Browsing by Author "Flintsch, Gerardo W."
Now showing 1 - 20 of 144
Results Per Page
Sort Options
- Aligning Public-Private Partnership Contracts with Public Objectives for Transportation InfrastructureGross, Martha E. (Virginia Tech, 2010-08-18)With its central role in the development of public-private partnership (PPP) contracts, procurement structure has a significant influence on the economic and policy success of privately-financed toll roads throughout their lifecycle. Following a review of PPP fundamentals and the public-policy differentiation between public interest and public objectives, several approaches for establishing the key contract strategies of toll pricing, concession length, and risk mitigation are explored. These underpinnings motivate the central research question: Given specific policy objectives for road pricing, how should public owners select PPP contract strategies which support these outcomes? Through qualitative comparative analysis (QCA), a recently-developed method for evaluating qualitative data quantitatively, patterns of PPP contract strategies which correspond to three common policy objectives--achieving a specific toll rate, managing congestion, and minimizing state subsidy/maximizing revenue--are identified through evaluation of 18 domestic and international projects. Three practical decision-making tools resulting from this work are illustrated through application to current PPP procurements: (1) a traffic-risk worksheet, which provides a rapid estimate of a toll-financed project's viability; (2) analytical QCA results, which offer guidance for structuring PPP contracts based on the desired pricing objectives; and (3) case-library comparisons, which enable drawing parallels between proposed procurements and established PPP projects. Additional insights explore the nature of risk in this study, which concludes with thoughts on the appropriate role of PPPs in infrastructure delivery.
- Analysis of Hot Mix Asphalt (HMA) Linear Viscoelastic and Bimodular Properties Using Uniaxial Compression and Indirect Tension (IDT) TestsKaticha, Samer (Virginia Tech, 2007-09-07)The major Hot-Mix Asphalt (HMA) input for mechanistic-empirical (M-E) flexible pavement design is the dynamic complex modulus obtained from either the uniaxial or triaxial compressive dynamic modulus test. Furthermore, as part of the performance-based mix design process, the triaxial dynamic modulus has been selected to predict rutting and fatigue cracking, and the Indirect Tension (IDT) creep compliance test to predict low-temperature thermal cracking. The creep compliance and dynamic modulus are measured responses (viscoelastic functions) of viscoelastic materials under transient and cyclic loading, respectively. Under the assumptions of linearity, linear viscoelastic functions are equivalent. Moreover, these properties should be the same whether they are obtained from a uniaxial compressive or IDT test. For this dissertation, we tested the applicability of linear viscoelastic (LVE) theory to HMA mixes and determined whether HMA need to be modeled as a bimodular material to analyze IDT creep compliance test results. The need to model HMA as a bimodular material is a result of a number of studies that suggest that HMA tensile and compressive properties are different. A testing program was developed to experimentally measure the uniaxial compression, and IDT creep compliance, and the uniaxial compression dynamic modulus for different HMA mixes. The uniaxial compressive creep compliance and dynamic modulus master curves are constructed and the shift factors obtained from each test are compared. Interconversion between the creep compliance and dynamic modulus experimental results confirm the applicability of LVE theory for the HMA mixes investigated. Based on the applicability of LVE theory, a methodology to determine HMA LVE properties from the combined creep compliance and dynamic modulus test results was developed. As a practical application that is relevant to the M-E flexible pavement design procedure, LVE theory was used and compared to proposed approximate methods to perform the conversion of testing frequency to loading time. Specifically, dynamic modulus results were converted to relaxation modulus, creep compliance, and resilient modulus. Finally, the HMA IDT creep compliance test results at low and intermediate temperature (<20oC) were successfully analyzed using a HMA bimodular material model based on the Ambartsumyan model. The difference between the compressive modulus and the modulus calculated from the IDT test using Hondros' stress distribution is calculated. In addition, a method to determine the compressive-to-tensile modulus ratio using uniaxial compressive and IDT test results is illustrated for one of the tested HMA mixes.
- Analysis of Repeated Network-Level Testing by the Falling Weight Deflectometer on I-81 in the Virginia Department of Transportation's Bristol DistrictBryce, James M.; Katicha, Samer W.; Diefenderfer, Brian K.; Flintsch, Gerardo W. (Virginia Transportation Research Council, 2016-11)This study was undertaken in an effort to determine the required time between subsequent rounds of network-level pavement deflection testing using a falling weight deflectometer (FWD) on the Virginia Department of Transportation’s (VDOT’s) interstate system. Network-level deflection testing was conducted in two separate years (2006 and 2011) on Interstate 81 in VDOT’s Bristol District. The testing was conducted using the FWD at an interval of 0.2 miles in the right-hand lane (travel lane) of the interstate. The objective of this study was to analyze the results from the 2011 testing and compare them to the results obtained from the 2006 study to determine if the previously completed FWD survey of VDOT’s entire interstate network needed to be repeated. First, deflection values that were obtained from pavement segments that received treatments between the two sets of tests were identified and omitted from any comparison. Second, the two datasets were compared directly (i.e., without accounting for errors) and were modeled to account for the expected errors in the data defined as the root mean square of the difference between 2006 and 2011 measurements. The results of the 2011 testing showed lesser deflection and greater structural number values when compared to the data collected in 2006. A characterization of the errors implicit in each set of measurement showed that the errors outweigh the changes in deflection values from the two datasets. Therefore, it was not possible to quantify a recommended time between subsequent rounds of deflection testing on the pavement network. Since the literature shows significant benefits to conducting pavement deflection testing on the network, VDOT will continue this practice based on local needs and as budgetary constraints allow.
