Permeable Interlocking Concrete Pavement Research Articles

Prediction of runoff characteristics in permeable pavements using experimental data and intelligent models.

Considering the growing use of permeable pavements, the prediction of runoff passing through this pavement model is of considerable importance. The prediction of rainfall-runoff relationships can be a challenge because of several factors including data uncertainty, non-linear relationships, and high temporal and spatial variability. To deal with these challenges, intelligent algorithms are often used to predict such complex phenomena. In this research, runoff control parameters were investigated in two types of permeable pavements (permeable interlocking concrete pavement (PICP) and high strength clogging resistant permeable pavement (CRP)) using support vector machine (SVM), support vector machine-bat (SVM-BA) and support vector machine-grasshopper (SVM-GOA). Variables used in the models included percentage of coverage by permeable pavement (A), rainfall intensity (I), slope (S), and pavement type coefficient (K) as input data, and runoff coefficient (C), time to runoff (Tr), and peak discharge (Qp) as output data. In this research, from the total of 108 data extracted from the experimental results, 86 data were used in the training period, and 22 data were used in the test period. The results of the test period show that the SVM-BA model has the best performance with values of MAE = 0.010 in predicting C, MAE = 1.330 min in predicting Tr, and MAE = 0.029 lit/min in predicting Qp. The SVM-GOA model is ranked second with values of MAE = 0.051 in predicting C, MAE = 3.285 min in predicting Tr, and MAE = 0.097 lit/min in predicting Qp. Also, the SVM model is ranked third with values of MAE = 0.063 in predicting C, MAE = 4.470 min in predicting Tr, and MAE = 0.121 lit/min in predicting Qp. In summary, the SVM-BA algorithm showed the best performance and the SVM algorithm showed the weakest performance in predicting runoff characteristics in permeable pavements.

Understanding the removal of heavy metals from stormwater runoff in permeable pavement system

Understanding the removal of heavy metals (HMs) in permeable pavement systems is of great significance for controlling urban runoff pollution and optimizing structural design. However, few studies have systematically investigated the mechanism of permeable pavement systems in removing HMs from stormwater runoff. In this study, we adopted a hierarchical strategy to understand the efficiency of individual structural layers on HMs removal in a permeable interlocking concrete pavement (PICP) system. Experimental results illuminated that the surface layer exhibited the highest uptakes of HMs, which can remove up to 64 % of Pb2+, 50 % of Cu2+, 28 % of Cd2+ and 13 % of Zn2+. Meanwhile, as the rainfall return period increased, the removal rates of HMs in PICP was gradually decreased. In addition, batch experiments were conducted and the adsorption results were in accordance with the rainfall filtration experiments. More importantly, X-ray Photoelectron Spectroscopy (XPS) and leaching results were investigated to understand the HMs removal mechanism, which found that the ion exchange is the main mechanism in the surface layer to remove HMs, whereas the chemical adsorption play a crucial role in the base and sub-base layers. Overall, these findings provided new insights into the transport patterns of HMs in the internal structural layers of the PICP.

Removal and fate of microplastics in permeable pavements: An experimental layer-by-layer analysis

The increasing prevalence of microplastics (MP) in urban environments has raised concerns over their negative effects on ecosystems and human health. Stormwater runoff, and road dust and sediment, act as major vectors of these pollutants into natural water bodies. Sustainable urban drainage systems, such as permeable pavements, are considered as potential tools to retain particulate pollutants. This research evaluates at laboratory scale the efficiency of permeable interlocking concrete pavements (PICP) and porous concrete pavements (PCP) for controlling microplastics, including tire wear particles (TWP) which constitute a large fraction of microplastics in urban environments, simulating surface pollution accumulation and Mediterranean rainfall conditions. Microplastic levels in road dust and sediments and stormwater runoff inputs were 4762 ± 974 MP/kg (dry weight) and 23.90 ± 17.40 MP/L. In infiltrated effluents, microplastic levels ranged from 2.20 ± 0.61 to 5.17 ± 1.05 MP/L; while tire wear particle levels ranged between 0.28 ± 0.28 and 3.30 ± 0.89 TWP/L. Distribution of microplastics within the layers of PICP and PCP were also studied and quantified. Microplastics tend to accumulate on the pavements surface and in geotextile layers, allowing microplastic retention efficiencies from 89 % to 99.6 %. Small sized (< 0.1 mm) fragment shaped microplastics are the most common in effluent samples. The results indicate that permeable pavements are a powerful tool to capture microplastics and tire wear particles, especially by surface and geotextile layers. The study aims to shed light on the complex mobilisation mechanisms of microplastics, providing valuable insights for addressing the growing environmental concern of microplastic pollution in urban areas.

