@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{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{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{keshavarzi_mocelin_kim_2022, title={A Composite Model for Predicting the Coefficient of Thermal Contraction for Asphalt Concrete Mixtures}, volume={50}, ISSN={["1945-7553"]}, DOI={10.1520/JTE2021003}, number={1}, journal={JOURNAL OF TESTING AND EVALUATION}, author={Keshavarzi, Behrooz and Mocelin, Douglas and Kim, Y. Richard}, year={2022}, month={Jan}, pages={1–23} }
 @article{cao_kim_2022, title={A Triaxial Viscoplastic Model with Temperature Dependence for Asphalt Concrete Permanent Deformation}, volume={14}, ISSN={["1758-826X"]}, DOI={10.1142/S1758825122500235}, abstractNote={Asphalt concrete is a composite material comprised of aggregate skeleton and asphalt cement. Its permanent or viscoplastic (VP) deformation is characterized by time and temperature dependence, memory effect, and pressure sensitivity. To the best knowledge of the authors, there have been no VP models explicitly considering the nonlinear temperature effects in permanent deformation of asphalt concrete. In previous work, the authors developed a triaxial VP model that featured a VP relaxation spectrum and a modulus parameter Evp,∞. The spectrum was postulated as a material function representing the time dependence and memory effect, while Evp,∞ was only a function of the stress condition to capture the pressure dependence. The objective of this study was to incorporate temperature dependence into the model. It was achieved by introducing the concept of VP shift factor solely to translate the relaxation spectrum. This strategy was inspired by the time–temperature superposition principle in the viscoelastic (VE) theory. The shift factor was identified experimentally at three temperatures different from the model calibration temperature. The VP shift factor function was thus established, and comparison with its VE counterpart showed that the VP response exhibited greater temperature sensitivity. Numerical simulation was conducted at several temperatures to illustrate the nonlinear temperature effects on the VP deformation and relaxation of the internal stress that served as the hardening/softening variable.}, number={03}, journal={INTERNATIONAL JOURNAL OF APPLIED MECHANICS}, author={Cao, Wei and Kim, Y. Richard}, year={2022}, month={Apr} }
 @article{cao_lacroix_kim_2022, title={A triaxial linear viscoelastic characterization framework for asphalt concrete based on the 2S2P1D model}, volume={92}, ISSN={["1873-7285"]}, DOI={10.1016/j.euromechsol.2021.104469}, abstractNote={Asphalt concrete materials are known to exhibit pressure dependence in response to mechanical loading. However, for conventional dense-graded asphalt mixtures , only weak pressure sensitivity was noted in the relaxation spectrum, time-temperature shift factors, and low-temperature moduli. Given these facts, a triaxial linear viscoelastic characterization framework was developed, which consisted of a convenient experimental protocol for the confined dynamic modulus test and a modeling approach based on the 2S2P1D model. In this framework, the same relaxation spectrum and time-temperature equivalence were applied across all different confining conditions, while the pressure dependence was fully assigned to the equilibrium modulus . The resultant prediction errors in dynamic modulus were in general below or comparable to typical test variability. Numerical implementation of the modeling method in the time domain was accomplished via Prony discretization of the continuous relaxation spectrum, and was demonstrated via application to triaxial relaxation and creep data. The model's satisfactory performance suggested that the confining condition had an insignificant impact on the molecular processes occurring in the asphalt phase during relaxation, owing to the low aggregate mobility and thus minimal asphalt flow as restrained by the dense structure. Limitations of the proposed modeling scheme as well as methods available from the literature were revealed lastly upon asphalt concrete materials with unconventional gap and open gradations. • The test protocol included standard .|E*| test and confined only at the highest temperature • The modeling assumed a single relaxation spectrum and time-temperature equivalence. • Pressure dependence was solely assigned to the equilibrium modulus. • Asphalt molecular relaxation processes were pressure insensitive in the dense structure. • Unconventionally graded mixtures exhibited full-range pressure sensitivity.}, journal={EUROPEAN JOURNAL OF MECHANICS A-SOLIDS}, author={Cao, Wei and Lacroix, Andrew and Kim, Y. Richard}, year={2022} }
 @article{bueno_schuster_specht_pereira_nascimento_kim_brenner_2022, title={Asphalt pavement design optimisation: a case study using viscoelastic continuum damage theory}, volume={23}, ISSN={["1477-268X"]}, DOI={10.1080/10298436.2020.1788030}, abstractNote={Fatigue cracking is the main type of distress in flexible pavements in Brazil. Numerical models that are based on viscoelastic continuum damage (VECD) theory can help to explain the damage evolutio...}, number={4}, journal={INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING}, author={Bueno, Lucas Dotto and Schuster, Silvio Lisboa and Specht, Luciano Pivoto and Pereira, Deividi da Silva and Nascimento, Luis Alberto Herrmann and Kim, Youngsoo Richard and Brenner, Maira Geane Birgeier}, year={2022}, month={Mar}, pages={1070–1082} }
 @article{spadoni_ingrassia_mocelin_kim_canestrari_2022, title={Comparison of asphalt mixtures containing polymeric compounds and polymer-modified bitumen based on the VECD theory}, volume={349}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2022.128725}, abstractNote={• Under the same volumetrics, the mixes have similar stiffness and fatigue resistance. • In the field, the mixtures modified with the dry method show a workability issue. • The mixtures modified with the dry method can be more prone to thermal damage. • An intermediate stiffness can ensure limited bottom-up cracking and thermal damage. • The polymer compounds improve the performance of a mixture with neat bitumen. The ‘dry’ method that can be used to produce modified asphalt mixtures is a less expensive, less energy-consuming, and faster process than the well-established ‘wet’ method. Moreover, the dry method allows the incorporation of hard plastics, even those plastics obtained from waste products. Although researchers agree that the dry method can improve the stiffness and rutting resistance (i.e., high-temperature performance) of asphalt mixtures, they have conflicting opinions regarding mixture fatigue and cracking resistance. In this regard, this paper aims to evaluate, through the application of viscoelastic continuum damage theory, the fatigue behavior of two compound asphalt mixtures that have been modified using the dry method. One of the studied compounds is composed of plastomeric polymer and the other is composed of waste plastic with the addition of graphene. A reference mixture containing polymer-modified bitumen (representing the wet modification method) was used for comparison. The experimental program involved dynamic modulus tests and uniaxial cyclic fatigue tests of laboratory-compacted specimens and cores extracted from full-scale field test sections. The test results from the laboratory-compacted specimens and field cores were input to FlexPAVE TM for pavement performance simulations. Under the same volumetric conditions, the three dense-graded mixtures broadly had comparable stiffness and fatigue resistance values at the material level. However, in the pavement-level simulations, the reference mixture exhibited much less damage after 30 years of service than the compound mixtures. Concerning the field test track, the air void contents of the mixtures varied due to workability issues related to the presence of the compounds. Optimum performance was obtained for asphalt layers that could be characterized by an intermediate stiffness level that ensured an adequate load distribution without negative consequences for the mixture’s fatigue resistance and thermal resistance.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Spadoni, Sara and Ingrassia, Lorenzo Paolo and Mocelin, Douglas and Kim, Y. Richard and Canestrari, Francesco}, year={2022}, month={Sep} }
 @article{bueno_pereira_specht_nascimento_schuster_fritzen_kim_back_2022, title={Contribution to the mechanistic-empirical roughness prediction in asphalt pavements}, ISSN={["2164-7402"]}, DOI={10.1080/14680629.2022.2029758}, journal={ROAD MATERIALS AND PAVEMENT DESIGN}, author={Bueno, Lucas Dotto and Pereira, Deividi da Silva and Specht, Luciano Pivoto and Nascimento, Luis Alberto Herrmann and Schuster, Silvio Lisboa and Fritzen, Marcos Antonio and Kim, Youngsoo Richard and Back, Ana Helena}, year={2022}, month={Feb} }
 @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{saleh_braswell_elwardany_rad_castorena_kim_2022, place={OXON, ENGLAND}, title={Field Calibration and Validation of a Pavement Aging Model}, volume={2}, ISSN={1477-268X}, url={https://doi.org/10.1080/10298436.2022.2027416}, DOI={10.1080/10298436.2022.2027416}, abstractNote={A pavement aging model (PAM) is established by calibrating and validating the NCHRP 09–54 kinetics model's predictions against field core measurements. Field cores, laboratory-mixed loose mixtures, and binders from a wide range of pavement sections are used, including both conventional hot mix asphalt (HMA) mixtures and modern materials (i.e. reclaimed asphalt pavement (RAP), warm mix asphalt (WMA), and polymer modified asphalt (PMA)). Field aging levels are measured at different depths from binder extracted and recovered from in-service field cores. The original component materials of these pavement sections are aged in the laboratory and used to calibrate the kinetics model. The measured field aging levels are compared against those predicted from the kinetics model to inform a depth and time dependent field calibration function for the PAM. The validation of PAM using an independent set of field sections shows that, within the limited data used in this study, the calibrated PAM may be able to predict the aging of the conventional HMA, RAP, WMA, and PMA mixtures. The PAM predictions are lastly found to outmatch the predictions by the Global Aging System (GAS) model.}, journal={International Journal of Pavement Engineering}, publisher={TAYLOR & FRANCIS LTD}, author={Saleh, N.F. and Braswell, E. and Elwardany, M. and Rad, F.Y. and Castorena, C. and Kim, Y.R.}, year={2022}, month={Feb} }
 @article{safavizadeh_cho_kim_2022, title={Interface shear strength and shear fatigue resistance of fibreglass grid-reinforced asphalt concrete test specimens}, volume={23}, ISSN={["1477-268X"]}, DOI={10.1080/10298436.2020.1861447}, abstractNote={This research was undertaken to study the effects of grid opening size and tack coat type on both the shear strength and shear fatigue resistance at the interface of fibreglass grid-reinforced asph...}, number={8}, journal={INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING}, author={Safavizadeh, Seyed Amirshayan and Cho, Seong-Hwan and Kim, Youngsoo Richard}, year={2022}, month={Jul}, pages={2531–2542} }
 @article{ragni_sudarsanan_canestrari_kim_2022, title={Investigation into fatigue life of interface bond between asphalt concrete layers}, volume={23}, ISSN={["1477-268X"]}, DOI={10.1080/10298436.2021.1894420}, abstractNote={A proper interface bond between adjacent asphalt concrete layers ensures the layers to act monolithically to withstand traffic and thermal loading. The presence of a weak interface results in delamination, slippage and fatigue cracks thereby affects the pavement performance; hence, requires careful evaluation. The objectives of this investigation are three-fold. The first objective is to develop a test protocol to investigate the damage characteristics of the interface bond. The proposed test applies a 5 Hz cyclic shear load on a double-layered asphalt concrete specimen using a Modified Advanced Shear Tester at 23°C. The second objective is to determine the effect of interlayer shear modulus on the pavement response of typical pavement sections using numerical simulations. The interface material model property used in this study is a set of arbitrary values that lies within the typical range of interlayer shear modulus values observed during cyclic shear tests. The third objective is to propose a failure criterion for shear fatigue testing that is based on the critical tensile strain obtained during pavement response analysis. The test outcomes show that specimens with a tack coat at the interface exhibit a significant increase in shear fatigue life resistance compared to specimens with no tack coat.}, number={10}, journal={INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING}, author={Ragni, Davide and Sudarsanan, Nithin and Canestrari, Francesco and Kim, Y. Richard}, year={2022}, month={Aug}, pages={3371–3385} }
 @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{zeng_lee_kim_2021, title={Determination of Dynamic Modulus Master Curve of Damaged Asphalt Pavements for Mechanistic-Empirical Pavement Rehabilitation Design}, volume={2}, ISSN={["2169-4052"]}, DOI={10.1177/0361198121996708}, abstractNote={For pavement rehabilitation design, the current mechanistic–empirical (ME) pavement design guide provides three levels of analysis methodology to determine dynamic modulus master curves for existing asphalt pavements. First, the ME pavement design guide recommends that Witczak’s predictive equation is employed to obtain the “undamaged” modulus master curve. Depending on the chosen level of analysis, either a falling weight deflectometer test (Level 1) or a condition survey (Levels 2 and 3) is conducted to determine the damage factor(s). The damage factor is used to shift the undamaged master curve downward to match the field conditions and obtain the “damaged” master curve. In this study, two pavement structures in North Carolina Highway 96 were selected to evaluate the accuracy of the ME pavement design guide using its three levels of analysis. Because this roadway is a multilayer full-depth pavement, the extracted field cores were divided into a top layer, bottom layer, and total core for investigative and comparative purposes. Accordingly, both laboratory measurements and pavement ME predictions of the dynamic modulus values were conducted separately. Results show that the predicted undamaged master curves are always higher than the measured master curves and Levels 1, 2, and 3 can each lead to significantly different damaged master curves. Considering both efficiency and accuracy for transportation agency practice, the Level 1 method is recommended, and if the existing pavement is a multilayered asphalt pavement, a total core extracted from all the layers is recommended to generate the input properties for Witczak’s predictive equation.}, journal={TRANSPORTATION RESEARCH RECORD}, author={Zeng, Zhe and Lee, Kangjin and Kim, Youngsoo Richard}, year={2021}, month={Feb} }
 @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{ashouri_wang_choi_kim_2021, title={Development of healing model and simplified characterization test procedure for asphalt concrete}, volume={271}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2020.121515}, abstractNote={Fatigue cracking is one of the major distresses in asphalt pavement. Numerous and significant efforts have been undertaken to predict the fatigue life of pavements. One of the mechanisms that affects fatigue life is healing, and thus, including healing in fatigue performance prediction models is necessary. For this study, twelve healing tests at three temperatures and four rest periods were conducted to evaluate the healing characteristics of asphalt materials. The percentage of healing (%Hs) used in this study is defined as the ratio of the internal state variable (S) before the rest period to the incremental internal state variable due to the rest period. A %Hs mastercurve was constructed by applying the time–temperature superposition (t-TS) principle to the %Hs versus rest period curves and thereby proved that the t-TS principle works for healing. The %Hs mastercurves at different damage levels were shifted vertically to construct one reference %Hs mastercurve. The amount of vertical shifting is referred to as the vertical healing shift factor. The reference %Hs mastercurve with the vertical healing shift factor and t-TS principle led to the proposed shift healing model as a function of rest period, temperature, and damage level. A test protocol to calibrate the model also is suggested in this work. The protocol requires only three specimens, and thus, testing can be completed within a day. The proposed shift healing model characterized by the suggested protocol test was implemented successfully in twelve healing tests to predict the healing behavior of the test specimens, which indicates the prediction capability of the suggested model and test protocol.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Ashouri, Morteza and Wang, Yizhuang and Choi, Yeong-Tae and Kim, Youngsoo}, year={2021}, month={Feb} }
 @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{wang_kim_2021, title={Effects of Aging on Pavement ME Predictions of Permanent Deformation for HMA and WMA Mixtures}, volume={147}, ISSN={["2573-5438"]}, DOI={10.1061/JPEODX.0000319}, abstractNote={AbstractThis paper presents an experimental investigation into the effects of aging on the rutting performance of both hot-mix asphalt (HMA) and warm-mix asphalt (WMA) mixtures and an analytical st...}, number={4}, journal={JOURNAL OF TRANSPORTATION ENGINEERING PART B-PAVEMENTS}, author={Wang, Yizhuang David and Kim, Youngsoo Richard}, year={2021}, month={Dec} }
 @article{jia_sheng_lv_kim_zhao_meng_xiong_2021, title={Effects of bamboo fiber on the mechanical properties of asphalt mixtures}, volume={289}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2021.123196}, abstractNote={Fiber addition could enhance the permanent deformation and crack resistance of the asphalt mixture. Previous research has found the effect of fibers on asphalt mixtures, while bamboo fibers have been overlooked. Bamboo fibers involve strength and toughness properties, and the addition of bamboo fibers is significant for studying the improvement of the mechanical performance in asphalt mixtures. In this paper, the reinforcing effects of bamboo fiber on the mechanical properties of asphalt binders and mixtures are investigated under various loading and temperature conditions. Bending beam rheometer tests and frequency sweep tests using dynamic shear rheometer were conducted in this study to characterize the relevant properties of asphalt binder with different fiber contents. A Superpave gyratory compactor was used to produce asphalt mixture specimens with 0.3% bamboo fiber. In addition, dynamic modulus, stress sweep rutting, and cyclic fatigue tests were conducted to investigate the mechanical properties of the test specimens. The results indicate that the high-temperature shear strength and low-temperature flexibility of the asphalt binders were improved by the inclusion of bamboo fiber. The inclusion of only 0.3% bamboo fiber improved the rutting resistance and fatigue life of the asphalt mixtures. In general, the dynamic modulus values of the asphalt mixtures increased and the phase angles decreased with the addition of bamboo fiber. The performance test results show that the inclusion of bamboo fiber enhances the stiffness and cracking performance of asphalt mixture at the intermediate temperature, but the improvements are not significant at high temperature. The research could evaluate the mechanical properties of bamboo fiber asphalt mixtures, and provide a reference for the engineering application of bamboo fiber in asphalt mixtures.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Jia, Haichuan and Sheng, Yanping and Lv, Hongli and Kim, Y. Richard and Zhao, Xiaorui and Meng, Jiandang and Xiong, Rui}, year={2021}, month={Jun} }
 @article{keshavarzi_mocelin_kim_2021, title={Predicting Thermal Stress Restrained Specimen Test Fracture Temperatures Using the Dissipated Pseudo Strain Energy Criterion}, volume={147}, ISSN={["2573-5438"]}, DOI={10.1061/JPEODX.0000236}, abstractNote={AbstractThermal cracking is the predominant failure mode for asphalt pavements constructed in regions with severe air temperature drops or significant daily temperature variations. The thermal stre...}, number={1}, journal={JOURNAL OF TRANSPORTATION ENGINEERING PART B-PAVEMENTS}, author={Keshavarzi, Behrooz and Mocelin, Douglas and Kim, Youngsoo Richard}, year={2021}, month={Mar} }
 @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{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={• Mixture samples were obtained from different truck loads during the field projects. • Four corners to develop the IVR were selected based on the mixture samples' AQCs. • Two rutting tests were conducted for the four corners and verification samples. • The IVRs were successfully developed and could predict the rutting performance well. • The field projects were evaluated by the developed IVRs. 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{keshavarzi_kim_2020, title={A dissipated pseudo strain energy-based failure criterion for thermal cracking and its verification using thermal stress restrained specimen tests}, volume={233}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2019.117199}, abstractNote={Low-temperature cracking is one of the most prevalent types of distress in asphalt concrete pavements in regions where the air temperature undergoes a significant daily drop. This paper proposes a failure criterion that correlates the dissipated pseudo strain energy (DPSE) at the time of failure with the reduced strain rate. Uniaxial direct tension monotonic tests, axial compression dynamic modulus tests, and direct tension cyclic fatigue tests were performed using the Asphalt Mixture Performance Tester (AMPT) for a wide range of asphalt mixtures with different reclaimed asphalt pavement (RAP) contents, binder contents, virgin binder performance grades, and aging levels. The results show that the simplified viscoelastic continuum damage (S-VECD) model, which is characterized by the dynamic modulus and cyclic fatigue test results, can predict the stress-strain behavior of a given mixture subjected to monotonic tests at different temperatures and loading rates. This finding allows the prediction of DPSE in monotonic tension tests using the S-VECD model. The thermal stress restrained specimen test (TSRST) was then used to verify the DPSE-based failure criterion and the ability of the S-VECD model to predict thermal fracture behavior. The study results show that the predicted fracture temperatures match the measured ones for the study mixtures with reasonable accuracy. The study also used data from mixtures whose RAP contents, binder contents, virgin binder grades, and aging levels were systematically altered to verify the reasonableness of the proposed procedure to evaluate the differences in thermal fracture performance that are due to changes in these factors. The ability to predict the fracture stress and fracture temperature measured via the TSRST using the S-VECD model and the suggested DPSE failure criterion is of substantial practical and technical importance because it allows the prediction of both fatigue cracking and thermal cracking using a single set of tests, i.e., AMPT dynamic modulus and cyclic fatigue tests.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Keshavarzi, Behrooz and Kim, Y. Richard}, year={2020}, month={Feb} }
 @article{sudarsanan_fonte_kim_2020, title={Application of time-temperature superposition principle to pull-off tensile strength of asphalt tack coats}, volume={262}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2020.120798}, abstractNote={Abstract Flexible pavements are multilayered structures that are designed to withstand vehicular traffic and thermal loading. Tack coat provides the bonding between these multilayers, which is a critical mechanism to provide a pavement with the monolithic action of asphalt layers to resist traffic and thermal loading, thereby dictating the pavement’s service life. Asphalt binder bond strength (BBS) is an indicator that can be used to evaluate the interlayer bonding ability of tack coat and changes as a function of temperature and loading rate. The focus of this paper is to prove that the time-temperature superposition principle is applicable to the BBS of various tack coat materials. In order to achieve this goal, BBS and dynamic shear rheometer (DSR) tests were conducted on four different tack coats, CRS-2, CRS-1h, NTCRS-1hM, and Ultrafuse. The Pneumatic Adhesion Tensile Testing Instrument (PATTI) was used to determine the BBS at 13 different temperatures ranging from 5 °C to 53 °C. The BBS data showed that adhesive failures between the binder and pull stub of PATTI caused the drop of BBS below 5 °C to 15 °C for hard (CRS-1h) and Non-tracking (NTCRS-1hM, Ultrafuse) tack coat. In addition to the BBS test, DSR tests were performed on the emulsion residue to measure the time-temperature shift factors at the reference temperature of 20 °C. It was found that the time-temperature shift factors determined from the DSR tests could be successfully used to shift the BBS vs. stress rate curves to construct the mastercurve for all four tack coat materials at a residual application rate of 0.14 L/m2 (0.03 Gal/yd2) as long as the BBS test exhibited cohesive failure between the binder and pull-off stubs. A simple method based on the BBS values at two temperatures is proposed to predict the mastercurve for routine characterization of the BBS mastercurve. No definite trend in the BBS mastercurve emerged among the different tack coat application rates for the different tack coats.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Sudarsanan, Nithin and Fonte, Benjamin Robert and Kim, Youngsoo Richard}, year={2020}, month={Nov} }
 @article{jeong_adams_kim_2020, title={Chip Seal Construction Variability and Its Impact on Performance}, volume={146}, ISSN={["2573-5438"]}, url={https://doi.org/10.1061/JPEODX.0000218}, DOI={10.1061/JPEODX.0000218}, abstractNote={This paper presents findings obtained from field and laboratory tests that were designed to assess chip seal construction variability in comparison to the targeted design, and to investigate the impact of any variability on the performance of chip seal treatments. The research approach involved three double-seal pavements in North Carolina. Granite 78M and No. 14 aggregate and CRS-2L emulsion were used in the construction. Chip seal specimens were sampled from each of the three test sections, and the aggregate application rate (AAR) and emulsion application rate (EAR) were determined using ignition oven tests. Chip seal performance was evaluated in terms of aggregate loss and bleeding using a third-scale model mobile load simulator (MMLS3). In addition, the fresh emulsions used in the test sections and the residue were tested using a rotational viscometer and dynamic shear rheometer, respectively. The construction variability reflected in the AARs and EARs and the emulsion residue properties were used to describe the aggregate loss and bleeding performance as determined by the MMLS3.}, number={4}, journal={JOURNAL OF TRANSPORTATION ENGINEERING PART B-PAVEMENTS}, publisher={American Society of Civil Engineers (ASCE)}, author={Jeong, Jaehoon and Adams, Javon M. and Kim, Y. Richard}, year={2020}, month={Dec} }
 @article{wang_jeong_kim_2020, title={Comparison of Treatment Timing between Aggregate Base and Full-Depth Asphalt Roads}, volume={146}, ISSN={["2573-5438"]}, url={https://doi.org/10.1061/JPEODX.0000216}, DOI={10.1061/JPEODX.0000216}, abstractNote={AbstractAggregate base-course (ABC) pavements and full-depth asphalt (FDA) pavements are the two most commonly used types of asphalt pavements. During pavement design and pavement management, engin...}, number={4}, journal={JOURNAL OF TRANSPORTATION ENGINEERING PART B-PAVEMENTS}, publisher={American Society of Civil Engineers (ASCE)}, author={Wang, Yizhuang David and Jeong, Jaehoon and Kim, Youngsoo Richard}, year={2020}, month={Dec} }
 @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{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{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{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{adams_castorena_kim_2019, title={Construction quality acceptance performance-related specifications for chip seals}, volume={6}, ISSN={["2095-7564"]}, DOI={10.1016/j.jtte.2019.05.003}, abstractNote={The research described herein details the establishment of a framework for construction quality acceptance performance-related specifications (PRS) for chip seal surface treatments. This paper establishes acceptance quality characteristics (AQCs) and relationships between the AQCs and related chip seal performance measures. This work is a critical step in developing PRS for constructed chip seal treatments and establishing suitable guidelines for the PRS. The main objective of this paper is to determine appropriate test methods to evaluate each defined AQC. The relationships that are established between the AQCs and chip seal performance are used to define performance ranges and threshold values for a particular performance measure. These performance ranges and threshold values then can be used to define pay factors for the constructed chip seal section. The threshold values and pay factors for each AQC described herein are preliminary recommendations and require further validation prior to implementation. However, this research demonstrates how these PRS would be utilized to ensure acceptable chip seal construction quality in the field. The developed construction quality acceptance PRS framework uses the percent within limits (PWL) concept to determine whether a chip seal lot passes the PRS threshold values and whether the contractor receives full pay, is subject to a pay penalty, or fails the construction PRS and must correct the chip seal within the first year in service, which constitutes the typical warranty period for contracted chip seal work. Finally, recommendations are made as to the next steps in the development and validation of these construction quality acceptance PRS that are needed for implementation by contractors and state roadway maintenance agencies. • A framework is developed for the performance-related specification of chip seal surface treatments. • Relationships are identified between acceptance quality characteristics (AQCs) and critical chip seal performance measures. • Practical test methods are identified to measure the AQCs. • Recommendations are made for the establishment and future implementation of pay factors for chip seal construction.}, number={4}, journal={JOURNAL OF TRAFFIC AND TRANSPORTATION ENGINEERING-ENGLISH EDITION}, author={Adams, Javon and Castorena, Cassie and Kim, Y. Richard}, year={2019}, month={Aug}, pages={337–348} }
