Evaluation of Solidified Wastewater Treatment Sludge as a Potential SCM in Pervious Concrete Pavements.

Waste and recycled materials have recently been used in the construction industry to comply with the principles of circular economy and sustainable development. The aim of this paper is to examine the potentials of solidified wastewater treatment sludge (SWWTS) as a supplementary cementitious material (SCM) in the production of lightweight pervious concrete pavers (LWPCP) suitable for pedestrian trails and rooftops (green) that comply with EU standards. Detailed characterization of SWWTS was performed, in order to understand its properties related to application as SCM, which led to the conclusion that it may be applied only as a filler, having 89.5% of Ca(OH)2. After thorough characterization, LWPCP samples were prepared and testing of physical and mechanical properties was conducted. The research showed that partial replacement of cement with SWWTS led to the decrease of all mechanical properties, ranging between 3.91 and 5.81 MPa for compressive strength and 0.97 to 1.23 MPa for flexural strength. However, all of the investigated mixtures showed a value higher than 3.5 MPa, which was defined as the lowest compressive strength in the range of pervious concrete properties. The addition of SWWTS led to a slight decrease in bulk density of the mixtures and an increase in water absorption. This could be explained by the reduction in hydration products that would fill in the micropores of the matrix, since SWWTS showed no pozzolanic reactivity. Pore sizes that prevail in the tested binder matrices are in accordance with the results measured on ordinary pervious concrete (the largest fraction of pores had a diameter between 0.02 and 0.2 µm). Low thermal conductivity nominates produced pavers as potential rooftop elements.

Performance synergism of pervious pavement on stormwater management and urban heat island mitigation: A review of its benefits, key parameters, and co-benefits approach.

Pervious pavement system (PPS) is a suitable alternative technique for mitigating urban flooding and urban heat island (UHI) simultaneously. However, existing literature has revealed that PPSs cannot achieve the expected permeability and evaporation. To overcome this gap, this study presents an elaborate review of problems associated with PPSs and highlights its benefits to stormwater management and UHI mitigation. We determined key parameters of PPSs that could influence urban flooding and UHI mitigation, including hydrological properties, thermal physical properties, structure design, and clogging resistance. We identified the co-benefits approach of PPS towards performance synergism on stormwater management and UHI mitigation from quality controlled design and fabrication, periodic maintenance, and effective evaluation system based on practice environments. The results indicate that existing studies of PPSs primarily focus on permeability, while little emphasis is given to the evaporative cooling performance, leading to a biased development with a loss of test standards and regulations that cannot control the cooling potential of the system. The performance synergism of permeability and evaporative cooling in PPS should be studied further, while considering quality control of the materials and in-situ practice design. Parameter controls (with commonly used standards) during fabrication, periodic maintenance (during operation), and pre- and post-evaluation processes of PPSs should work collectively to achieve optimal benefits and reduced costs.

Mechanical and Microscopic Characteristics of Polyurethane-Based Pervious Pavement Composites.

Conventional pervious pavement materials (PPM) that consist of cement and aggregate materials are known for poor durability due to their brittle behavior. Thus, to enhance the durability, we fabricated polymeric PPMs from durable and abundant polyurethane (PU) and undertook mechanical and microscopic characterizations. PU-based PPM samples with varying aggregate sizes were produced and examined to test their compressive strength and water permeability. Furthermore, X-ray micro-computed tomography (micro-CT) was implemented to analyze the samples' pore and tortuosity characteristics. Through the micro-CT analysis, the morphological characteristics of PPM's internal structures were identified and quantitively analyzed the correlations between the pore size distribution, connectivity, and tortuosity within the samples. Finally, the microstructures derived from micro-CT were generated as a finite element model and also numerically determined the stress distribution generated inside.

Pavement Overrides the Effects of Tree Species on Soil Bacterial Communities.

