LTPP Data Analysis Project Statements

Introduction:

The following preliminary Long-Term Pavement Performance (LTPP) data analysis project statements provide extra information on the work envisioned for projects identified in the Long-Term Pavement Performance Data Analysis Program. Some of the problem statements were prepared by LTPP staff and contractors, while others are the work of the Transportation Research Board (TRB) expert task group on LTPP Data Analysis, pooled fund project panel members, and others. Readers should note that these project statements are at various stages of development and review, and that all are subject to revision. Comments and recommendations about these problem statements are invited and may be submitted via ltppinfo@fhwa.dot.gov

Evaluation of Weigh In Motion (WIM) Site Data and Tools for Determining Load Data Confidence

PROBLEM NUMBER: 1A

RESEARCH PROBLEM STATEMENT

There is a need to know how accurate and consistent weigh in motion (WIM) systems are for collecting load data. Load data are critical factors in the study of LTPP. LTPP has undertaken a number of initiatives to improve the quality of load data, including the collection and submittal of calibration data by State highway agencies (SHA). Currently there is limited ability to evaluate the accuracy and variability of the calibration data. These data need to be analyzed to effectively determine their statistical confidence.

Data collection engineers have no way to evaluate the relative influence of the various sources of error on the accuracy of a particular WIM site. Consequently, engineers have no systematic way to decide on replacing WIM or on correcting pavement surface profiles at the site, which affects WIM performance rehabilitation strategies when these are needed.

RESEARCH OBJECTIVES AND TASKS

Objectives:

Understand the influence of pavement surface profiles on WIM accuracy.
Determine the confidence in load data through statistical analyses and synthesis of WIM calibration data (data mining) collected at the LTPP sites.
Quantify the influence of WIM system types and ages, pavement types and ages, levels of road roughness, profiles, geometries, and traffic speeds, on the performance of the WIM site.
Develop tools that can evaluate measured surface profiles at new and existing WIM sites.
Develop tools and procedures for characterizing the errors generated by WIM systems to enable diagnoses of problems and rehabilitation strategies for WIM sites.

Tasks:

Task 1 - Using LTPP data, assess the likely baseline accuracy—that is, the accuracy in the absence of surface roughness and dynamic loads—of a variety of existing WIM systems. (The difference between the real accuracy and the baseline accuracy is caused by dynamic loads.)
Task 2 - Develop tools for correlating the influence of measured surface profiles on WIM errors and for specifying surface rehabilitation requirements. Validate the tools using data from LTPP calibration and validation tests.
Task 3 - Develop user-friendly software tools for diagnosing and reporting the likely source of errors in measuring WIM data. Test the tools on a variety of existing LTPP WIM systems.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $450,000
Research Period: to be determined.

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

The determination of statistical confidence will quantify the quality of any analysis using LTPP load data parameters. These statistical parameters may be used for future estimation and analysis. These data can also be used to monitor ongoing quality and accuracy of the entire LTPP traffic load monitoring effort.

As the improved traffic data collection activities in LTPP begin to be implemented (e.g., the LTPP Specific Pavement Studies (SPS) Traffic Data Collection Pooled Fund Study), it is vital to ensure that WIM systems are maintained in prime operating condition and that any accuracy problems are handled in a timely and cost-effective way.

The anticipated product of this research is a user-friendly software tool for diagnosing and reporting the likely source of errors in the measurement of WIM data.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

Submittal of calibration information to LTPP's incorporation of wavelength specifications is expected for WIM-scale approaches. Ideally, the central database will include calibration information.

This problem needs to be pursued BEFORE the following proposed problems: None.

This problem should not be pursued until AFTER the following projects/problems are completed: None.

Procedures for Forecasting and Backcasting Traffic Loading Data Project 1: Development of Methods and Models Using Existing Data (Phase I)

PROBLEM NUMBER: 1C1

RESEARCH PROBLEM STATEMENT

Successful implementation of the 2002 Mechanistic-Empirical Pavement Design Guide (MEPDG) requires good prediction of axle load distributions. Currently, a number of studies have addressed this important topic, including the National Cooperative Highway Research Program (NCHRP) 1-37A (Development of the 2002 Guide for the Design of New and Rehabilitated Pavement Structures: Phase II), NCHRP 1-39 (Traffic Data Collection, Analysis, and Forecasting for Mechanistic Pavement Design), "Estimating Cumulative Traffic Loads, Phase 1 and 2 (Objective 1C)" (i.e., axle load extrapolation method), as well as many models developed locally and internationally. Lessons learned from these projects and the new data from WIM sites, other sources, or both, prompt the need to develop more accurate and reliable procedures for forecasting and backcasting traffic loading data. Potential products generated by this project will benefit the use of MEPDG in improving pavement design.

RESEARCH OBJECTIVES AND TASKS

Task 1 - Develop procedures for predicting baseline axle load distributions from road use factors including:

Land use and geography.
Roadway function.
Types and loads of trucks.
Hourly, weekly, and monthly axle load distributions with a minimum of 4 weeks of axle load data (1 full week in each season) at a discrete site and in a discrete lane.
Seasonal variations and adjustment factors.
Vehicle and axle load regulations, legal and permitted.
Coverage of demographic, economic, and technological trends and any other relevant factors.

Task 2 - Develop procedures and provide reliability for forecasting and backcasting axle load distributions at sites with sufficient, limited, or no WIM, Automatic Vehicle Classification (AVC), or Automatic Traffic Recorder (ATR) data.
Task 3 - Develop sensitivity analysis of the procedures to various design parameters.
Task 4 - Validate the procedures developed.
Task 5 - Update the study Estimating Cumulative Traffic Loads, Phase 1 and 2 (1C).
Task 6 - Develop a traffic load estimation guide and software.
Task 7 - Include Estimating Cumulative Traffic Loads, Phase 1 and 2 (1C) tables into the LTPP database.
Task 8 - Conduct a workshop using real data.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $250,000
Research Period: 24 months

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

This work has the potential to have significant impact on improving pavement design when using the MEPDG.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This problem needs to be pursued BEFORE the following proposed problems: None.

This problem should not be pursued until AFTER the following projects/problems are completed:

NCHRP 1-39, Traffic Data Collection, Analysis, and Forecasting for Mechanistic Pavement Design.
Estimating Cumulative Traffic Loads, Phase 1 and 2 (1C).
Traffic Pooled Fund Study Phase 1, Evaluation of Weigh-In-Motion (WIM) Site Data and Tools for Determining Load Data Confidence (1A).
Traffic Action Plan.

Review of LTPP SPS-9 Experiment Verification of SHRP Asphalt Specification and Mix Design (Superpave^TM)

PROBLEM NUMBER: 2A1

RESEARCH PROBLEM STATEMENT

The Long-Term Pavement Performance (LTPP) Specific Pavement Studies (SPS)-9 experiment was intended to provide data to validate the Strategic Highway Research Program (SHRP) Superpave^TM asphalt specifications and mix design. In addition, the experiment is to provide a direct comparison, in terms of pavement performance, between existing highway agencies' specifications and the Superpave^TM (Superior Performing Pavement) performance-based specifications. The SPS-9 experiment also provides an opportunity to evaluate stone matrix asphalt (SMA) and other innovative materials and features. The results from this experiment will also help in modifying the SHRP mix design system and in the development of performance-based specifications for asphalt mixtures.

The review of the LTPP SPS-9 experiment will provide an opportunity to check if the construction of the experiment sections conforms to the requirements of the experiment. It will also identify and resolve any discrepancies in the design and construction of the sections and will evaluate the data quality and completeness.

RESEARCH OBJECTIVES AND TASKS

Objectives:

Identify specific applications and analytical objectives that should be pursued, using the SPS-9 experimental data.
Evaluate the as-constructed SPS-9 sites to determine what was constructed. Identify areas of strength and weakness and recommend corrective measures to make the experiment capable of fulfilling its expectations.
Evaluate data quality and completeness (in relation to current data collection requirements) for each core and supplemental section. Submit feedback reports to ensure problems are fixed.
Identify confounding factors not accounted for in the original experimental design.
Evaluate the adequacy of existing data and current data collection requirements in relation to anticipated analytical needs.

Tasks:

Task 1 - Obtain and Review Required Data. SPS-9 construction, testing, and monitoring data will be obtained from the LTPP IMS. Data will be reviewed from the instrumented test sections, including the entire core and supplemental sections, using the most recently upgraded data in the IMS database.
Task 2 - Information on what was built and whether the pilot sections can be used will be obtained.
Task 3 - Review Construction Reports. Construction reports, construction-related sampling and testing plans, and test data will be reviewed for each SPS-9 project to identify the deviations in the as-constructed test sections. It is important to review construction reports because they document the construction activities and data. Construction reports will help identify any deviation from the original construction plan, the type and details of the supplemental test sections that were built, and any construction-related difficulties or factors that could have affected the construction of the test sections.
Task 4 - Prepare Feedback Reports. Feedback reports will be prepared to identify specific concerns with SPS-9 data so that improvements can be made as soon as possible. It is believed that some data, particularly materials, do exist and are in the regional centers and laboratories waiting to be processed.
Task 5 - Perform Preliminary Reviews of the Performance Data. Preliminary reviews will be performed of the key performance data from SPS-9 projects for the SHRP mix sections, State agency mix sections, and SMA sections. The research team will compare performance trends of the all three core sections within projects and between projects for local (onsite), regional, and national trends.
Task 6 - Prepare Recommendations for Changes in Future Data Collection Efforts. Recommendations will be prepared for changes in future data collection efforts to ensure that the SPS-9 experiment will realize its full potential with respect to expectations and objectives of the experiment.
Task 7 - Final Report. A final report will be prepared to document all of the reviews and findings. It will become a key resource for all researchers and for the LTPP staff and regional centers.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $100,000
Research Period: to be determined.

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

Feedback reports
Final report
Presentation of findings

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This problem needs to be pursued BEFORE the following proposed problems: None.

This problem should not be pursued until AFTER the following projects/problems are completed: None.

Review of Laboratory Resilient Modulus Testing of Hot Mix Asphalt (HMA) Mixtures

PROBLEM NUMBER: 2A2

RESEARCH PROBLEM STATEMENT

Resilient modulus is the primary material property that has been used to characterize HMA mixtures and other structural properties for flexible pavement design, in accordance with the 1993 American Association of State Highway and Transportation Officials (AASHTO) Guide for Design of Pavement Structures. Resilient modulus is simply a measure or estimate of the elastic modulus of the material at a given test temperature (i.e., assumed to be the modulus of elasticity) and is mathematically defined as the applied stress divided by the ”recoverable" strain that occurs when the applied repeated-load is removed from the test specimen. Resilient modulus has been generally measured in the laboratory using the repeated-load indirect tensile test; however, it can be also measured by other test procedures or determined through backcalculation.

LTPP has collected cores and samples of the mixtures from the SPS and General Pavement Studies (GPS) projects. The coring and sampling of the GPS projects initiated in the late 1980s. Many of these cores have been already tested using the indirect tensile test procedure. The indirect tensile resilient modulus tests were performed by different contractors for each of the four regional offices. However, Von Quintus and Killingsworth identified and reported potential problems with the test protocol during a study sponsored by the Federal Highway Administration (FHWA) in 1995, Analyses Relating to Pavement Material Characterizations and Their Effects on Pavement Performance (FHWA-RD-97-085). As a result of that work and as confirmation of its findings, the indirect tensile resilient modulus values were found to be suspect. The test protocol was revised, and the tests are now being completed by a single laboratory under contract with LTPP. These data have yet to be reviewed in detail.

RESEARCH OBJECTIVES AND TASKS

Objectives:

The primary objective of this project is to review the HMA resilient modulus test data to identify and explain any anomalous observations, and to recommend a procedure that can be used in the future to evaluate the reasonableness of the resilient modulus test results and to resolve any anomalous observations present in the data.

This study will provide a comprehensive review of the LTPP indirect tensile resilient modulus test data for HMA mixtures.

Tasks:

Task 1 - Initial Data Review for Completeness. This task will consist of extracting the data from the LTPP database and structuring the data into a form that can be easily evaluated. The data review will identify those tests at level E and also non-level E data. It will also identify any missing tests at specific temperatures. Other data will also be extracted to assist in the review process. For example these data will include asphalt content, density, air voids, age of the mix, and gradation. These extra data elements will be used in Task 4.
Task 2 - Data Evaluation. Data quality will be assessed for the HMA resilient modulus test results. These data will be examined in detail to identify and explain any anomalous data or readings such as unreasonably high or low resilient modulus, or a modulus that does not increase with decreasing temperatures. The variability in the resilient modulus test results will be defined both between the projects and within a project.
Task 3 - Identify Potential Outliers in the Database and Remedial Actions. Using the results from Task 2, tests will be identified that are suspect or represent different conditions. Based on the results, remedial actions will be recommended and provided to FHWA in the standard data feed back forms.
Task 4 - This will determine the correspondence between mix properties (e.g. asphalt content, density, voids in mineral aggregate (VMA), age, gradation, and temperature) and the indirect tensile resilient modulus.
Task 5 - To the extent possible, determine the correspondence between the backcalculated elastic modulus and the laboratory-determined resilient modulus.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $50,000
Research Period: to be determined.

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

To be determined.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This problem needs to be pursued BEFORE the following proposed problems: None.

This problem should not be pursued until AFTER the following projects/problems are completed: None.

Relationships Between Laboratory-Measured and Field-Derived Properties of Pavement Layers

PROBLEM NUMBER: 2B

RESEARCH PROBLEM STATEMENT

A number of prior research projects have found that the layer moduli backcalculated from pavement deflection data differs significantly from those obtained through laboratory resilient_modulus testing. This finding is reflected in the 1993 AASHTO Guide recommendation that backcalculated layer moduli be divided by a value in the range of 3 to 5 to obtain an estimate of the laboratory test result. Subsequent work was completed by Von Quintus and Killingsworth, Analyses Relating to Pavement Material Characterizations and Their Effects on Pavement Performance, (FHWA-RD-97-085), published in January 1998.

However, the relationships developed in past research are simplistic and are not considered adequate for use in the more sophisticated design procedures that are embodied in the 2002 Guide for the design of new and rehabilitated pavement structures. The LTPP database contains falling weight deflectometer (FWD) test results and material samples obtained on the same test date and time, which can be used to further explore this issue.

It would be useful if the backcalculated moduli derived from nondestructive pavement tests (such as FWD) could be used to estimate laboratory properties (or vice versa) such as dynamic and resilient modulus of asphalt, elastic modulus of portland cement concrete (PCC) and cement-stabilized material, and the resilient modulus of unbound materials. In some cases, new pavement designs could use laboratory-derived properties when FWD results are not yet available. These estimated properties could then be used to more accurately design the required structural section.

This project is intended to look at this issue in greater depth. The study should begin with the premise that backcalculated layer moduli and laboratory-resilient moduli are different, and that it may not be possible to derive simple relationships to enable interchangeable use. This project will be considered successful if it yields either relationships enabling the interchangeable use of laboratory-resilient modulus test data and backcalculated values, or a clear explanation of why it was not possible to derive such relationships.

This problem fits under Strategic Objective 2, Materials Characterization, of the LTPP Data Analysis Program. Within this objective it is under Subcategory B, Relationships to Enable Interchangeable Use of Laboratory- and Field-Derived Material Parameters.

RESEARCH OBJECTIVES AND TASKS

Objectives:

The primary objective is to determine whether relationships exist between laboratory-measured and field-derived properties of pavement layers and whether it is possible to use these relationships in the pavement design and analysis process. The research should include the following tasks:

Task 1 - Determine if relationships exists between laboratory properties and backcalculated moduli of pavement layers, using data in the LTPP database. Many conventional laboratory properties are available and should be investigated; however, the primary laboratory property to be considered in this investigation is the resilient modulus of the unbound layers.
Task 2 - If useful relationships between laboratory and backcalculated moduli are found, determine the statistical reliability for predictions from the different relationships developed in Task 1. For instance, with what degree of confidence can the resilient modulus of unbound layers be estimated from the backcalculated moduli obtained from FWD field measurements? Based on the findings of this investigation, develop recommendations and sample problems to demonstrate how the research results may be applied.

If Task 1 does not yield meaningful relationships, conduct further investigation as needed to explain the reasons underlying the discrepancies between laboratory and field moduli, and provide a clear explanation of the reasons that relationships could not be derived. It is expected that this explanation will focus on the factors that differ between the laboratory and field test situations, and the potential impact of those factors on the test results.

It is intended that data and background information that are necessary for this project will be available through the LTPP and related data analysis contracts. Backcalculated moduli should be available through two FHWA data analysis projects: Backcalculation of Layer Moduli (FHWA RD-97-086) and Review of LTPP Backcalculation Results (FHWA-HRT-05-152). Laboratory measured values are available in the database.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $200,000
Research Period: 36 months

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

Successful completion of this project potentially could provide information to pavement designers that may not be available without complicated and expensive laboratory testing. In some cases user agencies do not have the equipment necessary to perform the laboratory tests. There are times when the information could be obtained with a FWD in a timely fashion whereas laboratory testing, if possible, would require longer, or vice versa.

There is potential to complete jobs ahead of schedule and save money in testing. There is a high potential for a large number of user agencies to use the information developed from this project. By properly analyzing the existing pavement properties collected through nondestructive testing techniques, agencies will realize a cost savings in more accurately developing pavement rehabilitations. Cost savings will occur in not overdesigning (expensive initial construction) or underdesigning (premature failures and unanticipated maintenance) the initial rehabilitation.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This problem needs to be pursued BEFORE the following proposed problems: None.

This problem should not be pursued until AFTER the following projects/problems are completed: None.

Estimation of Key Hot-Mix Asphalt, Base, Subgrade, and Component Engineering Properties from Routine Tests and Physical Characteristics

PROBLEM NUMBER: 2E1

RESEARCH PROBLEM STATEMENT

Key material engineering properties are often measured using test methods that are too costly or complex to conduct routinely. For this reason, pavement designs are often based on assumed values, and the relationships among the design assumptions, laboratory test results, and as-constructed values are unknown. Relationships that will allow estimation of material engineering properties from routine test results, index properties, or other readily available information are needed: for example, relationships to estimate resilient modulus from index properties.

RESEARCH OBJECTIVES AND TASKS

Objectives:

Identify a set of material engineering properties for which predictive relationships would be useful in pavement design, construction quality control and quality assurance, and pavement management applications.
Establish and/or validate relationship(s) between these engineering properties and routine test results, index properties, and/or other readily available information.
Develop a practical guide (possibly accompanied by user-friendly software) for applying the results of Tasks 2 and 3 in pavement design, construction quality control and assurance, and pavement management.

