STRUCTURAL FACTORS FOR FLEXIBLE PAVEMENTS--INITIAL EVALUATION OF THE SPS-1 EXPERIMENT

The SPS-1 experiment entitled "Strategic Study of Structural Factors for Flexible Pavements" is one of the key experiments of the Long-Term Pavement Performance (LTPP) program. The objective of this experiment is to determine the relative influence and long-term effectiveness of hot mix asphalt (HMA) design features (including the surface and base thickness, base type, and drainage condition) and site conditions (traffic, subgrade type, and climatic factors) on performance. This report documents the first comprehensive review and evaluation of the SPS-1 experiment. Eighteen SPS-1 projects have been constructed and each site includes 12 core test sections and some sites also include supplemental sections. A total of 248 test sections are included in the SPS-1 experiment. The data for the SPS-1 experiment are fairly complete with two exceptions: the traffic and materials test data. However, a significant amount of some types of data is still missing, especially the distress data. These data deficiencies need to be addressed before a comprehensive analysis of the SPS-1 experiment is conducted. The majority of the SPS-1 data that has been collected is at level E. Required experimental design factors were compared with the actual constructed values. A large majority of SPS-1 sections follow the experimental design and can be characterized as good to excellent. Two projects are relatively new, and the data processing and materials testing are currently underway. The evaluation and detailed review have highlighted several significant problems that will clearly limit the results that can be obtained from the SPS-1 experiment. Specifically, these include the missing traffic and materials test data. These data must be collected in order for the SPS-1 experiment to meet the expectations for calibrating and validating mechanistic models. The performance trends and effects of several design features and site conditions were noted and documented.