SNF – Asphalt

Wetting and drying of porous asphalt pavement: a multiscale approach

Porous asphalt (PA) is a special type of asphalt concrete with a high porosity of about 20% by volume. Porous asphalt is used efficiently to improve driving conditions under rainy weather (reduction of aquaplaning risk) and the quality of the aural environment, given the noise reduction properties of this material. However, due to its high porosity, more surface area undergoes the detrimental effects of the environment leading to a life expectancy of around 10 years, compared to 20-30 years for dense asphalt concrete. A key issue in understanding PA, and in improving its durability and mechanical performance, is a thorough portrayal of its wetting and drying behavior under environmental loads. Used as a surface course in pavement systems, porous asphalt is exposed to mechanical (traffic) and environmental loads, both playing a significant role in its durability. Porous asphalt is subjected environmentally to a pallet of moisture and heat phenomena, such as (1) rain water impinging its surface, (2) water seepage and drainage in the PA by gravity in the coarse pore system, (3) capillary uptake and redistribution in the fine pore system, (4) film and corner flow on the rough surfaces, (5) drying by diffusion, (6) moisture sorption in the binder, (7) air flow above and through the surface layer of PA, thus convection with air at varying temperatures, (8) solar irradiation and long wave radiative exchanges with the environment. In addition, the passages of tires induce a significant repetitive air/water pumping effect. The interactions between the environment and porous asphalt are yet to be fully understood and captured. The global objective of this project is to develop an integrated multiscale methodology, based on a combination of experimentally validated models, to capture accurately the main physics of the wetting and drying of porous asphalt at the material scale (micro scale), and that can be used in road engineering at the pavement scale (macro scale), in the development and assessment of pavement solutions. The applicants combine the two expertises required for this project: first a deep knowledge of the material asphalt, porous asphalt and pavement systems and, second, a high capacity in determining and modeling the physical behavior and transport in porous materials. Given the importance of mobility in our society, better, safer, more durable and environmentally friendly pavement systems are sought for. Thriving towards an integrated methodology, the present project aims at filling the following gaps: at the material scale, acquiring an accurate knowledge and modeling of the complex mass transport processes occurring within the porous system and, by upscaling, determining the macroscopic mass transport properties of PA; at the pavement scale, developing validated continuum models to study the behavior of PA under environmental load such as rain, irradiation, wind, including the effects of air and water displacement due to traffic.

For further information please contact: Dominique Derome