The majority of state highway agencies have implemented the Superpave volumetric mix design process created during the Strategic Highway Research Program (SHRP) as part of their system for designing Hot Mix Asphalt (HMA) mixtures. However, at the conclusion of SHRP no simple test was available that provides information on the probable performance of asphalt mixtures designed using Superpave volumetric mix design. State highway agencies, as well as industry, have expressed the need for simple load tests to use during the mix design process and in field quality control to evaluate permanent deformation and fatigue cracking of Superpave-designed HMA. The Federal Highway Administration (FHWA) and the National Cooperative Highway Research Program (NCHRP) sponsor research to develop and validate advanced materials characterization models and related laboratory testing procedures for HMA. NCHRP Project 9-19 Superpave Support and Performance Models Management included the development of simple performance tests for permanent deformation and fatigue cracking to be incorporated in the volumetric mixture design process. The following three tests were recommended to evaluate permanent deformation of asphalt mixtures: dynamic modulus (E*) using the triaxial dynamic modulus test, flow time (Ft) using the triaxial static creep test, and flow number (Fn) using the triaxial repeated load test. The dynamic modulus at intermediate temperatures is recommended for fatigue cracking and a separate test, the indirect tensile creep test, is recommended for low-temperature cracking. As part of NCHRP Project 9-29 Simple Performance Tester for Superpave Mix Design, a Simple Performance Tester (SPT) designed to conduct all three tests recommended by NCHRP 9-19 was procured and evaluated for use in Superpave mix design and in HMA materials characterization for structural design. NCHRP 9-29 concluded that the Simple Performance Tester (SPT) is a reasonably priced, user-friendly device for testing stiffness and permanent deformation properties of asphalt concrete, however it should be noted that the capabilities of the SPT are limited compared to the specifications of NCHRP 9-19 and standards have been revised accordingly. The performance of the SPT protocol, which includes dynamic modulus, flow number and flow time, has been evaluated in laboratory studies using Long Term Pavement Performance (LTPP) program data and in field tests using Accelerated Pavement Testing (APT) facilities. Data from all three simple performance tests have been shown to correlate well with observed rutting in field pavements (NCHRP 9-29). The next step is to get the SPT in the hands of highway agencies, train technicians to properly use the device, and evaluate the device¿s ability to assess performance of asphalt mixes designed using the Superpave volumetric mix design method.

This pooled fund study is open to any highway agency interested in using simple performance tests to aid in material characterization for design and analysis of flexible pavements. The objectives of this pooled fund study are to: (i) nationally procure the SPT for highway agencies interested in obtaining and using the SPT to characterize asphalt mixtures designed using Superpave technology; (ii) provide support in training technicians to use the SPT to perform the proposed standard practices for measuring dynamic modulus, flow number and flow time of asphalt mixtures compacted using the Superpave Gyratory Compactor (SGC); and (iii) evaluate the nation-wide implementation and use of the SPT for assessing performance of asphalt mixtures over a wide range of climatic conditions, materials, and structures.

A Technical Advisory Committee (TAC) will be established to provide oversight and guidance for the project. Each project partner may appoint a representative to serve on the TAC. In addition, technical experts in SPT development, equipment, and Superpave technology implementation will be invited to serve on the TAC. Throughout the project the TAC will oversee the implementation of the SPT and review project progress reports, annual and final reports. This will be accomplished via electronic and telephone-based communication as much as possible; however periodic meetings are required. It is anticipated that the implementation process will encompass the following tasks (for more details please see project proposal link provided below): 1. Conduct TAC workshop; 2. Solicit proposals from manufacturers of the SPT that meet all necessary requirements specified in Task 1(iii). Based on the proposals received, FHWA will procure a limited number of SPTs from multiple manufacturers; 3. Selected laboratories will participate in the development of precision and bias experiments for developing dynamic modulus curves for HMA concrete using the SPT system; 4. Procure and implement the SPT for participating agencies; 5. Develop a training course to provide highway agency personnel a better understanding of the proposed standards, procedures, and requirements associated with the SPT; 6. Conduct experiments to showcase the correlation between characterization of HMA materials using the SPT and criteria for permanent deformation evaluation. There are criteria available to evaluate permanent deformation using dynamic modulus (NCHRP 9-29) and flow number (NCHRP 9-33) results. Sub-tasks will be further defined in the work plan developed by the TAC; 7. Prepare final report(s).

Each partner is asked to contribute a minimum of $105,000 which may be transferred over a three year period. FHWA will serve as the coordinator for this pooled-fund project. FHWA will issue task order contracts to support services contractors to conduct studies and develop training course. A memorandum will be sent to the FHWA division offices to solicit federal, state, tribal, regional, and local agencies for their interest and participation in this study.