Investigating the Effect of High Strength Clogging Resistant Permeable Pavement (CRP) and Permeable Interlocking Concrete Pavement (PICP) on the Characteristics of Runoff

Investigating the Effect of High Strength Clogging Resistant Permeable Pavement (CRP) and Permeable Interlocking Concrete Pavement (PICP) on the Characteristics of Runoff

Field investigation of clogging with different sediment types in a permeable pavement system with low-cost maintenance

Maintenance has a significant impact on permeable pavements’ service life. Proper cleaning procedures include pressure washing and heavy-duty wet/dry vacuum to remove accumulated sediment and maintain permeability. Aiming to analyze the influence of sediment type and size on the clogging process and the importance of preventive maintenance, six experimental permeable pavement modules were assessed. Pairs of in-situ Pervious Concrete (PC), Permeable Interlocking Concrete Pavement (PICP) and Permeable Interlocking Pervious Concrete Pavement (PIPCP) were monitored over two consecutive periods: i) under natural clogging process; ii) accelerated clogging under sand and clay sediment types. At the end of both periods, all modules received maintenance through water pressure washing. The results showed a reduction of up to 80% in the surface infiltration capacity during the natural clogging period, but that most of it could be recovered using pressure washing. Result in all situations also reinforced that periodic cleaning every 4-6 months, even with just pressure washing, as a key factor to extend permeable pavements’ life cycle.

Performance Comparison of 45° and 90° Herringboned Permeable Interlocking Concrete Pavement

Pavement deterioration is mainly caused by high traffic loading and by increased levels of runoff water resulting from storms, floods, or other reasons. Consequently, this issue can be efficiently solved by employing permeable pavement, such as permeable interlocking concrete pavement (PICP) to control water runoff and endure increased traffic loads. This study investigates the performance of PICP, in both 45° and 90° herringboned surface patterns, in terms of the infiltration of volumes of water, runoff water volumes, and the ability of pavement to withstand static loading. All the related tests in this study were implemented using a lab apparatus that was fabricated as a simulator for rainfall. Various conditions were adopted during the performance tests, including the application of longitudinal slopes (0, 2.5, 5, and 7.5%), side slopes (0, 2.5, and 5%), and different rainfall intensities (25, 50, 75, and 100 L/min). The results indicated that at high rainfall intensities (75 and 100 L/min), PICP with the 45° herringboned surface pattern had the highest volume of infiltrated water and the lowest runoff water at all the adopted longitudinal and side slopes. In addition, PICP with the 45° herringboned surface pattern showed higher resistance to deflection under a static loading test than the 90° herringboned pattern under the same conditions. Therefore, PICP with a 45° herringboned surface pattern showed supremacy in terms of runoff reduction and load resistance in comparison to PICP with a 90° herringboned pattern. Even though there are differences between the two types of PICP, they are both strongly recommended as alternatives to regular pavement.