Tasks:

Task 1 - Review the literature (including, but not limited to prior LTPP data analysis reports) for pertinent information. Particular attention should be paid to previously developed relationships that might be validated through this investigation.
Task 2 - Identify a set of material engineering properties applicable in pavement design, construction quality control and quality assurance, and/or pavement management for which predictive relationships would be useful.
Task 3 - Review available data (site distribution with respect to an appropriate sampling matrix, trends, etc.) and assess its adequacy in relation to the project objectives.
Task 4 - Prepare a detailed work plan and updated budget for the remainder of the project. In the work plan, identify any gaps, questions, and uncertainties in these LTPP data that may impact the end results of this investigation or future investigations of similar issues.
Task 5 - Upon approval of the work plan prepared in Task 4, conduct statistical analysis to validate or develop the required relationships.
Task 6 - If worthwhile relationships are found in Task 5, develop a practical guide (possibly accompanied by user-friendly software) for applying the results of Task 5 in pavement design, construction quality control and assurance, and pavement management.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $400,000
Research Period: 24 months

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

This project will yield information that will enable pavement design and materials engineers to make well-founded decisions on the material and material specifications to be used in pavement construction. Potential cost savings resulting from better materials selection, fewer premature pavement failures, or avoidance of overdesign are staggering.

The findings of this project will impact materials selection, materials specification, section design, and pavement management.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This problem needs to be pursued BEFORE the following proposed problems: None.

This problem should not be pursued until AFTER the following projects/problems are completed: None.

Estimation of Key PCC, Base, Subbase, and Component Engineering Properties from Routine Tests and Physical Characteristics

PROBLEM NUMBER: 2E2

RESEARCH PROBLEM STATEMENT

Traffic loading intertwined with environmental factors such as temperature fluctuations, freeze/thaw cycling, and seasonal variations in moisture will adversely impact the performance of concrete pavements over time. Selection of choice materials, use of new class of admixtures, proper proportioning, rational design, and good construction practices can result in better, longer lasting concrete pavements. Proper characterization of concrete paving materials, including stabilized base, and subgrade is one vital step toward achieving maximum pavement life. Non-homogeneity of naturally-occurring materials makes characterization of materials necessary on each project.

Key material engineering properties are often measured using test methods that are too costly or complex to conduct on a routine basis. For this reason, pavement designs are often based on assumed values, and the relationships among the design assumptions, laboratory test results, and as-constructed values are unknown. Relationships that will allow estimation of material engineering properties from routine test results, index properties, or other readily available information are needed: for example, relationships to estimate resilient modulus from index properties.

RESEARCH OBJECTIVES AND TASKS

Objectives:

Identify a set of material engineering properties for which predictive relationships would be useful in pavement design, construction quality control and quality assurance, and/or pavement management applications.
Establish and/or validate relationship(s) between these engineering properties and routine test results, index properties, and/or other readily available information.
Develop a practical guide (possibly accompanied by user-friendly software) for applying the results of Tasks 2 and 3 in pavement design, construction quality control and assurance, and pavement management.

Tasks:

The tasks enlisted below are intended to provide a framework for conducting the research. Proposers are expected to demonstrate their understanding of the problem and describe a research effort that can realistically be conducted within the constrains of available funds and contract time.

Phase 1:

Review the literature (including, but not limited to prior LTPP data analysis reports) for pertinent information. This information may be obtained from domestic and foreign literature, contacts with research agencies and industry organization, and other sources. Particular attention should be paid to previously developed relationships that might be validated through this investigation.
Identify a set of material engineering properties applicable in pavement design, construction quality control, quality assurance, and/or pavement management for which predictive relationships would be useful.
Review available data (site distribution with respect to an appropriate sampling matrix, trends, etc.) and assess its adequacy in relation to the project objectives. A wealth of information is available from the LTPP concrete studies of SPS-2 and SPS-8 Experiments. The sites for these studies are strategically selected to encompass varieties of materials and environments.
Prepare a detailed work plan and updated budget for the remainder of the project. In the work plan, identify any gaps, questions, and uncertainties in the LTPP data that may impact the end results of this investigation, or future investigations of similar issues.

Phase 2:

Upon approval of the work plan prepared in Task 4, conduct statistical analysis to validate or develop the required relationships.
Develop a practical guide (accompanied by user-friendly software) for applying the results of Task 5 in pavement design, construction quality control and assurance, and pavement management.
Submit a final report that documents the entire research effort. The report shall include an implementation plan for moving the results of the study into practice.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $400,000 (Phase I shall be limited to $80,000)
Research Period: 30 months.

Phase I: 8 months, including 2 moths for panel review and approval

Phase II: 22 months, including 3 months for panel review and revision of the final report

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

This project will yield information that will enable pavement design and materials engineers to make well-founded decisions about material and material specifications to be used in pavement construction. Potential cost savings resulting from better materials selection, fewer premature pavement failures, or avoidance of over-design are staggering.

The findings of this project will impact materials selection, materials specification, section design, and pavement management.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This problem needs to be pursued BEFORE the following proposed problems: None.

This problem should not be pursued until AFTER the following projects/problems are completed: None.

Improved Deflection-Based Analysis Methods for Materials Characterization

PROBLEM NUMBER: 2F1

RESEARCH PROBLEM STATEMENT

During the past 20 years, a number of backcalculation programs have been developed for use in the analysis of deflection data collected for the structural evaluation of pavements. Although these programs have proven useful, all have limitations, by virtue of discrepancies between the relatively simple theoretical models of the pavement structure on which they are based, and the true nature and characteristics of pavement structures.

Recent advances in computer technology and structural modeling have made it possible to develop and apply more realistic models in the analysis of pavement deflection data for the purpose of materials characterization. Evaluation and testing of analysis methods based on more realistic models is needed to assess the benefits to be gained through their application and to provide a basis for further development and refinement.

RESEARCH OBJECTIVES AND TASKS

Objective:

To develop improved, next-generation methods for deflection-based characterization of pavement materials.

Tasks:

Task 1 - Conduct a literature review to identify promising new (next-generation) methods for modeling the pavement structure in the interpretation of pavement deflection data, and document the current state of the practice in backcalculation of pavement layer parameters.
Task 2 - Based on the findings of Task 1, select one or more of the next-generation methods for indepth review and evaluation, and identify several state-of-the-practice backcalculation programs to be used as the standards for comparison.
Task 3 - Design an experiment or set of experiments using the LTPP data to (1) evaluate the next-generation analytical methods and (2) compare the material characterization results obtained with those derived from the state-of-the-practice backcalculation methods.
Task 4 - Conduct the experiment or set of experiments designed in Task 3.
Task 5 - Based on the outcome of Task 4, refine the next-generation analytical methods to the extent appropriate. This development should include preparation of guidelines to support practical application of the methods developed in pavement engineering practice.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: to be determined.
Research Period: to be determined.

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

To be determined.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This problem needs to be pursued BEFORE the following proposed problems: None.

This problem should not be pursued until AFTER the following projects/problems are completed: Review of LTPP Backcalculation Results (FHWA-HRT-05-152).

Evaluation of LTPP Site-Specific Climatic Data

PROBLEM NUMBER: 3A

RESEARCH PROBLEM STATEMENT

Onsite weather instrumentation is used to collect climatic data at the LTPP seasonal monitoring and SPS 1, 2, and 8 sites. Quality control checks are applied to these data as they are collected and processed for release from the LTPP database. Experience has shown that automated checks of data do not catch all of the anomalies that may occur in these data. Thus, there needs to be further assessment of these site-specific LTPP climatic data. This review of the climatic data collected at LTPP seasonal monitoring and SPS test sites will identify and resolve discrepancies in the LTPP climatic data and improve the quality control process.

RESEARCH OBJECTIVES AND TASKS

Objectives:

To examine the LTPP climatic data collected via onsite weather instrumentation to:

Evaluate completeness.
Evaluate quality.
Perform reasonableness checks for seasonal and site location.
Identify and explain other anomalous observations.
Identify issues and improvements for equipment and process.

Tasks: to be determined.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: to be determined.
Research Period: to be determined.

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

To be determined.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This problem needs to be pursued BEFORE the following proposed problems: None.

This problem should not be pursued until AFTER the following projects/problems are completed: None.

Assessment of the Effects of Loading and Environment on Pavement Life Using SPS Data

PROBLEM NUMBER: 3A1

RESEARCH PROBLEM STATEMENT

The rate of pavement deterioration over a long period is influenced by both loading and environment. Pavement deterioration on SPS-1 and SPS-2 projects includes both these causes inseparably. SPS-8 projects normally involve deterioration due to environment. Pavement design models need to be able to account for the effects of environment and of load-environmental interactions. This project will study available data from LTPP, Canadian-Strategic Highway Research Program (C-SHRP), and European LTPP studies, augmented by special parallel lane studies (inside lane versus outside lane) at the SPS sites.

RESEARCH OBJECTIVES AND TASKS

Objectives:

Determine the effects of environmentally induced pavement deterioration versus losses due to the interaction of load with environment.
Develop models that describe the individual and joint effects of load and environment on pavement deterioration.

Tasks: to be determined.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $500,000
Research Period: 30 months

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

To be determined.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This problem needs to be pursued BEFORE the following proposed problems: None.

This problem should not be pursued until AFTER the following projects/problems are completed: None.

Pavement Damage Caused by Swelling and Frost-Susceptible Soils

PROBLEM NUMBER: 3B2

RESEARCH PROBLEM STATEMENT

Volume change resulting from soil swelling and frost action is an important cause of pavement deterioration in areas affected by these phenomena. The only documented design procedure allowing for the prediction of long-term damage caused by these factors is in the 1993 AASHTO pavement design method. However, the proposed procedure is subjective and essentially empirical. Other procedures using mechanistic indices have been developed to predict volume changes. Distress-specific deterioration models are needed to support modern mechanistic-empirical pavement design procedures that are currently being developed. Practical procedures are also needed to capture the effect of volume changes in these design procedures.

RESEARCH OBJECTIVES AND TASKS

Objectives:

Validated (mechanistic) indices to characterize the effects of frost and swell susceptibility of soils.
Improve and/or develop procedures based on the indices to predict volume change in and underneath pavement structures.
Develop a procedure for estimating the impact of volume change on pavement deterioration (roughness and cracking).

Tasks: to be determined.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $300,000
Research Period: 30 months

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

Pavement design engineers in State, Provincial, and local highway agencies in areas affected by volume changes due to frost heave and soil swelling.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This problem needs to be pursued BEFORE the following proposed problems: None.

This problem should not be pursued until AFTER the following projects/problems are completed: None.

Evaluation of the Integrated Climatic Model Using LTPP Seasonal Monitoring Program Data

PROBLEM NUMBER: 3C1

RESEARCH PROBLEM STATEMENT

To properly design a pavement structure, the environmental effects on pavement materials must be considered. In the MEPDG, it is envisioned that the Integrated Climatic (IC) Model developed by the FHWA will be used to explain the environmental effects on pavement materials. The IC Model, however, has not been validated in a comprehensive, large-scale test. The LTPP Seasonal Monitoring Program (SMP) database provides data on seasonal changes in moisture, temperature, and frost depth on a national basis that could be used to evaluate and validate the model.
If the model is successfully validated, then a practical guideline should be developed to assist State design engineers to manage the many input parameters needed for use in the IC Model.

If the model is not found to be valid, then a framework should be identified that can further refine and improve the accuracy of the model. Alternative strategies for defining environmental effects on pavement materials that do not require the use of the IC Model should also be considered.

RESEARCH OBJECTIVES AND TASKS

Objectives:

Phase I: Use the SMP data to validate the IC Model.
Phase II: If Phase I is successful, develop a practical guideline to assist State design engineers in selecting input parameters for the use of the model. If Phase I is not successful, develop an extensive plan of work for improving the IC Model.

Tasks: to be determined.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $200,000
Research Period: 24 months (12 months Phase I, 12 months Phase II)

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

It is envisioned that the IC Model will be used in the MEPDG. The validity of the model must be determined immediately. A practical guideline to facilitate the use of the model is urgently needed. If the model is not found to be valid, then this project must either define what is needed to improve the model or identify alternative strategies for considering environmental effects on pavement materials.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This problem needs to be pursued BEFORE the following proposed problems: None.
This problem should not be pursued until AFTER the following projects/problems are completed:

NCHRP 1-37A , MEPDG.
NCHRP 9-23, Environmental Effects in Pavement Mix and Structural Design Systems (Objective 3A).

Seasonal Validity of the Assumptions Underlying In-Situ Mechanistic Pavement Evaluation Methods

PROBLEM NUMBER: 3C2

RESEARCH PROBLEM STATEMENT

The mechanistic theory for evaluating the structural capacity of pavement structures is based on a number of assumptions concerning material properties (e.g. elastic behavior), loading conditions, and boundary conditions. Seasonal fluctuations, such as changes in the moisture content of base course and subgrade materials, may lead to cases where these assumptions are so violated that mechanistic theory cannot adequately describe the distribution of stress and strain in the pavement layers. This in turn will affect both pavement design and pavement structural evaluation (e.g., backcalculation).

Research is needed to identify the conditions under which current mechanistic procedures for interpretation of pavement deflection data are most applicable in terms of their underlying assumptions. Furthermore, if these conditions are not available and testing must be conducted, agencies must be aware of the effect of suboptimal conditions (and the associated assumption violations) if the resulting deflection values are analyzed using mechanistic theories.

RESEARCH OBJECTIVES AND TASKS

Objectives:

Analyze the LTPP seasonal monitoring data and other data as required to determine the most appropriate conditions under which to conduct deflection testing based on existing mechanistic theory, and conduct sensitivity analyses to evaluate the relative effect of varying levels of assumption violations upon the results of mechanistic analysis.
Although the focus of the investigation will concern analysis of FWD deflection results and mechanistic analysis techniques, the project scope should also include deflection results in general such that the results of this investigation are applicable to other deflection test methods still in use around the world.

Tasks.

At a minimum, the required work will include the following:

Review existing mechanistic theory and identify all underlying assumptions.
Assess the effect of environment on pavement materials to determine whether or not the theoretical assumptions of mechanistic design are satisfied.
Characterize the environmental conditions under which the assumptions of mechanistic theory are either applicable or not.
Through sensitivity analysis, characterize the relative effect of assumption violations upon analysis results.
If possible, provide conversion factors or shift curves to compensate for assumption violations.
Determine whether the limitations affect all regions of the country, or only some regions.
The product of this research will be guidelines to assist agencies in determining the most appropriate conditions to conduct deflection testing, to provide input to pavement design and performance evaluation and also on the effect of suboptimal conditions upon the resulting deflection data and mechanistic analysis.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $400,000
Research Period: 24 months

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

Because of the increasing use of FWDs and backcalculation to make rehabilitation decisions, this project is very urgent.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This problem needs to be pursued BEFORE the following proposed problems: None.

This problem should not be pursued until AFTER the following projects/problems are completed: None.

Region-Specific Guidelines for Pavement Modeling and Design Considering Environmental Effects

PROBLEM NUMBER: 3E1

RESEARCH PROBLEM STATEMENT

To be determined.

RESEARCH OBJECTIVES AND TASKS

To be determined.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: to be determined.
Research Period: to be determined.

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

To be determined.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

To be determined.

Develop Improved Pavement Performance Default Values or Models for Life-Cycle Cost Determination

PROBLEM NUMBER: 4A1

RESEARCH PROBLEM STATEMENT

Accurate and defendable life-cycle cost estimates are dependent upon accurate information that defines the performance life of new pavements as well as the performance life of reconstruction, rehabilitation, and maintenance activities. Good life-cycle costing must also have information describing when (timing) to apply rehabilitation and maintenance activities during the life of a pavement, as well as what treatment to apply. LTPP data analysis has been conducted to allow the engineer to estimate the life cycles of typical pavement rehabilitation and maintenance alternatives, as well as to define when to apply these treatments. This LTPP information will continue to improve in its accuracy as the LTPP program continues. Only limited extra analysis will be necessary to accomplish this project.

RESEARCH OBJECTIVES AND TASKS

Objective:

To develop improved life-cycle costing default values and revise existing life-cycle costing software.

Tasks:

This research project will use available LTPP models and other information on both flexible and rigid pavements, and will recommend improved default values for life-cycle costing. In particular, the following information will be developed:

Life of typical newly constructed pavements.
Life of typical reconstruction, rehabilitation, and maintenance alternatives.
When (during the life of a pavement) to apply selected rehabilitation and maintenance activities.
What rehabilitation and maintenance treatment to apply.

The above life-cycle cost information might be used to revise the existing FHWA and individual public agency life-cycle costing software.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $150,000
Research Period: 15 months

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

The project will supply a product that can be immediately used by public agencies. There is a high potential for successful completion and implementation of the project.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This problem needs to be pursued BEFORE the following proposed problems: Information will be obtained from completed LTPP data analysis projects, including FHWA-sponsored SPS-3 and SPS-4 analysis projects and the pending NCHRP 20-50(3/4), "LTPP Data Analysis: Effectiveness of Maintenance and Rehabilitation Options (Objective 6A). The project will use the best available information to develop the default values. Updates of the default values and software should be developed periodically.

This problem should not be pursued until AFTER the following projects/problems are completed: None.

Developing Hierarchical Data Collection for Network- and Project-Level Pavement Management, Considering Types and Frequencies of Measurements

PROBLEM NUMBER: 4A2

RESEARCH PROBLEM STATEMENT

To be determined.

RESEARCH OBJECTIVES AND TASKS

To be determined.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: to be determined.
Research Period: to be determined.

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

To be determined.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

To be determined.

Types and Frequencies of Measurements for Accurate Description of Pavement Condition

PROBLEM NUMBER: 4A3

RESEARCH PROBLEM STATEMENT

States are continually addressing the issue of what types of data and how frequently to collect data in their pavement management systems. LTPP has developed an extensive database that permits comparative analysis for determining the optimum combination of data types, accuracy, and collection frequency. For example, the FWD data in the database is taken at four load levels, with multiple drops at each level at numerous locations along the test section. The question to be answered is "How much of these data are really needed to capture the structural condition for network- and project-level analysis, or are there different numbers of load levels, number of drops, and number of drop sites that would produce an improved description of structural condition?" Using the LTPP database, identify the data parameters needed to describe pavement condition, and define the frequencies of measurement recommended for collecting high-quality data suitable for model building and performance analysis. The optimum frequency of data collection to balance the cost of collection and accuracy of the test results, including issues of daily and seasonal variability, will be addressed.

RESEARCH OBJECTIVES AND TASKS

Objective:

To define the optimum data collection schedule to balance frequency, cost, and accuracy of test results for pavement management system (PMS) input.

Tasks: to be determined.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $250,000
Research Period: 18 months

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

This project will facilitate the collection of data sets describing pavement condition, which are suited to pavement performance analysis, model building, prediction of pavement performance, and decision-making with PMS. They will help practitioners in public agencies focus on key parameters and provide guidance on the level of data collection activity needed.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This problem needs to be pursued BEFORE the following proposed problems: None.

This problem should not be pursued until AFTER the following projects/problems are completed: None.

Numerical Pavement Evaluation Indices for Pavement Condition

PROBLEM NUMBER: 4A4

RESEARCH PROBLEM STATEMENT

Successful modeling of pavement performance requires the definition of a numerical value or index (for example, the International Roughness Index (IRI) or the friction number) by which each failure mechanism is measured. Although some functional measures (for example, skid or roughness) have well-known indices, there are indices needed for rutting, various types of pavement cracking, and other forms of distress. Use of accepted indices will facilitate data modeling and comparisons among public agencies.