 @article{niu_chen_richard kim_sheng_geng_guan_xiong_yang_2019, title={Damage assessment of asphalt concrete with composite additives at the FAM–coarse aggregate interfacial zone}, volume={198}, ISSN={0950-0618}, url={http://dx.doi.org/10.1016/J.CONBUILDMAT.2018.11.272}, DOI={10.1016/J.CONBUILDMAT.2018.11.272}, abstractNote={Abstract Asphalt concrete (AC) is of a three-phase system comprising of coarse aggregate, FAM (fine aggregate matrix) and interfacial zones (ITZ). The interfacial zone between FAM and coarse aggregate plays a critical role which determines the mechanical performance. This paper presents a numerical simulation of the mechanical behavior of ITZ, to quantitatively analyze damage of AC with or without composite additives. The results indicated that damage at the ITZ was initiated from the top area followed by a downward propagation. Both cohesive and adhesive damage of AC with composite additives were less serious than that without composite additives, and the damage severity was greatly affected by the thickness of FAM layer. The most serious damage was observed for the thick FAM layer under a rectangular loading pattern. As such, the adhesive damage area and cohesive damage area of AC with composite additives were found to be 1.7% and 33.8% respectively, less than that without composite additives.}, journal={Construction and Building Materials}, publisher={Elsevier BV}, author={Niu, Dongyu and Chen, Huaxin and Richard Kim, Y. and Sheng, Yanping and Geng, Jiuguang and Guan, Bowen and Xiong, Rui and Yang, Zhengxian}, year={2019}, month={Feb}, pages={587–596} }
 @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{wang_kim_2019, title={Development of a pseudo strain energy-based fatigue failure criterion for asphalt mixtures}, volume={20}, ISSN={["1477-268X"]}, DOI={10.1080/10298436.2017.1394100}, abstractNote={This paper presents a new energy-based failure criterion that is based on the simplified viscoelastic continuum damage model. This study found that the average reduction in pseudo stiffness up to f...}, number={10}, journal={INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING}, author={Wang, Yizhuang and Kim, Y. Richard}, year={2019}, month={Oct}, pages={1182–1192} }
 @article{etheridge_wang_kim_kim_2019, title={Evaluation of Fatigue Cracking Resistance of Asphalt Mixtures Using Apparent Damage Capacity}, volume={31}, ISSN={["1943-5533"]}, DOI={10.1061/(ASCE)MT.1943-5533.0002870}, abstractNote={AbstractThe prediction of fatigue cracking is one of the critical items to assess the service life of flexible pavements. Accordingly, researchers have developed several test methods and index para...}, number={11}, journal={JOURNAL OF MATERIALS IN CIVIL ENGINEERING}, author={Etheridge, Robert Austin and Wang, Yizhuang David and Kim, S. Sonny and Kim, Y. Richard}, year={2019}, month={Nov} }
 @article{geng_chen_shang_li_kim_kuang_2019, title={The Performance of Super Absorbent Polymer (SAP) Water-Retaining Asphalt Mixture}, volume={12}, ISSN={["1996-1944"]}, DOI={10.3390/ma12121964}, abstractNote={Lowering the temperature of the road surface is one efficient way to alleviate the urban heat island effect. Therefore water-retaining asphalt mixture was produced by adding super absorbent polymer (SAP) containing cement mortar to the porous asphalt mixture. In this study, the water absorption capacity, mechanical strength and fluidity of the cured water-retaining mortar were investigated to determine the optimum SAP dosage in water-retaining mortar. Furthermore, the microstructure of the hardened water-retaining mortar was studied using scanning electron microscopy (SEM) to determine the morphology and distribution of SAP in the final product, which may help to understand the influence of SAP on water retention performance and decipher its underlying mechanism. Compared to the raw porous asphalt mixture, the water-retaining asphalt mixture showed good moisture susceptibility (retained stability (RS) ≥ 88.2%, tensile strength ratio (TSR) ≥ 81.8%), good rutting resistance (9336–10,552 times/mm) and low temperature crack resistance (3383–3621 MPa), as well as significant cooling effects (10–12 °C). The results illustrate that the prepared SAP water-retaining asphalt mixture has good potential in reducing dust and enhancing road performance.}, number={12}, journal={MATERIALS}, author={Geng, Jiuguang and Chen, Mingyuan and Shang, Tao and Li, Xun and Kim, Y. Richard and Kuang, Dongliang}, year={2019}, month={Jun} }
 @article{rad_elwardany_castorena_kim_2018, title={Evaluation of Chemical and Rheological Aging Indices to Track Oxidative Aging of Asphalt Mixtures}, volume={2672}, ISSN={["2169-4052"]}, DOI={10.1177/0361198118784138}, abstractNote={Oxidative age hardening in asphalt binder leads to embrittlement. Embrittled asphalt is prone to fatigue and thermal cracking. Therefore, the ability to predict asphalt binder oxidative age hardening within a pavement throughout its service life could inform improved pavement material selection, design, and maintenance practices. Studying the evolution of oxidative aging requires the use of key properties to track oxidation levels, termed aging index properties (AIPs) here. The objective of this study is to identify suitable rheological and chemical AIPs to track oxidation levels in asphalt materials. A wide range of laboratory and field aged materials were evaluated in this study. A range of chemical AIPs determined by Fourier transform infrared spectroscopy (FTIR) absorbance peaks and areas were evaluated based on their correlation with laboratory aging duration. Rheological AIPs were evaluated based on the strength of their relationship to the chemical changes induced by oxidation. The rheological AIPs evaluated included the dynamic shear modulus, zero shear viscosity, Glover-Rowe parameter, and crossover modulus. The chemical AIP evaluation that most strongly correlated with laboratory aging duration is the carbonyl plus the sulfoxide absorbance peaks. The results indicate that both the dynamic shear modulus and Glover-Rowe parameter constitute rheological AIPs that relate directly to the chemical changes induced by oxidation.}, number={28}, journal={TRANSPORTATION RESEARCH RECORD}, author={Rad, Farhad Yousefi and Elwardany, Michael D. and Castorena, Cassie and Kim, Y. Richard}, year={2018}, month={Dec}, pages={349–358} }
 @article{wang_keshavarzi_kim_2018, title={Fatigue Performance Analysis of Pavements with RAP Using Viscoelastic Continuum Damage Theory}, volume={22}, ISSN={["1976-3808"]}, DOI={10.1007/s12205-018-2648-0}, number={6}, journal={KSCE JOURNAL OF CIVIL ENGINEERING}, author={Wang, Yizhuang David and Keshavarzi, Behrooz and Kim, Youngsoo Richard}, year={2018}, month={Jun}, pages={2118–2125} }
 @article{wang_keshavarzi_kim_2018, title={Fatigue Performance Prediction of Asphalt Pavements with FlexPAVE (TM), the S-VECD Model, and D-R Failure Criterion}, volume={2672}, ISSN={["2169-4052"]}, DOI={10.1177/0361198118756873}, abstractNote={Reliable predictions of asphalt materials and pavement performance are important elements in mixture design, mechanistic-empirical pavement design, and performance-related specifications. This paper presents FlexPAVE™, a pavement performance prediction program. FlexPAVE™ is a three-dimensional finite element program that is capable of moving load analysis under realistic climatic conditions. It utilizes the simplified viscoelastic continuum damage (S-VECD) model to predict asphalt pavement fatigue life. This S-VECD model currently incorporates the so-called G R failure criterion to define the failure of asphalt mixtures. In this study, a new failure criterion for the S-VECD model, designated as the D R criterion, has been developed to remedy some of the shortcomings of the G R failure criterion. This D R criterion has been implemented successfully in FlexPAVE TM . In this paper, FlexPAVE TM is used to simulate the fatigue performance of field test sections. These test sections include various pavement structures, such as perpetual pavements and accelerated load facility test pavements in the United States, South Korea, and China, as well as various materials, such as warm-mix asphalt, reclaimed asphalt pavement, and mixtures with modified binders. The D R -based FlexPAVE TM predictions have yielded good agreement with the field measurements and show more reasonable trends compared to predictions obtained using the G R failure criterion.}, number={40}, journal={TRANSPORTATION RESEARCH RECORD}, author={Wang, Yizhuang David and Keshavarzi, Behrooz and Kim, Y. Richard}, year={2018}, month={Dec}, pages={217–227} }
 @article{castorena_ilias_adams_kim_2018, title={Low-Temperature Emulsion Performance-Graded Specification for Chip Seals}, volume={2672}, ISSN={["2169-4052"]}, DOI={10.1177/0361198118790133}, abstractNote={Chip seals are applied to existing roadways to slow deterioration and improve pavement surface conditions without increasing the pavement’s structural capacity. Chip seals typically are comprised of asphalt emulsion and aggregate. Although it is well known that the properties of asphalt emulsion are critical to chip seal performance, the current specifications for these binders are empirical in nature and are not based on the properties that relate directly to chip seal performance. This study proposes emulsion performance-graded specifications that are designed to mitigate aggregate loss at low temperatures. To develop the proposed specifications, the research team executed an experimental plan to identify the residual binder properties that relate to chip seal aggregate loss at low temperatures. This research considered both fracture mechanics and rheology-based binder properties. Dynamic shear moduli, evaluated at critical phase angle values, demonstrated the strongest correlation to chip seal aggregate loss at low temperatures. Critical phase angle values were varied as a function of the low-temperature climatic emulsion performance grade of interest. This study also established preliminary specification limits for the dynamic shear modulus values based on critical chip seal performance thresholds.}, number={28}, journal={TRANSPORTATION RESEARCH RECORD}, author={Castorena, Cassie and Ilias, Mohammad and Adams, Javon and Kim, Y. Richard}, year={2018}, month={Dec}, pages={266–276} }
 @article{adams_ilias_castorena_kim_2018, title={Performance-Graded Specifications for Asphalt Emulsions Used in Chip Seal Preservation Treatments}, volume={2672}, ISSN={["2169-4052"]}, DOI={10.1177/0361198118770169}, abstractNote={This paper details the development of a framework for emulsion performance-grade (EPG) specifications for chip seal treatments. Chip seals are preservation surface treatments that are designed to improve the condition of the pavement surface while mitigating deterioration of the overall pavement structure. Asphalt emulsions used in chip seals often are selected based on factors that are not necessarily related to performance. Aggregate loss and bleeding have been identified as the most critical chip seal distresses that are related to binder performance. Storage stability, sprayability, and drain-out have been determined to be the most critical constructability concerns. For this study, binder and mixture test methods were identified to reflect the failure mechanisms for each critical distress type. The emulsion residue test methods that were identified to capture chip seal performance are the multiple stress creep and recovery test for bleeding and the dynamic shear rheometer frequency sweep test for low-temperature aggregate loss. The fresh emulsion test methods that were identified to capture chip seal constructability are the three-step shear test and storage stability test. The proposed EPG specifications for the fresh emulsion properties that are related to constructability were developed using statistical analysis of the binder test results. The proposed EPG specifications for the residual binder properties were developed by defining the temperature-independent relationships between the emulsion residue properties and mixture performance that correspond to each critical distress. Preliminary specification limits were then established based on the values of the binder properties that correspond to the critical mixture performance thresholds.}, number={12}, journal={TRANSPORTATION RESEARCH RECORD}, author={Adams, Javon and Ilias, Mohammad and Castorena, Cassie and Kim, Y. Richard}, year={2018}, month={Dec}, pages={20–31} }
 @article{kwon_kim_rhee_kim_2018, title={Spray injection patching for pothole repair using 100 percent reclaimed asphalt pavement}, volume={166}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2018.01.145}, abstractNote={Pothole repair of asphalt pavements is one of the most commonly performed roadway maintenance operations, and it is costly. Reclaimed asphalt pavement (RAP) has become an increasingly attractive material for pothole repair due to its economic and environmental advantages. This study investigated the performance of spray injection patching materials for pothole repair that utilize 100 percent RAP and compared the results to the performance of patching materials made with virgin aggregate. This study was designed to investigate how well different patching products resist critical types of distresses that are observed in the field and typically require patching. The primary characteristics examined in the study include stability, adhesion, moisture susceptibility, and durability of the patching material. The performance of various combinations of materials was observed in laboratory tests to determine the most cost-effective and best-performing patch material. The results show that the material’s performance depended on the type of aggregate and emulsion used in the mixtures. The results also indicate that the mixtures that contained RAP had good stability and adhesion properties compared to the mixtures made with virgin aggregate. This research proved the feasibility and advantages of using RAP for spray injection pothole repair.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Kwon, Bong Ju and Kim, Dahae and Rhee, Suk Keun and Kim, Y. Richard}, year={2018}, month={Mar}, pages={445–451} }
 @article{bastos_torquato e silva_soares_nascimento_kim_2018, title={Triaxial stress sweep test protocol considerations for permanent deformation characterisation of asphalt mixtures}, volume={19}, ISSN={1468-0629 2164-7402}, url={http://dx.doi.org/10.1080/14680629.2016.1261729}, DOI={10.1080/14680629.2016.1261729}, abstractNote={Rutting is one of the most usual distresses in Brazilian asphaltic pavements and prediction of such distress is a major challenge. State of the art methodologies need consistency between laboratory test and field conditions. This paper investigates a potential modification of the triaxial stress sweep (TSS) test, according to deviator and confining stresses typically found in Brazilian roadways which have thinner surface courses than those for which the original protocol was developed. Different structures were simulated with typical material properties and layer thicknesses found in Brazil. A more realistic confining stress was adopted, and a deviator stress was calculated for each load level of the test protocol. A modified TSS test and the uniaxial repeated load test were performed in three asphalt mixes. One of them did not reach the minimum number of cycles, preventing rutting prediction, and suggesting a fragility of this particular mix with respect to the investigated distress. Such a result was co...}, number={2}, journal={Road Materials and Pavement Design}, publisher={Informa UK Limited}, author={Bastos, Juceline Batista dos S. and Torquato e Silva, Samuel de A. and Soares, Jorge B. and Nascimento, Luís Alberto H. and Kim, Y. Richard}, year={2018}, pages={431–444} }
 @article{safavizadeh_wargo_kim_2018, title={Utilizing Digital Image Correlation (DIC) in Asphalt Pavement Testing}, volume={46}, ISSN={["1945-7553"]}, DOI={10.1520/jte20160262}, abstractNote={The digital image correlation (DIC) technique as a displacement and strain measurement method is one of the newest measurement technologies employed in asphalt pavement testing. Although DIC was introduced for material testing in the early 1980s; this technology is not yet being used to its highest potential as a reliable and flexible method for measuring displacements and strains and, more importantly, for investigating cracking phenomena and fracture characteristics in asphalt pavement testing. This research aimed to study the requirements for ensuring a reliable and accurate DIC system and to demonstrate areas where the technique could be used to provide an edge over traditional measurement methods. Using proprietary two-dimensional DIC software, the parameters that affect the accuracy of test results were evaluated and the proper analysis configurations for investigating cracked areas were determined. The results showed that the DIC technique, if used properly, is an extremely powerful tool for studying damage progression and fracture characteristics in the fatigue and fracture testing of asphalt concrete.}, number={3}, journal={JOURNAL OF TESTING AND EVALUATION}, author={Safavizadeh, S. A. and Wargo, A. and Kim, Y. Richard}, year={2018}, month={May}, pages={984–998} }
 @article{xie_castorena_wang_kim_2017, title={A framework to characterize the healing potential of asphalt binder using the linear amplitude sweep test}, volume={154}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2017.08.021}, abstractNote={Abstract The healing characteristics of asphalt binders affect the fatigue performance of asphalt mixtures and field pavements. The objective of this paper is to quantify the healing potential of asphalt binders using the linear amplitude sweep (LAS) test under various damage level and rest period durations. A healing protocol based on the LAS test is successfully established to measure the healing behaviour of asphalt binder by applying the rest periods before and after cohesive failure. Based on the simplified-viscoelastic continuum damage (S-VECD) model, the percent healing (%HS) is quantified from the healing recovery of the accumulated damage growths. The neat asphalt binder exhibits better %HS results than the SBS modified binder in the pre-failure conditions. However, the SBS modified binder exhibits a higher healing potential in the post-failure case. The rest-damage superposition principle (RDSP) is further investigated in the pre-failure cases to remove and unify the effects of damage level and rest period by constructing a %HS mastercurve at a given reference damage level. The developed healing mastercurve and related damage shift factor can be used to represent the intrinsic healing potential of a given asphalt binder. A series of healing indices are proposed and discussed based on the healing mastercurve to numerically compare the healing performance of asphalt binders.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Xie, Wei and Castorena, Cassie and Wang, Chao and Kim, Y. Richard}, year={2017}, month={Nov}, pages={771–779} }
 @article{cho_karshenas_tayebali_guddati_kim_2017, title={A mechanistic approach to evaluate the potential of the debonding distress in asphalt pavements}, volume={18}, ISSN={["1477-268X"]}, DOI={10.1080/10298436.2016.1149837}, abstractNote={AbstractThe debonding distress in asphalt pavement structures is a critical problem that affects the performance of asphalt concrete pavements. It occurs at the layer interface due to the poor bond quality between adjacent asphalt concrete layers and/or when stresses at the layer interface exceed the strengths of the material at the interface. The debonding of the adjacent layers, especially the top surface layer of an asphalt pavement, is a contributing factor to the premature cracking of pavements. Hence, the debonding distress can lead to a reduction in the life of the pavement. This paper presents an analytical and experimental framework to evaluate the potential for debonding at the layer interface of asphalt concrete pavements. Computational analysis was performed to determine the critical stress and strain states in layered asphalt pavements under moving vehicle loads using the Layered ViscoElastic pavement analysis for Critical Distresses (LVECD) computer program developed at North Carolina State ...}, number={12}, journal={INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING}, author={Cho, Seong-Hwan and Karshenas, Afshin and Tayebali, Akhtarhusein A. and Guddati, Murthy N. and Kim, Y. Richard}, year={2017}, pages={1098–1110} }
 @article{adams_castorena_im_ilias_kim_2017, title={Addressing Raveling Resistance in Chip Seal Specifications}, ISSN={["2169-4052"]}, DOI={10.3141/2612-05}, abstractNote={Chip seals are applied to existing roadways to slow deterioration and improve pavement surface conditions without increasing the pavement’s structural capacity. The raveling of chip seals can cause damage to vehicles and thus is a safety concern. Raveling resistance is related to both material application rates and material properties. The current chip seal specifications fail to adequately address the material-related aspects of raveling resistance. This study seeks to develop recommendations to address raveling resistance in future chip seal specifications. Strain sweep binder tests, binder bond strength (BBS) tests, and Vialit chip seal mixture tests were conducted to assess early raveling, late raveling, and wet raveling at two intermediate temperatures. The results demonstrate that the bond that develops between the residual binder and the aggregate is highly dependent on the interaction between the emulsion and the aggregate during curing. The importance of emulsion–aggregate compatibility in raveling resistance indicates that raveling resistance cannot be addressed in binder specifications alone. Rather, it is recommended that intermediate temperature raveling resistance should be addressed during chip seal mixture design. Vialit and BBS tests, in which emulsion is cured on rock, can both be used to effectively quantify the aggregate loss potential of a chip seal. These two tests are able to capture the benefits of polymer modification and produce results that correlate. However, the Vialit tests are easier to implement than the BBS tests and require no expensive equipment. Therefore, Vialit tests are recommended to address early, late, and wet raveling resistance in future chip seal specifications.}, number={2612}, journal={TRANSPORTATION RESEARCH RECORD}, author={Adams, Javon and Castorena, Cassie and Im, Jeong Hyuk and Ilias, Mohammad and Kim, Y. Richard}, year={2017}, pages={39–46} }
 @article{wang_castrorena_zhang_kim_2017, title={Application of Time-Temperature Superposition Principle on Fatigue Failure Analysis of Asphalt Binder}, volume={29}, ISSN={["1943-5533"]}, DOI={10.1061/(asce)mt.1943-5533.0001730}, abstractNote={The linear amplitude sweep (LAS) test has been proposed for fatigue specifications of asphalt binders. Recently, a newly developed fatigue failure definition and energy-based failure criterion have been proposed for improving the LAS procedure and data interpreting; however, these improvements only affect LAS data conducted at a constant temperature. This paper, therefore, discusses the loading temperature effects on LAS-based binder fatigue, damage evolution, and final fatigue failure occurrence. Experimental results indicate that both damage characteristic curves (DCCs) and the failure criterion derived from the simplified-viscoelastic continuum damage (S-VECD) model are strongly affected by the testing temperature. However, the temperature shift factors determined from the dynamic shear modulus testing within the linear viscoelastic domain have been proven to be effective in eliminating the temperature influence for both fatigue DCCs and the failure criterion. The validation on binder phase demonstrates that the time-temperature superposition principle (TTSP) shift factor is only a function of temperature and is independent of strain level. TTSP application on both undamaged and damaged material behaviors is able to greatly improve the testing efficiency of the LAS-based binder fatigue characterization.}, number={1}, journal={JOURNAL OF MATERIALS IN CIVIL ENGINEERING}, author={Wang, Chao and Castrorena, Cassie and Zhang, Jinxi and Kim, Y. Richard}, year={2017}, month={Jan} }
 @article{kim_kim_2017, title={Characterization of Permanent Deformation of Asphalt Mixtures with Minimum Strain Rate, LVECD Program, and Triaxial Stress Sweep Test}, ISSN={["2169-4052"]}, DOI={10.3141/2631-11}, abstractNote={The rutting resistance of asphalt concrete is typically assessed by using flow number tests in the lab in accordance with AASHTO TP 79. However, the flow number represents the rutting resistance of the material with regard to ranking for only a specific test condition. A significant amount of testing effort is needed to evaluate rutting resistance by using the flow number test under various loading conditions and temperatures. Therefore, researchers have developed alternative test methods to reduce the testing effort. For example, the incremental repeated-load permanent deformation test and the triaxial stress sweep (TSS) test are two promising protocols that can predict the permanent deformation of asphalt mixtures efficiently and accurately. This study compares the minimum strain rates (MSRs) obtained from incremental repeated-load permanent deformation and TSS tests to examine the ability of the TSS test to analyze the MSRs of asphalt mixtures. In addition, the viscoplastic shift model calibrated from the TSS test that is implemented in the layered viscoelastic pavement analysis for critical distresses (LVECD) program was used to predict the rut depths of 16 pavement sections from four sources. The MSRs and rut depths predicted from the LVECD program were compared with actual measured rut depths. The results of this study indicated that the MSR results could only be used to rank the rutting susceptibility of single-layer asphalt pavements. For a multilayered pavement system, structural level analysis is necessary to predict the accurate rutting performance and rut depths of the test sections.}, number={2631}, journal={TRANSPORTATION RESEARCH RECORD}, author={Kim, Dahae and Kim, Y. Richard}, year={2017}, pages={96–104} }
 @article{wargo_safavizadeh_kim_2017, title={Comparing the performance of fiberglass grid with composite interlayer systems in asphalt concrete}, number={2631}, journal={Transportation Research Record}, author={Wargo, A. and Safavizadeh, S. A. and Kim, Y. R.}, year={2017}, pages={123–132} }
 @article{safavizadeh_kim_2017, title={DIC Technique to Investigate Crack Propagation in Grid-Reinforced Asphalt Specimens}, volume={29}, ISSN={0899-1561 1943-5533}, url={http://dx.doi.org/10.1061/(ASCE)MT.1943-5533.0001839}, DOI={10.1061/(ASCE)MT.1943-5533.0001839}, abstractNote={Crack growth data are among the key parameters needed to characterize the materials used in asphalt concrete fatigue and fracture tests. The purpose of this study is to investigate the use of the digital image correlation (DIC) technique in monitoring the progression of damage and quantifying the length of cracks in asphalt concrete fatigue and fracture tests. To this end, cyclic interlayer shear tests and four-point bending notched beam fatigue tests were performed on double-layer fiberglass grid-reinforced asphalt concrete specimens. The tests were performed at 20°C and at frequencies of 5 and 10 Hz for the cyclic shear and bending beam fatigue tests, respectively. The full-field displacement and strain contours derived from DIC analysis of the specimens’ surface images proved to be powerful tools for monitoring the damage progression in the asphalt specimens under fatigue loading and for developing crack tip detection methods. Crack length measurement methods were developed based on DIC analysis displacement and strain results and were used successfully to determine interfacial crack lengths in the shear tests and vertical and interfacial crack lengths in the four-point bending notched beam fatigue tests.}, number={6}, journal={Journal of Materials in Civil Engineering}, publisher={American Society of Civil Engineers (ASCE)}, author={Safavizadeh, Seyed Amirshayan and Kim, Youngsoo Richard}, year={2017}, month={Jun}, pages={04017011} }
 @article{kim_kim_2017, title={Determination of Dynamic Modulus Values of Asphalt Mixtures Using Impact Resonance Testing of Thin Disk Specimens}, volume={45}, ISSN={["1945-7553"]}, DOI={10.1520/jte20150076}, abstractNote={The impact resonance (IR) test is a nondestructive test method that is used to characterize the linear viscoelastic behavior of asphalt concrete. This method is preferred over other methods because the setup of the IR test is simpler, more efficient, and less expensive than standard axial compression dynamic modulus (|E*|) tests. Researchers originally developed the IR test method for cylindrical specimens of asphalt mixtures and concluded that this method can serve as an alternative to |E*| tests. However, the geometry (100 mm in diameter by 150 mm in height) of the cylindrical specimens used in these tests prohibits the use of IR tests for field cores. Therefore, researchers began to consider thin disk-shaped specimens for IR testing because thinner geometry of such specimens better represents slices of field cores. In this study, a test procedure was developed to evaluate the use of thin disk-shaped specimens for IR tests in order to determine the |E*| values of asphalt mixtures. The IR test protocol was optimized using 2 IR test methods (referred to as Case 1 and Case 2 in this work) under various test conditions to ensure the highest possible quality of the data. Optimal test methods were proposed based on the repeatability and variability of the resonant frequency and phase angle data and the ability of the different test conditions to provide data that best match the |E*| values obtained from standard axial compression |E*| tests. The results demonstrate that the |E*| values of thin disk-shaped specimens determined from the optimized IR tests are similar to the |E*| values of long cylindrical specimens determined from conventional |E*| AASHTO T 342-11 tests and IR tests.}, number={2}, journal={JOURNAL OF TESTING AND EVALUATION}, author={Kim, D. and Kim, Y. R.}, year={2017}, month={Mar}, pages={509–520} }
 @article{lee_norouzi_kim_2017, title={Determining Specimen Geometry of Cylindrical Specimens for Direct Tension Fatigue Testing of Asphalt Concrete}, volume={45}, ISSN={["1945-7553"]}, DOI={10.1520/jte20140357}, abstractNote={This paper presented a specimen geometry study of cylindrical specimens used in the direct tension cyclic (DTC) fatigue testing of asphalt concrete using an asphalt mixture performance tester. The current specimen geometry for DTC fatigue testing is 100 mm in diameter and 150 mm in height with a linear variable differential transducer (LVDT) gauge length of 70 mm in the middle of the specimen. In order to use the displacement data for mechanistic fatigue performance modeling, specimen failure must occur within the length of the LVDT gauge. However, recent experiments using stiff mixtures have shown that failure often occurs outside the LVDT gauge length. This specimen geometry study was conducted to determine the specimen geometry that enhances the propensity of the failure inside the gauge length without sacrificing the advantage of the DTC testing that provides uniform stresses and strains in the middle of the specimen. Laboratory experiments were performed on cylindrical specimens of different geometries (i.e., different diameters and lengths). Test specimen diameters of 75 mm and 100 mm and specimen heights of 130 mm and 150 mm were used in this study. The specimen geometry effects on damage characteristic curves and failure criteria were identified through ANOVA tests and layered viscoelastic pavement analysis for critical distresses (LVECD) program. Based on analysis results and experimental verification tests, the specimen geometry recommended for the DTC testing is 100 mm in diameter and 130 mm in height with a 70-mm gauge length. The recommended specimen geometry is applicable when the gyratory-compacted specimen geometry is 150 mm in diameter and more than 178 mm in height.}, number={2}, journal={JOURNAL OF TESTING AND EVALUATION}, author={Lee, Jong-Sub and Norouzi, Amirhossein and Kim, Y. Richard}, year={2017}, month={Mar}, pages={613–623} }
