Composition and leaching of construction and demolition waste: inorganic elements and organic compounds

Comparative life cycle assessment of natural and recycled aggregate concrete: A review

Recycled aggregate concrete (RAC), mainly made from recycled materials such as construction and demolition waste (CDW), has emerged as a sustainable alternative to natural aggregate concrete (NAC). While RAC offers potential benefits in waste reduction and resource conservation, a comprehensive understanding of its environmental impact and sustainability compared to NAC has been lacking. This study addresses this gap by conducting a thorough review and analysis of comparative Life Cycle Assessment (LCA) studies between RAC and NAC. This paper synthesizes current literature to evaluate the environmental impact of both materials throughout their life cycles, from raw material extraction to disposal. It examines key factors such as energy consumption, greenhouse gas emissions, and resource depletion to provide a thorough comprehension of the effects on the environment of each concrete type throughout their life cycles. Challenges in using RAC as a sustainable concrete option, such as sourcing and quality control, are also discussed, along with recommendations for future research and industry practices. The findings indicate that the environmental impact of RAC compared to NAC is significantly influenced by transport distances and modes. In addition, the choice of functional units in LCAs substantially affects the comparison between RAC and NAC, with strength reliability offering a clear benefit by addressing concrete property variability and better reflecting real-world conditions.

A critical review on leaching of contaminants from asphalt pavements

Contaminant leaching from asphalt pavements poses a significant environmental concern, potentially damaging soil and groundwater quality. The growing interest in incorporating recycled materials in asphalt pavements has further raised concerns over the potential environmental hazards due to contaminant leaching. Consequently, this paper offers a comprehensive review of the literature over the past three decades structured into six sections: groundwater contamination via leaching, methodologies for evaluating leaching, analysis of contaminants, contaminants and leaching from road materials incorporating recycled waste, other factors affecting leaching of pollutants from asphalt pavements, and mathematical models to predict leaching from asphalt pavements. Despite the importance of addressing leaching issues, there is a lack of standardised leaching tests and guidelines specific to asphalt materials, limited attention to evaluating contaminants beyond heavy metals and PAHs in asphalt leachates, insufficient understanding of optimal instrument parameters for asphalt leachate analysis, and a scarcity of mathematical models to predict future leaching potential.

Metal(loid)s in urban soil from historical municipal solid waste landfill: Geochemistry, source apportionment, bioaccessibility testing and human health risks

Landfills, especially those poorly managed, can negatively affect the environment and human beings through chemical contamination of soils and waters. This study investigates the soils of a historical municipal solid waste (MSW) landfill situated in the heart of a residential zone in the capital of Slovakia, Bratislava, with an emphasis on metal (loid) contamination and its consequences. Regardless of the depth, many of the soils exhibited high metal (loid) concentrations, mainly Cd, Cu, Pb, Sb, Sn and Zn (up to 24, 2620, 2420, 134, 811 and 6220 mg/kg, respectively), classifying them as extremely contaminated based on the geo-accumulation index (Igeo >5). The stable lead isotopic ratios of the landfill topsoil varied widely (1.1679-1.2074 for 206Pb/207Pb and 2.0573-2.1111 for 208Pb/206Pb) and indicated that Pb contained a natural component and an anthropogenic component, likely municipal solid waste incineration (MSWI) ash and construction waste. Oral bioaccessibility of metal (loid)s in the topsoil was variable with Cd (73.2-106%) and Fe (0.98-2.10%) being the most and least bioaccessible, respectively. The variation of metal (loid) bioaccessibility among the soils could be explained by differences in their geochemical fractionation as shown by positive correlations of bioaccessibility values with the first two fractions of BCR (Community Bureau of Reference) sequential extraction for As, Cd, Mn, Ni, Pb, Sn and Zn. The results of geochemical fractionation coupled with the mineralogical characterisation of topsoil showed that the reservoir of bioaccessible metal (loid)s was calcite and Fe (hydr)oxides. Based on aqua regia metal (loid) concentrations, a non-carcinogenic risk was demonstrated for children (HI = 1.59) but no risk taking into account their bioaccessible concentrations (HI = 0.65). This study emphasises the need for detailed research of the geochemistry of wastes deposited in urban soils to assess the potentially hazardous sources and determine the actual bioaccessibility and human health risks of the accumulated metal (loid)s.

Do hazardous substances in demolition waste hinder circular economy?

Hazardous substances in demolition waste are often deemed a barrier to a circular economy owing to concerns about their fate in recycled materials. However, with the growing demand for recycling materials, it is essential to find circular solutions for construction materials but still protect health and the environment by managing hazardous substances. In this study, selected hazardous substance groups were analysed from demolition waste samples. Most of the concentrations did not raise any concerns when the safety of recycling materials was considered. However, the detection limits of laboratory chemical analysis can be discussed, as bromine was found in samples by an X-ray fluorescence (XRF)-analyser, but only one laboratory detected brominated flame retardants (BRFs). New technologies and practices are needed to follow the chemical content of materials used in the construction phase. Detecting hazardous substances in recyclable materials is the only way to achieve harmless material cycles.

Leaching characteristics of metals from recycled concrete aggregates (RCA) and reclaimed asphalt pavements (RAP)

Recycled concrete aggregates (RCA) and reclaimed asphalt pavements (RAP) are two construction waste products that are commonly used in the road construction industry. Besides many advantages, pollutants leaching from RCA and RAP are highlighted as the most concerning environmental issue. This study investigated metals leaching characteristics from RCA and RAP due to the variations in key influential factors of pH, dissolved organic carbon (DOC), compaction and liquid to solid ratio (L/S). The leaching tests for RCA and RAP were carried out separately and additionally, the standard leaching test was conducted as the benchmark for leaching investigations. Study outcomes revealed that the combined influences of factors are variable for RCA and RAP, while influences are also variable for individual metals. L/S ratios considerably affect the release of metals from RCA under saturated conditions, facilitating high metal concentrations in the leachate. On the other hand, acidic solutions are more favourable for leaching of metals from RAP. The influence of DOC in solution was minimal on the metal leachability. Interestingly, the increased degree of compaction with a higher density of materials presented the highest negative influence on metal leachability, suggesting that the metal leachability can significantly reduce, in particular when the RCA and RAP are used for the sub-base layers of road structure with a higher degree of compaction. However, the use of these recycled materials under field conditions should be further studied as there is an increasing concern of metal leaching from RCA and RAP with respect to recreational and drinking water thresholds.

Characterization of novel polysulfide polymer coated fly ash and its application in mitigating diffusion of contaminants

Fly ash consists of a considerable amount of hazardous elements with high mobility, posing substantial environmental risks during storage in surface impoundments and landfills. This hinders its efficient reuse in construction or material industries. To enhance the versatility of fly ash applications, a novel surface modification technique, termed SuMo, has been developed to create a hydrophobic polysulfide polymer coating on the surface of fly ash particles. The physicochemical properties of SuMo fly ash samples were examined using atomic force microscopy (AFM), environmental scanning electron microscopy (ESEM), thermal gravimetric analysis (TGA), Fourier Transform Infrared spectroscopy (FTIR), and leaching of hazardous elements was tested under practical environmental conditions (pH 4-12) based on the EPA's leaching environmental assessment framework (LEAF). The successful coating of polysulfide polymer on fly ash surface was verified through an increased percentage of C, S, and O in elemental mapping, coupled with the identification of S-O, CO, and C-H functional groups consistent with the chemical structure of polysulfide polymer. While the SuMo fly ash particles maintained their spherical shape, they exhibited increased surface roughness, robust hydrophobicity, and thermal stability up to 250 °C. Notably, owing to the coating's resilience against water leaching, the SuMo fly ash demonstrated a substantial reduction (up to 60-fold) in leachate concentrations of multiple concerning elements, including B, Be, Ba, Mn, Zn, As, Cr, Hg, etc., under various pH conditions compared to the uncoated fly ash. Furthermore, the polysulphide polymer coating effectively prevented Hg volatilization from fly ash below 163 °C. This study highlights the efficacy of the developed polysulfide polymer coating in mitigating the diffusion of hazardous elements from fly ash, thereby enhancing its potential reutilization in material, construction, and agriculture industries.

