Practices for Fabricating Asphalt Specimens for Performance Testing in Laboratories (2020)

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3 Introduction This chapter introduces background information on practices related to the fabrication of asphalt-mixture specimens for performance testing. The survey and interview processes and organization of the report will also be described. Background Performance testing of asphalt mixtures is becoming more widespread for a variety of reasons and with a variety of testing devices. The tests results are sensitive to the procedures used in preparation of the specimens. Guidelines exist for conducting the tests; however, they do not all provide uniform or comprehensive direction for fabricating test specimens. Addi- tionally, many state highway agencies are relatively new to fabrication of performance test specimens and are in various stages of gaining experience. There are few detailed ruggedness studies that identify critical sources of variability with respect to specimen fabrication proce- dures. Numerous research efforts have addressed some aspects of the specimen fabrication process on performance test results, but typically only have examined one aspect of specific tests and usually as a side objective of the main study. Therefore, individual laboratories tend to follow their own procedures, or no specific procedure, where the standards are not specific. Objective of the Synthesis The objective of this synthesis was to document procedures related to laboratory fabrication of asphalt performance test specimens at state highway agencies and partner laboratories that conduct performance testing on behalf of state highway agencies. For the purpose of this synthesis, fabrication begins with a mixture and results in a prepared test specimen. Other information about specimen fabrication to be gathered included aspects such as • Purpose of the testing (e.g., mix design, quality assurance, or research); • Methodologies used by state DOTs and targeted partner asphalt testing laboratories; • Tests performed and standards or procedures used; • Equipment used (e.g., for splitting, charging mold, compaction, coring, or cutting); • Short- and long-term aging procedures; • Laboratory testing sequencing and time limitations (e.g., maximum shelf life or operational disruptions); • Rejection rate of specimens produced (after cutting and coring) that never get tested; and • Research, common issues encountered, and solutions developed. The synthesis also includes suggestions for future research, based on existing gaps identified through the literature review, surveys, and case example interviews. The synthesis provides a C H A P T E R 1

4 Practices for Fabricating Asphalt Specimens for Performance Testing in Laboratories reference to transportation agencies and other entities regarding existing practices for fabrica- tion of performance test specimens. Study Approach A multifaceted approach was taken to document the various activities that have been conducted in recent years by both agencies and partner lab entities with respect to specimen fabrication for asphalt performance testing and related procedures. There is a need to quantify these efforts and collect examples of practices that are reported to be effective to facilitate the exchange of information and to help other agencies and industry partners. The approach to this study included a literature review, a survey of U.S. state and Canadian provincial trans- portation agencies, a survey of partner laboratories that conduct performance testing for state highway agencies, and interviews with transportation agencies in states identified as having existing practices for dealing with asphalt performance testing. The following sections provide more detail on each step in the approach. Literature Review A comprehensive literature review of sources both in the United States and internationally was used to establish current practice and emerging trends related to the fabrication of performance specimens for asphalt laboratory testing. The research team consulted a number of resources, including the Transport Research International Documentation (TRID), general web searches, FHWA and DOT internal reports, journal publications, conference proceedings, transpor- tation agency specifications and standards, and resources of professional associations. Particular attention focused on summarizing practices for fabrication of asphalt specimens for performance testing in laboratories used nationally and internationally; specimen fabrication practices used by agencies, private/commercial testing laboratories, university testing labo- ratories, non-DOT agencies (e.g., federal agencies, Canadian provincial transportation agen- cies, tollways, or local agencies), or other international agencies; and research on the impacts of specimen fabrication practices on performance test results. Survey of State Highway and Provincial Transportation Agency Laboratories The primary intent of the survey was to establish the current state of the practice for state transportation agencies with respect to the use of laboratory performance tests for asphalt mixtures and whether testing is conducted in house, by partner (consultant, university, or federal agency) laboratories, or both. In addition, the survey addressed specific details associ- ated with the specimen fabrication process and collected information on the process flow of the fabrication process, along with time constraints and challenges associated with each step. Finally, the survey solicited the identities of partner lab entities engaged in the fabrication of performance test specimens, as well as knowledge gaps and ideas for future research topics. The survey consisted of 27 questions and was sent to members of the AASHTO Committee on Materials and Pavements, with a recommendation for distribution to the agency’s materials engineers to complete the survey. The agency survey was sent to contacts in each of the state DOTs, the District of Columbia, and the 11 Canadian provincial transportation agencies. Eighty percent (40/50) of all state DOTs and the District of Columbia responded to the agency survey and are included in the survey analysis. The agency survey questions are included in Appendix A and the results are in Appendix B of this report. The map in Figure 1 shows the state highway agencies in the United States that

Introduction 5 completed the agency survey, along with specific agencies that were selected to serve as case examples, to be presented in Chapter 4 of this report. Survey of Partner Laboratories The partner laboratory survey consisted of 25 questions (included in Appendix A) and was sent to contacts at laboratories that conduct performance testing for state highway agencies that were identified in the literature review or from the responses gathered as part of the agency survey. There were 29 responses that were completed and included in the survey analysis (responses are documented in Appendix C). The map in Figure 2 shows the geographic distribution of organizations that completed the survey. A list of the agencies and partner laboratories that completed the survey is included in the analysis in Appendix D. Interviews of Transportation Practitioners for Case Examples Based on the survey responses, five states were selected for additional data gathering on practices used related to the fabrication of performance test specimens for asphalt paving mixtures. Several criteria were considered in the selection of the case example agencies to be interviewed. The criteria included (1) agencies that reported they have substantially moved into the development or use of asphalt performance testing and (2) the geographical distri- bution of states, in order to reflect a national perspective and varying climatic conditions (which influences the types of pavement distresses that agencies are designing against). Created with mapchart.net © Figure 1. Location of state highway agencies completing survey and interviewed for case examples.

