Investigation of the Hydraulic Properties of Pervious Pavement Mixtures: Characterization of Darcy and Non-Darcy Flow Based on Pore Microstructures

The significance of water flow behavior as one of the main properties of pervious pavements has long been recognized. However, the quantification of flow characteristics and the relationship to complex pore microstructures in pervious pavement remains incomplete. The aim of current research is to quantify the Darcy and non-Darcy flow in pervious pavement materials and carry out investigations on the different flow models for predicting hydraulic conductivity. Conventional porous asphalt (PA) and an innovative polyurethane-bound pervious mixture (PUPM) were adopted for comparative study in this research. A custom-made permeameter was used to analyze the water flow characteristics in pervious pavement mixtures subjected to different hydraulic gradients. The results illustrate the inapplicability of Darcy's law in the analysis of directional moisture transport in pervious pavement materials. In particular, the Reynolds number of pervious pavement materials increases with the hydraulic gradient, indicating that the flow in pervious pavement material transits from Darcy flow to Forchheimer flow. The pore microstructure of the pavement material is quantified using X-ray computed tomography (CT) images. ANOVA indicates that it is mainly the pore distribution characteristics, including air void content, void diameter, and tortuosity, that influence the flow in pervious pavement. Modified flow models are developed based on the pore microstructures, which present better consistency with the experimental results. The developed experiments and models can provide a firm foundation for the optimization of pervious pavement design in engineering applications.