- Analysis of the Use of Probe Vehicles for Road Infrastructure Data AnalysisValeri, Stephen M. (Virginia Tech, 2012-06-01)This thesis explores the concept of using sensors found in normal vehicles, also known as probe vehicles, to collect road infrastructure data. This concept was demonstrated by measuring vertical acceleration using in-vehicle sensors in order to describe road ride quality. Data collection was performed at the Virginia Smart Road using two instrumented vehicles. The gathered information was compared to road profile data collection, which is the current state-of-the-practice in ride quality assessment. Following the concept validation, the acceleration measurements were further analyzed for repeatability and effect of various independent variables (vehicle speed and type). A network-level simulation was completed using the robust set of measurements from the experiment. In addition, methodology for identifying rough sections and locations were established. Results show that under controlled testing conditions, roadway profile can accurately be estimated using probe vehicle acceleration data and may provide a more practical way to measure road smoothness. The analysis also showed that vertical acceleration data from a fleet of probe vehicles can successfully identify poorly-conditioned pavement areas. This suggests that instrumented probe vehicles might be a viable and effective way of implementing a network level roadway health monitoring program in the near future.
- Application of Balanced Mix Design Methodology to Optimize Surface Mixes with High-RAP ContentMeroni, Fabrizio; Flintsch, Gerardo W.; Diefenderfer, Brian K.; Diefenderfer, Stacey D. (MDPI, 2020-12-10)The most common use of reclaimed asphalt pavement (RAP) is in the lower layers of a pavement structure, where it has been proven as a valid substitute for virgin materials. The use of RAP in surface mixes is more limited, since a major concern is that the high-RAP mixes may not perform as well as traditional mixes. To reduce risks or compromised performance, the use of RAP has commonly been controlled by specifications that limit the allowed amount of recycled material in the mixes. However, the ability to include greater quantities of RAP in the surface mix while maintaining a satisfying field performance would result in potential cost savings for the agencies and environmental savings for the public. The main purpose of this research was to produce highly recycled surface mixes capable of performing well in the field, verify the performance-based design procedure, and analyze the results. To produce the mixes, a balanced mix design (BMD) methodology was used and a comparison with traditional mixes, prepared in accordance with the requirements of the Virginia Department of Transportation’s volumetric mix design, was performed. Through the BMD procedure, which featured the indirect tensile cracking test for evaluating cracking resistance and the Asphalt Pavement Analyzer (APA) for evaluating rutting resistance, it was possible to obtain a highly recycled mix (45% RAP) capable of achieving a better overall laboratory performance than traditional mixes designed using volumetric constraints while resulting in a reduction in production cost.
- The Application of Intelligent Tires and Model Base Estimation Algorithms in Tire-road Contact CharacterizationKhaleghian, Seyedmeysam (Virginia Tech, 2017-02-13)Lack of drivers knowledge about the abrupt changes in pavement friction and poor performance of the vehicle stability, traction and ABS controllers on the low friction surfaces are the most important factors affecting car crashes. Due to its direct relation to vehicle stability, accurate estimation of tire-road characteristics is of interest to all vehicle and tire companies. Many studies have been conducted in this field and researchers have used different tools and have proposed different algorithms. One such concept is the Intelligent Tire. The application of intelligent tire in tire-road characterization is investigated in this study. Three different test setups were used in this research to study the application of the intelligent tires to improve mobility; first, a wheeled ground robot was designed and built. A Fuzzy Logic algorithm was developed and validated using the robot for classifying different road surfaces such as asphalt, concrete, grass, and soil. The second test setup is a portable tire testing trailer, which is a quarter car test rig installed in a trailer and towed by a truck. The trailer was equipped with different sensors including an accelerometer attached to the center of the tire inner-liner. Using the trailer, acceleration data was collected under varying conditions and a Neural Network (NN) algorithm was developed and trained to estimate the contact patch length, effective tire rolling radius and tire normal load. The third test setup developed for this study was an instrumented Volkswagen Jetta. Different sensors were installed to measure vehicle dynamic response. Additionally, one front and one rear tire was instrumented with an accelerometer attached to their inner-liner. Two intelligent tire based algorithms, a tire pressure estimation algorithm and a road condition monitoring algorithm, were developed and trained using the experimental data from the instrumented VW Jetta. The two-step pressure monitoring algorithm uses the acceleration signal from the intelligent tire and the wheel angular velocity to monitor the tire pressure. Also, wet and dry surfaces are distinguished using the acceleration signal from the intelligent tire and the wheel angular velocity through the surface monitoring algorithm. Some of the model based tire-road friction estimation algorithms, which are widely used for tire-road friction estimation, were also introduced in this study and the performance of each algorithm was evaluated in high slip and low slip maneuvers. Finally a new friction estimation algorithm was developed, which is a combination of experiment based and vehicle dynamic based approaches and its performance was also investigated.