Developing a Prediction Model of Demolition-Waste Generation-Rate via Principal Component Analysis

Construction and demolition waste accounts for a sizable proportion of global waste and is harmful to the environment. Its management is therefore a key challenge in the construction industry. Many researchers have utilized waste generation data for waste management, and more accurate and efficient waste management plans have recently been prepared using artificial intelligence models. Here, we developed a hybrid model to forecast the demolition-waste-generation rate in redevelopment areas in South Korea by combining principal component analysis (PCA) with decision tree, k-nearest neighbors, and linear regression algorithms. Without PCA, the decision tree model exhibited the highest predictive performance (R2 = 0.872) and the k-nearest neighbors (Chebyshev distance) model exhibited the lowest (R2 = 0.627). The hybrid PCA-k-nearest neighbors (Euclidean uniform) model exhibited significantly better predictive performance (R2 = 0.897) than the non-hybrid k-nearest neighbors (Euclidean uniform) model (R2 = 0.664) and the decision tree model. The mean of the observed values, k-nearest neighbors (Euclidean uniform) and PCA-k-nearest neighbors (Euclidean uniform) models were 987.06 (kg·m-2), 993.54 (kg·m-2) and 991.80 (kg·m-2), respectively. Based on these findings, we propose the k-nearest neighbors (Euclidean uniform) model using PCA as a machine-learning model for demolition-waste-generation rate predictions.

Development of Machine Learning Model for Prediction of Demolition Waste Generation Rate of Buildings in Redevelopment Areas

Owing to a rapid increase in waste, waste management has become essential, for which waste generation (WG) information has been effectively utilized. Various studies have recently focused on the development of reliable predictive models by applying artificial intelligence to the construction and prediction of WG information. In this study, research was conducted on the development of machine learning (ML) models for predicting the demolition waste generation rate (DWGR) of buildings in redevelopment areas in South Korea. Various ML algorithms (i.e., artificial neural network (ANN), K-nearest neighbors (KNN), linear regression (LR), random forest (RF), and support vector machine (SVM)) were applied to the development of an optimal predictive model, and the main hyper parameters (HPs) for each algorithm were optimized. The results suggest that ANN-ReLu (coefficient of determination (R²) 0.900, the ratio of percent deviation (RPD) 3.16), SVM-polynomial (R² 0.889, RPD 3.00), and ANN-logistic (R² 0.883, RPD 2.92) are the best ML models for predicting the DWGR. They showed average errors of 7.3%, 7.4%, and 7.5%, respectively, compared to the average observed values, confirming the accurate predictive performance, and in the uncertainty analysis, the d-factor of the models appeared less than 1, showing that the presented models are reliable. Through a comparison with ML algorithms and HPs applied in previous related studies, the results herein also showed that the selection of various ML algorithms and HPs is important in developing optimal ML models for WG management.

Characterisation and Risk Assessment of Metal Contaminants in the Dust Fall in the Vicinity of a Construction Waste Dump in Beijing

In this study, a large construction waste dump in Beijing, China, was used as the study area. Nineteen effective atmospheric dust samples were collected. The mass fractions of 14 metal elements (Ca, Fe, Al, Mg, Mn, Zn, Cr, Cu, V, Pb, Ni, As, Co, and Cd) were determined for the samples using ICP-MS. The pollutants and the potential ecological risk levels of 10 different heavy metals were evaluated using the enrichment factor, geo-accumulation index, and a potential ecological risk assessment method. The results showed that the Ca, Fe, Al, and Mg contents in the dust fall were considerably high and accounted for 98.81% of the total mass of the analysed metals. Cd and Zn were the main metal contaminants in the dust fall in the vicinity of the construction waste dump, followed by Cu and Mn. The Cd, Zn, Cu, and Mn contents in the construction waste had a significant impact on atmospheric pollution within 250 m of the dump. Moreover, Cd had the largest contribution to the comprehensive ecological risk posed by the heavy metals in the dust fall and was determined to be the primary ecological risk factor in the atmospheric environment in the vicinity of the construction waste dump.

Construction, renovation, and demolition waste in landfill: a review of waste characteristics, environmental impacts, and mitigation measures

With the increase in global population, industrialization, and urbanization, waste from construction, renovation, and demolition (CRD) activities has grown rapidly. There are some issues associated with the disposal of CRD waste in landfills. Depositing in landfills is still the main method for CRD waste disposal from the global perspective. The objective of this study is to comprehensively review the environmental impacts and management technologies for CRD waste in landfills. It includes the overview of the current CRD waste flow and relevant policies worldwide. The main environmental problems caused by CRD waste in landfills include leachate and H2S gas emission. This paper summarizes the primary environmental impacts caused by landfilling CRD waste and the available mitigation technologies. It also includes the use of CRD waste as an alternative material in landfill barriers. Although many technologies can help mitigate the environmental impacts caused by landfilling CRD waste, the optimal solution is to divert the waste flow from landfills using the "3R" principle. In the end, the existing research gaps in CRD waste and landfill management are also discussed.

The effects of soil organic matter on leaching of hexavalent chromium from concrete waste: Batch and column experiments

Concrete is one of the most common building materials in the world and in accordance with the world's shift to a circular economy, there is a need of an increase in concrete reuse and recycling. One of the environmental concerns linked to concrete recycling is the leaching and spread of hexavalent chromium (Cr(VI)). In the present study the Cr(VI) leaching from crushed concrete waste and the effects of soil organic matter (SOM) on chromium (Cr) speciation has been investigated in realistic reuse scenarios by the means of batch shale tests and layered column tests. The effects of concrete properties (pH, grain size and age) on Cr(VI) leaching was also studied. Cr leaching from concrete alone is mainly in the form of Cr(VI), with the pH of the leachate being >10. The smaller the grainsize of the concrete, the higher the Cr(VI) concentration is in the leachate. There was no correlation between the age of the concrete and concrete leaching. When exposed to SOM the Total-Cr concentration in the leachate was reduced. The reduction increased with higher TOC level, with a 99% reduction at very high TOC (25%). The results indicate that Cr(VI) leaching from recycled concrete waste can be mitigated by exposing it to SOM in the desired recycling scenario.

Challenges in Using Handheld XRFs for In Situ Estimation of Lead Contamination in Buildings

Lead in buildings can be found in certain materials such as paints or can be a result of contamination during the use stage. In situ methods for lead identification can be vital for the proper treatment of hazardous CDW (from repair works or selective demolition). A conventional handheld XRF (HHXRF) spectrometer can be used for this purpose, and this study analysed its reliability. A laboratory experiment was conducted to test different calibrations, and to establish a procedure for the conversion of the HHXRF lead concentrations into lead loadings. Model latex paint with a constant lead content was used on two types of surfaces (plasterboard and concrete). A field study was performed to identify and quantify the lead in paint on masonry walls in a public building. ICP-MS analysis was performed in order to verify the lead content. The coefficients of proportionality in the proposed model depend on various parameters: the contamination type, the layer thickness, the substrate, and the built-in calibrations. Despite the limitations of the HHXRF and the discrepancy of the mean lead loadings from the HHXRF and ICP-MS analysis, the HHXRF can be useful for the identification of lead in paint layers up to 1 mm, with a low limit of detection of the order of 0.01 mg/cm2 at worst.

