlanta region exhibited a fatigue cracking increase of 40% while Phoenix area showed a lot of rutting increase of 30%. The difference in the distress results obtained for Level 2 and Level 3 analyses were not significant for the soil compacted at optimum condition, but the dry and wet of optimum conditions resulted in significant larger differences that depended on the location or climate where the pavement is constructed.}, booktitle={Proceedings of the Joint Geotechnical and Structural Engineering Congress}, author={Palanievelu, P. and Zapata, C.E. and Underwood, B.S.}, year={2016} }
 @article{mogawer_austerman_underwood_2016, title={Effect of binder modification on the performance of an ultrathin overlay pavement preservation strategy}, journal={Transportation Research Record}, author={Mogawer, W. and Austerman, A.A. and Underwood, B.S.}, year={2016}, pages={1–7} }
 @inproceedings{mogawer_austerman_underwood_2016, title={Effect of binder modification on the performance of an ultrathin overlay pavement preservation strategy}, booktitle={95th Annual Meeting of the Transportation Research Board}, author={Mogawer, W. and Austerman, A.A. and Underwood, B.S.}, year={2016} }
 @inproceedings{gundla_gudipudi_underwood_2016, title={Evaluation of the sensitivity of asphalt concrete modulus to binder oxidation with a multiple length scale study}, booktitle={95th Annual Meeting of the Transportation Research Board}, author={Gundla, A. and Gudipudi, P. and Underwood, B.S.}, year={2016} }
 @article{karki_bhasin_underwood_2016, title={Fatigue Performance Prediction of Asphalt Composites Subjected to Cyclic Loading with Intermittent Rest Periods}, volume={2576}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.3141/2576-08}, DOI={10.3141/2576-08}, abstractNote={This study investigated the use of a unified method to predict the fatigue cracking and self-healing characteristics of asphalt composites subjected to cyclic loading and intermittent rest periods. Displacement-controlled uniaxial tests were performed on cylindrical specimens of two asphalt composites with intermittent rest periods. Fatigue damage and healing behavior were modeled with their stress–strain history with viscoelastic continuum damage mechanics. An integrated method to predict the number of cycles required to degrade the materials by a certain amount with and without rest periods was devised and verified with actual cyclic test results in the tension–compression mode of loading.}, number={1}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Karki, Pravat and Bhasin, Amit and Underwood, B. Shane}, year={2016}, month={Jan}, pages={72–82} }
 @inproceedings{karki_bhasin_underwood_2016, title={Fatigue performance prediction of asphalt composites subjected to cyclic loading with intermittent rest periods}, booktitle={95th Annual Meeting of the Transportation Research Board}, author={Karki, P. and Bhasin, A. and Underwood, B.S.}, year={2016} }
 @article{mensching_rahbar-rastegar_underwood_daniel_2016, title={Identifying Indicators for Fatigue Cracking in Hot-Mix Asphalt Pavements Using Viscoelastic Continuum Damage Principles}, volume={2576}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.3141/2576-04}, DOI={10.3141/2576-04}, abstractNote={A critical distress in asphalt concrete pavements is fatigue cracking, which results in decreased ride quality and fuel economy, and provides an avenue for water intrusion, which causes a pavement system to deteriorate rapidly. Given the poor state of the infrastructure network, changes are needed in the current mixture design process to promote innovation and alternative approaches to production. This study addressed this need by pursuing the following objectives: ( a) relate mixture stiffness, fatigue, and pavement system characteristics for performance-based mixture design; ( b) identify a simplified viscoelastic continuum damage (S-VECD) output parameter that most clearly distinguishes between poor and satisfactory performance when combined with dynamic modulus information; and ( c) evaluate the impact of recycled materials on performance indicators for fatigue cracking. The results show that a pavement structure selection process related to the S-VECD failure criterion produces better performance predictions than does a stiffness-based approach. Promising correlations with performance exist for the pseudostiffness at failure and storage modulus for an Interstate pavement structure, phase angle for a state highway surface and base course, and model term alpha for the same state highway base course.}, number={1}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Mensching, David J. and Rahbar-Rastegar, Reyhaneh and Underwood, B. Shane and Daniel, Jo Sias}, year={2016}, month={Jan}, pages={28–39} }
 @article{mensching_daniel_underwood_2016, title={Identifying indicators for fatigue cracking in hot mix asphalt pavements using viscoelastic continuum damage principles}, volume={2576}, journal={Transportation Research Record}, author={Mensching, D. and Daniel, J. and Underwood, B.S.}, year={2016}, pages={28–39} }
 @article{zeiada_underwood_kaloush_2016, title={Impact of asphalt concrete fatigue endurance limit definition on pavement performance prediction}, volume={18}, ISSN={1029-8436 1477-268X}, url={http://dx.doi.org/10.1080/10298436.2015.1127372}, DOI={10.1080/10298436.2015.1127372}, abstractNote={Many well-constructed Hot Mix Asphalt pavements have been in service for 40 or more years without any evidence of fatigue cracking. This field experience suggests that there exists a strain level, known as the fatigue endurance limit (FEL), below which an asphalt concrete pavement will not exhibit fatigue cracks. Several studies have been conducted to define and verify this limit. Each of these methods is associated with certain assumptions regarding the nature of the FEL and heretofore a comprehensive comparison of each has not been made using a consistent set of mixtures. Likewise, the impact of any observed differences in FEL on the predicted pavement performance has not been made. This paper investigates and compares six different methods for identifying the FEL: NCHRP 9–44A approach, simplified viscoelastic continuum damage model, smeared-healing with continuum damage model, plateau value approach, pseudo-strain analysis method, and reduced cycles method. Each method is found to yield different values ranges from approximately 30–170 microstrains at 21.1 °C. The predicted FEL from each of the six methods are then used with the mechanistic empirical design algorithm to evaluate their effects on predicted pavement performance. Simulation outputs show different pavement performance and perpetual pavement structural design thicknesses from each of the methods. The study outcomes are expected to benefit future field verification research of FEL as it provides comprehensive analyses using six different methods. This future verification research may indicate the method that best represents actual perpetual pavement design and performance.}, number={11}, journal={International Journal of Pavement Engineering}, publisher={Informa UK Limited}, author={Zeiada, W. A. and Underwood, B. S. and Kaloush, K. E.}, year={2016}, month={Jan}, pages={945–956} }
 @inproceedings{nagarajan_khalil_underwood_2016, title={Impact of forecasted freight trends on highway pavement infrastructure}, booktitle={Arizona ITE-IMSA Annual Spring Conference}, author={Nagarajan, S. and Khalil, J. and Underwood, B.S.}, year={2016} }
 @article{gundla_medina_gudipudi_stevens_salim_zeiada_shane underwood_2016, title={Investigation of Aging in Hydrated Lime and Portland Cement Modified Asphalt Concrete at Multiple Length Scales}, volume={28}, ISSN={0899-1561 1943-5533}, url={http://dx.doi.org/10.1061/(ASCE)MT.1943-5533.0001501}, DOI={10.1061/(ASCE)MT.1943-5533.0001501}, abstractNote={The properties of asphalt concrete are the result of many interdependent physical and chemical mechanisms occurring across multiple length scales. Admixtures such as hydrated lime (HL) and portland cement (PC) are known to affect the behaviors of asphalt concrete at the macroscale, but their contribution at other scales and influences on overall performance of the material are not well understood. This paper presents the findings of a study that evaluates the potential for HL and PC for mitigating the effects of asphalt concrete aging with respect to modulus and fatigue resistance. The properties of interest were evaluated at multiple scales, which involved binder, mastic, and mixture testing. Rheological analyses of aged and non-aged control, HL modified, and PC modified mastics indicate that HL possesses greater potential to mitigate aging than PC. In mixture testing, the modulus results showed trends similar to that of mastics, in which the HL-modified samples were the stiffest and showed greater potential to mitigate aging. As expected, the relative increase in stiffness and relative potential to mitigate aging, averaged across temperatures, was found to be higher in mastics than the mixtures. The results from the uniaxial fatigue test show that HL mixtures possess higher fatigue resistance when aged, thus less negative effects from the oxidation process. Magnification of aging mitigation potential at the mastic scale, and its direct correlation to fatigue behavior, explains why multiple scale evaluations can be useful in evaluating the true benefits of the admixtures.}, number={5}, journal={Journal of Materials in Civil Engineering}, publisher={American Society of Civil Engineers (ASCE)}, author={Gundla, Akshay and Medina, Jose and Gudipudi, Padmini and Stevens, Ryan and Salim, Ramadan and Zeiada, Waleed and Shane Underwood, B.}, year={2016}, month={May}, pages={04015205} }
 @article{gundla_gudipudi_medina_salim_zeiada_underwood_2016, title={Investigation of aging in hydrated lime and portland cement modified asphalt concrete at multiple length scales}, volume={28}, number={5}, journal={Journal of Materials in Civil Engineering}, author={Gundla, A. and Gudipudi, P. and Medina, J. and Salim, R. and Zeiada, W. and Underwood, B.S.}, year={2016} }
 @article{nobakht_sakhaeifar_newcomb_underwood_2016, title={Mechanistic-empirical methodology for the selection of cost-effective rehabilitation strategy for flexible pavements}, volume={19}, ISSN={1029-8436 1477-268X}, url={http://dx.doi.org/10.1080/10298436.2016.1199878}, DOI={10.1080/10298436.2016.1199878}, abstractNote={A well-planned rehabilitation approach helps agencies to optimise the allocation of annual investment in pavement rehabilitation programs. Currently, many agencies are struggling with the selection of an optimal time-based and cost-effective rehabilitation solution to address the long-term needs of pavements. This study offers the use of a mechanistic-empirical methodology to develop a series of time-based rehabilitation strategies for high traffic volume flexible pavements located in Oklahoma. Six different pavement family groups are identified in the state, and comprehensive evaluation of existing pavements are conducted through analysis of falling weight deflectometer data and performance measures available in Oklahoma Pavement Management System database. The inadequacy of performance measures to fully characterise the condition of existing pavements are indicated, and damage factor determined from FWD data are suggested as trigger factor to select rehabilitation candidates. Three levels of rehabilitation activities including light, medium and heavy are considered as potential alternatives for rehabilitation candidates. A mechanistic-empirical methodology is employed to obtain an estimate of the performance of rehabilitation and extension in service lives of pavements. Also, an assessment output matrix is developed, which can be served as a supplemental tool to help the decision-makers in the highway agency with the rehabilitation related decision-making process. Cost-effectiveness of rehabilitation alternatives is determined through life cycle cost analysis, and three time-based renewal solutions are developed for pavement family groups that are in need of rehabilitation.}, number={8}, journal={International Journal of Pavement Engineering}, publisher={Informa UK Limited}, author={Nobakht, Mona and Sakhaeifar, Maryam S. and Newcomb, David and Underwood, Shane}, year={2016}, month={Jul}, pages={675–684} }