- Applying Pavement Life Cycle Assessment Results to Enhance Sustainable Pavement Management Decision MakingBryce, James Matthew (Virginia Tech, 2014-06-27)Sustainable pavement management implies maintaining acceptable condition of pavements while also considering the tradeoff between cost, environmental impacts and social impacts of pavement investments. Typical pavement management practices only consider economic considerations, and environmental mitigation techniques are employed after the selection of the maintenance action is complete. This dissertation presents a series of papers that demonstrate the impact of decision making on the environmental impact of the pavements both at the project and network levels of pavement management. An analysis was conducted of two models that relate pavement properties to vehicle rolling resistance and fuel consumption. These models were used, along with other tools to evaluate the impact of including the use phase of a pavement into pavement lifecycle assessments. A detailed project level lifecycle assessment was conducted, and it was found that the vehicles on the pavement during the use phase contribute the most to environmental pollutants by a significant margin over other phases of the lifecycle. Thus, relatively small improvements in the factors which contribute to rolling resistance may significantly influence the environmental impacts of the pavement. Building on this, a network level lifecycle assessment method was proposed to probabilistically quantify energy consumption for a given set of expected maintenance actions. It was shown that, although maintenance actions require a certain amount of energy consumption, this energy can be offset by improved road conditions leading to reduced rolling resistance. However, this tradeoff of reduced energy consumption also includes increased costs for a given network condition. In other words, the lowest energy consumption values did not tend to fall along the line defined by minimizing the cost divided by the pavement condition. In order to demonstrate how this tradeoff should be addressed, a novel decision analysis framework was developed, and implemented on a specific pavement network. Finally, a survey of transportation professionals was evaluated to determine their optimal points within the solution space defined by minimizing costs and energy consumption while maximizing pavement condition. It was found that the solution space could be greatly reduced by implementing their responses using the proposed decision analysis framework.
- Asphalt Materials Characterization in Support of Implementation of the Proposed Mechanistic-Empirical Pavement Design GuideFlintsch, Gerardo W.; Loulizi, Amara; Diefenderfer, Stacey D.; Galal, Khaled A.; Diefenderfer, Brian K. (Virginia Center for Transportation Innovation and Research, 2007-01-01)The proposed Mechanistic-Empirical Pavement Design Guide (MEPDG) procedure is an improved methodology for pavement design and evaluation of paving materials. Since this new procedure depends heavily on the characterization of the fundamental engineering properties of paving materials, a thorough material characterization of mixes used in Virginia is needed to use the MEPDG to design new and rehabilitated flexible pavements. The primary objective of this project was to perform a full hot-mix asphalt (HMA) characterization in accordance with the procedure established by the proposed MEPDG to support its implementation in Virginia. This objective was achieved by testing a sample of surface, intermediate, and base mixes. The project examined the dynamic modulus, the main HMA material property required by the MEPDG, as well as creep compliance and tensile strength, which are needed to predict thermal cracking. In addition, resilient modulus tests, which are not required by the MEPDG, were also performed on the different mixes to investigate possible correlations between this test and the dynamic modulus. Loose samples for 11 mixes (4 base, 4 intermediate, and 3 surface mixes) were collected from different plants across Virginia. Representative samples underwent testing for maximum theoretical specific gravity, asphalt content using the ignition oven method, and gradation of the reclaimed aggregate. Specimens for the various tests were then prepared using the Superpave gyratory compactor with a target voids in total mix (VTM) of 7% - 1% (after coring and/or cutting). The investigation confirmed that the dynamic modulus test is an effective test for determining the mechanical behavior of HMA at different temperatures and loading frequencies. The test results showed that the dynamic modulus is sensitive to the mix constituents (aggregate type, asphalt content, percentage of recycled asphalt pavement, etc.) and that even mixes of the same type (SM-9.5A, IM-19.0A, and BM 25.0) had different measured dynamic modulus values because they had different constituents. The level 2 dynamic modulus prediction equation reasonably estimated the measured dynamic modulus; however, it did not capture some of the differences between the mixes captured by the measured data. Unfortunately, the indirect tension strength and creep tests needed for the low-temperature cracking model did not produce very repeatable results; this could be due to the type of extensometers used for the test. Based on the results of the investigation, it is recommended that the Virginia Department of Transportation use level 1 input data to characterize the dynamic modulus of the HMA for projects of significant impact. The dynamic modulus test is easy to perform and gives a full characterization of the asphalt mixture. Level 2 data (based on the default prediction equation) could be used for smaller projects pending further investigation of the revised prediction equation incorporated in the new MEPDG software/guide. In addition, a sensitivity analysis is recommended to quantify the effect of changing the dynamic modulus on the asphalt pavement design. Since low-temperature cracking is not a widespread problem in Virginia, use of level 2 or 3 indirect tensile creep and strength data is recommended at this stage.