Construction and Demolition Waste Management Research: A Science Mapping Analysis

Construction and demolition waste treatment has become an increasingly pressing economic, social, and environmental concern across the world. This study employs a science mapping approach to provide a thorough and systematic examination of the literature on waste management research. This study identifies the most significant journals, authors, publications, keywords, and active countries using bibliometric and scientometric analysis. The search retrieved 895 publications from the Scopus database between 2001 and 2021. The findings reveal that the annual number of publications has risen from less than 15 in 2006 to more than 100 in 2020 and 2021. The results declare that the papers originated in 80 countries and were published in 213 journals. Review, urbanization, resource recovery, waste recycling, and environmental assessment are the top five keywords. Estimation and quantification, comprehensive analysis and assessment, environmental impacts, performance and behavior tests, management plan, diversion practices, and emerging technologies are the key emerging research topics. To identify research gaps and propose a framework for future research studies, an in-depth qualitative analysis is performed. This study serves as a multi-disciplinary reference for researchers and practitioners to relate current study areas to future trends by presenting a broad picture of the latest research in this field.

Biochar-based bioretention systems for removal of chemical and microbial pollutants from stormwater: A critical review

Biochar has been increasingly used as a filter medium in engineered low impact development systems (e.g., bioretention systems) for decontamination of urban stormwater and management of hydrology. This review paper critically analyzes the performance of biochar-based biofiltration systems for removal of chemical and microbial pollutants present in urban runoff. Biochar-amended biofiltration systems efficiently remove diverse pollutants such as total nitrogen (32 - 61%), total phosphorus: (45 - 94%), heavy metals (27 - 100%), organics (54 - 100%) and microbial pollutants (log₁₀ removal: 0.78 - 4.23) from urban runoff. The variation of biofiltration performance is due to changes in biochar characteristics, the abundance of dissolved organic matter and/or stormwater chemistry. The dominant mechanisms responsible for removal of chemical pollutants are sorption, ion exchange and/or biotransformation, whereas filtration/straining is the major mechanism for bacteria removal. The pseudo-second order and Langmuir isotherm are the best models that describe the kinetics and chemical equilibrium of pollutants, respectively. This critical review provides the fundamental scientific knowledge for designing highly efficient biochar-based bioretention systems for removal of diverse pollutants from urban stormwater. The key knowledge gaps that should be addressed in future research include long-term field-scale bioretention study, development of novel methods for filter media regeneration/reuse, and dynamics of filter media microbial communities.

Chemicals of concern in construction and demolition waste fine residues: A systematic literature review

Despite the increasing use of chemical additives in construction and their potential threat to the environment and human health, many C&DW studies lack a comprehensive view of chemicals of concern (COC) in C&DW. This study systematically reviewed published studies from 2010 to August 2021 using a keyword search methodology to explore COC in C&DW fine residues based on 73 articles identified from 5 prominent databases. Results show that trace/heavy metals (As, Cr, Cu, Cd, and Pb) as well as high concentrations of toxic gasses (methane, hydrogen sulphide and mercury vapour) have been reported in landfills. Besides, organic chemicals such as polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and brominated flame retardants have been found in landfill leachates in the Netherlands and widely detected in landfill leachates in Sweden, Japan, and Canada. The potential of these contaminants to cause health complications has also been reported. Carcinogenicity, liver and kidney damage, cumulative damage, neurological disorders and foetal damage were reported as associated health implications of exposure to COC from C&DW. A waste disposal lens was used to explore the factors that influence the environment and human health impacts (pH, gypsum and organic content, size fraction, atmospheric exposure and liquid infiltration rate). Despite environmental and health issues relating to C&DW fine residues, the ultimate destination for C&DW fine residues remains in general landfills. Although significant efforts in managing C&DW have been implemented at various levels, those specifically targeting C&DW fine residues remain sparse.

Long term leaching behavior of arsenic from cemented paste backfill made of construction and demolition waste: Experimental and numerical simulation studies

The arsenic long-term leaching behavior of the cemented paste backfill obtained from the construction and demolition waste (CPB-CDW) is captured, which can be utilized in the potential engineering application. Laboratory studies were conducted on samples obtained from a mining site and the test results were imported into a numerical simulation model. It was found that the Elovich equation can describe well the As leaching behavior. Initially, the As concentrations decreased in the roadway in the mine and then increased along the roadway and attained a maximum concentration (8.149 × 10^-3 mg/L) at the lower segment. When the groundwater was in the static mode, the As concentration increased dramatically followed by a gradual increase. Eventually, the concentration decreased gradually. For the dynamic condition, the As tended to move in a cluster form and the associated leaching and mass transfer process of As in the CPB-CDW were similar to those observed when the groundwater was in a static condition. However, the difference in the distribution of the amount of As in the leachate fluctuated continuously and the overall trend was to approach a steady state. As such, the time frame of such a mass transfer in the mobilized water is reduced significantly.

Comparison of Random Forest and Gradient Boosting Machine Models for Predicting Demolition Waste Based on Small Datasets and Categorical Variables

Construction and demolition waste (DW) generation information has been recognized as a tool for providing useful information for waste management. Recently, numerous researchers have actively utilized artificial intelligence technology to establish accurate waste generation information. This study investigated the development of machine learning predictive models that can achieve predictive performance on small datasets composed of categorical variables. To this end, the random forest (RF) and gradient boosting machine (GBM) algorithms were adopted. To develop the models, 690 building datasets were established using data preprocessing and standardization. Hyperparameter tuning was performed to develop the RF and GBM models. The model performances were evaluated using the leave-one-out cross-validation technique. The study demonstrated that, for small datasets comprising mainly categorical variables, the bagging technique (RF) predictions were more stable and accurate than those of the boosting technique (GBM). However, GBM models demonstrated excellent predictive performance in some DW predictive models. Furthermore, the RF and GBM predictive models demonstrated significantly differing performance across different types of DW. Certain RF and GBM models demonstrated relatively low predictive performance. However, the remaining predictive models all demonstrated excellent predictive performance at R2 values > 0.6, and R values > 0.8. Such differences are mainly because of the characteristics of features applied to model development; we expect the application of additional features to improve the performance of the predictive models. The 11 DW predictive models developed in this study will be useful for establishing detailed DW management strategies.

Investigating the environmental impacts and engineering performance of road asphalt pavement mixtures made up of jet grouting waste and reclaimed asphalt pavement

As a response to the reduction of environmental pollution and energy consumption in the maintenance or building of a road pavement, this research aims to provide innovative asphalt mixture solutions when designing asphalt base layers containing solidified Jet Grouting Waste (JGW) particles. This involved adding (or not) solutions made up from Reclaimed Asphalt Pavement (RAP) obtained by milling old pavements. The first step focused on a JGW and RAP leaching test before going on to design two non-traditional mixtures: a) a hot asphalt mixture made by replacing 4% of the limestone filler by the total weight of the aggregates with JGW (HMAJ), mixing all of them at a high temperature (160 ÷ 180°C), and b) a cold asphalt mixture made by adding 3% JGW as a filler, 70% RAP (CMRAJ), and 27% limestone by the total weight of the aggregates at low temperatures (40 ÷ 50°C). These innovative mixtures were investigated from the point of view of engineering performance by ascertaining their physico-mechanical features and environmental impact through a Life Cycle Assessment (LCA) test. Further comparison with traditional ones was then carried out using a hot mix asphalt (HMA) and a cold mixture made up from RAP, substituting a portion of the limestone aggregates (CMRA). Such mixtures are subject to special tender specification requirements. Engineering performance assessment showed that, compared with HMA, when JGW is added to both hot and cold mixtures, the ITS is 11% higher for HMAJ and CMRAJ, and cumulative strain is reduced by 17% for HMAJ and 39% for CMRA, while the cold asphalt mixtures (CMRA and CMRAJ) showed greater stiffness levels (on average 50%) at all test temperatures (10, 25, and 40°C). LCA analysis provided significant results for the solutions being compared. Specifically, use of HMAJ as the base layer helped save 65 g/m³ of CO₂ compared with HMA, at the same time helping to reduce 29.7 kg of CO_2eq./m³ global warming potential. On the other hand, the use of CMRA as the base layer, again compared with the HMA, helped save 45 g/m³ of phosphorous compound emissions in water. In terms of terrestrial ecotoxicity and human non-carcinogenic toxicity, the best performance was obtained using a CMRAJ mixture, whose indicators showed a 60% reduction compared with the HMA solution base layer.