 @inproceedings{noorvand_underwood_2016, title={Potential for impacts of autonomous vehicles on pavement infrastructure}, booktitle={2016 Roads and Streets Conference}, author={Noorvand, H. and Underwood, B.S.}, year={2016} }
 @article{gudipudi_underwood_2016, title={Reliability Analysis of Fatigue Life Prediction from the Viscoelastic Continuum Damage Model}, volume={2576}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.3141/2576-10}, DOI={10.3141/2576-10}, abstractNote={The fatigue resistance of asphalt concrete materials plays an important role in the service life of a pavement. Several empirical and mechanistic models and efforts are under way toward improving these models for accurate prediction of fatigue life. The reliability of predictions with these models has not received substantial attention. This study used the simplified viscoelastic continuum damage model to analyze the reliability of fatigue predictions. Modulus and fatigue tests were conducted on a standard dense graded asphalt mixture to characterize the model and create deterministic fatigue life predictions. Monte Carlo simulations were then used to calculate the reliability of the fatigue predictions, given the variation in input parameters. The analysis was conducted for combinations of three experimental failure criteria and two model failure criteria at two strain levels for a total of 12 study cases. Differences in reliability between the combinations of failure conditions are identified and discussed. There are three major findings of this study. First, depending on the selection of failure criteria, the prediction errors could range from ±22% to ±52% at a 50% level of reliability, depending on the exact combination of failure criterion and strain level. Second, with an experimental failure criterion of 50%, modulus reduction shows better reliability regardless of the model failure criterion chosen to predict fatigue life. Third, the model failure criterion based on constant pseudostiffness at failure was found to be more reliable than was the pseudostrain energy release rate criterion when characterization was performed with three tests.}, number={1}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Gudipudi, Padmini P. and Underwood, B. Shane}, year={2016}, month={Jan}, pages={91–99} }
 @inproceedings{gudipudi_underwood_2016, title={Reliability analysis of fatigue life prediction from the viscoelastic continuum damage model}, booktitle={95th Annual Meeting of the Transportation Research Board}, author={Gudipudi, P. and Underwood, B.S.}, year={2016} }
 @inproceedings{noorvand_underwood_sai_2016, title={The implications of uniform distribution of trucks on flexible pavement performance and design}, booktitle={Arizona ITE-IMSA Annual Spring Conference}, author={Noorvand, H. and Underwood, B.S. and Sai, G.}, year={2016} }
 @inproceedings{medina_underwood_2016, title={Use of particulate composite models and crumb rubber swelling to estimate stiffness of rubberized asphalt binders}, booktitle={International Society on Asphalt Pavements Symposium}, author={Medina, J. and Underwood, B.S.}, year={2016} }
 @inproceedings{gundla_underwood_2016, title={Using repeated stress sweep to investigate non-linearity in asphalt binders and mastics by fourier transform analysis}, booktitle={Proceedings International Society on Asphalt Pavements Symposium}, author={Gundla, A. and Underwood, B.S.}, year={2016} }
 @article{mogawer_austerman_roque_underwood_mohammad_zou_2015, title={Ageing and rejuvenators: evaluating their impact on high RAP mixtures fatigue cracking characteristics using advanced mechanistic models and testing methods}, volume={16}, ISSN={1468-0629 2164-7402}, url={http://dx.doi.org/10.1080/14680629.2015.1076996}, DOI={10.1080/14680629.2015.1076996}, abstractNote={Fatigue cracking of asphalt mixtures is highly dependent on ageing. Using larger amounts of reclaimed asphalt pavement (RAP) presents a concern that the resultant mixtures may be prone to fatigue cracking because of the aged binder in the RAP. Several studies have indicated that asphalt rejuvenators can allow more aged binder to be incorporated into asphalt mixtures. The four-point flexural beam fatigue test, HMA (hot-mix asphalt) fracture mechanics model, simplified viscoelastic continuum damage model, and the semi-circular bending test were used to evaluate the effect of ageing on the fatigue characteristics of high RAP mixtures modified with rejuvenators. The results from these tests were compared to see if they provided similar performance trends. The results indicated that the long-term ageing used in this study did not have a significant effect on the fatigue characteristics of the high RAP mixture with and without rejuvenators. Comparison of the fatigue tests did not show universal agreement.}, number={sup2}, journal={Road Materials and Pavement Design}, publisher={Informa UK Limited}, author={Mogawer, Walaa S. and Austerman, Alexander and Roque, Reynaldo and Underwood, Shane and Mohammad, Louay and Zou, Jian}, year={2015}, month={Aug}, pages={1–28} }
 @inbook{underwood_2015, title={Chapter 9: Multiscale Modeling Approach for Asphalt Concrete and its Implications on Oxidative Aging}, ISBN={9780081002711}, booktitle={Advances in Asphalt Materials}, publisher={Cambridge: Woodhead Publishing}, author={Underwood, B.S.}, editor={Huang, Shin-Che and Benedetto, Herve? DiEditors}, year={2015} }
 @article{underwood_2015, title={Continuum damage based constitutive model for asphalt binder and asphalt mastic}, volume={82}, number={3}, journal={International Journal of Fatigue}, author={Underwood, B.S.}, year={2015}, pages={287–401} }
 @article{stevens_stempihar_underwood_pal_2015, title={Evaluation of Multiple Stress Creep and Recovery (MSCR) Data for Arizona}, volume={8}, DOI={10.6135/ijprt.org.tw/2015.8(4).337}, number={5}, journal={International Journal of Pavement Research and Technology}, author={Stevens, R. and Stempihar, J. and Underwood, B.S. and Pal, D.}, year={2015}, pages={337–345} }
 @article{gundla_underwood_2015, title={Evaluation of in situ RAP binder interaction in asphalt mastics using micromechanical models}, volume={18}, ISSN={1029-8436 1477-268X}, url={http://dx.doi.org/10.1080/10298436.2015.1066003}, DOI={10.1080/10298436.2015.1066003}, abstractNote={In this article the mastic level structure of asphalt concrete containing reclaimed asphalt pavement (RAP) materials is investigated using the principles of micromechanics. Locally sourced RAP material was screened and sieved to separate the coated fines (smaller than 0.075 mm) from the remaining sizes. These binder coated fines were mixed with virgin filler at proportions commensurate with 0, 10, 30, 50 and 100% RAP dosage levels. Asphalt mastics were prepared with these blended fillers and a PG 64-22 binder at a filler content of 27% by volume. Temperature–frequency sweeps were conducted on the resulting composites as well as the constituents, virgin binder, solvent extracted RAP binder. The results from the experiments showed an expected increase in stiffness with increase in dosage levels. These results were also used to model the hypothesised structure of the composite. The study presented discusses the applicability of Herve and Zaoui model to predict the blended mastic composite and to quantify the amount of blending between RAP binder and newly added asphalt binder. It is found that as the RAP dosage level increases the amount of blending that occurs, as a proportion of the total RAP binder decreases.}, number={9}, journal={International Journal of Pavement Engineering}, publisher={Informa UK Limited}, author={Gundla, Akshay and Underwood, Shane}, year={2015}, month={Sep}, pages={798–810} }
 @inproceedings{underwood_2015, title={Fiber reinforced asphalt concrete: Overview, mechanisms, and applications}, booktitle={4th IRF Middle East Regional Congress}, author={Underwood, B.S.}, year={2015} }
 @inproceedings{kaloush_underwood_zeiada_stempihar_2015, title={Fiber reinforced asphalt concrete: Performance tests and pavement design consideration}, booktitle={International Conference on Bituminous Mixtures and Pavements}, author={Kaloush, K.E. and Underwood, B.S. and Zeiada, W.A. and Stempihar, J.}, year={2015} }
 @inproceedings{nagarajan_underwood_2015, title={Impact of freight movement trends on highway pavement infrastructure}, booktitle={2015 Roads and Streets Conference}, author={Nagarajan, S. and Underwood, B.S.}, year={2015} }
 @inproceedings{stempihar_zeiada_underwood_kaloush_2015, title={Laboratory cracking evaluation of a warm mix rubber modified pavement}, booktitle={Proceedings of the 6th Asphalt Rubber Conference}, author={Stempihar, J. and Zeiada, W. and Underwood, B.S. and Kaloush, K.}, year={2015} }
 @inproceedings{underwood_2015, title={Multiaxial viscoelastic continuum damage model under compressive and tensile deviatoric loading}, booktitle={94th Annual Meeting of the Transportation Research Board}, author={Underwood, B.S.}, year={2015} }
 @article{kim_underwood_2015, title={Perspectives on multiscale, multiphase, and multiphysics issues in bituminous materials and pavements}, volume={18}, ISSN={1029-8436 1477-268X}, url={http://dx.doi.org/10.1080/10298436.2015.1066008}, DOI={10.1080/10298436.2015.1066008}, abstractNote={AbstractThis special issue sets out to discuss various perspectives on multiscale, multiphase, and multiphysical issues in bituminous media (i.e. bituminous materials, mixtures, and pavements) by bringing together individual state-of-the-art approaches. It is meant to integrate theoretical, computational, and experimental methods along the above stated theme via significant efforts from relevant experts in our field. It is our eventual goal of this special issue to advance the current knowledge of bituminous materials/pavements with more fundamental aspects so as to improve our current practices in the materials selection, mixture design, structural design, and performance forecasting.}, number={9}, journal={International Journal of Pavement Engineering}, publisher={Informa UK Limited}, author={Kim, Yong-Rak and Underwood, B. Shane}, year={2015}, month={Jul}, pages={753–753} }
 @inproceedings{stempihar_stevens_underwood_dharminder_2015, title={Properties of Arizona TR+ binders in multiple stress creep and recovery test}, booktitle={Proceedings of the 6th Asphalt Rubber Conference}, author={Stempihar, J. and Stevens, S. and Underwood, B.S. and Dharminder, P.}, year={2015} }
 @inproceedings{medina_kaloush_underwood_2015, title={Properties of activated crumb rubber modified binders}, booktitle={Proceedings of the 6th Asphalt Rubber Conference}, author={Medina, J. and Kaloush, K. and Underwood, B.S.}, year={2015} }
 @inproceedings{nobakht_sakhaeifar_newcomb_underwood_freeman_2015, title={Techniques for selecting cost-effective pavement rehabilitation strategies}, booktitle={ASCE T&DI 2015 Annual Meeting}, author={Nobakht, M. and Sakhaeifar, M.S. and Newcomb, D. and Underwood, B.S. and Freeman, T.}, year={2015} }
