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

Long-term environmental performance of precast slabs in permeable pavements: hydraulic functionality and pollutant retention in a real-life installation | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Long-term environmental performance of precast slabs in permeable pavements: hydraulic functionality and pollutant retention in a real-life installation Darío Calzadilla-Cabrera, Eduardo García-Haba, Carmen Hernández-Crespo, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8173976/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract 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. Permeable pavements Urban runoff Nature-based solutions Stormwater pollution Microplastic Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Highlights Findings contribute to understanding the durability and functionality of permeable pavements as sustainable construction materials in urban infrastructure. Results highlight the dual role of permeable pavements in stormwater management and contaminant control. After five years, pavements still provide relevant pollutant retention, supporting long-term performance. Microplastic accumulation is associated with a progressive reduction in pavement permeability. Permeable pavements retain a significant fraction of microplastics in their surface and filter layers. 1. Introduction In the context of sustainable urban development, permeable pavements have become consolidated as a reliable nature-based solution to mitigate the environmental impacts of urbanization (Zhang et al., 2024 ). By enhancing infiltration and improving runoff quality, they contribute to restoring natural hydrological processes and reducing pollutant loads to receiving waters (Tota-Maharaj et al., 2024 ; Febriana et al., 2025 ; Castillo-Rodríguez et al., 2021 ). In addition, they can support aquifer recharge and reduce the urban heat island effect (Halder et al., 2021 ). However, their long-term performance can deteriorate due to progressive clogging of the pore structure, driven by the accumulation of sediments and organic matter (Rahman et al., 2025 ; García-Haba et al., 2023a ). This process not only reduces infiltration capacity but may also alter the pathways and retention of contaminants within the pavement matrix. Despite numerous studies on hydraulic efficiency, few have jointly examined the long-term coupling between hydrological decline and pollutant dynamics under real operating conditions (Rodríguez-Rojas et al. 2020 ; Qamhia et al. 2024 ). Beyond their hydrological role, permeable pavements act as reactive filters that improve the quality of urban runoff by retaining sediments and dissolved contaminants through filtration, sedimentation, and adsorption processes (Raimondi et al., 2023 ; Kong et al., 2025 ). Several studies have reported efficient removal of suspended solids and variable but generally positive efficiencies for nutrients such as nitrogen and phosphorus (Collins et al., 2009 ; Huang et al., 2012 ; Gilbert & Clausen, 2006 ). Heavy metals (Cu, Pb, Zn) and hydrocarbons have also been found to accumulate within the pavement layers (Dietz, 2007 ; Poor et al., 2023 Scholz & Grabowiecki, 2007 ; Brown et al., 2009 ). In recent years, microplastics (MPs) have emerged as pervasive contaminants of global concern due to their persistence, ubiquity, and potential toxicity (Chemysh et al., 2025). Numerous studies have documented their occurrence and environmental risks in aquatic systems (Auta et al., 2017 ; dos Santos et al., 2023 ; Ma et al., 2016 ; Prasertboonyai et al., 2025 ). MPs can release leachable additives and adsorb heavy metals and organic pollutants, acting as vectors that amplify chemical exposure in aquatic and terrestrial ecosystems (Lithner et al., 2011 ; Godoy et al., 2019 ; Zhang et al., 2015 ). In urban environments, stormwater runoff is recognized as a major transport pathway for MPs from impervious surfaces to drainage networks (Zhang et al., 2023 ), representing a key terrestrial source of marine pollution (Wang et al., 2022 ). Understanding how stormwater control measures influence this transport is therefore essential to prevent MP discharge to receiving waters. Within this context, permeable pavements have recently gained attention as potential sinks for MPs, intercepting them during infiltration and preventing their migration into surface waters (Kong et al., 2024 ; García-Haba et al., 2023b ). However, the long-term behavior of MPs within these systems, and how it evolves as the pavement structure clogs or ages, remains largely unexplored. It is still uncertain whether the same processes that reduce permeability also govern the accumulation or release of MPs. Addressing this question is critical to assess the real environmental role of permeable pavements as both stormwater treatment units and potential secondary sources of microplastics. This study investigates the long-term performance of a full-scale permeable pavement installation after five years of continuous operation, focusing on the coupled evolution of hydraulic behavior and pollutant retention (suspended solids, nutrients, and microplastics). Two complementary approaches were adopted: on-site permeability monitoring over a two-year period and laboratory analyses of extracted pavement slabs to evaluate pollutant accumulation, permeability recovery, and MPs retention. MPs were identified by Raman spectroscopy, and nutrients and solids were analyzed using standard methods. By combining field-scale evidence with controlled laboratory analyses, this work provides novel insights into how physical degradation processes influence the fate of pollutants in aging permeable pavements. These findings contribute to a better understanding of the environmental effectiveness and long-term sustainability of this nature-based solution in urban stormwater management. 2. Material and methods 2.1 Site description The study was conducted in a 10000 m² pedestrian area located in Valencia (Spain), constructed in 2020 and primarily used as a weekend open-air market. This activity involves intense pedestrian flow and intermittent vehicular access for logistics and maintenance, promoting heterogeneous loading conditions. The proximity to urban roads and the coast further contributes to the deposition of airborne particles. The surface is mechanically swept after each market day, following municipal cleaning practices. Approximately 3000 m² are paved with porous concrete slabs arranged in a mosaic pattern of varying sizes and tones, while the remaining surface consists of impervious concrete (Fig. 1 ). The permeable pavement follows a standard structural design (Woods-Ballard et al., 2015 ), except at the perimeter, where an infiltration trench configuration facilitates runoff infiltration. 2.2 Methodology The methodology combined field permeability tests performed between January 2023 and December 2024 with complementary laboratory analyses on both new and used slabs. In situ measurements were carried out bimonthly during the first year and quarterly during the second. Laboratory tests were conducted on two new slabs provided by the manufacturer and two slabs extracted directly from the site after five years of service. Field tests assessed the evolution of infiltration capacity under real operating conditions, while laboratory experiments focused on pollutant release and cleaning efficiency. Pressure washing was applied to both slab types, and the resulting wash water was collected to quantify the contaminants retained on the surface and within the slab matrix. 2.2.1 In situ methodology Five representative points were selected within the permeable area and along its perimeter, based on their position and surrounding land use. Two contiguous slabs were tested at each location, with duplicate measurements on both. An initial survey considered 18 slabs across 9 sites, but due to the low variability observed in preliminary results, the total number was reduced to ensure methodological consistency and long-term feasibility (Fig. 2 ). Small-format slabs were excluded, representing less than 10% of the total permeable surface. The porous concrete slabs were designed to maintain a high proportion of interconnected voids (15–30%), resulting from their coarse granular structure and cementitious matrix (Elizondo-Martínez et al., 2020 ; Rangelov et al., 2016 ; Brake et al., 2016 ; Giustozzi, 2016 ). Permeability tests were performed following the NLT-327/00 standard, based on a variable-head approach comparable to EN 12697-40. Each measurement consisted of a preliminary saturation followed by two consecutive readings at the same central point (García-Haba et al., 2023a ). Although the standard does not specify sealing between the device and pavement, some authors recommend silicone sealants to prevent lateral leakage and improve accuracy (Li et al., 2013 ; Kayhanian et al., 2012 ). However, other studies reported limited effectiveness in porous systems (Winston et al., 2016 ). Therefore, no sealing was applied in this study, ensuring comparability with previous works. It is worth noting that variable-head methods can yield permeability values 50–90% higher than constant-head approaches (Qin et al., 2015 ; Li et al., 2013 ). 