Investigation on flow resistance of fluid in permeable asphalt mixture

•Determine permeability equation of permeable asphalt mixture.•Develop the program to calculate multi-directional connective void content.•Propose a pore throat model to reveal the variation of flow resistance.•Explore the impacting parameters of inertia and viscous resistance distribution. Flow resistance distribution of fluid is the basis of comprehensively grasping the permeability of permeable asphalt mixture. This study aimed to investigate the flow resistance of fluid in permeable asphalt mixture. Considering the influence of anisotropy of permeable asphalt mixture, the vertical and transverse permeability tests of five types of permeable asphalt mixture were carried out using multidirectional permeability test instrument developed by our research group. The fitting equation of permeability was determined by comparing Darcy's law with Forchheimer equation. Moreover, the flow resistance is usually considered as an effective parameter to reveal the structural permeability. The connective void content of permeable asphalt mixture is important to calculate flow resistance. Accordingly, it is necessary to obtain the transverse and vertical connective voids of the asphalt mixture considering the influence of anisotropy. Therefore, a program for calculating the multi-directional connective void content was developed based on the theory of projection reconstruction. On this basis, a pore throat model was applied to reveal the variation of flow resistance of asphalt mixture. The results show that the weight of inertia resistance and viscous resistance is different in various seepage velocities. The viscous resistance is dominant when the fluid flow velocity is less than 0.0087 m/s under experimental conditions, and the inertial resistance is dominant when the fluid flow velocity is greater than 0.0087 m/s. The viscous resistance and inertia resistance of fluid are affected by the anisotropy and structure type of permeable asphalt mixture. When the vertical void content decreases by 3.3%, the corresponding viscous and inertial resistance increase by 7.92 kPa/m and 0.84 kPa/m, respectively. For the transverse void, the viscous and inertial resistance increase by 3.19 kPa/m and 2.02 kPa/m respectively as the content decreases by 3.5%. The influence of void structure of permeable asphalt mixtures on fluid flow is revealed from a microscopic perspective, which can be used to guide the optimization design of gradation of permeable asphalt mixtures.