Nondestructive measurements of moisture transport in asphalt mixtures

Many of the distresses observed in asphalt pavements are caused by or increase in severity due to the presence of moisture. The majority of the research on moisture damage is based on the hypothesis that infiltration of surface water is the main source of moisture damage. Of the two other principal mechanisms of water transport, permeation of water vapor and capillary rise of subsurface water, the latter has been least explored. In this study a laboratory test and analysis methods based on X-ray computed tomography (CT) were established to assess the water transport through capillary action. In addition, a computer program was developed to analyze the distribution of connected air voids. The amount and size of air voids filled with water were used in the capillary rise equation to estimate the distribution of contact angles between water and asphalt mastic. The results were able to show the influence of air void size on capillary rise and contact angles, and showed clear differences in capillary rise between the moisture conditioned and unconditioned specimens. The experimental results were explained based on the Washburn and Laplace equations. The findings of this study can be used to estimate the rate of moisture infiltration in asphalt mixtures with different air void distributions. They can also be useful to explore the causes of moisture damage in dry regions where capillary rise and moisture diffusion could be the main sources of moisture in the asphalt mixture rather than infiltration of surface water.