On-site Sorting Research Articles

INTERPRETIVE STRUCTURAL MODELING FOR INVESTIGATING FACTORS AND THEIR RELATIONSHIPS INFLUENCING ON-SITE SORTING OF CONSTRUCTION WASTE

ABSTRACT On-site sorting of construction waste has been perceived as an effective measure for promoting sustainable construction. Previous studies have identified factors influencing the implementation of such construction waste sorting activities on-site. Most of them, however, focused on examining the factors from a single standpoint, disregarding the interrelationships between them. This paper seeks to investigate influential factors in implementing on-site construction waste sorting activities, with particular emphasis on their interactive relationships. Data was collected via semi-structured interviews with ten experienced professionals. The intricate interactive relationships among these factors were described and analyzed through the application of an Interpretive Structural Modeling approach and a Matriced’ Impacts Croises-Multipication Applique a Classement analysis. This yielded 13 principal factors that could be sorted into four categories: autonomous, dependent, linkage and driving—with six being considered as fundamental for successful on-site construction waste sorting; i.e., difficulty in sorting materials from mixed construction waste, limited space & environment at the site, low benefits from this activity, interference causing regular disruptions to site activities, immature recycled material market, and lack of government regulation support. In contrast to prior studies, the lack of manpower is no longer seen as being as critical an issue as before. Factors such as the difficulty in sorting materials from mixed construction waste, the limited benefit from on-site construction waste sorting, and the lack of government regulation support have become more critical. This study not only helps to identify the critical elements that affect on-site sorting of construction waste and their relationships, but also assists policymakers and practitioners in understanding the priority of measures needed to increase on-site sorting of construction waste.

Cybernetic-parsimonious MCDM modeling with application to the adoption of Circular Economy in waste management

Construction and demolition waste (CDW) is the main contributor to economic loss, environmental pollution, and health hazards if the current linear economy model of ‘take-make-consume-dispose’ is not replaced by a Circular Economy (CE) as a solution approach to maximize the use of resources and reduce waste. However, successful CE concept implementation involves strategies that trigger construction and demolition waste management (CDWM) throughout its life cycle, rather than end-of-life strategies, such as reuse and recycling. By meticulously reviewing the literature, nineteen factors that affect CDWM from CE concept implementation throughout six stages of preconstruction, procurement, construction, demolition, transportation, and end-of-life are initially identified. A hybrid fuzzy Multi-Criteria Decision-Making approach is then utilized in two main stages, including an Enhanced Fuzzy Delphi Method in stage one, to refine the identified factors according to Tehran’s construction context, and a Cybernetic Parsimonious Fuzzy Analytic Hierarchy Process in stage two, to prioritize these factors. Three factors were identified during the first stage of the research methodology and added to the factors extracted from the literature. The results indicate that ‘on-site sorting, reusing, and recycling of waste materials’, ‘various procurement models’, and ‘precise implementation of waste management regulations and plans’ are the most important factors, respectively. A comprehensive list of the factors provided as part of the research findings has contributed to the body of knowledge to be used as a snapshot by researchers, while the ranking of the factors gives new insights to stakeholders on ways to manage CDW in projects.

Environmental impact evaluation of landfill mining of legacy waste with on-site sorting using life cycle assessment.

The present research is aimed at assessing the environmental impacts of landfill mining of soil-like material with on-site sorting for land application using life cycle assessment. The scenario is compared with no-landfill mining (base scenario) and future scenario (including material recycling and incineration). Soil-like material is processed using windrow composting. The impact assessment was performed using the EASETECH™ software tool. ReCipE 2016 midpoint world impact method with eight impact categories was used for assessing the environmental profiles. The functional unit of the assessment was 1 t of recovered waste in India. Overall, the results showed that excavation of landfilled waste with on-site recovery of soil and land application of soil resulted in higher environmental benefits compared to no mining condition in global warming potential (GWP), freshwater eutrophication (FEW), human toxicity (HT), and fossil depletion (FD), while higher impacts were observed in terrestrial acidification (TA), terrestrial ecotoxicity (TE), marine eutrophication (ME), and photochemical oxidation (PCO). After composting, land application of recovered soil contributed to environmental offsets in GWP, HT, and FEW while contributing to TE emissions. Emissions associated with excavation and on-site sorting contributed 55.1% to freshwater toxicity, 25.5% to human toxicity, 16.2% to climate change, and 10.8% to terrestrial acidification. The choice of energy, transportation, and fuel for waste activities affected the performance of alternative scenarios in GWP. Application of recovered metals in the manufacturing process, incineration of plastic, and textile components improved the environmental performance. The outcomes of this research will equip regulatory bodies in the development of guidelines and frameworks on material and energy recovery from the waste components mined from legacy waste.

