Evolution of dynamic flow behavior in asphalt mixtures exposed to freeze-thaw cycles

This study aims to understand the evolution of dynamic moisture flow in asphalt mixtures exposed to freeze-thaw cycles. X-ray CT was utilized to capture the moisture dynamics in unsaturated asphalt mixtures during simulated rainfall events. Three main characteristics of the dynamic flow behaviors within asphalt mixtures were measured and monitored, including wetting front position, directional velocity of wetting front, and inertia influence region. It was found that at a specific infiltration rate, freeze-thaw cycles increased the vertical flow penetration and decreased the horizontal flow penetration for both wetting front position and directional velocity, suggesting that seepage anisotropy was exacerbated in asphalt mixtures. The initial inertia of water droplet was mostly converted towards the vertical direction under freeze-thaw effect. As a result, the shape of water transmission was converted from a hemispherical shape to a slender shape under freeze-thaw cycles. Linear regression analysis between direction velocity growth rate in particular samples and freeze-thaw cycles to pore structure was conducted, and it was found that compared with dense-graded mixtures, open-graded mixtures displayed larger slopes for horizontal flow, and smaller slopes for vertical flow, demonstrating the non-negligible effect of pore structure on dynamic flow evolution under freeze-thaw cycles. (C) 2020 Elsevier Ltd. All rights reserved.