Pore‐system characteristics of pavement seam materials of urban sites

The original light‐brown sandy seam filling of pavements in urban areas turns dark and changes its properties by the time due to various inputs of urban dust. Deposited C_org inputs do mostly not have natural characteristics but are man‐made, e.g., diesel dust. Thus, properties of the seam material are not predictable from experiences with forest or agricultural soils. Semiperviously sealed urban areas are sites of contaminant deposition as well as groundwater recharge. For an assessment of the resulting groundwater‐contamination risk in these areas, the properties of the seam material, which influences transport processes, must be known. The aim of this study was to investigate the pore‐system build‐up, which includes size distribution and fractal character in the seam material of urban sites. The investigated samples were taken from pavements adjacent to roads in Berlin and Warsaw. The micropore parameters (nanometer range) were characterized using water‐vapor desorption isotherms, mesopore parameters (micrometer range) were estimated from mercury‐intrusion porosimetry and macropore parameters (millimeter range) from water‐retention curves. Particle density, dry bulk density, and particle‐size distribution were measured using standard methods. Volumes of micro‐ and mesopores as well as particle densities and dry bulk densities correlated with C_tot contents. However, no such relation was found for macropore volumes. Compared to the original sandy seam filling, the altered seam material shows significantly higher C_org contents and higher amounts of micro‐ and mesopores. Therefore, the available water capacity increases by 0.05–0.11 m³ m^–3, as compared to the original sandy seam filling. Compared to natural sandy soils having similar C_org contents, the seam material shows similar macropore volumes, but the volume of mesopores and micropores is a few times smaller. That is mainly because of the particulate character of the organic matter.