Optimizing City-Scale Demolition Waste Supply Chain Under Different Carbon Policies.

In order to establish a green, low-carbon circular development economic system, imperative goals include achieving carbon peaking and carbon neutrality. This research delves into the resource utilization of city-scale demolition waste (C&DW), aligning with environmental protection needs and sustainable development principles. The paper introduces a unique closed-loop supply chain (CLSC) model tailored for C&DW and employs a distinctive mixed integer nonlinear programming (MINLP) model for optimization. Guangzhou serves as a case study for thorough analysis, verification, and practical application of the proposed model, especially under diverse scenarios of carbon price (CP) and carbon trading (CT) policies. The key conclusions drawn from this study include the following: (1) The cost of carbon emissions is intricately influenced by both carbon emissions and carbon price, with the latter effectively regulating the carbon emissions during C&DW recycling. (2) The implementation of a CT policy, with a fixed carbon price, contributes to a further reduction in the cost of C&DW recycling treatment. (3) Under equivalent conditions, the CT policy demonstrates the potential to decrease costs and enhance the economic benefits within the building environmental protection product market. The research outcomes not only contribute to the advancement of management theory in the C&DW recycling supply chain (SC) but also provide a robust theoretical foundation for governmental initiatives aimed at introducing effective C&DW recycling management policies.

Decoupling economic growth from construction waste generation: Comparative analysis between the EU and China.

The reduction and management of construction waste is crucial for the sustainable development of the construction industry. This research aims to explore a comparative analysis on decoupling relationship between economic growth and construction waste generation on European Union (EU) and Chi et al., 2020 to 2020 in the construction industry, through an integrated method framework of "Tapio + Kaya + LMDI". The research results indicate that there are significant differences in construction waste generation among different countries. The growth rates of construction waste in the EU and China from 2004 to 2020 were 2.47 % and 10.5 %, respectively, showing an upward trend. The economic growth of the construction industry in most EU countries is in a decoupling and negative decoupling state with significant regional differences in decoupling status. The construction waste generation in China is mainly in a weak decoupling state. Economic and demographic factors are the main factors promoting the increase in construction waste generation, while technological factors are the main factors inhibiting construction waste generation in EU and China. However, the impact of each factor on construction was generation varies from EU countries. The research reveals the decoupling effect mechanism between construction waste generation and economic growth, and improves the theory of construction waste management, promotes sustainable development. These findings have feasible inspiration for construction waste management in developing countries with different economic growth levels.

Spatial differentiation of carbon emissions reduction potential for construction and demolition waste recycling.

Identifying the regional differences and drivers for carbon reduction of construction and demolition waste (C&DW) recycling is essential to combat climate change. This study aims to calculate the carbon reduction potential for C&DW recycling from 2006 to 2021 in China and investigates the spatial differences and driving factors of carbon reduction potential for C&DW waste by combining the Theil index, Gini coefficient, and geographic detector methods. The carbon reduction potential for C&DW recycling in China was "high in the east and low in the west" overall level, with an average annual growth rate of 6.27%. The overall differences in carbon reduction potential for C&DW recycling are decreasing, mainly due to intraregional differences and inter-provincial differences in Northeast China. The population size, urbanization rate, and technological effect are the key factors influencing carbon reduction potential for C&DW recycling. There are two types of interactions between influencing factor pairs: nonlinear enhancement and two-factor enhancement. This study's results can guide policymakers to devise relevant, regionally specific policies.

Economic benefit analysis of the carbon potential of construction waste resource management based on a simulation of carbon trading policy.

