Auburn, AL, United States
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Kim J.,National Center for Asphalt Technology | Lee H.S.,007 NE 39th Ave. | Kim N.,Korea University of Technology and Education
Journal of Engineering Mechanics | Year: 2010

Because of its efficiency in analyzing complex viscoelastic problems, the finite-element (FE) analysis has been widely used to identify the time- and rate-dependent effects of viscoelastic materials on various structural conditions. When performing the FE analysis on a viscoelastic structure, most FE programs require fundamental material properties, shear and bulk moduli, of the given viscoelastic material as their input. However, the shear and bulk modulus tests are difficult to perform, so they have been commonly estimated from a single material test on the basis of the assumption that the Poisson's ratio of viscoelastic materials is a time-independent constant. Such an assumption, however, might not be suitable because the Poisson's ratio of the viscoelastic materials is also a function of time. Therefore, this study developed computation algorithms for determining the time-dependent Poisson's ratio and shear and bulk moduli of asphalt mixtures, which have been well recognized as a viscoelastic material, by employing the indirect tension testing system. The shear and bulk moduli determined by the developed approach appear to be reasonable and realistic. Their applicability and reliability were also verified by comparing experimental data to the results of the FE analysis performed on the same circular specimen as that used in the indirect tension creep test. © 2010 ASCE.

Bianchini A.,National Center for Asphalt Technology | Bandini P.,New Mexico State University | Smith D.W.,New Mexico State University
Journal of Transportation Engineering | Year: 2010

Many government agencies are faced with the challenge of pavement evaluation and maintenance as part of their pavement management systems. These agencies perform or contract manual or automated distress surveys over the pavement network to monitor the structure performance and obtain the necessary data to calculate pavement condition indexes. Although manual distress ratings are done according to well-defined criteria, a certain amount of subjectivity and the experience of the raters have an undoubted influence on the ratings. This study proposes a new approach to estimate the interrater or intercrew reliability for manual or semiautomated distress data collection. The proposed analysis acknowledges that a certain degree of variability in the visual distress ratings is likely to occur and, thus, minimum acceptable values of complete and partial agreements of the crews or raters are suggested. The statistical approach to validate the level of agreement between the ratings of two raters or crews is based on the use of the chi-square distribution to test hypotheses about multinomial experiments. © 2010 ASCE.

Kim J.,Samsung | Kim J.,National Center for Asphalt Technology | Koh C.,University of Florida
Journal of Transportation Engineering | Year: 2012

Fatigue cracking is a major problem in asphalt pavement. It would be beneficial for predictions of the fatigue life of asphalt mixtures to be made with minimal effort and time, both at the design stage and the operating stage of pavement. For practicality, the indirect tension (IDT) test has widely been used for testing both laboratory-made and field-cored mixtures; however, a fatigue test using the IDT test needs to be performed in the stress-controlled mode rather than in the strain-controlled mode. Results may not be comparable to those from other mixture tests, such as the flexural beam fatigue or uniaxial tension test, so this study employed the viscoelastic continuum damage (VECD) model. The C1-S1 curve, which is a final product of the VECD model, is known as a single-characteristic curve of an asphalt mixture and is independent of loading types. Three C1-S1 curves obtained from two fatigue tests and one monotonic strength test using the IDT test were similar when superimposed into a single C1-S1 curve, indicating that the VECD model can be applicable both to the IDT fatigue test and the strength test. This also indicates that the fatigue life of a mixture subjected to sinusoidal strain loading can be determined through the model's damage principles using the IDT test results. Consequently, a system for predicting the fatigue life of asphalt mixtures was developed. It is expected that the predictive system will be useful in estimating the fatigue life of asphalt mixtures fabricated in the laboratory and those cored from field pavements. © 2012 American Society of Civil Engineers.