Hydrologic Performance of Permeable Pavers and a Dome Concrete Forming System: A Comparative Study

The hydrologic performance of permeable interlocking concrete pavers (PICP) and a dome concrete forming system (DCFS) was quantified and evaluated at a retrofitted residential laneway in Toronto, Ontario. The quantification and evaluation were performed by comparing their monitored performance over 14 months with an adjacent concrete pavement. Their monitored performance was then used to assess their ability to mimic predevelopment hydrologic behavior, estimated through modeling. The PICP and DCFS achieved (1) an average runoff volume reduction of 33% and 85%; (2) an average runoff coefficient of 0.48 and 0.12; and (3) an average peak flow reduction of 43% and 89%, respectively. The outflow duration from the DCFS was extended 4.1 times greater than the inflow duration, indicating its potential to attenuate flashy events. The peak flows produced by the DCFS were delayed by nearly 2.5 h from those occurring on the PICP. Correlation analyses indicated a more significant influence of rainfall depth and intensity on the performance of PICP than that of the DCFS. Compared with predevelopment levels, PICP did not match runoff volumes for smaller events (<10 mm) but produced less runoff for larger events (>30 mm). However, the PICP did not match predevelopment peak flows in 100% of occurrences. The DCFS reduced runoff volumes and peak flows to magnitudes lower than all predevelopment levels. Surface infiltration testing and subsurface hydraulic conductivity estimations indicated that infiltration capability in both systems could be reduced over time. The study demonstrated that the DCFS might need to be prioritized over permeable pavements, especially when installed over low-permeability soils.

Year-round monitoring of chloride releases from three zero-exfiltration permeable pavements and an asphalt parking lot

Winter deicers, though essential for maintaining safe pavement conditions in winter, increase chloride (Cl−) concentrations in receiving water bodies above recommended environmental guidelines. Zero-exfiltration or lined permeable pavement is an important technological innovation for controlling particulate-bound pollutants at the source. As stormwater does not infiltrate into the ground, soluble pollutants like Cl− are ultimately discharged into receiving water bodies. Our aim was to examine Cl− concentrations in effluents from three zero-exfiltration permeable pavement cells (Permeable Interlocking Concrete Pavement (PICP), Pervious Concrete (PC), Porous Asphalt (PA)) and compare them with runoff from a Conventional Asphalt (ASH) cell. The study conducted at a parking lot in St. Catharines, Ontario, Canada, from January 2016 to May 2017 observed that the permeable pavements provided only temporary attenuation of Cl− during winter but exhibited a quick release during spring melt. Cl− concentrations and loadings were different for each permeable pavement system in terms of timing and magnitude. Cl− concentration in ASH runoff frequently had very high spikes (21,780 mg/L); however, the median winter Cl− concentration in ASH runoff was lower than Cl− levels in the permeable pavements' effluents and later declined drastically after spring melt, but in few instances, was above the chronic water quality guideline (120 mg/L). The average event mean concentration (EMC) of Cl− was 1600 and 120 mg/L in the permeable pavements’ effluents during salting and non-salting season, respectively. In one year, each permeable pavement system released approximately 67–81 kg of Cl− with significant differences being observed in Cl− loads between the 2016 and 2017 seasons. Therefore, a multi-year data collection and monitoring plan captured the variability in winter conditions. The study provided insights into the behaviour, retention and release of Cl− from traditional and permeable hardscape surfaces and possible avenues for Cl− attenuation, source control and aquatic habitat conservation.

The behavior of permeable interlocking concrete pavement under different rainfall intensities and design conditions

ABSTRACT This study investigated the behaviour of permeable interlocking concrete pavement (PICP) in terms of water infiltration volume, surface runoff volume, and load resistance, using a specific lab apparatus, designed and manufactured as a rainfall simulator. The connecting pattern of the surface blocks is a stretcher bond pattern with a joint spacing of (5 and 10 mm) between the block pavers to be filled with a small-sized open-graded aggregate to finalise the permeable surface of joints. The adopted pattern has been examined under three rainfall intensities of (20, 40, and 60 l/min), four longitudinal slopes (0, 2, 4, and 6%), and three transverse slopes (0, 2, and 4%). The results showed that at high rainfall intensities (60 l/min), high longitudinal slopes (6%), and high transverse slopes (4%), the stretcher-bonded PICP with 5 mm spacing between the blocks infiltrates less water than the one with 10 mm. Furthermore, PICP with 5 mm spacing has higher surface runoff than PICP with 10 mm spacing at high rainfall intensities (60 l/min), high longitudinal slopes (6%), and all transverse slope percentages (0, 2, and 4%). In addition, the load resistance of stretcher-bonded PICP with 5 mm spacing between the blocks is higher than that of 10 mm at all the subjected loads in the load-deflection test. Despite the shown differences between both types of PICP, they are strongly recommended as an alternative choice for ordinary dense-graded pavement.