Human disturbance and vegetation are known to affect soil microorganisms. However, the interacting effects of pavement and plant species on soil bacterial communities have received far less attention. In this study, we collected soil samples from pine (Pinus tabuliformis Carr.), ash (Fraxinus chinensis), and maple (Acer truncatum Bunge) stands that grew in impervious, pervious, and no pavement blocks to investigate the way pavement, tree species, and their interaction influence soil bacterial communities by modifying soil physicochemical properties. Soil bacterial community composition and diversity were evaluated by bacterial 16S amplicon sequencing. The results demonstrated that soil bacterial community composition and diversity did differ significantly across pavements, but not with tree species. The difference in soil bacterial community composition across pavements was greater in pine stands than ash and maple stands. Soil bacterial diversity and richness indices decreased beneath impervious pavement in pine stands, and only bacterial richness indices decreased markedly in ash stands, but neither showed a significant difference across pavements in maple stands. In addition, bacterial diversity did not differ dramatically between pervious pavement and no pavement soil. Taken together, these results suggest that pavement overwhelmed the effects of tree species on soil bacterial communities, and had a greater effect on soil bacterial communities in pine stands, followed by ash and maple stands. This study highlights the importance of anthropogenic disturbance, such as pavement, which affects soil microbial communities.

State of a sustainable drainage system at end-of-life: assessment of potential water pollution by leached metals from recycled pervious pavement materials when used as secondary aggregate.

Sustainable drainage systems (SuDS) have emerged as an effective and attractive approach for stormwater management, prevention of water pollution and flood control due to its sustainable, environmentally friendly and cost-effective approaches. One of the SuDS devices widely used to infiltrate, store and treat surface runoff which allows it to recharge groundwater is the pervious paving systems (PPS). Previous studies have demonstrated relatively high pollution removal efficiencies typically ranging from 98.7% for total hydrocarbons to 89% of COD. Although a small number of the studies have assessed the performance characteristics of the PPS system in long-established installations in terms of retention of pollutants, hydrological features, biodegradation of pollutants etc., none has assessed the risk of potential groundwater and soil pollution by pollutants such as metals retained in the PPS materials either as a disposed waste material (in the case of used geotextiles) or during re-use as secondary aggregates. Thus, this study evaluated potential risks associated with the decommissioning and beneficial use of wastes produced during the disassembly of a PPS. The authors believe that this was the first PPS to be addressed in this way. The method involved the determination of leachable concentrations of 14 metals in the PPS samples made up of extracts from the model profile which included the geotextile fibre (G), dust alone (D), aggregates and dust (AD), aggregates alone (AA) and pavement blocks (P) which were analysed and compared with two different groups of regulatory threshold limits. The results showed that the measured concentrations of all the metals were below the appropriate threshold values for irrigation purposes as specified by FAO and USEPA. Furthermore, results all indicated that the dismantled materials were all below EU LFD WAC limits for inert waste, indicating relative ease of disposal and suitability for use as recycled aggregate. This, admittedly limited data, indicates that recycling of aggregates from demolition wastes arising from end of life PPS would not be limited by the potential leaching of heavy metals, including re-use within another PPS. This would minimise dependence on virgin aggregates and hence reduce rate of exploitation of natural resources and improve sustainability score card of SuDS.

Leaching of Pervious Concrete Produced Using Mixed Recycled Aggregates

Abstract Waste produced by the construction sector is a problem that has grown over the last few years. Construction and demolition waste makes up about 50% by mass of the total solid waste produced in Brazil. One alternative by which to reduce this volume is recycling this material in the form of aggregates. However, it is necessary to analyze the environmental risk that the use of recycled aggregates can entail for adjacent soil and the water table. The purpose of this work was to evaluate pervious concrete samples that contained recycled aggregates and to subject them to leaching tests. The results were compared with the limits established by the Italian methodology. Aggregates with 10, 25, 50, and 100% ceramic were used, as well as a recycled concrete aggregate and a natural aggregate. With the exception of the 25% ceramic trial, all the treatments introduced chromium to the water in which they were immersed, with accumulated concentrations varying from 0.009 to 0.099 mg L-1. Cadmium was found in higher quantities, with cumulated concentrations between 0.104 and 0.417 mg L-1. Sulfate concentrations were higher after 24 h of immersion, with a maximum release of 71.7 mg L-1. The concrete made with 100% ceramic aggregate leached more chromium and sulfate than the other aggregates.

The Effects of Pavement Types on Soil Bacterial Communities across Different Depths.