 @article{kim_kim_2017, title={Development of Stress Sweep Rutting (SSR) test for permanent deformation characterization of asphalt mixture}, volume={154}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2017.07.172}, abstractNote={Abstract The goal of this work is to develop a simple rutting test method, referred to as the Stress Sweep Rutting (SSR) test, which can be used to calibrate a permanent deformation model, known as the shift model, of asphalt mixtures. The effect of each shift model parameter, i.e., temperature, deviatoric stress, load time, and rest period, on permanent deformation has been explored and evaluated in an effort to minimize the test requirements of the rutting characterization. The accuracy of the SSR test method was evaluated using the Layered ViscoElastic pavement analysis for Critical Distresses (LVECD) program by predicting the permanent deformation and compared to the Triaxial Stress Sweep (TSS) method, which was originally developed to calibrate the shift model. The rut depths predicted from the SSR and TSS method using the LVECD program are in close agreement, thereby verifying the SSR test method.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Kim, Dahae and Kim, Y. Richard}, year={2017}, month={Nov}, pages={373–383} }
 @article{daniel_kim_roque_2017, title={Editorial}, volume={18}, ISSN={["2164-7402"]}, DOI={10.1080/14680629.2017.1389095}, journal={ROAD MATERIALS AND PAVEMENT DESIGN}, author={Daniel, Jo Sias and Kim, Y. Richard and Roque, Reynaldo}, year={2017}, pages={1–1} }
 @article{norouzi_kim_kim_yang_2017, title={Effect of Reclaimed Asphalt Pavement Content and Binder Grade on Fatigue-Resisting Performance of Asphalt Mixtures in Georgia}, volume={29}, ISSN={["1943-5533"]}, DOI={10.1061/(asce)mt.1943-5533.0001960}, abstractNote={This paper examines the effects of reclaimed asphalt pavement (RAP) content and binder grade on the fatigue resistance of Georgia asphalt concrete mixtures. The asphalt concrete mixtures were prepared based on two job mix formulas used in northern and southern Georgia and were composed of 12.5-mm nominal maximum aggregate size aggregate and three asphalt binders (PG 64-22, PG 67-22, and PG 76-22). Dynamic modulus and controlled crosshead cyclic tension fatigue tests were performed using the laboratory-prepared specimens. A simplified viscoelastic continuum damage (S-VECD) model was characterized for each mixture using the dynamic modulus and fatigue test results. The layered viscoelastic pavement analysis for critical distresses (LVECD) program was used to investigate the effects of RAP content and binder grade on the fatigue performance of pavements. The S-VECD model and LVECD program analyses showed that the addition of RAP up to 30% using corrected optimum asphalt content (COAC) method significantly improved the mixtures’ fatigue resistance, especially for the mixtures with PG 64-22 and PG 67-22 binders.}, number={9}, journal={JOURNAL OF MATERIALS IN CIVIL ENGINEERING}, author={Norouzi, Amirhossein and Kim, Y. Richard and Kim, S. Sonny and Yang, Jidong}, year={2017}, month={Sep} }
 @article{lee_pape_castorena_kim_2017, title={Evaluation of Small Specimen Geometries for Asphalt Mixture Performance Testing and Pavement Performance Prediction}, ISSN={["2169-4052"]}, DOI={10.3141/2631-09}, abstractNote={The use of small specimen geometries in asphalt mixture performance testing to enable the testing of as-built pavement layers has been gaining attention in recent years. Small specimens could also improve the testing efficiency of laboratory-fabricated specimens by allowing the extraction of multiple test specimens per gyratory-compacted sample. Rigorous assessment of the small specimen geometries is required before the use of such geometries is standardized. In this study, small specimens were evaluated for dynamic modulus and simplified viscoelastic continuum damage fatigue. Three specimen geometries (100-mm- and 38-mm-diameter cylindrical specimens and 25- × 50-mm prismatic specimens) were compared by using five mixtures with a nominal maximum aggregate size (NMAS) ranging from 9.5 to 25.0 mm. The results show that the dynamic modulus and phase angle master curves agreed at low and intermediate temperatures, regardless of the NMAS values of the mixture. At the high temperature, the small specimen dynamic modulus values were slightly higher and the phase angle values were slightly lower than those of the large specimens. The specimen-to-specimen variability for the large and small specimens was comparable. The fatigue test results for the mixtures evaluated were comparable, except for the 25-mm mixture, which proved problematic in the testing of both small and large specimens. Pavement performance was predicted by the layered viscoelastic analysis for critical distresses program by using the test results for the small and large specimens. These results suggest that specimen geometry had a minimal effect on pavement fatigue damage predictions, which indicates promise for the use of small specimen geometries in practice.}, number={2631}, journal={TRANSPORTATION RESEARCH RECORD}, author={Lee, Kangjin and Pape, Sonja and Castorena, Cassie and Kim, Y. Richard}, year={2017}, pages={74–82} }
 @article{elwardany_yousefi rad_castorena_kim_2017, title={Evaluation of asphalt mixture laboratory long-term ageing methods for performance testing and prediction}, volume={18}, ISSN={1468-0629 2164-7402}, url={http://dx.doi.org/10.1080/14680629.2016.1266740}, DOI={10.1080/14680629.2016.1266740}, abstractNote={Ageing has long been recognised as a major distress mechanism for asphalt concrete and, by extension, asphalt pavements. Ageing causes the material to stiffen and embrittle, which leads to a high potential for cracking. Although a significant amount of effort has been placed on understanding the ageing process of asphalt binder, less effort has been put forth to develop laboratory ageing procedures for producing aged mixture specimens for performance testing. An optimal laboratory conditioning procedure to simulate long-term ageing for performance testing and prediction is required in order to integrate the effects of long-term ageing in pavement prediction models and other mechanistic design and analysis methods. In this study, oven ageing and pressure ageing vessel ageing are applied to both loose mix and compacted specimens in order to evaluate and select an ageing method to simulate long-term ageing for performance testing and prediction. The selected method must be able to maintain specimen integrity...}, number={sup1}, journal={Road Materials and Pavement Design}, publisher={Informa UK Limited}, author={Elwardany, Michael D. and Yousefi Rad, Farhad and Castorena, Cassie and Kim, Y. Richard}, year={2017}, pages={28–61} }
 @article{safavizadeh_kim_2017, title={Fatigue and fracture characterization of fiberglass grid-reinforced beam specimens using four-point bending notched beam fatigue test and digital image correlation technique}, volume={50}, ISSN={["1871-6873"]}, DOI={10.1617/s11527-016-0980-8}, number={2}, journal={MATERIALS AND STRUCTURES}, author={Safavizadeh, Seyed Amirshayan and Kim, Youngsoo Richard}, year={2017}, month={Apr} }
 @article{sakhaeifar_kim_montano_2017, title={Individual temperature based models for nondestructive evaluation of complex moduli in asphalt concrete}, volume={137}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2016.12.145}, abstractNote={Abstract The rheological properties of bituminous materials play important roles in the selection of paving materials, and analysis and design of asphalt pavements. The series of models developed in this study are composed of five formulations for the creation of the dynamic modulus mastercurve at a wide range of testing temperatures. The predictability of these models is assessed by comparing the predicted dynamic modulus mastercurves of different mixtures with measured ones from a nondestructive impact resonance (IR) test. This assessment shows that the predictions match the dynamic modulus values measured from different techniques with a good level of accuracy.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Sakhaeifar, Maryam S. and Kim, Y. Richard and Montano, Blanca E. Garcia}, year={2017}, month={Apr}, pages={117–127} }
 @article{rad_elwardany_castorena_kim_2017, title={Investigation of proper long-term laboratory aging temperature for performance testing of asphalt concrete}, volume={147}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2017.04.197}, abstractNote={The performance implications of laboratory asphalt loose mixture aging at 135 °C were evaluated by comparing the performance of mixtures subjected to long-term aging at 95 °C and 135 °C to yield the same rheology. Although the rheology of the mixtures aged at 135 °C and 95 °C matched, their chemistry differed. Performance test results suggest that the chemical changes induced by aging at 135 °C can negatively impact performance. The relationship between binder chemistry and rheology was unaffected by aging temperatures at or below 95 °C. The rate of oxidation increased with an increase in temperature, and thus, the optimal loose mixture aging temperature is 95 °C.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Rad, Farhad Yousefi and Elwardany, Michael D. and Castorena, Cassie and Kim, Y. Richard}, year={2017}, month={Aug}, pages={616–629} }
 @article{norouzi_kim_2017, title={Mechanistic evaluation of fatigue cracking in asphalt pavements}, volume={18}, ISSN={["1477-268X"]}, DOI={10.1080/10298436.2015.1095909}, abstractNote={AbstractOver the last several decades, significant research has been conducted to predict the fatigue cracking performance of asphalt pavements. Recently, the simplified viscoelastic continuum damage (S-VECD) model was developed as an efficient method of characterising the fatigue performance of asphalt mixtures under a wide range of loading conditions. Two important material properties that can be determined from the S-VECD model are the damage characteristic curve that defines how damage evolves in a specimen and the energy-based failure criterion that defines when the specimen fails. These two material functions are unique for a given mixture regardless of temperature, mode of loading, stress/strain amplitude and loading history. This study presents the application of the Layered Viscoelastic Crirtical Distresses (LVECD) programme to predict the fatigue performance of 18 pavement sections from different locations in the United States and Canada. The capability of the LVECD programme to capture crack in...}, number={6}, journal={INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING}, author={Norouzi, Amirhossein and Kim, Y. Richard}, year={2017}, pages={530–546} }
 @article{kim_norouzi_kass_liske_kim_2017, title={Mechanistic performance evaluation of pavement sections containing RAP and WMA additives in Manitoba}, volume={133}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2016.12.035}, abstractNote={Over recent decades, the utilization of reclaimed asphalt pavement (RAP) and warm mix asphalt (WMA) in mixtures has increased dramatically due to the environmental and economic advantages of these materials. This paper presents the fatigue and rutting characterization of mixtures that contain RAP and/or WMA obtained from Manitoba in Canada. In addition to mechanical testing, numerical simulations of the fatigue cracking and rutting performance of the pavement sections were performed, and the results were compared to field observations. The results obtained from the Layered Viscoelastic pavement analysis for Critical Distresses (LVECD) program and from the field measurements show good agreement, thereby indicating that the LVECD program is able to predict reasonable pavement performance for the RAP and WMA mixtures. The field performance and the predicted performance were used to evaluate the effects of RAP and/or WMA additives on the fatigue cracking and rutting performance of the mixtures.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Kim, Dahae and Norouzi, Amirhossein and Kass, Said and Liske, Tara and Kim, Y. Richard}, year={2017}, month={Feb}, pages={39–50} }
 @article{norouzi_kim_2017, title={Ruggedness Study of Dynamic Modulus Testing of Asphalt Concrete in Indirect Tension Mode}, volume={45}, ISSN={["1945-7553"]}, DOI={10.1520/jte20150118}, abstractNote={The modulus is one of the primary asphalt mixture properties used for the mechanistic performance prediction of asphalt pavements. Dynamic modulus testing is a common method of measuring mixture modulus as a function of loading frequencies and temperatures. This paper presented the results of a ruggedness study of dynamic modulus testing in indirect tension mode to evaluate the factors that were most likely to affect the final results. Specimen thickness, air void content, gauge length, test temperature, and horizontal strain level, which are the critical factors that affect the dynamic modulus of asphalt concrete, were selected for the ruggedness analysis. Two different asphalt mixtures with the participation of two laboratories were used in the study. Based on the selected values for the different variables, air void content was found to be the significant factor that affected dynamic modulus testing and dynamic modulus values. The other factors did not appear to have a major impact on the test results; however, reasonable tolerances were obtained for the other parameters investigated in this paper.}, number={2}, journal={JOURNAL OF TESTING AND EVALUATION}, author={Norouzi, Amirhossein and Kim, Y. Richard}, year={2017}, month={Mar}, pages={601–612} }
 @article{cho_safavizadeh_kim_2017, title={Verification of the applicability of the time-temperature superposition principle to interface shear stiffness and strength of GlasGrid-reinforced asphalt mixtures}, volume={18}, ISSN={["2164-7402"]}, DOI={10.1080/14680629.2016.1189350}, abstractNote={This paper aims to verify the applicability of the time–temperature superposition (t–TS) principle to the interface shear performance of GlasGrid-reinforced asphalt specimens under monotonic and random cyclic shear loading. A double shear tester and a direct shear device, the Modified Advance Shear Tester that has the capability to apply confining loads, were used to fulfil this objective. Double-layered asphalt specimens were fabricated and reinforced using two types of fibreglass grids with 12.5-mm and 25-mm grid openings, respectively. PG 64-22 asphalt binder was used as the tack coat when the smaller opening grid was used, and SS-1 emulsion was applied as the tack coat when the larger opening grid was used. Approaches that employ the mixture dynamic modulus, tack coat residue complex modulus, and interface shear modulus shift factors for shifting the shear test results and constructing shear master curves were evaluated. The results show that the t–TS principle is applicable to the shear strength and ...}, number={4}, journal={ROAD MATERIALS AND PAVEMENT DESIGN}, author={Cho, Seong Hwan and Safavizadeh, Seyed Amirshayan and Kim, Y. Richard}, year={2017}, month={Jul}, pages={766–784} }
 @article{keshavarzi_kim_2016, title={A viscoelastic-based model for predicting the strength of asphalt. concrete in direct tension}, volume={122}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2016.06.089}, abstractNote={Abstract The modeling of asphalt concrete behavior under monotonic loading plays an important role in investigating the low temperature behavior of pavement material. Further, any proposed method should be able to consider the rate and temperature dependency of asphalt concrete. This paper presents a new method for simulating the behavior of asphalt concrete in uniaxial tension. Direct tension monotonic testing that incorporates a constant crosshead displacement rate and various temperatures was used in the experimental investigation to simulate thermal cracking of asphalt concrete. Viscoelastic continuum damage theory was applied to simulate the asphalt behavior in direct tension. This theory is able to model distributed damage within the material under both constant and dropping temperatures. A damage characteristic curve, which has been proven to represent the intrinsic property of the material, was used to simulate the damage evolution during testing. The proposed method features a single ordinary differential equation that is solved to provide the damage evolution. The results show that the predicted stress matches the measured data well for tests conducted at North Carolina State University and by other agencies. Implementing the proposed method in a finite element code provides a strong mechanistic model to predict asphalt fracture under thermal loading.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Keshavarzi, Behrooz and Kim, Y. Richard}, year={2016}, month={Sep}, pages={721–727} }
 @article{cao_kim_2016, title={A viscoplastic model for the confined permanent deformation of asphalt concrete in compression}, volume={92}, ISSN={["1872-7743"]}, DOI={10.1016/j.mechmat.2015.10.001}, abstractNote={Abstract This paper presents a viscoplastic model for the permanent deformation behavior of asphalt concrete in compression. Triaxial repeated load permanent deformation (TRLPD) tests with haversine-shaped load pulses and rest periods were used in the experimental investigations as they are able to simulate real traffic loading patterns. For the first time, the viscoelastic–viscoplastic coupling phenomenon in asphalt concrete is illustrated using experimental data, which motivates the direct collecting and modeling of permanent deformation history in the present work instead of modeling the viscoelastic and viscoplastic responses in a separate and uncoupled fashion as in the traditional scheme. By applying a long rest period (100 s) to allow the viscoelastic deformation to recover sufficiently, the permanent strain data can be collected directly for viscoplastic model development. The proposed viscoplastic model features a convolution integral enclosed in Macaulay brackets. A single viscoplastic relaxation spectrum is assumed as the material's intrinsic property, and the nonlinear stress effects are captured through the variable E∞, which is the infinite modulus expressed as a logarithmic function of the triaxiality ratio. Material hardening (or softening) is described via the increase (or decrease) of the internal stress during loading (or unloading and rest period). The model was characterized using TRLPD test data at three levels of deviatoric stress and confining pressure. Finally, the calibrated model was verified by applying it to random loading tests conducted at other confining levels. The proposed model provides an efficient and convenient approach that is able to determine the material's macroscopic deformation as well as to capture the material's internal hardening/softening mechanisms.}, journal={MECHANICS OF MATERIALS}, author={Cao, Wei and Kim, Y. Richard}, year={2016}, month={Jan}, pages={235–247} }
 @article{dehghan banadaki_guddati_kim_2016, title={An algorithm for virtual fabrication of air voids in asphalt concrete}, volume={17}, ISSN={["1477-268X"]}, DOI={10.1080/10298436.2014.979822}, abstractNote={Motivated by the virtual testing of asphalt concrete, the North Carolina State University research team has developed an algorithm to computationally generate air voids. After examining the X-ray tomographic images of real asphalt concrete microstructure, we concluded that the air void's shape and size are affected primarily by the surrounding local aggregate structure. Building on this observation, we developed an algorithm to generate random but representative air void configurations inside a given microstructure. By applying the algorithm to scanned aggregate structures, we show that the generated air voids not only look visually similar to actual air voids, but also are effective in capturing modulus reduction. The algorithm is included in a virtual aggregate structure generation framework, resulting in a streamlined virtual fabrication procedure for asphalt concrete that can qualitatively capture the effects of accelerated degradation due to the presence of air voids.}, number={3}, journal={INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING}, author={Dehghan Banadaki, Arash and Guddati, Murthy N. and Kim, Y. Richard}, year={2016}, month={Mar}, pages={225–232} }
 @article{cao_norouzi_kim_2016, title={Application of viscoelastic continuum damage approach to predict fatigue performance of Binzhou perpetual pavements}, volume={3}, ISSN={2095-7564}, url={http://dx.doi.org/10.1016/J.JTTE.2016.03.002}, DOI={10.1016/J.JTTE.2016.03.002}, abstractNote={For this study, the Binzhou perpetual pavement test sections constructed in Shandong Province, China, were simulated for long-term fatigue performance using the layered viscoelastic pavement analysis for critical distresses (LVECD) finite element software package. In this framework, asphalt concrete was treated in the context of linear viscoelastic continuum damage theory. A recently developed unified fatigue failure criterion that defined the boundaries of the applicable region of the theory was also incorporated. The mechanistic modeling of the fatigue mechanisms was able to accommodate the complex temperature variations and loading conditions of the field pavements in a rigorous manner. All of the material models were conveniently characterized by dynamic modulus tests and direct tension cyclic fatigue tests in the laboratory using cylindrical specimens. By comparing the obtained damage characteristic curves and failure criteria, it is found that mixtures with small aggregate particle sizes, a dense gradation, and modified asphalt binder tended to exhibit the best fatigue resistance at the material level. The 15-year finite element structural simulation results for all the test sections indicate that fatigue performance has a strong dependence on the thickness of the asphalt pavements. Based on the predicted location and severity of the fatigue damage, it is recommended that Sections 1 and 3 of the Binzhou test sections be employed for perpetual pavement design.}, number={2}, journal={Journal of Traffic and Transportation Engineering (English Edition)}, publisher={Elsevier BV}, author={Cao, Wei and Norouzi, Amirhossein and Kim, Y. Richard}, year={2016}, month={Apr}, pages={104–115} }
 @article{wang_norouzi_kim_2016, title={Comparison of Fatigue Cracking Performance of Asphalt Pavements Predicted by Pavement ME and LVECD Programs}, ISSN={["2169-4052"]}, DOI={10.3141/2590-06}, abstractNote={Mechanistic–empirical pavement design has received significant attention from the pavement community as the method for designing asphalt pavements in the future. Currently available software for mechanistic–empirical pavement design includes the AASHTOWare Pavement ME Design (Pavement ME) program. The Pavement ME program allows users to predict pavement distresses by applying layered elastic theory for the mechanical responses and using empirical models for the distress predictions. The layered viscoelastic pavement design for critical distresses (LVECD) program, which employs three-dimensional viscoelastic finite element analysis with moving loads, can also be used to predict the fatigue and rutting performance of pavements. The LVECD program employs the simplified viscoelastic continuum damage (S-VECD) model as the material model for the fatigue performance predictions of asphalt mixtures under complex loading and environmental conditions. This paper examines and compares the performance of 33 pavement sections from five research projects located in the United States, Canada, and South Korea by using both the Pavement ME and LVECD computer programs. To verify the results obtained from these two programs, the simulations were compared with the field performance data. In terms of ranking, the LVECD simulations provided better agreement with the field performance data than did the Pavement ME simulations. One of the main reasons for the better predictions obtained by the LVECD program is that its fatigue performance predictions depend on the mixture properties of all the layers, whereas the Pavement ME program considers the fatigue properties of only the bottom layer mixture.}, number={2590}, journal={TRANSPORTATION RESEARCH RECORD}, author={Wang, Yizhuang and Norouzi, Amirhossein and Kim, Y. Richard}, year={2016}, pages={44–55} }
 @article{sabouri_choi_wang_hwang_baek_kim_2016, title={Effect of Rejuvenator on Performance Properties of WMA Mixtures with High RAP Content}, volume={11}, ISBN={["978-94-017-7341-6"]}, ISSN={["2211-0852"]}, DOI={10.1007/978-94-017-7342-3_38}, abstractNote={The production of warm mix asphalt (WMA) mixtures with high percentages of reclaimed asphalt pavement (RAP) is gaining attention as a way to save costs and efficiently utilize existing resources. However, WMA must perform at least as well as hot mix asphalt (HMA) before it can be used as a replacement for HMA. In this study, the performance of a WMA mixture with a high percentage of RAP (40 % RAP) and a WMA additive (1.5 % of binder weight) that works as a rejuvenator was evaluated and compared with the performance of a HMA mixture with the same amount of RAP in order to evaluate the effects of the WMA rejuvenator. These mixtures were evaluated in terms of fatigue cracking using the simplified viscoelastic continuum damage (S-VECD) model and in terms of rutting using the triaxial stress sweep (TSS) test. In addition, layered viscoelastic pavement analysis for critical distresses (LVECD) was used to predict the fatigue resistance of these mixtures for future use. The WMA rejuvenator was found to improve the mixing and compaction ability of the WMA mixture. Also, compared to the HMA mixture, the WMA mixture showed better fatigue resistance, but the rejuvenator found to have an adverse effect on the rutting resistance of the mixture.}, journal={8TH RILEM INTERNATIONAL SYMPOSIUM ON TESTING AND CHARACTERIZATION OF SUSTAINABLE AND INNOVATIVE BITUMINOUS MATERIALS}, author={Sabouri, Mohammadreza and Choi, Yeong-Tae and Wang, Yizhuang and Hwang, Sungdo and Baek, Cheolmin and Kim, Richard Y.}, year={2016}, pages={473–484} }
 @article{jacques_daniel_bennert_reinke_norouzi_ericson_mogawer_kim_2016, title={Effect of Silo Storage Time on the Characteristics of Virgin and Reclaimed Asphalt Pavement Mixtures}, ISSN={["2169-4052"]}, DOI={10.3141/2573-10}, abstractNote={Many hot-mix asphalt plants store material in heated silos before it is ready to be transported to construction sites. The time that material is stored in the silo is not controlled and varies widely, depending on several factors. As the material is exposed to elevated temperatures, short-term aging of the binder may occur. Another important consideration is the interaction between reclaimed asphalt pavement (RAP) and virgin binders, as blending or diffusion could occur between the binders. In this study, a virgin and 25% RAP mixture were sampled at incremental silo storage times up to 10 h. Characterization testing included performance grading, rheological indexes, Glover–Rowe parameter evaluation, rolling thin film oven aging on the binders, complex modulus, a simplified viscoelastic continuum damage model (S-VECD) for fatigue, and thermal stress restrained specimen testing of the mixtures. Simulations that used layered viscoelastic critical distresses pavement analysis to predict fatigue behavior from the S-VECD model were used to show the potential effects of silo storage time on pavement life. Results from all tests indicated that mixtures aged with an increase in silo storage time. RAP materials experienced a greater effect; this effect may be a function of the air void content or indication of blending–diffusion in the silo. Rolling thin film oven aging showed that current laboratory conditioning methods do not necessarily simulate asphalt plant production. Production parameters, such as silo storage time, have a significant impact on mixture performance.}, number={2573}, journal={TRANSPORTATION RESEARCH RECORD}, author={Jacques, Christopher and Daniel, Jo Sias and Bennert, Thomas and Reinke, Gerald and Norouzi, Amirhossein and Ericson, Christopher and Mogawer, Walaa and Kim, Y. Richard}, year={2016}, pages={76–85} }
 @article{wang_zhang_castorena_zhang_kim_2016, title={Identifying fatigue failure in asphalt binder time sweep tests}, volume={121}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2016.06.020}, abstractNote={Abstract Identification of fatigue failure of asphalt binder in time sweep test results remains a question crucial to asphalt binder fatigue performance evaluation and prediction. This paper presents a comparison of different analysis approaches for defining the occurrence of fatigue failure during time sweep fatigue tests conducted in both control-displacement and control-stress loading modes. The candidate failure definitions evaluated include the traditional 50% reduction in stiffness parameter (S0.5), dissipated energy indicators including the dissipated energy ratio (DER) and the ratio of dissipated energy change (RDEC), as well as two phenomenological parameters corresponding to the peak in S × N and peak in phase angle. Both phenomenological parameters and dissipated energy based indicators were found to be effective in defining fatigue failure. Statistical analysis results further indicate that maximum S × N, maximum phase angle and RDEC approach provide equivalent fatigue life results, however, peak in S × N is strongly recommended for detecting fatigue failure of asphalt binder in time sweep tests because it is easy to calculate and well defined.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Wang, Chao and Zhang, Han and Castorena, Cassie and Zhang, Jinxi and Kim, Y. Richard}, year={2016}, month={Sep}, pages={535–546} }
 @article{safaei_castorena_kim_2016, title={Linking asphalt binder fatigue to asphalt mixture fatigue performance using viscoelastic continuum damage modeling}, volume={20}, ISSN={["1573-2738"]}, DOI={10.1007/s11043-016-9304-1}, number={3}, journal={MECHANICS OF TIME-DEPENDENT MATERIALS}, author={Safaei, Farinaz and Castorena, Cassie and Kim, Y. Richard}, year={2016}, month={Aug}, pages={299–323} }
