Directional distribution of three-dimensional connected voids in porous asphalt mixture and flow simulation of permeability anisotropy

Abstract

ABSTRACT This study aims to investigate the relationship between the anisotropy of permeability and the directional distribution of connected voids in permeable friction course (PFC) mixture. The compacted PFC-13 specimens with five air void contents were scanned using X-ray computer tomography (CT) to reconstruct three dimensional (3-D) structures of total and connected voids, respectively. The length, curvature, and size of 3-D connected voids in three directions were calculated. The unidirectional laminar flows in three directions of connected voids were simulated. The directional dependence of hydraulic conductivity and flowing velocity in connected voids were analyzed. The multi-directional laminar flow simulation was also conducted. Results show that the length of horizontal connected voids in PFC-13 mixture is 1.2–2.1 times more than that of vertical connected voids. The horizontally connected voids were found more uniform than vertically connected voids in terms of curvature and size. The less length of vertical connected voids is the main reason for lower hydraulic conductivity of PFC in vertical direction. As the connected void content decreases from 30.6% to 19.1%, the anisotropy degree in hydraulic conductivity of unidirectional flowing increases from 1.05 to 1.3; while the anisotropy degree of multi-directional flow increases from 2.67 to 15.7.