Probabilistic modeling of the effect of air voids on the mechanical performance of asphalt mixtures subjected to moisture diffusion

The internal air void structure of asphalt mixtures plays an important role in the durability of these materials. Voids are recognized as the main source of moisture access to the interior of the mixtures' microstructure. The deleterious effect of moisture on asphalt mixtures, usually referred to as moisture damage, is one of the main causes of early deterioration of asphalt pavements. This paper studies the effect of air voids on the mechanical performance of asphalt mixtures that are subjected to the combined action of moisture diffusion and mechanical loading. The analysis is conducted by means of a numerical micromechanical model that includes fracture mechanics principles and couples the effect of moisture diffusion with the mechanical properties of the mixture. The main advantage of the model is that it explicitly includes air void distribution (size and location) in the development of the microstructure geometry. This is achieved by applying a probabilistic distribution function of air void sizes - obtained from X-Ray Computed Tomography measurements - to create the microstructure model. Mixture response was quantified in terms of the total dissipated energy and stiffness. Results from the simulations provided insight on the influence of variation in percent air voids on mechanical performance. The developed model can be used to analyze the interrelated effects of internal structure distribution, moisture diffusion and mechanical properties of the mixture constituents on performance.