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1 SUMMARY Refining the Simple Performance Tester for Use in Routine Practice In Phases I and II of NCHRP Project 9-29, a detailed purchase specification for the Simple Performance Test System (SPT) was developed and two first article devices were procured and evaluated. This evaluation concluded that the SPT is a reasonably priced, user-friendly device for testing stiffness and permanent deformation properties of asphalt concrete. Addi- tional 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 directed 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 modulus master curve testing capability. 3. Development of equipment for rapid preparation of test specimens for the SPT. 4. Ruggedness testing for the dynamic modulus and flow number tests conducted in the SPT. The ruggedness experiments were performed in Phase V of the project. This report doc- uments the work completed in Phase IV. During Phase IV, a methodology was developed to construct dynamic modulus master curves for pavement structural design using an abbreviated testing protocol. With this pro- tocol, it is not necessary to perform dynamic modulus testing at the lowest temperature included in AASHTO TP62. Eliminating the low temperature testing offers three advantages. First, the cost of environment control capabilities is substantially less. Second, smaller, less expensive actuators can be used since the load required for dynamic modulus testing depends on the stiffness of the material that increases with decreasing temperature. Third, testing below 32°F is difficult and more variable due to potential icing of the instrumentation. Using the abbreviated protocol and the SPT, it is possible for highway agencies to routinely collect dynamic modulus data for the Mechanistic-Empirical Pavement Design Guide (MEPDG) and other applications. A recommended standard practice was developed to implement the abbreviated dynamic modulus protocol. This standard practice provides recommended testing temperatures and frequencies. It also describes how to fit the dynamic modulus master curve to the measured data and how to compute input data for Level 1 analysis in the MEPDG. The equipment specification for the Simple Performance Test System was modified to specify a device capable of performing the three simple performance tests and developing dynamic modulus master curves using the abbreviated testing protocol. The first article
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2 SPTs purchased in Phase II of the project were upgraded to meet the revised specification. Two new devices meeting the revised specification were purchased in Phase IV of the proj- ect. SPTs meeting the revised specification currently are available from three sources: Interlaken Technology Corporation, IPC Global, and Medical Device Testing Systems. The three devices are very similar. All are relatively small, bottom-loading, servo-hydraulic machines with automated testing chambers that serve as a confining pressure cell and tem- perature control chamber. The primary differences are in the hardware and software used for temperature control, the user friendliness of the equipment, and the operational details of the control software. Test specimen preparation for the SPT is a multi-step process. A recommended standard practice for SPT specimen fabrication was prepared. This standard practice addresses each step of the fabrication process in detail, and includes two important appendices that provide additional guidance for preparing SPT specimens. The first is a procedure for obtaining the target air void content for specimens from mixtures the technician is not familiar with. The second appendix provides a method for evaluating the uniformity of air void contents within SPT test specimens. In evaluating the specimen preparation process, it was determined that an automated sys- tem for coring and sawing the specimens would be beneficial to the future implementation of the SPT. A prototype automated coring and sawing system called FlexPrepTM was devel- oped by Shedworks, Inc. to meet specifications developed in NCHRP 9-29. The development of this equipment proved to be more difficult than the SPT systems, requiring approximately five years to complete. The machine is capable of preparing SPT specimens in less than 15 minutes with little technician intervention. While the FlexPrepTM is a promising prototype, additional development work must be completed before production models of the design can be made available.