 @article{norouzi_kim_kim_2016, title={Numerical evaluation of pavement design parameters for the fatigue cracking and rutting performance of asphalt pavements}, volume={49}, ISSN={["1871-6873"]}, DOI={10.1617/s11527-015-0744-x}, number={9}, journal={MATERIALS AND STRUCTURES}, author={Norouzi, Amirhossein and Kim, Dahae and Kim, Y. Richard}, year={2016}, month={Sep}, pages={3619–3634} }
 @article{im_kim_2016, title={Performance Evaluation of Chip Seals for Higher Volume Roads Using Polymer-Modified Emulsions: Laboratory and Field Study in North Carolina}, volume={44}, ISSN={["1945-7553"]}, DOI={10.1520/jte20140544}, abstractNote={This paper presented a study to evaluate the performance of chip seals for higher traffic volume roads. The evaporation test, bitumen bond strength (BBS) test, and Vialit test were used to investigate curing and adhesive behavior. For the laboratory performance, the third-scale model mobile load simulator (MMLS3) was employed to test for aggregate retention, bleeding, and rutting performance. In field, a total of ten test sections were constructed on three different traffic volume roads using different materials and seal types. Some of the field samples were extracted and moved to the laboratory for performance testing. Also, the field sections were monitored to compare the field performance with the laboratory performance. The main findings presented in this paper were as follows: (1) the laboratory test results indicated that the use of polymer modified emulsions (PMEs) improved the chip seal performance in all areas, i.e., curing and adhesive behavior, aggregate retention, bleeding, and rutting; and (2) the field observations indicated that PME-A (styrene butadiene styrene (SBS) polymer-modified emulsion) performs the best of all the emulsions, regardless of seal type and traffic volume.}, number={1}, journal={JOURNAL OF TESTING AND EVALUATION}, author={Im, Jeong Hyuk and Kim, Y. Richard}, year={2016}, month={Jan}, pages={484–497} }
 @article{cao_kim_2016, title={The extended shift model as a mechanistic-empirical approach to simulating confined permanent deformation of asphalt concrete in compression}, volume={115}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2016.04.079}, abstractNote={Abstract The extended shift model is presented as a convenient and effective mechanistic-empirical approach to simulating the densification induced permanent deformation of asphalt concrete under repeated loading. The model is composed of an incremental function that provides a reference deformation curve, and a shift factor function expressed in terms of three variables: reduced pulse time, confining pressure, and vertical stress. The model can be characterized by four triaxial stress sweep tests, and it fits in the state-of-practice frameworks to predict pavement rutting with improved reliability.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Cao, Wei and Kim, Y. Richard}, year={2016}, month={Jul}, pages={520–526} }
 @inproceedings{wargo_safavizadeh_kim_2016, title={The use of four-point bending notched beam fatigue tests to rank crack-mitigating interlayers}, volume={11}, booktitle={8th rilem international symposium on testing and characterization of sustainable and innovative bituminous materials}, author={Wargo, A. D. and Safavizadeh, S. and Kim, R. Y.}, year={2016}, pages={359–370} }
 @article{cho_kim_2016, title={Verification of Time-Temperature Superposition Principle for Shear Bond Failure of Interlayers in Asphalt Pavements}, ISSN={["2169-4052"]}, DOI={10.3141/2590-03}, abstractNote={Asphalt pavement structures are composed of different asphalt concrete layers with surface layers that are bonded together with a tack coat. Thus, interlayer bonding between pavement layers is a key factor that affects the performance of any pavement structure. However, relatively little attention has been given to the characterization and modeling of interlayer bonding or to associated test methods that can be used in the laboratory to evaluate the bond strength between asphalt concrete layers. This paper presents a test method for evaluating interface bonding between asphalt concrete layers in shear mode. Moreover, the time–temperature superposition (t-TS) principle with growing damage in shear failure mode is examined to characterize the shear bond strength of asphalt concrete pavements for a wide range of temperatures. The subsequent validation of the t-TS principle allows the shear bond strength between asphalt layers at various temperatures and loading rates to be determined with only three or four shear tests. Comparison of the shear stress values calculated from a mechanistic pavement analysis program for a critical condition with the shear strength values at the condition determined from the prediction model developed in this study can provide the foundation for a mechanistic design to prevent shear bond failure between asphalt layers.}, number={2590}, journal={TRANSPORTATION RESEARCH RECORD}, author={Cho, Seong-Hwan and Kim, Y. Richard}, year={2016}, pages={18–27} }
 @article{sabouri_bennert_daniel_kim_2015, title={A comprehensive evaluation of the fatigue behaviour of plant-produced RAP mixtures}, volume={16}, ISSN={["2164-7402"]}, DOI={10.1080/14680629.2015.1076997}, abstractNote={In this study, the fatigue performance of 12 plant-produced mixtures from New Hampshire and Vermont that contain reclaimed asphalt pavement (RAP) contents of 0–40% by total weight of mixture was evaluated. The mixture tests included dynamic modulus, uniaxial fatigue, beam fatigue, and overlay tests. Also, the simplified viscoelastic continuum damage (S-VECD) model failure criterion, called the GR method, was applied and input to the linear viscoelastic pavement analysis for critical distresses (LVECD) programme to predict the fatigue behaviour of the tested mixtures on thin and thick asphalt pavement structures. In order to explain the observed fatigue behaviour, the performance grades (PGs) of the binders that were extracted and recovered from the mixtures were determined. In general, the addition of RAP resulted in an increase in the stiffness of the materials. The magnitude of the impact of higher RAP percentages varied with each set of mixtures. The S-VECD model and beam fatigue test data showed a loss of fatigue resistance for high-percentage RAP mixtures in most of the cases. The overlay tester results showed clear drops in performance at higher RAP contents. The impact of lowering the PG of the virgin binder to compensate for higher levels of RAP also was studied. Lowering the PG led to improvement in the fatigue properties and was found to be a convenient practice. The changes in the measured properties also appeared to be a function of mix design variables that included the stiffness of the RAP, asphalt content, and production parameters such as silo storage times. In some cases, the effects of these factors outweighed the impact of the RAP level or PG of the virgin binder in the mixtures.}, journal={ROAD MATERIALS AND PAVEMENT DESIGN}, author={Sabouri, Mohammadreza and Bennert, Thomas and Daniel, Jo Sias and Kim, Y. Richard}, year={2015}, pages={29–54} }
 @article{zhang_yang_kim_2015, title={Characterization of mechanical behavior of asphalt mixtures under partial triaxial compression test}, volume={79}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2014.12.085}, abstractNote={Abstract The principle and procedures of partial triaxial compression test (PTCT) was introduced. The appropriate diameter and height of specimen and platen were determined for PTCT requirement. Three types of mixtures were tested by PTCT at a temperature of 60 °C. Stress–strain results indicate that the response of asphalt mixtures to various test conditions by PTCT is in accordance with that of typical triaxial compression tests. Also, both PTCT and traditional triaxial compression test represent the similar deformation characteristics of asphalt mixtures. The PTCT inherits many advantages possessed by the triaxial test, and is easier to be carried out considering the simplicity of experimental equipment, specimen preparation, and test operation.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Zhang, Jiantong and Yang, Jun and Kim, Y. Richard}, year={2015}, month={Mar}, pages={136–144} }
 @article{sabouri_bennert_daniel_kim_2015, title={Fatigue and rutting evaluation of laboratory-produced asphalt mixtures containing reclaimed asphalt pavement}, number={2506}, journal={Transportation Research Record}, author={Sabouri, M. and Bennert, T. and Daniel, J. S. and Kim, Y. R.}, year={2015}, pages={32–44} }
 @article{safavizadeh_wargo_guddati_kim_2015, title={Investigating reflective cracking mechanisms in grid-reinforced asphalt specimens use of four-point bending notched beam fatigue tests and digital image correlation}, number={2507}, journal={Transportation Research Record}, author={Safavizadeh, S. A. and Wargo, A. and Guddati, M. and Kim, Y. R.}, year={2015}, pages={29–38} }
 @article{veytskin_bobko_castorena_kim_2015, title={Nanoindentation investigation of asphalt binder and mastic cohesion}, volume={100}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2015.09.053}, abstractNote={Abstract A nanoindentation technique for determining the cohesive properties of neat, modified, and aged asphalt binders and mastics with varying filler volumetric concentrations is developed, tested, and verified. Cohesive properties of binder and mastic are critically important to the fracture resistance of asphalt concrete. A new approach to calculate and interpret important cohesive properties from nanoindentation data through low-load sphero-conical (blunt) nanoindentation is presented. Work of effective cohesion values are determined as the average response over multiple possible microstructures for three asphalt binders and 30 different mastics of varying filler volumetric concentrations. Results point to evidence of a critical filler volume fraction beyond which further addition of filler does not affect work of effective cohesion. This plateau in work of effective cohesion values is speculated to be related to the combined effects of volume-filling, particle interactions, and physicochemical interactions. The critical filler volumetric concentrations corresponding to the plateau in work of effective cohesion range between 0.20 and 0.30, which is within the range from literature of 0.15–0.30. Testing of binder and mastic through nanoindentation is an important step toward in situ testing of mastic within asphalt concrete, which is inaccessible using conventional macroscopic experimental methods.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Veytskin, Yuriy and Bobko, Christopher and Castorena, Cassie and Kim, Y. Richard}, year={2015}, month={Dec}, pages={163–171} }
 @article{sakhaeifar_kim_kabir_2015, title={New predictive models for the dynamic modulus of hot mix asphalt}, volume={76}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2014.11.011}, abstractNote={Abstract This paper presents a fundamental modeling framework for prediction of dynamic modulus of hot mix asphalt mixtures based on viscoelastic principles. The outcomes are two closed-form models that can be used to predict the mixture dynamic modulus for a wide range of temperatures (−10°, 4.4°, 37.8°, and 54.4 °C) recommended in the American Association of State Highway and Transportation Officials (AASHTO) TP62-03 test protocol. To develop and verify the models a large database that covers the complete range of potential input conditions was assembled. In general, the proposed models predict the dynamic modulus with a very good level of accuracy.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Sakhaeifar, Maryam S. and Kim, Y. Richard and Kabir, Pooyan}, year={2015}, month={Feb}, pages={221–231} }
 @article{im_kim_2015, title={Performance evaluation of fog seals on chip seals and verification of fog seal field tests}, volume={42}, ISSN={["1208-6029"]}, DOI={10.1139/cjce-2014-0340}, abstractNote={With an increasing emphasis on pavement preservation treatments due to economic concerns over the high costs of paving materials, one of the most cost-effective pavement preservation treatments, chip seals, now constitutes a significant proportion of the pavement preservation treatments used in the North Carolina highway network. To mitigate a major problem with chip seals, i.e., the loose aggregate particles, fog seals, which are composed of an emulsified product placed on top of the chip seal, can be used to help control the loose aggregate. For this study, fog seals were applied on top of newly fabricated chip. The surface texture of the fog-sealed chip seals was analyzed using the British pendulum test and a three-dimensional laser. Also, fog seal field test methods that were developed to suggest appropriate traffic opening times after fog seal construction were verified. The main findings presented in this paper are that: (i) the use of polymer-modified emulsions improves fog seal performance in terms of better aggregate retention and bleeding resistance; (ii) the skid resistance problems are not evident once the fog seal is applied on the recommended chip seal type; (iii) the relationship between skid number and mean profile depth can be determined based on three trends that are dependent on traffic loadings, and (iv) although the fog seal field tests were unable to be completed due to safety concerns, it can nonetheless be recommended that approximately 60 min after fog seal construction is an appropriate traffic opening time.}, number={11}, journal={CANADIAN JOURNAL OF CIVIL ENGINEERING}, author={Im, Jeong Hyuk and Kim, Y. Richard}, year={2015}, month={Nov}, pages={872–880} }
 @article{park_kim_2015, title={Primary causes of cracking of asphalt pavement in North Carolina: field study}, volume={16}, ISSN={["1477-268X"]}, DOI={10.1080/10298436.2014.943220}, abstractNote={Presently, North Carolina is experiencing higher than anticipated rates of fatigue cracking. Field materials and pavement conditions are investigated to find the primary causes of cracking in North Carolina. This study finds that pavements with high asphalt content tend to be in good condition based on the top-down cracking (TDC) observed in the top layer, and pavements with low air void contents tend also to be in good condition. In addition, fine-graded mixes tend to yield a better pavement condition than coarse-graded mixes. The structure-related comprehensive analysis suggests that debonding is one of the major causes of a poor pavement condition. Road widening is another cause of cracking that can develop into fatigue cracking. Regions in which bottom-up cracking is observed tend to have larger bending strains at the bottom of the asphalt layer than regions where TDC is observed.}, number={8}, journal={INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING}, author={Park, Hong Joon and Kim, Y. Richard}, year={2015}, month={Sep}, pages={684–698} }
 @article{lee_kim_lee_2015, title={Rutting performance evaluation of asphalt mix with different types of geosynthetics using MMLS3}, volume={16}, ISSN={["1477-268X"]}, DOI={10.1080/10298436.2014.972916}, abstractNote={This paper presents an evaluation of the rutting performance of geosynthetics in asphalt pavements. The rutting performance of both a fibreglass geogrid and a sheet reinforcement material were evaluated using the third-scale model mobile loading simulator (MMLS3). The surface profile of each type of reinforced slab (and a control slab) was monitored and compared. To investigate movement of the mixtures caused by MMLS3 loading as well as the interfaces of the reinforcements in the asphalt slabs, trench cuts were made once the MMLS3 rutting tests were complete. The results demonstrated that reinforcement can reduce downward ruts and that different types of reinforcement exhibited different shear flow behaviour. The geogrid-reinforced slabs showed the shallowest ruts and the most shear flow resistance due to the tension resistance of the geogrid. They exhibited confinement and increased friction due to the aggregate particles that were locked in the geogrid openings. The sheet-reinforced slabs exhibited the highest shear flow humps due to the lack of interlocking and bonding strength at the rutting test temperature. In addition, the geogrid openings, which were supposed to provide interlocking and anchoring, in fact generated a relatively high volume of voids at the interface between lifts. Further research is needed to evaluate the effects of high air voids at the lift interface on pavement performance.}, number={10}, journal={INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING}, author={Lee, Jusang and Kim, Y. Richard and Lee, Jaejun}, year={2015}, month={Nov}, pages={894–905} }
 @article{wang_castorena_zhang_kim_2015, title={Unified failure criterion for asphalt binder under cyclic fatigue loading}, volume={16}, ISSN={["2164-7402"]}, DOI={10.1080/14680629.2015.1077010}, abstractNote={Defining failure and developing a unified failure criterion for the fatigue testing of asphalt materials remain a challenge. This study seeks to develop a failure criterion for the fatigue testing of asphalt binders under cyclic loading in the dynamic shear rheometer. Newly developed pseudo-strain energy (PSE)-based failure analysis is introduced for both the time sweep fatigue test and the accelerated linear amplitude sweep (LAS) test (AASHTO TP101). The presented methodology builds upon recent advances in the simplified viscoelastic continuum damage (S-VECD) modelling of asphalt mixtures. Trends in stored PSE have been proven to be effective in defining failure for the LAS tests of asphalt binders. This new proposed failure definition is material-dependent and, thus, is effective in capturing the benefits of asphalt modification for binder fatigue resistance. In addition, it is found that a unique relationship that is independent of loading history exists between the PSE release rate and fatigue life. T...}, journal={ROAD MATERIALS AND PAVEMENT DESIGN}, author={Wang, Chao and Castorena, Cassie and Zhang, Jinxi and Kim, Y. Richard}, year={2015}, pages={125–148} }
 @article{lee_gibson_kim_2015, title={Use of Mechanistic Models to Investigate Fatigue Performance of Asphalt Mixtures Effects of Asphalt Mix Design Targets and Compaction}, ISSN={["2169-4052"]}, DOI={10.3141/2507-12}, abstractNote={Effects of design air void contents, design voids in mineral aggregate (VMA), and in-place air voids on the fatigue performance of asphalt mixtures were investigated with mechanistic analyses based on the viscoelastic continuum damage (VECD) analyses and the mechanistic–empirical pavement analysis using the AASHTOWare Pavement ME Design program. The VECD analyses included the simplified viscoelastic continuum damage model at the material level and two structural models: ( a) layered viscoelastic analysis and ( b) layered viscoelastic pavement analysis for critical distresses. The mix design of a 2013 accelerated loading facility test lane was selected to develop the volumetric mix designs with the design air voids of 3%, 4%, and 5%, design VMAs of 13%, 14%, and 15%, and in-place air void contents of 5%, 7%, and 9% with the Bailey method. Dynamic modulus and direct tension cyclic fatigue tests were performed in accordance with the AASHTO TP 107 procedure. The test results showed that the linear viscoelastic property was affected by the design VMA, design air void content, and in-place air void content in order of sensitivity. Also, the damage states at failure determined from the damage characteristic curves and the mechanistic fatigue predictions had consistent trends as observed for the design VMA, in-place air void, and design air void content in rank of sensitivity. Finally, the design VMA, in-place air void, and design air void parameters were found to be sensitive in the mechanistic analyses, whereas the parameter that was most sensitive in the pavement mechanistic–empirical analysis was the in-place air void content.}, number={2507}, journal={TRANSPORTATION RESEARCH RECORD}, author={Lee, Jong-Sub and Gibson, Nelson and Kim, Y. Richard}, year={2015}, pages={108–119} }
 @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={Abstract 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} }
 @book{asphalt pavements_2014, publisher={Boca Raton: CRC Press}, year={2014} }
 @article{sabouri_kim_2014, title={Development of a failure criterion for asphalt mixtures under different modes of fatigue loading}, number={2447}, journal={Transportation Research Record}, author={Sabouri, M. and Kim, Y. R.}, year={2014}, pages={117–125} }
 @article{buttlar_hill_kim_kutay_millien_montepara_paulino_petit_pop_romeo_et al._2014, title={Digital image correlation techniques to investigate strain fields and cracking phenomena in asphalt materials}, volume={47}, ISSN={["1871-6873"]}, DOI={10.1617/s11527-014-0362-z}, number={8}, journal={MATERIALS AND STRUCTURES}, author={Buttlar, William G. and Hill, Brian C. and Kim, Y. Richard and Kutay, M. Emin and Millien, Anne and Montepara, Antonio and Paulino, Glaucio H. and Petit, Christophe and Pop, Ion Octavian and Romeo, Elena and et al.}, year={2014}, month={Aug}, pages={1373–1390} }
 @inproceedings{im_kim_2014, title={Evaluation of early aggregate retention performance of chip seals with polymer-modified emulsions}, DOI={10.1201/b17219-20}, booktitle={Asphalt Pavements, vol 1}, author={Im, J. H. and Kim, Y. R.}, year={2014}, pages={105–114} }
 @article{choi_kim_2014, title={Implementation and verification of a mechanistic permanent deformation model (shift model) to predict rut depths of asphalt pavement}, volume={15}, ISSN={["2164-7402"]}, DOI={10.1080/14680629.2014.927085}, abstractNote={The shift model is implemented in the layered viscoelastic asphalt pavement analysis for critical distresses (LVECD) program to predict the rut depth of asphalt pavements. The rut depth measurements taken at the National Center for Asphalt Technology (NCAT) test track and the Federal Highway Administration Accelerated Facility (FHWA ALF) test sections are evaluated using the model. The model can successfully evaluate rut depth, which proves the capability of the model implemented in the LVECD program. The slight over-prediction of the NCAT sections can be explained by ageing in the field that increases the pavement's resistance to rutting. The simulation results support the hypothesis that triaxial stress sweep tests with confinement can represent the permanent deformation behaviour of asphalt concrete in the field. In this regard, excessive shear flow may be the reason for the under-prediction of the FHWA ALF mixtures. For better predictions, a correction factor (i.e. a transfer function) is suggested, which is quantified via the ratio of shear stress to shear resistance. After applying individual transfer functions, the permanent deformation model in the LVECD can evaluate the growth of the rut depth. Therefore, even though the shift model is a uniaxial model, the model can predict the rut depth of asphalt concrete by employing the transfer function.}, journal={ROAD MATERIALS AND PAVEMENT DESIGN}, author={Choi, Yeong-Tae and Kim, Y. Richard}, year={2014}, pages={195–218} }
 @article{safaei_lee_nascimento_hintz_kim_2014, title={Implications of warm-mix asphalt on long-term oxidative ageing and fatigue performance of asphalt binders and mixtures}, volume={15}, ISSN={1468-0629 2164-7402}, url={http://dx.doi.org/10.1080/14680629.2014.927050}, DOI={10.1080/14680629.2014.927050}, abstractNote={The use of warm mix asphalt (WMA) has been increasing in recent years due to its ability to reduce the production temperatures of asphalt concrete. The long-term implications of reduced production temperatures and, hence, reduced short-term ageing on long-term performance remain largely unknown. This study evaluates the effect of age hardening in WMA binders and mixtures compared with hot mix asphalt (HMA) binders and mixtures with respect to fatigue damage. Two WMA technologies are considered: foaming by water injection and Evotherm modification. For this study, the asphalt mixtures were subjected to laboratory conditioning in a forced air convection oven to simulate long-term field ageing according to AASHTO R30. The asphalt mixtures and extracted binders were subjected to linear viscoelastic and fatigue characterisation following ageing. Because oxidative ageing occurs within the asphalt binder phase of asphalt concrete, this paper focuses on the relative performance of WMA and HMA binders at various a...}, number={sup1}, journal={Road Materials and Pavement Design}, publisher={Informa UK Limited}, author={Safaei, Farinaz and Lee, Jong-sub and Nascimento, Luis Alberto Hermann do and Hintz, Cassie and Kim, Y. Richard}, year={2014}, month={Jun}, pages={45–61} }
 @article{karshenas_cho_tayebali_guddati_kim_2014, title={Importance of Normal Confinement to Shear Bond Failure of Interface in Multi layer Asphalt Pavements}, ISSN={["2169-4052"]}, DOI={10.3141/2456-17}, abstractNote={Several direct shear test devices are used to evaluate the shear bond strength of tack coat materials in interlayer bonding in asphalt pavements. Some devices have the capability of evaluating strength in direct shear with normal confinement, whereas other devices do not have that capability or use passive confinement to evaluate the interlayer bond strength. The literature indicates that interlayer bond strength increases with the application of normal confinement. However, the question remains as to the level of normal confinement, if any, that should be used in direct shear testing to evaluate the interlayer bond strength for specification acceptance or design. This study presents a methodology to interpret laboratory bond strength test results in relation to the state of stress at the layer interface in a representative pavement section. The results confirm the importance of normal confinement for shear bond strength evaluation and provide guidance for the selection of the appropriate level of normal ...}, number={2456}, journal={TRANSPORTATION RESEARCH RECORD}, author={Karshenas, Afshin and Cho, Seong-Hwan and Tayebali, Akhtarhusein A. and Guddati, Murthy N. and Kim, Y. Richard}, year={2014}, pages={170–177} }
 @article{adams_kim_2014, title={Mean profile depth analysis of field and laboratory traffic-loaded chip seal surface treatments}, volume={15}, ISSN={["1477-268X"]}, DOI={10.1080/10298436.2013.851790}, abstractNote={This paper presents a laboratory and field study to evaluate the mean profile depth (MPD) parameter that represents the surface texture of chip seal pavements. A three-dimensional laser profiler is used to determine the MPD values from both field pavement sections and field samples that have been tested in the laboratory using the third-scale model mobile loading simulator (MMLS3). Data obtained from five different field-constructed chip seal sections are used to evaluate the effects of different factors on the MPD of chip seal pavements. These factors include aggregate type, emulsion application rate, field versus MMLS3 traffic loading and traffic volume. The results presented in this paper suggest that: (1) chip seal pavements constructed using lightweight aggregate have larger initial MPD values and faster reduction in MPD as a function of the number of wheel passes than those constructed using granite 78M aggregate; (2) MPD values obtained from a drier section (with drier indicating a lower emulsion-to-aggregate ratio than that of the sections it is being compared against) initially drop quickly and significantly, resulting in a much smaller ultimate MPD value; (3) in general, the MPD values obtained under MMLS3 loading are similar to those obtained from field traffic loading, thus allowing the translation of the laboratory MMLS3 data to the field response data; (4) a short rest period in a high-traffic volume road retards the recovery of the binder and, therefore, leads to more permanent changes in the MPD and (5) the initial measured MPD value can help predict aggregate loss performance.}, number={7}, journal={INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING}, author={Adams, Javon M. and Kim, Y. Richard}, year={2014}, month={Aug}, pages={645–656} }
 @article{park_eslaminia_kim_2014, title={Mechanistic evaluation of cracking in in-service asphalt pavements}, volume={47}, ISSN={["1871-6873"]}, DOI={10.1617/s11527-014-0307-6}, number={8}, journal={MATERIALS AND STRUCTURES}, author={Park, Hong Joon and Eslaminia, Mehran and Kim, Y. Richard}, year={2014}, month={Aug}, pages={1339–1358} }
 @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} }
 @article{lacroix_kim_2014, title={Performance Predictions of Rutting for the National Center for Asphalt Technology Test Track}, ISSN={["2169-4052"]}, DOI={10.3141/2457-05}, abstractNote={Performance-related specifications base pay rates on tests that measure and predict the performance of the mixture. This study evaluated several methods for predicting the rutting resistance of asphalt mixtures. The mixtures and field performance data came from the National Center for Asphalt Technology test track. The pavement sections evaluated were part of an experiment that focused on warm-mix asphalt, high-content reclaimed asphalt pavement (50%), and a combination of the two. One method involved using the dynamic moduli of the mixtures in confined and unconfined conditions. The ranking of the mixtures predicted from both conditions was good compared with the observed ranking from the track but was more reasonable with the confined data. These predictions were compared with common current tests such as the asphalt pavement analyzer and the Hamburg wheel tracker tests. From the ranking of rut depths, these tests did not appear able to distinguish subtler changes to material properties needed for a performance-related specification. Another method employed a viscoplastic shift model implemented within the layered viscoelastic continuum damage program to predict the rut depth. The predicted rut depths were biased 2.5 mm higher than those measured in the field when all three layers (175 mm) of asphalt were used to predict the rut depth, but the ranking matched the field quite well. The results from the top two layers (100 mm) of asphalt were less biased but were more variable than the three-layer results. The results suggest that all pavement layers should be evaluated for predicting rut depths, not just the top two layers.}, number={2457}, journal={TRANSPORTATION RESEARCH RECORD}, author={Lacroix, Andrew and Kim, Y. Richard}, year={2014}, pages={41–50} }
 @article{lee_kim_2014, title={Performance-Based Moisture Susceptibility Evaluation of Warm-Mix Asphalt Concrete Through Laboratory Tests}, ISSN={["2169-4052"]}, DOI={10.3141/2446-03}, abstractNote={This study used the cyclic direct tension test, indirect tensile strength test, and Hamburg wheel tracking device (HWTD) test to evaluate the moisture susceptibility of warm-mix asphalt (WMA) mixtures. The stripped areas that were quantified by digital imaging analysis were derived from the cyclic direct tension, indirect tensile strength, and HWTD tests and were compared with the mechanical properties of the mixtures to identify sensitive moisture susceptibility indicators. These methods were applied to a Superpave® 9.5-mm hot-mix asphalt mixture and five corresponding WMA mixtures that used the following technologies: (a) Evotherm 3G that contained a chemical additive, (b) foaming, (c) WMA-A that contained a chemical additive and was under development, (d) WMA-B that contained an organic additive and was under development, and (e) WMA-C that also contained an organic additive (different from that used in WMA-B) and was under development. Fatigue life ratios obtained from the simplified viscoelastic cont...}, number={2446}, journal={TRANSPORTATION RESEARCH RECORD}, author={Lee, Jong-Sub and Kim, Y. Richard}, year={2014}, pages={17–28} }