The need for safer and cleaner environments for all humankind remains a topical issue that cannot be overemphasized. To provide an updated perspective, this study analyzes the carbon potential of construction waste resource management based on carbon trading policy. In this study, the system dynamics principle was used to establish a carbon potential model of construction and demolition waste (C&DW) resource treatment by taking the regeneration project of Xiancun Village as an example. The results showed that the use of construction waste for recycling and resource treatment can generate enormous opportunities to reduce carbon emission. The implementation of the carbon trading policy can create significant benefits in terms of reducing carbon emission, while the total reduction of carbon emission in the baseline scenario can reach 100.66% when compared to the scenario without a carbon trading policy. Moreover, the findings shows that the combination of the carbon trading policy of "carbon price + free allowance ratio" can improve the return on investment of resource utilization companies and the carbon reduction benefits of the combined policy are greater than those of the single policy, but only if the level of the carbon price or free allowance ratio in the combined policy is accepted by the carbon trading subjects. The results of this research contribute to the theory of construction waste resourceization management, provide the theoretical basis for government departments to introduce carbon reduction policies for construction waste resourceization, and provide guidance for the management of companies' carbon reduction.

Evolution game analysis on behavioral strategies of multiple stakeholders in construction waste resource industry chain.

Rapid urbanization in China in recent years has led to a dramatic increase in the number of construction engineering projects and amount of construction waste, and the resource utilization of construction waste is an effective way to low-carbon and energy conservation construction. However, the nation has experienced a low utilization rate of construction waste resources, slow development of its construction waste recycling industry chain in various areas, low coordination of various stakeholders in the industry chain, and incomplete industry chain management. Therefore, in this study, a game model is first used to analyze the decision-making game and its stability strategy among multiple stakeholders in the recycling of construction waste. An income matrix of the three parties, i.e., the government, construction companies, and recycling enterprises, in the construction waste industry chain is then established and the Jacobi matrix used to obtain their evolution and stability strategy (economic incentives, green production, and scale-up). Finally, conclusions are drawn from the simulation analysis of the model: (1) The ratio between fine and subsidy should be reasonably controlled such that the recycling of construction waste by the construction companies is positively related to government supervision. (2) The inflow of renewable products into the market should be promoted to change the perception of the public. (3) A new mode of construction waste management should be developed to link various stakeholders in the industry chain. This study provides scientific and reasonable management suggestions in line with the actual situation of China and provides a useful reference for local government to choose appropriate policies to address the problem of construction waste recycling industry chain.

Influencing factors for effective teaching evaluation of massively open online courses in the COVID-19 epidemics: An exploratory study based on grounded theory.

Many factors affect the teaching of massively open online courses (MOOCs). In this study, to explore the factors that influence the effective teaching of MOOCs, a large number of relevant studies are analyzed. Based on grounded theory, semi-structured interviews were conducted with 30 students and teachers who used MOOCs for online teaching. The interview data were subjected to four research processes -open coding, axial coding, selective coding, and saturation testing- to explore the factors influencing MOOCs' effective teaching and the interactions between them. The results demonstrate that: (1) Effective teachers, effective tuition, effective communication, active online learning, social support guarantees, and online course design have important positive effects on effective teaching, while only certain online learning behaviors will seriously affect the teaching effectiveness of MOOC, resulting in negative effects. (2) Effective communication is essential for effective teaching in MOOCs; effective teachers are the leading factor, thus teachers should take the initiative to study and understand the students to understand their various learning needs and difficulties. (3) Reasonable and effective classroom teaching design is key to improving MOOCs' teaching efficiency. (4) E-learning is respected, cared for, and valued by society, including cognition, emotion, and learning platform support from family, school, teachers, and classmates, and has an important impact on students' motivation and the effects of online learning. The results of this study further clarify factors influencing effective teaching of MOOCs, thus helping to enrich and supplement the theory of effective teaching and evaluation and providing theoretical guidance for teachers to effectively implement MOOC teaching.

Optimization of Site Selection for Emergency Medical Facilities considering the SEIR Model.

