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This report is an archived publication and may contain dated technical, contact, and link information
Publication Number: FHWA-HRT-01-167
Date: April 2005

Structural Factors of Jointed Plain Concrete Pavements: SPS-2—Initial Evaluation and Analysis

Chapter 1. Introduction

The Specific Pavement Studies 2 (SPS-2) project, titled Strategic Study of Structural Factors for Jointed Plain Concrete Pavements, was designed as a controlled field experiment that focuses on the study of specific design features (structural factors) for doweled jointed plain concrete pavements (JPCP). It is expected that the successful completion of this experiment will lead to improvements in design procedures and standards for construction of rigid pavements. These improvements will contribute to achieving the overall goal of the Long-Term Pavement Performance (LTPP) program-increased pavement life and better utilization of resources.

This goal is expected to be achieved through investigation of the effects of the specific experimental design features and site conditions (subgrade soil, traffic, and climate) and their interactions on pavement performance. That investigation will make possible the evaluation of existing design methods and performance equations, as well as the development of new and improved design equations and calibration of mechanistic models (including the 2002 Design Guide).


The SPS-2 experimental plans were originally designed to incorporate project sites in all four LTPP climatic regions (dry freeze, wet freeze, dry no-freeze, wet no-freeze) and on both fine-grained and coarse-grained subgrades. This requirement makes it possible to cover a large inference space of the continental United States. A major effort was made by the Strategic Highway Research Program (SHRP), State highway agencies (SHAs), and the Federal Highway Administration (FHWA) to identify appropriate SPS-2 sites and to construct all the sections according to their original experimental design. A wide range of specific data was collected during construction. Extensive field monitoring data (traffic, profile, cracking) have been collected from these sections over time.

The original expectations for the LTPP program are summarized in the SHRP-P-395 report.(1) Originally, the following objectives were established:

  • Evaluation of existing design methods.
  • Development of improved strategies and design procedures for the rehabilitation of existing pavements.
  • Development of improved design equations for new and reconstructed pavements.
  • Determination of the effects on pavement distress and performance of loading, environment, materials properties and variability, construction quality, and maintenance levels.
  • Determination of specific design procedures to improve pavement performance.
  • Establishment of a database to support these objectives and future needs.

The designs for various LTPP experiments were developed with a clear relationship to these objectives. The following products were identified for the LTPP program:

  1. General Products: Evaluation of existing design methods and performance equations, new and improved design equations, and calibration of mechanistic models.
  2. Specific Products: The effects of the specific experimental design features (i.e., permeable drainage layers, widened slabs, asphalt concrete (AC) overlay thickness, pre-overlay repair, and many others) and site conditions (e.g., subgrade soil, traffic, climate, and their interactions).
  3. Other Products: Test methods developed specifically for SPS test sections, correlations between material properties determined by different methods, study of other features and materials, and technology transfer.

The following objectives of the SPS-1 (new flexible pavement) and SPS-2 (new rigid pavement) experiments are stated in the same report:

  • "The SPS will develop a comprehensive database with information on construction, materials, traffic, environment, performance, and other features pertaining to the test sections."
  • "The primary objective of the experiments on structural factors for flexible and rigid pavements is to more precisely determine the relative influence and long-term effectiveness of the strategic factors that influence the performance of pavements."

As the SPS experiments have been constructed and monitored over time, many concerns have been expressed regarding the ability of those efforts to satisfactorily meet the stated expectations. These concerns include the following:

  • Lack of more detailed expectations and objectives from each of these SPS experiments.
  • The quality and completeness of available data now and in the future.
  • Deviations in the design and construction features of in-place test sections (e.g., layers built to a different thickness or lack of compaction of the subgrade).
  • Deficiencies in construction, materials, climate, traffic, and performance data in relation to current and future analysis needs.

The availability of reliable traffic and materials data is perhaps the major concern for the SPS experiments, and efforts are underway to resolve these concerns.