- Assessing the Performance of Public-Private Partnership Highway Projects: From Anecdotes to Comprehensive EvidenceAhmed, Manik (Virginia Tech, 2021-07-02)Over roughly the last three decades, governments worldwide have implemented public private partnerships (P3s) to mobilize both private funds and public resources to develop transportation infrastructure, which has provided private entities contemporary opportunities to design, finance, construct, operate and maintain these important assets. Typically, P3s are large and complex undertakings that involve and impact many stakeholders, including public officials, financiers, builders, business owners and taxpaying citizens. Consequently, their efficacy depends – to a great extent – on how well they meet the interests of this array of stakeholders. Hence, effective assessment of P3s is crucial to determine whether these infrastructure initiatives and project outcomes satisfy these stakeholders' interests throughout a P3's life-cycle. Researchers and practitioners have considered various aspects of P3s when considering their performance. In general, the current research landscape related to P3 performance includes two major areas: (1) the identification and implementation of critical success factors (CSFs) and key performance indicators (KPIs), and (2) the development of frameworks that conceptualize approaches to measure P3 performance. Numerous studies have focused on CSFs that are the "ingredients" of effective P3s. More recent studies have emphasized KPIs that are metrics to assess them. Alternatively, some research has taken a life-cycle approach to propose approaches for P3 evaluation that are more comprehensive than assessments of P3 delivery time and cost. While this research has produced useful insights, limited emphasis has been placed on assessing P3 performance comprehensively and beyond the public and private sector dichotomy. Therefore, this research develops a framework that identifies and assesses key stakeholder interests in P3s as a means to characterize their performance. Subsequently, this framework was employed in a case study of four P3 projects to evaluate how well these cases met stakeholder expectations and ultimately performed. The research to develop the framework and conduct the case study was organized in three integrated studies. The first study employed a systematic literature review of CSFs and KPIs where the extant literature remains largely segmented and fragmented. Synthesis of the literature helped to identify and characterize various CSFs and KPIs and their current employment within the P3 performance domain. This led to the development of a CSF-KPI framework that integrates these factors and indicators throughout a P3 project's lifecycle. The outcome of the first study served as the foundation for the second study where the framework to assess stakeholders' interests was constructed. In this process, the second study followed a systematic approach by integrating key components to assess performance. The development process involved several key steps: (1) identification of the key stakeholders – specifically the state (elected bodies and executive agencies), investors (equity providers), producers (project service providers) and users/citizens (individuals or groups impacted by a project); (2) characterization of their principal interests; (3) selection of indicators of these interests; (4) linkage of the indicators with 11 performance dimensions ranging from project environment to revenue and operations; and (5) connection of the performance dimensions with four levels of performance: planning, project management, business, and future potential. The framework was demonstrated and substantiated using data from the I-495 Capital Beltway Express project. The application confirmed the replicability of the framework. The final study utilized the framework to evaluate P3s effectiveness in serving stakeholders goals and objectives. A multiple case study was conducted of four P3 highway projects in the United States: I-495 Capital Beltway Express, LBJ Expressway, SR 125 (South Bay Expressway), and SH 130 (5and6) to examine the extent that state, investor, producer, and user/citizen interests were fulfilled. Overall, I-495 and LBJ Expressway met stakeholder interests more effectively than SR 125 and SH 130 (5and6); these two cases had stronger planning, project management, and business performance. Notably, the I-495 case was an unsolicited (or market lead) proposal that followed a collaborative planning process to shape and define the project to meet mutual interests while the LBJ Expressway case utilized a competitive best-value procurement to generate an innovative technical solution that reduced the project's cost and footprint. Whereas SR 125 and SH 130 (5and6) experienced various issues that led to their bankruptcy; the new owners of both projects have taken steps to improve their outlook. Overall, the research deepens understanding of the factors that impact stakeholder interests and their expectations of P3s, presents a holistic framework for P3 assessments, and provides evidence of how well multiple P3s performed, moving beyond conceptual frameworks that are currently found in the literature.