Seasonal variation in indicator organisms infiltrating from permeable pavement parking lots at the Edison Environmental Center, New Jersey.

Four types of permeable pavements were monitored at the Edison Environmental Center in Edison, New Jersey, for three water quality indicator organisms consisting of fecal coliform, enterococci, and Escherichia coli. This study expands a previously published result based on less than a year of available data. The current study reflects nearly 5 years of data collection with efforts focusing on collection of data in all four seasons to analyze seasonal effects and to understand the effects of pH on infiltrate concentrations. All three indicators were detected in infiltrates from all four permeable surfaces and as well as asphalt and roof runoff. Seasonally, the infiltrate during winter had fewer detections and lower enumerations and was most often significantly different than surface infiltrate and runoff for the other seasons. More significant concentration reductions were observed in summer and fall, and the lowest reduction was observed in winter. Pervious Asphalt treatment removed the most microorganisms for all three indicator organisms. A permeable interlocking concrete pavement (PICP) that was a replacement for pervious concrete during the study performed better than the original PICP most likely due to smaller gap spacing (8mm compared to 12.7mm) and correspondingly smaller specified surface aggregate compared to the original PICP. Percent concentration removal reductions based on geometric means were 89% or greater for PC, PA, and PICP for fecal coliform; 75% or better for PC, PA and PICP for E. coli; and 95% or greater for PC and PA for enterococci, while there were no annual removals for enterococci for original or new PICP nor removals for E. coli for original PICP and minimal removal for fecal coliform for original PICP. The major sources of fecal indicators in the stormwater runoff were most likely from the feces of deer, geese, and other wild animals. PRACTITIONER POINTS: The infiltrate during winter had fewer detections and lower enumerations and was most often significantly different than surface infiltrate and runoff for the other seasons. More significant concentration reductions were observed in summer and fall, and the lowest reduction was observed in winter. Pervious Asphalt treatment removed the most microorganisms for all three indicator organisms.

Predicting location and evaluating progression of clogging in a permeable pavement parking lot.

In 2009, a permeable pavement research and demonstration site was constructed at the Edison Environmental Center, Edison, NJ. Infiltration testing of three original permeable parking rows through August 2012 indicated that clogging occurred along the upgradient edge of these pavements from runoff that drained from adjacent impermeable driving lanes. A subsequent infiltration testing data collection effort from April 2017 through March 2020 focused on permeable interlocking concrete pavers (PICP) that replaces one of the original permeable surfaces. While the original infiltration study through 2012 used random locations throughout the permeable parking rows, the newer study targeted upgradient edge to identify where clogging would occur. Testing locations along the upgradient edge were selected based on a high-resolution survey (HRS) of the parking lot performed in December 2014. The HRS identified three low spots along the upgradient edge that eventually clogged in the new PICP infiltration study. The HRS may assist with maintenance routines. The newer study also supports the conclusion of the earlier study with regards to truncating the infiltration testing method, particularly for maintenance assessments.

