Analysis of nondestructive test data on flexible pavements acquired at the national airport pavement test facility

Nondestructive tests (NDT) were performed at various times on flexible pavement test items at the Federal Aviation Administration's (FAA) National Airport Pavement Test Facility (NAPTF) located at the William J. Hughes Technical Center, Atlantic City International Airport, New Jersey. The NDTs were performed with both falling weight deflectometer (FWD) and heavy failing weight deflectometer (HWD) equipment to document the uniformity of pavement and subgrade construction, as well as to acquire data on pavement response over time and increasing numbers of full-scale load repetitions. Since the pavements and subgrades were constructed to exacting standards of uniformity and the NDTs were performed on pavements of known and uniform thicknesses, this enabled the backcalculatcd subgrade moduli under flexible pavements to be correlated against conventional test results. The FAA's new backcalculation software, FAABACKCAL, was used to process the NAPTF NDT data. This paper discusses the evaluation of the NDT and other test data with respect to: . Description of the FAA's new backcalculation software, FAABACKCAL. . Linearity in pavement response and backcalculated subgrade modulus with applied HWD force. . Comparison of the stiffnesses of conventional and stabilized-base pavements on the same subgrade and like pavements on different subgrades. . Relationship between in situ California Bearing Ratio (CBR) and backcalculated subgrade modulus for low-, medium-, and high-strength subgrade. . The effect of the stiffness of underlying layers on backcalculated subgrade modulus.