 @article{gudipudi_underwood_2015, title={Testing and Modeling of Fine Aggregate Matrix and Its Relationship to Asphalt Concrete Mix}, volume={2507}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.3141/2507-13}, DOI={10.3141/2507-13}, abstractNote={The study of the fundamental properties of asphalt concrete (AC) can be used to improve and maximize the performance potential of these materials. In this paper, the fundamental approach is examined by coupling its essential hypothesis to an investigation of AC across multiple length scales. Asphalt and aggregate materials from the state of Arizona were used to prepare fine aggregate matrix (FAM) and AC samples. Laboratory tests on these materials were conducted to investigate the modulus and damage characteristics for two binder types. A comparison of mechanical response across length scales is not new, and the unique element of this study is testing both materials in the axial direction (tension–compression) for both modulus and fatigue. A strong relationship between these two materials was observed; this relationship suggests that tests on FAM samples can provide much needed insight in understanding the behavior of AC for various conditions. The study also investigated upscaling of the FAM properties to those of the AC mixture through a homogenized continua approach. Multiple upscale models were evaluated in this upscaling process, but the chosen method produced the best overall match to experimental data. The findings from this modeling effort were also used to upscale the behaviors of FAM to identify the fatigue characteristics of AC mixtures and evaluate the long-term performance of the material.}, number={1}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Gudipudi, Padmini and Underwood, B. Shane}, year={2015}, month={Jan}, pages={120–127} }
 @article{gudipudi_underwood_2015, title={Testing and modeling of fine aggregate matrix to asphalt mixture damage relationship}, volume={2507}, journal={Transportation Research Record}, author={Gudipudi, P. and Underwood, B.S.}, year={2015}, pages={120–127} }
 @article{underwood_kim_2014, title={A four phase micro-mechanical model for asphalt mastic modulus}, volume={75}, ISSN={0167-6636}, url={http://dx.doi.org/10.1016/j.mechmat.2014.04.001}, DOI={10.1016/j.mechmat.2014.04.001}, abstractNote={In this paper, existing formulations for predicting the stiffening effects of graded aggregate particles at moderate and high concentrations in a viscoelastic matrix (asphalt) are evaluated. These functions encompass dilute, micro-mechanical, and phenomenological solutions, but each is found to produce qualitatively and quantitatively unsatisfactory results at all particle concentrations. These shortcomings are hypothesized result from the inability of these models to consider a third phase of the composite, a physico-chemically influenced layer at the aggregate surface. A model to account for this layer is developed and applied to predict the stiffening of asphalt mastics across a range of volumetric concentrations. The model is found to predict the stiffening responses at moderate concentrations well, but under predicts the responses at the highest concentrations. At these concentrations, particulate contact and internal structure development occurs and provides an additional stiffening mechanism that the four phase model does not account for. The under predictions at these higher concentrations are thus expected and rational.}, journal={Mechanics of Materials}, publisher={Elsevier BV}, author={Underwood, B. Shane and Kim, Y. Richard}, year={2014}, month={Aug}, pages={13–33} }
 @article{zeiada_souliman_kaloush_mamlouk_underwood_2014, title={Comparison of Fatigue Damage, Healing, and Endurance Limit with Beam and Uniaxial Fatigue Tests}, volume={2447}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.3141/2447-04}, DOI={10.3141/2447-04}, abstractNote={The concept of an endurance limit assumes a strain value below which the net fatigue damage that occurs during a load cycle is zero. The fact that real traffic loads are separated by rest periods may allow for partial or full healing of the microcracks, which can affect this endurance limit. If the asphalt layer thickness is controlled to keep strains below the endurance limit, the fatigue life of the pavement can be extended considerably. In the study reported in this paper, it was hypothesized that the endurance limit in asphalt concrete developed from the interaction and balance of damage and healing during a load cycle. This hypothesis formed the basis of the testing and analysis program, which evaluated the effects of air voids, asphalt content, rest periods, and temperature on the endurance limit. Two types of fatigue tests were conducted: beam (flexural) and uniaxial. A regression model also was developed on the basis of the results of each test and used to obtain the endurance limit values. This paper compares fatigue damage, healing, and endurance limit results from the two tests under similar conditions. The comparison shows that the beam fatigue test yields less overall fatigue damage and less healing than the uniaxial fatigue test. Beam fatigue yields 8 to 14 times longer fatigue lives, while uniaxial fatigue yields higher healing (10.4 times for the only available case). Because damage and healing combined to govern the endurance limit, the two tests produced close values in which the overall uniaxial endurance limit values were 12% less than the beam fatigue endurance limit values.}, number={1}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Zeiada, Waleed Abdelaziz and Souliman, Mena I. and Kaloush, Kamil E. and Mamlouk, Michael and Underwood, B. Shane}, year={2014}, month={Jan}, pages={32–41} }
 @article{zeiada_underwood_pourshams_stempihar_kaloush_2014, title={Comparison of conventional, polymer, and rubber asphalt mixtures using viscoelastic continuum damage model}, volume={15}, ISSN={1468-0629 2164-7402}, url={http://dx.doi.org/10.1080/14680629.2014.914965}, DOI={10.1080/14680629.2014.914965}, abstractNote={In this study, a laboratory experimental programme was conducted to compare the material properties and fatigue performance characteristics for reference, polymer-modified and rubber-modified gap-graded mixtures. These mixtures were placed on E18 highway between the interchanges Järva Krog and Bergshamra in the Stockholm area of Sweden. The advanced material characterisation tests included dynamic (complex) modulus for stiffness evaluation and the uniaxial tension–compression for fatigue assessment. The data were used to compare the performance of the rubber-modified gap-graded mixture to the reference and polymer-modified gap mixtures using the viscoelastic continuum damage (VECD) approach. Different researchers have successfully applied the VECD model to describe the fatigue behaviour of asphalt concrete mixtures. The damage characteristic (C–S) curves were established for each of the three mixtures. The fatigue behaviour for the three mixtures was ranked based on the C–S curve results and the rubber-modified mixture showed the best fatigue damage resistance followed by the polymer-modified and reference mixtures. The VECD approach provides a more comprehensive analysis to evaluate fatigue resistance compared with the traditional fatigue evaluation using a number of cycles at a given stiffness reduction.}, number={3}, journal={Road Materials and Pavement Design}, publisher={Informa UK Limited}, author={Zeiada, Waleed A. and Underwood, B. Shane and Pourshams, Tina and Stempihar, Jeffrey and Kaloush, Kamil E.}, year={2014}, month={May}, pages={588–605} }
 @article{zeiada_souliman_kaloush_mamlouk_underwood_2014, title={Comparison of fatigue damage, healing, and endurance limit using beam fatigue and uniaxial fatigue tests}, journal={Transportation Research Record}, author={Zeiada, W.A. and Souliman, M. and Kaloush, K.E. and Mamlouk, M. and Underwood, B.S.}, year={2014}, pages={32–41} }
 @inproceedings{underwood_zeiada_kaloush_2014, title={Comparison of hot mix asphalt endurance limit using NCHRP 9-44A developed methodology to other analytical techniques}, booktitle={International Conference on Perpetual Pavement}, author={Underwood, B.S. and Zeiada, W.A. and Kaloush, K.}, year={2014} }
 @inproceedings{underwood_baek_kim_2014, title={Effect of asphalt binder oxidation on the modulus of asphalt concrete mixtures}, booktitle={Proceedings International Conference on Asphalt Pavements}, author={Underwood, B.S. and Baek, C.M. and Kim, Y.R.}, year={2014} }
 @inproceedings{underwood_farrar_hintz_kim_2014, title={Evaluation of methodologies for crossover modulus determination}, booktitle={2014 Petersen Asphalt Research Conference}, author={Underwood, B.S. and Farrar, M. and Hintz, C. and Kim, Y.R.}, year={2014} }
 @inproceedings{underwood_2014, title={Fibers in pavements}, booktitle={Arizona Pavement/Materials Conference}, author={Underwood, B.S.}, year={2014} }
 @article{underwood_zeiada_2014, title={Modeling the microdamage healing in asphalt concrete with a smeared continuum damage approach}, journal={Transportation Research Record}, author={Underwood, B.S. and Zeiada, W.A.}, year={2014}, pages={126–135} }
 @inproceedings{underwood_zeiada_2014, title={Modeling the microdamage healing in asphalt concrete with a smeared continuum damage approach}, booktitle={93rd Annual Meeting of the Transportation Research Record}, author={Underwood, B.S. and Zeiada, W.A.}, year={2014} }
 @article{underwood_kim_2014, title={Nonlinear viscoelastic analysis of asphalt cement and asphalt mastics}, volume={16}, ISSN={1029-8436 1477-268X}, url={http://dx.doi.org/10.1080/10298436.2014.943133}, DOI={10.1080/10298436.2014.943133}, abstractNote={The nonlinear viscoelastic (NLVE) behaviour of asphalt cement and asphalt mastic are studied using temperature and frequency sweep tests and repeated stress sweep cyclic load tests. These experiments show that the response functions of these materials are strain-level dependent. The experiments also show that NLVE occurs simultaneously with other mechanisms, which complicates isolation and subsequent characterisation. For the asphalt mastics studied, the NLVE is found to relate to only the influences of the asphalt cement. Based on these experiments and analyses, a thermodynamics-based constitutive equation is proposed. The proposed model is chosen based on the hypothesis that the observed NLVE is strain related, which is different from other similar models and agrees with existing frameworks for evaluating damage. The resulting model is found to capably predict the stress–strain behaviour of asphalt cement and asphalt mastics at different volumetric concentrations of filler under cyclic and constant rate loading.}, number={6}, journal={International Journal of Pavement Engineering}, publisher={Informa UK Limited}, author={Underwood, B. Shane and Kim, Y. Richard}, year={2014}, month={Aug}, pages={510–529} }
 @inproceedings{underwood_kim_2014, title={Structuralization as characteristic to link the mechanical behaviors of asphalt concrete at different length scales}, booktitle={Proceedings International Conference on Asphalt Pavements}, author={Underwood, B.S. and Kim, Y.R.}, year={2014} }
 @inproceedings{underwood_el asmar_2014, title={Sustainable construction practices}, booktitle={2014 Roads and Streets Conference}, author={Underwood, B.S. and El Asmar, M.}, year={2014} }
 @inproceedings{nobakht_sakhaeifar_newcomb_underwood_freeman_2014, title={Techniques for selecting cost-effective pavement rehabilitation strategies: Two case studies}, booktitle={Proceedings 2014 Airfield and Highway Pavements Conference}, author={Nobakht, M. and Sakhaeifar, M.S. and Newcomb, D. and Underwood, B.S. and Freeman, T.}, year={2014} }
 @inproceedings{zeiada_underwood_kaloush_2014, title={Uniaxial fatigue testing of diverse asphalt concrete mixtures}, booktitle={Proceedings International Conference on Asphalt Pavements}, author={Zeiada, W.A. and Underwood, B.S. and Kaloush, K.E.}, year={2014} }
