Dynamic effects on moisture transport in asphalt concrete

Permeability of an asphalt pavement is one of the most important parameters that have a direct influence on its design life. It is an intrinsic property that relates the average fluid velocity to a constant pressure gradient; however, the external pressures on a saturated pavement pore structure are often dynamic due to the repeated tire loading in the field. A dynamic permeability constant, therefore, is a more realistic representation of the response of a pavement pore structure to external stresses. In order to investigate the unsteady (dynamic) fluid flow in asphalt pavements, a three-dimensional fluid flow model was developed using the lattice Boltzmann method. The model was validated using the well-known closed form solution of oscillating flow through a circular tube. Simulations were carried out to calculate the permeabilities of different asphalt specimens exposed to pulsatile pressures as well as the pore pressures and shear stresses at the solid-water interfaces. The results indicated that the dynamic permeability of an asphalt pore structure collapses on a single curve for a given frequency, confirming a universal behavior. Dynamic effects were generally limited to near the surface of the specimens analyzed, and the pore pressures and velocities varied nonlinearly along the depth due to the heterogeneous nature of the asphalt specimens. The results are encouraging yet should be considered preliminary as they are based on stone matrix asphalt specimens and one type of pulsatile load analyzed.