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It is a well-established fact that moduli values backcalculated from deflection data of one particular NDT device will be different from those of another device. Although disconcerting at first glance, this should not be surprising to the pavement engineer. NDT devices often use widely different load levels and loading frequencies. Combining this with the complex nature of pavement materials and the fact that data are often collected under different temperature and moisture conditions emphasizes the need for theoretically sound procedures for converting measured values to standard levels of load, temperature, and loading frequency. This is the subject of this paper.
In this paper are the results of a recently completed Texas Transportation Institute study on nondestructive testing. One of the major recommendations of that study are standardized guidelines for applying temperature, frequency, and load level corrections. These will be described in detail, and typical examples will be given. Of particular interest are the load level correction factors. These are demonstrated in case studies which compare backcalculated moduli values from the Dynaflect, the Dynatest falling weight deflectometer, and the Road Rater 2000.
backcalculation, deflection basins, secant modulus, initial tangent modulus, standard load level, strain level correction, confining pressure correction, temperature and frequency corrections, stress sensitivity, hyperbolic stress-strain curve, NDT devices
Research assistant, Texas Transportation Institute, Texas A&M University, College Station, TX
Professor of civil engineering and research engineer, Texas Transportation Institute, Texas A&M University, College Station, TX