Transportation agencies traditionally design asphalt pavements for 20 or 25 years. However, innovative asphalt pavement projects such as those designed and constructed under warranty specifications or through public private partnership (P3) programs tend to demand a longer design period such as 30 or 35 years and beyond. This paper provides a case study of a P3 project. This project required a 30-year design life. In addition, this project required to be maintained at an acceptable serviceability level throughout the design life of the pavement (i.e. 30-year). Initially, the pavement structure was designed in accordance with the AASHTO 1993 Pavement Design Guide based on geotechnical and traffic information included in the preliminary pavement design report. The geotechnical information and material properties will be verified, and amended if necessary during the final design phase of this project. Based on the AASHTO 1993 pavement design method, two pavement structural design options were developed: • traditional asphalt surface constructed over granular base/subbase courses; and • full depth asphalt pavement Each design options was evaluated to assess the number of load repetitions (Equivalent Single Axle Loads – ESALs) to failure. A multi-layer elastic analysis routine was used to evaluate the stresses, strains and deflections at critical pavement locations. The pavement responses were evaluated using existing calibrated pavement performance models (transfer functions) to determine the number of load repetitions to both fatigue and rutting failures. Based on this information, the proposed pavement designs were adjusted to meet the number of load repetitions to failure; thereby resulting in a proposed pavement design that met both the structural and functional requirements over a 30-year design and analysis period. This methodology can be expanded to suit other project functional or serviceable requirements and is recommended to be utilized by other transportation agencies for their innovative pavement projects.