- Assessment of Fracture Resistance of Asphalt Overlays through Heavy Vehicle Simulator and Laboratory Testing: Synthetic Fiber and Rubber Modified SMA MixesSalado Martinez, Freddie Antonio (Virginia Tech, 2020-05-27)Road administrators have to make decisions regarding the maintenance and rehabilitation of many existing jointed Portland Cement Concrete (PCC) pavements in the road network. Since these pavements are in general expensive to rehabilitate, agencies often opt for overlaying the deteriorated PCC pavement with Hot Mix Asphalt (HMA), resulting in a composite pavement. Unfortunately, the tensile stresses and strains at the bottom of the overlay developed from the movement of the joints, which are caused by the traffic and the changes in temperature, will create cracks on the surface known as reflective cracking. Reflective cracking can reduce the life of a pavement by allowing water or other particles to get into the underlying layers, which causes the pavement structure to lose strength. To improve the performance of the composite pavement, road agencies have studied mitigations techniques to delay the initiation and propagation of those cracks reflected from the PCC joints and cracks. Traditionally, these studies have relied only on laboratory testing or nondestructive tests. This dissertation expands the traditional approach by adding full-scale Accelerate Pavement Testing (APT) to a laboratory effort to investigate enhanced asphalt overlays that delay the initiation and propagation of cracks reflected from the PCC joints. The study was organized into three complementary experiments. The first experiment included the first reflective cracking study of hot-mix asphalt (HMA) overlays over jointed Portland cement concrete pavements (PCCP) conducted at the Virginia APT facility. A Heavy Vehicle Simulator (HVS) was used to compare the reflective cracking performance of a Stone Matrix Asphalt (SMA) control mix with a modified mix with a synthetic fiber. The discussion includes the characterization of the asphalt mixes, the pavement structure, construction layout, the equipment used, the instrumentation installed, and lessons learned. Results showed that the fiber-modified mix had a higher resistance to fracture, which increases the pavement life by approximately 50%. The second experiment compared the cracking resistance of the same control and modified mixes in the laboratory. Four cracking resistance tests were performed on each mix. These four tests are: (1) Indirect Tensile Asphalt Cracking Test (IDEAL-CT), which measures the Cracking Test index (CTindex); (2) Semicircular Bend Test-Illinois (SCB-IL), which measures the critical strain energy release rate (Jc); (3) Semicircular Bend-Louisiana Transportation Research Center (SCB-LTRC), which measures the Flexibility Index (FI); and (4) Overlay Test (OT), which measures the Cracking Propagation Rate (CPR). The results from the four tests showed that the fiber-modified mix had a better resistance to cracking, confirming the APT test results. The laboratory assessment also suggested that the IDEAL-CT and SCB-IL test appear to be the most practical for implementation. The third phase evaluated the performance of mixes designed with a high content of Reclaimed Asphalt Pavement (RAP) and an enhanced asphalt-rubber extender, which comprises three primary components: plain soft bitumen, fine crumb rubber and an Activated Mineral Binder Stabilizer (AMBS). The experiment evaluated the fracture resistance of nine mixes designed with different rates of recycled asphalt pavement (RAP) and asphalt-rubber, compare them with a traditional mix, and propose an optimized mixture for use in overlays of concrete pavements. The mixes were designed with different rates of RAP (15, 30, 45%) and asphalt-rubber extender (0, 30, and 45%) following generally, the design requirements for an SMA mix in Virginia. The laboratory test recommended in the second experiment, IDEAL-CT and SCB-IL, were used to determine the fracture resistance of the mixes. The results showed that the addition of RAP decreases fracture resistance, but the asphalt-rubber extender improves it. A mix designed that replaced 30% of the binder with asphalt-rubber extender and 15% RAP had the highest resistance to fracture according to both. Also, as expected, all the mixed had a low susceptibility to rutting.
- Assessment of the Performance of Several Roadway Mixes under Rain, Snow, and Winter Maintenance ActivitiesFlintsch, Gerardo W. (Virginia Center for Transportation Innovation and Research, 2004-02-01)The purpose of this study was to assess the relative functional performance, including skid resistance and splash and spray, of five hot-mix-asphalt (HMA) surfaces and a tinned portland cement concrete highway surface during controlled wet and wintry weather events. The study compared the way that these surfaces respond to various deicing and anti-icing snow removal and ice control techniques under artificial wintry conditions. In addition, the splash and spray characteristics of the surfaces during and immediately after rain were also evaluated. The study focused on the surfaces placed within the all-weather testing area at the Virginia Smart Road. The winter maintenance techniques tested include the application of sodium chloride (salt) in granular, pre-wetted, and liquid forms. The snow removal and ice control measures that were used followed the recommendation of the FHWA Project T & E 28 and variations thereof. The experiments to compare the splash and spray characteristics of the mixes were conducted using artificial rain. The study defined and tested a methodology for testing winter maintenance operations under controlled, artificial wintry events. The winter maintenance test results were inconclusive, as the various maintenance treatments were unable to significantly improve the functional condition of the road. Under the temperature and precipitation conditions encountered, there were no significant differences in the performance of the different surface mixes tested. However, conditions encountered did not correspond to conditions normally encountered with natural snow. The researcher concluded that at temperatures at and just below freezing, artificial snow might not be appropriate for evaluating the effectiveness of winter maintenance chemicals. Studies that depend upon imitating the on-road attributes of natural snow, such as testing effectiveness of winter maintenance chemicals, should adhere to the ideal temperature-humidity guidelines for the snowmaking equipment. The open-graded friction course appears to have enhanced spray and splash performance when compared with the dense HMA surface mixes; however, a more objective measure of splash and spray characteristics of the surfaces is needed to quantify the beneficial effect of this type of mixes. No visual difference in performance was observed among the other mixes.
- Asset Management Data Collection for Supporting Decision ProcessesPantelias, Aristeidis (Virginia Tech, 2005-06-09)Transportation agencies engage in extensive data collection activities in order to support their decision processes at various levels. However, not all the data collected supply transportation officials with useful information for efficient and effective decision-making. This thesis presents research aimed at formally identifying links between data collection and the supported decision processes. The research objective identifies existing relationships between Asset Management data collection and the decision processes to be supported by them, particularly in the project selection level. It also proposes a framework for effective and efficient data collection. The motivation of the project was to help transportation agencies optimize their data collection processes and cut down data collection and management costs. The methodology used entailed two parts: a comprehensive literature review that collected information from various academic and industrial sources around the world (mostly from Europe, Australia and Canada) and the development of a web survey that was e-mailed to specific expert individuals within the 50 U.S. Departments of Transportation (DOTs) and Puerto Rico. The electronic questionnaire was designed to capture state officials' experience and practice on: asset management endorsement and implementation; data collection, management and integration; decision-making levels and decision processes; and identified relations between decision processes and data collection. The responses obtained from the web survey were analyzed statistically and combined with the additional resources in order to develop the proposed framework and recommendations. The results of this research are expected to help transportation agencies and organizations not only reduce costs in their data collection but also make more effective project selection decisions.