 @inproceedings{zeiada_kaloush_underwood_mamlouk_2013, title={Effect of air voids and asphalt content on fatigue damage using the viscoelastic continuum damage analysis}, DOI={10.1061/9780784413005.094}, abstractNote={In this study, a laboratory experimental program was conducted to investigate the effect of asphalt content and air voids on the material properties and fatigue performance characteristics of asphalt concrete mixtures. Two levels of asphalt content (4.2 and 5.2%) and air voids (4.5 and 9.5%) were considered to produce four asphalt concrete mixture combinations. The advanced material characterization tests included dynamic (complex) modulus for stiffness evaluation and the uniaxial tension-compression for fatigue assessment. The fatigue analysis was performed for each mixture using the simplified viscoelastic continuum damage (S-VECD) approach. The damage characteristic (C-S) curves were established for each of the four mixtures. To have more useful information about the fatigue resistance of the four mixtures, the C-S curves were used to obtain the fatigue relationships by performing simulated predictions of the fatigue life at specific conditions. It is found that the S-VECD simulations are able to reflect the observed material trends. Simulations performed with this model also suggest that the impact of air void and asphalt content changes differ between stress-controlled and strain-controlled loading. The quantification of these differences may have implications in both pavement and material analysis and design.}, booktitle={Proceedings 2013 Airfield and Highway Pavements Conference}, author={Zeiada, W.A. and Kaloush, K.E. and Underwood, B.S. and Mamlouk, M.S.}, year={2013} }
 @article{underwood_kim_2013, title={Effect of volumetric factors on the mechanical behavior of asphalt fine aggregate matrix and the relationship to asphalt mixture properties}, volume={49}, ISSN={0950-0618}, url={http://dx.doi.org/10.1016/j.conbuildmat.2013.08.045}, DOI={10.1016/j.conbuildmat.2013.08.045}, abstractNote={The multiscale study of asphalt concrete using fine aggregate matrix (FAM) has become widespread in recent years. Different laboratory fabrication procedures have been proposed, and since FAM’s sensitivity to compositional effects is unknown this literature cannot be coherently interpreted. In this paper, the mechanical responses of FAM at different volumetric compositions are systematically studied. The viscoelastic and tensile properties are found to be sensitive to volumetric composition. It is concluded that the use of FAM for modeling purposes requires accurate replication of FAM as it exists in the mixture. However, such strict requirements are not necessary for simpler, comparative evaluations.}, journal={Construction and Building Materials}, publisher={Elsevier BV}, author={Underwood, B. Shane and Kim, Y. Richard}, year={2013}, month={Dec}, pages={672–681} }
 @inproceedings{underwood_2013, title={Emerging methods of asphalt concrete mixture and pavement analysis}, booktitle={2013 Roads and Streets Conference}, author={Underwood, B.S.}, year={2013} }
 @inproceedings{underwood_gundla_2013, title={Evaluation of in-situ RAP binder interaction in asphalt cement composites}, booktitle={4th International Conference on Asphalt Materials}, author={Underwood, B.S. and Gundla, A.}, year={2013} }
 @article{zeiada_kaloush_underwood_mamlouk_2013, title={Improved method of considering air void and asphalt content changes on long-term performance of asphalt concrete pavements}, volume={15}, ISSN={1029-8436 1477-268X}, url={http://dx.doi.org/10.1080/10298436.2013.857775}, DOI={10.1080/10298436.2013.857775}, abstractNote={Mixture properties (aggregate gradation and volumetric quantities), rate of loading and environmental conditions are the most important factors that affect the |E*| values. The main objective of this study was to develop a rational approach to investigate and model the effect of air voids and asphalt content on the |E*| master curves and consequently predict pavement performance. In this study, |E*| tests were conducted on three asphalt concrete mixtures with the same aggregate gradation, but different binder grades. For each of these mixtures, the air void and asphalt contents were varied at three levels. It is found that the developed method provides a more accurate estimate of the effects of volumetric changes in hot mix asphalt. The application of the proposed approach would be most beneficial for quality control/quality assurance purposes, performance-related specifications and for estimating contractors' incentives and penalties, where |E*| is utilised to predict the pavement performance.}, number={8}, journal={International Journal of Pavement Engineering}, publisher={Informa UK Limited}, author={Zeiada, W.A. and Kaloush, K.E. and Underwood, B.S. and Mamlouk, M.E.}, year={2013}, month={Nov}, pages={718–730} }
 @inproceedings{underwood_kim_2013, title={Mechanistic behaviors of fine aggregate matrix and its relation to asphalt mixture behaviors}, booktitle={2013 Airfield and Highway Pavements Conference}, author={Underwood, B.S. and Kim, Y.R.}, year={2013} }
 @inproceedings{underwood_kim_2013, title={Micromechanical modeling of particle concentration effect in asphalt mastic to consider physico-chemical interaction}, booktitle={2013 Petersen Asphalt Research Conference}, author={Underwood, B.S. and Kim, Y.R.}, year={2013} }
 @article{underwood_kim_2013, title={Microstructural Association Model for Upscaling Prediction of Asphalt Concrete Dynamic Modulus}, volume={25}, ISSN={0899-1561 1943-5533}, url={http://dx.doi.org/10.1061/(ASCE)MT.1943-5533.0000657}, DOI={10.1061/(ASCE)MT.1943-5533.0000657}, abstractNote={Multiscale modeling is becoming an increasingly useful method of evaluating the behaviors of asphalt concrete. Reasons for this increased interest include the fact that many of the critical behaviors of this material are affected by localized behaviors that cannot be completely captured using more traditional continuum approaches. Computational methods are popular for this type of evaluation because in principle they can directly account for many of the localized mechanisms. However, computational expense can be excessive, particularly if all of these localized mechanisms are accounted for rigorously. An alternative method of multiscale modeling relying on analytical models is developed and presented in this paper. The model is referred to as the microstructure association model because it accounts for the ways that the multiple scales within asphalt concrete associate together to yield the gross behaviors of the finished composite, asphalt concrete. This model is formed from the hypothesis that asphaltic composites at different length scales evolve along a continuum, which is related to the degree of internal structuralization that exists within the composite. In this way asphalt mixture may behave in a quantitatively similar way as asphalt mastic if the concentration of particles within the mastic produces the same degree of internal structuralization as that which exists in the asphalt mixture. Through this modeling effort two separate, but possibly related, mechanisms are identified: (1) interaction of particles separated by some distance, but still influenced by an adsorbed and nonadsorbed asphalt binding medium; and (2) close-proximity contacts of aggregate particles that lead to a significant increase in stiffness with relatively small changes in volumetric concentration. Each of these mechanisms is modeled separately within the microstructural association model and combined using a rational mechanical analog approach. The model is characterized using only experiments on asphalt mastic at different concentrations, but is verified with its ability to upscale to the modulus of asphalt concrete. In the final section of this paper the ability of the model to perform useful engineering tasks is shown when it is used to assess the impact of asphalt content and air void content changes on the modulus of two different materials.}, number={9}, journal={Journal of Materials in Civil Engineering}, publisher={American Society of Civil Engineers (ASCE)}, author={Underwood, B. Shane and Kim, Y. Richard}, year={2013}, month={Sep}, pages={1153–1161} }
 @article{underwood_krim_2013, title={Microstructural association model for upscaling prediction of asphalt concrete dynamic modulus}, number={9}, journal={Journal of Materials in Civil Engineering}, author={Underwood, B.S. and Krim, Y.R.}, year={2013}, pages={1153–1161} }
 @article{underwood_kim_2013, title={Microstructural investigation of asphalt concrete for performing multiscale experimental studies}, volume={14}, ISSN={1029-8436 1477-268X}, url={http://dx.doi.org/10.1080/10298436.2012.746689}, DOI={10.1080/10298436.2012.746689}, abstractNote={In this paper, a microstructural hypothesis for asphalt concrete (AC) is developed in order to provide a basis for a multiscale experimental investigation. The hypothesis is consistent with the belief that AC can be considered as a four-scale assemblage of components with different characteristic length scale, binder, mastic, fine aggregate matrix (FAM) and finally AC. The hypothesis is supported with a series of direct microstructural experiments including morphological observations with digital and scanning electron microscopy as well as quantitative evaluation using a novel meso-gravimetric test method developed specifically for this research. Morphological evaluation shows that asphalt mastic effectively exists as a basic building block for AC. Meso-gravimetric analysis finds that the volumetric composition of this mastic is equal to that found when assuming that mastic contains all of the effective asphalt binder and the filler-sized particles. Other key volumetric properties including FAM gradation ...}, number={5}, journal={International Journal of Pavement Engineering}, publisher={Informa UK Limited}, author={Underwood, B. Shane and Kim, Y. Richard}, year={2013}, month={Jul}, pages={498–516} }
 @article{underwood_kim_2013, title={Nonlinear Viscoelastic Behavior of Asphalt Concrete and Its Implication for Fatigue Modeling}, volume={2373}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.3141/2373-11}, DOI={10.3141/2373-11}, abstractNote={Mechanistic models for asphalt concrete (AC) can consider many different physical mechanisms. However, as more mechanisms are considered, the complexity increases, and it becomes important to balance accuracy and complexity to create a model that can be used by the engineering community. In some cases, the material response is dominated by the effects of only some key processes, and smearing the effects of the minor ones is acceptable. In other cases, many processes are important and need to be considered. In this paper, the importance of modeling the nonlinear viscoelasticity (NLVE) of AC for fatigue response prediction is assessed. Two mechanistic hypotheses are considered for describing this phenomenon: linear viscoelastic with damage and NLVE with damage. The importance of explicitly considering NLVE effects under fatigue loading is evaluated with laboratory tests, the simplified viscoelastic continuum damage (S-VECD) model, and an NLVE form of the S-VECD model. These two models are characterized and used to simulate and compare AC fatigue response under constant and random controlled stress and strain conditions. It is found that while the NLVE-based formulation better represents the material response in random loading and suggests less overall damage accumulation during fatigue, the two models predict similar amounts of modulus reduction. The primary conclusion from this study is that because the goal for fatigue assessment is to find the change in modulus over a long period of time, fatigue response modeling of AC does not need to explicitly consider NLVE.}, number={1}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Underwood, B. Shane and Kim, Y. Richard}, year={2013}, month={Jan}, pages={100–108} }
 @inproceedings{underwood_kim_2013, title={Nonlinear viscoelastic behavior of asphalt concrete and its implication on fatigue modeling}, booktitle={92nd Annual Meeting of the Transportation Research Record}, author={Underwood, B.S. and Kim, Y.R.}, year={2013} }
 @inproceedings{underwood_el asmar_2013, title={Sustainable construction practices}, booktitle={2013 Arizona Pavements/Materials Conference}, author={Underwood, B.S. and El Asmar, M.}, year={2013} }
 @inproceedings{underwood_2013, title={Use of pavement models to evaluate impacts of RAP in pavement construction}, booktitle={2013 Airfield and Highway Pavements Conference}, author={Underwood, B.S.}, year={2013} }