It is anticipated that the research would involve a consideration of various possible indices related to specific distress types. Selection of the most useful index would be based on the extent that the index successfully indicates the pavement distress type (for example, transverse cracking), severity (for example, crack width), extent (for example, crack length) as well as the stability (for example, sensitivity) of the value and the ease of its use. The research should also consider the seasonal and daily variability of the indices by using site data from the Seasonal Monitoring Program. This will enable users of the indices to evaluate a reading made in one season to readings made at different times of the year.

RESEARCH OBJECTIVES AND TASKS

Objective:

To develop appropriate indices for both rigid and flexible pavements, to characterize the most common pavement conditions including such distresses as fatigue cracking, rutting, faulting, reflective cracking, raveling, environmental cracking, roughness, and surface friction. These indices will enable modeling of pavement performance and between-state comparison of pavement condition.

Tasks: to be determined.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $200,000
Research Period: 18 months

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

The products of this research will enable States to discuss, using common and clearly defined indices, pavement condition regarding distresses. These indices would also be a logical measure to use in modeling pavement performance. Indices will also be helpful to States in developing snapshots of their pavement systems.
Implementation of the results of this project would include potential adoption by AASHTO of a new protocol, and perhaps ultimately a new national standard. The initial draft of this protocol would be developed by the contractor as part of the final report.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This problem needs to be pursued BEFORE the following proposed problems: None.

This problem should not be pursued until AFTER the following projects/problems are completed: None.

Characterization of PCC Pavement Curvature

PROBLEM NUMBER: 4B1

RESEARCH PROBLEM STATEMENT

Bynum has developed a method to detect and characterize the apparent locked-in curvature of PCC pavements, through analysis of longitudinal profile data collected with high-speed pavement profilers. He has shown that use of the Curvature Index (CI) derived through his analysis significantly improves the predictive capability of PCC pavement performance models. The addition of this index to the LTPP database as a computed parameter is therefore under consideration.

RESEARCH OBJECTIVES AND TASKS

Objectives:

The objectives of this phased multitask analysis are to:

Provide the background material necessary to support an informed decision as to whether the CI should, in fact, be added to the LTPP database.
Compute the CI for all currently available PCC pavement longitudinal profile data.
Provide documentation of the CI to support its use in future analysis of the LTPP data.
Provide prototype software to enable computation of the CI as part of routine processing of LTPP longitudinal profile data.

Tasks:

Conduct a literature review focused on the CI.
Follow LTPP's steps for recommending a new computed LTPP parameter.
Populate the LTPP database with CI values (assuming the recommendation is approved).
Develop CI documentation for posting on the LTPP Web page.
Develop prototype software to compute CI from any profile data.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: to be determined.
Research Period: to be determined.

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

To be determined.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This problem needs to be pursued BEFORE the following proposed problems: None.

This problem should not be pursued until AFTER the following projects/problems are completed: None.

Simplified Techniques for Evaluation and Interpretation of Pavement Deflections for Network-Level Analysis

PROBLEM NUMBER: 4B2

RESEARCH PROBLEM STATEMENT

Network-level PMS are typically performed using only surface distress measurements. However, it is commonly accepted that the pavement structural capacity has a major effect on the rate of deterioration. Consequently, it is critical in forecasting future pavement conditions to know the structural capacity. Techniques currently available to estimate structural capacity from deflections are time consuming and require an experienced analyst. Additionally, these techniques may provide more detail than is necessary for network-level decisions. As a result, use of pavement deflections in network-level analysis has been limited, even in those agencies that use FWD extensively in their project-level testing. Results of this research would also have applications for agencies that do not use deflection testing in their PMS; a simplified index describing structural performance would be useful in comparing project segments or in project selection.

Using LTPP and other data should define the test spacing necessary to implement the technique(s) required to use pavement deflection data in a network-level PMS.

RESEARCH OBJECTIVES AND TASKS

Objective:

To recommend and verify simplified techniques suitable for rapid, automated screening of pavement deflection information for inclusion in network-level pavement analysis.

Tasks:

Literature search. Review previous work done on simplified techniques for deflection analysis, including but not limited to indices of surface curvature and closed-form, two-layer solutions. Surface deflections may be combined with other measurements, such as transverse profile.
Evaluation of techniques. After a review of existing techniques, identify and, if necessary, develop the most promising techniques for simplified evaluation and analysis. Use the LTPP database and other appropriate existing deflection information to compare the results of the simplified analysis to determine the consistency, stability, and repeatability of the simplified techniques.
Selection of technique. Based on the previous task, make recommendations on the most desirable technique for simplified evaluation.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $200,000
Research Period: 18 months

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

Network-level PMS are used to make decisions valued at hundreds of millions of dollars with a potentially incomplete assessment of pavement condition. Applicable techniques to assess pavement structural condition could improve the accuracy of these systems and potentially save transportation agencies considerable amounts of money as well as reduce delays to the public stemming from construction that is not optimally timed. This work should be tightly focused on providing solutions that are intended for easy implementation in State PMS.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This problem needs to be pursued BEFORE the following proposed problems: None.

This problem should not be pursued until AFTER the following projects/problems are completed: None.

Relating Ride Quality and Structural Adequacy for Pavement Rehabilitation/Design Decisions

PROBLEM NUMBER: 4C1

RESEARCH PROBLEM STATEMENT

Initial efforts in network PMS concentrated on the evaluation of visual distress survey data only. It is also important to include ride quality and some evaluation of the structural integrity of the pavement and subgrade. The public measure of ride and the engineering value of structural support will provide a more complete view of the roadway system, which is needed for network-level resource allocation. The research may identify a relationship between ride and structural support, or may show these factors to be independent of each other. In either case, the network pavement management can then account for all condition data in both resource allocation and the performance models employed. This may provide support information as State Departments of Transportation (DOTs) implement the upcoming AASHTO pavement design procedure.

Previous work related to this topic has included NCHRP 20-50(8/13), Factors Affecting Pavement Smoothness (Objective 7B), FHWA/LTPP reports on evaluating load transfer or PCC-jointed pavements, and FHWA/LTPP reports on profile devices. Three other projects, FHWA-RD-99-074, FHWA-RD-00-113, and FHWA-RD-00-076, considered the data variability of distress, profile, and faulting data. None of these projects evaluated the relationship between functional and structural pavement measures.

RESEARCH OBJECTIVES AND TASKS

Objective:

To identify a relationship between ride and structural support.

Tasks:

Review the results of previous data studies.
Determine the relationship between ride quality and structural adequacy, using the LTPP database.
Develop guidelines on ways to include both ride and structural adequacy values in network-level pavement management for State implementation.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $200,000
Research Period: 12 months

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

Urgency: High. This project will provide a rational basis for network-level pavement management resource allocation.
Payoff Potential: The relationship between structural adequacy and ride quality is a topic of frequent and continuing discussion in the pavement community. LTPP offers the opportunity to resolve this pesky problem.

Implementation: The results can be used by State DOT pavement management engineers to balance the desire for smooth roads with the need to have structurally adequate roads. It can also become a component of existing National Highway Institute courses in pavement management and data collection.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This problem needs to be pursued BEFORE the following proposed problems: None.

This problem should not be pursued until AFTER the following projects/problems are completed: None.

Criteria for Applying Performance Measures to Construction Quality Evaluation

PROBLEM NUMBER: 4D1

RESEARCH PROBLEM STATEMENT

To be determined.

RESEARCH OBJECTIVES AND TASKS

To be determined.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: to be determined.
Research Period: to be determined.

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

Priority: Low. It should be done if data allow it.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

To be determined.

Quantitative Information of Environmental Variables on Pavement Performance Measures

PROBLEM NUMBER: 4E1

RESEARCH PROBLEM STATEMENT

Because of the effects of environmental variables on pavement materials properties, variations in temperature and moisture, as well as frost penetration and freeze/thaw cycles, are important factors in determining pavement performance. However, the quantitative information is not well understood on how these environmental variables affect pavement performance measures such as profile, distress, friction, and deflection. Without this information, it is a difficult task to design long-lasting pavements. Data from the LTPP studies are available to provide this information.

RESEARCH OBJECTIVES AND TASKS

Objective:

To analyze and quantify, based on SMP data from LTPP studies, the effects of environmental variables on the pavement performance measures.

Tasks: to be determined.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $500,000
Research Period: 24 months

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

The potential payoff is very high because the quantitative information of environmental on pavement measures can be incorporated into the AASHTO Pavement Design Guide. It will be implemented by AASHTO Joint Task Force on Pavements (JTFOP).

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This problem needs to be pursued BEFORE the following proposed problems: None.

This problem should not be pursued until AFTER the following projects/problems are completed: NCHRP 20-50(5), Variations in Pavement Design Inputs (Objective 5B), and preliminary project statement 14, Assessment of the Effects of Loading and Environment on Pavement Life Using SPS Data (Objective 3A1).

PCCP Temperature Correction Factors for Interpretation of FWD Test Results

PROBLEM NUMBER: 4E2

RESEARCH PROBLEM STATEMENT

To be determined.

RESEARCH OBJECTIVES AND TASKS

To be determined.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: to be determined.
Research Period: to be determined.

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

Priority: Low. It should be done if data allows it.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This problem needs to be pursued BEFORE the following proposed problems: None.

This problem should not be pursued until AFTER the following projects/problems are completed: None.

Evaluation of Load-Response Models (Axle Load and Environment)

PROBLEM NUMBER: 5A1

RESEARCH PROBLEM STATEMENT

A variety of existing load-response models vary in accuracy and complexity. It is assumed that the more complex models (such as the 3-D finite element) give more accurate response predictions, but may be more difficult and expensive to use than simpler models. This study will evaluate the load-response models proposed by NCHRP 1-37A and the MEPDG, using data obtained from instrumented SPS-1 and SPS-2 sections. The researchers will make recommendations on the predictive capability of the MEPDG models and will also make recommendations on whether more complex models should be considered.

RESEARCH OBJECTIVES AND TASKS

Objective:

This study will evaluate the load-response models proposed by the NCHRP 1-37A study. The researchers will use the data obtained from instrumented SPS-1 and SPS-2 test sections to verify the accuracy of the MEPDG models. In cases where the predictive capabilities of the MEPDG models are found to be inadequate, other more complex models (such as the 3-D finite element) will be used to determine if better response estimates can be obtained. If more complex models are recommended, then the researchers will also evaluate cost and benefits associated with the more complex models.

Tasks: to be determined.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $200,000
Research Period: 24 months

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

This study will provide an independent evaluation of the MEPDG load-response models. Additional valuable information will be provided that compares the added benefit of more complex models to the cost and difficulty of using these more complex models.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This problem needs to be pursued BEFORE the following proposed problems: None.

This problem should not be pursued until AFTER the following projects/problems are completed: None.

Evaluation of the Performance Prediction Models in the 2002 Pavement Design Guide

PROBLEM NUMBER: 5B1

RESEARCH PROBLEM STATEMENT

States will begin using the MEPDG resulting from NCHRP 1-37A. There will be an independent validation of the reliability of NCHRP 1-37A MEPDG performance prediction models and enhancement of their usefulness as design tools for new construction. The report will assess the models using objective, statistical measures of predicted-to-observed distress. Sensitivity analyses will grade the models on the stability of their output, their responsiveness to significant input variables, and their ability to handle unique design configurations. Projected and actual life-cycle outcomes for selected LTPP sites using design guide recommendations and design procedures will be compared.
The selection of a pavement design procedure is a decision that has enormous economic consequences for a State DOT. Pavement design engineers need proof that new procedures will yield designs with predictable service lives. This work will provide that evidence and will allow States to confidently implement new design procedures.

RESEARCH OBJECTIVES AND TASKS

Objective:

The performance of appropriate GPS and SPS test sections will be compared to the performance predicted by NCHRP 1-37A design procedures for flexible and rigid pavements.

Tasks:

Analyze data such as as-built layer thicknesses, materials properties, traffic loadings, measurable distress, and climatic data.
Analyze SPS-1 and SPS-2 sections and appropriate GPS sections.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $400,000
Research Period: 24 months

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

This study is essential to support and establish the early credibility of the MEPDG. It should be accomplished as soon as practical to support acceptance by State DOTs.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This problem needs to be pursued BEFORE the following proposed problems: None.

This problem should not be pursued until AFTER the following projects/problems are completed: NCHRP 1-37A MEPDG.

Evaluation of Pavement Performance Models

PROBLEM NUMBER: 5C1

RESEARCH PROBLEM STATEMENT

Asphalt concrete (AC) overlays on PCC pavements or pavements with cement-treated bases tend to suffer from cracks in the surface of the overlay. The cracks reflect the pattern of joints and cracks in the PCC pavement, or the cracks reflect the transverse shrinkage cracks that appear on the surface of AC pavements with cement-treated bases. Similarly, reflection cracks can occur in AC overlays on cracked AC pavements.

When these cracks propagate through the depth of the AC overlay, infiltration of both water and de-icing salts can cause rapid deterioration of the underlying pavement structure and foundation. Overlay performance can thus be considerably reduced. Because pavement rehabilitation, and more specifically AC overlays of existing pavements, is the most important pavement construction activity in North America, there is a great need for engineering tools to help maximize the performance of AC overlays.

At least two international conferences (Rilem International Conferences on reflection cracking—one in Liege, Belgium, in 1996, and another in Ottawa, Canada, in 2000) have specifically dealt with the problem with reflection cracking on both flexible and rigid pavement. Several models on reflection cracking are documented in the literature and, more specifically, in the proceedings of these conferences. The development of these models is generally based on theoretical work or on limited field studies. Other proposed models are essentially empirical and are not necessarily associated to design variables.

A validated model to predict reflection cracking will provide guidance for future overlay pavement design, taking into account the factors that influence the formation of reflection cracking. The model will also provide maintenance engineers with a means of estimating crack sealing requirements for the management of their network. The models will take into account design, materials, and construction information, along with climate and traffic loading effects.

RESEARCH OBJECTIVES AND TASKS

Objectives:

To evaluate and refine models to predict the initiation and propagation of reflection cracking in the surface of an AC overlay on PCC pavements or on pavements with cement-treated bases.
To evaluate and refine existing models to predict the initiation and propagation of reflection cracking in an AC overlay on AC pavement exhibiting surface cracking.
To provide a sensitivity analysis indicating the effect of material and design factors on the initiation and propagation of reflection cracking.

Tasks: to be determined.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $200,000
Research Period: 24 months

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

At present there are no validated models in the United States to predict the occurrence and propagation of reflection cracking in AC overlays. The models will provide a basic understanding of the mechanisms involved, and these will serve to provide the design engineer with the means to minimize reflection cracking in future overlay designs. The model will also provide the maintenance engineer with a tool to predict future workloads for crack sealing or the AC overlays within the engineer’s network.

As soon as the models have been validated, they can be put into practice for pavement design and maintenance. AC overlay performance prediction will help maximize the performance of this widespread rehabilitation strategy. Thus, there is considerable payoff potential, in view of the importance of pavement rehabilitation activities on North American road networks.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This problem needs to be pursued BEFORE the following proposed problems: None.

This problem should not be pursued until AFTER the following projects/problems are completed: On hold pending outcome of proposed FY 2003 NCHRP project on same topic.

Development of Longitudinal Cracking Models for PCC Pavements

PROBLEM NUMBER: 5C2

RESEARCH PROBLEM STATEMENT

The MEPDG under development by NCHRP/AASHTO uses performance models to predict distresses on AC and PCC pavements. However, longitudinal cracking, a key distress found on PCC pavements, is not well addressed in the MEPDG.

When cracks propagate through the PCC pavement, infiltration of water and de-icing salts can cause rapid deterioration of concrete due to the loss of support in the underlying subbase and foundation. Thus, PCC pavement life can be considerably reduced. To predict the duration of PCC pavement life, there is a great need for performance models for this key distress.

Development of calibrated and validated performance models for this distress will provide an excellent tool for PCC pavement designers to predict the formation and propagation of longitudinal cracks. The models will also provide maintenance engineers with a means of predicting crack sealing requirements for the management of their network. The models will take into account design, materials, and construction practices together with climate and traffic loading effects.

RESEARCH OBJECTIVES AND TASKS

Objectives:

Develop models to predict the initiation and propagation of longitudinal cracking on JPC and CRC pavements: bottom-up and top-down cracking in either traditional width or widened lanes with asphalt or tied-concrete shoulders.
Conduct sensitivity analyses to provide an understanding of the effect of materials, design, construction practices, and environmental and traffic loading on the initiation and propagation of longitudinal cracks.

Tasks: to be determined.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $200,000
Research Period: 24 months

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

At present, there are no models in the United States to predict the initiation and propagation of longitudinal cracking in PCC pavements. Development of these models will provide a basic understanding of the mechanisms involved and will guide design engineers by providing them with a method for minimizing the occurrence of longitudinal cracking in future PCC pavement designs. The model will also provide maintenance engineers with a tool to predict their future workloads for crack sealing and for other maintenance works within their network.

As soon as the models have been validated they can be put into practice for pavement design, construction, and maintenance. Better understanding of the key elements in this mechanism of failure will help to maximize the life of PCC pavements. The payoff potential is thus considerable in view of the importance of PCC pavements on North American road networks.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This problem needs to be pursued BEFORE the following proposed problems: None.

This problem should not be pursued until AFTER the following projects/problems are completed: NCHRP 1-37A and the MEPDG.

Guidelines for Selecting Effective Pavement Rehabilitation Strategies

PROBLEM NUMBER: 6B1

RESEARCH PROBLEM STATEMENT

Although many options are available for the rehabilitation of flexible and rigid pavements, information on the impacts of these options on overall pavement performance, on the influences of traffic loading, and on initial pavement condition, are not well documented. The LTPP rehabilitation experiments were undertaken to provide this type of information. The data collected from the LTPP experiments on pavement rehabilitation provide information both to evaluate the effectiveness of several rehabilitation options and to develop guidelines for selecting appropriate strategies based on pavement type and condition, traffic loading, pavement performance enhancement, and other factors.

There is a need for an analysis of the performance of the rehabilitated LTPP test sections, to determine the effectiveness (in terms of overall pavement performance and life) of various treatment options. This analysis should consider the effects of pavement condition at the time of treatment, as well as of structural adequacy, base type, subgrade, and other pertinent factors to pavement performance and life extension. The findings of this analysis will form the basis of guidelines for the selection of effective pavement rehabilitation strategies.

RESEARCH OBJECTIVES AND TASKS

Objective:

The objective of this research is to develop, based on the data available from LTPP studies, guidelines for selecting appropriate pavement rehabilitation strategies for both rigid and flexible pavements. These guidelines should consider the impacts of traffic loadings, climatic conditions, measurable customer-related benefits, and pavement type and condition on the performance of the rehabilitated pavement.