6 Practices for Fabricating Asphalt Specimens for Performance Testing in Laboratories At least one representative from each of the organizations was interviewed over the phone to gather their input on issues and practices in their state or province related to practices for fabricating asphalt performance test specimens. A sampling of documents obtained as examples of current practice are included in Appendix E. Organization of the Report This synthesis report is organized into five chapters. The balance of Chapter 1 presents the report’s structure and defines key terms. The report structure is summarized with brief explanations of each chapter’s content. Chapter 2 introduces the details published in the literature and in online sources related to practices for fabricating asphalt specimens for laboratory performance testing throughout the United States and internationally. There is a section that introduces performance test procedures and equipment used for asphalt mixtures and includes information on tests for various types of asphalt mixtures. A section on the specimen fabrication procedures that are used for asphalt mixtures is presented. The chapter concludes with a discussion on research that is under way that is related to the impact of specimen fabrication protocols on performance test results of asphalt mixtures. Chapter 3 provides the state of the practice reported by the state DOTs and other organiza- tions on the procedures that are used to fabricate specimens for performance testing of asphalt mixtures in the laboratory. An overview of the various procedures that are used is presented, based on the survey responses from state DOTs as well as partner laboratories. It provides the Figure 2. Location of partner labs that the completed survey. Created with mapchart.net ©

Introduction 7 state of the practice in terms of the use of asphalt laboratory performance tests and in regard to which performance tests are conducted and for what purpose [mix design approval, quality assurance (QA), research]. It also summarizes the extent to which agencies conduct testing in-house or contract with outside laboratories to conduct the testing. Specific practices used by state DOTs and other laboratories to fabricate performance test specimens are identified, along with information related to compaction, cutting and coring, age conditioning, storage time limitations, the required equipment used, and so forth. The chapter concludes with a discus- sion on rejection rates and reasons, and other challenges identified with fabricating specimens are summarized. Chapter 4 examines the specific examples of specimen fabrication practices reported in case example interviews with selected agencies. The specific examples also summarize practices with respect to sampling of material, achieving air void tolerances, and storage of material and specimens. The majority of the information presented in this chapter was collected through the detailed interviews with personnel in various agencies in each of the five states selected for further study. Chapter 5 provides a summary of the key findings and conclusions of the project, including agency use of performance testing and purpose and information on whether testing is done in-house or contracted to an outside laboratory. It also presents findings and conclusions related to procedures used for fabricating asphalt-mixture specimens for performance testing along with performance testing time and equipment availability. A discussion of challenges related to specimen fabrication, including impacts on performance test results and rejection rates, is presented. The chapter concludes by outlining apparent knowledge gaps stemming from the agency’s and partner’s laboratory surveys and case example interviews. Suggestions for future research on the impact of specimen fabrication protocols on performance test results are also presented. The documented practices are drawn from the literature review and results of the agency and partner laboratory surveys, along with case example interviews. These chapters are followed by references and five appendices. Appendix A includes a copy of the agency and partner laboratory survey questions. Appendix B and Appendix C present the agency and partner labo- ratories survey results, respectively. Appendix D includes a list of the agencies and other orga- nizations that completed the surveys. Appendix E presents links to sample documents that are examples of practices that were shared by agencies in response to the surveys and interviews. Definitions Some key terms are defined that pertain to the synthesis scope. Additional terms are defined within the context of their relevant sections. A list of abbreviations is also included in the report. Asphalt Mixtures: The term asphalt mixtures is intended to represent any dense-graded hot-mix asphalt (HMA), warm-mix asphalt (WMA), or stone-matrix asphalt (SMA) mixture that is produced at a plant or in the laboratory. This term includes mixtures that have been modified with the use of recycled materials (e.g., reclaimed asphalt pavement, recycled asphalt shingles, crumb rubber from recycled tires, and so forth). This term does not include main- tenance mixtures (e.g., cold-mix asphalt, seal coats, and the like), in-place recycled mixtures (e.g., hot-in-place recycled asphalt, cold-in-place recycled asphalt, and so forth), or specialized surface mixtures (e.g., open-graded friction courses or gap-graded thin bonded overlays). Laboratory Asphalt-Mixture Performance Tests: Laboratory asphalt-mixture performance tests are defined as any laboratory test procedure for mechanical characterization of asphalt

8 Practices for Fabricating Asphalt Specimens for Performance Testing in Laboratories mixtures to determine a fundamental engineering or empirical property (e.g., resilient modulus, creep properties, and cracking properties) that can predict pavement performance and/or appear in primary performance-prediction relationships. Examples of performance– prediction relationships include models that can be used to predict pavement stress, distress, or performance from combinations of predictors that represent traffic, environmental, road- bed, and structural conditions. Pavement performance in this definition is in the context of asphalt-mixture durability and resistance to traffic and climate-induced distresses. Specimen Fabrication for Performance Testing: Specimen fabrication for this survey is defined as the comprehensive process by which loose asphalt mixture (made in a laboratory or sampled from a plant) is made into the finalized test specimen that is ready for mechanical characterization. The steps for fabrication include, but are not limited to, reheating, compac- tion, conditioning (e.g., laboratory aging or moisture), cutting, coring, air void determination, and gluing of loading platens or gage brackets. Partner Laboratories: These are organizations that conduct asphalt-mixture performance tests for state highway agencies and include federal agency laboratories (e.g., FHWA), state- agency-affiliated research laboratories [e.g., Virginia Transportation Research Council (VTRC)] along with consultant and university laboratories.