 @inproceedings{zeiada_underwood_pourshams_stempihar_kaloush_2012, title={Comparison of conventional, polymer, and rubber asphalt mixtures using viscoelastic continuum damage model}, booktitle={Proceedings of the 5th Asphalt Rubber Conference}, author={Zeiada, W.A. and Underwood, B.S. and Pourshams, T. and Stempihar, J. and Kaloush, K.}, year={2012} }
 @article{underwood_kim_2012, title={Comprehensive Evaluation of Small Strain Viscoelastic Behavior of Asphalt Concrete}, volume={40}, ISSN={0090-3973}, url={http://dx.doi.org/10.1520/JTE104521}, DOI={10.1520/jte104521}, abstractNote={Asphalt concrete (AC) is a heterogeneous material affected by viscoelastic and viscoplastic processes, as well as by damage and localized irregularities in the material fabric. However, under specific strain regimens, certain of these mechanisms are less active, and the constitutive relationships of the material can be modeled using simplified mechanistic principles. One simplifying assumption that is typically applied to AC for the purposes of response and performance modeling is that of linear viscoelasticity (LVE). In this paper, the behavior of AC at small strain levels, when LVE models can most accurately describe the constitutive relationship, is described. This work differs from the significant literature presented elsewhere because a more strict definition of the LVE strain regimen has been adhered to. This protocol limits the total peak-to-peak strain amplitude to 50 to 75 microstrains, the tensile strain amplitude to 37.5 microstrains, the total accumulated compressive strain to 1500 microstrains, and the total accumulated tensile strain to 150 microstrains. It is shown that when this stricter protocol is followed, AC exhibits the same fundamental characteristics whether loaded in compression, tension, or indirect tension. Evidence is also presented showing that AC, when compacted by gyratory compaction, does not show anisotropic tendencies at these strain levels. AC shows stress state and strain level dependencies that are inconsistent with rigorous LVE theory. Due to the inconsistencies between the material responses and the theory, the behavior of AC at even the small strain levels used in this research cannot be rigorously referred to as LVE. Further study is needed in order to fully assess the implications of this finding as it relates to day-to-day engineering practice and to the advanced mechanistic modeling of AC materials.}, number={4}, journal={Journal of Testing and Evaluation}, publisher={ASTM International}, author={Underwood, B. Shane and Kim, Y. Richard}, year={2012}, month={Jul}, pages={104521} }
 @article{baek_underwood_krim_2012, title={Effect of oxidative aging on asphalt mixture properties}, volume={2296}, journal={Transportation Research Record}, author={Baek, C.M. and Underwood, B.S. and Krim, Y.R.}, year={2012}, pages={77–85} }
 @inproceedings{baek_underwood_kim_2012, title={Effect of oxidative aging on asphalt mixture properties}, booktitle={91st Annual Meeting of the Transportation Research Record}, author={Baek, C.M. and Underwood, B.S. and Kim, Y.R.}, year={2012} }
 @article{baek_underwood_kim_2012, title={Effects of Oxidative Aging on Asphalt Mixture Properties}, volume={2296}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.3141/2296-08}, DOI={10.3141/2296-08}, abstractNote={Aging has long been recognized as a contributing factor to fatigue distress of asphalt concrete pavement. Several research studies have been undertaken to gain fundamental understanding of the aging phenomenon at the asphalt binder level. However, relatively little effort has been made to understand and to quantify the effects of aging on fundamental characteristics of asphalt mixtures. The effects of oxidative aging on the dynamic modulus and the fatigue performance of asphalt mixtures is examined. For this purpose, an asphalt mixture is aged in the laboratory at four aging levels. Mechanical tests for the four aged mixtures are performed to characterize the linear viscoelastic and damage properties. Such characterization is investigated to incorporate the aging effects into a more comprehensive analytical framework for predicting the performance of asphalt concrete pavements. Finally, this framework is used to evaluate the aging effects on an example asphalt concrete pavement. It is found that aging can significantly change the performance of an asphalt concrete pavement, depending on the location evaluated within the pavement structure as well as climate conditions.}, number={1}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Baek, Cheolmin and Underwood, B. Shane and Kim, Y. Richard}, year={2012}, month={Jan}, pages={77–85} }
 @inproceedings{underwood_kim_2012, title={Experimental investigation into the behavior of asphalt concrete at different length scales}, booktitle={2012 Engineering Mechanics Institute Conference}, author={Underwood, B.S. and Kim, Y.R.}, year={2012} }
 @article{tan_shan_kim_underwood_2012, title={Healing characteristics of asphalt binder}, volume={27}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2011.07.006}, abstractNote={Abstract The healing performance of asphalt binder has a critical impact on the fatigue performance of asphalt binders, mixture and pavement. Although studies of the healing characteristics of asphalt binder can be found in some references, the subject has not been researched thoroughly. No universal healing evaluation index currently exists, and the fatigue and healing processes are not fully understood. For this study, experiments were performed to characterize the healing characteristics of four typical asphalt binders. Healing indices are put forward, and factors that affect healing performance are examined in this paper. Finally, the fatigue and healing processes of asphalt binder are investigated by analyzing test specimen cross-sections. The findings from this study, although based on a limited number of binders, suggests that HI 1 (the modulus ratio) and HI 2 (the cycle number ratio) are suitable healing indices. Rest periods and microstructural configurations significantly affect the healing performance of asphalt binder. Healing affects the fatigue performance only when the modulus value is greater than the modulus value when rest periods are applied. During fatigue testing, damage starts at the outer edge of the specimen, and then develops towards the middle of the specimen.}, number={1}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Tan, Yiqiu and Shan, Liyan and Kim, Y. Richard and Underwood, B. Shane}, year={2012}, month={Feb}, pages={570–577} }
 @article{underwood_baek_kim_2012, title={Simplified Viscoelastic Continuum Damage Model as Platform for Asphalt Concrete Fatigue Analysis}, volume={2296}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.3141/2296-04}, DOI={10.3141/2296-04}, abstractNote={Cracking in asphalt concrete pavements is a major form of pavement distress in the United States. Because the cracking phenomenon is complex and cracking is often affected by both material and structural factors, field engineers have no quick and effective test and analysis protocols. A suite of fatigue analysis tools—as well as applications built around the simplified viscoelastic continuum damage (S-VECD) model—is presented. The S-VECD formulation is presented in a summarized form. Next, the characterization protocols, which are consistent with the capabilities of the asphalt mixture performance tester, are shown. Considerable attention is then given to S-VECD–based analysis tools for assessment of material- and pavement-level fatigue performance. Results show that the S-VECD model can be used to predict the number of cycles until fatigue failure for both constant stress and constant strain loading. The S-VECD model's sensitivity to mixture composition and external factors is shown through predictions of the endurance limit. Finally, pavement performance predictions are used to show how the S-VECD model can predict the field performance results of full-scale accelerated pavement tests, quantify the expected performance of pavement design alternatives, and identify factors that affect top-down cracking.}, number={1}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Underwood, B. Shane and Baek, Cheolmin and Kim, Y. Richard}, year={2012}, month={Jan}, pages={36–45} }
 @inbook{baek_thirunavukkarasu_underwood_guddati_kim_2012, title={Top-Down Cracking Prediction Tool for Hot Mix Asphalt Pavements}, ISBN={9789400745650 9789400745667}, url={http://dx.doi.org/10.1007/978-94-007-4566-7_45}, DOI={10.1007/978-94-007-4566-7_45}, booktitle={7th RILEM International Conference on Cracking in Pavements}, publisher={Springer Netherlands}, author={Baek, Cheolmin and Thirunavukkarasu, Senganal and Underwood, B. Shane and Guddati, Murthy N. and Kim, Y. Richard}, year={2012}, pages={465–474} }
 @inproceedings{baek_thirunavukkarasu_underwood_guddati_kim_2012, title={Top-down cracking prediction tool for hot mix asphalt pavements}, booktitle={Proceedings Pavement Cracking: Mechanisms, Modeling, Testing, Detection, Prevention and Case Histories}, author={Baek, C.M. and Thirunavukkarasu, S. and Underwood, B.S. and Guddati, M.N. and Kim, Y.R.}, year={2012} }
 @article{underwood_baek_krim_2012, title={Use of simplified viscoelastic continuum damage model as an asphalt concrete fatigue analysis platform}, journal={Transportation Research Record}, author={Underwood, B.S. and Baek, C.M. and Krim, Y.R.}, year={2012}, pages={36–45} }
 @article{underwood_krim_2011, title={A viscoelastoplastic continuum damage model for asphalt concrete in tension}, number={11}, journal={Journal of Engineering Mechanics}, author={Underwood, B.S. and Krim, Y.R.}, year={2011}, pages={732–739} }
 @article{underwood_kim_corley-lay_2011, title={Assessment of Use of Automated Distress Survey Methods for Network-Level Pavement Management}, volume={25}, ISSN={0887-3828 1943-5509}, url={http://dx.doi.org/10.1061/(ASCE)CF.1943-5509.0000158}, DOI={10.1061/(asce)cf.1943-5509.0000158}, abstractNote={The pavement network represents a visible and expensive component of a highway agency’s total transportation investment and, thus, requires proper management. Historically, the agencies managing these investments have relied on manual distress surveys carried out by personnel who drive the network and provide subjective condition assessments. Surveys completed by a highly instrumented vehicle driven at standard travel speeds have become a viable alternative. Questions regarding accuracy and consistency with existing survey protocols still remain with these automated survey methods. This paper reports on the findings from a study to evaluate automated distress surveys. Vendors and manual survey teams have evaluated the distresses along a test loop in North Carolina using two survey protocols: (1) an agency’s standard network level survey, and (2) the long-term pavement performance survey. Communication between the vendor and agency is the single most important factor that allows for the proper utilization of automated surveys for network-level surveys. For best results, agencies considering using automated methods may wish to utilize an initial test loop to calibrate the automated distress results.}, number={3}, journal={Journal of Performance of Constructed Facilities}, publisher={American Society of Civil Engineers (ASCE)}, author={Underwood, B. S. and Kim, Y. R. and Corley-Lay, J.}, year={2011}, month={Jun}, pages={250–258} }
 @article{underwood_ashouri_krim_2011, title={Effect of dynamic modulus measurement protocol on predicted pavement performance}, journal={Journal of the Association of Asphalt Paving Technologists}, author={Underwood, B.S. and Ashouri, M. and Krim, Y.R.}, year={2011}, pages={65–100} }
 @inproceedings{underwood_ashouri_kim_2011, title={Effect of dynamic modulus measurement protocol on predicted pavement performance}, booktitle={86th Annual Meeting of the Association of Asphalt Paving Technologists}, author={Underwood, B.S. and Ashouri, M. and Kim, Y.R.}, year={2011} }