It is known that some of SPS project sites were not constructed in some climatic areas because of lack of interest by the SHAs or lack of suitable sites, leaving a portion of the desired inference space with no performance data. It is also known that some of the SPS project sites were not constructed in complete conformity with the original experimental plans. Despite best efforts, the inventory and monitoring data collected from these sections during construction and for several years afterward may be deficient in some areas.

The full extent of deviation, and the potential impact of that deviation, have not yet been fully evaluated for most of the SPS experiments. Thus, this study was initiated to conduct a comprehensive review of all SPS-2 experimental sites. This review compares the experiment sites as they exist today with the original expectations and, in addition, compares these projects as they exist today with any new expectations for the 21st century. For example, there is now a greater emphasis on mechanistic-based design. This review provides a sound basis for the following:

  • Planning remedial actions that may be warranted due to various deficiencies in construction or data collection.
  • Decisions regarding future monitoring and data collection.
  • Planning future analysis of the collected data.

Issues of experimental design (e.g., existence of planned SPS projects), construction quality, data quality, and data completeness (with respect to both current data collection guidelines and anticipated pavement engineering needs) need to be addressed.

The SPS-2 projects were constructed between 1992 and 1997 (with one site completed in 2000), indicating that they are fairly young and may not yet directly support analysis activities to improve our knowledge in many of the above-listed areas. However, a few of the weaker SPS-2 sections have exhibited distress; thus, it may now be possible to make some preliminary evaluations. However, no in-depth assessment has been undertaken to date to determine the extent to which these two experiments will provide the necessary data to ensure that the broader expectations are attained.

This evaluation of SPS-2 is being conducted at the same time, and in coordination with, evaluation of the SPS-1 (new flexible pavement), SPS-5 (rehabilitated flexible pavement), and SPS-6 (rehabilitated rigid pavement) projects.

Study Objectives

This review concentrates on the core experimental sections that were included in the experimental design for SPS-2 projects. In addition, the SHAs often added supplementary sections to each SPS project that do not fit any formal controlled experimental plan. The value of these sections was also evaluated.

The objectives of this study are as follows:

  1. Identify specific objectives and expectations that should be pursued for the SPS-2 experiment, given the original expectations and future needs. Consider the expectations at the local SHA level, the regional level, and the national level as appropriate.
  2. Evaluate the set of core and supplemental test sections constructed in the SPS-2 experiment in relation to their ability to support the objectives and characterize the overall health and analytical potential of each SPS experiment. Identify areas of strength and weakness, and recommend corrective measures, as appropriate, to strengthen the SPS-2 experiment to accomplish its objectives. Develop analysis plans for both the short term and the long term.
  3. Identify confounding factors introduced into each SPS experiment by virtue of construction deviations or other factors not accounted for in the original experimental design.
  4. Evaluate the quality and completeness (in relation to current data collection requirements) of the SPS construction data. Provide recommendations for the resolution or correction of data that are anomalous or of inadequate quality.
  5. Evaluate the adequacy of existing data and current data collection requirements in relation to anticipated analytical needs. Identify areas where current requirements are excessive or deficient, and provide recommendations where adjustments (in quantity, quality, frequency, or data type) are warranted.
  6. Consider both short-term and long-term timeframes in the evaluation and preparation of data analysis recommendations.
  7. Evaluate the opportunities for local, regional, or national analysis of the core and supplemental sections.

Report Organization

Chapter 2 focuses on the original SPS-2 experimental design and compares this with the SPS-2 projects actually constructed. Chapter 3 reviews the SPS-2 experiment data availability and completeness. This includes a detailed discussion of the quantity and percentage of level E data available in the Information Management System (IMS) database. Chapter 4 presents a comparison of the designed versus constructed section parameters. A comprehensive status assessment of each of the SPS-2 experimental projects is provided in chapter 5. Initial evaluations of the key performance trends are discussed in chapter 6. Finally, chapter 7 provides a summary, conclusions, and recommendations.

Appendix A presents a summary of the SPS-2 project nomination and construction guidelines. SPS-2 project construction and deviation reports are summarized in appendix B.

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