 @inproceedings{wargo_islam_kim_2014, title={The reflective cracking tester: A third-scale accelerated pavement tester for reflective cracking}, booktitle={Asphalt Pavements, vols 1 and 2}, author={Wargo, A. D. and Islam, S. and Kim, Y. R.}, year={2014}, pages={1685–1693} }
 @article{choi_kim_2013, title={A Mechanistic Permanent Deformation Model for Asphalt Concrete in Compression}, volume={82}, ISSN={["0270-2932"]}, DOI={10.1080/14680629.2013.812847}, abstractNote={Permanent deformation modelling research at North Carolina State University has produced the so-called incremental model that fits the primary and secondary regions in permanent strain growth. Triaxial repeated load permanent deformation tests are conducted on Federal Highway Administration-Accelerated Loading Facility and NY9.5B mixtures to evaluate the effects of temperature, stress, and load time on permanent deformation and, therefore, to determine the form of the incremental model to account for these effects. The test results suggest that the slope in the log(ϵvp)−log(N) plot is constant regardless of these three major factors. This observation provides the basis for two modelling approaches: the functionalised model and the shift model. The functionalised model is formulated by expressing the coefficients of the incremental model in terms of the reduced load time and deviatoric stress. The shift model, based on the time-temperature–stress superposition principle, utilises the strain mastercurve and reduced load time and deviatoric stress shift functions. A composite loading test that is composed of varying load times and deviatoric stresses is proposed as the model calibration test. It is found that the permanent strain growth under the complex loading histories predicted by the calibrated models is in good agreement with the measured permanent strain growth.}, journal={ASPHALT PAVING TECHNOLOGY 2013, VOL 82}, author={Choi, Yeong-Tae and Kim, Y. Richard}, year={2013}, pages={617–649} }
 @inproceedings{choi_kim_2013, title={A mechanistic permanent deformation model for asphalt concrete in compression}, volume={82}, booktitle={Asphalt paving technology 2013, vol 82}, author={Choi, Y. T. and Kim, Y. R.}, year={2013}, pages={617–649} }
 @article{subramanian_guddati_kim_2013, title={A viscoplastic model for rate-dependent hardening for asphalt concrete in compression}, volume={59}, ISSN={["1872-7743"]}, DOI={10.1016/j.mechmat.2012.10.003}, abstractNote={Abstract This paper presents a new type of viscoplastic model based on viscoelastic convolution integrals for explaining the behavior of asphalt concrete in compression under repeated loading. Triaxial compression cyclic tests carried out for long rest periods, with different loading times and two different pulse shapes, square and haversine, were used in developing and validating the model. These tests demonstrate that the evolution of permanent deformation depends on load history. This history-dependent behavior is not captured accurately by some of the existing Perzyna-type viscoplastic models in which permanent deformation evolution depends on the current values of stress and viscoplastic strain. Therefore, in this study, viscoelastic-like convolution integrals were used in the model to capture the effect of history. The proposed model is applicable to compressive creep and recovery experiments at 54 °C with (1) several hundreds of cycles of loading including the secondary creep region, (2) haversine loading shapes at three different peak deviatoric stress levels, 620 kPa, 827 kPa, and 1034 kPa, and square loading shapes at 827 kPa peak deviatoric stress, and (3) long rest periods that allow complete viscoelastic recovery.}, journal={MECHANICS OF MATERIALS}, author={Subramanian, Vijay and Guddati, Murthy N. and Kim, Y. Richard}, year={2013}, month={Apr}, pages={142–159} }
 @article{choi_kim_2013, title={Development of Calibration Testing Protocol for Permanent Deformation Model of Asphalt Concrete}, ISSN={["2169-4052"]}, DOI={10.3141/2373-04}, abstractNote={Recent permanent deformation modeling research at North Carolina State University has resulted in the shift model, which is capable of expressing the permanent strain growth of asphalt concrete as a function of deviatoric stress, load time, and temperature on the basis of the time–temperature superposition and time–stress superposition principles. This paper presents an efficient calibration test protocol for the shift model as well as verification of the model. The proposed test protocol is comprised of triaxial stress sweep (TSS) tests and a reference test. The TSS test is suggested to reduce the number of tests required by applying three deviatoric stresses within one test. Each TSS test was performed at three temperatures: high (T H ), intermediate (T I ), and low (T L ). The reference test was a triaxial repeated load permanent deformation test conducted at T H only. The shift model was calibrated for the polymer-modified dense-graded NY9.5B mix, and the calibrated model was applied successfully to predict strain growth for the composite tests at the three study temperatures and for random load tests at T H . The calibration testing procedure was optimized for the asphalt mixture performance tester. The TSS tests take approximately 2.9 h at T H and 1.5 h at T I and T L . Thus, about a day was required to complete one set of calibration tests under the proposed test protocol. Within 2 to 3 days of testing, depending on the number of replicates, the calibrated shift model is capable of predicting permanent strain growth for different temperatures, load times, and deviatoric stresses.}, number={2373}, journal={TRANSPORTATION RESEARCH RECORD}, author={Choi, Yeong-Tae and Kim, Y. Richard}, year={2013}, pages={34–42} }
 @inproceedings{zhang_sabouri_guddati_kim_2013, title={Development of a failure criterion for asphalt mixtures under fatigue loading}, volume={82}, booktitle={Asphalt paving technology 2013, vol 82}, author={Zhang, J. and Sabouri, M. and Guddati, M. N. and Kim, Y. R.}, year={2013}, pages={1–22} }
 @article{zhang_sabouri_guddati_kim_2013, title={Development of a failure criterion for asphalt mixtures under fatigue loading}, volume={14}, ISSN={["2164-7402"]}, DOI={10.1080/14680629.2013.812843}, abstractNote={The failure criterion defines the applicable region associated with the continuum damage model and is important in characterising the service life of asphalt mixtures. A proper failure criterion should consistently predict the failure of the material that reaches macro-fracture. A previously developed criterion that uses the viscoelastic continuum damage (VECD) model exhibits high variability and is considered to be inefficient because it requires calibration tests at different temperatures. In this paper, a new concept that involves released pseudo strain energy is introduced. This released pseudo strain energy concept focuses on the dissipated energy that is related to stiffness reduction only and is fully compatible and predictable using the VECD model. A characteristic relationship is found between the stable rate of pseudo energy release during testing and the final fatigue life of the same mixture, independent of strain amplitude and temperature. Based on these observations, a new failure criterion ...}, journal={ROAD MATERIALS AND PAVEMENT DESIGN}, author={Zhang, Jun and Sabouri, Mohammadreza and Guddati, Murthy N. and Kim, Y. Richard}, year={2013}, month={Aug}, pages={1–15} }
 @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} }
 @article{shan_tan_kim_2013, title={Establishment of a universal healing evaluation index for asphalt binder}, volume={48}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2013.06.039}, abstractNote={Abstract The healing performance of asphalt binder is important to the overall performance of asphalt pavement. A suitable healing evaluation index is critical in order to compare the healing performance of different asphalt binders and choose the binder with the best healing properties. However, current studies focus primarily on the healing performance of asphalt binder and seem to ignore the importance of the healing evaluation index. In this paper, the healing performance of four different asphalt binders is analyzed. By comparing the healing curve to the initial curve, a ratio that is based on the areas created by the curves is found to reflect the healing performance of asphalt binders. Once the healing evaluation indices are established, they are also used to evaluate the mastics, and the applicability of the indices is analyzed. Also, a healing function for asphalt binder is established. The results show that the HI m-c index (based on the curve of the normalized modulus versus load cycles), the HI em-c index (based on the curve of the elastic modulus versus load cycles) and the HI vm-c index (based on the curve of the viscous modulus versus load cycles) suggest the same rankings for the healing of the studied binders. The healing ranking of the binders is also the same as that of the corresponding mastics evaluated by the HI m-c index. Based on the established healing function, it is found that the effect of terminal cases on the healing performance of asphalt binder is greater than the effect of rest periods.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Shan, Liyan and Tan, Yiqiu and Kim, Y. Richard}, year={2013}, month={Nov}, pages={74–79} }
 @article{park_kim_2013, title={Investigation into Top-Down Cracking of Asphalt Pavements in North Carolina}, ISSN={["2169-4052"]}, DOI={10.3141/2368-05}, abstractNote={Top-down cracking has become a commonly reported cracking mechanism in asphalt pavements worldwide. In top-down cracking, a crack initiates at the surface of an asphalt concrete pavement and propagates to the bottom of the asphalt pavement layer. Because the location and governing state of stress for top-down cracking are different from those for bottom-up cracking, analysis of pavement cracking performance must be robust enough to account for the complex mechanisms that are involved in top-down cracking. This study applies the viscoelastic continuum damage finite element model to the evaluation of two pavement sections in North Carolina where top-down cracking has been identified. Small specimen geometries are used to perform simplified viscoelastic continuum damage testing on individual asphalt layers obtained from field cores. This testing model and the Fourier finite element program are used together for pavement cracking performance simulations, and the joint model uses the structure and layer material properties obtained from the two study pavements. The simulation results clearly support the propensity of these pavements to exhibit top-down cracking. In addition to laboratory testing and analysis, the deflection-based method suggested by Uhlmeyer et al. is applied to the data obtained from pavement sections with known crack initiation locations, and that method's validity is investigated. The Uhlmeyer method uses the AREA parameter, which is determined from falling weight deflectometer deflections, and pavement thicknesses. The analysis results show a clear difference in the AREA versus pavement thickness relationship between the pavement sections with top-down cracking and those with full-depth cracking.}, number={2368}, journal={TRANSPORTATION RESEARCH RECORD}, author={Park, Hong Joon and Kim, Y. Richard}, year={2013}, pages={45–55} }
 @article{im_kim_2013, title={Methods for Fog Seal Field Test with Polymer-Modified Emulsions Development and Performance Evaluation}, ISSN={["2169-4052"]}, DOI={10.3141/2361-11}, abstractNote={Findings from a laboratory evaluation of fog seal emulsions are presented. Curing time and adhesive behavior of polymer-modified emulsions (PMEs) were compared with those of unmodified emulsions as fog seal materials. The study showed that polymer modification could improve certain properties of emulsions, such as an increase in adhesion. The evaporation test and the pneumatic adhesion tension testing instrument were used to investigate emulsion curing and adhesive behavior. Also, the rolling ball test and the damping test were developed as in situ test methods to determine an appropriate traffic opening time for roadways treated with fog seals. Finally, the third-scale Model Mobile Load Simulator was employed to compare the performance properties of the fog seal emulsions. The following main findings are presented: use of PMEs improved the emulsion bond strength and lessened the time a road was closed to traffic; PMEs showed more effective emulsion curing rates than did unmodified emulsions; strong relationships existed between the bond strength and both the measured rolling distance (from the rolling ball test) and the measured percentage of stained area (from the damping test); field test methods could be used to help determine whether emulsions were fully cured; and PMEs exhibited better aggregate retention and bleeding performance properties than did unmodified emulsions as a fog seal.}, number={2361}, journal={TRANSPORTATION RESEARCH RECORD}, author={Im, Jeong Hyuk and Kim, Y. Richard}, year={2013}, pages={88–97} }
 @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={AbstractMultiscale 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 a...}, 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_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} }
 @article{lee_lee_kwon_kim_2013, title={Use of Cyclic Direct Tension Tests and Digital Imaging Analysis to Evaluate Moisture Susceptibility of Warm-Mix Asphalt Concrete}, ISSN={["2169-4052"]}, DOI={10.3141/2372-08}, abstractNote={This paper presents a simplified viscoelastic continuum damage material model for the evaluation of moisture susceptibility of asphalt concrete. The model is based on cyclic direct tension testing and layered viscoelastic analysis. The visual stripping inspection afforded by digital imaging analysis is also proposed as an intuitive and straightforward method for moisture susceptibility evaluation. These methods were applied to a Superpave ® 19-mm hot-mix asphalt mixture and corresponding warm-mix asphalt mixtures modified by a polyethylene wax-type additive with and without an antistripping agent. The fatigue life predicted by the simplified viscoelastic continuum damage and layered viscoelastic analysis models had a strong correlation with the percentage of stripping determined from specimen surfaces that were fractured during cyclic direct tension testing of the hot-mix and warm-mix asphalt mixtures with various asphalt contents. In addition, a polyethylene wax-type additive combined with an antistripping agent was found to provide a longer fatigue life and less stripping than a pure polyethylene wax-type additive. The findings from this paper should provide guidance to agencies and material engineers in developing asphalt binder modifiers that lengthen the fatigue life of pavements and reduce moisture susceptibility.}, number={2372}, journal={TRANSPORTATION RESEARCH RECORD}, author={Lee, Jong-Sub and Lee, Jae-Jun and Kwon, Soo-Ahn and Kim, Y. Richard}, year={2013}, pages={61–71} }
 @article{yun_kim_2013, title={Viscoelastoplastic modeling of the behavior of hot mix asphalt in compression}, volume={17}, ISSN={["1976-3808"]}, DOI={10.1007/s12205-013-0352-7}, number={6}, journal={KSCE JOURNAL OF CIVIL ENGINEERING}, author={Yun, Taeyoung and Kim, Y. Richard}, year={2013}, month={Sep}, pages={1323–1332} }
 @article{lee_lee_kim_mun_2012, title={A Comparison Study of Friction Measurements for Chip Seal}, volume={40}, ISSN={["1945-7553"]}, DOI={10.1520/jte103863}, abstractNote={This paper presents a development in measuring skid resistance in a laboratory performance test for chip seal. It is important to develop a relationship between the British pendulum test (BPT) and the locked-wheel skid test (LWST), or grip tester (GT). The chip seal is a typical pavement preservation treatment used by the North Carolina Dept. of Transportation (NCDOT). In North America, loss of skid resistance is a common road condition that indicates the need for a chip seal, as one of the major advantages of chip seal is an increase in skid resistance. Most agencies have a specified cycle in which skid resistance is measured as a part of their pavement-management system. These skid resistance measurements are invaluable when deciding which roads require chip seal [Gransberg, D. D. and James, D. M. B., “Chip Seal Best Practices,” NCHRP Synthesis of Highway Practice 342, Transportation Research Board of the National Academies, Washington, D.C., 2005]. In this study, skid resistance was evaluated on 14 selected chip seals using three different tests: the BPT, LWST, and GT. The correlation between British pendulum number (BPN) and skid number (SN) was relatively strong with an R2 value of 0.74. This finding indicated that the BPN measured in the laboratory could be utilized for predicting the SN, which cannot be measured in the laboratory.}, number={4}, journal={JOURNAL OF TESTING AND EVALUATION}, author={Lee, Jusang and Lee, Jaejun and Kim, Y. Richard and Mun, Sungho}, year={2012}, month={Jul}, pages={603–611} }
 @article{kim_alexander_edmonson_2012, title={A Dataflow Framework for DSP Algorithm Refinement}, DOI={10.1109/isvlsi.2012.74}, abstractNote={Current video compression algorithms are increasingly complicated and difficult to analyze and profile. Design tools and system level languages often prove to be inefficient and incapable of providing complexity analysis as a first step directed toward at the implementation of video compression algorithms. This paper proposes framework that will help to develop a methodology that facilitates the derivation of analytical dataflow models. The framework proposes dataflow models for quantifying the underlying algorithm's memory complexity, related timing considerations, and verification of the correctness of the video compression algorithm.}, journal={2012 IEEE COMPUTER SOCIETY ANNUAL SYMPOSIUM ON VLSI (ISVLSI)}, author={Kim, Youngsoo and Alexander, Winser E. and Edmonson, William W.}, year={2012}, pages={1-+} }
 @inbook{eslaminia_thirunavukkarasu_guddati_kim_2012, title={Accelerated Pavement Performance Modeling Using Layered Viscoelastic Analysis}, ISBN={9789400745650 9789400745667}, url={http://dx.doi.org/10.1007/978-94-007-4566-7_48}, DOI={10.1007/978-94-007-4566-7_48}, abstractNote={An efficient pavement performance analysis framework is developed by combining the ideas of time-scale separation and Fourier transform-based layered analysis. First, utilizing the vast difference in time scales associated with temperature and traffic load variations, the number of stress analysis runs are reduced from several million to a few dozen. Second, the computational cost of the pavement stress analysis is reduced significantly by using Fourier transform-based analysis. The resulting pavement performance prediction tool, named the layered viscoelastic continuum damage (LVECD) program, can capture the effects of viscoelasticity, temperature (thermal stresses and changes in viscoelastic properties) and the moving nature of the traffic load. The efficiency of the LVECD program is shown through 20-year pavement simulations.}, booktitle={7th RILEM International Conference on Cracking in Pavements}, publisher={Springer Netherlands}, author={Eslaminia, Mehran and Thirunavukkarasu, Senganal and Guddati, Murthy N. and Kim, Y. Richard}, year={2012}, pages={497–506} }
 @article{shan_tan_kim_2012, title={Applicability of the Cox-Merz relationship for asphalt binder}, volume={37}, ISSN={["0950-0618"]}, DOI={10.1016/j.conbuildmat.2012.07.020}, abstractNote={Asphalt binder has a critical effect on the performance of asphalt mixtures. Thus, asphalt binder is of great concern to pavement engineers and researchers. Usually, asphalt binder is studied in dynamic space and steady-state space separately, and the property indices are researched separately. As researchers delved deeper, they found that it is important to combine the dynamic properties and steady-state properties, especially for establishing rheological curves and constitutive equations. The Cox–Merz relationship can connect the properties in dynamic space to those in steady-state space. This relationship is widely used in polymer system and shows good results. This study focused on the applicability of the Cox–Merz relationship as it pertains to asphalt binder. The Cox–Merz relationship was applied to six neat asphalt binders. Then, the applicability of the Cox–Merz relationship for asphalt binder was studied and the criterion to verify whether the Cox–Merz relationship is followed or not was established. Finally the viscosity functions when the Cox–Merz relationship used were studied, and the Cross model and the Carreau model were compared. The results show that the Cox–Merz relationship is followed in the shear-thinning region and not always followed in the zero-shear-rate-limiting viscosity region, and it is useful when obtaining the viscosity function.}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Shan, Liyan and Tan, Yiqiu and Kim, Y. Richard}, year={2012}, month={Dec}, pages={716–722} }
 @article{jadoun_kim_2012, title={Calibrating Mechanistic-Empirical Pavement Design Guide for North Carolina: Genetic Algorithm and Generalized Reduced Gradient Optimization Methods}, ISSN={["2169-4052"]}, DOI={10.3141/2305-14}, abstractNote={The Mechanistic–Empirical Pavement Design Guide (MEPDG) is the state-of-the-practice pavement analysis software developed under NCHRP Project 1–37A. Recently, AASHTO announced the first commercial version of the software, DARWin-ME, to replace the 1993 AASHTO design guide DARWin software. The MEPDG and DARWin-ME use similar models for predicting rutting and bottom-up fatigue cracking. Both distress models were nationally calibrated with measured performance data collected from hundreds of long-term pavement performance sections across the United States and Canada. Verification work indicated that these nationally calibrated models did not reflect North Carolina's local materials, construction practices, and local traffic. Therefore, the performance models must be recalibrated to reflect local conditions. The scope includes rutting and alligator cracking in flexible pavements. The development of rutting and fatigue model coefficients (k-values) is investigated for 12 commonly used hot-mix asphalt (HMA) mixtures in North Carolina, and two approaches for recalibrating the rutting and fatigue cracking model coefficients (β-factors) are compared to reflect local materials and conditions. The two optimization methods evaluated are generalized reduced gradient (GRG) and genetic algorithm (GA) optimization. Results indicate that rutting and fatigue cracking k-values for North Carolina HMA mixtures are generally different from national averages. The GA optimization method does a better job of predicting local distresses than do the GRG method and nationally calibrated models.}, number={2305}, journal={TRANSPORTATION RESEARCH RECORD}, author={Jadoun, Fadi M. and Kim, Y. Richard}, year={2012}, pages={131–140} }
 @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_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} }
 @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{choi_subramanian_guddati_kim_2012, title={Incremental Model for Prediction of Permanent Deformation of Asphalt Concrete in Compression}, ISSN={["2169-4052"]}, DOI={10.3141/2296-03}, abstractNote={Permanent deformation (rutting) is one of the major distresses in asphalt pavement. To predict permanent deformation of asphalt concrete, repeated creep and recovery (or flow number) tests are typically used in the laboratory. However, models for the prediction of permanent deformation that incorporate flow number testing cannot represent the primary region because they concentrate on the secondary region. A new simple permanent deformation model called the incremental model is proposed. The proposed model is derived from the rate model, which is a rigorous mechanical model based on viscoplasticity. Four parameters of the new model provide an understanding of the permanent deformation. Parameter A is related to the initial permanent strain level, and Parameter C provides information about where the secondary region starts. That is, Parameters A and C govern the primary region, where α (alpha) is the slope of the secondary region, and B represents the permanent deformation level of the secondary region. Two mixtures are selected to investigate the deformation characteristics, and repeated creep and recovery tests are performed in compression. The incremental model is verified by applying it to various loading conditions for two mixtures. Furthermore, it is found that α is the material constant and the time-temperature superposition principle is applicable to each parameter. All parameters, except a, depend on both deviatoric stress and reduced load time, which is the product of load time and temperature. The incremental model describes ways to apply the time-temperature supposition principle to permanent deformation.}, number={2296}, journal={TRANSPORTATION RESEARCH RECORD}, author={Choi, Yeong-Tae and Subramanian, Vijay and Guddati, Murthy N. and Kim, Y. Richard}, year={2012}, pages={24–35} }
 @inbook{banadaki_guddati_kim_little_2012, title={Multiscale Micromechanical Lattice Modeling of Cracking in Asphalt Concrete}, ISBN={9789400745650 9789400745667}, url={http://dx.doi.org/10.1007/978-94-007-4566-7_47}, DOI={10.1007/978-94-007-4566-7_47}, abstractNote={A multiscale micromechanical lattice modeling technique is proposed from amongst several computational methods for predicting the performance of hot mix asphalt (HMA) under service loads. Although the lattice model has shown promise, many important details need to be addressed to ensure realistic predictions. This paper presents enhancements to the original model that have been developed over the past two years. These revisions are geared towards capturing the material behavior more accurately and efficiently than was possible with the original lattice model. Among the new enhancements that are presented in this paper are the incorporation of viscoelastic fracture with the help of the work potential-based viscoelastic continuum damage model, computationally efficient simulations under a large number of load cycles, and the incorporation of air voids to capture the reduction in stiffness and strength of the material. Efficiency of the model is improved further by incorporating novel algorithms.}, booktitle={7th RILEM International Conference on Cracking in Pavements}, publisher={Springer Netherlands}, author={Banadaki, Arash Dehghan and Guddati, Murthy N. and Kim, Y. Richard and Little, Dallas N.}, year={2012}, pages={487–496} }
 @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} }
 @article{yun_kim_2011, title={A viscoplastic constitutive model for hot mix asphalt in compression at high confining pressure}, volume={25}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2010.12.025}, abstractNote={In this study, the experimentally observed rate-dependent viscoplastic hardening–softening of hot mix asphalt (HMA) is modeled using Perzyna’s flow rule and a rate-dependent yield stress function. The yield stress function, which is adopted from the convolution integral in linear viscoelasticity, is applied with a strain hardening rule in order to address both the sudden and gradual changes in rate dependence of the viscoplastic media that are due to repetitive creep and recovery loading. The experimental study is performed to characterize the behavior of HMA and verify the developed model at 55 °C with 500 kPa confining pressure. The developed model shows good agreement with the measured viscoplastic responses of HMA under various load levels and pulse times of repetitive creep and recovery loading histories.}, number={5}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Yun, Taeyoung and Kim, Y. Richard}, year={2011}, month={May}, pages={2733–2740} }
 @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 ...}, 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{sayyady_stone_list_jadoun_kim_sajjadi_2011, title={Axle load distribution for mechanistic-empirical pavement design in North Carolina multidimensional clustering approach and decision tree development}, number={2256}, journal={Transportation Research Record}, author={Sayyady, F. and Stone, J. R. and List, G. F. and Jadoun, F. M. and Kim, Y. R. and Sajjadi, S.}, year={2011}, pages={159–168} }
 @article{lee_lee_kim_2011, title={Evaluation of Healing Effect by Rest Periods on Asphalt Concrete Slab Using MMLS3 and NDE Techniques}, volume={15}, ISSN={["1976-3808"]}, DOI={10.1007/s12205-011-0909-2}, number={3}, journal={KSCE JOURNAL OF CIVIL ENGINEERING}, author={Lee, Ju Sang and Lee, Sangyum and Kim, Y. Richard}, year={2011}, month={Mar}, pages={553–560} }
 @article{yun_kim_2011, title={Experimental Investigation of Rate-Dependent Hardening-Softening Behavior of Hot Mix Asphalt in Compression}, volume={12}, ISSN={["2164-7402"]}, DOI={10.3166/rmpd.12.99-114}, abstractNote={ABSTRACT The characteristic behaviors of hot mix asphalt (HMA) in compression are studied using various repetitive creep and recovery tests. Important characteristic behaviors of HMA, i.e., rate-dependent hardening and softening, are observed from the experimental study. Rate-dependent softening is found to have a significant effect on viscoplastic strain development. The implication of this effect is that the flow number test, which has been developed as a simple performance test to supplement the Superpave volumetric mix design, is not sufficiently comprehensive to evaluate the viscoplastic characteristics of HMA pavement subjected to loadings with various rest periods. The experimental results and mathematical derivations suggest that for a more realistic prediction of the viscoplastic behavior of HMA, a hardening rule, which is capable of describing both rate-dependent hardening and softening, needs to be incorporated into viscoplastic models.}, number={1}, journal={ROAD MATERIALS AND PAVEMENT DESIGN}, author={Yun, Taeyoung and Kim, Y. Richard}, year={2011}, pages={99–114} }