 @article{underwood_yun_kim_2011, title={Experimental Investigations of the Viscoelastic and Damage Behaviors of Hot-Mix Asphalt in Compression}, volume={23}, ISSN={0899-1561 1943-5533}, url={http://dx.doi.org/10.1061/(ASCE)MT.1943-5533.0000197}, DOI={10.1061/(asce)mt.1943-5533.0000197}, abstractNote={In this paper, the characteristic behaviors of hot-mix asphalt (HMA) in compression are studied by using concepts from the viscoelastic continuum damage (VECD) modeling approach. Temperature and frequency sweep tests with and without confining pressure were performed to determine the linear viscoelastic properties of HMA. The analysis of these tests showed that HMA exhibits significant and reversible stress-hardening behavior. This behavior was subsequently modeled by using a model developed from similar efforts for granular materials. To prove the importance of considering this characteristic behavior, constant crosshead rate tests were performed and analyzed with and without stress hardening. The VECD analysis framework was utilized for this purpose. When stress-hardening behavior was taken into account, it was found that microdamage-induced softening occurred over a range of temperatures from 5°C to 55°C. This finding suggests that microdamage may be significant for conditions in which HMA rutting is a...}, number={4}, journal={Journal of Materials in Civil Engineering}, publisher={American Society of Civil Engineers (ASCE)}, author={Underwood, B. Shane and Yun, Taeyoung and Kim, Y. Richard}, year={2011}, month={Apr}, pages={459–466} }
 @inproceedings{underwood_kim_2011, title={Experimental investigation into the behavior of asphalt concrete at different length scales}, booktitle={2011 Engineering Mechanics Institute Conference}, author={Underwood, B.S. and Kim, Y.R.}, year={2011} }
 @article{underwood_kim_2011, title={Experimental investigation into the multiscale behaviour of asphalt concrete}, volume={12}, ISSN={1029-8436 1477-268X}, url={http://dx.doi.org/10.1080/10298436.2011.574136}, DOI={10.1080/10298436.2011.574136}, abstractNote={Multiscale modelling is an increasingly popular technique for understanding the mechanisms affecting the performance of asphalt concrete. Significant efforts have been made in computational modelling techniques; however, relatively little experimental data have been gathered on the effect of volumetric composition on the material behaviour, and no published data have been found assessing the sensitivity of computational models to these effects. It is believed that the overall importance of identifying and utilising the material with proper characteristics in these computational models has been largely overlooked. The purpose of this paper is to discuss the findings of an extensive experimental programme to identify the sensitivity of the dynamic shear modulus to changes in material composition. Tests were performed on four different material scales (asphalt binder to asphalt mixture). It is found that these materials can be very sensitive to changes in the volumetric composition, particularly in the case of asphalt mastics.}, number={4}, journal={International Journal of Pavement Engineering}, publisher={Informa UK Limited}, author={Underwood, B. Shane and Kim, Y. Richard}, year={2011}, month={Aug}, pages={357–370} }
 @article{underwood_yun_krim_2011, title={Experimental investigations of the viscoelastic and damage behaviors of hot mix asphalt in compression}, number={4}, journal={Journal of Materials in Civil Engineering}, author={Underwood, B.S. and Yun, T.Y. and Krim, Y.R.}, year={2011}, pages={459–466} }
 @phdthesis{underwood_2011, place={Raleigh, N.C}, title={Multiscale Constitutive Modeling of Asphalt Concrete}, school={North Carolina State University}, author={Underwood, B.S.}, year={2011} }
 @article{lacroix_underwood_kim_2011, title={Reduced Testing Protocol for Measuring the Confined Dynamic Modulus of Asphalt Mixtures}, volume={2210}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.3141/2210-03}, DOI={10.3141/2210-03}, abstractNote={Research project NCHRP 9–19 identifies the confined dynamic modulus as one of three favorable indicators for evaluating the rutting potential of a mixture. Though important, dynamic modulus testing at multiple confining pressures takes too long for state highway agencies to use it routinely. Therefore, several methods have been suggested to measure and predict confined dynamic modulus values without the need to run numerous tests. Experimental results show that the linear viscoelastic properties of an asphalt mixture are not affected by different confinements and that all confining stress effects are manifest in the elastic modulus at equilibrium, similar to unbound granular materials. The proposed method uses a Prony series representation of the dynamic modulus curve and master curve shift factors obtained from unconfined testing. This method uses the elastic modulus values predicted from a modified version of the universal material model to predict dynamic moduli at different levels of confinement. Beyond the typical AASHTO TP62 testing procedure under an unconfined condition, additional testing is conducted at 54°C at three levels of confinement. This reduced testing protocol provides reasonable results, with most errors less than 20%. The largest errors between the measured confined and unconfined data were generally overpredicted values at 54°C because the universal model overpredicted the elastic modulus. The applicability of this method is verified for the asphalt mixture performance tester as long as three levels less than 250 kPa are used, because 250 kPa is the maximum confining pressure that the tester can handle.}, number={1}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Lacroix, Andrew and Underwood, B. Shane and Kim, Y. Richard}, year={2011}, month={Jan}, pages={20–29} }
 @article{lacroix_underwood_krim_2011, title={Reduced testing protocol for measuring the confined dynamic modulus of asphalt mixtures}, journal={Transportation Research Record}, author={Lacroix, A. and Underwood, B.S. and Krim, Y.R.}, year={2011}, pages={20–29} }
 @article{shan_tan_underwood_kim_2011, title={Separation of Thixotropy from Fatigue Process of Asphalt Binder}, volume={2207}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.3141/2207-12}, DOI={10.3141/2207-12}, abstractNote={The fatigue performance of asphalt binder is critical to understanding the fatigue performance of asphalt mixtures. For the fatigue process to be modeled properly, the mechanism responsible for the fatigue behavior must be understood properly. In asphalt binder, it is widely accepted that the fatigue process is related to damage. However, some researchers have used the concept of thixotropy to describe the fatigue process in binder with equal success. If the real mechanism responsible for the observed reduction in modulus during a fatigue test is not properly understood, misinterpretation may occur. Such misinterpretation may lead to an improper assessment of a given material's quality and the acceptance of bad or rejection of good materials. This study attempted to separate the influence of thixotropy from other mechanisms during a fatigue experiment Tests were performed to characterize the exponential thixotropy model of four typical asphalt binders. The relationships between dynamic modulus and phase angle in a fatigue test and in a healing test were compared to determine the thixotropy-influence phase. According to the thixotropy model and fatigue test results, thixotropy is separated from the damage process for the entire fatigue test. A value of 50% |G * | after separation is put forward to evaluate the true fatigue characteristics of asphalt binder. The findings from this study, although based on a limited number of binders, suggest that thixotropy plays an important role in the fatigue characteristics of asphalt binder. The findings also provide a reasonable failure criterion for defining a fatigue evaluation index.}, number={1}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Shan, Liyan and Tan, Yiqiu and Underwood, B. Shane and Kim, Y. Richard}, year={2011}, month={Jan}, pages={89–98} }
 @article{shan_tan_underwood_krim_2011, title={Separation of thixotropy from fatigue process of asphalt binder}, journal={Transportation Research Record}, author={Shan, L. and Tan, Y. and Underwood, B.S. and Krim, Y.R.}, year={2011}, pages={89–98} }
 @article{shan_tan_underwood_kim_2011, title={Thixotropic Characteristics of Asphalt Binder}, volume={23}, ISSN={0899-1561 1943-5533}, url={http://dx.doi.org/10.1061/(ASCE)MT.1943-5533.0000328}, DOI={10.1061/(asce)mt.1943-5533.0000328}, abstractNote={Asphalt binder has thixotropic characteristics that significantly affect its overall performance, but specifically fatigue performance, healing performance, and high temperature performance. Therefore, a clear understanding of the thixotropy of asphalt binder, together with proper modeling, is useful in researching the performance of the material. However, research in this area is still in the early stages of investigation. For the study reported in this paper, the thixotropy of four types of asphalt binder is examined by using various methods to establish corresponding thixotropy models. The results show that the exponential thixotropy model, the extended exponential function, and the structural kinetic model can be established by using different methods, and they all reflect the thixotropy of asphalt binder to some extent.}, number={12}, journal={Journal of Materials in Civil Engineering}, publisher={American Society of Civil Engineers (ASCE)}, author={Shan, Liyan and Tan, Yiqiu and Underwood, B. Shane and Kim, Y. Richard}, year={2011}, month={Dec}, pages={1681–1686} }
 @article{underwood_kim_2011, title={Viscoelastoplastic Continuum Damage Model for Asphalt Concrete in Tension}, volume={137}, ISSN={0733-9399 1943-7889}, url={http://dx.doi.org/10.1061/(ASCE)EM.1943-7889.0000277}, DOI={10.1061/(asce)em.1943-7889.0000277}, abstractNote={A viscoelastoplastic continuum damage model has been derived and characterized for describing the behavior of asphalt concrete subject to an all-around confining pressure and deviatoric tension loading. The primary application of this model is to better understand the fatigue damage process in asphalt concrete pavements. As a result of this application and because of the bimodal behavior of this material outside the linear viscoelastic range, the modeling effort has focused primarily on the tensile characteristics. The developed model uses the elastic-viscoelastic correspondence principle, work-potential theory with damage mechanics, time-temperature superposition with growing damage, and strain-hardening viscoplasticity to arrive at a constitutive relationship. This relationship considers the experimentally observed transformation of asphalt concrete from an initially isotropic material to a transversely isotropic one by using a single-state parameter and three different damage functions. The relationship between these damage functions and the more conventional values of the modulus and Poisson’s ratio is shown to gain further physical insight into the material. Characterization of the model is performed by using constant crosshead rate monotonic tension tests with and without confinement and low strain temperature and frequency sweep complex modulus tests. The model is found to adequately describe the response of asphalt concrete under constant crosshead rate tension tests at various rates and two temperatures, the conditions that are not used in characterization.}, number={11}, journal={Journal of Engineering Mechanics}, publisher={American Society of Civil Engineers (ASCE)}, author={Underwood, Shane B. and Kim, Richard Y.}, year={2011}, month={Nov}, pages={732–739} }
