Backcalculation of Dynamic Modulus Mastercurve from Falling Weight Deflectometer Surface Deflections

Abstract

The need to characterize the structural condition of existing pavements accurately has increased with the recent development, release, and ongoing implementation of the new Mechanistic–Empirical Pavement Design Guide (MEPDG). There is a strong need to identify and evaluate the way that falling weight deflectometer (FWD) testing is operated and integrated into the new design procedure. One of the key inputs in the MEPDG for asphalt pavements is the dynamic modulus (|E*|) mastercurve. If the damaged |E*| mastercurve of the asphalt concrete in an existing pavement can be obtained from FWD deflections, a more accurate prediction of its remaining service life can be achieved. A methodology backcalculates the |E*| mastercurve of the asphalt pavement layer by using the time history of FWD surface deflections. The method uses a layered viscoelastic forward algorithm in an iterative backcalculation procedure for linear viscoelastic characteristics of asphalt pavements. With deflection time histories from a typical FWD test, it was possible to backcalculate the relaxation modulus curve, E(t), up to about t ∼ 10⁻¹ s and the complex modulus curve, |E*|, from f = 10⁻³ Hz and above. Recommendations to improve the accuracy of the backcalculated |E*| mastercurve are provided in the context of enhancing current FWD technology and test procedures.

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