Characterization of Two Perpetual Pavements at the NCAT Test Track

Abstract

Two experimental asphalt pavement sections were built at the National Center
for Asphalt Technology (NCAT) Test Track in 2003. Designed according to the 1993
AASHTO Design Guide, they were expected to fail after 10 million equivalent single axle
loads (ESALs). However, they performed well throughout the initial 10 million ESALs and
have far exceeded their performance expectations with an additional 20 million ESALs
applied with excellent performance during the past six years. Though designed as
conventional pavements, these sections have performed effectively as perpetual pavements.
The main objective of this investigation was to evaluate the long-term structural and
performance characteristics of these unexpected perpetual pavements. The investigation
included backcalculation of falling weight deflectometer data to monitor in situ asphalt
concrete (AC) moduli versus time and traffic. It was found that the AC moduli increased
approximately 12 to 20% during the past six years. Weekly monitoring of ride quality, mean
texture depth and rutting have shown no appreciable change over time, indicative of a
perpetual pavement. Though some minor cracking was observed after 30 million ESALs,
forensic investigations indicated it was top-down which was also consistent with a perpetual
pavement. Finally, endurance limits determined through laboratory beam fatigue testing were
compared against pavement responses measured from embedded strain gauges. The
measured strain levels in situ were significantly higher than the endurance limits,
approximately double at the 90th percentile, which suggested the need to revise conventional
approaches to perpetual pavement design.