Assessment of the Current Frequency Calculation Methods Used in the Determination of the Dynamic Modulus Value in Pavement Design and Analysis

Abstract

The dynamic modulus |E*| is used in the Mechanistic-Empirical Pavement Design Guide (MEPDG) to express the viscoelasticity of asphalt material at a range of temperatures and loading frequencies. As a result, the current MEPDG method assumes that frequency is calculated as the opposite of vehicular loading pulse time. In addition, the loading pulse time can be calculated using the Odemark thickness equivalency method according to the MEPDG. On the other hand, the loading frequency as per Qatar Highway Design Manual (QHDM 2021) is estimated based on the average vehicle speed using Losa and Di Natale formula. However, studies found major inadequacies in the adopted method of MEPDG, which might affect the accuracy of the loading frequency and |E*| accordingly which leads to an impact on the pavement design and performance analysis. Hence, it was recommended that alternative frequency determination approaches like the Fast Fourier Transform (FFT) be used rather than traditional time-domain techniques. Therefore, this paper compares the results of the MEPDG and QHDM loading frequency procedure with the dominant frequencies (DF) obtained using the FFT. On the other hand, the loading time pulses are estimated using the Odemark approach and, compared to the ones simulated using 3D Move Analysis software that accurately considers the tire contact pressure, viscoelastic properties, & vehicle speed. It was found that the used frequency determination approach in the pavement design in Qatar, overestimates the frequency values by about 30% to 88%. Furthermore, the findings showed that the MEPDG method for determining loading time and frequency is not conservative.