Bianchini A.,U.S. Army | Heitzman M.,National Center for Asphalt Technology | Maghsoodloo S.,Auburn University
Journal of Transportation Engineering | Year: 2011

Many aspects influence the skid resistance of a pavement surface including surface texture, tire characteristics, vehicle operations, and environmental factors. The objective of this paper is to quantify the temperature influence on the skid number of asphalt pavement surfaces when measured by the locked-wheel friction tester. Specifically, this study aims to determine an adjustment factor for friction readings to a standard reference temperature, removing the seasonal temperature variations influencing measurements. This allows agencies to improve the comparison of pavement sections and to provide a more objective assessment of pavement conditions for safety. The friction database employed is from the National Center for Asphalt Technology Test Track facility. The data includes friction measurements with a locked-wheel trailer on sections from the 2000 and 2003 research cycles. The approach calculates the temperature adjustment factor, CT, from a grouping of the data by temperature values at the time of the measurements. The results show that it is possible to define a reference temperature to adjust friction measured at any other temperature value. The reference temperature identified is between 19.5°C (67.1°F) and 20.2°C (68.4°F). The study concludes that when testing, if the air temperature is greater than the reference temperature, the friction reading is biased by a positive quantity. Therefore the adjustment factor, CT, reduces the measured friction, whereas for measurements performed at temperatures lower than the reference temperature, CT increases the measured friction. © 2011 American Society of Civil Engineers.

Kim J.,Samsung | Kim J.,National Center for Asphalt Technology
Journal of Materials in Civil Engineering | Year: 2011

Since the linear elastic layer solution for the layered systems was developed in the 1940s, the linear elastic layer analysis has been systemized and widely used for the designs of roadway pavements as a tool for evaluating the structural soundness of pavements. The primary assumption made in the analysis is that the layered system consisting of materials that are linear elastic; and hence, an application of the elastic layer analysis to asphalt mixtures, which is a well-known viscoelastic material, has been limited. Therefore, the intention of the study was to derive a viscoelastic solution able to take into account the time- and rate-dependent nature of the viscoelastic materials in the multilayered system. In this paper, a linear viscoelastic solution for the multilayered system subjected to a cylindrical unit step (static) load was derived from the elastic solution by using the principle of elastic-viscoelastic correspondence and the numerical inversion of Laplace transforms. The solution was then extended to simulating pavement responses subjected to a moving load by employing the Boltzmann's superposition principle. The soundness of output from the viscoelastic solution was confirmed by comparing them to those of the finite-element analysis (FEA). Compared to the time and effort required in FEA, the analysis based on the viscoelastic solution was much faster. Therefore, it is expected that the viscoelastic solutions derived in this study will be an effective tool for the design of flexible pavements. © 2011 American Society of Civil Engineers.

Lee H.S.,007 NE 39th Avenue | Kim J.,National Center for Asphalt Technology
Canadian Journal of Civil Engineering | Year: 2011

For the past few decades, the stiffness of asphalt material has been commonly characterized by means of resilient modulus. However, the resilient modulus is not a fundamental material property, and hence, the concept of resilient modulus has been subsequently diminished in the latest Mechanistic-Empirical Pavement Design Guide (MEPDG). Although the MEPDG could not endorse the resilient modulus as the primary means for asphalt concrete characterization, it has been a primary mixture test, and a considerable amount of laboratory testing has been conducted to date. In this paper, an analysis methodology for backcalculating the dynamic modulus from the resilient modulus test data is introduced. The strong advantage of such a methodology is that the existing resilient modulus data can be reused for estimating the dynamic modulus. The approach would significantly save time and effort in reevaluating the dynamic modulus of asphalt mixture for which the resilient modulus test data are available.

Willis J.R.,National Center for Asphalt Technology | Timm D.H.,Auburn University
Asphalt Paving Technology: Association of Asphalt Paving Technologists-Proceedings of the Technical Sessions | Year: 2010