Leaching of Chlorides, Sulphates, and Phosphates from Ashes Formed as a Result of Burning Conventional Fuels, Alternative Fuels, and Municipal Waste in Household Furnaces

The aim of the study was to assess leaching of Cl−, SO42−, and PO43− from ashes formed in household furnaces. The ashes were obtained following the combustion of conventional fuels, namely wood and hard coal, and alternative fuels with various fractions of municipal waste in a household boiler. Aqueous leachates of the ashes were used to determine concentrations of chlorides by titration (Mohr’s method) (21.3–3049.6 mg/dm3), sulphates by the gravimetric method (12.2–244.1 mg/dm3), and phosphates by spectrophotometry (0.01–67.2 mg/dm3). It was found that co-combustion of municipal waste with plastic-coated paper cartons, diapers, or a mixed waste fraction leaves the greatest amount of ashes on the furnace grate. The highest amounts of Cl−, SO42−, and PO43− were leached from ashes generated from burning a mix of wood and coals, or wood alone (different species). The addition of municipal waste to the process of burning the conventional and alternative fuels studied did not significantly increase Cl−, SO42−, and PO43− content in aqueous extracts of ashes, the exception being diapers and plywood. In light of the study results, it was concluded that all the ashes could be reused (as an additive to concrete) except for the ash generated from the combustion of a mixed municipal waste fraction and coal (due to the content of Cl−) and diapers (due to the content of PO43−). It was demonstrated that Cl−, SO42−, and PO43− content in the entire set of samples and in individual ash groups is highly heterogeneous and variable.

Stabilization of expansive soils with biomass bottom ashes for an eco-efficient construction

Green philosophy is gaining popularity worldwide. Recycling materials from building demolitions, reutilizing by-products from industrial facilities and exploring the potential uses of waste during a second life cycle are the objectives of this philosophy. In the present article, bottom ashes from electric power generation plants using biofuel combustion were evaluated to verify their potential use as expansive clay stabilizers. Two objectives are pursued: (1) finding a new use for waste that is typically landfilled despite its great potential arising from its technical properties and (2) improving the mechanical properties and reducing the expansive nature of the expansive clays identified during the construction of a motorway. Based on this framework, the present study demonstrated the potential of biomass bottom ashes to stabilize expansive clays. The optimum dosage to improve the properties of clays was determined based on performance parameters, such as plasticity, free swelling or soil collapse. Afterwards, the contaminating potential of ashes was evaluated, being classified as hazardous waste. However, the stabilized mixtures were classified as inert products, thus guaranteeing the environmental feasibility of their use. Finally, the technical application of the stabilized clays as filling materials for embankments and subgrade for light traffic roads was proved. Graphical abstract.

Estimation of construction waste generation based on an improved on-site measurement and SVM-based prediction model: A case of commercial buildings in China

Estimation of construction waste generation (CWG) at the field scale is a crucial but challenging task for effective construction waste management (CWM). Extant field-scale CWG modeling approaches have faced difficulties in obtaining accurate results due to a lack of detailed CWG data, and most of them fail to consider the complex relationship among predictive variables. This study attempts to tackle this issue by proposing a novel CWG modeling approach that integrates improved on-site measurement (IOM) and a support vector machine (SVM)-based prediction model. To achieve this goal, 206 ongoing commercial construction sites were investigated to obtain the predictor values and waste generation rates (WGRs) of five types of waste (i.e., inorganic nonmetallic waste, organic waste, metal waste, composite waste, and hazardous waste) generated at three construction stages (i.e., the understructure stage, superstructure stage, and finishing stage). The data were introduced to the SVM to develop the relationships between predictive variables and WGRs. An actual commercial building under construction was used to demonstrate the applicability of the proposed approach. The results showed that the superiority of the IOM can be used as a basis to implement robust CWG data collection. In addition, the SVM-based WGR prediction model (SWPM) can obtain more accurate prediction results (R² = 86.87%) than the back-propagation neural network (R² = 75.14%) and multiple linear regression (R² = 61.93%).

Chemical and Leaching Behavior of Construction and Demolition Wastes and Recycled Aggregates

Construction and demolition wastes are widely recognized as the main waste stream in the EU, and their recycling and recovery is an important issue in sustainable building industry development. The composition of construction and demolition wastes is highly heterogeneous and is influenced by several factors, including the raw materials and construction products used. The environmental performance of these materials are therefore considerably variable and, in some cases, do not comply with the regulatory limits established to ensure the protection of the natural environment. In this context, this paper presents a data analysis on the environmental behavior of construction and demolition wastes and recycled aggregates in terms of both chemical composition and the release of contaminants according to a leaching test. Subsequently, the most critical parameters for recovery were identified and statistically evaluated. The leaching results showed that SO4, Cu, and COD are critical compounds for both CDWs and RAs.

Development of a Prediction Model for Demolition Waste Generation Using a Random Forest Algorithm Based on Small DataSets

Recently, artificial intelligence (AI) technologies have been employed to predict construction and demolition (C&D) waste generation. However, most studies have used machine learning models with continuous data input variables, applying algorithms, such as artificial neural networks, adaptive neuro-fuzzy inference systems, support vector machines, linear regression analysis, decision trees, and genetic algorithms. Therefore, machine learning algorithms may not perform as well when applied to categorical data. This article uses machine learning algorithms to predict C&D waste generation from a dataset, as a way to improve the accuracy of waste management in C&D facilities. These datasets include categorical (e.g., region, building structure, building use, wall material, and roofing material), and continuous data (particularly, gloss floor area), and a random forest (RF) algorithm was used. Results indicate that RF is an adequate machine learning algorithm for a small dataset consisting of categorical data, and even with a small dataset, an adequate prediction model can be developed. Despite the small dataset, the predictive performance according to the demolition waste (DW) type was R (Pearson's correlation coefficient) = 0.691-0.871, R2 (coefficient of determination) = 0.554-0.800, showing stable prediction performance. High prediction performance was observed using three (for mortar), five (for other DW types), or six (for concrete) input variables. This study is significant because the proposed RF model can predict DW generation using a small amount of data. Additionally, it demonstrates the possibility of applying AI to multi-purpose DW management.

A multi-faceted, environmental forensic characterization of a paradigmatic brownfield polluted by hazardous waste containing Hg, As, PAHs and dioxins

Hg and As mining-metallurgy plants have severely impacted environmental compartments. La Soterraña site (northern Spain) has been previously studied in this context. However, here we used a novel multi-purpose forensic approach to examine accumulations not only of mining-metallurgical waste (volumes above 80,000 t) but also C&D waste as a repository of pollutants (above 10% of As leached in standard tests) at this site. High Hg and As content in very fine grain-size fractions (up to 100,000 mg/kg of As in metallurgy waste below 10 μm) was significant, as was the predominance of As (III) in metallurgy waste. In addition, GC-MS techniques revealed the predominance of PAHs (secondarily Oxy-PAHs and PCBs), which showed a pyrogenic fingerprint, as determined by molecular ratios. Moreover, toxic organometallics (Hg-aromatics) were detected and metallurgy waste was identified as a source of dioxins and furanes (TEQ close to 30). On the basis of our observations, La Soterraña emerges as one of the most polluted sites in Europe and therefore requires urgent remediation. Our key findings indicate that C&D waste should be considered hazardous. Metallurgy waste, in turn, raises maximum concern given the simultaneous presence of toxic inorganic and organic contaminants.