Assessing the Benefits of Early and Repeated Maintenance with Regenerative Air Street Sweepers on Permeable Interlocking Concrete Pavements

Assessing the Benefits of Early and Repeated Maintenance with Regenerative Air Street Sweepers on Permeable Interlocking Concrete Pavements

An experimental comparison between different types of surface patterns of permeable interlocking concrete pavement for roadway subsurface drainage

In dense-graded pavements, which are used for composing and recomposing roads in the paving industry around the world, failures occur due to increasing traffic loads and the rising runoff of water caused by storms or floods, or any other reason. Therefore, this kind of issue can be treated by adopting a permeable pavement system such as the permeable interlocking concrete pavement (PICP) to manage the runoff of water and tolerate the increasing loads of traffic efficiently. In this study, a laboratory apparatus has been designed and fabricated as an artificial rainfall simulator to investigate the behavior of different surface concrete block patterns under different rainfall intensities. Measuring the levels of runoff and the volume of infiltrated water are the fundamental factors in creating an essential comparison between the elected surface patterns. In this study, stretcher bond, 90º herringbone, and 45° herringbone patterns are chosen with (5 mm and 10 mm) joint spacing between the concrete blocks. All three surface block patterns are tested in terms of four longitudinal slopes (0%, 2.5%, 5%, and 7.5%) and three side slopes (0%, 2.5%, and 5%) under three rainfall intensities (25 l/min, 50 l/min, and 75 l/min). Based on the results, the stretcher bond pattern showed superior results to other bonds because it reduces surface runoff and spreads the water evenly under the permeable concrete block roadway. The 90° herringbone and 45° herringbone patterns, on the other hand, are the best for increasing the durability of roads.

Comparative performance and cost-integrated life cycle assessment of low impact development controls for sustainable stormwater management

Climate change and urbanization have led to an increase in the frequency and intensity of floods in urban regions. To cope with such extreme events, low impact development (LID) has been adopted as a sustainable alternative to conventional stormwater management systems. LID controls mitigate runoff and manage flooding at the source by providing additional storage, filtration, and infiltration of stormwater. This study aims to investigate the techno-economic and environmental performance of multiple LID controls: bioretention cells (BC), infiltration trenches (IT), and permeable interlocking concrete pavement (PICP) compared to a conventional stormwater pipe drainage system. A cost-integrated life cycle analysis was conducted to assess the environmental impacts and evaluate the financial feasibility of the examined stormwater management systems. An eco-efficiency analysis (EEA) was carried out to quantify the environmental costs of LID controls by incorporating the results of a life cycle assessment (LCA) and life cycle cost analysis (LCCA). The technical analysis showed that LID controls significantly reduced runoff by 67%, 53%, and 36% for IT, BC, and PICP, respectively compared to the conventional system. Moreover, the LCA results revealed that the pipe drainage system was the least favorable with a single score of 191 mPt, followed by PICP (188 mPt), BC (40 mPt), and IT (30 mPt). Over a 30-year assessment period, the LCCA findings indicated that the IT and BC controls had the lowest net present costs of $11.6 and $14.5 million, respectively, compared to the PICP ($17.0 million) and conventional ($19.5 million) systems. The EEA revealed that IT was the most eco-efficient (EI = 0.34 Pt/$) among the LID systems, whereas PICP was the least cost-efficient (EI = 0.97 Pt/$). It was also found that applying hybrid LID models further reduced the runoff, environmental impacts, and financial burdens by up to 79%, 84%, and 48%, respectively. Overall, these findings emphasized the potential environmental and financial benefits of implementing integrated LID controls as sustainable stormwater management systems.

Numerical Comparison of the Hydrological Response of Different Permeable Pavements in Urban Area

Floods are becoming more frequent, especially in urban environments where most of the surface is waterproofed. Permeable pavement (PP) can be applied as low impact development (LID) systems for runoff mitigation in urban areas. Their effectiveness can be assessed, case by case, by numerical simulations. In this study, the effectiveness of mitigating runoff of different permeable pavements has been evaluated. In particular, porous asphalt (PA), pervious concrete (PC), permeable interlocking concrete pavement (PICP) and grid pavement (GP) have been investigated using EPA Storm Water Management Model (SWMM) software. To this aim, a car parking area located in the University Campus of Palermo (Italy) has been taken as a case study, considering several scenarios, each having a different percentage and planimetric layout of a PP type combined with an impermeable pavement. All the scenarios were tested assuming four synthetic rainfall events, referring to return periods of 5, 10, 50 and 100 years, and a real high return period event that occurred in Palermo in 2020. The results showed that amongst the different PPs considered, only the PA, bounded at the bottom by an impermeable layer, was practically ineffective. The other three PPs, proved to be effective in a noticeable way and furthermore for each scenario studied, they proved to bear almost the same mitigated runoff. The results proved appreciable differences in runoff as a function of the location of the PP over the study area.

