Moisture seepage in asphalt mixture using X-ray imaging technology

Abstract

Understanding moisture flow in asphalt mixtures is the first step in analyzing moisture-induced damage caused by moisture in pavements. However, the precise quantities of the dynamic movements of wetting fronts and their relationship with the internal structures of asphalt mixtures are yet to be determined. The aims of this study are (1) to quantify the dynamic movements of wetting fronts in asphalt mixtures with X-ray computed tomography (X-ray CT) and (2) to investigate the effects of internal structures of asphalt structures on seepage characteristics. In this study, purified water and three types of asphalt mixtures were used as liquid and pavement materials, respectively. We initially applied sensitivity analysis to determine optimal experimental condition and then performed X-ray CT to balance scanning time and measurement precision in the capture of microscale moisture distribution. The characteristics of moisture seepage, including wetting front, seepage velocity, and initial inertial region, were quantified by tracing the flow at different moments. At a fixed infiltration rate, all the local seepage velocities decreased in power function over time, suggesting the existence of unsteady flow during the seepage. The initial inertia of water droplet had a stronger influence on the vertical migration than in the horizontal migration. This result indicated that the hemispherical shape transport pattern shifted to a trapezoidal shape with the increase of penetration time. Water droplets were easily broken, and water was prone to spread in horizontal direction owing to the decrease in void size, thereby consequently resulting in the directional distribution of the initial inertial region. These findings contribute to the understanding of dynamic moisture movement on the micro-scale of asphalt mixtures and provide an effective opportunity to reveal the evolutionary path of moisture-induced damage in asphalt pavement.