 @article{yun_kim_2011, title={Experimental Investigation of Rate-Dependent Hardening-Softening Behavior of Hot Mix Asphalt in Compression}, volume={12}, ISSN={1468-0629 2164-7402}, url={http://dx.doi.org/10.1080/14680629.2011.9690354}, DOI={10.1080/14680629.2011.9690354}, abstractNote={ABSTRACT The characteristic behaviors of hot mix asphalt (HMA) in compression are studied using various repetitive creep and recovery tests. Important characteristic behaviors of HMA, i.e., rate-dependent hardening and softening, are observed from the experimental study. Rate-dependent softening is found to have a significant effect on viscoplastic strain development. The implication of this effect is that the flow number test, which has been developed as a simple performance test to supplement the Superpave volumetric mix design, is not sufficiently comprehensive to evaluate the viscoplastic characteristics of HMA pavement subjected to loadings with various rest periods. The experimental results and mathematical derivations suggest that for a more realistic prediction of the viscoplastic behavior of HMA, a hardening rule, which is capable of describing both rate-dependent hardening and softening, needs to be incorporated into viscoplastic models.}, number={1}, journal={Road Materials and Pavement Design}, publisher={Informa UK Limited}, author={Yun, Taeyoung and Kim, Y. Richard}, year={2011}, month={Jan}, pages={99–114} }
 @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} }
 @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 ...}, 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{lee_mun_kim_2011, title={Fatigue and rutting performance of lime-modified hot-mix asphalt mixtures}, volume={25}, ISSN={["1879-0526"]}, DOI={10.1016/j.conbuildmat.2011.04.059}, abstractNote={Abstract This paper describes the effect of lime on composite hot-mix asphalt (HMA) mixtures of aggregate and asphalt binder evaluated using viscoelastic continuum damage analysis, which is based on predicting the effective stress vs. strain equations and microcrack growth. The performance characteristics evaluated in this study included fatigue cracking and rutting resistance in both moisture-damaged and undamaged states. The test methods used in this evaluation were the dynamic modulus test for stiffness characterization, the direct tension test for fatigue cracking characterization, and the triaxial repeated-load permanent deformation test for rutting characterization. The main contribution of this paper is the demonstration of advanced test methods and models that can be used to evaluate the performance of various mixtures with respect to the fatigue damage and rutting performance.}, number={11}, journal={CONSTRUCTION AND BUILDING MATERIALS}, author={Lee, Sangyum and Mun, Sungho and Kim, Y. Richard}, year={2011}, month={Nov}, pages={4202–4209} }
 @article{yun_kim_2011, title={Modeling of viscoplastic rate-dependent hardening-softening behavior of hot mix asphalt in compression}, volume={15}, ISSN={["1573-2738"]}, DOI={10.1007/s11043-010-9116-7}, number={1}, journal={MECHANICS OF TIME-DEPENDENT MATERIALS}, author={Yun, Taeyoung and Kim, Y. Richard}, year={2011}, month={Feb}, pages={89–103} }
 @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{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{sayyady_stone_taylor_jadoun_kim_2010, title={Clustering Analysis to Characterize Mechanistic-Empirical Pavement Design Guide Traffic Data in North Carolina}, ISSN={["2169-4052"]}, DOI={10.3141/2160-13}, abstractNote={This paper presents attempts to generate regional average truck axle load distribution factors (ALFs), monthly adjustment factors (MAFs), hourly distribution factors (HDFs), and vehicle class distributions (VCDs) for North Carolina. The results support Mechanistic–Empirical Pavement Design Guide (MEPDG) procedures. Weigh-in-motion data support the analysis and generate seasonal factors. MEPDG damage-based sensitivity analysis shows that pavement performance is sensitive to North Carolina site-specific ALFs, MAFs, and VCDs. Similar results occur for national default values of ALF, MAF, and VCD. Hierarchical clustering analysis based on North Carolina ALFs and MAFs develops representative seasonal traffic patterns for different regions of the state. Findings show that seasonal truck traffic has distinct characteristics for the eastern coastal plain, the central Piedmont, and the western mountains. A simplified decision tree and a related table help the pavement designer select the proper representative patterns of ALF and MAF. To develop VCD factors, the approach uses 48–h classification counts and a seasonal factoring procedure to account for day-of-week and seasonal variations. The approach incorporates site-specific truck traffic to improve the accuracy of pavement design. On the basis of sensitivity analysis results, pavement performance is found to be insensitive to North Carolina site-specific and national default values of HDF; thus, the average statewide HDF values may be used as input to MEPDG. Specific contributions of this research are the relative insensitivity of pavement performance to HDF, the use of 48-h classification counts to estimate VCD inputs, and a decision tree and table to help pavement designers select the proper ALF and MAF inputs.}, number={2160}, journal={TRANSPORTATION RESEARCH RECORD}, author={Sayyady, Fatemeh and Stone, John R. and Taylor, Kent L. and Jadoun, Fadi M. and Kim, Y. Richard}, year={2010}, pages={118–127} }
 @article{corley-lay_jadoun_mastin_kim_2010, title={Comparison of Flexible Pavement Distresses Monitored by North Carolina Department of Transportation and Long-Term Pavement Performance Program}, ISSN={["2169-4052"]}, DOI={10.3141/2153-10}, abstractNote={The Long-Term Pavement Performance (LTPP) program has collected pavement distresses for general pavement study (GPS) sites throughout the country. These sites were used in the initial calibration of the Mechanistic–Empirical Pavement Design Guide, so it is important for states to compare their distress identification procedures and results with the LTPP distresses as part of the local calibration process. North Carolina has 24 GPS sites, of which four are concrete, one went out of service very early, and the remainder are flexible pavements. This paper focuses on the flexible pavement distresses. The GPS sites are 500-ft sections of much longer roadways. The LTPP distress data were extracted for the North Carolina Department of Transportation (NCDOT) GPS sites. Corresponding locations and their distress histories were pulled from the NCDOT pavement management system. In addition, rut depth measurements taken by high-speed profilometer were obtained for many of the sections for comparison with LTPP rut depth measurements. As might be expected, the LTPP walking survey revealed higher amounts of distress than the NCDOT windshield survey. Alligator cracking is the major distress for NCDOT pavements, and a roughly two-to-one relationship was found between alligator cracking by LTPP compared to NCDOT. Rut depths measured by LTPP were also found to be larger than those measured by high-speed profilometer, but in either measure, rut depths measured for NCDOT sections were low (less than 10 mm for all sites).}, number={2153}, journal={TRANSPORTATION RESEARCH RECORD}, author={Corley-Lay, Judith and Jadoun, Fadi M. and Mastin, Jeffery Neil and Kim, Y. Richard}, year={2010}, pages={91–96} }
 @article{lee_kim_2010, title={Determination of the optimal number of coverages for the rolling of chip seals}, volume={37}, ISSN={["1208-6029"]}, DOI={10.1139/l09-129}, abstractNote={This paper presents a method to determine the optimal protocol for rolling chip seals based on aggregate retention performance and aggregate embedment depth. To evaluate performance, the flip-over test (FOT), the Vialit test, the modified sand circle test, and the third-scale model mobile loading simulator (MMLS3) were employed. Two chip seal types (single and double) and three numbers of coverages (1, 3, and 5) were used as parameters to determine an optimal number of coverages. It was found from the aggregate retention test results and measured aggregate embedment depths that three coverages is the optimum number of coverages and the extra time needed for the two additional coverages cannot be justified.}, number={1}, journal={CANADIAN JOURNAL OF CIVIL ENGINEERING}, author={Lee, Jaejun and Kim, Y. Richard}, year={2010}, month={Jan}, pages={54–65} }
 @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{lee_seo_kim_2010, title={Effect of hydrated lime on dynamic modulus of asphalt-aggregate mixtures in the state of North Carolina}, volume={14}, ISSN={["1976-3808"]}, DOI={10.1007/s12205-010-0944-4}, number={6}, journal={KSCE JOURNAL OF CIVIL ENGINEERING}, author={Lee, Sangyum and Seo, Youngguk and Kim, Y. Richard}, year={2010}, month={Nov}, pages={829–837} }
 @article{lee_kim_2010, title={Evaluation of Performance and Cost-Effectiveness of Polymer-Modified Chip Seals}, ISSN={["2169-4052"]}, DOI={10.3141/2150-10}, abstractNote={Chip seals provide a durable and functional pavement surface and serve as a highly economical highway maintenance option when constructed properly. Data and literature suggest that chip seal sections constructed with polymer-modified emulsions (PMEs) provide better initial and long-term performance than those with unmodified emulsions and extend the overall service life of pavements. Laboratory test results were used to compare the performance of chip seals constructed with PME (CRS-2L) with those constructed with unmodified emulsion (CRS-2). Both types of emulsion are used to fabricate samples in the laboratory. The overall performance evaluation in the study is based on rutting, bleeding, and aggregate retention performance measured by the third-scale model mobile loading simulator (MMLS3). Results from these MMLS3 tests indicate that, because of improved mechanical properties, the CRS-2L PME enhances chip seal performance to extend the service life of the pavement. Life-cycle cost analysis of two scenarios (one rehabilitation technique that uses chip seal over existing hot-mix asphalt pavement and another that uses chip seal as original construction), indicates that PME becomes a cost-effective solution if the polymer modification can extend the service life of the chip seal from 5 years (typical service life of an unmodified chip seal) to 7 years. The limited laboratory performance test results provide strong evidence that this extension is possible with the CRS-2L PME used in the study.}, number={2150}, journal={TRANSPORTATION RESEARCH RECORD}, author={Lee, Jaejun and Kim, Y. Richard}, year={2010}, pages={79–86} }
 @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{lee_seo_kim_2010, title={Nondestructive Fatigue Damage Analysis of a Thin Asphalt Concrete Course Using the Wavelet Correlation Method}, volume={38}, ISSN={["1945-7553"]}, DOI={10.1520/jte102417}, abstractNote={Stress wave analysis is employed herein as a nondestructive monitoring tool to assess the level of fatigue damage in a thin asphalt concrete (AC) overlay. A frequency-dependent cross-correlation procedure is developed to specify a stress wave at a desired frequency by using a wavelet kernel. This procedure is referred to as the wavelet correlation method (WCM). Once synthetic surface waves are constructed and subjected to simulated disturbances, such as structural damage or nearby frequencies, their phase velocities are computed using the WCM with over 96 % accuracy. The generated stress waves are periodically processed, while laboratory hot-mix asphalt pavements are trafficked by the third-scale model mobile loading simulator. The dispersion curves are then analyzed to validate that a wave of 16 kHz travels mainly within a 40∼60 mm thickness of a surface layer. Fatigue damage levels are quantified at intervals by the phase velocity that represents the AC elastic modulus. Microdamage healing of the AC during rest periods is then indexed and corrected by shifting the damage progress profile. Consequently, an early reduction in phase velocity, which is caused by microcracking, can be visually observed in the surface cracking once the phase velocity is reduced to about 50 % of the initial value regardless of pavement density and aggregate gradation. Thus, the WCM allows the optimal timing and scheduling of the preservation construction of a thin AC overlay by indicating the critical microdamage stage immediately prior to the visual evidence of surface cracking.}, number={3}, journal={JOURNAL OF TESTING AND EVALUATION}, author={Lee, S. Joon and Seo, Youngguk and Kim, Y. Richard}, year={2010}, month={May}, pages={324–331} }
 @article{lee_kim_2010, title={Optimal Distribution of Rolling Coverage in Multiple Chip Seals}, ISSN={["2169-4052"]}, DOI={10.3141/2150-09}, abstractNote={A study investigated the optimal rolling coverage distribution of different layers of multiple chip seals (double and triple seals). The chip seal samples were fabricated in the field for laboratory testing. The chip seal sections were constructed with the use of two different rolling distributions per seal type (double and triple seals) with no rolling or one rolling for the bottom layer. A 5-ton pneumatic tire roller was used to fabricate these samples in the field. The double seals were composed of granite 78M aggregate for the bottom layer and lightweight aggregate for the top layer. The triple seals were constructed with granite 78M aggregate for both the bottom and middle layers and lightweight aggregate for the top layer using CRS-2 emulsion. The aggregate retention performance was evaluated by the flip-over test, the Vialit test, and the third-scale model mobile loading simulator. It was found that the double seal clearly required rolling for the bottom layer, and the triple seal did not; therefore, the rolling operation may be eliminated for the bottom layer of the triple seal.}, number={2150}, journal={TRANSPORTATION RESEARCH RECORD}, author={Lee, Jaejun and Kim, Y. Richard}, year={2010}, pages={70–78} }
 @article{lee_kim_2010, title={Optimizing Rolling Patterns for Chip Seals Using Laboratory Aggregate Loss Performance Tests on Field Fabricated Samples}, volume={24}, ISSN={["1943-5509"]}, DOI={10.1061/(asce)cf.1943-5509.0000096}, abstractNote={This paper presents a study to determine the optimal rolling patterns for chip seals based on aggregate retention performance. Chip seal sections composed of single seals of granite 78M and CRS-2 emulsion are constructed using five different rolling patterns with two or three rollers. Both pneumatic tire and combination rollers are used in developing these patterns. Chip seal samples are obtained from the sections for laboratory testing. The aggregate retention performance is evaluated using the flip-over test, Vialit test, and the third-scale model mobile loading simulator. It is found that the time delay between aggregate spreading and rolling is an important parameter for the aggregate retention performance. The laboratory aggregate retention test results are used along with typical roller speeds and the maximum allowable time delay between aggregate spreading and rolling to develop optimal rolling patterns for two and three rollers.}, number={3}, journal={JOURNAL OF PERFORMANCE OF CONSTRUCTED FACILITIES}, author={Lee, Jaejun and Kim, Y. Richard}, year={2010}, pages={249–257} }
 @inproceedings{feng_zhang_guddati_kim_2010, title={The Development and Evaluation of a Virtual Testing Procedure for the Prediction of the Cracking Performance of Hot Mix Asphalt}, ISBN={9780784411292 9780784476086}, url={http://dx.doi.org/10.1061/41129(385)13}, DOI={10.1061/41129(385)13}, abstractNote={Motivated by the ultimate goal of linking the binder and aggregate properties to the cracking performance of asphalt concrete, a multiscale virtual testing methodology is developed in this paper. The main components of the proposed methodology are: (a) a virtual fabrication technique that generates the microstructure of asphalt concrete specimens without the need for physical fabrication, (b) a lattice modeling approach that simulates the micromechanical behavior of cracked asphalt concrete specimens, and (c) a multiscale methodology that incorporates the effects of aggregates of widely varying sizes. The resulting methodology is calibrated to simulate the load-deformation behavior of real uniaxial tension test specimens. A comparison of the predicted response against the measured response indicates that the proposed method shows promise, but requires further work aimed at the fundamental understanding of the micromechanical behavior.}, booktitle={Pavements and Materials}, publisher={American Society of Civil Engineers}, author={Feng, Zhen and Zhang, Pu and Guddati, Murthy N. and Kim, Y. Richard}, year={2010}, month={Aug} }
 @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} }
 @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} }
 @article{mun_kim_2009, title={Backcalculation of subgrade stiffness under rubblised PCC slabs using multilevel FWD loads}, volume={10}, ISSN={["1477-268X"]}, DOI={10.1080/10298430701827650}, abstractNote={Rubblisation is an effective rehabilitation method for deteriorated Portland cement concrete (PCC) pavements due to its low initial costs, minimal traffic disruption and ability to minimise reflective cracking in asphalt overlays. However, the loss of strength in the PCC slab due to rubblisation creates the demand for a subgrade that is strong enough to handle traffic after rubblisation. This paper presents a research effort to develop an analysis method that allows the realistic estimation of subgrade stiffness after rubblisation from deflection measurements on intact PCC slabs before rubblisation. As a forward model, stress- and strain-dependent nonlinear subgrade models are incorporated into a finite element analysis (FEA). Based on the synthetic database generated from the FEA, different methodologies are developed to predict the coefficients in the nonlinear subgrade model from deflections under multilevel falling weight deflectometer loads.}, number={1}, journal={INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING}, author={Mun, Sungho and Kim, Y. Richard}, year={2009}, pages={9–18} }
 @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{lee_kim_2009, title={Performance-Based Uniformity Coefficient of Chip Seal Aggregate}, ISSN={["0361-1981"]}, DOI={10.3141/2108-06}, abstractNote={Development of a new chip seal performance indicator called the performance-based uniformity coefficient (PUC) is presented. The PUC uses the concepts of McLeod's failure criteria for chip seals and the uniformity coefficient used for soil, sand, and aggregate. The aggregate loss performance test, using the third-scale model mobile loading simulator, is used for evaluating the PUC. Results demonstrate that the methodology introduced in this research and McLeod's failure criteria can be excellent tools for narrowing the aggregate specifications required for chip seal construction. In addition to these results, the PUC, which is a gradation-based performance indicator, is an improvement over the previous uniformity coefficient for chip seal construction. The PUC can also aid in aggregate selection for the chip seal, and it can ease and clarify engineering communications within the chip seal industry.}, number={2108}, journal={TRANSPORTATION RESEARCH RECORD}, author={Lee, Ju Sang and Kim, Y. Richard}, year={2009}, pages={53–60} }
 @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} }
 @article{lacroix_kim_ranjithan_2008, title={Backcalculation of Dynamic Modulus from Resilient Modulus of Asphalt Concrete with an Artificial Neural Network}, ISSN={["2169-4052"]}, DOI={10.3141/2057-13}, abstractNote={The NCHRP Project 1-37A Guide for Mechanistic–Empirical Design of New and Rehabilitated Pavement Structures introduces the dynamic modulus (|E * |) as the material property for the characterization of hot-mix asphalt mixtures. This is a significant change from the resilient modulus used in the previous AASHTO Guide for the Design of Pavement Structures. One of the challenges of changing the material characterization is that databases, such as the Long-Term Pavement Performance Materials Database, contain older material characterization information. Thus, such databases must convert their data to the currently accepted standard (i.e., |E * |). Other investigators have presented evidence that the resilient modulus can be predicted from the dynamic modulus by using the theory of viscoelasticity. By using their prediction method, this study proposes the population of a database of measured dynamic moduli with the corresponding predicted resilient moduli to train an artificial neural network (ANN). The ANN model was verified with four 12.5-mm surface course mixtures with different aggregate types and binder types and one 25.0-mm base mixture. The dynamic moduli predicted from the measured resilient moduli with the trained ANN were found to be reasonable compared with the measured dynamic moduli.}, number={2057}, journal={TRANSPORTATION RESEARCH RECORD}, author={Lacroix, Andrew and Kim, Y. Richard and Ranjithan, S. Ranji}, year={2008}, pages={107–113} }
 @article{kim_lee_se_el-haggan_2008, title={Determination of price reduction factors for density-deficient asphalt pavements}, volume={36}, DOI={10.1520/jte101460}, abstractNote={This paper presents the research undertaken for the development of price reduction factors for density-deficient asphalt pavements. Performance characteristics included in this study are fatigue cracking and rutting. The following laboratory tests were performed on two North Carolina Superpave mixtures with varying air void contents: (1) axial compression dynamic modulus tests for modulus determination; (2) indirect tension tests for fatigue performance evaluation; (3) triaxial repeated load permanent deformation tests for rutting evaluation; and (4) accelerated pavement tests on laboratory pavement slabs for fatigue and rutting evaluation using the third-scale Model Mobile Loading Simulator (MMLS3). Air void models for the dynamic modulus, fatigue cracking, and rutting were developed using the laboratory test data. These models and the results from the MMLS3 testing were used to develop the price reduction factors for density-deficient asphalt mixtures. In order to determine the effect of deficient density of hot-mix asphalt (HMA) on the performance of asphalt pavement as a system, a computer program called AP4 (Asphalt Pavement Performance Prediction Program) was developed. The algorithm adopted in AP4 for the damage calculation is based on the incremental damage concept and is very similar to that used in the National Cooperative Highway Research Program (NCHRP) 1-37A Mechanistic-Empirical Pavement Design Guide. This program allows the determination of the service life for fatigue cracking and rutting based on the inputs of air void contents in all the HMA layers. Case studies of five density-deficient pavements were conducted, and the price reduction factors were determined.}, number={4}, journal={Journal of Testing and Evaluation}, author={Kim, Y. R. and Lee, S. J. and Se, Y. and El-Haggan, O.}, year={2008}, pages={335–344} }
 @article{muthadi_kim_2008, title={Local Calibration of Mechanistic-Empirical Pavement Design Guide for Flexible Pavement Design}, ISSN={["2169-4052"]}, DOI={10.3141/2087-14}, abstractNote={This paper presents the calibration of the Mechanistic-Empirical Pavement Design Guide (MEPDG) for flexible pavements located in North Carolina. Two distress models, permanent deformation and bottom-up fatigue cracking, were used for this effort. A total of 53 pavement sections were selected from the Long-Term Pavement Performance (LTPP) program and the North Carolina Department of Transportation databases for the calibration and validation process. The verification runs for the LTPP sections performed with the parameters developed during the national calibration effort under NCHRP Project 1-37A showed promising results. The Microsoft Excel Solver program was used to fit the predicted rut depth values to the measured values by changing the coefficients in the permanent deformation models for hot-mix asphalt (HMA) and unbound materials. In this process, the sum of the squared errors was minimized for each of the permanent deformation models separately. For the alligator cracking model, the only possibility of reducing the standard error and bias was through the transfer function. Again, the Microsoft Excel Solver program was used to minimize the sum of the squared errors of the measured and the predicted cracking by varying the C 1 and C 2 parameters of the transfer function. The standard error for the HMA permanent deformation model, as well as that for the alligator cracking model, was found to be significantly less than the global standard error after the calibration. It was decided that both models would be kept for a more robust calibration in the future that would increase the number of sections and include more detailed inputs (mostly Level 1 inputs).}, number={2087}, journal={TRANSPORTATION RESEARCH RECORD}, author={Muthadi, Naresh R. and Kim, Y. Richard}, year={2008}, pages={131–141} }
 @article{lee_kim_2008, title={Understanding the effects of aggregate and emulsion application rates on performance of asphalt surface treatments}, ISSN={["0361-1981"]}, DOI={10.3141/2044-08}, abstractNote={Presented are the effects of aggregate and emulsion application rates on the performance of asphalt surface treatments (ASTs), as evaluated by the third-scale Model Mobile Loading Simulator (MMLS3) and digital image processing. Performance characteristics evaluated in this study include aggregate loss and bleeding. Lightweight aggregate and granite aggregate with different gradations were used with CRS-2 emulsion to design the various combinations of aggregate and emulsion application rates. The MMLS3 test protocol was applied to these AST specimens, and performance measurements were analyzed as a function of the application rates. Results demonstrated that the new AST performance test method introduced in this study was an excellent means of evaluating AST performance. It was found that the major factor affecting AST performance was aggregate gradation. Also, a method was developed to determine the optimum aggregate and emulsion application rates from the MMLS3 test results. The optimum rates determined from this method were confirmed by a blind test performed by bituminous supervisors and road maintenance unit engineers at the North Carolina Department of Transportation. Finally, results from this study were used to study the voids concept, which serves as the foundation for AST mix design. It was concluded that the reference voids (the compacted voids resulting from MMLS3 trafficking) depend on the voids in the loose aggregate that are, in turn, affected by the aggregate gradation type.}, number={2044}, journal={TRANSPORTATION RESEARCH RECORD}, author={Lee, Ju Sang and Kim, Y. Richard}, year={2008}, pages={71–78} }
 @article{seo_kim_2008, title={Using Acoustic Emission to Monitor Fatigue Damage and Healing in Asphalt Concrete}, volume={12}, ISSN={["1976-3808"]}, DOI={10.1007/s12205-008-0237-3}, number={4}, journal={KSCE JOURNAL OF CIVIL ENGINEERING}, author={Seo, Youngguk and Kim, Y. Richard}, year={2008}, month={Jul}, pages={237–243} }
 @article{seo_el-haggan_king_lee_kim_2007, title={Air void models for the dynamic modulus, fatigue cracking, and rutting of asphalt concrete}, volume={19}, DOI={10.1061/(ASCE)0899-1561(2007)19:10(874)}, abstractNote={A laboratory study has been carried out to develop mechanical models for the dynamic modulus, fatigue life, and rutting performance of asphalt concrete as a function of air void content. The experimental program includes an axial compression complex modulus test, indirect tensile (IDT) fatigue test, and triaxial repeated load permanent deformation (TRLPD) test on the two most commonly used asphalt–aggregate mixtures in North Carolina. The dynamic moduli are determined using axial compression tests with and without confining pressure, and the results are compared to evaluate the effect of confining pressure on the dynamic modulus. The relationship between the dynamic moduli that are determined from the uniaxial compression test and the air void content is developed. The growth of the tensile strain and axial permanent strain is measured from the IDT fatigue test and TRLPD test, respectively, and is used to determine the fatigue life and rutting behavior of the mixtures. The fatigue and rutting models adopted in the new NCHRP 1-37A Mechanistic-Empirical Pavement Design Guide have been refined to represent the IDT and TRLPD test results more accurately and to incorporate the air void content as an input parameter.}, number={10}, journal={Journal of Materials in Civil Engineering}, author={Seo, Y. G. and El-Haggan, O. and King, M. and Lee, S. J. and Kim, Y. R.}, year={2007}, pages={874–883} }
 @article{mun_chehab_kim_2007, title={Determination of Time-domain Viscoelastic Functions using Optimized Interconversion Techniques}, volume={8}, ISSN={1468-0629 2164-7402}, url={http://dx.doi.org/10.1080/14680629.2007.9690078}, DOI={10.1080/14680629.2007.9690078}, abstractNote={ABSTRACT Several viscoelastic response functions are available to characterize the LVE behavior of asphalt concrete, some in time domain such as relaxation modulus E(t) and creep compliance D(t) and other such as complex modulus E* in frequency domain. The use of the complex modulus test has risen sharply after it has been incorporated in the M-E Pavement Design Guide and in the Superpave Simple Performance Test. With the availability of E* data it becomes advantageous to use mathematical interconversion techniques to obtain time-domain functions E(t) and D(t) which are typically used for constitutive modeling and other applications. This paper addresses the steps involved in conducting the interconversion between frequency-domain and time-domain functions. Issues considered include: a) presmoothing of raw data, b) refinement of phase angle data, c) Prony series representation of the fitted data including determination and sign-control of the Prony series coefficients, and d) interconversion techniques: a...}, number={2}, journal={Road Materials and Pavement Design}, publisher={Informa UK Limited}, author={Mun, Sungho and Chehab, Ghassan R. and Kim, Y. Richard}, year={2007}, month={Jan}, pages={351–365} }
 @article{lacroix_khandan_kim_2007, title={Predicting the resilient modulus of asphalt concrete from the dynamic modulus}, ISSN={["0361-1981"]}, DOI={10.3141/2001-15}, abstractNote={The NCHRP 1-37A Guide for Mechanistic-Empirical Design of New and Rehabilitated Design Structures introduces the dynamic modulus as the material property to characterize asphalt concrete. This is a significant change from the resilient modulus used in the previous AASHTO pavement design guide. This paper presents an analytical method of calculating the resilient modulus from the dynamic modulus. It involves the application of multiaxial linear viscoelastic theory to linear elastic solutions for the indirect tension test developed by Hondros. The prediction method is verified by using three 12.5-mm surface course mixtures with different aggregate shapes and binder types and one 25.0-mm base mixture. Results show that the predicted and measured resilient modulus values are in close agreement. The results provide a forward model for the potential back-calculation of the dynamic modulus from resilient modulus databases already available in highway agencies, such as the Long-Term Pavement Performance Materials Database.}, number={2001}, journal={TRANSPORTATION RESEARCH RECORD}, author={Lacroix, Andrew and Khandan, A. Ardalan Mosavi and Kim, Y. Richard}, year={2007}, pages={132–140} }