2.2.2 Laboratory methodology Laboratory tests were conducted on four slabs: two new (N) provided by the manufacturer, and two used (U) extracted directly from the site after five years of exposure. Each slab was placed on a drainage cell within a perforated-bottom chamber elevated on a metal frame (Fig. 3 ). A 30 L container positioned underneath collected all effluent water. The same permeability procedure described earlier was applied before and after pressure washing (140 bar, 1 min per side), following Andrés-Valeri et al. ( 2016 ). To maintain consistent conditions, 22 L of tap water were used per test. The resulting water was homogenized, and 1 L subsamples were taken for water quality analyses including pH, conductivity (WTW Multi 340i TetraCon® and SenTix® 41 probes), turbidity (TN100 Eutech), chemical oxygen demand (COD), ammonium, nitrite, nitrate, total nitrogen, phosphate, and total phosphorus (Spectroquant® kits according to ISO standards), as well as total and volatile suspended solids (UNE-EN 872:2006; UNE 77034:2002). The remaining volume was used for microplastic (MP) analysis following Calzadilla-Cabrera et al. ( 2023 ). Samples were sieved through 425, 75, and 40 µm meshes to classify retained fractions by size. Each fraction underwent oxidation with 30% H₂O₂ and two-phase density separation (CaCl₂ and KI). Filtered residues were then analyzed by stereomicroscopy and Raman spectroscopy for identification and classification. 2.2.3 Statistics Statistical analyses were conducted using STATGRAPHICS Centurion 19 (version 19.1.2). Normality was first verified, applying the t-test for comparison of means when assumptions were met, and the Kruskal–Wallis test otherwise. A significance level of p ≤ 0.05 was adopted in all tests. 3. Results and discussion 3.1 Original slab permeability The new slabs exhibited an average permeability of 3558 mm/h, below the minimum initial value of 4500 mm/h recommended by the local SUDS guideline for Valencia (de la Fuente García et al., 2021 ). This value is also substantially lower than those reported for other porous concretes under laboratory conditions, which typically range from 14400–33500 mm/h (Anjos Viana et al., 2023 ) to 36000–72000 mm/h (Huang et al., 2010 ). Such differences may be related to aggregate gradation, maximum particle size, and the aggregate-to-cement ratio, all of which control pore connectivity and effective porosity (Zhang et al., 2021 ; Huang et al., 2010 ). After pressure washing, permeability increased by approximately 32%, likely due to the removal of fine particles remaining from the manufacturing process. Nevertheless, even after cleaning, permeability values remained well below those typically recorded in real installations, where initial values can reach up to 24480 mm/h (Sañudo-Fontaneda et al., 2018 ) or even higher ranges, from 6000 to 76000 mm/h (Bean et al., 2007 ; Razzaghmanesh & Beecham, 2018 ). These results highlight the variability among porous concretes depending on their mix design and manufacturing process, and suggest that factory residues may substantially limit initial infiltration performance. 3.2 In situ permeability evolution After five years of operation, the mean in situ permeability was 1659.9 mm/h, representing a reduction of approximately 48 ± 15% relative to the initial laboratory value. This decrease, while substantial, remains well above the design threshold of 450 mm/h established by the local SUDS guideline (de la Fuente García et al., 2021 ). Thus, the observed decline appears moderate considering the site’s intense activity and exposure conditions. The reduction in permeability can be attributed to progressive clogging caused by sediment deposition and limited maintenance frequency. Similar trends have been reported by García-Haba et al. ( 2023a ) and Hernández-Crespo et al. ( 2019 ), who emphasized that the nature of sediment, accumulation rate, and local climate strongly influence the rate of hydraulic decline. This evidence supports the applicability of a 2:1 impermeable-to-permeable surface ratio for sustained performance, as recommended in many SUDS guidelines. The spatial variability observed across the test points (Table 1 ) is consistent with previous field studies (Pieralisi et al., 2025 ) and can be partly explained by differences in local exposure. Lower permeability values at points I1, I2, and P1 corresponded to areas of higher pedestrian and service traffic or proximity to walls, which favor sediment accumulation through the barrier effect (Donzelli et al., 2021 ). Moreover, the NLT-327/00 method presented practical limitations, as water leakage occasionally occurred through the device–pavement interface, particularly in clogged areas. A revision of the standard to include a perimeter seal could improve test reliability and comparability among studies. Finally, the Mediterranean climatic regime, marked by alternating droughts and intense rainfall, likely contributes to the cyclic saturation and desaturation of the pavement, accelerating the redistribution of fine sediments. This seasonal dynamic should be considered when defining maintenance schedules (Palla & Gnecco, 2020 ; Brunetti et al., 2016 ). Table 1 Permeability values (mm/h) determined from the NLT-327/00 test, mean and standard deviation for the selected slabs at the 5 points of the site. In red, permeabilities below the minimum permeability threshold required in the València SUDS Design Guide (De la Fuente et al. 2021). Permeability (mm/h) I 1a I 1b I 2a I 2b I 3a I 3b I 4a I 4b P 1a P 1b Mean 323.81 696.81 1656.78 1643.14 6845.83 1144.52 5763.93 3878.44 231.08 431.72 SE 28.18 54.14 225.09 204.10 434.01 130.01 376.96 269.18 38.50 42.16 3.3 Permeability recovery capacity Laboratory cleaning tests on used slabs revealed a mean permeability recovery of 42.5%, increasing from 1076 to 1531 mm/h. Both samples showed similar behavior, indicating that clogging occurred mainly in the upper layer and was partially reversible. Although the cleaning was conducted under controlled conditions, these findings suggest that combining mechanical vacuuming and pressure washing in the field could substantially improve hydraulic recovery (Winston et al., 2016 ). The observed recovery is consistent with previous reports in similar pavements (García-Haba et al., 2023a ), although Danz et al. ( 2020 ) recorded higher gains (up to 123%) when both methods were applied sequentially. However, recovery potential depends strongly on sediment characteristics, pore structure, and exposure conditions (Kia et al., 2017 ; Andrés-Valeri et al., 2016 ). Overall, the results confirm that the permeability loss is not entirely irreversible and that maintenance interventions can partially restore hydraulic functionality, emphasizing the importance of periodic cleaning under Mediterranean conditions. 3.4 Pollutant Retention Capacity The results shown in Table 2 reveal clear differences between the new and used slabs after five years of operation, particularly in parameters related to the accumulation of solid and organic pollutants (p < 0.05). Used slabs exhibited increases of 258% in COD, 123% in total phosphorus, 28% in total nitrogen, and 48% in total suspended solids, indicating a notable buildup of organic matter and particulate material within the porous structure. Turbidity was also higher in used slabs, while the relatively elevated values observed in new slabs may be associated with residual particles from the manufacturing process. Table 2 Average concentrations and surface loads of pollutants in the analyzed slabs. Slab Id. Conductivity µS/cm Turbidity NTU COD mg/L NH 4 + mg/L NO 2 − mg/L NO 3 − mg/L TN mg/L PO 4 3− mg/L TP mg/L TSS mg/L Used 941 127.5 83.5 0.05 0.06 1 2.75 0.03 0.58 304.8 New 980.5 83.6 23.3 0.04 0.04 0.9 2.15 0.02 0.26 205.9 COD g/m 2 NH 4 + mg/m 2 NO 2 − mg/m 2 NO 3 − mg/m 2 TN mg/m 2 PO 4 3− mg/m 2 TP mg/m 2 TSS g/m 2 Used load 13.60 7.08 8.97 158.84 441.36 4.63 94.00 48.92 New load 3.17 6.81 4.97 122.63 292.94 4.09 34.74 28.05 These findings provide clear evidence that permeable pavements can act as long-term sinks for pollutants in urban environments, contributing to the interception of contaminants before they reach receiving waters. The observed accumulation patterns suggest that pollutant retention is primarily associated with physical trapping and adsorption processes within the upper and intermediate layers of the slabs. Nevertheless, these mechanisms are less effective for dissolved pollutants, which are more likely to pass through the pore network with the infiltrating water. Similar results have been reported in other field-scale studies, confirming the ability of these systems to retain suspended solids, organic matter, and nutrients over extended periods of operation (Hernández-Crespo et al., 2019 ; Liu et al., 2019 ; García-Haba et al., 2023a ). Although this study did not directly estimate removal efficiencies, the pollutant concentrations and loads retained within the slabs are consistent with the high retention values observed in complete permeable pavement systems incorporating additional filter layers such as gravels or geotextiles (Rowe et al., 2009 ; Pezzaniti et al., 2009 ). The Mediterranean rainfall regime under which the system has operated for five years could also play a determining role, as previous studies have shown that intermittent and intense precipitation patterns may reduce the total amount of contaminants retained compared with more continuous rainfall conditions typical of Atlantic climates (Hernández-Crespo et al., 2019 ). From an environmental perspective, these results highlight the relevance of permeable pavements as decentralized infrastructures capable of intercepting particulate and nutrient pollution at the source. However, the progressive accumulation of solids and organic matter observed here suggests a gradual saturation of the porous matrix, which could ultimately reduce both hydraulic conductivity and pollutant retention efficiency. This process underscores the importance of long-term monitoring and maintenance strategies to sustain the dual hydraulic and water quality functions of these systems. In addition to concentration differences, the estimated pollutant loads further confirm the system’s capacity to immobilize contaminants. Used slabs accumulated up to 13.6 g/m² of COD and nearly 49 g/m² of suspended solids, compared to 3.17 g/m² and 28 g/m², respectively, in new slabs (Table 2 ). Nutrient loads such as total nitrogen and total phosphorus also showed marked increases, reinforcing the evidence of long-term pollutant entrapment within the porous structure. These results emphasize the role of permeable pavements not only as hydrologic regulators but also as functional filters mitigating the transfer of urban-derived pollutants to downstream aquatic ecosystems. 