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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:
The designs for various LTPP experiments were developed with a clear relationship to these objectives. The following products were identified for the LTPP program:
The following objectives of the SPS-1 (new flexible pavement) and SPS-2 (new rigid pavement) experiments are stated in the same report:
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:
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:
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.
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:
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.