Environmental behavior of construction and demolition waste as recycled aggregates for backfilling in mines: Leaching toxicity and surface subsidence studies

Environmental behavior of construction and demolition waste in cemented backfilling mining technology (CW-CBMT) is studied, with the aim of expanding the scope of construction and demolition waste (CDW) utilization, as well as developing strategies to release coal resources. Toxicity leaching, scanning electron microscopy (SEM), and mechanical properties testing about on-site sampling are carried out, and surface subsidence is surveyed. The results reveal that the maximum leaching concentration (0.00113 mg/L) of arsenic from cemented backfilling body with construction and demolition waste (CBCW) is small, the leaching solution is alkaline, and the leaching of heavy metals is influenced by aggregate particle size and by acidity and alkalinity. The results also show that the average compressive strength of CBCW is 2.4 MPa. The distribution of aggregates and elemental content influence the spatial distribution of compressive strength. The variation of internal distribution of elemental content of the CBCW can be interpreted by multifractal parameters. The maximum surface subsidence value is 245 mm, with the fastest sinking speed occurring in the mining stage and a return of surface subsidence stability after halting of mining. A comprehensive analysis of the test results shows that, from an environmental viewpoint, the application of CW-CBMT is successful.

Recent applications of waste solid materials in pavement engineering

Solid waste materials refer to those municipal or industrial or even domestic wastes that are massively produced during manufacture as well as daily life. A wide variety of solid wastes are generated, but only a few of them are employed in pavement structures. To achieve the task, papers between 2014 and 2019 from top journals which address waste management, waste characterization, and economic and environmental assessment were collected at first. Then, the scope of solid waste materials was narrowed down based on their applications, In the end, six most popular solid waste materials were selected for further study and for the review, namely recycled concrete aggregates, reclaimed asphalt pavement, fly ash, bottom ash, waste rubber, and waste plastics. The reason why only these six solid waste materials are selected is that the rest are neither massively produced not can they be directly used in pavement structures. This review article contains structural properties, treatments, novel researches, environmental analysis, and economic analysis of each solid waste material. The objective of this review article is to provide future researchers with the latest research findings, limitations and improvements in this subject. In conclusion, quite a few novel researchers in terms of workmanship, construction methodology, and treatments are collected for all six materials. Furthermore, an increasing number of findings have proven that most solid waste materials have both environmental and economic benefits when applied in field. Future researchers are encouraged to implement researches on solid waste materials in pavement engineering with consideration of both material properties and environmental/economic effects.

Polycyclic aromatic hydrocarbons (PAHs) leachates from cigarette butts into water

Cigarette butts (CBs) are the most common littered items in the environment and may contain high amounts of polycyclic aromatic hydrocarbons (PAHs) from incomplete tobacco leave burning. The potential relevance of PAHs stemming from CBs for aquatic systems remain unclear since to date there is no systematic study on PAHs leaching from CBs. Therefore, in this study the leaching concentrations of 16 EPA-PAHs (except benzo(ghi)perylene) in 3 different types of water were measured. The concentrations of ΣPAHs leachates from 4 h to 21 days ranged from 3.9 to 5.7, 3.3-5.5, and 3.0-5.0 μg L^-1 for deionized, tap, and river waters, respectively. For all contact times, there were no substantial differences of the leachate concentrations of PAHs among different water types. Lighter PAHs had the highest concentrations among the detected PAHs and they were detected in the leachates already after 4 h. Concentrations of indeno(1,2,3-cd)pyrene, and dibenz(a,h)anthracene were below the limit of detection in all water samples at different contact times. At all contact times naphthalene and fluorene had the highest concentrations among the studied PAHs. Tap and river water samples with addition of sodium azide as chemical preservative contained significantly higher concentration of ΣPAHs. Our leaching data showed that leached concentrations of PAHs exceeded the Water Framework Directive (WFD) standards and considering the number of CBs annually littered this may pose a risk to aquatic organisms and potentially also humans.

An empirical study on waste generation rates at different stages of construction projects in China

Estimation of construction waste generation is critical to construction waste management decisions. However, current construction waste estimation methods have various limitations (e.g. small samples). To address those limitations, this research conducts an empirical study to evaluate the waste generation rate of different types of waste at different construction stages. In this study, construction waste from 148 new-built residential construction sites in China were sorted and weighted on site and their waste generation rates were estimated separately. The results indicated that the amount of inorganic nonmetallic waste with a generation rate of 16.59 kg m^-2 was the highest among the five types of waste (i.e. inorganic nonmetallic waste, organic waste, metallic waste, composite waste, hazardous waste), while the waste generation rate for the underground construction stage, which was 27.57 kg m^-2, was the highest among the three stages (i.e. underground stage, superstructure stage, finishing stage). Compared with previous data, the new waste generation rate proposed in this research can better estimate the actual waste generation situation in construction sites, which provides reliable information for proper decision-making. Furthermore, based on the result of the empirical study, some recommendations for construction waste reduction are proposed.

Recycled concrete aggregate in base course applications: Review of field and laboratory investigations of leachate pH

The prevalence of construction and demolition (C&D) waste and the concurrent demand for construction aggregate presents the opportunity to recycle C&D waste materials as substitutes for virgin aggregate. Commonly, recycled concrete aggregate (RCA) is used as base course in pavement construction. Environmentally responsible applications of RCA must consider the high pH leachate and trace element leaching risks reported in the literature. This review presents the methodology, results, and limitations of existing laboratory and field investigations of RCA leachate chemistry. Long-term highway field studies of RCA leachate illustrate that an initially high leachate pH approaches neutral within approximately one to two years of construction. Conversely, laboratory investigations of RCA leachate pH using batch reactor leaching tests and column leaching tests measure consistently high leachate pH (pH > 10). The discrepancies between field and laboratory measurements of RCA leachate pH suggest that the current laboratory methodology inadequately describes leachate conditions in the field. The authors recommend that future laboratory investigations consider intermittent wetting and drying cycles, eliminate particle abrasion, employ relevant contact times, and consider additional environmental processes that reduce leachate pH such as soil acidity and carbonation.

The contents and release behavior of heavy metals in construction and demolition waste used in freeway construction

A large volume (more than 4.0 million m³) of treated construction and demolition waste (CDW) is planned to be used in the construction of the Xi'an-Xianyang north loop line freeway in West China. These CDW were preliminarily separated into broken concretes, bricks, and porcelains in the treatment plants. In this study, a total of 190 CDW samples including 80 concretes, 80 bricks, 20 porcelains, and 10 mixed samples were collected from five treatment plants. Five farmland soil samples near treatment plants were collected as controls. The contents of 10 elements including cadmium (Cd), arsenic (As), copper (Cu), nickel (Ni), zinc (Zn), chromium (Cr), lead (Pb), manganese (Mn), silver (Ag), and mercury (Hg) in these samples were measured. The contents of 8 elements (Cu, Ni, Zn, Cr, Pb, Mn, Ag, and Hg) in all CDW samples were qualified for the third-level criterion of the Standard of Soil Environment (GB15618-2008). However, Cd contents in 37 concretes, 34 bricks, 6 porcelain samples, and 4 mixed CDW samples exceeded the national third-level standards (1 mg/kg) in GB15618-2008. And As contents in 28 concretes, 21 bricks, 5 porcelain samples, and 3 mixed CDW samples were higher than the national third-level standards (40 mg/kg). The total exceeding standard rates (ESRs) of Cd and As were 42.6% and 30%, respectively. The leaching tests for Cd and As were also done due to their higher ESRs. The results showed that the release amounts (μg/kg) of Cd and As from CDW were increased with increasing liquid to solid ratio (0.4-10 l/kg) but decreased with increasing pH (4-7). The leached concentrations of Cd and As from four types of CDW samples were both in a descending order: brick, mixed materials, concrete, and porcelain. The measured concentrations (μg/L) of Cd and As in leachate were all lower than second-grade criteria of Standard for Groundwater Quality (GB3838-2002). By comparing the leached concentrations of Cd and As with the value in European criteria (EU Council Decision 2003/33/EC) for hazardous wastes, all the CDW samples should be classified as inert or non-hazardous wastes. Thus, it could be concluded that heavy metals in these CDW would not pollute surrounding soil, surface water, and groundwater environment when applied in freeway construction.

