Supporting Materials for NCHRP Report 626 (2009)

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NCHRP Project 10-65—Volume 2: Research Report June 2008 Part I—Introduction Final Report         PART I—INTRODUCTION    29

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NCHRP Project 10-65—Volume 2: Research Report June 2008 Part I—Introduction Final Report CHAPTER 1 INTRODUCTION 1.1 Background Good materials and construction practices are important to producing high-quality, long-life pavements. QA programs provide the owner and contractor a means to ensure that the desired results are obtained—that the final product meets with specifications and design requirements. Traditional flexible pavement construction QC/QA procedures include a variety of laboratory and field test methods that measure volumetric and surface properties of pavement materials. The test methods to measure the volumetric properties have changed little in the past couple of decades. Most QA test methods rely on nuclear density and other volumetric measurements. Although traditional QA tests for bound and unbound materials have been used successfully in the past, these tests do have some major limitations: • The traditional test methods are time-intensive, and more importantly, lack a sampling frequency that is adequate for highly variable materials that are used in pavement construction, such as soils and unbound aggregate base materials. In general, the required sampling and testing frequency for acceptance was found to be inadequate in some of the earlier work completed for the FHWA based on pavement performance predictions (Von Quintus et al., 1985). • Many of the traditional QA test methods produce indirect measures of pavement quality. In other words, the values are not used in performance prediction equations. For example, unbound material densities only provide a gross estimate of the modulus and strength of the in-place material. This limitation is a distinct disadvantage in trying to develop performance-related specifications (PRS) or in applying these tests to warranty projects. • The density and fluids content of an unbound or bound material are not particularly relevant by themselves, but only as they relate to the maximum dry unit weight or maximum density of the material. NDT has been used in numerous industries involving the evaluation, inspection, and quality control of materials or constructed facilities. Historically, NDT has not been used in the pavements area as extensively as in other industries. Within the past decade, however, the pavement industry has seen a significant increase in the development and application of NDT technology in the control and acceptance of pavement materials. Nondestructive testing and evaluation of construction quality offers an excellent, high production method of determining the structural and volumetric properties of pavement layers that can be tied directly back to the same properties that are required for both mixture 31

NCHRP Project 10-65—Volume 2: Research Report June 2008 Part I—Introduction Final Report and structural design. This direct relationship to the mixture and structural design methods is important when developing and implementing PRS. The MEPDG developed under NCHRP Project 1-37A and 1-40D as well as the simple performance tests developed under NCHRP Project 9-19 in support of the Superpave volumetric mixture design procedure use modulus and other fundamental engineering properties for characterizing the materials (Applied Research Associates, Inc. [ARA], 2004; 2006, Witczak et al., 2002). Thus, it would be highly advantageous that QA programs use the same tests for estimating construction quality. Many of the NDT technologies (such as seismic test methods, GPR, FWD, and DCP) have been used to evaluate pavement construction. However, there is a need to more clearly assess the ability of different NDT technologies to evaluate the quality of pavement materials and layers during construction. This project is to identify NDT technologies that have immediate application for routine, practical QA operations to assist agency and contractor personnel in judging the quality of the individual pavement layers and overall pavement structure. 1.2 Definition of Highway Quality Assurance Terms The Transportation Research Board (TRB) released a circular (TRB, 2005) containing a glossary of highway quality assurance terms to provide a uniform understanding of technical terms that have specific meanings in the highway engineering field. The various terms are introduced through definitions cited from the reference and reflect their usage throughout this document. QA: All those planned and systematic actions necessary to provide confidence that a product or facility will perform satisfactorily in service. QA addresses the overall problem of obtaining the quality of a service, product, or facility in the most efficient, economical, and satisfactory manner possible. Within this broad context, QA involves continued evaluation of the activities of planning, design, development of plans and specifications, advertising and awarding of contracts, construction, and maintenance, and the interactions of these activities. In summary, QA ensures that the quality of the finished product meets specifications, and is the responsibility of the highway agency. QA process comprises of quality control (QC), acceptance, inspection, and independent assurance (IA). QC: QC is also called process control and includes those QA actions and considerations necessary to assess and adjust production and construction processes so as to control the level of quality being produced in the end product. QC is motivated by QA and acceptance procedures, and typically is the responsibility of the contractor or producer. Acceptance: The process of deciding, through inspection, whether to accept or reject a product, including what pay factor to apply. Where contractor test results are used in the agency’s acceptance decision, the acceptance process includes contractor testing, agency verification, and possible dispute resolution. 32

