Drainage Considerations for Porous Asphalt Surface Course Design

Abstract

The drainage performance of a porous asphalt surface course depends on the drainage properties of the asphalt mixture as well as the geometric design of the individual road sections. Hence, the minimum thickness requirement may vary from one section to another in a single road project because of changes in road geometric design, even though the same asphalt mixture is used for the surface course. However, the influence of road geometric properties and the effects of longitudinal gradient and cross slope on the thickness design of the surface course have not received the deserved attention. No readily available design tools allow highway engineers to effectively perform design checks on thickness requirements. Convenient plots were developed to meet this need. A three-dimensional finite element program was used to study the effects of cross and longitudinal slopes on the drainage performance of the porous asphalt surface course. Both the longitudinal gradient and the cross slope of a road section significantly affect the drainage capacity of the porous surface course. A family of thickness-requirement graphs was prepared for easy application. These graphs were plotted as functions of design rainfall, thickness of surface course layer, width of pavement, and longitudinal and cross slopes.