3.5 Microplastic Retention Capacity MPs are increasingly recognized as ubiquitous contaminants in urban environments, largely mobilized by stormwater runoff from paved surfaces (Zhang et al., 2023 ). Permeable pavements can intercept these contaminants at the source, but the mechanisms governing their long-term retention under field conditions remain poorly constrained. In this study, used slabs accumulated 10272 ± 5829 MPs/m², about 7.5 times more than the load measured in new slabs (1343 ± 194 MPs/m²; p < 0.05). From these values we estimate an annual accumulation rate 2054 MPs/m²/yr for the site, which can be used as a reference for comparable urban contexts subject to intense plastic loading. The exceptionally high accumulation recorded here must be interpreted in light of the site context. The study area hosts a weekly flea market that concentrates intense pedestrian activity and generates abundant degraded plastic waste (toys, tarpaulins, textile debris), producing a local MP input far above typical residential or commercial areas (see images in Supplementary Material). Several studies have estimated concentrations of MPs in urban runoff to better understand the inputs to these systems, finding values between 2 and 110 MP/L depending on basin characteristics and precipitation conditions (Zhang et al., 2023 ; Sang et al., 2021 ). The most representative estimate in relation to the present study is that of García-Haba et al. ( 2024 ), with 24 ± 17 MP/L in runoff from an urban catchment in Valencia. Moreover, climatic and hydrological conditions also play a decisive role in MP dynamics, Kong et al. ( 2025 ) demonstrated that MP retention efficiencies in porous pavements decline under high rainfall intensities. Together, these observations emphasize that both local emissions and climatic drivers determine the magnitude of MPs accumulation in permeable pavements under real operating conditions. Morphological and size data provide mechanistic insight into MPs retention within the porous slabs (Fig. 4 ). The retained fraction was dominated by fibers (73%), followed by particles (26%) and a negligible proportion of films (≤ 1%). Although particles are often the dominant form reported in urban runoff (Zhang et al., 2023 ; Sang et al., 2021 ), several studies have shown that effluents from permeable pavements tend to contain a higher proportion of small particles (García-Haba et al., 2024 ; Kong et al., 2024 ), suggesting that fibers are more effectively retained within the pavement matrix. Their elongated and flexible morphology favors mechanical entanglement and physical trapping within the interstices of the porous concrete, whereas compact particles are more likely to migrate with advective flows unless captured by pore constrictions or by fines filling the voids. In terms of size, the MPs retained in the slabs were mostly within the medium (425–75 µm) and large (> 425 µm) fractions (Fig. 4 ), indicating preferential capture of these classes. Conversely, fine particles (< 75 µm) were less represented, aligning with the general tendency of smaller MPs to be more easily transported through permeable systems. Together, these patterns reveal that the porous pavement acts as an effective filter for medium- and large-sized fibers, while finer and more compact MPs are selectively transmitted through the system. Polymeric composition (Fig. 5 ) revealed PE (35%), PP (31%) and polyester (22%) as dominant, with minor PVC (4%), PS and PU (3% each) and trace ABS (1%). This composition mirrors global production and typical urban waste streams (Sang et al., 2021 ; Kong et al., 2024 ), and the relatively high polyester fraction is consistent with textile-derived fibers dominating in residential or pedestrian contexts. Notably, water-soluble polymers such as PVA reported in shorter-term studies (García-Haba et al., 2024 ) were almost absent here, plausibly due to dissolution or degradation during five years of exposure, an observation that underlines how service time alters polymer detectability and the residual MP fingerprint in aged infrastructures. Comparative evidence highlights the role of pavement design and use patterns. Studies that include full system configurations (gravel, sand layers, geotextiles) often report high effluent removal efficiencies (> 90%) for MPs (Kong et al., 2024 ; García-Haba et al., 2024 ). However, high removal in the effluent implies internal trapping rather than elimination, thereby converting the pavement into a temporary sink. Over time, progressive accumulation increases the probability of secondary emissions during maintenance, extreme hydrological events, or material disturbance. Our data show clear long-term entrapment but also reveal limitations in capturing small and dissolved fractions, meaning pavements act as partial barriers that reduce but do not fully prevent MP export. From an environmental management perspective, these results have several implications. First, permeable pavements can substantially reduce the load of medium and large MPs reaching downstream water bodies, particularly under moderate loading scenarios. Second, the site-specific nature of MP sources means that adoption of permeable pavements in high-pressure sites (markets, industrial yards) must be accompanied by adapted maintenance strategies and possibly upstream source control to avoid rapid matrix saturation. Third, design modifications, for example incorporating adsorptive amendments or additional fine filter layers (Chen et al., 2022 ), could enhance retention of smaller fractions and reduce the risk of pavements becoming secondary MP sources. Limitations of this study must be acknowledged. Our estimates are site-specific and reflect an extreme loading context; extrapolation to other urban settings requires careful scaling with local emission rates and hydrological regimes. Also, while Raman spectroscopy provides robust polymer identification, weathering and biofouling can complicate spectra interpretation for certain polymers after long exposure. Future work should combine lower-size detection limits, tracer experiments, and targeted assessment of maintenance-related mobilization to better quantify the net fate of MPs in permeable pavement systems. In sum, the evidence indicates that permeable pavements function as effective long-term sinks for medium-to-large MPs under real urban conditions, but their limited retention of fine fractions and potential for saturation demand integrated design and maintenance strategies to prevent the emergence of secondary pollution sources. 4. Conclusions This study provides field-based evidence of the long-term behavior of full-scale permeable pavements operating for five years under high urban pollutant loads. The results demonstrate their dual functionality: effective retention of suspended solids, organic matter, nutrients, and microplastics, together with a progressive reduction in permeability due to clogging. Laboratory restoration tests confirmed a high recovery potential, underscoring the critical role of maintenance in preserving hydraulic and treatment performance. The marked accumulation of microplastics, mainly polyethylene and polypropylene fibers, highlights the capacity of the porous matrix to retain emerging contaminants over extended timescales. These findings emphasize that microstructural attributes such as pore connectivity and tortuosity control both hydraulic decline and contaminant entrapment. Conducting laboratory analyses on aged field materials is therefore essential to constrain realistic long-term retention mechanisms. The variability observed among new slabs also indicates that nominal permeability values should be interpreted as ranges rather than fixed design parameters, encouraging the development of certification frameworks that reflect manufacturing heterogeneity. The extreme loading context examined here provides a useful upper bound for assessing pavement resilience and defining operational limits under demanding urban conditions. Overall, this work advances understanding of permeable pavements as multifunctional stormwater infrastructures capable of simultaneously managing runoff and contaminant loads. Ensuring their long-term sustainability will require design and maintenance strategies that explicitly integrate hydraulic capacity, pollutant retention, and durability under real-world exposure. Altogether, the findings reinforce the utility of permeable pavements as multifunctional tools for stormwater management. However, to ensure long-term effectiveness, their design and regulation must increasingly consider aspects beyond hydraulic capacity, integrating contaminant retention, maintenance feasibility, and pollutant-specific behaviors into a holistic approach to sustainable urban infrastructure. Declarations Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Funding: This research is developed within the framework of the project SUDSLong- VLC Grant PID2021-122946OB-C32 funded by MICIU/AEI/10.13039/501100011033 and by “ERDF A way of making Europe”. Darío Calzadilla Cabrera appreciates the pre-doctoral contracts funding received for doctors training Grant PRE2022-102831 funded by MICIU/AEI/10.13039/501100011033 and by “ESF+”. Eduardo García Haba appreciates the pre-doctoral contracts funding received for doctors training Grant PRE2019-089409 funded by MICIU/ AEI/10.13039/501100011033 and by “ESF Investing in your future”. The authors would like to thank the Valencia City Council, the construction company Bertolín, and the slab supplier Fenollar for their collaboration. Competing interest: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Author contributions: CRediT Darío Calzadilla-Cabrera: Data curation, formal analysis, investigation, methodology, visualization, writing. Eduardo García-Haba: Data curation, investigation, methodology, supervision, validation. 