Relationship between Backcalculated and Estimated Asphalt Concrete Dynamic Modulus with Respect to Falling Weight Deflectometer Load and Temperature

Abstract

<jats:p> There are several methods for determining the stiffness of asphalt concrete in an existing pavement. The three primary methods are: dynamic modulus testing in the laboratory, predictive equations, and falling weight deflectometer (FWD) testing. Asphalt over asphalt (AC/AC) overlay design procedures allow the use of multiple methods to characterize fatigue damage in the existing asphalt concrete. Therefore, understanding the difference between these methods is critical for AC/AC overlay design. The differences between the methods for determining asphalt concrete stiffness and how these differences are related to FWD load magnitude and asphalt temperature are examined. Data from the Federal Highway Administration’s Long-Term Pavement Performance Program (LTPP) are used in this investigation. It is found that the stiffness determined through FWD testing and backcalculation is generally less than that estimated using the Witczak predictive equation and binder aging models. Furthermore, it is found that both FWD load magnitude and asphalt temperature have a significant effect on the difference between backcalculated and estimated stiffness of asphalt concrete. Backcalculated stiffness increases relative to estimated stiffness as FWD load and temperature increase. These effects must be considered when multiple methods of determining asphalt concrete stiffness are used interchangeably for overlay design. </jats:p>

An Approach for Adjusting the Laboratory-Determined Dynamic Modulus Master Curve of Asphalt Layers Based on Falling Weight Deflectometer Measurements

“…Equation (6), which was proposed by Solatifar et al [4], is used to fit the sigmoidal function to determine the final FWD-Adjusted E * j j master curve: where E * FWD−adjusted is the FWD-Adjusted (i.e., in situ) dynamic modulus of the asphalt layer in MPa; E m−FWD : FWD back-calculated moduli, MPa; E * p : predicted dynamic modulus at the corresponding reduced frequency of FWD loading, MPa; and δ, α, β, γ, and f r are as previously defined in Equations ( 2) and (3).…”

“…This assessment is used to estimate the pavement's remaining service life and to select appropriate preventive and rehabilitation strategies [1,2]. Generally, the most important parameters required to assess pavement conditions are layer moduli, which can be obtained by nondestructive field tests such as the falling weight deflectometer (FWD) or laboratory tests of field cores [3][4][5][6]. The FWD device applies a load pulse to the pavement surface and measures the resulting surface deflections.…”