In recent years, there has been a push towards designing roadways which will sustain 50 years of trafficking without having any structural fatigue damage. These "perpetual pavements" are designed using mechanistic-empirical design methods which limit the strain imposed at the bottom of the bituminous layer of a pavement structure to a specific value which negates bottom-up fatigue damage. Previously, only laboratory data had been developed to identify this strain threshold, which is likely to be too conservative for design purposes. Therefore, the objective of this research was to develop field-based strain thresholds for perpetual pavement design. This will ultimately lead to more efficient perpetual pavement design. To accomplish this objective, strain distributions were developed for 21 test sections at the National Center for Asphalt Technology (NCAT) Pavement Test Track. These sections represented three cycles of research using both calculated and measured strains. A unique method of characterizing the entire cumulative probability distribution of strains experienced by each test section was developed, and strain distributions of those sections that experienced fatigue cracking were compared with the distributions of those that did not crack. It was found that sections with bottom-up fatigue cracking experienced higher strain levels above the 55th percentile strain compared to those that did not crack. New strain criteria, in the form of a recommended maximum strain distribution, for perpetual pavement designof flexible pavements were developed using the average of four sections which experienced the most traffic without fatigue cracking. This strain distribution can be used provisionally for the design of perpetual pavements to prevent fatigue cracking. Further research is needed to more fully develop the strain distribution concept for wider application and use.

Willis J.R.,National Center for Asphalt Technology
Airfield and Highway Pavement 2013: Sustainable and Efficient Pavements - Proceedings of the 2013 Airfield and Highway Pavement Conference | Year: 2013

The asphalt pavement industry is currently investigating incorporating ground tire rubber into its asphalt mixtures. While some state agencies look at these products as a chance to become more environmentally friendly, other states are investigating ground rubber as a substitute for polymer modification of asphalt binders. In 2010, the Alabama Department of Transportation built a test section on US 231-S near Dothan, Alabama, to determine if 11% ground tire rubber would be an adequate substitute for styrene-butadiene-styrene in asphalt mixtures. Two mixtures were constructed approximately 1.6 inches thick at 93 percent density. Over the next year, the test sections were monitored for field performance and laboratory performance. Based on field experimentation and laboratory evaluation, the mixture comparison suggests that when properly designed rubber-modified mixture can be used as an adequate polymer substitute without sacrificing asphalt mixture performance. © 2013 American Society of Civil Engineers.

Kim J.,National Center for Asphalt Technology | West R.C.,National Center for Asphalt Technology
Journal of Engineering Mechanics | Year: 2010

The viscoelastic continuum damage model, developed based on Schapery's correspondence principle and the continuum damage mechanics, has received a great deal of attention because of its mathematical soundness and effectiveness in describing damage growth in viscoelastic media and has been used to make reliable estimations on the fatigue lives of asphalt mixtures. Its applications to field mixtures, however, have been limited because the model requires performing the uniaxial tension test. As an alternative, this study developed an analytical methodology for applying the model to the indirect tension test, which has been successfully used in testing both laboratory-made and field-cored mixtures. From the results of the indirect tension tests conducted on asphalt mixture at three different crosshead-controlled rates, it was found that the stress-pseudostrain curves could be superimposed onto one equality line in the linear viscoelastic range of the given mixture, and its rate dependency was successfully eliminated in the C1 and S1 plots. This indicates that the methodology developed for the indirect tension test has a capability of evaluating damage development in asphalt mixtures through the viscoelastic continuum damage model. It would be potentially of great benefit to pavement engineers who want to estimate the remaining lives of field mixtures. © 2010 ASCE.

Willis J.R.,National Center for Asphalt Technology | Leatherman K.,National Center for Asphalt Technology
Airfield and Highway Pavements 2015: Innovative and Cost-Effective Pavements for a Sustainable Future - Proceedings of the 2015 International Airfield and Highway Pavements Conference | Year: 2015

Moisture susceptibility of asphalt mixtures is a commonly addressed concern in mixture designs. As the industry shifts toward the use of warm mix asphalt (WMA) technology from the traditional hot mix asphalt (HMA) there has been increased concern regarding the performance of WMA technology in regards to moisture susceptibility. This concern is primarily driven by the decrease in required production temperatures of the asphalt mixtures which may result in aggregates that have not been dried thoroughly prior to being coated with asphalt binder. To assess this concern, 87 mixtures were evaluated for their resistance to moisture damage using the most common laboratory test for assessing such damage: AASHTO T 283. As a result of this study, it was determined that there was no statistical difference between field compacted specimens versus laboratory reheated specimens for tensile strength ratio (TSR). WMA consistently showed statistically lower TSR values compared to HMA control mixtures. © ASCE.

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