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Supplementary Files GraphicalAbstractCalzadillaCabreraetal2025.tiff SupplementaryMaterialCalzadillaCabreraetal.2025.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8173976","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":550536376,"identity":"790c7a7e-12af-4c6b-a6d3-1580d1486bc5","order_by":0,"name":"Darío 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1","display":"","copyAsset":false,"role":"figure","size":906939,"visible":true,"origin":"","legend":"\u003cp\u003eAerial view of the site, showing the permeable pavement, the perimeter infiltration trenches (red dashed line), and the slope direction (blue dashed line). (Source of the image: Google Maps).\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8173976/v1/9d4697da4af680f4cacfec27.png"},{"id":97142803,"identity":"ce54d307-6d79-4aec-a355-899f7ac86704","added_by":"auto","created_at":"2025-12-01 10:07:58","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":927747,"visible":true,"origin":"","legend":"\u003cp\u003eLocation of the points inside the site (I 1, I 2, I 3, I 4) and its perimeter (P 1), selected for the permeability study (Source of the image: Google Maps).\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8173976/v1/6718d886ef82cf6145a13d07.png"},{"id":97142558,"identity":"a32003fe-ae5c-4d23-b9ba-ed9bb48f7687","added_by":"auto","created_at":"2025-12-01 10:07:43","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":412224,"visible":true,"origin":"","legend":"\u003cp\u003eStructure used to perform the permeability and washout tests of the slabs in the laboratory (left). Interior of chamber with perforated bottom and porous concrete slab supported on a drainage cell during the permeability test with the LCS permeameter (right).\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8173976/v1/c63c8fc9b8fb55a7f1f20eac.png"},{"id":97128668,"identity":"18e49263-b505-491f-bde1-91b801cfe42f","added_by":"auto","created_at":"2025-12-01 08:35:47","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":24031,"visible":true,"origin":"","legend":"\u003cp\u003eDistribution of MPs in the analyzed slabs by form and size (%).\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8173976/v1/add7bb595c3b78c80cc4602b.png"},{"id":97142346,"identity":"0befa684-1970-46e6-bbf2-84690cb9f6e1","added_by":"auto","created_at":"2025-12-01 10:07:33","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":50303,"visible":true,"origin":"","legend":"\u003cp\u003eComponents of the MPs found, in percentage, in the analyzed slabs.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8173976/v1/7a3bb7c4a475f48b00dfc814.png"},{"id":100358284,"identity":"4cb7a98a-ed57-460f-ab5f-9561e4d6021b","added_by":"auto","created_at":"2026-01-16 07:20:52","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3544643,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8173976/v1/299aa359-f54d-4df2-830a-df6fb6c0afd2.pdf"},{"id":97128688,"identity":"112b6948-cc85-455d-b186-1114854a9c68","added_by":"auto","created_at":"2025-12-01 08:35:47","extension":"tiff","order_by":6,"title":"","display":"","copyAsset":false,"role":"supplement","size":18187764,"visible":true,"origin":"","legend":"","description":"","filename":"GraphicalAbstractCalzadillaCabreraetal2025.tiff","url":"https://assets-eu.researchsquare.com/files/rs-8173976/v1/2d291e594786276b49b3a330.tiff"},{"id":97128679,"identity":"04ab481a-bfd5-47bd-a41b-99d1dfae4799","added_by":"auto","created_at":"2025-12-01 08:35:47","extension":"docx","order_by":8,"title":"","display":"","copyAsset":false,"role":"supplement","size":4088233,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryMaterialCalzadillaCabreraetal.2025.docx","url":"https://assets-eu.researchsquare.com/files/rs-8173976/v1/72bbd3526334b8dba3668b44.docx"}],"financialInterests":"","formattedTitle":"Long-term environmental performance of precast slabs in permeable pavements: hydraulic functionality and pollutant retention in a real-life installation","fulltext":[{"header":"Highlights","content":"\u003cul\u003e\n \u003cli\u003eFindings contribute to understanding the durability and functionality of permeable pavements as sustainable construction materials in urban infrastructure.\u003c/li\u003e\n \u003cli\u003eResults highlight the dual role of permeable pavements in stormwater management and contaminant control.\u003c/li\u003e\n \u003cli\u003eAfter five years, pavements still provide relevant pollutant retention, supporting long-term performance.\u003c/li\u003e\n \u003cli\u003eMicroplastic accumulation is associated with a progressive reduction in pavement permeability.\u003c/li\u003e\n \u003cli\u003ePermeable pavements retain a significant fraction of microplastics in their surface and filter layers.\u003c/li\u003e\n\u003c/ul\u003e"},{"header":"1. Introduction","content":"\u003cp\u003eIn the context of sustainable urban development, permeable pavements have become consolidated as a reliable nature-based solution to mitigate the environmental impacts of urbanization (Zhang et al., \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). By enhancing infiltration and improving runoff quality, they contribute to restoring natural hydrological processes and reducing pollutant loads to receiving waters (Tota-Maharaj et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Febriana et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; Castillo-Rodr\u0026iacute;guez et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). In addition, they can support aquifer recharge and reduce the urban heat island effect (Halder et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eHowever, their long-term performance can deteriorate due to progressive clogging of the pore structure, driven by the accumulation of sediments and organic matter (Rahman et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; Garc\u0026iacute;a-Haba et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2023a\u003c/span\u003e). This process not only reduces infiltration capacity but may also alter the pathways and retention of contaminants within the pavement matrix. Despite numerous studies on hydraulic efficiency, few have jointly examined the long-term coupling between hydrological decline and pollutant dynamics under real operating conditions (Rodr\u0026iacute;guez-Rojas et al. \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Qamhia et al. \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eBeyond their hydrological role, permeable pavements act as reactive filters that improve the quality of urban runoff by retaining sediments and dissolved contaminants through filtration, sedimentation, and adsorption processes (Raimondi et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Kong et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Several studies have reported efficient removal of suspended solids and variable but generally positive efficiencies for nutrients such as nitrogen and phosphorus (Collins et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Huang et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Gilbert \u0026amp; Clausen, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Heavy metals (Cu, Pb, Zn) and hydrocarbons have also been found to accumulate within the pavement layers (Dietz, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Poor et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2023\u003c/span\u003e Scholz \u0026amp; Grabowiecki, \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Brown et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2009\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eIn recent years, microplastics (MPs) have emerged as pervasive contaminants of global concern due to their persistence, ubiquity, and potential toxicity (Chemysh et al., 2025). Numerous studies have documented their occurrence and environmental risks in aquatic systems (Auta et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; dos Santos et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Ma et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Prasertboonyai et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). MPs can release leachable additives and adsorb heavy metals and organic pollutants, acting as vectors that amplify chemical exposure in aquatic and terrestrial ecosystems (Lithner et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Godoy et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eIn urban environments, stormwater runoff is recognized as a major transport pathway for MPs from impervious surfaces to drainage networks (Zhang et al., \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), representing a key terrestrial source of marine pollution (Wang et al., \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Understanding how stormwater control measures influence this transport is therefore essential to prevent MP discharge to receiving waters.