 @inproceedings{kim_lee_seo_el-haggan_2006, title={A Mechanistic Approach to Determine Price Reduction Factors for Density-Deficient Asphalt Pavements}, ISBN={9780784408384}, url={http://dx.doi.org/10.1061/40838(191)86}, DOI={10.1061/40838(191)86}, abstractNote={This paper presents the research undertaken for the development of price reduction factors for density-deficient asphalt pavements. Performance characteristics included in this study are fatigue cracking and rutting. Air void models for the dynamic modulus, fatigue cracking, and rutting were developed using laboratory test data. The results from the material level performance tests and the third-scale Model Mobile Loading Simulator (MMLS3) tests allowed the calculation of the PRF values. It was found that the PRF values are not sensitive to the testing methodology used; rather, they are significantly different depending upon which performance characteristic is used (i.e., fatigue cracking vs. rutting). Pavement performance prediction methodologies based on the cumulative damage analysis were developed that predict the fatigue life and permanent deformation growth of the asphalt pavement under the MMLS3 loading. These methodologies are based on material level performance models, multilayered elastic analysis, and the time-temperature superposition principle to account for the differences between the material level testing conditions and the MMLS3 testing conditions. It was found that the prediction methodologies yield reasonable predictions of fatigue life and permanent deformation growth of asphalt slabs under the MMLS3 loading. These pavement performance prediction methodologies were implemented into the computer program called AP4 (Asphalt Pavement Performance Prediction Program). This program allows the determination of the service life for fatigue cracking and rutting based on the inputs of air void contents in all the HMA layers. Case studies of five density-deficient pavements were conducted, which resulted in reasonable price reductions.}, booktitle={Airfield and Highway Pavement}, publisher={American Society of Civil Engineers}, author={Kim, Y. Richard and Lee, S. Joon and Seo, Youngguk and El-Haggan, Omar}, year={2006}, month={Apr} }
 @article{lee_seo_kim_2006, title={Experimental validation of laboratory performance models using the third scale accelerated pavement testing}, volume={10}, ISSN={1226-7988 1976-3808}, url={http://dx.doi.org/10.1007/BF02829299}, DOI={10.1007/BF02829299}, number={1}, journal={KSCE Journal of Civil Engineering}, publisher={Springer Science and Business Media LLC}, author={Lee, Sugjoon and Seo, Youngguk and Kim, Y. Richard}, year={2006}, month={Jan}, pages={9–14} }
 @article{seo_kim_zhang_2006, title={Laboratory evaluation of CCM parameters for mode-I cracks in HMAs}, volume={10}, ISSN={1226-7988 1976-3808}, url={http://dx.doi.org/10.1007/BF02824062}, DOI={10.1007/BF02824062}, number={3}, journal={KSCE Journal of Civil Engineering}, publisher={Springer Science and Business Media LLC}, author={Seo, Youngguk and Kim, Y. Richard and Zhang, Zhiwang}, year={2006}, month={May}, pages={201–206} }
 @inproceedings{lee_kim_2006, title={Performance Evaluation of Asphalt Surface Treatments Using the MMLS3}, ISBN={9780784408384}, url={http://dx.doi.org/10.1061/40838(191)8}, DOI={10.1061/40838(191)8}, abstractNote={This paper presents the research effort to evaluate the aggregate retention and skid performance of various asphalt surface treatments (ASTs). The study includes two types of aggregate for the aggregate retention tests and fourteen field AST sections for the skid resistance tests. A new test protocol for the performance evaluation of ASTs is developed using a third-scale Model Mobile Loading Simulator (MMLS3). The AST performance characteristics that are covered by this protocol include aggregate retention, bleeding, skid resistance, aggregate embedment depth, cracking and rutting. In this study, the new MMLS3 AST performance test method is applied to evaluate the effects of various mix parameters on aggregate retention and bleeding; these parameters include aggregate and emulsion applications rates, fine content, and aggregate gradation. It has been confirmed that the amount of aggregate loss decreases as the aggregate application rate decreases, the emulsion application rate increases, the fine content decreases, and the gradation becomes more uniform. The aggregate gradation factor plays a critical role in the aggregate retention performance, regardless of the type of aggregate. The correlation between the British Pendulum Test numbers (BPNs) and the skid resistance numbers (SNs) is found to be relatively strong, which allows the prediction of the SN from the laboratory BPN.}, booktitle={Airfield and Highway Pavement}, publisher={American Society of Civil Engineers}, author={Lee, Jusang and Kim, Y. Richard}, year={2006}, month={Apr} }
 @inbook{lee_kim_mcgraw_2006, title={Performance evaluation of bituminous surface treatment using third-scale Model Mobile Loading Simulator}, DOI={10.3141/1958-07}, abstractNote={This paper presents a new test protocol for the performance evaluation of bituminous surface treatments (BSTs) using the third-scale Model Mobile Loading Simulator (MMLS3). The BST performance characteristics covered by this protocol include aggregate retention, bleeding, skid resistance, aggregate embedment depth, cracking, and rutting. In this study, the new MMLS3 BST performance test method was applied to evaluate effects of various mix parameters on aggregate retention and bleeding; these parameters include aggregate and emulsion application rates, fines content, and aggregate gradation. Results demonstrate that the BST performance test method developed in this study is an excellent means of supporting current BST design and evaluating effects of various factors on performance of BSTs.}, number={1958}, booktitle={Managing and maintaining highway structures and pavements}, publisher={Washington: Transportation Research Board Natl Research Council}, author={Lee, J. and Kim, Y. R. and McGraw, E. O.}, year={2006}, pages={59–70} }
 @inbook{lee_seo_kim_2006, title={Validation of material-level performance models - Using the third-scale Model Mobile Loading Simulator}, DOI={10.3141/1949-07}, abstractNote={A mechanistic pavement analysis with laboratory fatigue cracking and rutting models was validated with the response and performance measured from asphalt pavements. Asphalt pavements with different air void contents were tested using the third-scale Model Mobile Loading Simulator (MMLS3). The fatigue life prediction algorithm adopts a cumulative damage analysis; the permanent deformation prediction algorithm uses a sublayering method. These algorithms, which are similar to the ones adopted in the NCHRP 1-37A Mechanistic-Empirical Pavement Design Guide (MEPDG), account for the loading rate and temperature variation along the depth of the pavements. The major difference between the algorithms used in this study and the ones in the MEPDG is that the difference in loading frequencies between the laboratory test method and the MMLS3 test was accounted for in this study using the time-temperature superposition principle with growing damage. The predictions of fatigue life and permanent deformation growth in the...}, number={1949}, booktitle={Pavement rehabilitation, strength and deformation characteristics, and surface properties-vehicle interaction 2006}, publisher={Washington: Transportation Research Board Natl Research Council}, author={Lee, S. J. and Seo, Y. and Kim, Y. R.}, year={2006}, pages={75–82} }
 @article{mun_guddati_kim_2006, title={Viscoelastic continuum damage finite element modeling of asphalt pavements for fatigue cracking evaluation}, volume={10}, ISSN={1226-7988 1976-3808}, url={http://dx.doi.org/10.1007/BF02823927}, DOI={10.1007/BF02823927}, number={2}, journal={KSCE Journal of Civil Engineering}, publisher={Springer Science and Business Media LLC}, author={Mun, Sungho and Guddati, Murthy N. and Kim, Y. Richard}, year={2006}, month={Mar}, pages={97–104} }
 @article{park_kim_park_2005, title={Assessment of pavement layer condition with use of multiload-level failing weight deflectometer deflections}, ISBN={["0-309-09377-5"]}, ISSN={["0361-1981"]}, DOI={10.3141/1905-13}, abstractNote={A condition assessment procedure for pavement layers that uses multiload-level falling weight deflectometer (FWD) deflections is presented. A dynamic finite element program that incorporates a stress-dependent soil model was used to generate the synthetic deflection database. On the basis of the data in this database, the relationships between surface deflections and critical pavement responses, such as the stresses and strains in each layer, have been established. The FWD deflection data, distress survey results, temperature, and laboratory testing results used to develop this procedure were collected from the Long-Term Pavement Performance project database. Research efforts also focused on the effect of the FWD load level on the condition assessment procedure. The results indicate that the proposed procedure can estimate the asphalt concrete (AC), base, and subgrade layer conditions. The AC layer modulus and the tensile strain at the bottom of the AC layer were found to be better indicators of the condition of the AC layer than the deflection basin parameter. It was also found that the structurally adjusted base damage index and base curvature index were good indicators for prediction of the stiffness characteristics of the aggregate base and subgrade, respectively. An FWD test with a load of 71.2 kN or less does not improve the accuracy of this procedure. The results from the study of the nonlinear behavior of a pavement structure indicate that the deflection ratio obtained from multiload-level deflections can predict the type and quality of the base and subgrade materials.}, number={1905}, journal={PAVEMENT REHABILITATION, STRENGTH AND DEFORMATION CHARACTERISTICS, AND SURFACE PROPERTIES 2005}, author={Park, HM and Kim, YR and Park, SW}, year={2005}, pages={107–116} }
 @article{mun_guddati_kim_2005, title={Continuum damage finite element modeling of asphalt concrete}, volume={9}, ISSN={1226-7988 1976-3808}, url={http://dx.doi.org/10.1007/BF02829051}, DOI={10.1007/BF02829051}, number={3}, journal={KSCE Journal of Civil Engineering}, publisher={Springer Science and Business Media LLC}, author={Mun, Sungho and Guddati, Murthy N. and Kim, Y. Richard}, year={2005}, month={May}, pages={205–211} }
 @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{lee_rust_hamouda_kim_borden_2005, title={Fatigue cracking resistance of fiber-reinforced asphalt concrete}, volume={75}, ISSN={["0040-5175"]}, DOI={10.1177/004051750507500206}, abstractNote={The influence of fibers on the fatigue cracking resistance of asphalt concrete is investigated using fracture energy. Nylon, a popular facing yarn of carpets, is used for the actual recycled carpet fibers in asphalt pavement. The experimental program is designed with two phases: the single fiber pull-out test and the indirect tension strength test. Through pull-out tests of 15-denier single nylon fibers, the critical fiber embedded length is determined to be 9.2 mm. As for indirect tension strength tests, samples of asphalt concrete mixed with nylon fibers of two lengths, 6 and 12 mm, based on results of the pull-out tests (critical embedded length) and three volume fractions, 0.25, 0.5, and 1%, are prepared and tested. Asphalt concrete samples fabricated with fibers of 1% and 12 mm results in 85% higher fracture energy than non-reinforced specimens, showing improved fatigue cracking resistance. Although an optimized asphalt mix design with fibers has not been developed for this study, the increased fracture energy represents a potential for improving asphalt fatigue life, which may be facilitated through the use of recycled carpet fibers.}, number={2}, journal={TEXTILE RESEARCH JOURNAL}, author={Lee, SJ and Rust, JP and Hamouda, H and Kim, YR and Borden, RH}, year={2005}, month={Feb}, pages={123–128} }
 @article{chehab_kim_2005, title={Viscoelastoplastic continuum damage model application to thermal cracking of asphalt concrete}, volume={17}, DOI={10.1061/(ASCE)0899-1561(2005)17:4(384)}, abstractNote={A viscoelastoplastic continuum damage (VEPCD) model has recently been developed and validated under the auspices of the National Cooperative Highway Research Program 9-19 project, entitled “Advanced Mixture Characterization for Superpave Support and Performance Models Management.” The VEPCD model is able to characterize the viscoelastic and viscoplastic responses of asphalt concrete (AC) in addition to microcracking. The primary objective of this paper is to validate the model under thermal loading conditions that are distinctively different from the mechanical loading conditions used in model development and calibration. Viscoplastic (VP) behavior is a typical response in AC at high temperatures; however, based on the t-T superposition principle, it is the slow strain rate observed in thermal cracking that triggers the VP response. Measured responses and fracture parameters from thermal strain restrained specimen tensile (TSRST) strength tests were compared with those predicted using the VEPCD model, th...}, number={4}, journal={Journal of Materials in Civil Engineering}, author={Chehab, G. R. and Kim, Y. R.}, year={2005}, pages={384–392} }
 @article{nilsson_chehab_kim_2004, title={Application of a viscoelastoplastic continuum damage tensile model to asphalt mixes in Sweden}, volume={5}, ISSN={1468-0629 2164-7402}, url={http://dx.doi.org/10.1080/14680629.2004.9689991}, DOI={10.1080/14680629.2004.9689991}, abstractNote={ABSTRACT The objective of the research presented herein was to apply a viscoelastoplastic continuum damage (VEPCD) model on three Swedish mixes. The procedure includes the theoretical models and the supporting experimental testing protocols necessary for predicting responses of asphalt mixtures subjected to uniaxial tension loading. The model encompasses the elastic, viscoelastic, plastic and viscoplastic components of asphalt concrete behavior. Addressed are some of the major factors affecting asphalt concrete response, such as rate of loading, loading time, stress/strain amplitude, temperature, and damage. The modeling strategy is based on developing separate models for strain components and then integrating those models to form a viscoelastoplastic continuum damage (VEPCD) model. The developed model accurately predicts responses up to localization when microcracks start to coalesce and grow. However, once major macrocracks develop and propagate, the currently developed model ceases to predict responses...}, number={sup1}, journal={Road Materials and Pavement Design}, publisher={Informa UK Limited}, author={Nilsson, B. Richard and Chehab, Ghassan R. and Kim, Y. Richard}, year={2004}, month={Jan}, pages={133–161} }
 @article{mun_kim_2004, title={Determination of subgrade stiffness under intact portland cement concrete slabs for rubblization projects}, volume={8}, ISSN={1226-7988 1976-3808}, url={http://dx.doi.org/10.1007/BF02899579}, DOI={10.1007/BF02899579}, number={5}, journal={KSCE Journal of Civil Engineering}, publisher={Springer Science and Business Media LLC}, author={Mun, Sungho and Kim, Y. Richard}, year={2004}, month={Sep}, pages={527–533} }
 @article{kim_seo_king_momen_2004, title={Dynamic modulus testing of asphalt concrete in indirect tension mode}, ISBN={["0-309-09485-2"]}, ISSN={["0361-1981"]}, DOI={10.3141/1891-19}, abstractNote={This study presents the results from an analytical and experimental study on the dynamic modulus testing of hot-mix asphalt using the indirect tension (IDT) mode. An analytical solution for the dynamic modulus in the IDT mode was developed with the use of linear viscoelasticity. To verify the analytical solution, temperature and frequency sweep tests were conducted on 12 asphalt mixtures commonly used in North Carolina; both axial compression and IDT test methods were used. A modified dynamic modulus test protocol is introduced to reduce the required testing time by using more frequencies and fewer temperatures on the basis of the time-temperature superposition principle. A comparison of results from the axial compression and IDT test methods shows that the dynamic modulus master curves and shift factors derived from the two methods are in good agreement. It also was found that Poisson's ratio was a weak function of the loading frequency; its effect on the phase angle master curve is discussed.}, number={1891}, journal={BITUMINOUS PAVING MIXTURES 2004}, author={Kim, YR and Seo, Y and King, M and Momen, M}, year={2004}, pages={163–173} }
 @article{mun_guddati_kim_2004, title={Fatigue cracking mechanisms in asphalt pavements with viscoelastic continuum damage finite-element program}, ISBN={["0-309-09489-5"]}, ISSN={["0361-1981"]}, DOI={10.3141/1896-10}, abstractNote={A study of fatigue-cracking mechanisms in asphalt pavements used the finite-element program VECD-FEP++. This program employs the viscoelastic continuum damage model for the asphalt layer and a nonlinear elastic model for unbound layers. Both bottom-up and top-down cracks are investigated by taking several important variables, such as asphalt layer thickness, layer stiffness, pressure distribution under loading, and load level applied on the pavement surface, into account. The cracking mechanisms in various pavement structures under different loading conditions are studied by monitoring a damage contour. Preferred conditions for top-down cracking were identified with the results from this parametric study. The conjoined damage contours in thicker pavements suggest that a through-the-thickness crack may develop as the bottom-up and top-down cracks propagate simultaneously and coalesce; that idea supports observations from field cores and raises the question of the validity of traditional fatigue performance models that account for the growth of the bottom-up cracking only.}, number={1896}, journal={PAVEMENT DESIGN AND ACCELERATED TESTING 2004}, author={Mun, S and Guddati, MN and Kim, YR}, year={2004}, pages={96–106} }
 @article{daniel_chehab_kim_2004, title={Issues affecting measurement of the complex modulus of asphalt concrete}, volume={16}, DOI={10.1061/(ASCE)0899-1561(2004)16:5(469)}, abstractNote={This paper addresses issues of machine compliance and instrumentation that affect the measurement of asphalt concrete material properties in the laboratory. Accurate determination of fundamental material properties is becoming increasingly important as the asphalt industry moves toward more mechanistic design procedures. This issue is particularly timely for the simple performance test and American Association of State Highway and Transportation Officials 2002 design guide that require the measurement of dynamic modulus, phase angle, and creep. The primary objective of this paper is to increase the awareness of the possible existence of these issues in the laboratory and the importance of attending to them appropriately. Machine compliance was found to affect the strains actually occurring in the specimen under various loading conditions, resulting in differences of several magnitudes between dynamic modulus values measured by the actuator and by surface-mounted deformation transducers. Instrumentation issues resulted in errors greater than 10% in the measurement of dynamic modulus for the mixtures studied and caused irrational trends in phase angle values as a function of frequency. Creep compliance testing was also found to be affected by instrumentation issues.}, number={5}, journal={Journal of Materials in Civil Engineering}, author={Daniel, J. S. and Chehab, G. R. and Kim, Y. R.}, year={2004}, pages={469–476} }
 @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{lee_kim_lee_2003, title={Prediction of asphalt mix fatigue life with viscoelastic material properties}, ISBN={["0-309-08566-7"]}, ISSN={["0361-1981"]}, DOI={10.3141/1832-17}, abstractNote={A simplified fatigue model is presented that can predict the fatigue life of asphalt mixes using viscoelastic properties only. This fatigue model was originally developed with the elastic-viscoelastic correspondence principle and continuum damage mechanics and was reduced to a simple version that can predict fatigue life with viscoelastic properties only. On the basis of the experimental study conducted on 12 different types of asphalt mixes, it was observed that the fatigue behavior of asphalt mixes is affected by both the viscoelastic properties and the fatigue characteristics, but mostly by the viscoelastic properties. In addition, it was found that the coefficient of conventional strain-based fatigue models could be expressed in terms of viscoelastic material properties. In the verification study, the fatigue model was able to predict the fatigue life of various types of mixes at the same level of prediction accuracy without change in model coefficients. The fatigue model was also able to accurately predict the changes in the fatigue life of an asphalt mix due to the changes in the volumetric mix properties.}, number={1832}, journal={BITUMINOUS PAVING MIXTURES 2003}, author={Lee, HJ and Kim, YR and Lee, SW}, year={2003}, pages={139–147} }
 @inbook{park_kim_2003, title={Prediction of remaining life of asphalt pavement with failing-weight deflectometer multiload-level deflections}, ISBN={0309085977}, DOI={10.3141/1860-06}, abstractNote={The development of prediction methods for the remaining life of flexible pavements using falling-weight deflectometer (FWD) multiload-level deflections is presented. Pavement response models and pavement performance models were used in developing this procedure. The pavement response models were designed to predict critical pavement responses from surface deflections and deflection basin parameters. The pavement performance models were used to develop the relationships between critical pavement responses obtained from pavement response models and actual pavement performance. Pavement distress data and FWD multiload-level deflection data obtained from the Long-Term Pavement Performance database were used to verify the performance prediction procedure. It was found that the performance of fatigue cracking can be predicted using the proposed procedure except for pavements with high and rapidly increasing cracking in wet-freeze regions. Such trends may be due to environment-induced distresses such as low-temperature cracking, permanent deformation of unbound layers, or both, during the spring thaw period. Predicted rut depths using both single-load and multiload-level deflections show good agreement with measured rut depths over a wide range of rutting potentials. However, the procedure using single–load-level deflections consistently underpredicts the rut depths. This observation demonstrates that the rutting prediction procedure using multiload-level deflections can estimate an excessive level of rutting quite well and thus improve the prediction quality of rutting potential in flexible pavements.}, number={1860}, booktitle={Pavement assessment, monitoring and evaluation 2003}, publisher={Washington, DC: Transportation Research Board}, author={Park, H. M. and Kim, Y. R.}, year={2003}, pages={48–56} }
 @article{zhao_kim_2003, title={Time-temperature superposition for asphalt mixtures with growing damage and permanent deformation in compression}, ISBN={["0-309-08566-7"]}, ISSN={["0361-1981"]}, DOI={10.3141/1832-20}, abstractNote={The objective in this study was to check the validity of the time–temperature superposition principle for hot-mix asphalt (HMA) with growing damage and viscoplastic strain in the compression state, which is essential for the permanent deformation characterization of HMA. Constant crosshead rate compression tests were conducted at temperatures between 25°C and 55°C, and data were analyzed to construct the stresslog reduced-time master curves for various strain levels. Research results indicate that HMA with growing damage remains thermorheologically simple in the temperature range used in this study and that the time–temperature shift factor is only a function of temperature and is independent of the strain level. Two types of tests, the repeated creep and recovery test and the cyclic sinusoidal loading test, were performed in this study to validate the time–temperature superposition in loading histories commonly used in asphalt mixture testing. The results further confirm that the time–temperature superposition is valid for HMA with growing damage and permanent deformation and that the response of HMA depends only on the reduced loading history.}, number={1832}, journal={BITUMINOUS PAVING MIXTURES 2003}, author={Zhao, YQ and Kim, YR}, year={2003}, pages={161–172} }
 @inbook{xu_ranjithan_kim_2003, title={Using the asphalt pavement layer condition assessment program - Case studies}, ISBN={0309085977}, DOI={10.3141/1860-08}, abstractNote={The Asphalt Pavement Layer Condition Assessment Program (APLCAP) is developed in this research to help highway agencies assess layer conditions of asphalt pavements. APLCAP implements a new integrated procedure for condition assessment from falling-weight deflectometer (FWD) deflections. The main components of this procedure include screening of FWD raw deflections, predictions of condition indicators from FWD measurements, structural adjustments for the predicted condition indicators, and layer condition evaluation based on the adjusted condition indicators. This procedure was developed on the basis of dynamic nonlinear finite element analysis and calibrated using field measurements. The three case studies presented show that the APLCAP algorithms can predict the asphalt concrete modulus, pavement critical strains, and strengths of the base and subgrade quite well, but not the compressive strain in the aggregate base layer. Although the APLCAP procedure includes the complicated dynamic effect of FWD loading and nonlinear behavior of unbound materials, the time to obtain results from this procedure is insignificant and therefore suitable for real-time evaluation of pavement conditions.}, number={1860}, booktitle={Pavement assessment, monitoring and evaluation 2003}, publisher={Washington, DC: Transportation Research Board}, author={Xu, B. and Ranjithan, S. R. and Kim, Y. R.}, year={2003}, pages={66–75} }
 @article{seo_kim_witczak_bonaquist_2002, title={Application of digital image correlation method to mechanical testing of asphalt-aggregate mixtures}, ISBN={["0-309-07714-1"]}, ISSN={["0361-1981"]}, DOI={10.3141/1789-18}, abstractNote={The digital image correlation (DIC) method, a noncontact, full-field displacement measurement technique, has been applied to mechanical testing of asphalt concrete. A single couple charged device camera acquires images of an area of interest from a specimen in the undeformed and deformed states. These images are correlated to determine deformations, and advanced mathematical procedures are applied to these deformations to calculate strains. To verify the DIC measurements, vertical displacements for the middle and bottom sections of a specimen subjected to monotonic tension are compared with conventional linear variable differential transformer measurements. A series of DIC images captured during the monotonic and cyclic tests visualizes the evolution of the failure zone (i.e., the fracture process zone) at the crack tip. Also, it is demonstrated that the full-field measurement and post-processing nature of DIC allows a more accurate determination of the stress-strain behavior of the fracture process zone. The applicability of this method to a cylindrical specimen with a curved surface is also investigated by testing a 75-mm-diameter cylindrical specimen. Finally, the DIC method is extended to cyclic testing of asphalt mixtures with the aid of a synchronized image acquisition technique.}, number={1789}, journal={BITUMINOUS PAVING MIXTURES 2002}, author={Seo, Y and Kim, YR and Witczak, MW and Bonaquist, R}, year={2002}, pages={162–172} }
 @inbook{xu_ranjithan_kim_2002, title={New condition assessment procedure for asphalt pavement layers using failing weight deflectometer deflections}, ISBN={030907732X}, DOI={10.3141/1806-07}, abstractNote={Nondestructive condition assessment criteria were developed for application in conjunction with the condition evaluation indicators that are estimated based on falling weight deflectometer (FWD) deflections. Data obtained from state departments of transportation and DATAPAVE 2.0 were used in developing these criteria. To account for the effects of pavement structure and temperature on FWD deflection analysis, structure and temperature correction procedures based on synthetic databases were applied. Also, a deflection prescreening procedure was established to identify and correct any irregular deflection basins potentially arising from measurement errors. All the calibrated predictive procedures, structure and temperature correction procedures, and prescreening algorithms were incorporated into the user-friendly deflection analysis program with graphical interface, Asphalt Pavement Layer Condition Assessment Program, or APLCAP.}, number={1806}, booktitle={Assessing and evaluating pavements, 2002}, publisher={Washington, D.C.: National Academy Press}, author={Xu, B. and Ranjithan, S. R. and Kim, Y. R.}, year={2002}, pages={57–69} }
 @inbook{xu_ranjithan_kim_2002, title={New relationships between failing weight deflectometer deflections and asphalt pavement layer condition indicators}, ISBN={030907732X}, DOI={10.3141/1806-06}, abstractNote={New relationships have been identified between the layer condition indicators of flexible pavements and falling weight deflectometer (FWD) deflections. Synthetic databases were generated using dynamic finite element analysis with nonlinear material models. The sensitivity of various deflection basin parameters (DBPs) to layer conditions was comprehensively examined on the basis of the developed databases. Three types of layer condition indicators were identified in the study, including DBPs, effective layer moduli, and stresses and strains. The DBPs identified from the sensitivity study were used in developing new relationships between the selected condition indicators and FWD deflections by applying regression and artificial neural network techniques. Even though these relationships include the complicated dynamic effect of FWD loading and nonlinear behavior of unbound materials, the time to obtain results from these procedures is insignificant, thus making the procedures suitable for field implementation.}, number={1806}, booktitle={Assessing and evaluating pavements, 2002}, publisher={Washington, D.C.: National Academy Press}, author={Xu, B. and Ranjithan, S. R. and Kim, Y. R.}, year={2002}, pages={48–56} }
