Conversion of Testing Frequency to Loading Time Applied to the Mechanistic-Empirical Pavement Design Guide

Abstract

This paper investigates the issue of converting testing frequency in a dynamic modulus test of hot-mix asphalt (HMA) to loading time for implementation in the proposed mechanistic-empirical pavement design guide. Two methods have been proposed in the literature. The first is to convert the test frequency (f; in hertz) to loading time (t; in seconds) by using t = 1/f. The second method is to convert the test angular frequency (to) to the loading time (in seconds) by using t = 1/ω = 1/2πf. An exact interconversion based on the representation of dynamic modulus results by using a generalized Kelvin model and a generalized Maxwell model is presented. The exact interconversion is compared with the two debated methods of converting the dynamic modulus or the storage modulus to a stiffness (inverse of creep compliance) and relaxation modulus. It is shown that both methods result in error in determining either the relaxation modulus or stiffness. On the other hand, it is shown that the resilient modulus can be adequately approximated by the dynamic modulus taken at a frequency of 1/t.