\u003c/p\u003e\u003cp\u003eWithin this context, permeable pavements have recently gained attention as potential sinks for MPs, intercepting them during infiltration and preventing their migration into surface waters (Kong et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Garc\u0026iacute;a-Haba et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2023b\u003c/span\u003e). However, the long-term behavior of MPs within these systems, and how it evolves as the pavement structure clogs or ages, remains largely unexplored. It is still uncertain whether the same processes that reduce permeability also govern the accumulation or release of MPs. Addressing this question is critical to assess the real environmental role of permeable pavements as both stormwater treatment units and potential secondary sources of microplastics.\u003c/p\u003e\u003cp\u003eThis study investigates the long-term performance of a full-scale permeable pavement installation after five years of continuous operation, focusing on the coupled evolution of hydraulic behavior and pollutant retention (suspended solids, nutrients, and microplastics). Two complementary approaches were adopted: on-site permeability monitoring over a two-year period and laboratory analyses of extracted pavement slabs to evaluate pollutant accumulation, permeability recovery, and MPs retention. MPs were identified by Raman spectroscopy, and nutrients and solids were analyzed using standard methods.\u003c/p\u003e\u003cp\u003eBy combining field-scale evidence with controlled laboratory analyses, this work provides novel insights into how physical degradation processes influence the fate of pollutants in aging permeable pavements. These findings contribute to a better understanding of the environmental effectiveness and long-term sustainability of this nature-based solution in urban stormwater management.\u003c/p\u003e"},{"header":"2. Material and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Site description\u003c/h2\u003e\u003cp\u003eThe study was conducted in a 10000 m\u0026sup2; pedestrian area located in Valencia (Spain), constructed in 2020 and primarily used as a weekend open-air market. This activity involves intense pedestrian flow and intermittent vehicular access for logistics and maintenance, promoting heterogeneous loading conditions. The proximity to urban roads and the coast further contributes to the deposition of airborne particles. The surface is mechanically swept after each market day, following municipal cleaning practices.\u003c/p\u003e\u003cp\u003eApproximately 3000 m\u0026sup2; are paved with porous concrete slabs arranged in a mosaic pattern of varying sizes and tones, while the remaining surface consists of impervious concrete (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The permeable pavement follows a standard structural design (Woods-Ballard et al., \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), except at the perimeter, where an infiltration trench configuration facilitates runoff infiltration.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Methodology\u003c/h2\u003e\u003cp\u003eThe methodology combined field permeability tests performed between January 2023 and December 2024 with complementary laboratory analyses on both new and used slabs. In situ measurements were carried out bimonthly during the first year and quarterly during the second. Laboratory tests were conducted on two new slabs provided by the manufacturer and two slabs extracted directly from the site after five years of service.\u003c/p\u003e\u003cp\u003eField tests assessed the evolution of infiltration capacity under real operating conditions, while laboratory experiments focused on pollutant release and cleaning efficiency. Pressure washing was applied to both slab types, and the resulting wash water was collected to quantify the contaminants retained on the surface and within the slab matrix.\u003c/p\u003e\u003cdiv id=\"Sec5\" class=\"Section3\"\u003e\u003ch2\u003e2.2.1 In situ methodology\u003c/h2\u003e\u003cp\u003eFive representative points were selected within the permeable area and along its perimeter, based on their position and surrounding land use. Two contiguous slabs were tested at each location, with duplicate measurements on both. An initial survey considered 18 slabs across 9 sites, but due to the low variability observed in preliminary results, the total number was reduced to ensure methodological consistency and long-term feasibility (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Small-format slabs were excluded, representing less than 10% of the total permeable surface.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe porous concrete slabs were designed to maintain a high proportion of interconnected voids (15\u0026ndash;30%), resulting from their coarse granular structure and cementitious matrix (Elizondo-Mart\u0026iacute;nez et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Rangelov et al., \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Brake et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Giustozzi, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Permeability tests were performed following the NLT-327/00 standard, based on a variable-head approach comparable to EN 12697-40. Each measurement consisted of a preliminary saturation followed by two consecutive readings at the same central point (Garc\u0026iacute;a-Haba et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2023a\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eAlthough the standard does not specify sealing between the device and pavement, some authors recommend silicone sealants to prevent lateral leakage and improve accuracy (Li et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Kayhanian et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). However, other studies reported limited effectiveness in porous systems (Winston et al., \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Therefore, no sealing was applied in this study, ensuring comparability with previous works. It is worth noting that variable-head methods can yield permeability values 50\u0026ndash;90% higher than constant-head approaches (Qin et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Li et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2013\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section3\"\u003e\u003ch2\u003e2.2.2 Laboratory methodology\u003c/h2\u003e\u003cp\u003eLaboratory tests were conducted on four slabs: two new (N) provided by the manufacturer, and two used (U) extracted directly from the site after five years of exposure. Each slab was placed on a drainage cell within a perforated-bottom chamber elevated on a metal frame (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). A 30 L container positioned underneath collected all effluent water.\u003c/p\u003e\u003cp\u003eThe same permeability procedure described earlier was applied before and after pressure washing (140 bar, 1 min per side), following Andr\u0026eacute;s-Valeri et al. (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). To maintain consistent conditions, 22 L of tap water were used per test. The resulting water was homogenized, and 1 L subsamples were taken for water quality analyses including pH, conductivity (WTW Multi 340i TetraCon\u0026reg; and SenTix\u0026reg; 41 probes), turbidity (TN100 Eutech), chemical oxygen demand (COD), ammonium, nitrite, nitrate, total nitrogen, phosphate, and total phosphorus (Spectroquant\u0026reg; kits according to ISO standards), as well as total and volatile suspended solids (UNE-EN 872:2006; UNE 77034:2002).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe remaining volume was used for microplastic (MP) analysis following Calzadilla-Cabrera et al. (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Samples were sieved through 425, 75, and 40 \u0026micro;m meshes to classify retained fractions by size. Each fraction underwent oxidation with 30% H₂O₂ and two-phase density separation (CaCl₂ and KI). Filtered residues were then analyzed by stereomicroscopy and Raman spectroscopy for identification and classification.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section3\"\u003e\u003ch2\u003e2.2.3 Statistics\u003c/h2\u003e\u003cp\u003eStatistical analyses were conducted using STATGRAPHICS Centurion 19 (version 19.1.2). Normality was first verified, applying the t-test for comparison of means when assumptions were met, and the Kruskal\u0026ndash;Wallis test otherwise. A significance level of p\u0026thinsp;\u0026le;\u0026thinsp;0.05 was adopted in all tests.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Original slab permeability\u003c/h2\u003e\u003cp\u003eThe new slabs exhibited an average permeability of 3558 mm/h, below the minimum initial value of 4500 mm/h recommended by the local SUDS guideline for Valencia (de la Fuente Garc\u0026iacute;a et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). This value is also substantially lower than those reported for other porous concretes under laboratory conditions, which typically range from 14400\u0026ndash;33500 mm/h (Anjos Viana et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) to 36000\u0026ndash;72000 mm/h (Huang et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). Such differences may be related to aggregate gradation, maximum particle size, and the aggregate-to-cement ratio, all of which control pore connectivity and effective porosity (Zhang et al., \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Huang et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2010\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eAfter pressure washing, permeability increased by approximately 32%, likely due to the removal of fine particles remaining from the manufacturing process. Nevertheless, even after cleaning, permeability values remained well below those typically recorded in real installations, where initial values can reach up to 24480 mm/h (Sa\u0026ntilde;udo-Fontaneda et al., \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) or even higher ranges, from 6000 to 76000 mm/h (Bean et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Razzaghmanesh \u0026amp; Beecham, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThese results highlight the variability among porous concretes depending on their mix design and manufacturing process, and suggest that factory residues may substantially limit initial infiltration performance.