An experimental method to design porous asphalts to account for surface requirements

Porous asphalts have supplementary surface and volumetric properties (e.g., acoustic absorption, drain ability, texture, and friction). These properties are linked to intrinsic factors (e.g., gradation and bitumen content) and extrinsic factors (e.g., traffic load), while their evolution over time depends on complex phenomena and processes that cause their deterioration and therefore affect safety, noise, and budget. Despite the decay of so many and complex properties over time, there is a lack of criteria to synergistically optimize the pavement system. Consequently, the objective of this study is to set up and validate a design method that synergistically addresses the most relevant properties of friction courses as a part of a pavement structure. The abovementioned method is based on in-depth analyses of the literature and on laboratory and on-site tests carried for several years in order to evaluate the decay over time of the main surface and volumetric properties. The method was applied to a case study. Results show that 1) the level of fulfilment of single requirements varies over time and among the characteristics; 2) a sound optimization of the design of the mix in order to balance the different characteristics is needed; 3) further studies are needed because of uncertainty in predicting the main surface properties.