U.S. Department of Transportation
Federal Highway Administration
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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
|This report is an archived publication and may contain dated technical, contact, and link information|
Publication Number: FHWA-RD-01-168
Date: July 2006
One objective of the Long-Term Pavement Performance (LTPP) studies is to develop improved methodologies and strategies for rehabilitating flexible pavements. Those factors that can affect the performance of overlaid flexible pavements include, as a minimum, surface preparation, overlay thickness, overlay material, environment, and condition of the original pavement. The LTPP program incorporated all of these factors into a single experiment to study the rehabilitation of flexible pavements–the Specific Pavement Studies (SPS) 5, entitled Rehabilitation of Asphalt Concrete (AC) Pavements.
This controlled field experiment focuses on the study of the specific features noted above for the rehabilitation of hot mix asphalt (HMA) flexible pavements. It is expected that the successful completion of this experiment will lead to improvements in design procedures and standards for overlaying HMA–surfaced pavements. These improvements should contribute to achieving the overall goals of the LTPP program–increased pavement life and better utilization of resources.
Investigating the effects of the specific experimental design features and site conditions (surface preparation, overlay thickness, overlay material, environment, and original pavement condition), as well as their interactions on pavement performance makes it possible to evaluate existing rehabilitation design methods and predict performance of overlaid flexible pavements. It also makes it possible to develop new and improved HMA overlay design equations and to calibrate mechanistic-empirical models.
The SPS-5 experimental plans were originally designed to incorporate project sites built in all four LTPP climatic regions on fine-grained subgrade soils. The Strategic Highway Research Program (SHRP), Federal Highway Administration (FHWA), and U.S. State and Canadian Province highway agencies made a major effort to identify appropriate SPS-5 sites and to construct all test sections according to the original experimental design.
A wide range of specific data was collected during and after construction of the HMA overlays. An effort was made to collect field data (profile, cracking, and materials data) before the construction of the HMA overlays in order to quantify the surface condition of the HMA pavement before rehabilitation.
The original expectations for the LTPP program are summarized in the SHRP-P-395 report.(1) Originally, the following objectives were established:
The experimental designs for LTPP were developed to achieve these objectives. The following products were identified for the LTPP program:
Two objectives of the SPS-5 (rehabilitated flexible pavement) and SPS-6 (rehabilitated rigid pavement) experiments are stated in the same report:
The SPS-5 experiment was designed to evaluate some more common rehabilitation techniques currently used in North America. The experimental factors include the condition of the pavement before overlay (both structurally and functionally), the loading conditions to which the test sections are exposed (both environment and traffic), and the various treatment applications. Five products are expected from the SPS-5 experiment:(2)
The SPS-5 experiment also was designed to identify trends associated with various rehabilitation methodologies on pavement performance and life expectancy. In addition, it is expected to provide data to improve and/or validate current design procedures. With these improved methodologies and procedures, highway agencies should be able to determine more appropriate strategies to rehabilitate flexible pavements. However, the ability of the SPS-5 experiment to meet these expectations has been questioned.(4, 5) Some concerns are:
The full extent of the deviations and deficiencies, and the potential impact of those deficiencies, are not yet quantified for the SPS-5 experiment. Issues of experimental design, construction quality, data quality, and data completeness (with respect to both current data-collection guidelines and anticipated pavement engineering needs) also need to be addressed.
The SPS-5 projects were constructed between 1989 and 1997. Therefore, at the time this review was performed in 1999-2000, the data were sparse in many of the above-listed areas. However, several of the SPS-5 sections had begun to exhibit distress; thus, it was possible to make preliminary evaluations.
As of 2000, the only in-depth assessment of the SPS-5 experiment was Performance of Rehabilitated Asphalt Concrete Pavements in the LTPP Experiments–Data Collected Through February 1997 (using the LTPP data public release of February 1997). That study summarized early performance trends and observations of the 17 SPS–5 projects built as of 1996.(6) The study neither focused on nor addressed the completeness of the experimental data, nor did it evaluate the adequacy of the experiment to provide data necessary to ensure that the broader expectations of this experiment could be attained. Therefore, the effort described in this report was initiated to conduct a comprehensive review of all SPS-5 experimental sites to determine the adequacy and potential of data from this experiment to satisfy future pavement engineering needs.
This review compared the experiment sites, as they existed in 1999-2000, with the original expectations and measured the projects against new expectations for the 21st century. For example, there was a greater emphasis on mechanistic-based design in 2000 than existed a decade previously. This review provides a sound basis for:
This evaluation of the SPS-5 experiment was conducted at the same time as and in cooperation with the evaluation of the SPS-1 (new flexible pavement), SPS-2 (new rigid pavement), and SPS-6 (rehabilitated rigid pavement).
The primary objective of the SPS-5 experiment on rehabilitation of flexible pavements is to determine the relative influence and long-term effectiveness of factors that influence the performance of overlaid flexible pavements. The study described in this report was to conduct a detailed review and to determine the extent to which this experiment would provide the necessary data to ensure that the objectives and expectations are attained. This review concentrated on the core experimental test sections and on the supplementary test sections that were built by the individual agencies for each project. Five specific activities were completed for this review:
Specifically, this report focused on four areas of the SPS-5 experimental data:
It should be understood that the LTPP database is dynamic– data are continually checked and entered. This review and detailed assessment of the experiment represents a "snapshot" of the database and the Level E data at a particular point in time.
The report is subdivided into six chapters including the introduction. The second chapter is an overview of the status, as of 2000, of the SPS-5 experiment in comparison to the original experiment designs. The third chapter looks at the project requirements for each SPS-5 project. The fourth chapter is an overall summary of each project detailing the construction difficulties, experimental deviations, and data completeness; in other words, it summarizes each SPS-5 project that had been built (as of 2000), notes the data that are available for each project, and identifies construction difficulties and any data deficiencies. The fifth chapter presents an analysis of the initial observations of the key distress and performance indicators completed on a project-by-project basis and across the entire experiment. Chapter six summarizes effects that data deficiencies may have on the results that can be obtained from this experiment.
More detailed information and data are provided in the appendices. Appendix A presents a summary of the construction and deviation reports, as well as other data elements that were available for each project. Appendix B presents a summary of the available construction data for each project.