Measurements of the moisture diffusion coefficient of asphalt mixtures and its relationship to mixture composition

The presence of moisture in asphalt pavements detrimentally affects the bond between the aggregate and binder and the bond within the binder. The loss of these bonds leads to the deterioration of asphalt pavements. In regions with low rainfall, moisture diffusion is an important source of moisture transport in asphalt mixtures. The diffusion coefficient is a necessary input for models simulating moisture transport and, consequently, moisture damage in asphalt pavements. In this study, an experimental protocol was developed for determining the moisture diffusion coefficient of asphalt mixtures. The experimental set-up relies on measuring suction over time in test specimens using thermocouple psychrometers. The proposed protocol successfully determined a wide range of diffusion coefficients (i.e. from 5.67 x 10(-5) to 2.92 x 10(-6) cm(2)/s) of different asphalt mixtures. X-ray computed tomography was used to characterise the air void structure of test specimens. The results revealed good correlation between the diffusion coefficient value and the per cent of air voids and the average radius of air voids in the test specimens. The diffusion coefficient values determined in this study can be used as an input in models for determining the rate of moisture diffusion in asphalt mixtures with different per cents of air voids.