Role of Grain Size Distribution and Pier Aspect Ratio in Scouring and Sorting around Bridge Piers

Several bridge piers were visited, and their scour hole was characterized into three zones: scour, transition, and mound zones. The observed onsite sorting and scouring patterns were recreated through flume experiments with varying pier aspect ratio (1:1, 1:2, 1:4 and 1:6) and sediment geometric standard deviation (σg). The experiments showed that maximum scour depth decreased with non-uniformity; 52.7 mm, 20.2 mm, and 16.6 mm are the respective maximum scour depth of beds with σg = 1.4, 2.5, and 5.2. While aspect ratio has minimal effect on maximum scour depth values, it has noticeable effects on scour shape and asymmetry. The location of the lowest point of the scour shifted further downstream as σg increased. The number of occurrences where the location of the lowest point is outside the upstream cylindrical hemisphere is zero (0) for σg = 1.4, three (3) for σg = 2.5, and five (5) for σg = 5.2. The observed processes of upstream-to-downstream propagation of scour may explain the gradual decrease in fines on the surface, as well as the asymmetry of the scour, confirming the role of combined effects of grading of the bed material and piers’ aspect ratio in the scour-forming process.

Circular Economy of Construction and Demolition Waste: A Literature Review on Lessons, Challenges, and Benefits.

Conventionally, in a linear economy, C&D (Construction and Demolition) waste was considered as zero value materials, and, as a result of that, most C&D waste materials ended up in landfills. In recent years, with the increase in the awareness around sustainability and resource management, various countries have started to explore new models to minimize the use of limited resources which are currently overused, mismanaged, or quickly depleting. In this regard, the implementation of CE (Circular Economy) has emerged as a potential model to minimize the negative impact of C&D wastes on the environment. However, there are some challenges hindering a full transition to CE in the construction and demolition sectors. Therefore, this review paper aims to critically scrutinize different aspects of C&D waste and how CE can be integrated into construction projects. Reviewing of the literature revealed that the barriers in the implementation of CE in C&D waste sectors fall in five main domains, namely legal, technical, social, behavioral, and economic aspects. In this context, it was found that policy and governance, permits and specifications, technological limitation, quality and performance, knowledge and information, and, finally, the costs associated with the implementation of CE model at the early stage are the main barriers. In addition to these, from the contractors’ perspective, C&D waste dismantling, segregation, and on-site sorting, transportation, and local recovery processes are the main challenges at the start point for small-scale companies. To address the abovementioned challenges, and also to minimize the ambiguity of resulting outcomes by implementing CE in C&D waste sectors, there is an urgent need to introduce a global framework and a practicable pathway to allow companies to implement such models, regardless of their scale and location. Additionally, in this paper, recommendations on the direction for areas of future studies for a reduction in the environmental impacts have been provided. To structure an effective model approach, the future direction should be more focused on dismantling practices, hazardous material handling, quality control on waste acceptance, and material recovery processes, as well as a incentivization mechanism to promote ecological, economic, and social benefits of the CE for C&D sectors.

The Building Information Modeling (BIM)-Based System Framework to Implement Circular Economy in Construction Waste Management

The tremendous quantity of waste produced from construction and demolition is a major cause of environmental degradation. This quantity tends to increase due to the rapid growth of building development and renovation. Meanwhile, construction waste management is a complex and costly process due to the fact that it requires different kinds of resources such as money, land, and technology. It is often ignored by all project participants even though it is an essential element of construction project management. However, it has been discovered that modern construction waste management is structured based on the concept of circular economy which focuses on eliminating construction waste and maximizing the value of materials. Therefore, this research proposes an innovative framework to implement the circular economy using building information modeling (BIM) in order to improve the construction waste management process. This involved a thorough review of past literature to identify the implementation of the concept of circular economy, waste management, and the application of BIM, also the research gaps observed were used to develop the functionality of the proposed framework. The five functionalities include (1) visualization and data integration, (2) direct construction waste quantity take-off, (3) BIM-based sorting system and selection of appropriate disposal parties, (4) estimating cost and schedule of waste disposal, and (5) simulation and monitoring report. This BIM system was designed to analyze material waste, quantity, disposal time, and waste treatment based on project conditions, material quantities, and schedule. It can also be used to plan and monitor the construction waste process, thereby making it possible to avoid the disruption of productivity and project time usually caused by unplanned waste management activities. Moreover, the proposed on-site sorting system also has the ability to facilitate the adoption of the circular economy concept during the construction phase.

