National Academies Press: OpenBook

Refining the Simple Performance Tester for Use in Routine Practice (2008)

Chapter: Chapter 1 - Introduction and Research Approach

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Suggested Citation:"Chapter 1 - Introduction and Research Approach." National Academies of Sciences, Engineering, and Medicine. 2008. Refining the Simple Performance Tester for Use in Routine Practice. Washington, DC: The National Academies Press. doi: 10.17226/14158.
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Suggested Citation:"Chapter 1 - Introduction and Research Approach." National Academies of Sciences, Engineering, and Medicine. 2008. Refining the Simple Performance Tester for Use in Routine Practice. Washington, DC: The National Academies Press. doi: 10.17226/14158.
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31.1 Problem and Purpose NCHRP Project 9-19: Superpave Support and Performance Models Management recommended three candidate simple performance tests to compliment the Superpave volumetric mixture design method. These are: flow time, flow number, and dynamic modulus. The recommended tests are con- ducted in uniaxial or triaxial compression on cylindrical spec- imens that are sawed and cored from over-height gyratory compacted samples. Data from all three candidates were shown to correlate well with observed rutting in field pave- ments, and the dynamic modulus appears to have potential as a simple performance test for fatigue cracking (1). The dynamic modulus is also the primary material input for flexi- ble pavement structural design in the Mechanistic-Empirical Pavement Design Guide (MEPDG) completed in NCHRP Project 1-37A (2). The use of this test for both mixture evalu- ation and structural design offers a potential link between mixture design and structural analysis that has been an underlying goal of a substantial amount of past flexible pave- ment research. The objective of NCHRP Project 9-29 is to stimulate the development of commercial testing equipment capable of performing the NCHRP Project 9-19 performance tests. It is envisioned that this equipment will be used for two purposes: 1. As a simple performance test to compliment Superpave volumetric mixture design, and 2. For the asphalt concrete material characterization required by the MEPDG and other similar flexible pavement struc- tural design methods. In Phase I of NCHRP Project 9-29, a detailed purchase specification for the Simple Performance Test System (SPT) was developed. The SPT is capable of performing the three NCHRP Project 9-19 performance tests, and standardizes the instrumentation, data acquisition, and data analysis associated with each test. In Phase II, two First Article devices were pro- cured and evaluated. This evaluation concluded that the SPT is a reasonably priced, user-friendly device for measuring stiffness and permanent deformation properties of asphalt concrete. Additional work, however, was needed to further refine the SPT for use in routine practice. This additional work was undertaken in Phases IV and V of NCHRP Project 9-29. These phases of the project included four major activities di- rected at implementation of the SPT in routine practice: 1. Enhancement of the SPT to perform dynamic modulus master curve testing required for pavement structural design and analysis. 2. Procurement and evaluation of SPTs with dynamic mod- ulus master curve testing capability. 3. Development of equipment for rapid preparation of test specimens for the SPT. 4. Ruggedness testing for dynamic modulus and flow num- ber tests conducted in the SPT. The ruggedness experiments were performed and docu- mented in Phase V of the project. This report documents the work completed in Phase IV of the project. 1.2 Scope and Research Approach 1.2.1 Simple Performance Test System Phase IV included two major tasks aimed at continued de- velopment of the SPT. The first of these was the development of an abbreviated testing protocol for developing dynamic modulus master curves for use in routine mixture evaluation and flexible pavement design. AASHTO TP62, Determining Dynamic Modulus of Hot-Mix Asphalt Concrete Mixtures, is the recommended standard describing the testing and analysis required to develop dynamic modulus master curves for the MEPDG. This standard requires testing at five temperatures C H A P T E R 1 Introduction and Research Approach