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e3.2 In situ permeability evolution\u003c/h2\u003e\u003cp\u003eAfter five years of operation, the mean in situ permeability was 1659.9 mm/h, representing a reduction of approximately 48\u0026thinsp;\u0026plusmn;\u0026thinsp;15% relative to the initial laboratory value. This decrease, while substantial, remains well above the design threshold of 450 mm/h established by the local SUDS guideline (de la Fuente Garc\u0026iacute;a et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Thus, the observed decline appears moderate considering the site\u0026rsquo;s intense activity and exposure conditions.\u003c/p\u003e\u003cp\u003eThe reduction in permeability can be attributed to progressive clogging caused by sediment deposition and limited maintenance frequency. Similar trends have been reported by Garc\u0026iacute;a-Haba et al. (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2023a\u003c/span\u003e) and Hern\u0026aacute;ndez-Crespo et al. (\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), who emphasized that the nature of sediment, accumulation rate, and local climate strongly influence the rate of hydraulic decline. This evidence supports the applicability of a 2:1 impermeable-to-permeable surface ratio for sustained performance, as recommended in many SUDS guidelines.\u003c/p\u003e\u003cp\u003eThe spatial variability observed across the test points (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) is consistent with previous field studies (Pieralisi et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2025\u003c/span\u003e) and can be partly explained by differences in local exposure. Lower permeability values at points I1, I2, and P1 corresponded to areas of higher pedestrian and service traffic or proximity to walls, which favor sediment accumulation through the barrier effect (Donzelli et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eMoreover, the NLT-327/00 method presented practical limitations, as water leakage occasionally occurred through the device\u0026ndash;pavement interface, particularly in clogged areas. A revision of the standard to include a perimeter seal could improve test reliability and comparability among studies.\u003c/p\u003e\u003cp\u003eFinally, the Mediterranean climatic regime, marked by alternating droughts and intense rainfall, likely contributes to the cyclic saturation and desaturation of the pavement, accelerating the redistribution of fine sediments. This seasonal dynamic should be considered when defining maintenance schedules (Palla \u0026amp; Gnecco, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Brunetti et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003ePermeability values (mm/h) determined from the NLT-327/00 test, mean and standard deviation for the selected slabs at the 5 points of the site. In red, permeabilities below the minimum permeability threshold required in the Val\u0026egrave;ncia SUDS Design Guide (De la Fuente et al. 2021).\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"11\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colspan=\"10\" nameend=\"c11\" namest=\"c2\"\u003e\u003cp\u003ePermeability (mm/h)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eI 1a\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eI 1b\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eI 2a\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eI 2b\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eI 3a\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eI 3b\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003eI 4a\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\"\u003e\u003cp\u003eI 4b\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c10\"\u003e\u003cp\u003eP 1a\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c11\"\u003e\u003cp\u003eP 1b\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eMean\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e323.81\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e696.81\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e1656.78\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e1643.14\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e6845.83\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e1144.52\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e5763.93\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e3878.44\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e231.08\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e\u003cp\u003e431.72\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eSE\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e28.18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e54.14\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e225.09\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e204.10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e434.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e130.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e376.96\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e269.18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e38.50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e\u003cp\u003e42.16\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003e3.3 Permeability recovery capacity\u003c/h2\u003e\u003cp\u003eLaboratory cleaning tests on used slabs revealed a mean permeability recovery of 42.5%, increasing from 1076 to 1531 mm/h. Both samples showed similar behavior, indicating that clogging occurred mainly in the upper layer and was partially reversible. Although the cleaning was conducted under controlled conditions, these findings suggest that combining mechanical vacuuming and pressure washing in the field could substantially improve hydraulic recovery (Winston et al., \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe observed recovery is consistent with previous reports in similar pavements (Garc\u0026iacute;a-Haba et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2023a\u003c/span\u003e), although Danz et al. (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) recorded higher gains (up to 123%) when both methods were applied sequentially. However, recovery potential depends strongly on sediment characteristics, pore structure, and exposure conditions (Kia et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Andr\u0026eacute;s-Valeri et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eOverall, the results confirm that the permeability loss is not entirely irreversible and that maintenance interventions can partially restore hydraulic functionality, emphasizing the importance of periodic cleaning under Mediterranean conditions.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003e3.4 Pollutant Retention Capacity\u003c/h2\u003e\u003cp\u003eThe results shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e reveal clear differences between the new and used slabs after five years of operation, particularly in parameters related to the accumulation of solid and organic pollutants (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Used slabs exhibited increases of 258% in COD, 123% in total phosphorus, 28% in total nitrogen, and 48% in total suspended solids, indicating a notable buildup of organic matter and particulate material within the porous structure. Turbidity was also higher in used slabs, while the relatively elevated values observed in new slabs may be associated with residual particles from the manufacturing process.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eAverage concentrations and surface loads of pollutants in the analyzed slabs.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"11\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSlab Id.\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eConductivity\u003c/p\u003e\u003cp\u003e\u0026micro;S/cm\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eTurbidity\u003c/p\u003e\u003cp\u003eNTU\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eCOD\u003c/p\u003e\u003cp\u003emg/L\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eNH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e\u003c/p\u003e\u003cp\u003emg/L\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eNO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e\u003c/p\u003e\u003cp\u003emg/L\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eNO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e\u003c/p\u003e\u003cp\u003emg/L\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003eTN\u003c/p\u003e\u003cp\u003emg/L\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\"\u003e\u003cp\u003ePO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e\u003c/p\u003e\u003cp\u003emg/L\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c10\"\u003e\u003cp\u003eTP\u003c/p\u003e\u003cp\u003emg/L\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c11\"\u003e\u003cp\u003eTSS\u003c/p\u003e\u003cp\u003emg/L\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eUsed\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e941\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e127.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e83.