Environmental Performance of Mature Precast Slabs in Permeable Pavements: Hydraulic Functionality and Pollutant Retention Under Real-Life Conditions

Permeable pavements are increasingly integrated into urban environments as sustainable systems that enhance stormwater infiltration, mitigate runoff, and contribute to pollutant control. However, long-term accumulation of contaminants within their porous structure may impair hydraulic performance and environmental functionality, particularly regarding microplastics (MPs), an emerging pollutant of growing concern. This study investigates the five-year environmental performance of porous concrete pavement slabs operating under real urban conditions, focusing on infiltration capacity and retention of nutrients, suspended solids, and MPs. A dual methodology combining continuous on-site permeability monitoring with laboratory analyses of aged slabs was used to assess performance decline and recovery after maintenance. Results show a 48% reduction in infiltration over five years, while maintaining effective functionality, and a 42.5% recovery after pressure cleaning. Used slabs exhibited substantial pollutant accumulation relative to new slabs, including increases of +258% in COD, +123% in total phosphorus, +28% in total nitrogen, and +48% in suspended solids. MP abundance reached 10,272 ± 5829 MPs/m2, 7.5 times higher than in new slabs, dominated by fibers (~70%) and polymers such as PE, PP, and PET. These findings highlight the pavement surface layer as both hydraulic infrastructure and contaminant sink supporting improved maintenance and sustainable urban stormwater management.