Long-term leaching and mechanical behaviour at recycled aggregate with different gypsum contents

Construction and demolition recycling is regarded as an essential subject in the EU, as the target established by its policies to 2020 ratio is far from being achieved. The use of materials recycled from such waste has been widely deemed a contribution to the sustainability of the construction sector. Gypsum is one the limiting components of recycled aggregates used as a base layer in road construction. The aim of this research was to analyse the effect on mechanical properties, leaching behaviour and dimensional changes at long term in recycled aggregates with different gypsum contents. Load bearing capacity was conducted by California bearing ratio on prepared samples. Moreover, the compressive strength was conducted on samples prepared with a 3% cement addition. Both tests were studied long term. Dimensional changes were studied through swelling in California bearing ratio test mould under the modified Proctor conditions for 1 year and using an oedometer device for 5 months. Furthermore, environmental risk assessment was performed, classifying the material with gypsum addition as non-hazardous, given that sulphate anion was above the inert limit. Good mechanical behaviour in the long term and no significant dimensional changes were found regardless of gypsum content.

Polychlorinated biphenyls in stormwater sediments: Relationships with land use and particle characteristics

Polychlorinated biphenyls (PCBs) are classified as persistent organic pollutants (POPs). Concentrations of 209 PCB congeners as well as profiles of the ten homologues were determined in stormwater sediments collected from various (primarily roadway) sites with different land use. The total PCB concentrations ranged from 8.3 to 57.4 ng/g dry weight (dw), with a mean value of 29.2 ng/g dw. PCB concentrations varied with nearby land use. Higher stormwater sediment PCB concentrations were found in dense urban areas (average: 39.8 ± 10.5 ng/g) and residential areas (average: 35.3 ± 6.2 ng/g) compared to highways passing through greenspace (average: 18.0 ± 0.4 ng/g). The number of chlorines per biphenyl ranged from 3.63 to 5.39 and the toxic equivalency (TEQs) of the PCBs were between 1.5 and 18.0 pg/g at all sites. A non-Aroclor congener, PCB 11, was detected in all samples and was dominant at two sites. PCBs were sorbed to smaller stormwater particulate matter (≤75 μm) at higher concentrations compared to larger particles (>75 μm). PCB sorption tended to increase with the total organic carbon (TOC) of the particulate matter in the sediment samples. However, greater PCB mass (almost 80%) was present in the larger particles. Information on sediment PCB concentrations from different land uses, along with stormwater particulate matter data can allow the estimation of PCB loads and load reductions using stormwater control measures.

Role of policy in managing mined resources for construction in Europe and emerging economies

Rapid urbanisation, with associated housing and infrastructure demands, leads to increased mining and use of non-renewable mineral raw materials needed for the construction industry including concrete and cement. In an emerging economy, like Thailand, which is part of Association of Southeast Asian Nations (ASEAN), current environmental management policies are insufficient to reduce raw material requirements or waste from demolition by generating inputs to construction through reuse or recycling. As part of the European Union (EU), Great Britain has successfully implemented integrated policies and achieved high rates of recycled aggregates in construction (29%) and a 70% reuse and recycling target for construction and demolition (C&D) waste. In this paper, Material Flow Analysis (MFA) of cement/concrete materials is combined with an interpretation of related policies to provide a deeper understanding how to achieve more sustainable management of natural resources. A comparative MFA for the construction industry in Great Britain and Thailand (representing an ASEAN country) has been developed that quantifies raw material inputs, buildings and infrastructure outputs, so that the practices in the two countries can be contrasted. We report domestic cement production and import/export data, and calculate the raw materials needed for cement and its calcination process for concrete production. Considering the most relevant policies and taxation in Great Britain, we identify possible ways forward for Thailand by introducing new policies and taxation that will have positive effects on raw material extraction, processing, construction and disposal practices and disposal behaviors. Following the MFA and policy analysis, we believe that similar benefits apply to other emerging economies.

Resource quality of wood waste: The importance of physical and chemical impurities in wood waste for recycling

Recycling of post-consumer wood waste into particleboard may be hindered by the presence of physical and chemical impurities in the waste stream, therefore calling for increased attention on the quality of wood waste. However, wood waste comprises several uses/types of wood, along with different levels of contamination. This study provides the detailed sampling and characterisation of wood waste according to its source, type and resource quality grade. Eight tonnes of wood waste, intended for recycling and collected at three Danish recycling centres, were subdivided into 34 individual material fractions and characterised with respect to the presence of three classes of physical impurities (misplacements, interfering materials and low-quality wood waste) as well as chemical concentrations of more than hundred chemical elements and persistent organic pollutants (POPs). The results demonstrated that contaminant and concentration levels vary significantly according to wood waste type and source, thus emphasising that wood waste should not be viewed as a single material flow but rather be understood and managed according to the presence of individual fractions. Including only clean wood waste fractions at the three recycling centres, 41-87% of the collected wood waste per weight could be recycled - the rest being physical impurities. The results showed that chemical contamination was significantly higher for low-quality wood waste, thus clearly indicating that improvements in separate collection, sorting and handling of wood waste may improve the resource quality of wood waste and potentially achieve cleaner recycling practices.

Life cycle assessment of construction and demolition waste management in a large area of São Paulo State, Brazil

The study evaluated the environmental performance of the construction and demolition waste (C&DW) management in the area of PCJ Watershed, located in the São Paulo State, Brazil, by means of an attributional Life Cycle Assessment. The entire C&DW management under the responsibility of the municipal government was considered. The potential environmental impacts were assessed by using two specific life cycle impact assessment methodologies, CML baseline (v3.03) and Impact 2002+ (v2.12). The results obtained by both methodologies highlighted the importance of the avoided impacts from recovered materials, mainly those related to steel, glass and plastics recycling. In particular, the CML baseline indicated "Human Toxicity" as the most important category, mainly due to the avoided impacts from steel recycling and the generated impacts from transportation in all the C&DW management stages. The Impact 2002+ highlighted instead the role of the categories of "Respiratory Inorganics" and "Global Warming", in accordance with the results related again to steel recycling and transportation but also to landfilling of solid residues. The study considered some alternative scenarios of the mineral fraction management, which quantified the expected advantages of increasing C&DW recycling and improving the quality of recycled aggregates.

Risk assessment by percolation leaching tests of extensive green roofs with fine fraction of mixed recycled aggregates from construction and demolition waste

Extensive green roofs are urban construction systems that provide thermal regulation and sound proofing for the buildings involved, in addition to providing an urban heat island mitigation or water retention. On the other hand, policies towards reduction of energy consumption, a circular economy and sustainability are core in the European Union. Motivated by this, an experimental study was carried out to evaluate the environmental risk assessment according to release levels of polluting elements on leachates of different green roof substrate mixtures based on recycled aggregates from construction and demolition waste through (i) the performance in laboratory of two procedures: compliance and percolation tests and (ii) an upscaled experimental leaching test for long-term on-site prediction. Four plots were built on a building roof and covered with autochthonous Mediterranean plants in Córdoba, South of Spain. As growing substrate, four mixtures were used of a commercial growing substrate with different proportions of a fine mixed recycled aggregate ranging from 0 to 75% by volume. The results show that these mixtures were classified as non-hazardous materials according to legal limits of the Landfill Directive 2003/33/CE. The release levels registered in extensive green roofs were lower compared to the laboratory test data. This shows how laboratory conditions can overestimate the potential pollutant effect of these materials compared to actual conditions.