Since the outbreak of COVID-19, the rapid construction and operation of Wuhan Vulcan Mountain Hospital and Raytheon Hospital have attracted positive responses from local and international observers. At the same time, it has also highlighted the urgency for the construction of emergency medical facilities for public health emergencies. Before construction, the practical location of medical facilities is the basis for improving the city's emergency management ability. Based on the classic susceptible, exposed, infected, and recovered (SEIR) epidemic model and epidemic data in Guangzhou, we established a multi-stage time-delay SEIR epidemic model that is suitable for epidemic research in Guangzhou. According to the results of the model, the five areas with the highest number of infected patients were identified, which included Baiyun District, Panyu District, Haizhu District, Tianhe District, and Zengcheng District. We then centralized infected individuals at five demand points. Based on the distribution of these points and by combining the characteristics of the emergency medical facilities, we built and solved the set covering location decision model, and considered the economy, society, and environment as the starting points to optimize the site location. Finally, based on simulations, we concluded that appropriate site selection can increase the time required to reach the maximum number of patients and reduce the proportion of infected and exposed people by 11.3% and 1.11%, respectively. This is indicative of the effectiveness of the site selection model and the rational selection of facility points in this study. It solves the optimization problem of the location decision of emergency medical facilities for public health emergencies in China, and also provides some valuable references for site selection decisions of emergency medical facilities in other areas.

Exploring spatial heterogeneity and factors influencing construction and demolition waste in China.

Natural disasters, new urbanization, and urban renewal activities generated a large amount of construction and demolition waste (C&DW), and managing C&DW has become an urgent problem to be solved in the construction of "Zero-waste cities." Based on the calculation of C&DW generation in China from 2005 to 2019, this study explored spatial heterogeneity and factors influencing C&DW in China by Exploratory Spatial Data Analysis (ESDA) and Geographically Weighted Regression (GWR) method. The results showed that C&DW generation in China increased every year, and the overall distribution was characterized as "high in the east and low in the west," with distinct regional differences. The generation intensity of C&DW in China showed a decreasing trend every year. The regions with rapid growth of C&DW generation were concentrated in the eastern coastal areas, and there was significant spatial heterogeneity in the growth trend. There is a significant spatial autocorrelation in C&DW generation in China. The factors of population size, per capita gross domestic product, and the scale of the construction industry played a positive role in promoting C&DW generation in each province, whereas labor efficiency played a negative role inhibiting C&DW generation, which has a significant temporal and spatial heterogeneity. The results extend C&DW management theory and help the policy maker to formulate regional differentiation policies as China and developing country.

Risk sharing for PPP project in construction waste recycling industry in China.

With the deepening urbanization, urban renewal, and reconstruction movement in China, a large amount of construction waste has been generated. In order to ease the financial pressure on the government to deal with construction waste, introducing the PPP model in the construction waste recycling industry has become popular. Based on the theory of system dynamics, this paper studies the risks of using the PPP model in construction waste recycling industry. First, a causal loop diagram was depicted according to the interaction of the main risk factors. Then, using the system dynamics software Vensim, a dynamic model of the risks of the PPP project was constructed. The results show the following: (1) the PPP project in the construction waste recycling industry is profitable; (2) For the PPP project in the construction waste recycling industry, the tendering risk will break out in 6~7 years, the greatest impact on tendering risk is the cooperation environment risk, where cooperation environment risk entropy is increased by 50% and tendering risk entropy is increased by 53.66%; (3) Construction risks will break out in 7~8 years. The construction cost, construction delay, and design defects have the greatest impact on construction risks, where entropy is increased by 50% and construction risk entropy is increased by 19.30%, 19.25%, and 19.08%, respectively; (4) The operational risk has not broken out in 10 years and is expected to break out in 10 to 20 years. Raw material power supply, production technology level, and operations management efficiency have the greatest impact on operational risk, where entropy is increased by 50% and operational risk entropy is increased by 21.52%, 20.84%, and 20.76%, respectively. These results can provide suggestions and references for the risk management of PPP projects in China's construction waste recycling industry.

A Hybrid Blockchain Model for Trusted Data of Supply Chain Finance.