An Accelerated Clogging Method by Manual Application of Sediments for Permeable Interlocking Concrete Pavements

Abstract The primary function of permeable interlocking concrete pavements (PICP) is to allow water to rapidly infiltrate through the surface and percolate to underlying sublayers, soils, or underdrains. However, as pavements age, surface infiltration rates diminish as sediments and debris accumulate on the pavement surface, eventually leading to surface ponding and runoff if no maintenance is applied. These studies clog PICP surfaces to better understand clogging mechanisms under different sediment types and to evaluate maintenance technologies intended to restore surface permeability. Clogging studies use different materials and methods to clog PICP surfaces, which impedes comparisons and interpretations across projects. This paper presents a new methodology to (1) create a realistic synthetic clogging material and (2) rapidly clog a PICP surface for experiments. The method described herein can be easily repeated by others to test a broad range of research questions for PICP surfaces while producing comparable results for studies conducted at different scales (lab, meso, field) and locations or with different sediment mixes. The proposed method was used to clog six identical PICP meso-cells in the field. Five cells were clogged with graded street sweepings collected from local municipal waste yards, and a sixth cell was clogged with a mixture of street sweepings and soils collected on-site. Over five weeks, the PICP surface infiltration rates were reduced from postconstruction levels (&amp;gt;10,800 mm/h) to approximately 250 mm/h. Statistical spatial analysis indicates that the surfaces were clogged evenly, but repeating infiltration measurements at the same location was observed to influence the resulting surface infiltration data. The PICP surface clogged with mixed street sweepings and on-site soils required approximately 43 % less material than surfaces clogged with street sweepings only to reduce surface infiltration rates to 250 mm/h.

Assessing maintenance techniques and in-situ pavement conditions to restore hydraulic function of permeable interlocking concrete pavements

Permeable pavements are increasingly implemented to mitigate the negative hydrologic outcomes associated with impervious surfaces. However, the hydraulic function of permeable pavements is hindered by clogging in their joint openings, and systematic maintenance is needed to ensure hydraulic functionality throughout the design lifespan of these systems. To quantify the effectiveness of various maintenance measures, surface infiltration rates (SIRs) were measured before and after five different maintenance techniques were applied to five permeable interlocking concrete pavements (PICPs) in central Ohio, USA. Three maintenance techniques, the Municipal Cleaning Vehicle (MCV), the Rejuvenater, and a pressure washer and the Rejuvenater performed in series, significantly improved median SIRs from 16 to 26, 5 to 106, and 11 to 37 mm/min, respectively. However, pressure washing alone resulted in no significant difference to PICP SIR (median SIRs increased from 8 to 20 mm/min). Regenerative air street sweeping significantly worsened SIRs when performed during wet weather (median SIRs decreased from 19 to 4 mm/min) but had no significant impact on SIRs during dry weather (median SIRs decreased from 21 to 18 mm/min). This work captured the maintenance effectiveness of two techniques for the first or second time, namely the Rejuvenater and MCV, to investigate their use as a suitable maintenance technique. Further, the maintenance techniques were tested on multiple PICPs, thus the effect of in-situ pavement conditions had on hydraulic improvement via maintenance could be addressed. Differences in general upkeep, traffic, and runoff routed to a PICP affected the depth of clogging below the pavement surface, which forestalled hydraulic improvement. Though shown to improve the SIR of PICP systems, results indicate that the maintenance techniques were not capable of restoring pavement hydraulics to initial conditions. These results demonstrate the need for regular, routine maintenance and topping up of joint aggregate before clogging migrates deeper into the pavement profile.