- Automated Characterization of Bridge Deck Distress Using Pattern Recognition Analysis of Ground Penetrating Radar DataScott, Michael L. (Virginia Tech, 1999-08-02)Many problems are involved with inspecting and evaluating the condition of bridges in the United States. Concrete bridge deck inspection and evaluation presents one of the largest problems. The deterioration of these concrete decks progresses more rapidly than any other bridge component, which leads to early concrete deck replacements that must be done before the bridge superstructure needs to be replaced. The primary cause of deterioration in these concrete bridge decks is corrosion-induced concrete cracking, which frequently results in delaminations. Delamination distress increases the life cycle cost of maintaining a concrete bridge deck, particularly when it is not detected early on. Early detection of delamination distress can facilitate economical repair and rehabilitation work, but bridge engineers must recommend deck replacement if repairs are delayed too long or inspection tools cannot detect delaminations early enough. The Federal Highway Administration has responded to the need for a better bridge deck inspection tool by contracting Lawrence Livermore National Laboratory to develop two new prototype ground penetrating radar systems. These two systems generate three-dimensional data that provide a representation of features that lie below the bridge deck surface. Both of these systems produce large amounts of data for an individual bridge deck, which makes automated data processing very desirable. The primary goal of the automated processing is to characterize bridge deck distress represented in the data. This study presents data collected from sample bridge deck sections using one of the prototype systems. It also describes the development and implementation of appropriate methods for automating data processing. The automated data processing is accomplished using image processing and pattern recognition algorithms developed in the study.
- Best Practices and Performance Assessment for Preventative Maintenance Treatments for Virginia Pavementsde León Izeppi, Edgar; Morrison, Akyiaa; Flintsch, Gerardo W.; McGhee, Kevin K. (Virginia Transportation Research Council, 2015-08)Preventive maintenance has the potential to improve network condition by retarding future pavement deterioration. This report outlines guidelines for implementing a preventive maintenance policy for bituminous pavements. Preventive maintenance treatments currently being used in Virginia include chip seal, slurry seal, microsurfacing, and thin hot mix asphalt overlays. Historical pavement condition data were obtained from the Virginia Department of Transportation’s Pavement Management System for these treatments, and treatment performance models were developed. A district-level treatment selection tool was developed to facilitate the district-level decision-making process. A prioritized list of pavement sections was generated, maximizing the cost-effectiveness of the selected treatments subject to budgetary constraints set by the Central Office. As a pilot implementation, the treatment selection tool was then run for each pavement classification in each district. The results of this pilot suggest that this selection tool has the potential to be a practical decision support tool.
- Binder Film Thickness Effect on Aggregate Contact BehaviorWang, Dong (Virginia Tech, 2007-08-02)This study presents a study on the binder film thickness effect on aggregate contact behavior. As a three-phase material composed of aggregates, asphalt binder and air voids, asphalt mixture could be considered as a visco-elastic material in the low stress level. Since the behavior of the mixture depends largely on the relationship of different components, a well developed contact model for micro-structural modeling is very important for understanding the deformation mechanism of the mixture. In this study, the contact modeling of asphalt mixture was reviewed and the numerical tools used to investigate the micromechanical behavior of asphalt mixture will also be introduced. By using the cabinet x-ray tomography system, the displacement and resistant force of a system of particles bonded by a thin layer binder are measured and recorded. Then, the results are compared with the theoretical solutions of a normal compliance model for a system comprised of two elastic particles bonded by a thin layer of visco-elastic binder. A closed-form time-dependent relationship between the contact forces and the relative particle/binder movements was developed. A reasonable agreement between experiments results and model predicted results is obtained combined with parametric analysis.