Supply chain finance is an effective way to solve the problem of capital turnover of construction enterprises and stabilize economic growth under epidemic situation. Blockchain technology can solve the problems in the current supply chain finance business, such as incorrect information between banks and enterprises, lack of visibility in transaction process, and possible joint fraud in the core enterprise model. However, it still has problems such as inconvenient information verification, data fraud, and difficulty to achieve a balance between efficiency, security and cost. This paper presents a hybrid chain model combining PANDA (a consensus algorithm based on public chain) and X-Alliance (a consensus algorithm based on alliance chain). Such proposed hybrid chain model can process the transaction of each account in parallel, asynchronize from other unrelated accounts in the network, provide more reliable data storage and authority management, and ensure the ownership of change tracking data, which has higher performance and lower protection cost while ensuring data security and privacy security. According to the data of network crawling, the experimental results show that the throughput can reach 1200tps when four nodes are deployed. The model serves for the supply chain financial data management of engineering projects, making trade authenticity review, risk assessment and credit transmission of core enterprises more efficient. On this basis, each participant can carry out analysis and give early warning of capital flow, timely analyze and calculate the authenticity of transaction background. The proposed method provides a reference for the normal operation of the project fund under the COVID-19 epidemic.

Economic benefits of construction waste recycling enterprises under tax incentive policies.

To further explore the development of construction waste recycling enterprises and promote the recycling of construction waste resources in China, a system dynamics model of the economic benefits of construction waste recycling enterprises is established using the system dynamics method and taking the tax incentive of the Guangzhou Municipal Government as an example. The economic benefits of construction waste recycling enterprises are analyzed from the perspective of the total cost, total revenue, and total recycling amount. The results of the MATLAB simulation and numerical analysis show that (1) by simulating the effects of different taxes such as value-added tax (VAT), education surcharge, urban construction tax, and enterprise income tax on the economic benefits of construction waste recycling enterprises, it is found that when tax incentives reach 70%, the VAT favorable policies bring the highest gains, followed by enterprise income tax, whereas favorable education surcharge policies and urban construction tax have the least impact on economic benefits. (2) Taking the monetary subsidy of the Guangzhou municipal government as an example, it is estimated that the total revenue of construction waste recycling enterprises will increase by 33.56% annually in 2030. When the new production technology is adopted, the return on investment (ROI) will reach 46.8% in 2030 compared to previous technological improvements. In the simulation scenario, the ROI will be 42.2%, which has a good incentive effect on the cost control of enterprises. (3) Increasing the available power to VAT and corporate income tax can improve the profitability of construction waste recycling enterprises in China; however, tax incentive policy will no longer be the main factor affecting the benefits of enterprises when a certain time is reached. (4) It is suggested that the government improves the relevant tax laws incentive policies, increase tax incentives, and add equipment tax incentive policies, actively change the tax mode, and increase indirect tax models to improve the economic benefits of enterprises. The research results provide a decision-making reference for the government to formulate laws and policies related to the economic benefits of construction waste recycling and promote the development of the construction waste recycling industry, the development of new industries, such as waste recycling and treatment, and the formation of industrial chains, to achieve the strategic goal of sustainable development.

System dynamic analysis of construction waste recycling industry chain in China.

With the acceleration of China's urbanization process, construction activities have led to a substantial increase in construction waste. However, as China's construction waste recycling rate is low, it is difficult to convert construction waste into valuable products for the sustainable development of waste resources. The biggest reason for this is the construction waste industrial chain, which is imperfect and has many problems. In this study, a simulation model is established using system dynamics software Vensim PLE. The analogue simulation shows that (1) China generates a large amount of construction waste every year. If construction waste source reduction measures are implemented, it will inhibit 50% of the waste generated. Upstream enterprises in the industry chain should actively develop waste reduction technology and improve waste reduction management; (2) marginal effect exists in the single waste reduction measure, but the government should implement more portfolio reduction measures to enhance the reduction effect, which is often three times that of the single policy; (3) the middle stream recycling enterprises in the industry chain cannot solely rely on government subsidies to reduce the cost of waste recycling. It is necessary to create synergistic linkages with more responsible entities upstream and downstream of the industry chain, thus creating a new model in construction waste management. (4) Government policies tend to drive the purchasing power of building material market. The government should actively exert its subjective initiative, supervise and provide policies to help the downstream enterprises that supply recycled building materials in the industry chain, and change the rigid understanding of contractors and owners about recycled building materials. The research conclusions can provide theoretical guidance for industry chain-related enterprises and government management departments in policy formulation, so that construction waste is sustainably developed.

