Analysis of Pore Characteristics and Flow Pattern of Open-Graded Asphalt Mixture in Different Directions

Abstract

The permeability of porous asphalt pavement is an important hydraulic property that is affected by the microstructure of connected pores. This paper investigates the pore characteristics and water flow pattern of open-graded friction course (OGFC) mixture using image analysis and numerical simulation. Firstly, four groups of OGFC samples were scanned by computational tomography (CT) to obtain the pore distributions and the shape parameters of voids (number of voids per unit area, the area ratio of voids to cross section, the equivalent circle diameter, and the ratio of the long and short axis in equivalent ellipse) along both horizontal and vertical directions. Secondly, the three-dimensional (3D) pore structure of the OGFC mixture was reconstructed by an image-processing technique. The connected pores were separated, and the pore length, pore curvature, and hydraulic diameter were calculated and analyzed. Finally, the two-dimensional (2D) water flow in pore structures was simulated. The results showed that the length and curvature of horizontal pores were larger than those of vertical pores, but the diameter was smaller for horizontal pores. It was found that pores had different distribution characteristics in the horizontal and vertical directions. The pore length and curvature along the vertical direction of the OGFC mixture were smaller than those along the horizontal direction, but the hydraulic diameter along the vertical direction was larger than that along the horizontal direction. The simulation results showed that the water flow rate in the horizontal direction was greater than that in the vertical direction when the gravity is not considered. With the increase of water pressure and the decrease of void ratio, the difference between horizontal and vertical flow rates became greater.