Upscaling the pollutant emission from mixed recycled aggregates under compaction for civil applications

In general terms, plant managers of sites producing construction wastes assess materials according to concise, legally recommended leaching tests that do not consider the compaction stage of the materials when they are applied on-site. Thus, the tests do not account for the real on-site physical conditions of the recycled aggregates used in civil works (e.g., roads or embankments). This leads to errors in estimating the pollutant potential of these materials. For that reason, in the present research, an experimental procedure is designed as a leaching test for construction materials under compaction. The aim of this laboratory test (designed specifically for the granular materials used in civil engineering infrastructures) is to evaluate the release of pollutant elements when the recycled aggregate is tested at its commercial grain-size distribution and when the material is compacted under on-site conditions. Two recycled aggregates with different gypsum contents (0.95 and 2.57%) were used in this study. In addition to the designed leaching laboratory test, the conventional compliance leaching test and the Dutch percolation test were performed. The results of the new leaching method were compared with the conventional leaching test results. After analysis, the chromium and sulphate levels obtained from the newly designed test were lower than those obtained from the conventional leaching test, and these were considered more seriously pollutant elements. This result confirms that when the leaching behaviour is evaluated for construction aggregates without density alteration, crushing the aggregate and using only the finest fraction, as is done in the conventional test (which is an unrealistic situation for aggregates that are applied under on-site conditions), the leaching behaviour is not accurately assessed.

Development of a leaching procedure to assess the risk of uranium leaching due to construction and demolition waste disposal

Naturally-occurring uranium can be found at elevated concentrations in groundwater throughout the world, with the potential to cause kidney damage in chronically exposed individuals. Empirical evidence shows that uranium mobilization can be enhanced in the presence of ions that are associated with leachate from construction and demolition (C&D) disposal sites. There is need for a simple and effective procedure to evaluate soil and rock formations for uranium mobility prior to the permitting of waste disposal facilities which could alter groundwater chemistry. A series of leachate extractions were performed to represent the impact of C&D leachate on uranium-bearing rocks, focusing on the impact of calcium, sodium, chloride, sulphate, and bicarbonate concentrations on uranium mobilization. Based on these observations a uranium leaching procedure (ULP) was developed and compared to the synthetic precipitation leaching procedure (SPLP). The ULP was capable of mobilizing an order of magnitude more uranium than the SPLP from six rock samples and shows promise as a tool for assessing the risk of groundwater contamination by C&D waste through uranium mobilization.

Toxicity of Recycled Concrete Aggregates: Review on Leaching Tests

Background:

The toxicity of building materials can be addressed in the areas of occupational and environ-mental toxicology. In the first case, the harmful effects to workers caused by exposure to a specific substance during building materials production are analysed. In the latter case, the toxic effects of that substance on living organisms is examined.

Several studies analysed the environmental impact of concrete production, considering a significant number of concrete constituents and compositions, in order to find ways of minimizing it. However, some of the traditional constituents of concrete may be potentially hazardous, presenting different levels of toxicity, but only a few studies are focused on this area. Still, and in order to reduce the potential environmental impact, studies have already started on the incorporation of alternative raw materials, which may affect concrete toxicity.

It is important to develop more concrete toxicity studies analysing different mixes and constituents, in order to identify several ways of minimizing the potential toxicity of this construction material.

Objective:

Different procedures and results of the leaching tests of Recycled Concrete Aggregates (RCA) from previous studies will be presented and discussed in this paper.

Method:

The ecotoxicological characterization of materials is based on the analysis of the eluates resulting from leaching tests. There are several researches that apply different experimental leaching procedures according to existing standards and others with some variations in the standard test conditions: particle size, duration of the test, among others.

Results and conclusion:

The main characteristics of RCA that affect the results of the leaching tests will be identified.

Characterizing the environmental impact of metals in construction and demolition waste

Large quantities of construction and demolition (C&D) waste are generated in China every year, but their potential environmental impacts on the surrounding areas are rarely assessed. This study focuses on metals contained in C&D waste, characterizing the metal concentrations and their related environmental risks. C&D waste samples were collected in Shenzhen City, China, from building demolition sites, renovation areas undergoing refurbishment, landfill sites, and recycling companies (all located in Shenzhen city) that produce recycled aggregate, in order to identify pollution levels of the metals As, Cd, Cr, Cu, Pb, Ni, and Zn. The results showed that (1) the metal concentrations in most demolition and renovation waste samples were below the soil environmental quality standard for agricultural purposes (SQ-Agr.) in China; (2) Cd, Cu, and Zn led to relatively higher environmental risks than other metals, especially for Zn (DM5 tile sample, 360 mg/kg; R4 tile sample, 281 mg/kg); (3) non-inert C&D waste such as wall insulation and foamed plastic had high concentrations of As and Cd, so that these materials required special attention for sound waste management; and (4) C&D waste collected from landfill sites had higher concentrations of Cd and Cu than did waste collected from demolition and refurbishment sites.

Assessment of derelict soil quality: Abiotic, biotic and functional approaches

The intensification and subsequent closing down of industrial activities during the last century has left behind large surfaces of derelict lands. Derelict soils have low fertility, can be contaminated, and many of them remain unused. However, with the increasing demand of soil surfaces, they might be considered as a resource, for example for non-food biomass production. The study of their physico-chemical properties and of their biodiversity and biological activity may provide indications for their potential re-use. The objective of our study was to investigate the quality of six derelict soils, considering abiotic, biotic, and functional parameters. We studied (i) the soil bacteria, fungi, meso- and macro-fauna and plant communities of six different derelict soils (two from coking plants, one from a settling pond, two constructed ones made from different substrates and remediated soil, and an inert waste storage one), and (ii) their decomposition function based on the decomposer trophic network, enzyme activities, mineralization activity, and organic pollutant degradation. Biodiversity levels in these soils were high, but all biotic parameters, except the mycorrhizal colonization level, discriminated them. Multivariate analysis showed that biotic parameters co-varied more with fertility proxies than with soil contamination parameters. Similarly, functional parameters significantly co-varied with abiotic parameters. Among functional parameters, macro-decomposer proportion, enzyme activity, average mineralization capacity, and microbial polycyclic aromatic hydrocarbon degraders were useful to discriminate the soils. We assessed their quality by combining abiotic, biotic, and functional parameters: the compost-amended constructed soil displayed the highest quality, while the settling pond soil and the contaminated constructed soil displayed the lowest. Although differences among the soils were highlighted, this study shows that derelict soils may provide a biodiversity ecosystem service and are functional for decomposition.

Impact of pre-equilibration and diffusion limited release kinetics on effluent concentration in column leaching tests: Insights from numerical simulations

Column leaching tests have become a standard method for assessing leaching of pollutants from materials used, e.g., for road and railway constructions and in landscaping measures. Column tests showed to be practical in laboratories yielding robust and reproducible results. However, considerable uncertainty still exists related particularly to the degree of equilibration of the pore water with the solids during preparation (pre-equilibration) and percolation of the column. We analyse equilibration time scales and sensitivity of concentrations in column leachate with respect to initial conditions in a series of numerical experiments covering a broad spectrum of material and solute properties. Slow release of pollutants from solid materials is described by a spherical diffusion model of kinetic sorption accounting for multiple grain size fractions and sorption capacities. Results show that the cumulative concentrations are rather independent of the pre-equilibration level for a broad spectrum of parameter settings, e.g. if intra-particle porosity is high, grain size is small, or if the sorption coefficient is large. Sensitivity increases with decreasing liquid solid ratios and contact time during percolation. Significant variations with initial column conditions are to be expected for material and compound properties leading to slow release kinetics. In these cases, sensitivity to initial conditions may have to be considered.