(14, 40, 70, 100, and 130 °F) and six frequencies of loading (0.1, 0.5, 1.0, 5.0, 10, and 25 Hz). It is desirable that equipment for performing such testing be available to highway agencies at a reasonable cost, and that the test procedure be appropri- ate for agency laboratories. A recently completed FHWA pooled fund study identified several issues associated with the test protocol, and concluded that the overall time required to perform the testing must be shortened if highway agencies are going to use it for routine testing (3). The most efficient approach to reducing the time requirements for dynamic modulus master curve testing is to minimize the number of temperatures used in the testing. The current low temperature testing requirement of 14 °F significantly increases the cost of the environmental system and increases the loading capacity and cost of the testing equipment. If testing at this tempera- ture can be eliminated, the cost of the equipment, the com- plexity of the procedure, and the overall time required to develop a master curve can be significantly reduced. In Phase IV of NCHRP Project 9-29, an abbreviated testing protocol for developing dynamic modulus master curves was developed based on analysis of numerous dynamic modulus master curves produced using AASHTO TP62. Details of this analy- sis are presented in Chapter 2 and a recommended standard practice for developing dynamic modulus master curves for routine mixture evaluation and flexible pavement design is presented in Appendix A. The abbreviated testing protocol includes testing at three temperatures between 39.2 and 115 °F using four frequen- cies of loading between 0.01 and 10 Hz. The low tempera- ture required some modification of the SPT developed in Phases I and II of NCHRP Project 9-29. To minimize costs, the SPT was originally designed for testing only at room temperature and above. The modifications required for master curve testing were: (1) improved cooling capacity, (2) additional load capacity, and (3) software required mod- ification to include 0.01 Hz load control. Cost estimates from potential vendors indicated that the additional cool- ing and loading capacity would only add approximately 5 percent to the cost of the SPT. In the second task to continue the development of the SPT, the equipment specification was revised to produce a device capable of performing dynamic modulus master curves using the abbreviated protocol. This equipment also maintains the capability to perform the flow number and flow time testing. The revised equipment specification is presented in Appen- dix B. The revised equipment specification was used to upgrade the First Article devices that were purchased and evaluated in Phase II of the project and to procure and eval- uate additional production units. New equipment was procured from Industrial Process Controls, Ltd. and Medical Device Testing Services, Inc. Chapter 3 includes details of the evaluation of the First Article upgrades and the production units. 1.2.2 Simple Performance Test Specimen Fabrication System A major criticism of the NCHRP Project 9-19 performance tests is the size of the specimen used in the testing. To ensure that fundamental properties are measured, a 3.94 in. diame- ter by 5.91 in. tall test specimen must be used. These test spec- imen dimensions were determined through an extensive specimen size and geometry study conducted during NCHRP Project 9-19 (4). Test specimens are obtained by first manu- facturing gyratory specimens that are 5.91 in. diameter by 6.5 to 6.9 in. tall. The test specimen is then obtained by cutting a 3.94 in. diameter core from the middle of the gyratory sam- ple, and sawing the ends to produce a test specimen 5.91 in. tall with smooth, parallel ends. Many engineers and techni- cians consider this multi-step test specimen fabrication process a significant obstacle to implementation of the SPT in routine practice. In Phase I of NCHRP Project 9-29, workshops were held with potential users and manufacturers of the SPT. Both users and manufacturers agreed that a low-cost, automated system for test specimen fabrication would enhance the SPT. An equipment specification for such a system was developed in Phase I of the project. The primary purpose of the specification for the Simple Performance Test Specimen Fabrication System was to encourage equipment manufacturers to develop equip- ment for test specimen fabrication that speeds the process of preparing the required test specimen. The specification pro- vided tolerances for critical specimen dimensions and required that the test specimen be fabricated from an existing gyratory sample in 15 minutes or less. In Phase II of the project, Shed- works’ Inc. was awarded a contract for final design and fabri- cation of an innovative device where the gyratory specimen is gripped by a chuck similar to that used in a lathe. Automated diamond-tipped cutoff blades saw the gyratory specimen to length, and an automated diamond-core barrel then cores the test specimen from the gyratory specimen. Shedworks encountered many problems during final design and fabrication of the equipment in Phase II; therefore, deliv- ery of the first-article device was extended to Phase IV of the project. Chapter 4 presents the results of a series of specifi- cation compliance tests that were performed on the Shedworks device. Appendix C presents the equipment specification for the Simple Performance Test Specimen Fabrication System. A Recommended Standard Practice for preparing SPT specimens is included in Appendix A. This practice is a generic procedure for SPT specimen fabrication that does not require use of the Simple Performance Test Specimen Fabrication System. 4

Next: Chapter 2 - Abbreviated Dynamic Modulus Master Curve Testing »
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TRB's National Cooperative Highway Research Program (NCHRP) Report 614: Refining the Simple Performance Tester for Use in Routine Practice explores the develop of a practical, economical simple performance tester (SPT) for use in routine hot-mix asphalt (HMA) mix design and in the characterization of HMA materials for pavement structural design with the Mechanistic-Empirical Pavement Design Guide.

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