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11 CHAPTER 1 - INTRODUCTION 1.1 INTRODUCTION The Long Term Pavement Performance (LTPP) Specific Pavement Studies (SPS) 1 and 2 are the experiments designed to provide information on the relative merits of different design features in newly constructed pavements for achieving different levels of performance under heavy traffic. Typical features include HMA surface layer and PCC slab thickness, base type and thickness, drainage (presence or absence thereof), PCC flexural strength, etc. In addition to this, instrumented sections were included in the SPS monitoring sites located in Ohio (SPS-1 and SPS-2) and North Carolina (SPS-2). The effects of environment in the absence of heavy traffic are studied through the SPS-8 experiment. For specific site conditions (e.g., traffic level, climatic conditions, and subgrade type), the response and performance of flexible and rigid pavements will depend not only on pavement layer thicknesses and material properties, but also on other design and construction features (e.g., presence of in-pavement drainage, base type and thickness, etc.). Recent research based on limited analyses has documented the effects of these features on pavement response (as measured by deflection and strain) and performance (as measured by type and extent of distress or smoothness) using very limited data. The data available from the LTPP studies, including instrumented SPS-1 and -2 test sections in Ohio and North Carolina, are expected to provide the information needed for a more rigorous analysis to enhance understanding of the effects of these features on pavement response and performance and to develop well-supported conclusions regarding their influence. There is therefore a need to determine the effects of design and construction features on pavement performance and response, and to establish their relative importance. This research should provide guidance for assessing the relative importance of design and construction features for different pavement types, preliminary information on the relationship between pavement response and performance, and recommendations for improving data collection activities. The methodology that was employed for this research could be applicable for any in-service pavement data and thus the methodology presented
12 here will help pavement engineers perform more appropriate statistical analyses and obtain more meaningful results. 1.2 PROJECT OBJECTIVES The objectives of this research are (1) to determine, for specific site conditions, the effects of design and construction features on pavement response and (2) to determine the contributions of design and construction features to achieving different levels of performance. Also, it is expected that the research will provide information on the apparent relationship between pavement response and performance. The research is limited to new (i.e., non-rehabilitated) flexible and rigid pavements. The research is based on the data available from the LTPP experiments SPS-1 (strategic study of structural factors for flexible pavements), SPS-2 (strategic study of structural factors for rigid pavements) and SPS-8 (a study of environmental factors in absence of heavy loads). The analysis is limited to using the data available in the LTPP National Information Management System (NIMS) database classified as "Level E" (DataPave) and data available from LTPP instrumented test sections. 1.3 SCOPE OF STUDY The scope of the study included the review and analysis of LTPP data (DataPave) pertaining to the SPS-1, SPS-2 and SPS-8 experiments. All relevant data for these experiments were obtained and reviewed from Release 17.0 (January 2004) of the NIMS database. After the data were obtained, a relational database was prepared for analyses of the study. Based on the availability of the data and the extent (and occurrence) of distresses, appropriate analyses (site-level and overall analyses) were conducted to fulfill the objectives of the study. At the site-level analysis each site was considered separately and the consistency of the effects across the sites was studied. The overall analyses were conducted, using the wealth of data from all the experiment sections in order to draw broad conclusions. Attempts were also made to verify apparent relationships between response (Falling Weight Deflectometer data and Dynamic Load Response data) and performance of the test sections in the SPS-1 and SPS-2 experiments. Based on all analyses (site-level and overall), the effects of design and construction features on pavement performance and response were studied. Finally, recommendations for future research and data collection are given.
13 1.4 REPORT ORGANIZATION The report is divided into eight chapters including this introductory chapter. A description of the experiment designs and the current status of SPS-1, SPS-2 and SPS-8 experiments are presented in Chapter 2. A summary of data availability and extent/ occurrence of distresses are presented for the three experiments in Chapter 3. Based on the extent/occurrence of distresses, different methods of analysis were employed. A brief description of each of these analytical methods is given in Chapter 4. Chapters 5, 6 and 7 are summaries of results from all analyses conducted on SPS-1, SPS-2 and SPS-8 data, respectively. A synopsis of the salient findings from all the analyses, for each experiment, is presented in Chapter 8. Finally, based on the experience with LTPP data gained from this research, recommendations for future data collection and research are presented in Chapter 8.