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.05\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" 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colname=\"c5\"\u003e\u003cp\u003e0.04\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.04\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e2.15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e0.02\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e0.26\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e\u003cp\u003e205.9\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eCOD\u003c/b\u003e\u003c/p\u003e\u003cp\u003eg/m\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" 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colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003eTN\u003c/b\u003e\u003c/p\u003e\u003cp\u003emg/m\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u003cb\u003ePO\u003c/b\u003e\u003csub\u003e\u003cb\u003e4\u003c/b\u003e\u003c/sub\u003e\u003csup\u003e\u003cb\u003e3\u0026minus;\u003c/b\u003e\u003c/sup\u003e\u003c/p\u003e\u003cp\u003emg/m\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e\u003cb\u003eTP\u003c/b\u003e\u003c/p\u003e\u003cp\u003emg/m\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e\u003cb\u003eTSS\u003c/b\u003e\u003c/p\u003e\u003cp\u003eg/m\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eUsed load\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e13.60\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e7.08\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e8.97\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e158.84\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e441.36\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e4.63\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e94.00\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e48.92\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eNew load\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e3.17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e6.81\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e4.97\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e122.63\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e292.94\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e4.09\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e34.74\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e28.05\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThese findings provide clear evidence that permeable pavements can act as long-term sinks for pollutants in urban environments, contributing to the interception of contaminants before they reach receiving waters. The observed accumulation patterns suggest that pollutant retention is primarily associated with physical trapping and adsorption processes within the upper and intermediate layers of the slabs. Nevertheless, these mechanisms are less effective for dissolved pollutants, which are more likely to pass through the pore network with the infiltrating water. Similar results have been reported in other field-scale studies, confirming the ability of these systems to retain suspended solids, organic matter, and nutrients over extended periods of operation (Hern\u0026aacute;ndez-Crespo et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Liu et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Garc\u0026iacute;a-Haba et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2023a\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eAlthough this study did not directly estimate removal efficiencies, the pollutant concentrations and loads retained within the slabs are consistent with the high retention values observed in complete permeable pavement systems incorporating additional filter layers such as gravels or geotextiles (Rowe et al., \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Pezzaniti et al., \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). The Mediterranean rainfall regime under which the system has operated for five years could also play a determining role, as previous studies have shown that intermittent and intense precipitation patterns may reduce the total amount of contaminants retained compared with more continuous rainfall conditions typical of Atlantic climates (Hern\u0026aacute;ndez-Crespo et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eFrom an environmental perspective, these results highlight the relevance of permeable pavements as decentralized infrastructures capable of intercepting particulate and nutrient pollution at the source. However, the progressive accumulation of solids and organic matter observed here suggests a gradual saturation of the porous matrix, which could ultimately reduce both hydraulic conductivity and pollutant retention efficiency. This process underscores the importance of long-term monitoring and maintenance strategies to sustain the dual hydraulic and water quality functions of these systems.\u003c/p\u003e\u003cp\u003eIn addition to concentration differences, the estimated pollutant loads further confirm the system\u0026rsquo;s capacity to immobilize contaminants. Used slabs accumulated up to 13.6 g/m\u0026sup2; of COD and nearly 49 g/m\u0026sup2; of suspended solids, compared to 3.17 g/m\u0026sup2; and 28 g/m\u0026sup2;, respectively, in new slabs (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Nutrient loads such as total nitrogen and total phosphorus also showed marked increases, reinforcing the evidence of long-term pollutant entrapment within the porous structure. These results emphasize the role of permeable pavements not only as hydrologic regulators but also as functional filters mitigating the transfer of urban-derived pollutants to downstream aquatic ecosystems.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003e3.5 Microplastic Retention Capacity\u003c/h2\u003e\u003cp\u003eMPs are increasingly recognized as ubiquitous contaminants in urban environments, largely mobilized by stormwater runoff from paved surfaces (Zhang et al., \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Permeable pavements can intercept these contaminants at the source, but the mechanisms governing their long-term retention under field conditions remain poorly constrained. In this study, used slabs accumulated 10272\u0026thinsp;\u0026plusmn;\u0026thinsp;5829 MPs/m\u0026sup2;, about 7.5 times more than the load measured in new slabs (1343\u0026thinsp;\u0026plusmn;\u0026thinsp;194 MPs/m\u0026sup2;; p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). From these values we estimate an annual accumulation rate 2054 MPs/m\u0026sup2;/yr for the site, which can be used as a reference for comparable urban contexts subject to intense plastic loading.\u003c/p\u003e\u003cp\u003eThe exceptionally high accumulation recorded here must be interpreted in light of the site context. The study area hosts a weekly flea market that concentrates intense pedestrian activity and generates abundant degraded plastic waste (toys, tarpaulins, textile debris), producing a local MP input far above typical residential or commercial areas (see images in Supplementary Material). Several studies have estimated concentrations of MPs in urban runoff to better understand the inputs to these systems, finding values between 2 and 110 MP/L depending on basin characteristics and precipitation conditions (Zhang et al., \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Sang et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The most representative estimate in relation to the present study is that of Garc\u0026iacute;a-Haba et al. (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), with 24\u0026thinsp;\u0026plusmn;\u0026thinsp;17 MP/L in runoff from an urban catchment in Valencia. Moreover, climatic and hydrological conditions also play a decisive role in MP dynamics, Kong et al. (\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2025\u003c/span\u003e) demonstrated that MP retention efficiencies in porous pavements decline under high rainfall intensities. Together, these observations emphasize that both local emissions and climatic drivers determine the magnitude of MPs accumulation in permeable pavements under real operating conditions.\u003c/p\u003e\u003cp\u003eMorphological and size data provide mechanistic insight into MPs retention within the porous slabs (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The retained fraction was dominated by fibers (73%), followed by particles (26%) and a negligible proportion of films (\u0026le;\u0026thinsp;1%). Although particles are often the dominant form reported in urban runoff (Zhang et al., \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Sang et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), several studies have shown that effluents from permeable pavements tend to contain a higher proportion of small particles (Garc\u0026iacute;a-Haba et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Kong et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), suggesting that fibers are more effectively retained within the pavement matrix. Their elongated and flexible morphology favors mechanical entanglement and physical trapping within the interstices of the porous concrete, whereas compact particles are more likely to migrate with advective flows unless captured by pore constrictions or by fines filling the voids.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIn terms of size, the MPs retained in the slabs were mostly within the medium (425\u0026ndash;75 \u0026micro;m) and large (\u0026gt;\u0026thinsp;425 \u0026micro;m) fractions (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e), indicating preferential capture of these classes. Conversely, fine particles (\u0026lt;\u0026thinsp;75 \u0026micro;m) were less represented, aligning with the general tendency of smaller MPs to be more easily transported through permeable systems. Together, these patterns reveal that the porous pavement acts as an effective filter for medium- and large-sized fibers, while finer and more compact MPs are selectively transmitted through the system.