 @article{shan_tan_underwood_kim_2010, title={Application of Thixotropy to Analyze Fatigue and Healing Characteristics of Asphalt Binder}, volume={2179}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.3141/2179-10}, DOI={10.3141/2179-10}, abstractNote={The fatigue performance of asphalt binder is critical to understanding the fatigue performance of asphalt mixtures, especially the effects of healing. Although research into the fatigue and healing characteristics of asphalt binder is found in numerous references, an efficient technique to evaluate these characteristics still does not exist. Thixotropy is a concept that may help explain the material behavior and provide an efficient evaluation technique. This property is related to the breakdown and buildup of microstructure that may cause the changes observed during fatigue and healing tests. Thus, tracking the thixotropy of asphalt binders may be a good method to study fatigue and healing. For this study, experiments were performed to characterize the fatigue and healing characteristics of three typical asphalt binders. Then a common thixotropic model was characterized with a relatively simple stepped-flow test and oscillation experiment. The resulting model shows good correlation with the measured fatigue and healing tests. This finding, though based on a limited number of binders, suggests that thixotropy may play a role in the fatigue and healing characteristics of asphalt binder.}, number={1}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Shan, Liyan and Tan, Yiqiu and Underwood, Shane and Kim, Y. Richard}, year={2010}, month={Jan}, pages={85–92} }
 @article{shan_tan_underwood_krim_2010, title={Application of thixotropy to analyze fatigue and healing characteristics of asphalt binder}, journal={Transportation Research Record}, author={Shan, L. and Tan, Y. and Underwood, B.S. and Krim, Y.R.}, year={2010}, pages={85–92} }
 @inproceedings{underwood_eslaminia_thirunavukkarasu_guddati_kim_2010, title={Asphalt concrete pavement response and fatigue performance modeling using advanced techniques}, booktitle={Proceedings of the 11th International Conference on Asphalt Pavements}, author={Underwood, B.S. and Eslaminia, M. and Thirunavukkarasu, S. and Guddati, M.N. and Kim, Y.R.}, year={2010} }
 @inproceedings{underwood_yun_kim_2010, title={Comparison of fundamental and engineering properties of asphalt concrete mixtures subjected to compressive and tensile loadings}, booktitle={Proceedings of the 11th International Conference on Asphalt Pavements}, author={Underwood, B.S. and Yun, T.Y. and Kim, Y.R.}, year={2010} }
 @article{sakhaeifar_underwood_kim_puccinelli_jackson_2010, place={Washington D.C}, title={Development of Artificial Neural Network Predictive Models for Populating the Dynamic Moduli of Long-Term Pavement Performance Sections}, volume={2181}, ISSN={["2169-4052"]}, DOI={10.3141/2181-10}, abstractNote={This paper presents a set of dynamic modulus (|E*|) predictive models to estimate the |E*| of hot-mix asphalt layers in long-term pavement performance (LTPP) test sections. These predictive models use artificial neural networks (ANNs) trained with different sets of parameters. A large national data set that covers a substantial range of potential input conditions was utilized to train and verify the ANNs. The data consist of mixture dynamic moduli measured with two test protocols: the asphalt mixture performance tester and AASHTO TP-62, under different aging conditions. The data include binder dynamic moduli values measured under different aging conditions. The ANN predictive models were trained and ranked with a common independent data set that was not used for calibrating any of the ANN models. A decision tree was developed from these rankings to prioritize the models for any available inputs. Next, the models were used to estimate the |E*| for the LTPP database materials and ultimately to characterize the master curve and shift factor function. To ensure adequate data quality, a series of quality control checks was developed and applied to grade the inputs and outputs for each prediction. Approximately 30% to 50% of all LTPP layers contained enough information to obtain reliable moduli predictions.}, number={1}, journal={Transportation Research Record: Journal of the Transportation Research Board}, author={Sakhaeifar, M.S. and Underwood, B.S. and Kim, Y.R. and Puccinelli, J. and Jackson, N.}, year={2010}, pages={88–97} }
 @article{sakhaei far_underwood_krim_puccinelli_jackson_2010, title={Development of artificial neural network predictive models for populating the dynamic modulus of ltpp sections}, volume={2181}, journal={Transportation Research Record}, author={Sakhaei Far, M.S. and Underwood, B.S. and Krim, Y.R. and Puccinelli, J. and Jackson, N.}, year={2010}, pages={88–97} }
 @article{hou_underwood_krim_2010, title={Fatigue performance prediction of north carolina mixtures using the simplified viscoelastic continuum damage model}, journal={Journal of the Association of Asphalt Paving Technologists}, author={Hou, T. and Underwood, B.S. and Krim, Y.R.}, year={2010}, pages={35–80} }
 @article{underwood_kim_guddati_2010, title={Improved calculation method of damage parameter in viscoelastic continuum damage model}, volume={11}, ISSN={1029-8436 1477-268X}, url={http://dx.doi.org/10.1080/10298430903398088}, DOI={10.1080/10298430903398088}, abstractNote={Modelling the performance of asphalt concrete using continuum damage theories is an approach that has gained international attention in recent years. These types of models are advantageous because they ignore many of the complicated physical interactions at the microscale level and instead characterise a material using macroscale observations. One such model, the viscoelastic continuum damage model, is used in this study to examine the fatigue performance of asphalt concrete mixtures. A mathematically rigorous exploration is undertaken to specialise the model for easy prediction and characterisation using cyclic fatigue tests on cylindrical specimens. This process reveals that certain theoretical shortcomings are evident in other similar models and corrects them with a newly developed model. The resulting model is capable of capturing the underlying material property, i.e. the damage characteristic curve, which is responsible for the performance of controlled stress, controlled crosshead strain and consta...}, number={6}, journal={International Journal of Pavement Engineering}, publisher={Informa UK Limited}, author={Underwood, B. Shane and Kim, Y. Richard and Guddati, Murthy N.}, year={2010}, month={Dec}, pages={459–476} }
 @article{yun_underwood_kim_2010, title={Time-Temperature Superposition for HMA with Growing Damage and Permanent Strain in Confined Tension and Compression}, volume={22}, ISSN={0899-1561 1943-5533}, url={http://dx.doi.org/10.1061/(ASCE)MT.1943-5533.0000039}, DOI={10.1061/(asce)mt.1943-5533.0000039}, abstractNote={The objective of this paper is to verify the time-temperature superposition (t-TS) principle for hot-mix asphalt (HMA) with growing damage and permanent strain at different confining pressures in both the tension and compression stress states. Dynamic modulus tests at various confining pressures were conducted both in tension compression and in compression. The results were investigated to evaluate the effects of confining pressure and stress on the thermorheological simplicity of HMA within the linear viscoelastic range. Constant crosshead rate tests, both in tension and in compression, and repetitive creep and recovery tests in compression were also performed to check the t-TS principle with growing damage and permanent strain level with regard to the effects of confining pressure and stress. The analysis results show that the HMA remains thermorheologically simple regardless of stress state, damage, and permanent strain level under the same confining pressure. However, confining pressure does have an effect on the dynamic modulus and shift factor, especially at a high temperature and/or low reduced frequency.}, number={5}, journal={Journal of Materials in Civil Engineering}, publisher={American Society of Civil Engineers (ASCE)}, author={Yun, Taeyoung and Underwood, B. Shane and Kim, Y. Richard}, year={2010}, month={May}, pages={415–422} }
 @article{mitchell_link_underwood_far_kim_2010, title={Using Limited Purchase Specification Tests to Perform Full Linear Viscoelastic Characterization of Asphalt Binder}, volume={38}, ISSN={0090-3973}, url={http://dx.doi.org/10.1520/JTE102591}, DOI={10.1520/jte102591}, abstractNote={The linear viscoelastic dynamic modulus, |E∗|, has become the primary material property of interest for asphalt concrete mixtures. The shift towards linear viscoelastic characterization of asphalt concrete is due in large part to national efforts to develop new fundamentally based pavement design tools and techniques. Within the pavement community, there is a substantial interest in using predictive models to estimate | E∗| because key structural design decisions are based on its value. Moreover, for many projects, these critical decisions must be made even before the materials are selected. In response to the need for predictive capability, numerous equations have been developed, but most require knowing the asphalt binder shear modulus, |G∗|. This property is currently measured as part of the purchase specification process, but it is not measured at enough temperatures and frequencies to be directly useful with these predictive models. Instead, agencies that want to use the predictive equations must complete additional testing that may require several days to complete and requires the purchase of more sophisticated equipment. It is the purpose of this paper to show ways that the specification data can be processed to provide nearly the same information as a more complete testing suite. This effort is possible because although the specification data are sparse, they still cover the range of conditions that need to be assessed. Additional surrogate models are needed to fully apply the proposed methodology, and the development and verification of these models are presented as well. The ability of the limited data calibration process to match characterization from more complete testing is demonstrated. Finally, it is shown that observed differences between the complete and limited calibration processes are reduced when applying two |E∗| predictive models.}, number={5}, journal={Journal of Testing and Evaluation}, publisher={ASTM International}, author={Mitchell, M. R. and Link, R. E. and Underwood, B. Shane and Far, Maryam Sadat Sakhaei and Kim, Y. Richard}, year={2010}, pages={102591} }
 @inproceedings{underwood_kim_2009, title={Analytical techniques for determining the endurance limit of hot mix asphalt concrete}, booktitle={2nd International Conference on Perpetual Pavements}, author={Underwood, B.S. and Kim, Y.R.}, year={2009} }
 @article{far_underwood_ranjithan_kim_jackson_2009, title={Application of Artificial Neural Networks for Estimating Dynamic Modulus of Asphalt Concrete}, volume={2127}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.3141/2127-20}, DOI={10.3141/2127-20}, abstractNote={This paper presents outcomes from a research effort to develop models for estimating the dynamic modulus (| E * |) of hot-mix asphalt (HMA) layers on long-term pavement performance test sections. The goal of the work is the development of a new, rational, and effective set of dynamic modulus | E * | predictive models for HMA mixtures. These predictive models use artificial neural networks (ANNs) trained with the same set of parameters used in other popular predictive equations: the modified Witczak and Hirsch models. The main advantage of using ANNs for predicting | E * | is that an ANN can be created for different sets of variables without knowing the form of the predictive relationship a priori. The primary disadvantage of ANNs is the difficulty in predicting responses when the inputs are outside of the training database (i.e., extrapolation). To overcome this shortcoming, a large data set that covers the complete range of potential input conditions is needed. For this study, modulus values from multiple mixtures and binders were required and were assembled from existing national efforts and from data obtained at North Carolina State University. The data consisted of measured moduli from both modified and unmodified mixtures from numerous geographical locations across the United States. Prediction models were developed by using a portion of the data from these databases and then verified by using the remaining data in the databases. When these new ANN models are used, the results show that the predicted and measured | E * | values are in close agreement.}, number={1}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Far, Maryam Sadat Sakhaei and Underwood, B. Shane and Ranjithan, S. Ranji and Kim, Y. Richard and Jackson, Newton}, year={2009}, month={Jan}, pages={173–186} }
