Investigations on microstructure characteristics of porous pavement based on X-ray CT scanning

Gathering insights on materials at pore scale using digital imaging techniques, such as X-ray computed tomography (CT), gains more and more attention in various fields of engineering disciplines. The better understanding of material properties, internal structures, and material behaviour has generated many scientific and industrial advances. Investigations on porous materials, especially the visualisation of the pore space, allow the derivation of macroscopic material properties and provide a basis for numerical calculations, e. g. flow or contaminant transport through threedimensional pore structures. The investigated porous material in this study is used in water-permeable road constructions as a novel pavement material aiming at instant drainage of rainfall into the subgrade and subsoil. Commonly used porous asphalt is made utilising bitumen-based binder materials. In this case, however, an innovative binder material based on polyurethane (PU) is used to form a flexible and porous pavement layer. The utilisation of this binder material not only increases the functionalities of the pavement layer but also increases rutting resistance and fatigue behaviour. This paper gives insights on the pore space obtained from CT-scans of two different pavement compositions of novel porous pavement material. The compositions vary in terms of particle size distribution of the utilised grains and the maximum grain diameter. The segmentation process of the obtained CT-images into the components of the multiphase media, i. e. grains, pore space, and binder material, as well as the reproduction of the three-dimensional models will be presented. Also results of investigations on the representative elementary volume for two volume-dependent properties will be demonstrated.