Monitoring Stiffness Evolution of Asphalt Concrete Through Modal Analysis

The stiffness of asphalt concrete, which is used for thickness design of pavements, is known to increase with time due to age hardening of the binder. Therefore, aging models to account for the stiffness evolution over time are in some applications considered with the aim to improve pavement life predictions. Modal analysis is an economic test method with a verified precision for characterizing the complex moduli of asphalt concrete. In this paper, the stiffness evolution of asphalt concrete has been monitored through modal analysis. The simplicity of the modal test set-up facilitates accurate repeated testing under identical conditions. Therefore, modal testing was performed repeatedly at the temperatures of 20 and −20 °C over a period up to around 300 days. The testing was performed on samples in a controlled laboratory environment and does not intend to provide a measure of the age hardening of real pavements. The aim of this paper is to characterize the stiffness evolution of asphalt mixes with modified and unmodified binders in a controlled environment. Cyclic indirect tensile tests were performed in addition to modal analysis to characterize the stiffness evolution under different loading configurations. Results from the modal analysis clearly showed that the rate of the stiffness evolution is initially slower for the modified binder in comparison to the unmodified binder.