NCHRP Project 10-65—Volume 2: Research Report June 2008 Part I—Introduction Final Report Quality characteristic: That characteristic of a unit or product that is actually measured to determine conformance with a given requirement. When the quality characteristic is measured for acceptance purposes, it is an acceptance quality characteristic (AQC).” Inspection: The act of examining, measuring, or testing to determine the degree of compliance with requirements. Independent Assurance: A management tool that requires a third party, not directly responsible for process control or acceptance, to provide an independent assessment of the product or the reliability of test results, or both, obtained from process control and acceptance. The results of independent assurance tests are not to be used as a basis of product acceptance. 1.3 Research Problem Statement Test methods used for in-place QC/QA of individual flexible pavement layers and of new and rehabilitated flexible pavement systems have changed little in past decades. Such operations typically rely on nuclear density measurements or the results of testing conducted on pavement cores. Roughness measurements often are used to confirm that the newly constructed pavement has adequate initial smoothness. More recently, NDT methods, including lasers, ground-penetrating radar, falling weight deflectometers, penetrometers, and infrared and seismic technologies, have been significantly improved and have shown potential for use in QC/QA of flexible pavement construction. Furthermore, the MEPDG uses layer stiffness or modulus as a key material property. This should lead to increased measurement of layer moduli by owner agencies, an activity that currently is not a typical component in the acceptance of a completed project. This research study investigated the application of existing NDT technologies for measuring the quality of flexible pavement materials and construction workmanship. Promising technologies were assessed on actual field projects for their ability to evaluate the quality of pavement layers during or immediately after placement or to accept the entire pavement at its completion. The study focused on measuring quality characteristics that affect pavement performance and life cycle costs. The results from this project identified NDT technologies ready and appropriate for implementation in routine, practical QC/QA operations. 1.4 Research Objectives As stated in the research project statement, there were two objectives of this research: 1. Conduct a field evaluation of selected NDT technologies to determine their effectiveness and practicality for QC/QA of flexible pavement construction. 2. Recommend appropriate test protocols, based on the field evaluation results. Effectiveness and practicality are key words in the first objective. The field experimental plan was developed to determine the effectiveness and practicality of different NDT 33

NCHRP Project 10-65—Volume 2: Research Report June 2008 Part I—Introduction Final Report technologies for use in QA programs. Both terms are defined below, as used in NCHRP Project 10-65: • Effectiveness of NDT Technology – Ability or capability of the technology and device to detect changes in unbound materials or HMA mixtures that affect the performance and design life of flexible pavements and HMA overlays. • Practicality of NDT Technology – Capability of the technology and device to collect and interpret data on a real-time basis to assist project construction personnel (quality control and acceptance) in making accurate decisions in controlling and accepting the final product. 1.5 Project Organization To achieve the research objective, NCHRP Project 10-65 was subdivided into two phases. Phase 1 identified existing NDT technologies with potential for in-place testing of individual flexible pavement layers and of the entire flexible pavement structure at its completion. The flexible pavement layers include HMA, unbound aggregate base material and subgrade soil during new construction, and HMA overlays during rehabilitation. Phase 1 consisted of three tasks, which are listed below: 1. Summarize State of Knowledge of NDT Technologies for Application to Quality Assurance 2. Design Field Experiments to Evaluate NDT Technologies 3. Prepare and Submit Interim Report Phase 2 was a field evaluation of those NDT technologies judged ready and appropriate for implementation in flexible pavement construction. It also consisted of three tasks as a follow on to phase 1 study, which are listed below: 1. Conduct Field Experiment 2. Conduct Analyses for NDT Technologies from Field Experiment 3. Prepare and Submit Draft Final and Final Reports Phase 2 was further subdivided into two parts—Parts A and B. Part A was to confirm the applicability and use of different NDT technologies identified from Phase 1 that were judged to be ready and appropriate for implementation into routine, practical, and effective QA programs for measuring the quality of flexible pavement construction and HMA overlays. Part A of the field evaluation also included selecting those NDT technologies and devices that could consistently and accurately identify construction anomalies that were built into the pavement structure or HMA overlay. Part B of Phase 2 used those NDT technologies and devices selected from Part A and refined the test protocols and data interpretation procedures for judging the quality of flexible pavement construction. Part B also included identifying limitations and boundary conditions of the selected NDT test methods. 34

NCHRP Project 10-65—Volume 2: Research Report June 2008 Part I—Introduction Final Report 35 1.6 Scope of Project Document and Research Report The final document for NCHRP Project 10-65 has been divided into three major volumes or reports. Volume 1 is the procedural manual for implementing the NDT methods for QA application, Volume 2 (included herein) is the standard NCHRP Research Report, and Volume 3 includes the appendices for the other two parts. Volume 3 also includes the data generated from this project. This research report in Volume 2 is sectioned into four major parts, including the introduction (Part I) to the project. Part II is a summary of the research findings, Part III presents the interpretation and appraisal of the test results, and Part IV summarizes the research conclusions and recommendations. Part IV is followed by the references to the research report. The appendices, included in Volume 3, present important information relevant to this study but excluded from the main body of the research report: • Appendix A lists the topics and questions used in collecting information from agencies on their QA procedures, and application of NDT technologies and devices. • Appendix B provides a description and summary of the projects that were included in the field evaluation of selected NDT technologies and devices. • Appendix C includes a summary of the data collected and measured during the project. • Appendix D contains the recommended NDT test methods in AASHTO standard format.

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