Comparisons of asphalt pavement responses computed using layer properties backcalculated from dynamic and static approaches

Abstract

The falling weight deflectometer (FWD) testing is widely used as a nondestructive technique to backcalculate layer properties of in-situ asphalt pavement structures. Traditionally, static backcalculation methods based on the layered elastic theory (LET) are employed to analyze FWD data. However, the static method can not take into consideration the dynamic effects of the impulse loading generated in FWD testing, as well as the viscoelastic behaviour of asphalt concrete (AC). Therefore, the layer properties backcalculated from the static approach and the pavement responses computed using these layer properties are questionable. In this study, FWD tests were conducted on two asphalt pavements, one with a flexible base and the other with a semi-rigid base. The field FWD data were backcalculated using the traditional static approach and the dynamic approach which uses the spectral element method as the forward analysis engine. The elastic modulus of each layer was obtained from the static backcalculation, while in the dynamic backcalculation, the complex modulus master curve, which is the fundamental property of viscoelastic materials, was obtained for each AC layer, and elastic moduli were obtained for other layers. The two sets of backcalculated results were employed to analyze pavement responses to moving vehicular loading using the LET and layered viscoelastic theory, respectively. The results show that responses from the viscoelastic analyses are significantly larger than those from the elastic analyses except for the vertical strain at the asphalt treated base layer at high speeds. At a low speed of 16 km/h, most of the responses from the viscoelastic analyses are more than two times those from the elastic analyses. The results presented in this study pose a serious concern over the traditional approach in which both the backcalculation of FWD data and computation of pavement response to traffic loading are based on the LET.