Modelling the hydraulic performance of open graded asphalt using the discrete element method and computational fluid dynamics

Porous asphalt (PA) pavements are used as an alternative for non-permeable pavements to tackle hydroplaning issues and reduce splash and spray. The key aspect of designing a PA pavement is its hydraulic performance. This study introduces a novel numerical approach combining the discrete element method (DEM) and computational fluid dynamics (CFD) to model the hydraulic performance of PA. Different from the traditional methods of scanning the internal asphalt matrix using X-rays, this study uses a photogrammetry-analysis technique to convert the aggregate structure into a DEM. DEM modelling was then used to create a random aggregate structure with different sizes to simulate the asphalt samples for testing. The information about the sample structure was transferred to CFD for the hydraulic performance simulation. The effects of the air voids content, air voids distribution, and sample structure on the vertical and horizontal hydraulic performance were investigated. The results showed that the proposed approach is capable of producing virtual test samples resembling the laboratory PA sample structure for hydraulic performance tests. It was found that the outlet flow rate was mainly affected by the total air voids content of the sample. Higher content and evenly distributed air voids over the depth of the PA samples led to better hydraulic conductivity. Samples created and tested using DEM-CFD methodology could also effectively predict the flow rate at the outlet and demonstrate the flow movement between connected pores inside the sample structure.