 @article{wen_kim_2002, title={Simple performance test for fatigue cracking and validation with WesTrack mixtures}, ISBN={["0-309-07714-1"]}, ISSN={["0361-1981"]}, DOI={10.3141/1789-07}, abstractNote={Viscoelastic characterization of asphalt concrete in indirect tensile (IDT) testing and development of a simple performance test for fatigue cracking are described. A 50-mm gauge length was adopted to measure the horizontal and vertical deformations with surface-mounted linear variable differential transducers on an IDT specimen with a 100- or 150-mm diameter and 38-mm thickness. The effect of a concentrated load under loading strips on vertical displacement within the 50-mm gauge length was evaluated by the digital image correlation method, a noncontact, full-field displacement and strain measurement technique. The theory of viscoelasticity was used to develop analytical solutions for creep compliance and center strain from displacements measured on the specimen surface. These solutions were verified by three-dimensional finite element viscoelastic analysis. IDT creep and strength tests were performed on fine and coarse mixtures from WesTrack with various asphalt contents and air void contents, and various parameters determined from the analysis of these data were compared with the known fatigue performance of these mixtures from the WesTrack testing facility. The fracture energy obtained from viscoelastic analysis of the IDT strength test at 20°C correlated highly with the field performance of these mixtures at WesTrack.}, number={1789}, journal={BITUMINOUS PAVING MIXTURES 2002}, author={Wen, HF and Kim, YR}, year={2002}, pages={66–72} }
 @inbook{park_kim_park_2002, title={Temperature correction of multiload-level failing weight deflectometer deflections}, ISBN={030907732X}, DOI={10.3141/1806-01}, abstractNote={A new temperature correction procedure was developed for multiload-level falling weight deflectometer (FWD) deflections for flexible pavements in North Carolina. In this procedure, temperature correction factors were dependent on the radial offset distance from the FWD load plate. Temperature and FWD multiload-level deflection data used in developing this procedure were collected from 11 pavements in three different climatic regions of North Carolina. The effect of the FWD load level on this temperature correction procedure was investigated. Research efforts focused on improving the accuracy of the current temperature correction procedure of the North Carolina Department of Transportation. The measured deflection and temperature data were also used to validate the long-term pavement performance (LTPP) temperature correction procedure. It was found that the effective pavement temperature prediction algorithm in the LTPP procedure is relatively accurate and that the temperature-deflection correction procedure undercorrects the deflections at higher temperatures in pavements with an asphalt concrete layer thicker than 242 mm. The main reason for this deficiency is that the LTPP procedure was developed from the national database and cannot fully consider the local variation in mixture characteristics.}, number={1806}, booktitle={Assessing and evaluating pavements, 2002}, publisher={Washington, D.C.: National Academy Press}, author={Park, H. M. and Kim, Y. R. and Park, S.}, year={2002}, pages={3–8} }
 @article{guddati_feng_kim_2002, title={Toward a micromechanics-based procedure to characterize fatigue performance of asphalt concrete}, ISBN={["0-309-07714-1"]}, ISSN={["0361-1981"]}, DOI={10.3141/1789-13}, abstractNote={A lattice-based micromechanics approach is proposed to characterize the cracking performance of asphalt concrete. A random truss lattice model was introduced and investigated for simulating the following: ( a) linear elastic and viscoelastic deformation of homogeneous materials in axial compression and shear loading experiments, ( b) linear elastic deformation and the stress field in heterogeneous materials in an axial compression loading experiment, and ( c) damage evolution in elastic solids under an indirect tensile test. The simulation results match well with the theoretical solutions and show excellent promise in predicting cracking patterns in the indirect tensile test. A brief discussion about ongoing work is also presented.}, number={1789}, journal={BITUMINOUS PAVING MIXTURES 2002}, author={Guddati, MN and Feng, Z and Kim, YR}, year={2002}, pages={121–128} }
 @article{park_kim_2001, title={Fitting prony-series viscoelastic models with power-law presmoothing}, volume={13}, DOI={10.1061/(asce)0899-1561(2001)13:1(26)}, abstractNote={An efficient method of fitting Prony-series models to viscoelastic experimental data with power-law presmoothing is presented. A direct fitting of a Prony-series function to experimental data without appropriate presmoothing is difficult when the data have significant variance. A power-law series comprising multiple power-law terms is found capable of portraying a globally smooth, broadband viscoelastic behavior with minimal impact from local variance in the data. However, from a computational point of view, a Prony series representation is preferred to a power-law series representation because of the computational efficiency associated with the exponential basis functions of a Prony series. In this paper, a procedure involving presmoothing of experimental data via power-law-series representation followed by fitting of a Prony-series model to the presmoothed data is discussed and illustrated. Discussion focuses on how experimental data with significant variance can be effectively presmoothed through power-law series representation and how presmoothing improves the quality of the subsequent Prony series fit. The feasibility and effectiveness of the approach are demonstrated through numerical examples in which Prony-series representations of the creep compliance and relaxation modulus of asphalt concrete are determined from available experimental data.}, number={1}, journal={Journal of Materials in Civil Engineering}, author={Park, S. W. and Kim, Y. R.}, year={2001}, pages={26–32} }
 @article{daniel_kim_2001, title={Laboratory evaluation of fatigue damage and healing of asphalt mixtures}, volume={13}, DOI={10.1061/(ASCE)0899-1561(2001)13:6(434)}, abstractNote={The changes in the stiffness of two asphalt concrete mixtures due to temperature, fatigue damage growth, and healing during rest periods are evaluated using the impact resonance method. The impact resonance method is a means of determining the dynamic modulus of elasticity of a specimen nondestructively. The dynamic modulus of elasticity decreases as temperature increases and as microcrack damage growth occurs in the specimen due to fatigue. The impact resonance method also detects increases in dynamic modulus of elasticity after the application of rest periods. A gain in flexural stiffness was also observed from measurements and is attributed to closure of microcracks or healing during the rest period. The amount of healing or stiffness gain appeared to increase when specimens were subject to a higher temperature during the rest period. A qualitative study of the two asphalt mixtures showed that there is a difference between the two with respect to healing performance.}, number={6}, journal={Journal of Materials in Civil Engineering}, author={Daniel, J. S. and Kim, Y. R.}, year={2001}, pages={434–440} }
 @article{lee_daniel_kim_2000, title={Continuum damage mechanics-based fatigue model of asphalt concrete}, volume={12}, DOI={10.1061/(ASCE)0899-1561(2000)12:2(105)}, abstractNote={A fatigue performance prediction model of asphalt concrete is developed from a uniaxial constitutive model based on the elastic-viscoelastic correspondence principle and continuum damage mechanics through mathematical simplifications. This fatigue model has a form similar to the phenomenological tensile strain-based fatigue model. Therefore, a comparison between the new model and the phenomenological model yields that the regression coefficients in the phenomenological model are functions of viscoelastic properties of the materials, loading conditions, and damage characteristics. The experimental study on two mixtures with compound loading histories demonstrates that the fatigue model maintains all of the strengths of the constitutive model such as its accuracy and abilities to account for the effects of rate of loading, stress/strain level dependency, rest between loading cycles, and mode-of-loading on fatigue life of asphalt concrete.}, number={2}, journal={Journal of Materials in Civil Engineering}, author={Lee, H. J. and Daniel, J. S. and Kim, Y. R.}, year={2000}, pages={105–112} }
 @article{chehab_e o'quinn_kim_2000, title={Specimen geometry tension test based study for direct on mechanical tests and air void variation in asphalt concrete specimens compacted by Superpave gyratory compactor}, ISBN={["0-309-06725-1"]}, ISSN={["0361-1981"]}, DOI={10.3141/1723-16}, abstractNote={Reliable materials characterization and performance prediction testing of asphalt concrete requires specimens that can be treated as statistically homogeneous and representative of the material being tested. The objective of this study was to select a proper specimen geometry that could be used for uniaxial tensile testing. Selection was based on the variation of air void content along the height of specimens cut and cored from specimens compacted by the Superpave gyratory compactor (SGC) and on the representative behavior under mechanical testing. From measurement and comparison of air void contents in cut and cored specimens, it was observed for several geometries that sections at the top and bottom and those adjacent to the mold walls have a higher air void content than do those in the middle. It is thus imperative that test specimens be cut and cored from larger-size SGC specimens. Complex modulus and constant crosshead-rate monotonic tests were conducted for four geometries—75 × 115, 75 × 150, 100 × 150, and 100 × 200 mm—to study the effect of geometry boundary conditions on responses. On the basis of graphical and statistical analysis, it was determined that there was an effect on the dynamic modulus at certain frequencies but no effect on the phase angle. Except for 75 × 115 mm, all geometries behaved similarly under the monotonic test. From these findings and other considerations, it is recommended that the 75- × 150-mm geometry, which is more conservative, and the 100- × 150-mm geometry be used for tensile testing.}, number={1723}, journal={2000 TRB DISTINGUISHED LECTURE, PT 1 - ASPHALT MIXTURES 2000, PT 2}, author={Chehab, GR and E O'Quinn and Kim, YR}, year={2000}, pages={125–132} }
 @article{park_kim_lee_1999, title={Fracture toughness for microcracking in a viscoelastic particulate composite}, volume={125}, DOI={10.1061/(ASCE)0733-9399(1999)125:6(722)}, abstractNote={Fracture toughness for microcracking in a viscoelastic particulate composite is derived theoretically from the relationship between a continuum damage model and a micromechanical model. The continuum model presented by Park et al. and the micromechanical model presented by Schapery, which account for viscoelasticity and growing damage, are reviewed and compared in this paper. The condition for local microcrack growth is linked to the evolution law for damage growth in the homogenized continuum. Local microcrack growth is governed by an energy-based fracture criterion. Damage growth in the continuum is described by a phenomenological evolution law determined from an experiment. The resulting fracture toughness for asphalt concrete decreases rapidly with loading duration.}, number={6}, journal={Journal of Engineering Mechanics}, author={Park, S. W. and Kim, Y. R. and Lee, H. J.}, year={1999}, pages={722–725} }
 @article{park_kim_1999, title={Interconversion between relaxation modulus and creep compliance for viscoelastic solids}, volume={11}, DOI={10.1061/(ASCE)0899-1561(1999)11:1(76)}, abstractNote={Methods of interconversion between relaxation modulus and creep compliance for linear viscoelastic materials are discussed and illustrated using data from asphalt concrete. Existing methods of approximate interconversion are reviewed and compared for their approximating schemes. A new approximate interconversion scheme that uses the local log-log slope of the source function is introduced. The new scheme is based on the concept of equivalent time determined by rescaling the physical time. The rescaling factor, which can be interpreted as a shift factor on a logarithmic time axis, is dictated by the local slope of the source function on log-log scales. The unknown target function at a given time is obtained by taking the reciprocal of the source function evaluated at an equivalent time. Although the method is developed using a mathematical relationship based on the power-law representations of relaxation modulus and creep compliance, the method is not limited to material functions characterized by power-laws but can be applied to general, non-power-law material functions as long as the relevant material behaviors are broadband and smooth on logarithmic scales. The new method renders good results especially when the log-log slope of the source function varies smoothly with logarithmic time.}, number={1}, journal={Journal of Materials in Civil Engineering}, author={Park, S. W. and Kim, Y. R.}, year={1999}, pages={76–82} }
 @article{lee_kim_kim_1999, title={Viscoelastic constitutive modeling of asphalt concrete with growing damage}, volume={7}, ISSN={["1225-4568"]}, DOI={10.12989/sem.1999.7.2.225}, abstractNote={This paper presents a mechanistic approach to uniaxial viscoelastic constitutive modeling of asphalt concrete that accounts for damage evolution under cyclic loading conditions. An elasticviscoelastic correspondence principle in terms of pseudo variables is applied to separately evaluate viscoelasticity and time-dependent damage growth in asphalt concrete. The time-dependent damage growth in asphalt concrete is modeled by using a damage parameter based on a generalization of microcrack growth law. Internal state variables that describe the hysteretic behavior of asphalt concrete are determined. A constitutive equation in terms of stress and pseudo strain is first established for controlled-strain mode and then transformed to a controlled-stress constitutive equation by simply replacing physical stress and pseudo strain with pseudo stress and physical strain. Tensile uniaxial fatigue tests are performed under the controlled-strain mode to determine model parameters. The constitutive equations in terms of pseudo strain and pseudo stress satisfactorily predict the constitutive behavior of asphalt concrete all the way up to failure under controlled-strain and -stress modes, respectively.}, number={2}, journal={STRUCTURAL ENGINEERING AND MECHANICS}, author={Lee, HJ and Kim, YR and Kim, SH}, year={1999}, month={Feb}, pages={225–240} }
 @article{park_kim_1998, title={Analysis of layered viscoelastic system with transient temperatures}, volume={124}, DOI={10.1061/(asce)0733-9399(1998)124:2(223)}, abstractNote={A method for quasi-static analysis of a layered viscoelastic system with different loading and temperature histories is presented. First, the response of the system to the unit step load with a constant temperature is obtained from the corresponding elastic solution. The response to a transient load is then obtained through a linear superposition integral using the unit response as the kernel function. The effects of spatially homogeneous, transient temperature on the mechanical response of the system are taken into account through the time-temperature superposition principle. The method is not based on the Laplace transform–based correspondence principle and no transform-inversion process is required. An illustration of the method is presented through an analysis of the stresses and the displacements in a three-layer, elastic-viscoelastic, composite half-space subjected to a distributed surface load and different temperature conditions.}, number={2}, journal={Journal of Engineering Mechanics}, author={Park, S. W. and Kim, Y. R.}, year={1998}, pages={223–231} }
 @inbook{lee_kim_ranjithan_1998, title={Dynamic analysis-based approach to determine flexible pavement layer moduli using deflection basin parameters}, ISBN={0309065119}, DOI={10.3141/1639-04}, abstractNote={Most of the deflection analysis programs used today to analyze falling weight deflectometer (FWD) data are based on static analysis, which often underestimates the subgrade strength. Unfortunately, dynamic analysis usually involves complex calculations and requires significant computation time, thus making it impractical for routine applications. A methodology based on deflection basin parameters and artificial neural networks (ANN) for processing dynamic FWD measurements to estimate layer strengths is presented in this paper. Two-dimensional, dynamic finite element analysis using the ABAQUS program was employed to develop the deflection information for this study. Unlike the majority of the existing backcalculation programs that iteratively adjust the layer moduli to match the measured deflections, the proposed method first determines the subgrade modulus by means of two deflection basin parameters—Base Damage Index and Shape Factor F2—and then applies the estimated subgrade modulus and other parameters as input variables to a trained ANN to estimate the upper layers’ moduli. In contrast to other programs that require the input of seed values for layer moduli, this method does not require initial estimates as input. A set of field FWD measurements were analyzed both by this method and by the MODULUS program. Results reveal that the proposed method is able to better predict the asphalt concrete layer modulus while taking into account the dynamic effects of the FWD test. This method is also shown to be computationally efficient, which makes it applicable for routine tasks and field use.}, number={1639}, booktitle={Recent pavement research issues}, publisher={Washington, DC: Transportation Research Board}, author={Lee, Y. C. and Kim, Y. R. and Ranjithan, S. R.}, year={1998}, pages={36–42} }
 @article{daniel_kim_lee_1998, title={Effects of aging on viscoelastic properties of asphalt-aggregate mixtures}, ISBN={["0-309-06501-1"]}, ISSN={["0361-1981"]}, DOI={10.3141/1630-03}, abstractNote={The effects of aging on asphalt-aggregate mixtures is a topic that has been gaining attention in recent years. Of special interest is how the fatigue performance of asphalt concrete mixtures changes with time because of changing material properties. The fatigue performance of a mixture is related to its viscoelastic material properties. An investigation of the effects of aging on viscoelastic properties of an asphalt-aggregate mixture, such as creep compliance, relaxation modulus, dynamic modulus, and phase angle, is discussed in this paper. The framework for including the effect of aging in an existing uniaxial constitutive model is established, and the applicability of Schapery’s elastic-viscoelastic correspondence principle to aged mixtures is validated.}, number={1630}, journal={ASPHALT MIXTURES}, author={Daniel, JS and Kim, YR and Lee, HJ}, year={1998}, pages={21–27} }
 @article{kim_kim_1998, title={Prediction of layer moduli from falling weight deflectometer and surface wave measurements using artificial neural network}, ISBN={["0-309-06511-9"]}, ISSN={["0361-1981"]}, DOI={10.3141/1639-06}, abstractNote={A new algorithm for predicting layer moduli using measurements from both falling weight deflectometer (FWD) and surface wave tests is presented. This algorithm employs numerical solutions of a multilayered half-space based on Hankel transforms as a forward model and an artificial neural network (ANN) for the inversion process. Phase velocities for frequencies ranging from 10 Hz to 10,000 Hz are calculated using the forward model for varying pavement structures with a range of layer moduli and thicknesses. These phase velocities, along with the layer moduli and thicknesses, are used to train an ANN to backcalculate layer moduli from dispersion curves (i.e., phase velocity versus frequency curves) constructed from the FWD and stress wave test data. To account for the effect of bedrock on the moduli prediction, another network is trained with layer thicknesses and phase velocities for predicting the depth to bedrock. Combining this network with the network for the moduli prediction results in a sequential dispersion analysis technique in which the depth to bedrock predicted from the first network becomes an input to the second network for predicting layer moduli. FWD and stress wave test measurements from an intact pavement and an asphalt overlay over cracked asphalt layer are processed using the sequential dispersion analysis technique and MODULUS 5.0 backcalculation program. Comparison of the results indicates that the dispersion analysis technique yields less variable subgrade moduli and is more sensitive to changes in the asphalt surface layer, because the high-frequency data from the stress wave test is incorporated.}, number={1639}, journal={RECENT PAVEMENT RESEARCH ISSUES}, author={Kim, Y and Kim, YR}, year={1998}, pages={53–61} }
 @inbook{daniel_kim_1998, title={Relationships among rate-dependent stiffnesses of asphalt concrete using laboratory and field test methods}, ISBN={0309065011}, DOI={10.3141/1630-01}, abstractNote={As the application of nondestructive testing on pavements in service becomes more frequent, it is increasingly important to relate the resulting stiffnesses to those from laboratory test methods. The relationship among stiffnesses measured from five test methods currently used for asphalt concrete is addressed: creep compliance, complex modulus, impact resonance, falling weight deflectometer, and surface wave. Established relationships from linear viscoelastic theory are used to relate stiffnesses, including a comparison of creep stiffness, S( t), and relaxation modulus, E( t), calculated from creep compliance, D( t). Using laboratory and field measured stiffnesses, a linear relationship was discovered between stiffness and frequency on a log-log scale.}, number={1630}, booktitle={Asphalt mixtures: Stiffness characterization, variables and performance}, publisher={Washington, DC: Transportation Research Board}, author={Daniel, J. S. and Kim, Y. R.}, year={1998}, pages={3–9} }
 @article{lee_kim_1998, title={Viscoelastic constitutive model for asphalt concrete under cyclic loading}, volume={124}, DOI={10.1061/(ASCE)0733-9399(1998)124:1(32)}, abstractNote={This paper presents a mechanistic approach to uniaxial viscoelastic constitutive modeling of asphalt concrete that accounts for damage evolution under cyclic loading conditions. Schapery's elastic-viscoelastic correspondence principle is applied as a means of separately evaluating viscoelasticity and time-dependent damage growth in asphalt concrete. The time-dependent damage growth in asphalt concrete is modeled by using a damage parameter based on a generalization of microcrack growth law. Internal state variable formulation was used in developing the analytical representation of the model. Tensile uniaxial fatigue tests were performed under the controlled-strain mode to determine model parameters. Then, the resulting constitutive equation was used to predict the stress-strain behavior of the same materials under controlled-stress mode. The constitutive equation proposed in this paper satisfactorily predicts the constitutive behavior of asphalt concrete all the way up to failure under various loading conditions including different stress-strain amplitudes, monotonic versus cyclic loadings, and different modes of loading.}, number={1}, journal={Journal of Engineering Mechanics}, author={Lee, H. J. and Kim, Y. R.}, year={1998}, pages={32–40} }
 @article{lee_kim_1998, title={Viscoelastic continuum damage model of asphalt concrete with healing}, volume={124}, DOI={10.1061/(ASCE)0733-9399(1998)124:11(1224)}, abstractNote={A viscoelastic constitutive model of asphalt mixtures that accounts for the rate-dependent damage growth and microdamage healing is presented in this paper. An elastic continuum damage model, which is based on thermodynamics of irreversible processes with internal state variables, is first reviewed and extended to a corresponding viscoelastic model using an elastic-viscoelastic correspondence principle. A rate-type internal state evolution law is employed to describe the damage growth and microdamage healing in asphalt concrete. An analytical representation of the model is established for the uniaxial loading condition. Tensile uniaxial cyclic tests were performed under the controlled-strain mode with different strain amplitudes to determine model parameters. The resulting constitutive model successfully predicts the damage growth and recovery in asphalt concrete under multilevels of loading, varying rates of loading, different modes of loading (controlled-strain and controlled-stress), and random rest periods.}, number={11}, journal={Journal of Engineering Mechanics}, author={Lee, H. J. and Kim, Y. R.}, year={1998}, pages={1224–1232} }
 @inproceedings{khosla_satish_kim_kim_1997, title={A comparative study of performance of different designs for flexible pavements}, booktitle={Eighth International Conference on Asphalt Pavements, August 10-14, 1997, Seattle, Washington: Proceedings.}, publisher={Seattle, Wash.: University of Washington}, author={Khosla, N. P. and Satish, S. and Kim, N. and Kim, Y. R.}, year={1997}, pages={328–335} }
 @inbook{shao_park_kim_1997, title={A simplified procedure for prediction of asphalt pavement subsurface temperatures based on heat transfer theories}, ISBN={0309059747}, DOI={10.3141/1568-14}, abstractNote={Surface deflection measurements and backcalculation of layer moduli in flexible pavements are significantly affected by the temperature of the asphalt concrete (AC) layer. Correction of deflections or backcalculated moduli to a reference temperature requires determination of an effective temperature of the AC layer. For routine deflection testing and analysis in state highway agencies, it is preferable, from a practical point of view, to use a nondestructive prediction method for determining the effective AC layer temperature instead of measuring the temperature directly from a small hole drilled into the AC layer. A simplified procedure to predict asphalt pavement subsurface temperatures is presented. The procedure is based on fundamental principles of heat transfer and uses the surface temperature history since yesterday morning to predict the AC layer mid-depth temperature at the time of falling weight deflectometer (FWD) testing today. The surface temperature history is determined using yesterday’s maximum air temperature and cloud condition, the minimum air temperature of today’s morning, and surface temperatures measured during FWD tests. FWD tests and temperature measurements have been conducted on seven pavement sections with varying structural designs located in three different climatic regions of North Carolina. The field temperature records from these pavements have provided values of pavement thermal parameters and coefficients in temperature functions that are needed in the prediction procedure. A set of verification results are presented using examples with different climatic regions, changing AC layer thicknesses, and varying weather patterns in different seasons.}, number={1568}, booktitle={Pavement rehabilitation and design}, publisher={Washington, DC: National Academy Press}, author={Shao, L. and Park, S. and Kim, Y. R.}, year={1997}, pages={114–123} }
 @article{kim_lee_little_1997, title={Fatigue characterization of asphalt concrete using viscoelasticity and continuum damage theory}, volume={66}, number={1997}, journal={Journal of the Association of Asphalt Paving Technologists}, author={Kim, Y. R. and Lee, H. J. and Little, D. N.}, year={1997}, pages={520–569} }
 @inbook{kim_kim_1997, title={In-situ evaluation of fatigue damage growth and healing of asphalt concrete pavements using stress wave method}, ISBN={0309059747}, DOI={10.3141/1568-13}, abstractNote={Accurate in situ evaluation of the changes in material properties of an asphalt surface layer due to fatigue loading and rest periods is important for a better understanding of fatigue mechanisms of asphalt concrete in the field and therefore more realistic prediction of the fatigue life of asphalt pavements. A nondestructive technique based on the stress wave propagation method is presented as a means of measuring the changes in the “apparent” modulus of an asphalt surface layer due to fatigue damage growth and healing during rest periods. The method was applied to four asphalt pavements in the FHWA Turner Fairbank Highway Research Center that were loaded by the Accelerated Loading Facility to induce fatigue damage. The dispersion analysis is performed using the Short Kernel Method on the wave transients measured at different loading cycles and after rest periods. The results indicate that ( a) the test and analysis technique used provides a sensitive means of evaluating the changes in asphalt surface layer properties during fatigue loads and rest periods, ( b) the elastic modulus of the asphalt layer decreases as the number of loading cycles increases in an S-shape decaying curve, and ( c) the effective modulus of the asphalt layer increases because of the introduction of rest between loading cycles.}, number={1568}, booktitle={Pavement rehabilitation and design}, publisher={Washington, DC: National Academy Press}, author={Kim, Y. and Kim, Y. R.}, year={1997}, pages={106–113} }
 @inproceedings{kim_lee_kim_little_1997, title={Mechanistic evaluation of fatigue damage growth and healing of asphalt concrete: Laboratory and field experiments}, booktitle={Eighth International Conference on Asphalt Pavements, August 10-14, 1997, Seattle, Washington: Proceedings.}, publisher={Seattle, Wash.: University of Washington}, author={Kim, Y. R. and Lee, H. J. and Kim, Y. and Little, D. N.}, year={1997}, pages={1089–1108} }
 @inbook{little_lytton_williams_kim_1997, title={Propagation and healing of microcracks in asphalt concrete and their contributions to fatigue}, booktitle={Asphalt science and technology}, publisher={New York, NY: Marcel Dekker, Inc.}, author={Little, D. N. and Lytton, R. L. and Williams, D. and Kim, Y. R.}, year={1997}, pages={149–195} }
 @inbook{park_kim_1997, title={Temperature correction of backcalculated moduli and deflections using linear viscoelasticity and time-temperature superposition}, ISBN={0309061539}, DOI={10.3141/1570-13}, abstractNote={New analytical procedures for temperature correction of backcalculated asphalt concrete moduli and surface deflections were developed based on the theory of linear viscoelasticity and the time-temperature superposition principle and verified using falling weight deflectometer data and field temperature measurements. The new correction procedures explicitly utilize the thermorheological properties of the asphalt mixture. The resulting temperature-modulus correction factors depend only on the relaxation modulus and time-temperature shift factor of the mixture. The temperature-deflection correction factor depends on both the material properties and the layer thicknesses of the pavement section. Emphasis has been placed on the analytical description of the mixture’s thermoviscoelasticity responsible for temperature effects on mixture modulus and pavement deflection. A mechanistic framework for dealing with temperature correction problems for asphalt pavement has been introduced.}, number={1570}, booktitle={Pavement research issues}, publisher={Washington, DC: National Academy Press}, author={Park, S. and Kim, Y. R.}, year={1997}, pages={108–117} }