Tasks:

Collect and review reports relative to LTPP studies on the rehabilitation of flexible and rigid pavements (GPS-6B, SPS-5, and SPS-6) and other relevant research. The results of NCHRP 20-50(3/4), Effectiveness of Maintenance and Rehabilitation Options (Objective 6A), should be among those considered. Scrutiny of the LTPP data is required to eliminate biased data, e.g., situations where test sections in which the joints were sealed for many years, then the sealant was stripped out, and now the performance is considered that of an unsealed test section (when actually the current performance might have been predetermined by the previously sealed condition).
Obtain and organize the LTPP data required to achieve the project objectives.
Analyze the data collected n Task 2 to evaluate the effectiveness of different rehabilitation strategies, considering the impact of varying original pavement types and conditions, as well as of varying climatic and traffic conditions. It should be noted that the impact of the treatment on overall pavement performance, and not the life and performance of the treatment, is the issue of concern.
Based on the results of Task 3, develop guidelines for selection of effective rehabilitation strategies. The guidelines should consider the impact of the various rehabilitation strategies under varying original pavement types and conditions, as well as under varying climatic and traffic conditions, on the performance of the original pavement.
Prepare a final report documenting the research. The recommended guidelines for selecting effective pavement rehabilitation strategies are to be provided as a stand-alone document.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $300,000
Research Period: 24 months

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

Billions of dollars are being spent on rehabilitation work, and the information currently available to guide selection of rehabilitation strategies is incomplete. Several LTPP experiments have been conducted to address this need, but the collected data must be analyzed to obtain the required information. Pursuit of this analysis is urgently needed.

The findings of this research will be delivered in the form of guidelines to facilitate implementation. If implemented, these guidelines will help agencies select the most appropriate rehabilitation strategy for a given set of circumstances. Selection of the appropriate strategies is needed for owner agencies to assure sound pavement management practices and to assure the most benefit to the highway customer per dollar spent. The potential payoff resulting from the use of cost-effective strategies is tremendous.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This problem needs to be pursued BEFORE the following proposed problems: None.

This research should build on the findings of NCHRP 20-50(3/4), Effectiveness of Maintenance and Rehabilitation Options (Objective 6A). Further collection of data and analysis of the data from the rehabilitated LTPP test sections is required to build upon the findings of this previous work.

Impact of Design Features on Pavement Response and Performance in Rehabilitated Flexible and Rigid Pavements

PROBLEM NUMBER: 7A1

RESEARCH PROBLEM STATEMENT

The performance of a rehabilitated flexible or rigid pavement section not only will depend on the site conditions (e.g., traffic level, climatic conditions, and material properties), but also on other design and construction features (e.g., type and details of subdrainage, base, shoulders, maintenance and rehabilitation measures, etc.). A number of researches, e.g. NCHRP 20-50(10/16), have been undertaken focusing on the effects of design and construction features on new flexible and rigid pavements as well as on the effects of subdrainage and pavement structural layers on all flexible and rigid pavements. With new data available in the LTPP database, it is necessary to obtain more understanding of the effects of design and construction features on pavement response and performance of rehabilitated flexible and rigid pavements. There is research needed to determine the effects of design and construction features on pavement response and performance and to establish their relative importance. This research will provide preliminary information on the relationship between pavement response and performance, guidance for identifying appropriate features for different pavement types, and recommendations for improving data collection activities.

RESEARCH OBJECTIVES AND TASKS

Objectives:

Based on the pavement response and performance data accumulated for the LTPP SPS-5 (rehabilitated asphalt concrete pavements) and SPS-6 (rehabilitated jointed plain concrete pavements) as well as any applicable experiments, determine for specific site conditions:

Impact of the different design, construction, and rehabilitation features considered on pavement response (as measured by deflection and strain)
Contributions of these features to achieving different levels of performance (as measured by type and extent of distress or smoothness).

Based on these findings, report whatever inferences can be drawn from the LTPP experiments, as to the likely long-term performance impact of these features. In addition, if indicated, provide recommendations on any corrective actions that should be considered to improve the future analytical potential of the experiment considered in this investigation.

Tasks: to be determined.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: to be determined.
Research Period: to be determined.

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

The SPS experiments were undertaken to provide critically needed information to support pavement rehabilitation decisions. Findings drawn from this study can help highway agency engineers and managers make sound pavement design, construction, and rehabilitation decisions. Analyses pursued at this time can maximize both the near-term and long-term benefits accrued from the tremendous investment made in the construction and monitoring of these test sites.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This project is linked strongly to the research results identified in Objective 5 (development of performance prediction models) of the LTPP Strategic Plan and the 2002 Mechanistic-Empirical Pavement Design Guide (MEPDG). The analyses returned in this study will be an integral part of both the determination of the causes of distress and the formulation of models predicting performance.

Evaluation and Characterization of Pavement Drainage

PROBLEM NUMBER: 7B

RESEARCH PROBLEM STATEMENT

In the United States , it has become common to incorporate subsurface drainage features (e.g., permeable, edgedrains) into pavements to handle surface infiltration water. However, there has always been controversy about the design, performance, and benefits of subsurface drainage. The problematic history of design and construction of features such as open-graded bases, longitudinal edgedrains, and day-lighted bases adds to the controversy. Recent studies have shown that only one-third of the edgedrains in existing pavements are functioning as designed. Other studies have shown that some open-graded bases are being infiltrated with fines from underlying layers, significantly affecting their effectiveness. There have also been reports about construction difficulties and early cracking supposedly related to open-graded bases.

The primary effect of pavement drainage is to reduce the detrimental effects of free moisture in the granular layers beneath the bound layers, particularly both after the pavement cracks and at joints with sealant failure (rigid pavements). Although this effect is mostly positive, there can be a negative effect on pavement life. In fact, drainage could have any of the following effects on the performance of a pavement:

Negative effect on pavement life caused by the stripping of the permeable asphalt-treated bases (PATB) or clogging of the edgedrains and lateral outlets (this has occurred often in the United States).
Little or no effect on pavement life because it acts similarly to a granular layer beneath the bound layers.
Positive effect on flexible pavement life, which is attributable to the layer draining out excess water from the pavement structure and thereby increasing the modulus of the underlying unbound base layers. Positive effects also include the drainage of water infiltrating through cracks, thus reducing their deterioration. Positive effect on rigid pavement life is attributable to the layer draining out excess water from the pavement structure and thereby reducing pumping and weakening of the subgrade and pavement layers. Positive effects also include the drainage of water infiltrating through cracks and unsealed joints, thus reducing deterioration. The benefits of improved drainage also include minimizing the potential and severity of durability-related distresses such as D-cracking.

Softening of the subgrade and unbound base layers caused by poor drainage results in higher deflections and strains. High deflections and strains can result in fatigue cracking and rutting in flexible pavements, and in pumping and faulting in rigid pavements. Thus, poor drainage contributes to distresses and roughness in both flexible and rigid pavements.

Status of LTPP Drainage-Related Projects

The LTPP database contains a wide variety of information, including drainage-related data collected on GPS and SPS test sections across the United States. In particular, the SPS-1, SPS-2, and SMP sections contain a wealth of performance information on pavements with and without drainage features. The early evaluation results of these three experiments are summarized as follows.

SPS-1 Experiments

The LTPP SPS-1 experiment, entitled Strategic Study of Structural Factors for Flexible Pavements, is a key experiment in the LTPP program. The objective of this experiment is to determine the relative influence and long-term effectiveness of flexible pavement design features. Eighteen SPS-1 projects have been constructed in different States across the Nation. At each site, there are 12 core sections plus various numbers of supplemental sections. A total of 248 test sections are included in the SPS-1 experiment.

Each SPS-1 experiment includes several sections with PATB. The SPS-1 projects are also relatively young pavements, with some projects (Montana and Wisconsin) less than 2 years old. Some of the early performance trends are listed below. Of course, any long-term performance might differ from short-term performance. Higher rut depths occurred on test sections with dense aggregate base layers than on sections with dense asphalt-treated base (ATB) or PATB. However, rutting appears to be related more to the HMA mixture properties than to the structural characteristics. Sections with PATB have a lower percentage of test sections (20 percent) with rut depths exceeding 8 millimeters (mm) than sections (32 percent) with dense bases. The percentage of core test sections with fatigue cracking is slightly less for those test sections with PATB than for those without PATB.

SPS-2 Experiments

The LTPP SPS-2 experiment, entitled Strategic Study of Structural Factors for Rigid Pavements, is another key experiment in the LTPP program. It was designed as a controlled field experiment that focuses on the study of specific design features (structural factors) for doweled jointed plain concrete (JPC) pavements. Thirteen SPS-2 projects have been constructed in different States across the Nation. At each site, there are 12 core sections plus various numbers of supplemental sections. Each SPS-2 section length is 152 meters (m) long. Key design features common to all SPS-2 sections include the following:

4.6-m uniform joint spacing.
Doweled perpendicular transverse joints with 32-mm dowel bars for the 203-mm-thick pavements and 38-mm dowel bars for the 279-mm-thick pavements.

Each SPS-2 experiment includes several sections with PATB. The SPS-2 projects are relatively young pavements, ranging from 2 years old in Wisconsin to 7.5 years old in Kansas. Therefore, as expected, most SPS-2 sections are showing good performance and low distress levels. As of January 2000, only 43 of 155 sections (28 percent) are showing any noticeable distresses. Also, 95 percent of the SPS-2 sections have less than 1 mm of edge joint faulting, 87 percent of the SPS-2 sections are showing zero transverse cracking, and 78 percent of the sections have zero longitudinal cracking.

Based on the initial statistical analyses and comparisons, the following initial performance trends are noted (long-term performance may differ from short-term performance):

JPC pavements constructed on PATB were smoother than when they were constructed on a lean concrete base (LCB) or an untreated aggregate base.
Sections with PATB are showing the lowest total longitudinal cracking levels, while the sections with LCB show the highest longitudinal cracking levels.
Sections with PATB are showing the lowest percentage of slabs cracked transversely, while the sections with LCB show the highest percentage of transverse cracking.
Sections with aggregate base are showing the highest joint-faulting levels. Sections with LCB and PATB have the lowest joint-faulting levels.

SMP Experiments

Temperature and moisture in a pavement structure vary on both a daily and yearly basis. To understand the impact of these changes on the pavement structure and its response to loads, 63 sites were selected from the GPS and the SPS projects for continuous temperature and moisture monitoring. Time domain reflectometry probes and thermistor probes are used to monitor changes in subsurface moisture and temperature, electrical resistivity probes are used for frost/thaw depth measurements, and piezometers are used for ground-water table determinations. In addition, air temperature probes and tipping-bucket rain gauges are used to monitor ambient temperature and precipitation. Deflection, profile, and distress data are collected at frequent intervals using LTPP equipment and testing protocols. A summary of the program is contained in the Data Users Reference Manual. Each SMP site had two monitoring rounds that each lasted approximately 1 year. Intensive data collection was carried out every other year for the 4-year duration of the study. Half of the sites were instrumented in each year.

RESEARCH OBJECTIVES AND TASKS

Objectives:

Determine if the LTPP sections as built are feasible for a comprehensive drainage study.
Determine the sufficiency of climatic events for evaluating the effects of drainage on pavement performance.
Evaluate the effect of the drainage layer and the absence of adequate drainage on base, subbase, subgrade, and pavement performance.

Tasks:

To be determined.
Expected products are (1) documented information on the benefits of drainage layers on pavement performance, (2) estimated cost-benefit ratio of drainage layers, and (3) guidelines for application of drainage layers.
Deliverables are (1) a report documenting the feasibility of the LTPP program for a comprehensive drainage study, (2) a comprehensive final report documenting the information on the benefits and application guidelines for drainage layers, and (3) a separate document (five pages or less) identifying key findings and/or products expected to be of interest to highway agencies.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: to be determined.
Research Period: to be determined.

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

The exact amount of increase in pavement life due to pavement drainage varies widely because there are several construction- and maintenance-related issues that affect the performance of pavement drainage. As a result of this variability in performance, some sections with drainage features have poorer performance and other sections perform better than a comparable conventional dense aggregate base pavement section.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This problem needs to be pursued BEFORE the following proposed problems: None.

This problem should not be pursued until AFTER the following projects/problems are completed: NCHRP 1-34D, Effects of Subsurface Drainage on Performance of Asphalt and Concrete Pavements: Further Evaluation and Analysis of LTPP SPS-1 and SPS-2 Field Sections (Objective 7B).

Analysis of LTPP SPS-1 and SPS-8 Data and Related GPS Data to Quantify the Impact of AC Pavement Design Features on Measured Pavement Distresses

PROBLEM NUMBER: 7B1a

RESEARCH PROBLEM STATEMENT

The LTPP experiments used specific design features as the basis for establishing individual sections. The SPS-1 sites are specially constructed, new AC test sections. These sites provide a unique opportunity to analyze and quantify the association of distress and design features. The SPS-8 sites evaluate asphalt pavements in the absence of high traffic volumes. The SPS sites have detailed information on features, materials, and initial conditions as well as on continued monitoring of distresses over time. Several of the sites have already gone out of service, and the number of sites reaching the terminal point will increase in the next few years. For this reason, this project has a high probability of success.

Only limited information on the impact of design features on measured pavement distress is currently available to pavement designers. These analytical investigations will define the relative effectiveness of certain design features on distress for flexible pavements. Specific design features studied in one or more of the LTPP experiments include:

Surface course thickness.
Base course thickness.
Base type—
- Dense-graded aggregate.
- Open-graded aggregate.
- Asphalt treated.
- Permeable asphalt treated.
- Cement treated.
- Lime stabilized.
- Full depth asphalt.
Subsurface drainage.

A qualification of how distresses are associated with design features should be performed to identify whether they are unique to a feature or whether they are manifested as a result of other distresses that appear concurrently. Distresses should be characterized quantitatively as phenomena of their physical environment (e.g., environment, wheel load, combination, or other). Interdependencies of distress, feature, and load environment should be identified. A second phase of these analyses should include the quantification of the associations of distresses with design features. Using the relationships addressed above, determine these associations using a probabilistic approach. For example, determine the probability of having a distress manifested in the presence of either a single design feature or a combination of features throughout its appropriate loading sequence.

RESEARCH OBJECTIVES AND TASKS

Objectives:

Determine how distresses are associated with design features for asphalt concrete pavements.
Determine the interaction of distress, design features, and load environment(s) using a probabilistic approach.

Tasks: to be determined.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $300,000
Research Period: 24 months

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

A successful outcome of this project will allow pavement designers to make better-informed decisions on when or whether to use specific design features such as type and location of drainage systems, treated or untreated bases, and relative thicknesses of base and surface. When coupled with the results of NCHRP 20-50(10/16), The Influence of Design and Construction Features on the Response and Performance of New Flexible and Rigid Pavements (Objective 7A), the results will also strengthen pavement management by relating changes in pavement response to the onset and progress of pavement distress, in light of specific design features.

The relationships to be considered in this study are those that administrators from highway agencies and other governmental entities have emphasized as being the greatest need from LTPP studies. Historical LTPP documents suggest that users and supporters of LTPP data are awaiting the results of these analyses. Publications and electronic media that make trends and trend analyses available to the users have a high probability for widespread use.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This project will use results of an FHWA project on the estimation of traffic axle load spectra that is scheduled for completion in late 2001. As described above, the project is related to the NCHRP project on pavement response as a function of design features. This project is a necessary precursor to the guidelines for selecting pavement design features.

This project is linked strongly to the research results identified in Problem Statement 5A1 of the LTPP Strategic Plan, Evaluation of Load-Response Models (Axle Load and Environment). The analyses returned in this study will be an integral part of both the determination of cause of distress and the formulation of performance prediction models.

Analysis of LTPP SPS-2 and SPS-8 Data and Related GPS Data to Quantify the Impact of Rigid Pavement Design Features on Measured Pavement Distresses

PROBLEM NUMBER: 7B1b

RESEARCH PROBLEM STATEMENT

The LTPP experiments used specific design features as the basis for establishing individual sections. The SPS-2 sites are specially constructed, new, rigid test sections. These sites provide a unique opportunity to analyze and quantify the association of distress and design features. The SPS-8 sites evaluate concrete pavements in the absence of high volumes of traffic. The SPS sites have detailed information on features, materials, and initial conditions as well as on continued monitoring of distresses over time.

Only limited information on the impact of design features on measured pavement distress is currently available to pavement designers. These analytical investigations will define the relative effectiveness of certain design features on distress for rigid pavements. Specific design features studied in one or more of the LTPP experiments include:

Surface course thickness.
Concrete strength.
Base course thickness.
Joints.
Dowels.
Tied shoulders.
Subbase thickness.
Subbase type—
- Dense-graded aggregate.
- Open-graded aggregate.
- Asphalt treated.
- Permeable asphalt treated.
- Cement treated.
- Permeable cement treated.
- Lime stabilized.
Subsurface drainage.

RESEARCH OBJECTIVES AND TASKS

Objectives:

Determine how distresses are associated with design features for rigid concrete pavements.
Determine the interaction of distress, design features, and load environment(s) using a probabilistic approach.

Tasks: to be determined.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: $300,000
Research Period: 24 months

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

A successful outcome of this project will allow pavement designers to make better-informed decisions on when or whether to use specific design features such as type and location of drainage systems, treated or untreated subbases, and relative thickness of subbase and slab. When coupled with the results of NCHRP 20-50(10/16), The Influence of Design and Construction Features on the Response and Performance of New Flexible and Rigid Pavements (Objective 7A), the results will also strengthen pavement management by relating changes in pavement response to the onset and progress of pavement distress in light of specific design features.

The relationships to be considered in this study are those that administrators from highway agencies and other governmental entities have emphasized as being the greatest need from LTPP studies. Historical LTPP documents suggest that users and supporters of LTPP data are awaiting the results of these analyses. Publications and electronic media that make trends and trend analysis available to the users have a very high probability for widespread use.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

This project will use results of an FHWA project on estimation of traffic axle load spectra that is scheduled for completion in late 2001. As described above, the project is related to the NCHRP project on pavement response as a function of design features. This project is a necessary precursor to the guidelines for selecting pavement design features.

This project is linked strongly to the research results identified in Problem Statement 5A1 of the LTPP Plan, Evaluation of Load-Response Models (Axle Load and Environment). The analyses returned in this study will be an integral part of both the determination of cause of distress and the formulation of performance prediction models.

Guidelines for the Selection of Pavement Design Features

PROBLEM NUMBER: 7C1

RESEARCH PROBLEM STATEMENT

A number of LTPP data analysis projects address the need for information on the impact of design features on pavement response and performance. A "capstone" project is needed to assemble the findings of those projects in a form that is readily implemented by practicing pavement engineers.

RESEARCH OBJECTIVES AND TASKS

Objective:

To review the findings of all pertinent LTPP data analysis and related pavement performance research, and develop comprehensive guidelines for the selection of pavement design features.

Tasks: to be determined.

ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD

Recommended Funding: to be determined.
Research Period: to be determined.

URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION

To be determined.

RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS

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Data Collection Analysis Products Pooled Fund Studies Operations/Analysis Feedback Reports LTPP Customer Survey	LTPP Data Analysis Project Statements Introduction: The following preliminary Long-Term Pavement Performance (LTPP) data analysis project statements provide extra information on the work envisioned for projects identified in the Long-Term Pavement Performance Data Analysis Program. Some of the problem statements were prepared by LTPP staff and contractors, while others are the work of the Transportation Research Board (TRB) expert task group on LTPP Data Analysis, pooled fund project panel members, and others. Readers should note that these project statements are at various stages of development and review, and that all are subject to revision. Comments and recommendations about these problem statements are invited and may be submitted via ltppinfo@fhwa.dot.gov Evaluation of Weigh In Motion (WIM) Site Data and Tools for Determining Load Data Confidence PROBLEM NUMBER: 1A RESEARCH PROBLEM STATEMENT There is a need to know how accurate and consistent weigh in motion (WIM) systems are for collecting load data. Load data are critical factors in the study of LTPP. LTPP has undertaken a number of initiatives to improve the quality of load data, including the collection and submittal of calibration data by State highway agencies (SHA). Currently there is limited ability to evaluate the accuracy and variability of the calibration data. These data need to be analyzed to effectively determine their statistical confidence. Data collection engineers have no way to evaluate the relative influence of the various sources of error on the accuracy of a particular WIM site. Consequently, engineers have no systematic way to decide on replacing WIM or on correcting pavement surface profiles at the site, which affects WIM performance rehabilitation strategies when these are needed. RESEARCH OBJECTIVES AND TASKS Objectives: Understand the influence of pavement surface profiles on WIM accuracy. Determine the confidence in load data through statistical analyses and synthesis of WIM calibration data (data mining) collected at the LTPP sites. Quantify the influence of WIM system types and ages, pavement types and ages, levels of road roughness, profiles, geometries, and traffic speeds, on the performance of the WIM site. Develop tools that can evaluate measured surface profiles at new and existing WIM sites. Develop tools and procedures for characterizing the errors generated by WIM systems to enable diagnoses of problems and rehabilitation strategies for WIM sites. Tasks: Task 1 - Using LTPP data, assess the likely baseline accuracy—that is, the accuracy in the absence of surface roughness and dynamic loads—of a variety of existing WIM systems. (The difference between the real accuracy and the baseline accuracy is caused by dynamic loads.) Task 2 - Develop tools for correlating the influence of measured surface profiles on WIM errors and for specifying surface rehabilitation requirements. Validate the tools using data from LTPP calibration and validation tests. Task 3 - Develop user-friendly software tools for diagnosing and reporting the likely source of errors in measuring WIM data. Test the tools on a variety of existing LTPP WIM systems. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $450,000 Research Period: to be determined. URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION The determination of statistical confidence will quantify the quality of any analysis using LTPP load data parameters. These statistical parameters may be used for future estimation and analysis. These data can also be used to monitor ongoing quality and accuracy of the entire LTPP traffic load monitoring effort. As the improved traffic data collection activities in LTPP begin to be implemented (e.g., the LTPP Specific Pavement Studies (SPS) Traffic Data Collection Pooled Fund Study), it is vital to ensure that WIM systems are maintained in prime operating condition and that any accuracy problems are handled in a timely and cost-effective way. The anticipated product of this research is a user-friendly software tool for diagnosing and reporting the likely source of errors in the measurement of WIM data. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS Submittal of calibration information to LTPP's incorporation of wavelength specifications is expected for WIM-scale approaches. Ideally, the central database will include calibration information. This problem needs to be pursued BEFORE the following proposed problems: None. This problem should not be pursued until AFTER the following projects/problems are completed: None. Procedures for Forecasting and Backcasting Traffic Loading Data Project 1: Development of Methods and Models Using Existing Data (Phase I) PROBLEM NUMBER: 1C1 RESEARCH PROBLEM STATEMENT Successful implementation of the 2002 Mechanistic-Empirical Pavement Design Guide (MEPDG) requires good prediction of axle load distributions. Currently, a number of studies have addressed this important topic, including the National Cooperative Highway Research Program (NCHRP) 1-37A (Development of the 2002 Guide for the Design of New and Rehabilitated Pavement Structures: Phase II), NCHRP 1-39 (Traffic Data Collection, Analysis, and Forecasting for Mechanistic Pavement Design), "Estimating Cumulative Traffic Loads, Phase 1 and 2 (Objective 1C)" (i.e., axle load extrapolation method), as well as many models developed locally and internationally. Lessons learned from these projects and the new data from WIM sites, other sources, or both, prompt the need to develop more accurate and reliable procedures for forecasting and backcasting traffic loading data. Potential products generated by this project will benefit the use of MEPDG in improving pavement design. RESEARCH OBJECTIVES AND TASKS Task 1 - Develop procedures for predicting baseline axle load distributions from road use factors including: Land use and geography. Roadway function. Types and loads of trucks. Hourly, weekly, and monthly axle load distributions with a minimum of 4 weeks of axle load data (1 full week in each season) at a discrete site and in a discrete lane. Seasonal variations and adjustment factors. Vehicle and axle load regulations, legal and permitted. Coverage of demographic, economic, and technological trends and any other relevant factors. Task 2 - Develop procedures and provide reliability for forecasting and backcasting axle load distributions at sites with sufficient, limited, or no WIM, Automatic Vehicle Classification (AVC), or Automatic Traffic Recorder (ATR) data. Task 3 - Develop sensitivity analysis of the procedures to various design parameters. Task 4 - Validate the procedures developed. Task 5 - Update the study Estimating Cumulative Traffic Loads, Phase 1 and 2 (1C). Task 6 - Develop a traffic load estimation guide and software. Task 7 - Include Estimating Cumulative Traffic Loads, Phase 1 and 2 (1C) tables into the LTPP database. Task 8 - Conduct a workshop using real data. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $250,000 Research Period: 24 months URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION This work has the potential to have significant impact on improving pavement design when using the MEPDG. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem needs to be pursued BEFORE the following proposed problems: None. This problem should not be pursued until AFTER the following projects/problems are completed: NCHRP 1-39, Traffic Data Collection, Analysis, and Forecasting for Mechanistic Pavement Design. Estimating Cumulative Traffic Loads, Phase 1 and 2 (1C). Traffic Pooled Fund Study Phase 1, Evaluation of Weigh-In-Motion (WIM) Site Data and Tools for Determining Load Data Confidence (1A). Traffic Action Plan. Review of LTPP SPS-9 Experiment Verification of SHRP Asphalt Specification and Mix Design (Superpave^TM) PROBLEM NUMBER: 2A1 RESEARCH PROBLEM STATEMENT The Long-Term Pavement Performance (LTPP) Specific Pavement Studies (SPS)-9 experiment was intended to provide data to validate the Strategic Highway Research Program (SHRP) Superpave^TM asphalt specifications and mix design. In addition, the experiment is to provide a direct comparison, in terms of pavement performance, between existing highway agencies' specifications and the Superpave^TM (Superior Performing Pavement) performance-based specifications. The SPS-9 experiment also provides an opportunity to evaluate stone matrix asphalt (SMA) and other innovative materials and features. The results from this experiment will also help in modifying the SHRP mix design system and in the development of performance-based specifications for asphalt mixtures. The review of the LTPP SPS-9 experiment will provide an opportunity to check if the construction of the experiment sections conforms to the requirements of the experiment. It will also identify and resolve any discrepancies in the design and construction of the sections and will evaluate the data quality and completeness. RESEARCH OBJECTIVES AND TASKS Objectives: Identify specific applications and analytical objectives that should be pursued, using the SPS-9 experimental data. Evaluate the as-constructed SPS-9 sites to determine what was constructed. Identify areas of strength and weakness and recommend corrective measures to make the experiment capable of fulfilling its expectations. Evaluate data quality and completeness (in relation to current data collection requirements) for each core and supplemental section. Submit feedback reports to ensure problems are fixed. Identify confounding factors not accounted for in the original experimental design. Evaluate the adequacy of existing data and current data collection requirements in relation to anticipated analytical needs. Tasks: Task 1 - Obtain and Review Required Data. SPS-9 construction, testing, and monitoring data will be obtained from the LTPP IMS. Data will be reviewed from the instrumented test sections, including the entire core and supplemental sections, using the most recently upgraded data in the IMS database. Task 2 - Information on what was built and whether the pilot sections can be used will be obtained. Task 3 - Review Construction Reports. Construction reports, construction-related sampling and testing plans, and test data will be reviewed for each SPS-9 project to identify the deviations in the as-constructed test sections. It is important to review construction reports because they document the construction activities and data. Construction reports will help identify any deviation from the original construction plan, the type and details of the supplemental test sections that were built, and any construction-related difficulties or factors that could have affected the construction of the test sections. Task 4 - Prepare Feedback Reports. Feedback reports will be prepared to identify specific concerns with SPS-9 data so that improvements can be made as soon as possible. It is believed that some data, particularly materials, do exist and are in the regional centers and laboratories waiting to be processed. Task 5 - Perform Preliminary Reviews of the Performance Data. Preliminary reviews will be performed of the key performance data from SPS-9 projects for the SHRP mix sections, State agency mix sections, and SMA sections. The research team will compare performance trends of the all three core sections within projects and between projects for local (onsite), regional, and national trends. Task 6 - Prepare Recommendations for Changes in Future Data Collection Efforts. Recommendations will be prepared for changes in future data collection efforts to ensure that the SPS-9 experiment will realize its full potential with respect to expectations and objectives of the experiment. Task 7 - Final Report. A final report will be prepared to document all of the reviews and findings. It will become a key resource for all researchers and for the LTPP staff and regional centers. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $100,000 Research Period: to be determined. URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION Feedback reports Final report Presentation of findings RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem needs to be pursued BEFORE the following proposed problems: None. This problem should not be pursued until AFTER the following projects/problems are completed: None. Review of Laboratory Resilient Modulus Testing of Hot Mix Asphalt (HMA) Mixtures PROBLEM NUMBER: 2A2 RESEARCH PROBLEM STATEMENT Resilient modulus is the primary material property that has been used to characterize HMA mixtures and other structural properties for flexible pavement design, in accordance with the 1993 American Association of State Highway and Transportation Officials (AASHTO) Guide for Design of Pavement Structures. Resilient modulus is simply a measure or estimate of the elastic modulus of the material at a given test temperature (i.e., assumed to be the modulus of elasticity) and is mathematically defined as the applied stress divided by the ”recoverable" strain that occurs when the applied repeated-load is removed from the test specimen. Resilient modulus has been generally measured in the laboratory using the repeated-load indirect tensile test; however, it can be also measured by other test procedures or determined through backcalculation. LTPP has collected cores and samples of the mixtures from the SPS and General Pavement Studies (GPS) projects. The coring and sampling of the GPS projects initiated in the late 1980s. Many of these cores have been already tested using the indirect tensile test procedure. The indirect tensile resilient modulus tests were performed by different contractors for each of the four regional offices. However, Von Quintus and Killingsworth identified and reported potential problems with the test protocol during a study sponsored by the Federal Highway Administration (FHWA) in 1995, Analyses Relating to Pavement Material Characterizations and Their Effects on Pavement Performance (FHWA-RD-97-085). As a result of that work and as confirmation of its findings, the indirect tensile resilient modulus values were found to be suspect. The test protocol was revised, and the tests are now being completed by a single laboratory under contract with LTPP. These data have yet to be reviewed in detail. RESEARCH OBJECTIVES AND TASKS Objectives: The primary objective of this project is to review the HMA resilient modulus test data to identify and explain any anomalous observations, and to recommend a procedure that can be used in the future to evaluate the reasonableness of the resilient modulus test results and to resolve any anomalous observations present in the data. This study will provide a comprehensive review of the LTPP indirect tensile resilient modulus test data for HMA mixtures. Tasks: Task 1 - Initial Data Review for Completeness. This task will consist of extracting the data from the LTPP database and structuring the data into a form that can be easily evaluated. The data review will identify those tests at level E and also non-level E data. It will also identify any missing tests at specific temperatures. Other data will also be extracted to assist in the review process. For example these data will include asphalt content, density, air voids, age of the mix, and gradation. These extra data elements will be used in Task 4. Task 2 - Data Evaluation. Data quality will be assessed for the HMA resilient modulus test results. These data will be examined in detail to identify and explain any anomalous data or readings such as unreasonably high or low resilient modulus, or a modulus that does not increase with decreasing temperatures. The variability in the resilient modulus test results will be defined both between the projects and within a project. Task 3 - Identify Potential Outliers in the Database and Remedial Actions. Using the results from Task 2, tests will be identified that are suspect or represent different conditions. Based on the results, remedial actions will be recommended and provided to FHWA in the standard data feed back forms. Task 4 - This will determine the correspondence between mix properties (e.g. asphalt content, density, voids in mineral aggregate (VMA), age, gradation, and temperature) and the indirect tensile resilient modulus. Task 5 - To the extent possible, determine the correspondence between the backcalculated elastic modulus and the laboratory-determined resilient modulus. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $50,000 Research Period: to be determined. URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION To be determined. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem needs to be pursued BEFORE the following proposed problems: None. This problem should not be pursued until AFTER the following projects/problems are completed: None. Relationships Between Laboratory-Measured and Field-Derived Properties of Pavement Layers PROBLEM NUMBER: 2B RESEARCH PROBLEM STATEMENT A number of prior research projects have found that the layer moduli backcalculated from pavement deflection data differs significantly from those obtained through laboratory resilient_modulus testing. This finding is reflected in the 1993 AASHTO Guide recommendation that backcalculated layer moduli be divided by a value in the range of 3 to 5 to obtain an estimate of the laboratory test result. Subsequent work was completed by Von Quintus and Killingsworth, Analyses Relating to Pavement Material Characterizations and Their Effects on Pavement Performance, (FHWA-RD-97-085), published in January 1998. However, the relationships developed in past research are simplistic and are not considered adequate for use in the more sophisticated design procedures that are embodied in the 2002 Guide for the design of new and rehabilitated pavement structures. The LTPP database contains falling weight deflectometer (FWD) test results and material samples obtained on the same test date and time, which can be used to further explore this issue. It would be useful if the backcalculated moduli derived from nondestructive pavement tests (such as FWD) could be used to estimate laboratory properties (or vice versa) such as dynamic and resilient modulus of asphalt, elastic modulus of portland cement concrete (PCC) and cement-stabilized material, and the resilient modulus of unbound materials. In some cases, new pavement designs could use laboratory-derived properties when FWD results are not yet available. These estimated properties could then be used to more accurately design the required structural section. This project is intended to look at this issue in greater depth. The study should begin with the premise that backcalculated layer moduli and laboratory-resilient moduli are different, and that it may not be possible to derive simple relationships to enable interchangeable use. This project will be considered successful if it yields either relationships enabling the interchangeable use of laboratory-resilient modulus test data and backcalculated values, or a clear explanation of why it was not possible to derive such relationships. This problem fits under Strategic Objective 2, Materials Characterization, of the LTPP Data Analysis Program. Within this objective it is under Subcategory B, Relationships to Enable Interchangeable Use of Laboratory- and Field-Derived Material Parameters. RESEARCH OBJECTIVES AND TASKS Objectives: The primary objective is to determine whether relationships exist between laboratory-measured and field-derived properties of pavement layers and whether it is possible to use these relationships in the pavement design and analysis process. The research should include the following tasks: Task 1 - Determine if relationships exists between laboratory properties and backcalculated moduli of pavement layers, using data in the LTPP database. Many conventional laboratory properties are available and should be investigated; however, the primary laboratory property to be considered in this investigation is the resilient modulus of the unbound layers. Task 2 - If useful relationships between laboratory and backcalculated moduli are found, determine the statistical reliability for predictions from the different relationships developed in Task 1. For instance, with what degree of confidence can the resilient modulus of unbound layers be estimated from the backcalculated moduli obtained from FWD field measurements? Based on the findings of this investigation, develop recommendations and sample problems to demonstrate how the research results may be applied. If Task 1 does not yield meaningful relationships, conduct further investigation as needed to explain the reasons underlying the discrepancies between laboratory and field moduli, and provide a clear explanation of the reasons that relationships could not be derived. It is expected that this explanation will focus on the factors that differ between the laboratory and field test situations, and the potential impact of those factors on the test results. It is intended that data and background information that are necessary for this project will be available through the LTPP and related data analysis contracts. Backcalculated moduli should be available through two FHWA data analysis projects: Backcalculation of Layer Moduli (FHWA RD-97-086) and Review of LTPP Backcalculation Results (FHWA-HRT-05-152). Laboratory measured values are available in the database. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $200,000 Research Period: 36 months URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION Successful completion of this project potentially could provide information to pavement designers that may not be available without complicated and expensive laboratory testing. In some cases user agencies do not have the equipment necessary to perform the laboratory tests. There are times when the information could be obtained with a FWD in a timely fashion whereas laboratory testing, if possible, would require longer, or vice versa. There is potential to complete jobs ahead of schedule and save money in testing. There is a high potential for a large number of user agencies to use the information developed from this project. By properly analyzing the existing pavement properties collected through nondestructive testing techniques, agencies will realize a cost savings in more accurately developing pavement rehabilitations. Cost savings will occur in not overdesigning (expensive initial construction) or underdesigning (premature failures and unanticipated maintenance) the initial rehabilitation. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem needs to be pursued BEFORE the following proposed problems: None. This problem should not be pursued until AFTER the following projects/problems are completed: None. Estimation of Key Hot-Mix Asphalt, Base, Subgrade, and Component Engineering Properties from Routine Tests and Physical Characteristics PROBLEM NUMBER: 2E1 RESEARCH PROBLEM STATEMENT Key material engineering properties are often measured using test methods that are too costly or complex to conduct routinely. For this reason, pavement designs are often based on assumed values, and the relationships among the design assumptions, laboratory test results, and as-constructed values are unknown. Relationships that will allow estimation of material engineering properties from routine test results, index properties, or other readily available information are needed: for example, relationships to estimate resilient modulus from index properties. RESEARCH OBJECTIVES AND TASKS Objectives: Identify a set of material engineering properties for which predictive relationships would be useful in pavement design, construction quality control and quality assurance, and pavement management applications. Establish and/or validate relationship(s) between these engineering properties and routine test results, index properties, and/or other readily available information. Develop a practical guide (possibly accompanied by user-friendly software) for applying the results of Tasks 2 and 3 in pavement design, construction quality control and assurance, and pavement management. Tasks: Task 1 - Review the literature (including, but not limited to prior LTPP data analysis reports) for pertinent information. Particular attention should be paid to previously developed relationships that might be validated through this investigation. Task 2 - Identify a set of material engineering properties applicable in pavement design, construction quality control and quality assurance, and/or pavement management for which predictive relationships would be useful. Task 3 - Review available data (site distribution with respect to an appropriate sampling matrix, trends, etc.) and assess its adequacy in relation to the project objectives. Task 4 - Prepare a detailed work plan and updated budget for the remainder of the project. In the work plan, identify any gaps, questions, and uncertainties in these LTPP data that may impact the end results of this investigation or future investigations of similar issues. Task 5 - Upon approval of the work plan prepared in Task 4, conduct statistical analysis to validate or develop the required relationships. Task 6 - If worthwhile relationships are found in Task 5, develop a practical guide (possibly accompanied by user-friendly software) for applying the results of Task 5 in pavement design, construction quality control and assurance, and pavement management. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $400,000 Research Period: 24 months URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION This project will yield information that will enable pavement design and materials engineers to make well-founded decisions on the material and material specifications to be used in pavement construction. Potential cost savings resulting from better materials selection, fewer premature pavement failures, or avoidance of overdesign are staggering. The findings of this project will impact materials selection, materials specification, section design, and pavement management. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem needs to be pursued BEFORE the following proposed problems: None. This problem should not be pursued until AFTER the following projects/problems are completed: None. Estimation of Key PCC, Base, Subbase, and Component Engineering Properties from Routine Tests and Physical Characteristics PROBLEM NUMBER: 2E2 RESEARCH PROBLEM STATEMENT Traffic loading intertwined with environmental factors such as temperature fluctuations, freeze/thaw cycling, and seasonal variations in moisture will adversely impact the performance of concrete pavements over time. Selection of choice materials, use of new class of admixtures, proper proportioning, rational design, and good construction practices can result in better, longer lasting concrete pavements. Proper characterization of concrete paving materials, including stabilized base, and subgrade is one vital step toward achieving maximum pavement life. Non-homogeneity of naturally-occurring materials makes characterization of materials necessary on each project. Key material engineering properties are often measured using test methods that are too costly or complex to conduct on a routine basis. For this reason, pavement designs are often based on assumed values, and the relationships among the design assumptions, laboratory test results, and as-constructed values are unknown. Relationships that will allow estimation of material engineering properties from routine test results, index properties, or other readily available information are needed: for example, relationships to estimate resilient modulus from index properties. RESEARCH OBJECTIVES AND TASKS Objectives: Identify a set of material engineering properties for which predictive relationships would be useful in pavement design, construction quality control and quality assurance, and/or pavement management applications. Establish and/or validate relationship(s) between these engineering properties and routine test results, index properties, and/or other readily available information. Develop a practical guide (possibly accompanied by user-friendly software) for applying the results of Tasks 2 and 3 in pavement design, construction quality control and assurance, and pavement management. Tasks: The tasks enlisted below are intended to provide a framework for conducting the research. Proposers are expected to demonstrate their understanding of the problem and describe a research effort that can realistically be conducted within the constrains of available funds and contract time. Phase 1: Review the literature (including, but not limited to prior LTPP data analysis reports) for pertinent information. This information may be obtained from domestic and foreign literature, contacts with research agencies and industry organization, and other sources. Particular attention should be paid to previously developed relationships that might be validated through this investigation. Identify a set of material engineering properties applicable in pavement design, construction quality control, quality assurance, and/or pavement management for which predictive relationships would be useful. Review available data (site distribution with respect to an appropriate sampling matrix, trends, etc.) and assess its adequacy in relation to the project objectives. A wealth of information is available from the LTPP concrete studies of SPS-2 and SPS-8 Experiments. The sites for these studies are strategically selected to encompass varieties of materials and environments. Prepare a detailed work plan and updated budget for the remainder of the project. In the work plan, identify any gaps, questions, and uncertainties in the LTPP data that may impact the end results of this investigation, or future investigations of similar issues. Phase 2: Upon approval of the work plan prepared in Task 4, conduct statistical analysis to validate or develop the required relationships. Develop a practical guide (accompanied by user-friendly software) for applying the results of Task 5 in pavement design, construction quality control and assurance, and pavement management. Submit a final report that documents the entire research effort. The report shall include an implementation plan for moving the results of the study into practice. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $400,000 (Phase I shall be limited to $80,000) Research Period: 30 months. Phase I: 8 months, including 2 moths for panel review and approval Phase II: 22 months, including 3 months for panel review and revision of the final report URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION This project will yield information that will enable pavement design and materials engineers to make well-founded decisions about material and material specifications to be used in pavement construction. Potential cost savings resulting from better materials selection, fewer premature pavement failures, or avoidance of over-design are staggering. The findings of this project will impact materials selection, materials specification, section design, and pavement management. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem needs to be pursued BEFORE the following proposed problems: None. This problem should not be pursued until AFTER the following projects/problems are completed: None. Improved Deflection-Based Analysis Methods for Materials Characterization PROBLEM NUMBER: 2F1 RESEARCH PROBLEM STATEMENT During the past 20 years, a number of backcalculation programs have been developed for use in the analysis of deflection data collected for the structural evaluation of pavements. Although these programs have proven useful, all have limitations, by virtue of discrepancies between the relatively simple theoretical models of the pavement structure on which they are based, and the true nature and characteristics of pavement structures. Recent advances in computer technology and structural modeling have made it possible to develop and apply more realistic models in the analysis of pavement deflection data for the purpose of materials characterization. Evaluation and testing of analysis methods based on more realistic models is needed to assess the benefits to be gained through their application and to provide a basis for further development and refinement. RESEARCH OBJECTIVES AND TASKS Objective: To develop improved, next-generation methods for deflection-based characterization of pavement materials. Tasks: Task 1 - Conduct a literature review to identify promising new (next-generation) methods for modeling the pavement structure in the interpretation of pavement deflection data, and document the current state of the practice in backcalculation of pavement layer parameters. Task 2 - Based on the findings of Task 1, select one or more of the next-generation methods for indepth review and evaluation, and identify several state-of-the-practice backcalculation programs to be used as the standards for comparison. Task 3 - Design an experiment or set of experiments using the LTPP data to (1) evaluate the next-generation analytical methods and (2) compare the material characterization results obtained with those derived from the state-of-the-practice backcalculation methods. Task 4 - Conduct the experiment or set of experiments designed in Task 3. Task 5 - Based on the outcome of Task 4, refine the next-generation analytical methods to the extent appropriate. This development should include preparation of guidelines to support practical application of the methods developed in pavement engineering practice. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: to be determined. Research Period: to be determined. URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION To be determined. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem needs to be pursued BEFORE the following proposed problems: None. This problem should not be pursued until AFTER the following projects/problems are completed: Review of LTPP Backcalculation Results (FHWA-HRT-05-152). Evaluation of LTPP Site-Specific Climatic Data PROBLEM NUMBER: 3A RESEARCH PROBLEM STATEMENT Onsite weather instrumentation is used to collect climatic data at the LTPP seasonal monitoring and SPS 1, 2, and 8 sites. Quality control checks are applied to these data as they are collected and processed for release from the LTPP database. Experience has shown that automated checks of data do not catch all of the anomalies that may occur in these data. Thus, there needs to be further assessment of these site-specific LTPP climatic data. This review of the climatic data collected at LTPP seasonal monitoring and SPS test sites will identify and resolve discrepancies in the LTPP climatic data and improve the quality control process. RESEARCH OBJECTIVES AND TASKS Objectives: To examine the LTPP climatic data collected via onsite weather instrumentation to: Evaluate completeness. Evaluate quality. Perform reasonableness checks for seasonal and site location. Identify and explain other anomalous observations. Identify issues and improvements for equipment and process. Tasks: to be determined. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: to be determined. Research Period: to be determined. URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION To be determined. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem needs to be pursued BEFORE the following proposed problems: None. This problem should not be pursued until AFTER the following projects/problems are completed: None. Assessment of the Effects of Loading and Environment on Pavement Life Using SPS Data PROBLEM NUMBER: 3A1 RESEARCH PROBLEM STATEMENT The rate of pavement deterioration over a long period is influenced by both loading and environment. Pavement deterioration on SPS-1 and SPS-2 projects includes both these causes inseparably. SPS-8 projects normally involve deterioration due to environment. Pavement design models need to be able to account for the effects of environment and of load-environmental interactions. This project will study available data from LTPP, Canadian-Strategic Highway Research Program (C-SHRP), and European LTPP studies, augmented by special parallel lane studies (inside lane versus outside lane) at the SPS sites. RESEARCH OBJECTIVES AND TASKS Objectives: Determine the effects of environmentally induced pavement deterioration versus losses due to the interaction of load with environment. Develop models that describe the individual and joint effects of load and environment on pavement deterioration. Tasks: to be determined. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $500,000 Research Period: 30 months URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION To be determined. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem needs to be pursued BEFORE the following proposed problems: None. This problem should not be pursued until AFTER the following projects/problems are completed: None. Pavement Damage Caused by Swelling and Frost-Susceptible Soils PROBLEM NUMBER: 3B2 RESEARCH PROBLEM STATEMENT Volume change resulting from soil swelling and frost action is an important cause of pavement deterioration in areas affected by these phenomena. The only documented design procedure allowing for the prediction of long-term damage caused by these factors is in the 1993 AASHTO pavement design method. However, the proposed procedure is subjective and essentially empirical. Other procedures using mechanistic indices have been developed to predict volume changes. Distress-specific deterioration models are needed to support modern mechanistic-empirical pavement design procedures that are currently being developed. Practical procedures are also needed to capture the effect of volume changes in these design procedures. RESEARCH OBJECTIVES AND TASKS Objectives: Validated (mechanistic) indices to characterize the effects of frost and swell susceptibility of soils. Improve and/or develop procedures based on the indices to predict volume change in and underneath pavement structures. Develop a procedure for estimating the impact of volume change on pavement deterioration (roughness and cracking). Tasks: to be determined. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $300,000 Research Period: 30 months URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION Pavement design engineers in State, Provincial, and local highway agencies in areas affected by volume changes due to frost heave and soil swelling. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem needs to be pursued BEFORE the following proposed problems: None. This problem should not be pursued until AFTER the following projects/problems are completed: None. Evaluation of the Integrated Climatic Model Using LTPP Seasonal Monitoring Program Data PROBLEM NUMBER: 3C1 RESEARCH PROBLEM STATEMENT To properly design a pavement structure, the environmental effects on pavement materials must be considered. In the MEPDG, it is envisioned that the Integrated Climatic (IC) Model developed by the FHWA will be used to explain the environmental effects on pavement materials. The IC Model, however, has not been validated in a comprehensive, large-scale test. The LTPP Seasonal Monitoring Program (SMP) database provides data on seasonal changes in moisture, temperature, and frost depth on a national basis that could be used to evaluate and validate the model. If the model is successfully validated, then a practical guideline should be developed to assist State design engineers to manage the many input parameters needed for use in the IC Model. If the model is not found to be valid, then a framework should be identified that can further refine and improve the accuracy of the model. Alternative strategies for defining environmental effects on pavement materials that do not require the use of the IC Model should also be considered. RESEARCH OBJECTIVES AND TASKS Objectives: Phase I: Use the SMP data to validate the IC Model. Phase II: If Phase I is successful, develop a practical guideline to assist State design engineers in selecting input parameters for the use of the model. If Phase I is not successful, develop an extensive plan of work for improving the IC Model. Tasks: to be determined. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $200,000 Research Period: 24 months (12 months Phase I, 12 months Phase II) URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION It is envisioned that the IC Model will be used in the MEPDG. The validity of the model must be determined immediately. A practical guideline to facilitate the use of the model is urgently needed. If the model is not found to be valid, then this project must either define what is needed to improve the model or identify alternative strategies for considering environmental effects on pavement materials. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem needs to be pursued BEFORE the following proposed problems: None. This problem should not be pursued until AFTER the following projects/problems are completed: NCHRP 1-37A , MEPDG. NCHRP 9-23, Environmental Effects in Pavement Mix and Structural Design Systems (Objective 3A). Seasonal Validity of the Assumptions Underlying In-Situ Mechanistic Pavement Evaluation Methods PROBLEM NUMBER: 3C2 RESEARCH PROBLEM STATEMENT The mechanistic theory for evaluating the structural capacity of pavement structures is based on a number of assumptions concerning material properties (e.g. elastic behavior), loading conditions, and boundary conditions. Seasonal fluctuations, such as changes in the moisture content of base course and subgrade materials, may lead to cases where these assumptions are so violated that mechanistic theory cannot adequately describe the distribution of stress and strain in the pavement layers. This in turn will affect both pavement design and pavement structural evaluation (e.g., backcalculation). Research is needed to identify the conditions under which current mechanistic procedures for interpretation of pavement deflection data are most applicable in terms of their underlying assumptions. Furthermore, if these conditions are not available and testing must be conducted, agencies must be aware of the effect of suboptimal conditions (and the associated assumption violations) if the resulting deflection values are analyzed using mechanistic theories. RESEARCH OBJECTIVES AND TASKS Objectives: Analyze the LTPP seasonal monitoring data and other data as required to determine the most appropriate conditions under which to conduct deflection testing based on existing mechanistic theory, and conduct sensitivity analyses to evaluate the relative effect of varying levels of assumption violations upon the results of mechanistic analysis. Although the focus of the investigation will concern analysis of FWD deflection results and mechanistic analysis techniques, the project scope should also include deflection results in general such that the results of this investigation are applicable to other deflection test methods still in use around the world. Tasks. At a minimum, the required work will include the following: Review existing mechanistic theory and identify all underlying assumptions. Assess the effect of environment on pavement materials to determine whether or not the theoretical assumptions of mechanistic design are satisfied. Characterize the environmental conditions under which the assumptions of mechanistic theory are either applicable or not. Through sensitivity analysis, characterize the relative effect of assumption violations upon analysis results. If possible, provide conversion factors or shift curves to compensate for assumption violations. Determine whether the limitations affect all regions of the country, or only some regions. The product of this research will be guidelines to assist agencies in determining the most appropriate conditions to conduct deflection testing, to provide input to pavement design and performance evaluation and also on the effect of suboptimal conditions upon the resulting deflection data and mechanistic analysis. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $400,000 Research Period: 24 months URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION Because of the increasing use of FWDs and backcalculation to make rehabilitation decisions, this project is very urgent. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem needs to be pursued BEFORE the following proposed problems: None. This problem should not be pursued until AFTER the following projects/problems are completed: None. Region-Specific Guidelines for Pavement Modeling and Design Considering Environmental Effects PROBLEM NUMBER: 3E1 RESEARCH PROBLEM STATEMENT To be determined. RESEARCH OBJECTIVES AND TASKS To be determined. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: to be determined. Research Period: to be determined. URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION To be determined. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS To be determined. Develop Improved Pavement Performance Default Values or Models for Life-Cycle Cost Determination PROBLEM NUMBER: 4A1 RESEARCH PROBLEM STATEMENT Accurate and defendable life-cycle cost estimates are dependent upon accurate information that defines the performance life of new pavements as well as the performance life of reconstruction, rehabilitation, and maintenance activities. Good life-cycle costing must also have information describing when (timing) to apply rehabilitation and maintenance activities during the life of a pavement, as well as what treatment to apply. LTPP data analysis has been conducted to allow the engineer to estimate the life cycles of typical pavement rehabilitation and maintenance alternatives, as well as to define when to apply these treatments. This LTPP information will continue to improve in its accuracy as the LTPP program continues. Only limited extra analysis will be necessary to accomplish this project. RESEARCH OBJECTIVES AND TASKS Objective: To develop improved life-cycle costing default values and revise existing life-cycle costing software. Tasks: This research project will use available LTPP models and other information on both flexible and rigid pavements, and will recommend improved default values for life-cycle costing. In particular, the following information will be developed: Life of typical newly constructed pavements. Life of typical reconstruction, rehabilitation, and maintenance alternatives. When (during the life of a pavement) to apply selected rehabilitation and maintenance activities. What rehabilitation and maintenance treatment to apply. The above life-cycle cost information might be used to revise the existing FHWA and individual public agency life-cycle costing software. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $150,000 Research Period: 15 months URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION The project will supply a product that can be immediately used by public agencies. There is a high potential for successful completion and implementation of the project. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem needs to be pursued BEFORE the following proposed problems: Information will be obtained from completed LTPP data analysis projects, including FHWA-sponsored SPS-3 and SPS-4 analysis projects and the pending NCHRP 20-50(3/4), "LTPP Data Analysis: Effectiveness of Maintenance and Rehabilitation Options (Objective 6A). The project will use the best available information to develop the default values. Updates of the default values and software should be developed periodically. This problem should not be pursued until AFTER the following projects/problems are completed: None. Developing Hierarchical Data Collection for Network- and Project-Level Pavement Management, Considering Types and Frequencies of Measurements PROBLEM NUMBER: 4A2 RESEARCH PROBLEM STATEMENT To be determined. RESEARCH OBJECTIVES AND TASKS To be determined. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: to be determined. Research Period: to be determined. URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION To be determined. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS To be determined. Types and Frequencies of Measurements for Accurate Description of Pavement Condition PROBLEM NUMBER: 4A3 RESEARCH PROBLEM STATEMENT States are continually addressing the issue of what types of data and how frequently to collect data in their pavement management systems. LTPP has developed an extensive database that permits comparative analysis for determining the optimum combination of data types, accuracy, and collection frequency. For example, the FWD data in the database is taken at four load levels, with multiple drops at each level at numerous locations along the test section. The question to be answered is "How much of these data are really needed to capture the structural condition for network- and project-level analysis, or are there different numbers of load levels, number of drops, and number of drop sites that would produce an improved description of structural condition?" Using the LTPP database, identify the data parameters needed to describe pavement condition, and define the frequencies of measurement recommended for collecting high-quality data suitable for model building and performance analysis. The optimum frequency of data collection to balance the cost of collection and accuracy of the test results, including issues of daily and seasonal variability, will be addressed. RESEARCH OBJECTIVES AND TASKS Objective: To define the optimum data collection schedule to balance frequency, cost, and accuracy of test results for pavement management system (PMS) input. Tasks: to be determined. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $250,000 Research Period: 18 months URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION This project will facilitate the collection of data sets describing pavement condition, which are suited to pavement performance analysis, model building, prediction of pavement performance, and decision-making with PMS. They will help practitioners in public agencies focus on key parameters and provide guidance on the level of data collection activity needed. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem needs to be pursued BEFORE the following proposed problems: None. This problem should not be pursued until AFTER the following projects/problems are completed: None. Numerical Pavement Evaluation Indices for Pavement Condition PROBLEM NUMBER: 4A4 RESEARCH PROBLEM STATEMENT Successful modeling of pavement performance requires the definition of a numerical value or index (for example, the International Roughness Index (IRI) or the friction number) by which each failure mechanism is measured. Although some functional measures (for example, skid or roughness) have well-known indices, there are indices needed for rutting, various types of pavement cracking, and other forms of distress. Use of accepted indices will facilitate data modeling and comparisons among public agencies. It is anticipated that the research would involve a consideration of various possible indices related to specific distress types. Selection of the most useful index would be based on the extent that the index successfully indicates the pavement distress type (for example, transverse cracking), severity (for example, crack width), extent (for example, crack length) as well as the stability (for example, sensitivity) of the value and the ease of its use. The research should also consider the seasonal and daily variability of the indices by using site data from the Seasonal Monitoring Program. This will enable users of the indices to evaluate a reading made in one season to readings made at different times of the year. RESEARCH OBJECTIVES AND TASKS Objective: To develop appropriate indices for both rigid and flexible pavements, to characterize the most common pavement conditions including such distresses as fatigue cracking, rutting, faulting, reflective cracking, raveling, environmental cracking, roughness, and surface friction. These indices will enable modeling of pavement performance and between-state comparison of pavement condition. Tasks: to be determined. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $200,000 Research Period: 18 months URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION The products of this research will enable States to discuss, using common and clearly defined indices, pavement condition regarding distresses. These indices would also be a logical measure to use in modeling pavement performance. Indices will also be helpful to States in developing snapshots of their pavement systems. Implementation of the results of this project would include potential adoption by AASHTO of a new protocol, and perhaps ultimately a new national standard. The initial draft of this protocol would be developed by the contractor as part of the final report. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem needs to be pursued BEFORE the following proposed problems: None. This problem should not be pursued until AFTER the following projects/problems are completed: None. Characterization of PCC Pavement Curvature PROBLEM NUMBER: 4B1 RESEARCH PROBLEM STATEMENT Bynum has developed a method to detect and characterize the apparent locked-in curvature of PCC pavements, through analysis of longitudinal profile data collected with high-speed pavement profilers. He has shown that use of the Curvature Index (CI) derived through his analysis significantly improves the predictive capability of PCC pavement performance models. The addition of this index to the LTPP database as a computed parameter is therefore under consideration. RESEARCH OBJECTIVES AND TASKS Objectives: The objectives of this phased multitask analysis are to: Provide the background material necessary to support an informed decision as to whether the CI should, in fact, be added to the LTPP database. Compute the CI for all currently available PCC pavement longitudinal profile data. Provide documentation of the CI to support its use in future analysis of the LTPP data. Provide prototype software to enable computation of the CI as part of routine processing of LTPP longitudinal profile data. Tasks: Conduct a literature review focused on the CI. Follow LTPP's steps for recommending a new computed LTPP parameter. Populate the LTPP database with CI values (assuming the recommendation is approved). Develop CI documentation for posting on the LTPP Web page. Develop prototype software to compute CI from any profile data. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: to be determined. Research Period: to be determined. URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION To be determined. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem needs to be pursued BEFORE the following proposed problems: None. This problem should not be pursued until AFTER the following projects/problems are completed: None. Simplified Techniques for Evaluation and Interpretation of Pavement Deflections for Network-Level Analysis PROBLEM NUMBER: 4B2 RESEARCH PROBLEM STATEMENT Network-level PMS are typically performed using only surface distress measurements. However, it is commonly accepted that the pavement structural capacity has a major effect on the rate of deterioration. Consequently, it is critical in forecasting future pavement conditions to know the structural capacity. Techniques currently available to estimate structural capacity from deflections are time consuming and require an experienced analyst. Additionally, these techniques may provide more detail than is necessary for network-level decisions. As a result, use of pavement deflections in network-level analysis has been limited, even in those agencies that use FWD extensively in their project-level testing. Results of this research would also have applications for agencies that do not use deflection testing in their PMS; a simplified index describing structural performance would be useful in comparing project segments or in project selection. Using LTPP and other data should define the test spacing necessary to implement the technique(s) required to use pavement deflection data in a network-level PMS. RESEARCH OBJECTIVES AND TASKS Objective: To recommend and verify simplified techniques suitable for rapid, automated screening of pavement deflection information for inclusion in network-level pavement analysis. Tasks: Literature search. Review previous work done on simplified techniques for deflection analysis, including but not limited to indices of surface curvature and closed-form, two-layer solutions. Surface deflections may be combined with other measurements, such as transverse profile. Evaluation of techniques. After a review of existing techniques, identify and, if necessary, develop the most promising techniques for simplified evaluation and analysis. Use the LTPP database and other appropriate existing deflection information to compare the results of the simplified analysis to determine the consistency, stability, and repeatability of the simplified techniques. Selection of technique. Based on the previous task, make recommendations on the most desirable technique for simplified evaluation. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $200,000 Research Period: 18 months URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION Network-level PMS are used to make decisions valued at hundreds of millions of dollars with a potentially incomplete assessment of pavement condition. Applicable techniques to assess pavement structural condition could improve the accuracy of these systems and potentially save transportation agencies considerable amounts of money as well as reduce delays to the public stemming from construction that is not optimally timed. This work should be tightly focused on providing solutions that are intended for easy implementation in State PMS. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem needs to be pursued BEFORE the following proposed problems: None. This problem should not be pursued until AFTER the following projects/problems are completed: None. Relating Ride Quality and Structural Adequacy for Pavement Rehabilitation/Design Decisions PROBLEM NUMBER: 4C1 RESEARCH PROBLEM STATEMENT Initial efforts in network PMS concentrated on the evaluation of visual distress survey data only. It is also important to include ride quality and some evaluation of the structural integrity of the pavement and subgrade. The public measure of ride and the engineering value of structural support will provide a more complete view of the roadway system, which is needed for network-level resource allocation. The research may identify a relationship between ride and structural support, or may show these factors to be independent of each other. In either case, the network pavement management can then account for all condition data in both resource allocation and the performance models employed. This may provide support information as State Departments of Transportation (DOTs) implement the upcoming AASHTO pavement design procedure. Previous work related to this topic has included NCHRP 20-50(8/13), Factors Affecting Pavement Smoothness (Objective 7B), FHWA/LTPP reports on evaluating load transfer or PCC-jointed pavements, and FHWA/LTPP reports on profile devices. Three other projects, FHWA-RD-99-074, FHWA-RD-00-113, and FHWA-RD-00-076, considered the data variability of distress, profile, and faulting data. None of these projects evaluated the relationship between functional and structural pavement measures. RESEARCH OBJECTIVES AND TASKS Objective: To identify a relationship between ride and structural support. Tasks: Review the results of previous data studies. Determine the relationship between ride quality and structural adequacy, using the LTPP database. Develop guidelines on ways to include both ride and structural adequacy values in network-level pavement management for State implementation. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $200,000 Research Period: 12 months URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION Urgency: High. This project will provide a rational basis for network-level pavement management resource allocation. Payoff Potential: The relationship between structural adequacy and ride quality is a topic of frequent and continuing discussion in the pavement community. LTPP offers the opportunity to resolve this pesky problem. Implementation: The results can be used by State DOT pavement management engineers to balance the desire for smooth roads with the need to have structurally adequate roads. It can also become a component of existing National Highway Institute courses in pavement management and data collection. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem needs to be pursued BEFORE the following proposed problems: None. This problem should not be pursued until AFTER the following projects/problems are completed: None. Criteria for Applying Performance Measures to Construction Quality Evaluation PROBLEM NUMBER: 4D1 RESEARCH PROBLEM STATEMENT To be determined. RESEARCH OBJECTIVES AND TASKS To be determined. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: to be determined. Research Period: to be determined. URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION Priority: Low. It should be done if data allow it. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS To be determined. Quantitative Information of Environmental Variables on Pavement Performance Measures PROBLEM NUMBER: 4E1 RESEARCH PROBLEM STATEMENT Because of the effects of environmental variables on pavement materials properties, variations in temperature and moisture, as well as frost penetration and freeze/thaw cycles, are important factors in determining pavement performance. However, the quantitative information is not well understood on how these environmental variables affect pavement performance measures such as profile, distress, friction, and deflection. Without this information, it is a difficult task to design long-lasting pavements. Data from the LTPP studies are available to provide this information. RESEARCH OBJECTIVES AND TASKS Objective: To analyze and quantify, based on SMP data from LTPP studies, the effects of environmental variables on the pavement performance measures. Tasks: to be determined. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $500,000 Research Period: 24 months URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION The potential payoff is very high because the quantitative information of environmental on pavement measures can be incorporated into the AASHTO Pavement Design Guide. It will be implemented by AASHTO Joint Task Force on Pavements (JTFOP). RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem needs to be pursued BEFORE the following proposed problems: None. This problem should not be pursued until AFTER the following projects/problems are completed: NCHRP 20-50(5), Variations in Pavement Design Inputs (Objective 5B), and preliminary project statement 14, Assessment of the Effects of Loading and Environment on Pavement Life Using SPS Data (Objective 3A1). PCCP Temperature Correction Factors for Interpretation of FWD Test Results PROBLEM NUMBER: 4E2 RESEARCH PROBLEM STATEMENT To be determined. RESEARCH OBJECTIVES AND TASKS To be determined. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: to be determined. Research Period: to be determined. URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION Priority: Low. It should be done if data allows it. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem needs to be pursued BEFORE the following proposed problems: None. This problem should not be pursued until AFTER the following projects/problems are completed: None. Evaluation of Load-Response Models (Axle Load and Environment) PROBLEM NUMBER: 5A1 RESEARCH PROBLEM STATEMENT A variety of existing load-response models vary in accuracy and complexity. It is assumed that the more complex models (such as the 3-D finite element) give more accurate response predictions, but may be more difficult and expensive to use than simpler models. This study will evaluate the load-response models proposed by NCHRP 1-37A and the MEPDG, using data obtained from instrumented SPS-1 and SPS-2 sections. The researchers will make recommendations on the predictive capability of the MEPDG models and will also make recommendations on whether more complex models should be considered. RESEARCH OBJECTIVES AND TASKS Objective: This study will evaluate the load-response models proposed by the NCHRP 1-37A study. The researchers will use the data obtained from instrumented SPS-1 and SPS-2 test sections to verify the accuracy of the MEPDG models. In cases where the predictive capabilities of the MEPDG models are found to be inadequate, other more complex models (such as the 3-D finite element) will be used to determine if better response estimates can be obtained. If more complex models are recommended, then the researchers will also evaluate cost and benefits associated with the more complex models. Tasks: to be determined. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $200,000 Research Period: 24 months URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION This study will provide an independent evaluation of the MEPDG load-response models. Additional valuable information will be provided that compares the added benefit of more complex models to the cost and difficulty of using these more complex models. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem needs to be pursued BEFORE the following proposed problems: None. This problem should not be pursued until AFTER the following projects/problems are completed: None. Evaluation of the Performance Prediction Models in the 2002 Pavement Design Guide PROBLEM NUMBER: 5B1 RESEARCH PROBLEM STATEMENT States will begin using the MEPDG resulting from NCHRP 1-37A. There will be an independent validation of the reliability of NCHRP 1-37A MEPDG performance prediction models and enhancement of their usefulness as design tools for new construction. The report will assess the models using objective, statistical measures of predicted-to-observed distress. Sensitivity analyses will grade the models on the stability of their output, their responsiveness to significant input variables, and their ability to handle unique design configurations. Projected and actual life-cycle outcomes for selected LTPP sites using design guide recommendations and design procedures will be compared. The selection of a pavement design procedure is a decision that has enormous economic consequences for a State DOT. Pavement design engineers need proof that new procedures will yield designs with predictable service lives. This work will provide that evidence and will allow States to confidently implement new design procedures. RESEARCH OBJECTIVES AND TASKS Objective: The performance of appropriate GPS and SPS test sections will be compared to the performance predicted by NCHRP 1-37A design procedures for flexible and rigid pavements. Tasks: Analyze data such as as-built layer thicknesses, materials properties, traffic loadings, measurable distress, and climatic data. Analyze SPS-1 and SPS-2 sections and appropriate GPS sections. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $400,000 Research Period: 24 months URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION This study is essential to support and establish the early credibility of the MEPDG. It should be accomplished as soon as practical to support acceptance by State DOTs. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem needs to be pursued BEFORE the following proposed problems: None. This problem should not be pursued until AFTER the following projects/problems are completed: NCHRP 1-37A MEPDG. Evaluation of Pavement Performance Models PROBLEM NUMBER: 5C1 RESEARCH PROBLEM STATEMENT Asphalt concrete (AC) overlays on PCC pavements or pavements with cement-treated bases tend to suffer from cracks in the surface of the overlay. The cracks reflect the pattern of joints and cracks in the PCC pavement, or the cracks reflect the transverse shrinkage cracks that appear on the surface of AC pavements with cement-treated bases. Similarly, reflection cracks can occur in AC overlays on cracked AC pavements. When these cracks propagate through the depth of the AC overlay, infiltration of both water and de-icing salts can cause rapid deterioration of the underlying pavement structure and foundation. Overlay performance can thus be considerably reduced. Because pavement rehabilitation, and more specifically AC overlays of existing pavements, is the most important pavement construction activity in North America, there is a great need for engineering tools to help maximize the performance of AC overlays. At least two international conferences (Rilem International Conferences on reflection cracking—one in Liege, Belgium, in 1996, and another in Ottawa, Canada, in 2000) have specifically dealt with the problem with reflection cracking on both flexible and rigid pavement. Several models on reflection cracking are documented in the literature and, more specifically, in the proceedings of these conferences. The development of these models is generally based on theoretical work or on limited field studies. Other proposed models are essentially empirical and are not necessarily associated to design variables. A validated model to predict reflection cracking will provide guidance for future overlay pavement design, taking into account the factors that influence the formation of reflection cracking. The model will also provide maintenance engineers with a means of estimating crack sealing requirements for the management of their network. The models will take into account design, materials, and construction information, along with climate and traffic loading effects. RESEARCH OBJECTIVES AND TASKS Objectives: To evaluate and refine models to predict the initiation and propagation of reflection cracking in the surface of an AC overlay on PCC pavements or on pavements with cement-treated bases. To evaluate and refine existing models to predict the initiation and propagation of reflection cracking in an AC overlay on AC pavement exhibiting surface cracking. To provide a sensitivity analysis indicating the effect of material and design factors on the initiation and propagation of reflection cracking. Tasks: to be determined. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $200,000 Research Period: 24 months URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION At present there are no validated models in the United States to predict the occurrence and propagation of reflection cracking in AC overlays. The models will provide a basic understanding of the mechanisms involved, and these will serve to provide the design engineer with the means to minimize reflection cracking in future overlay designs. The model will also provide the maintenance engineer with a tool to predict future workloads for crack sealing or the AC overlays within the engineer’s network. As soon as the models have been validated, they can be put into practice for pavement design and maintenance. AC overlay performance prediction will help maximize the performance of this widespread rehabilitation strategy. Thus, there is considerable payoff potential, in view of the importance of pavement rehabilitation activities on North American road networks. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem needs to be pursued BEFORE the following proposed problems: None. This problem should not be pursued until AFTER the following projects/problems are completed: On hold pending outcome of proposed FY 2003 NCHRP project on same topic. Development of Longitudinal Cracking Models for PCC Pavements PROBLEM NUMBER: 5C2 RESEARCH PROBLEM STATEMENT The MEPDG under development by NCHRP/AASHTO uses performance models to predict distresses on AC and PCC pavements. However, longitudinal cracking, a key distress found on PCC pavements, is not well addressed in the MEPDG. When cracks propagate through the PCC pavement, infiltration of water and de-icing salts can cause rapid deterioration of concrete due to the loss of support in the underlying subbase and foundation. Thus, PCC pavement life can be considerably reduced. To predict the duration of PCC pavement life, there is a great need for performance models for this key distress. Development of calibrated and validated performance models for this distress will provide an excellent tool for PCC pavement designers to predict the formation and propagation of longitudinal cracks. The models will also provide maintenance engineers with a means of predicting crack sealing requirements for the management of their network. The models will take into account design, materials, and construction practices together with climate and traffic loading effects. RESEARCH OBJECTIVES AND TASKS Objectives: Develop models to predict the initiation and propagation of longitudinal cracking on JPC and CRC pavements: bottom-up and top-down cracking in either traditional width or widened lanes with asphalt or tied-concrete shoulders. Conduct sensitivity analyses to provide an understanding of the effect of materials, design, construction practices, and environmental and traffic loading on the initiation and propagation of longitudinal cracks. Tasks: to be determined. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $200,000 Research Period: 24 months URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION At present, there are no models in the United States to predict the initiation and propagation of longitudinal cracking in PCC pavements. Development of these models will provide a basic understanding of the mechanisms involved and will guide design engineers by providing them with a method for minimizing the occurrence of longitudinal cracking in future PCC pavement designs. The model will also provide maintenance engineers with a tool to predict their future workloads for crack sealing and for other maintenance works within their network. As soon as the models have been validated they can be put into practice for pavement design, construction, and maintenance. Better understanding of the key elements in this mechanism of failure will help to maximize the life of PCC pavements. The payoff potential is thus considerable in view of the importance of PCC pavements on North American road networks. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem needs to be pursued BEFORE the following proposed problems: None. This problem should not be pursued until AFTER the following projects/problems are completed: NCHRP 1-37A and the MEPDG. Guidelines for Selecting Effective Pavement Rehabilitation Strategies PROBLEM NUMBER: 6B1 RESEARCH PROBLEM STATEMENT Although many options are available for the rehabilitation of flexible and rigid pavements, information on the impacts of these options on overall pavement performance, on the influences of traffic loading, and on initial pavement condition, are not well documented. The LTPP rehabilitation experiments were undertaken to provide this type of information. The data collected from the LTPP experiments on pavement rehabilitation provide information both to evaluate the effectiveness of several rehabilitation options and to develop guidelines for selecting appropriate strategies based on pavement type and condition, traffic loading, pavement performance enhancement, and other factors. There is a need for an analysis of the performance of the rehabilitated LTPP test sections, to determine the effectiveness (in terms of overall pavement performance and life) of various treatment options. This analysis should consider the effects of pavement condition at the time of treatment, as well as of structural adequacy, base type, subgrade, and other pertinent factors to pavement performance and life extension. The findings of this analysis will form the basis of guidelines for the selection of effective pavement rehabilitation strategies. RESEARCH OBJECTIVES AND TASKS Objective: The objective of this research is to develop, based on the data available from LTPP studies, guidelines for selecting appropriate pavement rehabilitation strategies for both rigid and flexible pavements. These guidelines should consider the impacts of traffic loadings, climatic conditions, measurable customer-related benefits, and pavement type and condition on the performance of the rehabilitated pavement. Tasks: Collect and review reports relative to LTPP studies on the rehabilitation of flexible and rigid pavements (GPS-6B, SPS-5, and SPS-6) and other relevant research. The results of NCHRP 20-50(3/4), Effectiveness of Maintenance and Rehabilitation Options (Objective 6A), should be among those considered. Scrutiny of the LTPP data is required to eliminate biased data, e.g., situations where test sections in which the joints were sealed for many years, then the sealant was stripped out, and now the performance is considered that of an unsealed test section (when actually the current performance might have been predetermined by the previously sealed condition). Obtain and organize the LTPP data required to achieve the project objectives. Analyze the data collected n Task 2 to evaluate the effectiveness of different rehabilitation strategies, considering the impact of varying original pavement types and conditions, as well as of varying climatic and traffic conditions. It should be noted that the impact of the treatment on overall pavement performance, and not the life and performance of the treatment, is the issue of concern. Based on the results of Task 3, develop guidelines for selection of effective rehabilitation strategies. The guidelines should consider the impact of the various rehabilitation strategies under varying original pavement types and conditions, as well as under varying climatic and traffic conditions, on the performance of the original pavement. Prepare a final report documenting the research. The recommended guidelines for selecting effective pavement rehabilitation strategies are to be provided as a stand-alone document. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $300,000 Research Period: 24 months URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION Billions of dollars are being spent on rehabilitation work, and the information currently available to guide selection of rehabilitation strategies is incomplete. Several LTPP experiments have been conducted to address this need, but the collected data must be analyzed to obtain the required information. Pursuit of this analysis is urgently needed. The findings of this research will be delivered in the form of guidelines to facilitate implementation. If implemented, these guidelines will help agencies select the most appropriate rehabilitation strategy for a given set of circumstances. Selection of the appropriate strategies is needed for owner agencies to assure sound pavement management practices and to assure the most benefit to the highway customer per dollar spent. The potential payoff resulting from the use of cost-effective strategies is tremendous. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem needs to be pursued BEFORE the following proposed problems: None. This research should build on the findings of NCHRP 20-50(3/4), Effectiveness of Maintenance and Rehabilitation Options (Objective 6A). Further collection of data and analysis of the data from the rehabilitated LTPP test sections is required to build upon the findings of this previous work. Impact of Design Features on Pavement Response and Performance in Rehabilitated Flexible and Rigid Pavements PROBLEM NUMBER: 7A1 RESEARCH PROBLEM STATEMENT The performance of a rehabilitated flexible or rigid pavement section not only will depend on the site conditions (e.g., traffic level, climatic conditions, and material properties), but also on other design and construction features (e.g., type and details of subdrainage, base, shoulders, maintenance and rehabilitation measures, etc.). A number of researches, e.g. NCHRP 20-50(10/16), have been undertaken focusing on the effects of design and construction features on new flexible and rigid pavements as well as on the effects of subdrainage and pavement structural layers on all flexible and rigid pavements. With new data available in the LTPP database, it is necessary to obtain more understanding of the effects of design and construction features on pavement response and performance of rehabilitated flexible and rigid pavements. There is research needed to determine the effects of design and construction features on pavement response and performance and to establish their relative importance. This research will provide preliminary information on the relationship between pavement response and performance, guidance for identifying appropriate features for different pavement types, and recommendations for improving data collection activities. RESEARCH OBJECTIVES AND TASKS Objectives: Based on the pavement response and performance data accumulated for the LTPP SPS-5 (rehabilitated asphalt concrete pavements) and SPS-6 (rehabilitated jointed plain concrete pavements) as well as any applicable experiments, determine for specific site conditions: Impact of the different design, construction, and rehabilitation features considered on pavement response (as measured by deflection and strain) Contributions of these features to achieving different levels of performance (as measured by type and extent of distress or smoothness). Based on these findings, report whatever inferences can be drawn from the LTPP experiments, as to the likely long-term performance impact of these features. In addition, if indicated, provide recommendations on any corrective actions that should be considered to improve the future analytical potential of the experiment considered in this investigation. Tasks: to be determined. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: to be determined. Research Period: to be determined. URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION The SPS experiments were undertaken to provide critically needed information to support pavement rehabilitation decisions. Findings drawn from this study can help highway agency engineers and managers make sound pavement design, construction, and rehabilitation decisions. Analyses pursued at this time can maximize both the near-term and long-term benefits accrued from the tremendous investment made in the construction and monitoring of these test sites. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This project is linked strongly to the research results identified in Objective 5 (development of performance prediction models) of the LTPP Strategic Plan and the 2002 Mechanistic-Empirical Pavement Design Guide (MEPDG). The analyses returned in this study will be an integral part of both the determination of the causes of distress and the formulation of models predicting performance. Evaluation and Characterization of Pavement Drainage PROBLEM NUMBER: 7B RESEARCH PROBLEM STATEMENT In the United States , it has become common to incorporate subsurface drainage features (e.g., permeable, edgedrains) into pavements to handle surface infiltration water. However, there has always been controversy about the design, performance, and benefits of subsurface drainage. The problematic history of design and construction of features such as open-graded bases, longitudinal edgedrains, and day-lighted bases adds to the controversy. Recent studies have shown that only one-third of the edgedrains in existing pavements are functioning as designed. Other studies have shown that some open-graded bases are being infiltrated with fines from underlying layers, significantly affecting their effectiveness. There have also been reports about construction difficulties and early cracking supposedly related to open-graded bases. The primary effect of pavement drainage is to reduce the detrimental effects of free moisture in the granular layers beneath the bound layers, particularly both after the pavement cracks and at joints with sealant failure (rigid pavements). Although this effect is mostly positive, there can be a negative effect on pavement life. In fact, drainage could have any of the following effects on the performance of a pavement: Negative effect on pavement life caused by the stripping of the permeable asphalt-treated bases (PATB) or clogging of the edgedrains and lateral outlets (this has occurred often in the United States). Little or no effect on pavement life because it acts similarly to a granular layer beneath the bound layers. Positive effect on flexible pavement life, which is attributable to the layer draining out excess water from the pavement structure and thereby increasing the modulus of the underlying unbound base layers. Positive effects also include the drainage of water infiltrating through cracks, thus reducing their deterioration. Positive effect on rigid pavement life is attributable to the layer draining out excess water from the pavement structure and thereby reducing pumping and weakening of the subgrade and pavement layers. Positive effects also include the drainage of water infiltrating through cracks and unsealed joints, thus reducing deterioration. The benefits of improved drainage also include minimizing the potential and severity of durability-related distresses such as D-cracking. Softening of the subgrade and unbound base layers caused by poor drainage results in higher deflections and strains. High deflections and strains can result in fatigue cracking and rutting in flexible pavements, and in pumping and faulting in rigid pavements. Thus, poor drainage contributes to distresses and roughness in both flexible and rigid pavements. Status of LTPP Drainage-Related Projects The LTPP database contains a wide variety of information, including drainage-related data collected on GPS and SPS test sections across the United States. In particular, the SPS-1, SPS-2, and SMP sections contain a wealth of performance information on pavements with and without drainage features. The early evaluation results of these three experiments are summarized as follows. SPS-1 Experiments The LTPP SPS-1 experiment, entitled Strategic Study of Structural Factors for Flexible Pavements, is a key experiment in the LTPP program. The objective of this experiment is to determine the relative influence and long-term effectiveness of flexible pavement design features. Eighteen SPS-1 projects have been constructed in different States across the Nation. At each site, there are 12 core sections plus various numbers of supplemental sections. A total of 248 test sections are included in the SPS-1 experiment. Each SPS-1 experiment includes several sections with PATB. The SPS-1 projects are also relatively young pavements, with some projects (Montana and Wisconsin) less than 2 years old. Some of the early performance trends are listed below. Of course, any long-term performance might differ from short-term performance. Higher rut depths occurred on test sections with dense aggregate base layers than on sections with dense asphalt-treated base (ATB) or PATB. However, rutting appears to be related more to the HMA mixture properties than to the structural characteristics. Sections with PATB have a lower percentage of test sections (20 percent) with rut depths exceeding 8 millimeters (mm) than sections (32 percent) with dense bases. The percentage of core test sections with fatigue cracking is slightly less for those test sections with PATB than for those without PATB. SPS-2 Experiments The LTPP SPS-2 experiment, entitled Strategic Study of Structural Factors for Rigid Pavements, is another key experiment in the LTPP program. It was designed as a controlled field experiment that focuses on the study of specific design features (structural factors) for doweled jointed plain concrete (JPC) pavements. Thirteen SPS-2 projects have been constructed in different States across the Nation. At each site, there are 12 core sections plus various numbers of supplemental sections. Each SPS-2 section length is 152 meters (m) long. Key design features common to all SPS-2 sections include the following: 4.6-m uniform joint spacing. Doweled perpendicular transverse joints with 32-mm dowel bars for the 203-mm-thick pavements and 38-mm dowel bars for the 279-mm-thick pavements. Each SPS-2 experiment includes several sections with PATB. The SPS-2 projects are relatively young pavements, ranging from 2 years old in Wisconsin to 7.5 years old in Kansas. Therefore, as expected, most SPS-2 sections are showing good performance and low distress levels. As of January 2000, only 43 of 155 sections (28 percent) are showing any noticeable distresses. Also, 95 percent of the SPS-2 sections have less than 1 mm of edge joint faulting, 87 percent of the SPS-2 sections are showing zero transverse cracking, and 78 percent of the sections have zero longitudinal cracking. Based on the initial statistical analyses and comparisons, the following initial performance trends are noted (long-term performance may differ from short-term performance): JPC pavements constructed on PATB were smoother than when they were constructed on a lean concrete base (LCB) or an untreated aggregate base. Sections with PATB are showing the lowest total longitudinal cracking levels, while the sections with LCB show the highest longitudinal cracking levels. Sections with PATB are showing the lowest percentage of slabs cracked transversely, while the sections with LCB show the highest percentage of transverse cracking. Sections with aggregate base are showing the highest joint-faulting levels. Sections with LCB and PATB have the lowest joint-faulting levels. SMP Experiments Temperature and moisture in a pavement structure vary on both a daily and yearly basis. To understand the impact of these changes on the pavement structure and its response to loads, 63 sites were selected from the GPS and the SPS projects for continuous temperature and moisture monitoring. Time domain reflectometry probes and thermistor probes are used to monitor changes in subsurface moisture and temperature, electrical resistivity probes are used for frost/thaw depth measurements, and piezometers are used for ground-water table determinations. In addition, air temperature probes and tipping-bucket rain gauges are used to monitor ambient temperature and precipitation. Deflection, profile, and distress data are collected at frequent intervals using LTPP equipment and testing protocols. A summary of the program is contained in the Data Users Reference Manual. Each SMP site had two monitoring rounds that each lasted approximately 1 year. Intensive data collection was carried out every other year for the 4-year duration of the study. Half of the sites were instrumented in each year. RESEARCH OBJECTIVES AND TASKS Objectives: Determine if the LTPP sections as built are feasible for a comprehensive drainage study. Determine the sufficiency of climatic events for evaluating the effects of drainage on pavement performance. Evaluate the effect of the drainage layer and the absence of adequate drainage on base, subbase, subgrade, and pavement performance. Tasks: To be determined. Expected products are (1) documented information on the benefits of drainage layers on pavement performance, (2) estimated cost-benefit ratio of drainage layers, and (3) guidelines for application of drainage layers. Deliverables are (1) a report documenting the feasibility of the LTPP program for a comprehensive drainage study, (2) a comprehensive final report documenting the information on the benefits and application guidelines for drainage layers, and (3) a separate document (five pages or less) identifying key findings and/or products expected to be of interest to highway agencies. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: to be determined. Research Period: to be determined. URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION The exact amount of increase in pavement life due to pavement drainage varies widely because there are several construction- and maintenance-related issues that affect the performance of pavement drainage. As a result of this variability in performance, some sections with drainage features have poorer performance and other sections perform better than a comparable conventional dense aggregate base pavement section. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem needs to be pursued BEFORE the following proposed problems: None. This problem should not be pursued until AFTER the following projects/problems are completed: NCHRP 1-34D, Effects of Subsurface Drainage on Performance of Asphalt and Concrete Pavements: Further Evaluation and Analysis of LTPP SPS-1 and SPS-2 Field Sections (Objective 7B). Analysis of LTPP SPS-1 and SPS-8 Data and Related GPS Data to Quantify the Impact of AC Pavement Design Features on Measured Pavement Distresses PROBLEM NUMBER: 7B1a RESEARCH PROBLEM STATEMENT The LTPP experiments used specific design features as the basis for establishing individual sections. The SPS-1 sites are specially constructed, new AC test sections. These sites provide a unique opportunity to analyze and quantify the association of distress and design features. The SPS-8 sites evaluate asphalt pavements in the absence of high traffic volumes. The SPS sites have detailed information on features, materials, and initial conditions as well as on continued monitoring of distresses over time. Several of the sites have already gone out of service, and the number of sites reaching the terminal point will increase in the next few years. For this reason, this project has a high probability of success. Only limited information on the impact of design features on measured pavement distress is currently available to pavement designers. These analytical investigations will define the relative effectiveness of certain design features on distress for flexible pavements. Specific design features studied in one or more of the LTPP experiments include: Surface course thickness. Base course thickness. Base type— Dense-graded aggregate. Open-graded aggregate. Asphalt treated. Permeable asphalt treated. Cement treated. Lime stabilized. Full depth asphalt. Subsurface drainage. A qualification of how distresses are associated with design features should be performed to identify whether they are unique to a feature or whether they are manifested as a result of other distresses that appear concurrently. Distresses should be characterized quantitatively as phenomena of their physical environment (e.g., environment, wheel load, combination, or other). Interdependencies of distress, feature, and load environment should be identified. A second phase of these analyses should include the quantification of the associations of distresses with design features. Using the relationships addressed above, determine these associations using a probabilistic approach. For example, determine the probability of having a distress manifested in the presence of either a single design feature or a combination of features throughout its appropriate loading sequence. RESEARCH OBJECTIVES AND TASKS Objectives: Determine how distresses are associated with design features for asphalt concrete pavements. Determine the interaction of distress, design features, and load environment(s) using a probabilistic approach. Tasks: to be determined. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $300,000 Research Period: 24 months URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION A successful outcome of this project will allow pavement designers to make better-informed decisions on when or whether to use specific design features such as type and location of drainage systems, treated or untreated bases, and relative thicknesses of base and surface. When coupled with the results of NCHRP 20-50(10/16), The Influence of Design and Construction Features on the Response and Performance of New Flexible and Rigid Pavements (Objective 7A), the results will also strengthen pavement management by relating changes in pavement response to the onset and progress of pavement distress, in light of specific design features. The relationships to be considered in this study are those that administrators from highway agencies and other governmental entities have emphasized as being the greatest need from LTPP studies. Historical LTPP documents suggest that users and supporters of LTPP data are awaiting the results of these analyses. Publications and electronic media that make trends and trend analyses available to the users have a high probability for widespread use. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This project will use results of an FHWA project on the estimation of traffic axle load spectra that is scheduled for completion in late 2001. As described above, the project is related to the NCHRP project on pavement response as a function of design features. This project is a necessary precursor to the guidelines for selecting pavement design features. This project is linked strongly to the research results identified in Problem Statement 5A1 of the LTPP Strategic Plan, Evaluation of Load-Response Models (Axle Load and Environment). The analyses returned in this study will be an integral part of both the determination of cause of distress and the formulation of performance prediction models. Analysis of LTPP SPS-2 and SPS-8 Data and Related GPS Data to Quantify the Impact of Rigid Pavement Design Features on Measured Pavement Distresses PROBLEM NUMBER: 7B1b RESEARCH PROBLEM STATEMENT The LTPP experiments used specific design features as the basis for establishing individual sections. The SPS-2 sites are specially constructed, new, rigid test sections. These sites provide a unique opportunity to analyze and quantify the association of distress and design features. The SPS-8 sites evaluate concrete pavements in the absence of high volumes of traffic. The SPS sites have detailed information on features, materials, and initial conditions as well as on continued monitoring of distresses over time. Only limited information on the impact of design features on measured pavement distress is currently available to pavement designers. These analytical investigations will define the relative effectiveness of certain design features on distress for rigid pavements. Specific design features studied in one or more of the LTPP experiments include: Surface course thickness. Concrete strength. Base course thickness. Joints. Dowels. Tied shoulders. Subbase thickness. Subbase type— Dense-graded aggregate. Open-graded aggregate. Asphalt treated. Permeable asphalt treated. Cement treated. Permeable cement treated. Lime stabilized. Subsurface drainage. A qualification of how distresses are associated with design features should be performed to identify whether they are unique to a feature or whether they are manifested as a result of other distresses that appear concurrently. Distresses should be characterized quantitatively as phenomena of their physical environment (e.g., environment, wheel load, combination, or other). Interdependencies of distress, feature, and load environment should be identified. A second phase of these analyses should include the quantification of the associations of distresses with design features. Using the relationships addressed above, determine these associations using a probabilistic approach. For example, determine the probability of having a distress manifested in the presence of either a single design feature or a combination of features throughout its appropriate loading sequence. RESEARCH OBJECTIVES AND TASKS Objectives: Determine how distresses are associated with design features for rigid concrete pavements. Determine the interaction of distress, design features, and load environment(s) using a probabilistic approach. Tasks: to be determined. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: $300,000 Research Period: 24 months URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION A successful outcome of this project will allow pavement designers to make better-informed decisions on when or whether to use specific design features such as type and location of drainage systems, treated or untreated subbases, and relative thickness of subbase and slab. When coupled with the results of NCHRP 20-50(10/16), The Influence of Design and Construction Features on the Response and Performance of New Flexible and Rigid Pavements (Objective 7A), the results will also strengthen pavement management by relating changes in pavement response to the onset and progress of pavement distress in light of specific design features. The relationships to be considered in this study are those that administrators from highway agencies and other governmental entities have emphasized as being the greatest need from LTPP studies. Historical LTPP documents suggest that users and supporters of LTPP data are awaiting the results of these analyses. Publications and electronic media that make trends and trend analysis available to the users have a very high probability for widespread use. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This project will use results of an FHWA project on estimation of traffic axle load spectra that is scheduled for completion in late 2001. As described above, the project is related to the NCHRP project on pavement response as a function of design features. This project is a necessary precursor to the guidelines for selecting pavement design features. This project is linked strongly to the research results identified in Problem Statement 5A1 of the LTPP Plan, Evaluation of Load-Response Models (Axle Load and Environment). The analyses returned in this study will be an integral part of both the determination of cause of distress and the formulation of performance prediction models. Guidelines for the Selection of Pavement Design Features PROBLEM NUMBER: 7C1 RESEARCH PROBLEM STATEMENT A number of LTPP data analysis projects address the need for information on the impact of design features on pavement response and performance. A "capstone" project is needed to assemble the findings of those projects in a form that is readily implemented by practicing pavement engineers. RESEARCH OBJECTIVES AND TASKS Objective: To review the findings of all pertinent LTPP data analysis and related pavement performance research, and develop comprehensive guidelines for the selection of pavement design features. Tasks: to be determined. ESTIMATE OF PROBLEM FUNDING AND RESEARCH PERIOD Recommended Funding: to be determined. Research Period: to be determined. URGENCY, PAYOFF POTENTIAL, AND IMPLEMENTATION To be determined. RELATIONSHIP TO OTHER PROPOSED LTPP ANALYSIS PROJECTS This problem should not be pursued until AFTER the following projects/problems are completed: NCHRP 1-34D, Effects of Subsurface Drainage on Performance of Asphalt and Concrete Pavements: Further Evaluation and Analysis of LTPP SPS-1 and SPS-2 Field Sections (Objective 7B). Back to Analysis PDF files can be viewed with the Acrobat® Reader®	More Information Completed/Active Projects Expanded Strategic Plan in HTML NCHRP Projects Preliminary Analysis Project Statements Strategic Plan in PDF Events View all Upcoming Pavements Events Contact Customer Service 202-493-3035 E-mail Customer
	This page last modified on 12/06/07