An environmental assessment model of construction and demolition waste based on system dynamics: a case study in Guangzhou.

At present, China is in the rapid development stage of urbanization, and construction activities are becoming more frequent. This is accompanied by a large amount of construction and demolition waste (C&DW), which raises many problems with its governance, such as occupying valuable land resources, causing air pollution, and consuming raw materials. In this study, taking Guangzhou as an example, the system dynamics principle was used to establish an environmental assessment model of C&DW, and Vensim software was used to simulate and analyze the environmental, economic, and social impacts of various disposal methods of C&DW. The results showed that (1) among all waste disposal methods, landfill disposal had the highest greenhouse gas emissions. It was estimated that the greenhouse gas emissions from landfill disposal will account for 75% of the total emissions in 2030, while the greenhouse gas emissions from recycling disposal will only account for 0.5%. (2) The simulation results showed that, according to the current data, the land area occupied by waste landfills and illegal dumping in 2030 will be about 4.88 million m2, and the economic loss caused by land loss and global warming will account for 9.1% of Guangzhou's GDP in 2030, which is equivalent to the national economy of a regional city with a less developed economy. (3) Enhanced supervision could significantly reduce the amount of illegal dumping, but its effect on landfill disposal and recycling would be very limited. According to the results of the simulation analysis, some suggestions were put forward to improve the environmental, economic, and social impact of C&DW disposal in Guangzhou.

A cost compensation model for construction and demolition waste disposal in South China.

Construction and demolition waste (C&D waste) is a worldwide issue that concerns the sustainable development of the construction industry. In this paper, detailed formulas are listed for calculating the costs of four typical kinds of disposal routes of C&D waste. They are illegal dumping, controlled dumping (landfill), centralized recycling, and on-site recycling. Through the specific formulas, the costs of the new construction project in Guangzhou are also estimated. Then, a cost compensation model of construction waste disposal is constructed, which serves to calculate the amount of compensation that the government shall make to the contractor's disposal cost. The results of this study include the following: (1) steps taken to ensure the appropriate measures for C&D waste disposal sites and recycling centers; (2) the on-site recycling will become the future trend of C&D waste disposal due to its lowest cost; (3) the brick cement mortar and scattered concrete take a relatively larger proportion in the total C&D waste generated during the new construction project, and their disposal costs are higher; (4) we find that the cost of illegal dumping is the lowest among four varieties of waste treatment options if only the direct cost of waste treatment is taken account. However, the cost of on-site recycling becomes the lowest if the total cost is considered; (5) according to the case study, the full estimated cost of construction waste disposal is 9074.56 CNY and the total cost compensation is 15,084.21 CNY. The amount of compensation is greater than the disposal cost and contractors make a profit, thus stimulating them to recycle and reuse construction waste. Based on the empirical findings, we make several policy proposals. The research puts forward some operational advice as a reference for decision-makers of C&D waste management.

Attitudes and behaviour towards construction waste minimisation: a comparative analysis between China and the USA.

With the spread of the concept of sustainable development, people have gained awareness about the problem of massive illegal dumping of construction waste. In this research, a questionnaire survey was carried out in the USA and China. The results indicated the following. (1) Workers in both the countries had positive minimisation attitudes, and the attitude of Chinese construction workers was not significantly different from that of American construction workers. Furthermore, their average values were 3.9 and 4.07, respectively. (2) Business owners had a poor understanding of the obligations that should be fulfilled by contractors and construction workers, which greatly reduced (a) construction workers' and contractors' motivation to implement waste minimisation management and (b) the benefit-driven effect. (3) In terms of perceived behavioural control, Chinese construction workers had poorer minimisation technologies and knowledge than American construction workers, and it was very difficult for them to implement construction waste minimisation. The research conclusions and relevant suggestions may be used to improve the construction waste minimisation behaviour and awareness of Chinese people and promote China's construction waste minimisation management.

WITHDRAWN: A case-study of critical success factors for construction and demolition waste management: the pearl river delta region of china.

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