Pavements have remarkable effects on topsoil micro-organisms, but it remains unclear how subsoil microbial communities respond to pavements. In this study, ash trees (Fraxinus Chinensis) were planted on pervious pavement (PP), impervious pavement (IPP), and non-pavement (NP) plots. After five years, we determined the soil bacterial community composition and diversity by high-throughput sequencing of the bacterial 16S rRNA gene. The results of our field experiment reveal that the presence of pavement changed soil bacterial community composition and decreased the Shannon index, but had no impact on the Chao 1 at the 0-20 cm layer. However, we achieved the opposite result at a depth of 20-80 cm. Furthermore, there was a significant difference in bacterial community composition using the Shannon index and the Chao 1 at the 80-100 cm layer. Soil total carbon (TC), total nitrogen (TN), available phosphorus (AP), NO3--N, and available potassium (AK) were the main factors that influenced soil bacterial composition and diversity across different pavements. Soil bacterial composition and diversity had no notable difference between PP and IPPs at different soil layers. Our results strongly indicate that pavements have a greater impact on topsoil bacterial communities than do subsoils, and PPs did not provide a better habitat for micro-organisms when compared to IPPs in the short term.

Reuse of materials from a Sustainable Drainage System device: Health, Safety and Environment assessment for an end-of-life Pervious Pavement Structure.

Pervious pavement systems can have a life span of about 20years but, at end-of-life, it becomes necessary to evaluate the state of the infrastructure to determine whether they pose a health and safety risk to workers during dismantling, and also determine potential reuse of the waste material generated. In this paper, we report of an investigation conducted to evaluate whether Pervious pavement systems are hazardous to human health at end-of-life and also to assess the mobility of the stormwater pollutants trapped in the system as a measure of their potential release to receiving systems such as water-bodies and groundwater systems. After decommissioning, the pervious pavement structure was sampled for analysis including Gas Chromatography, inductively coupled plasma spectroscopy and, leachate analysis. Results show that carcinogenic risks were significantly below the regulatory limit of 1×10-6 while, the hazard quotients and cumulative hazard indices were also below regulatory value of 1, based on United States Environmental Protection Agency standards. Furthermore, mean concentrations of benzene, toluene, ethylbenzene and xylene were significantly less than the UK soil guideline values. The results of the leachate analysis show that the metals of concern, Pb, Zn, Cr, Ni, Cd and Cu were all below the threshold for reuse applications such as irrigation purposes as they were all below the regulatory limits such as Food and Agriculture Organization and, United States Environmental Protection Agency standards. Finally, the evaluation of potential reuse and recycling purposes indicate that wastes generated from the dismantling of the PPS are within limits for recycling as aggregates for other civil engineering projects as per European Union standards. This has potential to enhance UK's drive to achieve the target of 70% level of construction & demolition waste recovery for reuse and recycling by the year 2020 as per European Union Water Framework Directive.

The leaf phenophase of deciduous species altered by land pavements.

It has been widely reported that the urban environment alters leaf and flowering phenophases; however, it remains unclear if land pavement is correlated with these alterations. In this paper, two popular deciduous urban trees in northern China, ash (Fraxinus chinensis) and maple (Acer truncatum), were planted in pervious and impervious pavements at three spacings (0.5 m × 0.5 m, 1.0 m × 1.0 m, and 2.0 m × 2.0 m apart). The beginning and end dates of the processes of leaf budburst and senescence were recorded in spring and fall of 2015, respectively. The results show that leaf budburst and senescence were significantly advanced in pavement compared to non-pavement lands. The date of full leaf budburst was earlier by 0.7-9.3 days for ash and by 0.3-2.3 days for maple under pavements than non-pavements, respectively. As tree spacing increases, the advanced days of leaf budburst became longer. Our results clearly indicate that alteration of leaf phenophases is attributed to land pavement, which should be taken into consideration in urban planning and urban plant management.

An assessment of the potential use of compost filled plastic void forming units to serve as vents on historic landfills and related sites.

Much of the solid municipal waste generated by society is sent to landfill, where biodegrading processes result in the release of methane, a major contributor to climate change. This work examined the possibility of installing a type of biofilter within paved areas of the landfill site, making use of modified pervious paving, both to allow the escape of ground gas and to avoid contamination of groundwater, using specially designed test models with provision for gas sampling in various chambers. It proposes the incorporation of an active layer within a void forming box with a view to making dual use of the pervious pavement to provide both a drainage feature and a ground gas vent, whilst providing an active layer for the oxidation of methane by microbial action. The methane removal was observed to have been effected by microbial oxidation and as such offers great promise as a method of methane removal to allow for development of landfills.