Long-term environmental performance of precast slabs in permeable pavements: hydraulic functionality and pollutant retention in a real-life installation

Permeable pavements are increasingly integrated into the urban built environment as sustainable surface 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 compromise their environmental functionality, particularly regarding microplastics (MPs), a persistent and emerging pollutant of growing concern in cities. This study investigates the five-year environmental performance of porous concrete pavement slabs operating in a real urban setting, focusing on changes in infiltration capacity and the retention of nutrients, suspended solids, and MPs. A dual methodology, combining continuous on-site permeability monitoring with laboratory analyses of aged slabs, was employed to assess degradation patterns and recovery potential following maintenance. Results show a 48% decline in infiltration over five years, with a 42.5% recovery after pressure cleaning. Substantial pollutant accumulation was observed in used slabs, including increases of + 258% in COD, + 123% in total phosphorus, + 28% in total nitrogen, and + 48% in suspended solids. MP abundance reached 10272 ± 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 dual role of permeable pavements as hydraulic infrastructure and contaminant sinks within the built environment, providing evidence-based insights for improving maintenance strategies, enhancing urban resilience, and supporting the long-term sustainability of nature-based stormwater solutions.