Leaching behaviour of hazardous waste under the impact of different ambient conditions

The overall objective of this study is to provide an improved basis for the assessment of the leaching behaviour of waste marked as hazardous partly stabilised (European waste catalogue code 19 03 04^∗). Four samples of hazardous partly stabilised waste were subjected to two leaching tests: up-flow column tests and batch equilibrium tests. The research was carried out in two directions: the first aims at comparing the results of the two experimental setups while the second aims at assessing the impact of different ambient conditions on the leaching behaviour of waste. Concerning this latter objective the effect of mesophilic temperature, mechanical constraints and acid environment were tested through column percolation tests. Results showed no significant differences between batch and column leaching test outcomes when comparing average concentrations calculated at a liquid to solid ratio of 10:1 l kg^-1 TS. Among the tested ambient conditions, the presence of an acid environment (pH=4.5) accelerated the leaching process resulting in a higher cumulative released quantity measured on the majority of the investigated polluting substances. On the contrary, the effect of temperature and mechanical constraints seemed to not affect the process showing final contents even lower than values found for the standard test. This result was furthermore confirmed by the application of the principal component analysis.

Evaluation of recycled concrete aggregates for their suitability in construction activities: An experimental study

Construction and demolition waste disposal is a major challenge in developing nations due to its ever increasing quantities. In this study, the recycling potential of waste concrete as aggregates in construction activities was studied. The metal leaching from the recycled concrete aggregates (RCA) collected from the demolition site of a 50year old building, was evaluated by performing three different leaching tests (compliance, availability and Toxic Characteristic Leaching Procedure). The metal leaching was found mostly within the permissible limit except for Hg. Several tests were performed to determine the physical and mechanical properties of the fine and coarse aggregates produced from recycled concrete. The properties of recycled aggregates were found to be satisfactory for their utilization in road construction activities. The suitability of using recycled fine and coarse aggregates with Portland pozzolanic cement to make a sustainable and environmental friendly concrete mix design was also analyzed. No significant difference was observed in the compressive strength of various concrete mixes prepared by natural and recycled aggregates. However, only the tensile strength of the mix prepared with 25% recycled fine aggregates was comparable to that of the control concrete. For other mixes, the tensile strength of the concrete was found to drop significantly. In summary, RCA should be considered seriously as a building material for road construction, mass concrete works, lightly reinforced sections, etc. The present work will be useful for the waste managers and policy makers particularly in developing nations where proper guidelines are still lacking.

Characterization of brominated flame retardants in construction and demolition waste components: HBCD and PBDEs

The vast majority of construction material is inert and can be managed as nonhazardous. However, structures may have either been built with some environmentally unfriendly substances such as brominated flame retardants (BFRs), or have absorbed harmful elements such as heavy metals. This study focuses on end-of-life construction materials, i.e. construction and demolition (C&D) waste components. The aim was to characterize the concentration of extremely harmful substances, primarily BFRs, including hexabromocyclododecane (HBCD) and polybrominateddiphenyl ethers (PBDEs). Results revealed extremely high contents of HBCD and PBDEs in typical C&D waste components, particularly polyurethane foam materials. Policies should therefore be developed for the proper management of C&D waste, with priority for POP-containing debris. The first priority is to develop a classification system and procedures to separate out the harmful materials for more extensive processing. Additionally, identification and quantification of the environmental implications associated with dumping-dominated disposal of these wastes are required. Finally, more sustainable materials should be selected for use in the construction industry.

Comparison of scenarios for the integrated management of construction and demolition waste by life cycle assessment: A case study in Brazil

Brazil, as a result of economic development and strengthening of the construction industry in recent years, is generating an increasing amount of construction and demolition waste (CDW). Hence, environmental assessment of the management systems is vital. A life cycle assessment (LCA) is presented of CDW management in a medium-sized municipality located in the southeast region of Brazil, where the impacts of leaching were not considered due to absence of consistent data. Six different proposed scenarios for the current CDW management situation have been considered. These scenarios comprised the combined use of landfilling, sorting, and recycling, and the use of CDW as paving material for landfill roads, in different percentages. Considering 0.8 ton of waste as the functional unit, the life cycle inventory was performed using primary data obtained from field survey and secondary data from the database Ecoinvent version 3.1, and from the literature. The method CML 2 baseline 2001 was used for environmental impacts evaluation. The results highlight that recycling is beneficial when efficient CDW sorting takes place at construction sites, avoiding the transport of refuse to sorting and recycling facilities, and the distance between the generation source and the recycling unit is within 30 km. Thus, our results are helpful to ensure that the decision-making processes are based on environmental and technical aspects, and not only on economic and political factors, and also provide data and support for other LCA studies on CDW.

Leaching of chloride, sulphate, heavy metals, dissolved organic carbon and phenolic organic pesticides from contaminated concrete

Concrete samples from demolition waste of a former pesticide plant in Sweden were analysed for total contents and leachate concentrations of potentially hazardous inorganic substances, TOC, phenols, as well as for pesticide compounds such as phenoxy acids, chlorophenols and chlorocresols. Leachates were produced by means of modified standard column leaching tests and pH-stat batch tests. Due to elevated contents of chromium and lead, as well as due to high chloride concentrations in the first leachate from column tests at L/S 0.1, recycling of the concrete as a construction material in groundworks is likely to be restricted according to Swedish guidelines. The studied pesticide compounds appear to be relatively mobile at the materials own pH>12, 12, 9 and 7. Potential leaching of pesticide residues from recycled concrete to ground water and surface water might exceed water quality guidelines for the remediation site and the EU Water Framework Directive. Results of this study stress the necessity to systematically study the mechanism behind mobility of organic contaminants from alkaline construction and demolition wastes rather than rely on total content limit values.

Assessing the environmental performance of construction materials testing using EMS: An Australian study

This paper reports the audit findings of the waste management practices at 30 construction materials testing (CMT) laboratories (constituting 4.6% of total accredited CMT laboratories at the time of the audit) that operate in four Australian jurisdictions and assesses the organisation's Environmental Management System (EMS) for indicators of progress towards sustainable development (SD). In Australia, waste indicators are 'priority indicators' of environmental performance yet the quality and availability of waste data is poor. National construction and demolition waste (CDW) data estimates are not fully disaggregated and the contribution of CMT waste (classified as CDW) to the national total CDW landfill burden is difficult to quantify. The environmental and human impacts of anthropogenic release of hazardous substances contained in CMT waste into the ecosphere can be measured by construing waste indicators from the EMS. An analytical framework for evaluating the EMS is developed to elucidate CMT waste indicators and assess these indicators against the principle of proportionality. Assessing against this principle allows for: objective evaluations of whether the environmental measures prescribed in the EMS are 'proportionate' to the 'desired' (subjective) level of protection chosen by decision-makers; and benchmarking CMT waste indicators against aspirational CDW targets set by each Australian jurisdiction included in the audit. Construed together, the EMS derived waste indicators and benchmark data provide a composite indicator of environmental performance and progress towards SD. The key audit findings indicate: CMT laboratories have a 'poor' environmental performance (and overall progress towards SD) when EMS waste data are converted into indicator scores and assessed against the principle of proportionality; CMT waste recycling targets are lower when benchmarked against jurisdictional CDW waste recovery targets; and no significant difference in the average quantity of waste diversion away from landfill was observed for laboratories with ISO14001 EMS certification compared to non-ISO14001 certified laboratories.