Cost Analysis of Green Infrastructure Compared to Conventional Stormwater Storage

Low Impact Development (LID), or green infrastructure, refers to a land planning and engineering design practice to address urban storm runoff. The nature of LID is to mimic the pre-development environment to retain runoff through infiltration, retention, and evaporation. Despite the fact that numerous studies have analyzed the performance of runoff volume reduction and peak flow of various green infrastructures, little is known regarding the economic benefits of adopting LID practices. In this research, three completed construction projects in the Phoenix, Arizona metropolitan area were selected to perform an alternative LID design including extensive green roof (GR) and permeable interlocking concrete pavement (PICP), to determine the cost effectiveness of using LID to reduce the use of a conventional stormwater storage system. A life cycle cost (LCC) analysis was conducted to better understand the cost benefits of applying LID to meet current drainage design criteria as per the project requirements. The results found that applying LID resulted in an average LCC saving rate of 23% compared to a conventional stormwater storage system over a 50 year service life and 15.1% over a full LID (GR+PICP) strategy. Furthermore, it was discovered that LID has little cost savings benefits when constructing above-ground retention basins due to cheaper associated construction costs.

Winter Maintenance of Permeable Interlocking Concrete Pavement: Evaluating Opportunities to Reduce Road Salt Pollution and Improve Winter Safety

Permeable interlocking concrete pavement (PICP) is a type of permeable pavement system that uses the joint spaces between pavers to drain water from the surface into an aggregate base and subbase layer below. Because of its ability to rapidly drain surface water, PICP has the potential to reduce the amount of ice formed on the surface during winter conditions compared with traditional impervious pavements. As a result, PICP may reduce the amount of road salt needed for de-icing paved surfaces and may also reduce the risk of pedestrian slipping and vehicle skidding throughout the winter. This study evaluates the performance of an outdoor PICP and asphalt test pad over two winter seasons in Vaughan, Ontario, Canada, by assessing differences in surface conditions, surface friction, and surface temperatures. The results of this study indicate that PICP provides equivalent or higher levels of safety compared with asphalt when treated with de-icing products at medium (0.049 kg/m2) or low (0.024 kg/m2) application rates. Re-freezing of melted snow and ice after sunset was observed on the asphalt surface creating black ice, but not on the PICP cells. Consequently, compared with asphalt pavements, PICP surfaces will require use of less de-icer and will have lower risk of slips and falls for pedestrians, and lower risk of skidding for vehicles throughout the winter.

The Link between Permeable Interlocking Concrete Pavement (PICP) Design and Nutrient Removal

The construction of ‘hard’ impermeable surfaces in urban areas results in the increased flow of stormwater runoff and its associated pollutants into downstream receiving waters. Permeable Pavement Systems (PPS) can help mitigate this. The most common type of PPS in South Africa is permeable interlocking concrete pavement (PICP), but there is currently insufficient information available on the relative treatment performance of different PICP designs. This paper describes an investigation into the performance of ten different PICP systems constructed in the Civil Engineering Laboratory at the University of Cape Town for the treatment of various nutrients commonly found in stormwater runoff. It was found that removal efficiencies ranged from 27.5% to 78.7% for ammonia-nitrogen and from −37% to 11% for orthophosphate-phosphorus; whilst 4% to 20.2% more nitrite-nitrogen and 160% to 2580% more nitrate-nitrogen were simultaneously added. The presence of a geotextile resulted in higher ammonia-nitrogen removal efficiencies but also higher nitrate-nitrogen addition than those cells without—with small differences between various types. The cell with a permanently wet ‘sump’ had the highest nitrate-nitrogen addition of all. Lower pH results in higher nitrate-nitrogen concentrations, whilst the electrical conductivity strongly depends on the length of the periods between rainfall ‘seasons’, decreasing rapidly during wet periods but increasing during dry periods. Paver type also had a minor impact on nutrient removal.