 @inproceedings{underwood_hou_kim_2009, title={Application of simplified VECD modeling to the fatigue prediction of asphalt concrete mixtures}, booktitle={7th International RILEM Symposium on Advanced Testing and Characterization of Bituminous Materials}, author={Underwood, B.S. and Hou, E.T. and Kim, Y.R.}, year={2009} }
 @inproceedings{underwood_kim_2009, title={Asphalt pavement response and fatigue performance prediction with viscoelastic continuum damage modeling approach}, booktitle={2009 Pavement Prediction Symposium: Validation of Predictive Models Using Full-Scale and Field Pavement Performance}, author={Underwood, B.S. and Kim, Y.R.}, year={2009} }
 @inbook{kim_underwood_chehab_daniel_lee_yun_2009, title={Chapter 7. VEPCD Modeling of Asphalt Concrete with Growing Damage}, booktitle={Modeling of Asphalt Concrete}, publisher={New York :McGraw-Hill}, author={Kim, Y.R. and Underwood, B.S. and Chehab, G.R. and Daniel, J.S. and Lee, H.J. and Yun, Y.R.}, year={2009} }
 @article{underwood_kim_2009, title={Determination of the appropriate representative elastic modulus for asphalt concrete}, volume={10}, ISSN={1029-8436 1477-268X}, url={http://dx.doi.org/10.1080/10298430701827668}, DOI={10.1080/10298430701827668}, abstractNote={The National Cooperative Highway Research Program (NCHRP) 1-37A mechanistic-empirical pavement design guide (MEPDG) utilises the dynamic modulus of asphalt concrete in a multilayered elastic analysis to determine the primary responses in asphalt pavements. The dynamic modulus depends on temperature and loading frequency. In the MEPDG, the pulse time is used to determine the loading frequency. This methodology has been under scrutiny due to the large modulus it estimates. This paper evaluates several approximation methods, including the current MEPDG analysis, for the calculation of stresses and strains in linear viscoelastic materials by comparing analysis results with the solutions from the exact linear viscoelastic analysis. Sources of the errors that result from various approximation methods are discussed. Also, an alternative method to that of the MEPDG is proposed for determining the appropriate representative elastic modulus of asphalt concrete.}, number={2}, journal={International Journal of Pavement Engineering}, publisher={Informa UK Limited}, author={Underwood, B.S. and Kim, Y.R.}, year={2009}, month={Apr}, pages={77–86} }
 @article{underwood. b.s._y.r._s. thirunavukkarasu_m.n._2009, title={Response and fatigue performance modeling of ALF pavements using 3-D finite element analysis and a simplified viscoelastic continuum damage model}, journal={Journal of the Association of Asphalt Paving Technologists}, author={Underwood. B.S., Krim and Y.R., Savadatti and S. Thirunavukkarasu, S. and M.N., Guddati}, year={2009}, pages={829–868} }
 @inproceedings{underwood_kim_savadatti_thirunavukkarasu_guddati_2009, title={Simplified fatigue performance modeling of ALF pavements using VECD+3-D finite element modeling}, booktitle={7th International RILEM Symposium on Advanced Testing and Characterization of Bituminous Materials}, author={Underwood, B.S. and Kim, Y.R. and Savadatti, S. and Thirunavukkarasu, S. and Guddati, M.N.}, year={2009} }
 @article{sakhaei far_underwood_ranjithan_krim_jackson_2009, title={The application of artificial neural networks for estimating the dynamic modulus of asphalt concrete}, journal={Transportation Research Record}, author={Sakhaei Far, M.S. and Underwood, B.S. and Ranjithan, S.R. and Krim, Y.R. and Jackson, N.}, year={2009}, pages={173–186} }
 @inbook{kim_underwood_chehab_daniel_lee_yun_2009, place={Reston, VA}, title={VEPCD Modeling of Asphalt Concrete with Growing Damage}, booktitle={Modeling of Asphalt Concrete}, publisher={ASCE Press/McGraw Hill}, author={Kim, Y.R. and Underwood, B.S. and Chehab, G.R. and Daniel, J.S. and Lee, H.J. and Yun, T.Y.}, editor={Kim, Y.R.Editor}, year={2009}, pages={163–203} }
 @article{kim_baek_underwood_subramanian_guddati_lee_2008, title={Application of viscoelastic continuum damage model based finite element analysis to predict the fatigue performance of asphalt pavements}, volume={12}, ISSN={1226-7988 1976-3808}, url={http://dx.doi.org/10.1007/s12205-008-0109-x}, DOI={10.1007/s12205-008-0109-x}, number={2}, journal={KSCE Journal of Civil Engineering}, publisher={Springer Science and Business Media LLC}, author={Kim, Y. Richard and Baek, Cheolmin and Underwood, B. Shane and Subramanian, Vijay and Guddati, Murthy N. and Lee, Kwangho}, year={2008}, month={Mar}, pages={109–120} }
 @inproceedings{comparison of automated and manual data collection for pavement distresses_2008, booktitle={National Workshop on Highway Asset Inventory and Data Collection}, year={2008} }
 @article{underwood_krim_seo_lee_2008, title={Development of ViscoElastoPlastic Continuum Damage (VEPCD) model for response prediction of HMAs under tensile loading}, volume={28}, number={1}, journal={KSCE Journal of Civil Engineering}, author={Underwood, B.S. and Krim, Y.R. and Seo, Y. and Lee, K.H.}, year={2008}, pages={45–55} }
 @inproceedings{baek_underwood_subramanian_guddati_kim_lee_2008, title={Viscoelastic continuum damage model based finite element analysis of fatigue cracking}, booktitle={7th RILEM International Conference on Cracking in Pavements}, author={Baek, C. and Underwood, B.S. and Subramanian, V. and Guddati, M.N. and Kim, Y.R. and Lee, K.}, year={2008} }
 @article{underwood_krim_guddati_2006, title={Characterization and performance prediction of ALF mixtures using a viscoelastoplastic continuum damage model}, volume={75}, journal={Journal of the Association of Asphalt Paving Technologists}, author={Underwood, B.S. and Krim, Y.R. and Guddati, M.N.}, year={2006}, pages={577–636} }
 @inproceedings{underwood_kim_guddati_2006, title={Characterization and performance prediction of alf mixtures using a viscoelastoplastic continuum damage model}, booktitle={81st Annual Meeting of the Association of Asphalt Paving Technologists}, author={Underwood, B.S. and Kim, Y.R. and Guddati, M.N.}, year={2006} }
 @inproceedings{kim_underwood_mun_guddati_2006, title={Perpetual pavement evaluation using the viscoelastic continuum damage finite element program}, booktitle={Proceedings of the 2006 International Conference on Perpetual Pavement}, author={Kim, Y.R. and Underwood, B.S. and Mun, S. and Guddati, M.N.}, year={2006} }
 @inproceedings{underwood_kim_chehab_2006, title={Viscoelastoplastic continuum damage model of asphalt concrete in tension}, booktitle={10th International Conference on Asphalt Pavements}, author={Underwood, B.S. and Kim, Y.R. and Chehab, G.}, year={2006} }
 @inproceedings{underwood_kim_chehab_2006, title={Viscoelastoplastic continuum damage model of asphalt concrete in tension, proceedings of the 10th International Conference on Asphalt Pavements}, booktitle={International Society on Asphalt Pavements Symposium}, author={Underwood, B.S. and Kim, Y.R. and Chehab, G.}, year={2006} }
 @article{underwood_heidari_guddati_kim_2005, title={Experimental Investigation of Anisotropy in Asphalt Concrete}, volume={1929}, ISBN={["0-309-09403-8"]}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.1177/0361198105192900128}, DOI={10.3141/1929-28}, abstractNote={Accurate multiaxial characterization of asphalt concrete requires a thorough understanding of its anisotropic behavior. For that purpose a study has been conducted to examine the anisotropic properties of asphalt concrete in the linear viscoelastic range, with growing damage, and during volumetric deformation. Tests were conducted on specimens cored in the vertical and horizontal directions from gyratory-compacted specimens. Anisotropy was found to have no effect on the linear viscoelastic properties of the material. This finding is supported by subsequent results from monotonic constant crosshead rate uniaxial tension and uniaxial compression tests. It was also found that anisotropy contributes greatly to the behavior of asphalt concrete in compression, but shows little, if any, effect on tensile properties. In addition, the strong dependence of anisotropy on temperature and strain rate is presented. Finally, promising results from a simplified method of extracting the anisotropic behavior of asphalt concrete with the use of the hydrostatic test are also introduced.}, number={1}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Underwood, Shane and Heidari, A. Homayoun and Guddati, Murthy and Kim, Y. Richard}, year={2005}, month={Jan}, pages={238–247} }
 @article{underwood_heidari_guddati_krim_2005, title={Experimental investigation of anisotropy in asphalt concrete}, journal={Transportation Research Record}, author={Underwood, B.S. and Heidari, A.H. and Guddati, M. and Krim, Y.R.}, year={2005} }
 @article{underwood_kim_2003, title={Determination of Depth of Surface Cracks in Asphalt Pavements}, volume={1853}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.3141/1853-16}, DOI={10.3141/1853-16}, abstractNote={Nondestructive measurement of crack depths of asphalt pavements in situ could be a valuable tool for engineers in rehabilitation planning. Such measurements currently must be made by first coring or trenching a pavement and then measuring the crack by hand. Two methods for performing this task nondestructively are presented. The two methods, surface wave and ultrasonic, use the slowing effect that a crack has on a wave. Two signal-processing techniques were used to analyze the surface wave method—the fast Fourier transform (FFT) and the short kernel method (SKM). The FFT method provided a frequency spectrum that was used to find the energy carried by specific frequencies. The percent energy reduction (PER) was computed and plotted at each crack depth; this plot revealed that PER values increase as crack depth increases. The SKM method showed the wave velocity to decrease as the crack depth in creased. By comparing the wave velocity of the cracked pavement with that of the undamaged pavement, a phase velocity ratio plot was developed and was shown to be adequate for predicting crack depth. Ultrasonic testing proved to be a simpler and more direct method than surface wave testing. It was not necessary to know the wave properties of an undamaged pavement with this method, and a quantitative prediction of crack depth was obtained. While encouraging results were observed with both methods, ultrasonic testing showed the most promise for application because of the commercial availability of ultrasonic meters and the direct prediction of crack depth.}, number={1}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Underwood, Shane and Kim, Y. Richard}, year={2003}, month={Jan}, pages={143–149} }
 @article{underwood_krim_2003, title={Determination of depth of surface cracks in asphalt pavements}, journal={Transportation Research Record}, author={Underwood, B.S. and Krim, Y.R.}, year={2003} }
 @inproceedings{underwood_kim_2003, title={Determination of depth of surface cracks in asphalt pavements}, booktitle={82nd Annual Meeting of the Transportation Research Record}, author={Underwood, B.S. and Kim, Y.R.}, year={2003} }