- Characterizing the Dynamics of Vulnerability for Roadway Infrastructure SystemsDehghani Sanij, Mohammad Saied (Virginia Tech, 2013-12-30)Critical infrastructure systems, such as transportation, energy, water and communication, are the backbones of sustainable economic and social development. The tragedies and catastrophic events in the past few years have motivated researchers to study the vulnerability of infrastructure systems to disastrous events. A number of existing studies address roadway networks where researchers have characterized the robustness and vulnerability of roadways to earthquakes, floods, and targeted attacks. However, extreme events with infrequent return periods are not very likely to occur in a 50-60 year analysis period of roadways, while many roadways are located in areas that are not even exposed to floods or earthquakes at all. On the other hand, roadway network endogenous characteristics such the condition and degradation over time not only increases the vulnerability of roadways to disastrous events, but also makes the roadway network vulnerable to disruptions that are caused by maintenance and repair activities on the roadways system. Nevertheless, the impacts of these endogenous network characteristics on roadway vulnerability have not been explicitly addressed in the existing studies. This dissertation introduces the concept of condition-based vulnerability assessment (CBVA) to capture the effect of roadway endogenous characteristics such as condition and condition uncertainties, roadway network deterioration over time, topological properties of roadways, and travel rate and travel pattern on the dynamics of roadway network vulnerably. First a methodological framework is developed and the method is applied to an illustrative roadway system. The results show that the vulnerability of roadway system is more affected by the average condition of the roadway network than by the condition of individual roads in the system. Moreover, the findings show that small uncertainties associated with the condition of individual roads can significantly increase the variance of the predicated vulnerability. This initial methodological framework is then enhanced to account for physical degradation of the network over time and network equilibrium, and is applied to a real highway system. For the network studied network degradation increases roadway system vulnerability in a nonlinear mode. The result also suggest that the network vulnerability pattern is not very sensitive to travel pattern and link topological properties when the average network disruption probability (representing average network condition) is less than about 0.5. In other words, at low values of average disruption probability, it does not matter what link has what disruption probability level or how the travelers move across the network. However with further network degradation and as the average network disruption probability increases, the dynamics of network vulnerability depends on travel pattern on the network as well as on the link topological properties.
- Co-Location Decision Tree for Enhancing Decision-Making of Pavement Maintenance and RehabilitationZhou, Guoqing (Virginia Tech, 2011-01-17)A pavement management system (PMS) is a valuable tool and one of the critical elements of the highway transportation infrastructure. Since a vast amount of pavement data is frequently and continuously being collected, updated, and exchanged due to rapidly deteriorating road conditions, increased traffic loads, and shrinking funds, resulting in the rapid accumulation of a large pavement database, knowledge-based expert systems (KBESs) have therefore been developed to solve various transportation problems. This dissertation presents the development of theory and algorithm for a new decision tree induction method, called co-location-based decision tree (CL-DT.) This method will enhance the decision-making abilities of pavement maintenance personnel and their rehabilitation strategies. This idea stems from shortcomings in traditional decision tree induction algorithms, when applied in the pavement treatment strategies. The proposed algorithm utilizes the co-location (co-occurrence) characteristics of spatial attribute data in the pavement database. With the proposed algorithm, one distinct event occurrence can associate with two or multiple attribute values that occur simultaneously in spatial and temporal domains. This research dissertation describes the details of the proposed CL-DT algorithms and steps of realizing the proposed algorithm. First, the dissertation research describes the detailed colocation mining algorithm, including spatial attribute data selection in pavement databases, the determination of candidate co-locations, the determination of table instances of candidate colocations, pruning the non-prevalent co-locations, and induction of co-location rules. In this step, a hybrid constraint, i.e., spatial geometric distance constraint condition and a distinct event-type constraint condition, is developed. The spatial geometric distance constraint condition is a neighborhood relationship-based spatial joins of table instances for many prevalent co-locations with one prevalent co-location; and the distance event-type constraint condition is a Euclidean distance between a set of attributes and its corresponding clusters center of attributes. The dissertation research also developed the spatial feature pruning method using the multi-resolution pruning criterion. The cross-correlation criterion of spatial features is used to remove the nonprevalent co-locations from the candidate prevalent co-location set under a given threshold. The dissertation research focused on the development of the co-location decision tree (CL-DT) algorithm, which includes the non-spatial attribute data selection in the pavement management database, co-location algorithm modeling, node merging criteria, and co-location decision tree induction. In this step, co-location mining rules are used to guide the decision tree generation and induce decision rules. For each step, this dissertation gives detailed flowcharts, such as flowchart of co-location decision tree induction, co-location/co-occurrence decision tree algorithm, algorithm of colocation/co-occurrence decision tree (CL-DT), and outline of steps of SFS (Sequential Feature Selection) algorithm. Finally, this research used a pavement database covering four counties, which are provided by NCDOT (North Carolina Department of Transportation), to verify and test the proposed method. The comparison analyses of different rehabilitation treatments proposed by NCDOT, by the traditional DT induction algorithm and by the proposed new method are conducted. Findings and conclusions include: (1) traditional DT technology can make a consistent decision for road maintenance and rehabilitation strategy under the same road conditions, i.e., less interference from human factors; (2) the traditional DT technology can increase the speed of decision-making because the technology automatically generates a decision-tree and rules if the expert knowledge is given, which saves time and expenses for PMS; (3) integration of the DT and GIS can provide the PMS with the capabilities of graphically displaying treatment decisions, visualizing the attribute and non-attribute data, and linking data and information to the geographical coordinates. However, the traditional DT induction methods are not as quite intelligent as one's expectations. Thus, post-processing and refinement is necessary. Moreover, traditional DT induction methods for pavement M&R strategies only used the non-spatial attribute data. It has been demonstrated from this dissertation research that the spatial data is very useful for the improvement of decision-making processes for pavement treatment strategies. In addition, the decision trees are based on the knowledge acquired from pavement management engineers for strategy selection. Thus, different decision-trees can be built if the requirement changes.
