@article{ding_jeong_lee_underwood_kim_castorena_2023, title={Repeatability and Reproducibility Analysis for Functional Test Results from Asphalt Mixture Performance Tester Cyclic Fatigue Test}, volume={4}, ISSN={["2169-4052"]}, url={https://doi.org/10.1177/03611981231159409}, DOI={10.1177/03611981231159409}, abstractNote={ The standards for asphalt mixture performance tester (AMPT) cyclic fatigue testing (AASHTO T 400-22 and AASHTO TP 133-21) enable pavement engineers to predict asphalt mixture performance over a wide range of loading and climate conditions. To enable widespread implementation of AMPT cyclic fatigue testing, precision statements that define the repeatability and reproducibility of the tests are needed. ASTM E691-20 and ASTM C670-15 provide guidance for conducting an interlaboratory study to determine the precision of a test method. However, the standards are written for test methods that yield a single numerical figure as the test result, whereas the cyclic fatigue test yields the damage characteristic curve—a functional relationship—as a primary test result. In this study, a vnorm index was established to quantify variation in the entire damage characteristic curve. Repeatability and reproducibility analysis was conducted using vnorm, six single-point measures of damage characteristic curve variation, and one single-point measure for the fatigue test failure criterion ( D R). The major findings are: (1) the outcomes of repeatability and reproducibility analysis using single-point measures of the damage characteristic curve vary with the chosen point of reference; (2) vnorm demonstrates clear increases in within- and between-laboratory variations with increasing mixture nominal maximum aggregate size (NMAS) values; (3) within-laboratory variation of D R results increases with increasing NMAS for a given specimen geometry while the reproducibility of D R does not depend on the NMAS. Correspondingly, precision limits for both vnorm and D R were recommended and evaluated using a broad set of test results. }, journal={TRANSPORTATION RESEARCH RECORD}, author={Ding, Jing and Jeong, Jaehoon and Lee, Kangjin Caleb and Underwood, B. Shane and Kim, Youngsoo Richard and Castorena, Cassie}, year={2023}, month={Apr} }
 @article{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{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{evaluation of fatigue cracking performance in a debonded asphalt pavement_2019, url={http://dx.doi.org/10.1007/s42947-019-0046-8}, DOI={10.1007/s42947-019-0046-8}, journal={International Journal of Pavement Research and Technology}, year={2019}, month={Jul} }
 @article{lee_pape_castorena_underwood_kim_2019, title={Strain-Level Determination Procedure for Small-Specimen Cyclic Fatigue Testing in the Asphalt Mixture Performance Tester}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.1177/0361198119845357}, DOI={10.1177/0361198119845357}, abstractNote={ With an increase in small-specimen cyclic fatigue testing using the Asphalt Mixture Performance Tester (AMPT), researchers have observed that the strain-selection guidelines in AASHTO TP 107-14 that are intended for large AMPT cyclic fatigue tests are inadequate for testing small specimens. The machine compliance factor is significantly different for testing small specimens compared with large specimens because of different required load levels, resulting in a significant offset in the relationship between the input strain and the number of cycles to failure. To this end, this paper presents the development and verification of a phenomenological model that relates strain levels to dynamic modulus and number of cycles to failure for small-specimen AMPT cyclic fatigue tests, as well as the development of a corresponding stepped strain-level determination procedure that takes into account cases when the initially selected strain-level results in an unexpected number of cycles to failure. The final procedure includes a table with input strain levels and step strain increments for a wide range of dynamic modulus values as well as a flow chart to guide the use of the step strain adjustment procedure. }, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Lee, Kangjin “Caleb” and Pape, Sonja and Castorena, Cassie and Underwood, B. Shane and Kim, Y. Richard}, year={2019}, month={Jun}, pages={036119811984535} }
 @article{improving the reliability of damage characteristic curves in the simplified viscoelastic continuum damage model_2018, url={http://dx.doi.org/10.1177/0361198118797808}, DOI={10.1177/0361198118797808}, abstractNote={ One of the major advantages of the cyclic fatigue test (AASHTO TP 107) is that the results can be used to calibrate the Simplified Viscoelastic Continuum Damage (S-VECD) model, which is used for mechanistic pavement performance predictions. The crux of the S-VECD model is the damage characteristic curve, which has been shown to be independent of mode of loading, loading history, and temperature. Consequently, a model can be fitted to the damage characteristic curve and used to predict the damage response for any given loading history of interest using limited test results. AASHTO TP 107 currently lacks a specific procedure for fitting a model to the damage characteristic curve and evaluating the repeatability of test replicates. In this study, a robust and practical method is proposed for fitting a power law model to the damage characteristic curve. The proposed fitting method was verified using cyclic fatigue test results of 19 mixtures sourced from the United States, Canada, and South Korea. In addition, a means to evaluate the specimen-to-specimen variability of damage characteristic curves using a shape factor is proposed. Thresholds for acceptable variability in the shape factor were derived using confidence interval analysis and verified through FlexPAVE™ pavement performance predictions. The findings of this study can be used to improve the reliability of the damage characteristic curves derived from cyclic fatigue tests for pavement performance predictions. }, year={2018}, month={Dec} }
 @article{optimization of the laboratory fabrication of small specimens for asphalt mixture performance testing_2018, url={http://dx.doi.org/10.1177/0361198118790845}, DOI={10.1177/0361198118790845}, abstractNote={ The use of 38-mm-diameter small specimens for uniaxial dynamic modulus and cyclic fatigue asphalt mixture performance testing offers a significant opportunity to improve the efficiency of laboratory-fabricated specimen testing because multiple test specimens can be extracted per Superpave gyratory-compacted (SGC) sample. This study seeks to optimize the procedure used for the extraction of small specimens from SGC samples for dynamic modulus and cyclic fatigue tests. To this end, small cylindrical specimens were cored horizontally and vertically from SGC samples and subjected to performance testing. The dynamic modulus and fatigue test results indicate that the effects of anisotropy are minimal. However, all of the horizontally extracted small specimens exhibited fatigue failure at the specimen ends, outside the range of the gauges; the failure was likely due to the peripheral air void gradients in the SGC samples. Therefore, the authors concluded that small specimens should be vertically cored from SGC samples for the laboratory fabrication of small specimens. Specifically, four small specimens were cored vertically from the inner 100 mm of SGC samples where the air void content is relatively uniform. Four mixtures with different nominal maximum aggregate sizes (NMASs) were used to prepare small specimens using the proposed extraction procedure. These specimens were subjected to dynamic modulus and cyclic fatigue testing. The results demonstrate an increase in specimen-to-specimen variability with an increase in NMAS, which also is expected in large specimen testing. }, year={2018}, month={Dec} }
 @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{development of deduct value curves for the pavement condition index of asphalt airfield pavement_2013, url={http://dx.doi.org/10.7855/ijhe.2013.15.3.037}, DOI={10.7855/ijhe.2013.15.3.037}, abstractNote={PURPOSES: This study is to develop the deduct value curves for the calculation of pavement condition index of asphalt airfield pavement. METHODS: To develop the deduct value curves of asphalt airfield pavement, panel rating was conducted to decide the pavement condition based on pavement distress type, severity, and density. RESULTS: Results show that standard deviation of deduct values by panel rating is increased at higher severity level and as damage density increases. The deduct value of alligator cracking show the highest. CONCLUSIONS: The deduct value curves based on panel rating could be used without existing problems which were occurred in Shahin`s method.}, year={2013}, month={Jun} }