\u003c/p\u003e\u003cp\u003ePolymeric composition (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) revealed PE (35%), PP (31%) and polyester (22%) as dominant, with minor PVC (4%), PS and PU (3% each) and trace ABS (1%). This composition mirrors global production and typical urban waste streams (Sang et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Kong et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), and the relatively high polyester fraction is consistent with textile-derived fibers dominating in residential or pedestrian contexts. Notably, water-soluble polymers such as PVA reported in shorter-term studies (Garc\u0026iacute;a-Haba et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) were almost absent here, plausibly due to dissolution or degradation during five years of exposure, an observation that underlines how service time alters polymer detectability and the residual MP fingerprint in aged infrastructures.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eComparative evidence highlights the role of pavement design and use patterns. Studies that include full system configurations (gravel, sand layers, geotextiles) often report high effluent removal efficiencies (\u0026gt;\u0026thinsp;90%) for MPs (Kong et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Garc\u0026iacute;a-Haba et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). However, high removal in the effluent implies internal trapping rather than elimination, thereby converting the pavement into a temporary sink. Over time, progressive accumulation increases the probability of secondary emissions during maintenance, extreme hydrological events, or material disturbance. Our data show clear long-term entrapment but also reveal limitations in capturing small and dissolved fractions, meaning pavements act as partial barriers that reduce but do not fully prevent MP export.\u003c/p\u003e\u003cp\u003eFrom an environmental management perspective, these results have several implications. First, permeable pavements can substantially reduce the load of medium and large MPs reaching downstream water bodies, particularly under moderate loading scenarios. Second, the site-specific nature of MP sources means that adoption of permeable pavements in high-pressure sites (markets, industrial yards) must be accompanied by adapted maintenance strategies and possibly upstream source control to avoid rapid matrix saturation. Third, design modifications, for example incorporating adsorptive amendments or additional fine filter layers (Chen et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), could enhance retention of smaller fractions and reduce the risk of pavements becoming secondary MP sources.\u003c/p\u003e\u003cp\u003eLimitations of this study must be acknowledged. Our estimates are site-specific and reflect an extreme loading context; extrapolation to other urban settings requires careful scaling with local emission rates and hydrological regimes. Also, while Raman spectroscopy provides robust polymer identification, weathering and biofouling can complicate spectra interpretation for certain polymers after long exposure. Future work should combine lower-size detection limits, tracer experiments, and targeted assessment of maintenance-related mobilization to better quantify the net fate of MPs in permeable pavement systems.\u003c/p\u003e\u003cp\u003eIn sum, the evidence indicates that permeable pavements function as effective long-term sinks for medium-to-large MPs under real urban conditions, but their limited retention of fine fractions and potential for saturation demand integrated design and maintenance strategies to prevent the emergence of secondary pollution sources.\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eThis study provides field-based evidence of the long-term behavior of full-scale permeable pavements operating for five years under high urban pollutant loads. The results demonstrate their dual functionality: effective retention of suspended solids, organic matter, nutrients, and microplastics, together with a progressive reduction in permeability due to clogging. Laboratory restoration tests confirmed a high recovery potential, underscoring the critical role of maintenance in preserving hydraulic and treatment performance.\u003c/p\u003e\n\u003cp\u003eThe marked accumulation of microplastics, mainly polyethylene and polypropylene fibers, highlights the capacity of the porous matrix to retain emerging contaminants over extended timescales. These findings emphasize that microstructural attributes such as pore connectivity and tortuosity control both hydraulic decline and contaminant entrapment. Conducting laboratory analyses on aged field materials is therefore essential to constrain realistic long-term retention mechanisms.\u003c/p\u003e\n\u003cp\u003eThe variability observed among new slabs also indicates that nominal permeability values should be interpreted as ranges rather than fixed design parameters, encouraging the development of certification frameworks that reflect manufacturing heterogeneity. The extreme loading context examined here provides a useful upper bound for assessing pavement resilience and defining operational limits under demanding urban conditions.\u003c/p\u003e\n\u003cp\u003eOverall, this work advances understanding of permeable pavements as multifunctional stormwater infrastructures capable of simultaneously managing runoff and contaminant loads. Ensuring their long-term sustainability will require design and maintenance strategies that explicitly integrate hydraulic capacity, pollutant retention, and durability under real-world exposure.\u003c/p\u003e\n\u003cp\u003eAltogether, the findings reinforce the utility of permeable pavements as multifunctional tools for stormwater management. However, to ensure long-term effectiveness, their design and regulation must increasingly consider aspects beyond hydraulic capacity, integrating contaminant retention, maintenance feasibility, and pollutant-specific behaviors into a holistic approach to sustainable urban infrastructure.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eDeclaration of competing interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eFunding:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research is developed within the framework of the project SUDSLong- VLC Grant PID2021-122946OB-C32 funded by MICIU/AEI/10.13039/501100011033 and by \u0026ldquo;ERDF A way of making Europe\u0026rdquo;. Dar\u0026iacute;o Calzadilla Cabrera appreciates the pre-doctoral contracts funding received for doctors training Grant PRE2022-102831 funded by MICIU/AEI/10.13039/501100011033 and by \u0026ldquo;ESF+\u0026rdquo;. Eduardo Garc\u0026iacute;a Haba appreciates the pre-doctoral contracts funding received for doctors training Grant PRE2019-089409 funded by MICIU/ AEI/10.13039/501100011033 and by \u0026ldquo;ESF Investing in your future\u0026rdquo;. The authors would like to thank the Valencia City Council, the construction company Bertol\u0026iacute;n, and the slab supplier Fenollar for their collaboration.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interest:\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions: CRediT\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDar\u0026iacute;o Calzadilla-Cabrera: Data curation, formal analysis, investigation, methodology, visualization, writing.\u003c/p\u003e\n\u003cp\u003eEduardo Garc\u0026iacute;a-Haba: Data curation, investigation, methodology, supervision, validation.\u003c/p\u003e\n\u003cp\u003eCarmen Hern\u0026aacute;ndez-Crespo: Methodology, resources, supervision, validation.\u003c/p\u003e\n\u003cp\u003eMiguel Mart\u0026iacute;n: Funding acquisition, resources, supervision, validation.\u003c/p\u003e\n\u003cp\u003eIgnacio Andr\u0026eacute;s Dom\u0026eacute;nech: Funding acquisition, methodology, project administration, resources, supervision, validation.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAndr\u0026eacute;s-Valeri, V., Marchioni, M., Sa\u0026ntilde;udo-Fontaneda, L., Giustozzi, F., \u0026amp; Becciu, G., 2016. 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Effects of specimen shape and size on the permeability and mechanical properties of porous concrete. Construction and Building Materials, 266, 121074.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Permeable pavements, Urban runoff, Nature-based solutions, Stormwater pollution, Microplastic","lastPublishedDoi":"10.21203/rs.3.rs-8173976/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8173976/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePermeable 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 +\u0026thinsp;258% in COD, +\u0026thinsp;123% in total phosphorus, +\u0026thinsp;28% in total nitrogen, and +\u0026thinsp;48% in suspended solids. MP abundance reached 10272\u0026thinsp;\u0026plusmn;\u0026thinsp;5829 MPs/m\u0026sup2;, 7.5 times higher than in new slabs, dominated by fibers (\u0026asymp;\u0026thinsp;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.\u003c/p\u003e","manuscriptTitle":"Long-term environmental performance of precast slabs in permeable pavements: hydraulic functionality and pollutant retention in a real-life installation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-01 08:35:42","doi":"10.21203/rs.3.rs-8173976/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"e2fc503e-a030-4e09-a060-51db937f62f0","owner":[],"postedDate":"December 1st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-01-09T11:48:04+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-01 08:35:42","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8173976","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8173976","identity":"rs-8173976","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}