Designing of reverse vending machine to improve its sorting efficiency for recyclable materials for its application in convenience stores

Plastics have multiple applications in disposable products, high-end technology parts, etc., owing to their functionality and manufacturing flexibility. However, their increased use has increased the global proportion of plastic wastes, which creates a serious environmental issue, thereby, creating a demand for plastic waste management techniques. Improving the efficiency of resource recovery by appropriate sorting and collection systems is necessary for successful plastic recycling. Therefore, this study proposed a three-step optimization process of a reverse vending machine (RVM), a small automatic recyclable waste sorter/collector system, for acquiring an optimal design and enhanced efficiency. The RVM system categorized recyclable wastes as plastics, glass, and cans using barcode, vision, and near infrared sensors. The average sorting efficiency of the designed RVM system was 94%, 95% for polyethylene terephthalate, and 98% for glass bottles. Therefore, the RVM system, with the average sorting efficiency of 95%, is suitable for application in on-site sorting in small-sized areas, such as convenience stores, which generate wastes on a small scale.

The classification of construction waste material using a deep convolutional neural network

The management of Construction and Demolition Waste (C&DW) is complex and adds significantly to the overall life cycle cost of projects. On site waste sorting using technologies that automatically identify different materials has the potential to assist in classifying C&DW and reduce costs. The aim of this research was to design and describe a deep convolutional neural network (CNN) to identify 7 typical C&DW classifications (both single and mixed disposal) using digital images of waste deposited in a construction site bin (artefact). This approach emulated authentic construction site scenarios where on-site sorting is difficult. A novel design science methodology was used. The experiments delivered 94% accuracy, classifying both single and mixed C&DW. This accuracy is important on projects where on-site sorting is attempted, as in practice bin contamination escalates project costs and reduces C&DW diversion from landfill. To illustrate potential of the research the innovative artefact is incorporated within a hypothetical case study describing its use in a circular C&DW business model.

Challenges in current construction and demolition waste recycling: A China study

China produced a large amount of construction and demolition (C&D) waste, owing to the rapid development of construction industry. Although a set of policies and regulations are being drafted in China for promoting C&D waste recycling, execution of these policies in practice seems to be far from effective. Currently, approximately 75% of Chinese cities are still surrounded by large volumes of C&D waste. Therefore, identification of challenges in the development of C&D waste management, specially recycling, is essential. This paper employs site visits to 10 recycling plants in 10 Chinese cities (Shanghai, Hangzhou, Suzhou, Chongqing, Chengdu, Xi’an, Changsha, Shenzhen, Nanjing, and Zhoukou) and interviews with 25 industry practitioners for examining the challenges. Eight challenges are identified: (1) unstable source of C&D waste for recycling, (2) absence of subsidies for recycling activities and high cost for land use, (3) insufficient attention paid to design for waste minimisation, (4) absence of regulations on on-site sorting, (5) unregulated landfill activities, (6) a lack of coordination among different government administration departments, (7) a lack of accurate estimation of waste quantity and distribution, and (8) a lack of an effective waste tracing system. Recommendations to address these challenges are presented. The results of this study are expected to aid policy makers in formulation of proper C&D waste management in China and provide a useful reference for researchers who are interested in C&D waste recycling industry.

Factors affecting construction waste management streams in Australia

Construction and Demolition Waste (C&DW) represents a significant proportion of industrial waste going to landfill. The aim of this research was to determine the current factors affecting C&DW management on construction sites in New South Wales (NSW), Australia. In order to achieve this aim, semi-structured interviews were conducted with 19 C&D practitioners and stakeholders, interview data were analysed using Nvivo software. Key factors that underlined waste management processes on construction sites were identified. These include; identifying economic values of diverted material, potential for onsite sorting, knowledge, experience and training of site operatives, a need for tenders to include accurate predictions of waste management costs and the identification of improved methods of C&DW collection and disposal. This research reveals the key factors identified by the industry specialists in NSW that would potentially hinder C&DW management targets. Accordingly, the findings are valuable to managers and environmental stakeholders concerned with C&DW management.

