The NCAT Pavement Test Track was originally constructed as a result of interest and support from state Departments of Transportation (DOTs) who shared a concern for reducing and predicting distresses in their flexible pavements. The cost for other states to sponsor the construction, testing, trucking and evaluation of the original experimental surface mixes was greatly reduced by a commitment from the Alabama Department of Transportation (ALDOT) to fund the overall construction of the facility up to the top of the supporting pavement structure. The inaugural track was completed in the summer of 2000 and subjected to 10 million ESALs of heavy truck traffic through December of 2002. Built as a perpetual pavement, the first cycle of testing was a study of surface mix performance for forty-six 200 ft test sections. The facility was rebuilt in the summer of 2003 and loaded with another 10 million ESALs, this time with a combination of mill/inlay surface mixes and variable thickness structural sections. Based on these experiences, the 2006 track will be a combination of more varied thickness structural sections and mill/inlay surface mixes. Utilization of as many sections as possible for structural purposes would facilitate the implementation of mechanistic-empirical (M-E) methods for structural pavement design. For example, the development of the new Recommended Guide for Mechanistic-Empirical Design of Pavements represents a significant change and advancement over existing design methodologies. Historically, the structural design of asphalt pavements has been largely empirical based upon vehicle designs, axle loads, and material properties. The new design guide, however, will rely heavily on principles of engineering mechanics to produce thickness designs that control specific modes of pavement distress. Before this new methodology gains wide acceptance or use, it must be validated and calibrated to ensure that it provides adequate design guidance using modern methods and materials under traffic by actual design vehicles. Calibration of the distress models that could eliminate only a 10 percent margin of error in excess design thickness would generate an annual taxpayer savings nationwide of as much as one billion dollars. To this end, there is a need for a full-scale structural experiment to validate the methodology. The existing infrastructure available at the NCAT Pavement Test Track presents a unique opportunity to accomplish this objective. By constructing an array of sections on the 2006 track with varying structural designs and material types, a practical study can be completed within 3 years that will make widespread, cost-effective adoption of the new Guide possible. Additionally, a comprehensive structural experiment will build upon the experiences of the 2003 track in which all 8 sections exhibited varying amounts and types of distress.

The primary objectives of the pooled fund project described herein will be: 1. Constructing 200 ft test sections on the existing 1.7 mile NCAT test oval that are representative of in-service roadways on the open transportation infrastructure; 2. Applying a design lifetime of truck traffic in the 2 years following construction; 3. Assessing/comparing the functional and structural field performance of trafficked sections on a regular basis via surface and subsurface measures; 4. Validating the M-E approach to pavement analysis and design using both surface and subsurface measures; 5. Calibrating new and existing M-E approaches to pavement analysis and design using pavement surface condition, pavement load response, precise traffic and environmental logging, and cumulative damage; 6. Correlating field results with laboratory data; and 7. Answering practical questions posed by research sponsors. For example, can an innovative mix design utilized in one state be implemented in another sponsor¿s practice using locally available aggregates? Will a specific material source provide for a safe roadway surface if adopted for widespread use? If not, what maximum percentage will work?

The scope of work for the pooled fund project will include: 1. Hauling materials to the project from offsite locations. Material donations are typically secured by state sponsors, while reasonable hauling expenses are handled by the pooled fund; 2. Rebuilding sections in accordance with sponsors¿ directives via a competitively bid contract administered by ALDOT under the direction and oversight of NCAT; 3. Installing both environmental (i.e., multi-depth pavement temperature probes) and response instrumentation (i.e., high speed stress and strain gages) in new experimental sections; 4. Operating a 5-truck fleet for approximately 16 hours a day in order to apply a design lifetime of truck traffic in the 2 years following construction. Actual human drivers pilot the vehicles in order to best induce representative vehicle wander; 5. Measuring field performance each week when the fleet is parked to fully document the development of densification, rutting and cracking as a function of traffic and temperature. High-speed pavement response will also be measured on a weekly basis. Pavement deflection and surface friction will be measured on a monthly basis; 6. Conducting laboratory testing to quantify basic material and mix performance properties, which will serve as the basis of performance model development; and 7. Comparing predicted and measured pavement response as well as predicted and measured cumulative pavement damage in order to validate then calibrate prevailing M-E methodologies.

Each state participating in the study is asked to contribute funding as a function of the scope of their selected research. For example, the cost to continue traffic on existing mix performance sections is $50,000 per section per year for 3 years. The cost to mill and inlay new mix performance sections on top of the existing perpetual foundation is $100,000 per section per year for 3 years. The cost to participate in the structural experiment is $150,000 per section per year for 3 years. Funding requirements are based on reasonable assumptions; however, if the cost for construction and/or the cost to operate the fleet are significantly impacted by diesel fuel prices a proportionate amount of additional funding may be required. Please visit the project web at www.pavetrack.com for additional information. Subjects: Accelerated Performance Testing and Pavement and M-E Design and Validation