- Collaborative En Route Airspace Management Considering Stochastic Demand, Capacity, and Weather ConditionsHenderson, Jeffrey Michael (Virginia Tech, 2008-03-26)The busiest regions of airspace in the U.S. are congested during much of the day from traffic volume, weather, and other airspace restrictions. The projected growth in demand for airspace is expected to worsen this congestion while reducing system efficiency and safety. This dissertation focuses on providing methods to analyze en route airspace congestion during severe convective weather (i.e. thunderstorms) in an effort to provide more efficient aircraft routes in terms of: en route travel time, air traffic controller workload, aircraft collision potential, and equity between airlines and other airspace users. The en route airspace is generally that airspace that aircraft use between the top of climb and top of descent. Existing en route airspace flight planning models have several important limitations. These models do not appropriately consider the uncertainty in airspace demand associated with departure time prediction and en route travel time. Also, airspace capacity is typically assumed to be a static value with no adjustments for weather or other dynamic conditions that impact the air traffic controller. To overcome these limitations a stochastic demand, stochastic capacity, and an incremental assignment method are developed. The stochastic demand model combines the flight departure uncertainty and the en route travel time uncertainty to achieve better estimates for sector demand. This model is shown to reduce the predictive error for en route sector demand by 20\% at a 30 minute look-ahead time period. The stochastic capacity model analyzes airspace congestion at a more macroscopic level than available in existing models. This higher level of analysis has the potential to reduce computational time and increase the number of alternative routing schemes considered. The capacity model uses stochastic geometry techniques to develop predictions of the distribution of flight separation and conflict potential. A prediction of dynamic airspace capacity is calculated based on separation and conflict potential. The stochastic demand and capacity models are integrated into a graph theoretic framework to generate alternative routing schemes. Validation of the overall integrated model is performed using the fast time airspace simulator RAMS. The original flight plans, the routing obtained from an integer programming method, and the routing obtained from the incremental method developed in this dissertation are compared. Results of this validation simulation indicate that integer programming and incremental routing methods are both able to reduce the average en route travel time per flight by 6 minutes. Other benefits include a reduction in the number of conflict resolutions and weather avoidance maneuvers issued by en route air traffic controllers. The simulation results do not indicate a significant difference in quality between the incremental and integer programming methods of routing flights around severe weather.
- Comparison of Creep Compliance Master Curve Models for Hot Mix AsphaltJeong, Myunggoo (Virginia Tech, 2005-07-08)Creep compliance of Hot Mix Asphalt (HMA) is an important property to characterize the material's viscoelatic behavior. It is used to predict HMA thermal cracking at low temperature and permanent deformation at high temperatures. There are several experimental methods to measure the creep compliance. Two of these methods were used in this thesis; uniaxial compressive and indirect tension (IDT) creep compliance. The tests were conducted at five temperatures (-15, 5, 20, 30, and 40°C) with a static loading for 1000-sec to characterize two typical HMA mixes used in Virginia, a base and a surface mix. Creep compliance master curves (CCMC) were developed by shifting the curves to a reference temperature using time-temperature superposition. Three mathematical functions, Prony series, power and sigmoidal, were fitted to the experimental data using regression analysis. Uniaxial CCMC were also predicted based on dynamic modulus measurements using method for interconversion of vicoelastic properties recommended in the literature. Finally, the susceptibility of the mixes to thermal cracking was evaluated based on the creep compliance measurements at low temperature. The regression analysis showed that the three mathematical models considered are appropriate to model the CCMC over a wide ranger of reduced times. The sigmoidal model provided the best fit over the entire range of reduced times investigated. This model also produced the best results when used in the interconversion procedures. However, there were noticeable differences between the CCMC predicted using interconversion and the experimental measurements, probably due to nonlinearity in the material behavior. The m-values for the base mix were higher using the creep results measured with both configurations.
- Comparison of Macrotexture Measuring Devices Used in VirginiaHuang, ManQuan (Virginia Tech, 2004-05-13)This thesis compared macrotexture measurements obtained using the volumetric method (Sand Patch) and three laser-based devices: MGPS system, ICC laser profiler, and Circular Texture Meter (CTMeter). The study used data from three sources: two controlled experiments conducted at the Virginia Smart Road, field data collected on eight newly constructed hot-mix-asphalt (HMA) roadway surfaces, and data collected on airport surfaces at the Wallops flight facility, Virginia. The data collected at the Virginia Smart Road, a controlled-access two-lane road that includes various HMA and concrete surfaces, was used for the main analysis. The other two sets of data were used for verification and validation of the model developed. The analysis of the data collected at the Virginia Smart Road showed that the CTMeter mean profile depth (MPD) has the highest correlation with the volumetric (Sand Patch) mean texture depth (MTD). Furthermore, texture convexity had a significant effect on the correlation between the measurements obtained with different devices. Two sets of models for converting the laser-based texture measurements to an estimated MTD (ETD) were developed. One set of equations considered all the data collected at the Virginia Smart Road, and the other excluded the measurements on the Open-Graded Friction Course (OGFC). The developed models were tested using measurements collected at eight roadway sections throughout Virginia and the Wallops flight facility. The model, excluding the OGFC section, was successfully applied to other sites.