Integrated Freight Terminal and Automated Freight Management System: A theoretical approach

The author proposes the use of customized conveyor belts for handling goods like cement, fertilizers, grains and other packaged commodities. These terminals will allow efficient running of multi-point trains and facilitate train-to-train transfers. At commercially viable places facilities for handling other traffic like containers, perishable products, and automobiles can be integrated. Common facilities will help to decrease the unit costs for the customers and increase the revenue earning potential for the transporter and terminal operator. Value added services like consolidation and breaking up of cargo, packaging, labelling, bar coding, reverse logistics, customs processing etc.; it will enable many customers to dispense with their own supply and forwarding warehouses. Such terminals at Dedicated Freight Corridors in India can capture the emerging fast moving consumer goods and e-commerce traffic. This will simplify supply chains and aid in the reduction of the prices of goods. This is particularly important for India where logistics occupies 13% to 15% of the GDP. Railways having a greater freight market share mean significant environmental benefits. Also the proposed concept will reduce the fleet of trucks and highway congestion. Integrated Freight Terminals (IFT) aided by Automated Freight Management System (AFMS) with automated loading/unloading systems, on-site sorting, storage and transshipment facilities will transform the way commodities are transported by railways. Moreover, faster freight service means faster turnover and return on investment.

An off-site snapshot methodology for estimating building construction waste composition - a case study of Hong Kong

Waste composition analysis is essential for implementing appropriate management strategies. In Hong Kong, on-site waste quantification is often not practical due to site space limitation at construction sites. In addition, as the construction waste problem urgently needs addressing, reliable waste generation rates need to be derived over a short time. To address these two issues, this study presents an off-site snapshot methodology for estimating construction waste composition. Three construction sites, at the initial stage, mid-stage, and end stage respectively, are selected for illustrating the proposed snapshot methodology. It is found that the composition of inert and non-inert waste varies significantly at different construction stages. Non-inert waste is an important component of building construction waste, of which wood & timber waste contributes the largest proportion. Following wood & timber waste, metal waste is the second largest source of non-inert waste. Results show that the proposed off-site snapshot methodology can sufficiently solve the problem of limited on-site sorting space and derive reliable detailed waste generation information over a certain short time.

A system dynamics-based environmental benefit assessment model of construction waste reduction management at the design and construction stages

Construction waste generation and its environmental impact reduction have become an urgent issue to be solved with the acceleration of urbanization process in China. However, limited research has been conducted to cover both the design stage and the construction stage such that the overall construction waste reduction outcome could be comprehensively assessed. Based on interview data and literature review, Vensim software was used to build a two-stage environmental benefit assessment system dynamics (SD) model which covered construction waste reduction management subsystem, waste generation and disposal subsystem, and environmental benefit assessment subsystem. Simulation results highlight that the reduction management can reduce 40.63% of waste generation. In the meantime, the reduction management achieves good environmental benefits including the reduction of greenhouse-gas emissions of 12,623.30 kg, saving waste landfill of 3901.05 m3 and reducing the use of public vacant site for the illegal dumping of 688.42 m3. The simulation results demonstrate that the dynamic model could assess the environmental benefits of construction waste reduction effectively at the design and the construction stage. This research can provide insight to the design and construction professionals for waste reduction measures such as prefabricated components application, reduced design modification at the design stage, on-site sorting and material reuse at the construction stage, and to provide references for governments in assessing the reduction management outcomes of construction projects and the environmental benefits.

Comparative environmental evaluation of construction waste management through different waste sorting systems in Hong Kong

This study aimed to compare the environmental performance of building construction waste management (CWM) systems in Hong Kong. Life cycle assessment (LCA) approach was applied to evaluate the performance of CWM systems holistically based on primary data collected from two real building construction sites and secondary data obtained from the literature. Different waste recovery rates were applied based on compositions and material flow to assess the influence on the environmental performance of CWM systems. The system boundary includes all stages of the life cycle of building construction waste (including transportation, sorting, public fill or landfill disposal, recovery and reuse, and transformation and valorization into secondary products). A substitutional LCA approach was applied for capturing the environmental gains due to the utilizations of recovered materials. The results showed that the CWM system by using off-site sorting and direct landfilling resulted in significant environmental impacts. However, a considerable net environmental benefit was observed through an on-site sorting system. For example, about 18–30kg CO2 eq. greenhouse gases (GHGs) emission were induced for managing 1 t of construction waste through off-site sorting and direct landfilling, whereas significant GHGs emission could be potentially avoided (considered as a credit −126 to −182kg CO2 eq.) for an on-site sorting system due to the higher recycling potential. Although the environmental benefits mainly depend on the waste compositions and their sortability, the analysis conducted in this study can serve as guidelines to design an effective and resource-efficient building CWM system.

Life Cycle Assessment of Landfill Mining Project

Abstract The objective of the research is to develop a life cycle assessment (LCA) model for environmental evaluation of two landfill mining alternatives – on-site sorting of mined waste using mobile sorting equipment or sorting at a centralised waste sorting plant located 12.6 km from the mined territory. Life cycle inventory data is based on the real landfill mining project implemented in Latvia and additional experimental data collected from the scientific papers. The results show that waste sorting at the landfill site succeeds in minimizing the effects to the environment by 28% more than sorting of waste at the centralised plant.

Critical success factors for on-site sorting of construction waste: A china study

Benefits of conducting on-site sorting of construction waste, typically including increasing the rates of reuse and recycling, reducing the cost for waste transportation and disposal, prolonging the lifespan of landfills designed for receiving non-inert construction waste, and lessening the pollution resulted from the huge amount of construction waste, have been extensively investigated by previous studies. However, effective implementation of construction waste sorting requires a wide range of factors involving human beings, management, technology, environment and resources. So far, we know little about how to conduct effective construction waste sorting in China. This research therefore aims to identify the critical success factors (CSFs) for on-site sorting of construction waste in China. A set of methods including CSF approach, pilot study, questionnaire survey and face-to-face interview are adopted to facilitate the identification and analysis of the CSFs. Six factors including (1) manpower, (2) market for recycled materials, (3) waste sortability, (4) better management, (5) site space, (6) equipment for sorting of construction waste, are considered the CSFs for effective on-site sorting of construction waste in Shenzhen, China. These CSFs are of great significance both to researchers and industry practitioners.

Management of construction waste in public housing projects in Hong Kong

Waste management in the building industry in Hong Kong has become a major environmental issue in recent years. Of particular concern is the increasing amount of construction and demolition (C&D) waste being dumped at landfill sites. Greater consideration must be given to waste generation and management at the planning stage of a building development to reduce wastage levels. The causes and quantities of building construction waste generated on public housing building sites in Hong Kong have been analysed. Five public housing construction sites were selected for the study by regular site visits. Timber boards used in formwork were the most significant waste type requiring disposal followed by waste derived from wet trades. Waste generation could be significantly reduced by the use of precasting and system formworks. The major causes of wastes were improper preparation and handling, misuse, and incorrect processing. In general, little on-site waste sorting was carried out. Appropriate planning including the preparation of a detailed waste management plan is essential for effective waste minimization. At the construction stage, better house keeping and more vigorous on-site sorting of inert from non-inert materials are necessary. Waste indices calculated from waste monitoring data should be publicized and used for future waste estimations.

On-site sorting of construction and demolition waste in Hong Kong

Abstract The construction industry is the major solid waste generator in Hong Kong. In 1998, it generated about 32 710 t per day of construction and demolition (C&D) waste. In the management of such a huge quantity of C&D waste, Hong Kong has adopted a strategy of depositing the inert portion (e.g. sand, bricks and concrete) of the waste at public filling areas for land reclamation and the non-inert portion (e.g. plastics, paper, wood) at municipal solid waste landfills. However, the C&D waste arisen is usually in the form of a mixture of both inert and non-inert materials. As a result, the waste has to be disposed of at landfills, aggravating the landfill shortage problem. There is a paramount need to separate the C&D waste into its constituent parts before it is delivered to either the landfills or the public filling areas for disposal. In order to study the feasibility of carrying out on-site waste sorting and the current situation of the building relating C&D waste generated in Hong Kong, a survey was conducted. This paper presents the results of the survey undertaken to evaluate three alternative waste sorting methods on building construction sites and to compare them with the use of an off-site central waste sorting facility. The results indicate source separation has the advantages of requiring less effort and resulting in better segregation of inert and non-inert wastes as compared with waste sorting centrally carried out at a designated area on- or off-site. In addition, the views of the building industry participants were also obtained through a questionnaire survey to give a better understanding of their attitude on on-site waste sorting. The results indicate that the building construction participants are reluctant to carry out on-site waste sorting. Even when high a tipping fee is imposed, they have little incentive to perform on-site waste sorting which is considered to be time and labour demanding. Only through contractual requirements or legislation can on-site waste sorting be fully implemented and becomes a long-term solution to the landfill shortage problem in Hong Kong.

Theory, Characteristics, and Operating Parameters of Portable Optical Emission Spectrometers for the On-Site Sorting and Identification of Steels

Abstract Portable optical emission spectrometers are evolving as important tools for the on-site sorting and identification of metals. Their analytical precision and accuracy, while not quite as good as laboratory systems, are more than adequate for sorting mixes and most grade verification requirements. The intentions of this paper are to provide a brief review of the technology and history of emission spectrometers, and then to describe parameters, operation, capabilities and limitations of the device for plain carbon, low alloy, and stainless steels.