System dynamic modeling on construction waste management in Shenzhen, China.

This article examines the complexity of construction waste management in Shenzhen, Mainland China. In-depth analysis of waste generation, transportation, recycling, landfill and illegal dumping of various inherent management phases is explored. A system dynamics modeling using Stella model is developed. Effects of landfill charges and also penalties from illegal dumping are also simulated. The results show that the implementation of comprehensive policy on both landfill charges and illegal dumping can effectively control the illegal dumping behavior, and achieve comprehensive construction waste minimization. This article provides important recommendations for effective policy implementation and explores new perspectives for Shenzhen policy makers.

What is the "DNA" of healthy buildings? A critical review and future directions.

Since the outbreak of COVID-19, buildings that provide improved performance have aroused extensive discussion. Nowadays, the connotation of healthy building is becoming complex, performance metrics for healthy buildings vary significantly from different regions in the world and there may be information asymmetry among stakeholders. Consequently, building health performance cannot be effectively achieved. However, previous studies have launched extensive reviews on green building, and there remains a lack of comprehensive and systematic reviews on healthy buildings. To address the above issues, therefore, this research aims to (1) conduct a thorough review of healthy building research and reveal its nature; and (2) identify the current research gaps and propose possible future research directions. Content analysis using NVivo were applied to review 238 relevant publications. A DNA framework of healthy buildings, which clarifies the characteristics, triggers, guides and actions, was then constructed for better understanding of the nature of them. Subsequently, the application of DNA framework and the directions of future research were discussed. Six future research directions were finally recommended, including life-cycle thinking, standard systems improvement, policies & regulations, awareness increase, healthy building examination, and multidisciplinary integration. This research differs from previous ones because it painted a panorama of previous healthy building research. Findings of this research contribute to reveal knowledge map of healthy buildings, guide researchers to fill existing knowledge gaps, provide a standardized platform for healthy building stakeholders, and promote high-quality development of healthy buildings.

Digital inspection techniques of modular integrated construction.

As a new construction form, modular integrated construction (MiC) can effectively improve the construction quality and productivity, especially for the construction of high-density and high-rise buildings. However, the current MiC quality inspection relies on manual inspection, which is inefficient and unreliable. Systematic research on digital inspection techniques (DITs) is fragmented and unable to fully realize the potential of the MiC industry. This study aims to explore the current state of DIT applications in MiC and to summarize the knowledge in the field through an analysis of 248 relevant literatures. Accordingly, this study combines bibliometric analysis, and a system engineering evaluation approach based on 3D structures (time, knowledge, and logic) to provide an overview of the current state of DIT development. The overview includes the application of DITs from a whole life cycle perspective, the DIT knowledge structure, specific DIT applications, as well as current challenges and future prospects.

Extensible carbon emission factor database: empirical study for the Chinese construction industry.

A carbon emission factor (CEF) database is required for the basis of carbon emission calculation in construction projects. However, the default values for existing CEF databases cannot cover the complex resources involved in a construction project. Therefore, this paper proposes a three-step method to guide the establishment of an extensible CEF database for the construction industry, including (1) data collection and parser, (2) data extension, and (3) data encoding and storage. The data extension mechanisms provide the supply chain perspective considering temporal issues and the accounting perspective to streamline the process. Aiming to address the lack of a comprehensive CEF database for the construction industry in China, this paper uses this method to establish a carbon emission factor database for the Chinese construction industry (CEFD for CCI). This database is open and free with 646 CEFs, including five parts: energy, human, material, machinery, and greenspace. This paper provides a way for developing and less developed countries to establish an expandable CEF database, which benefits the parser, extension, encoding, and storage of new resources, as well as computer access.

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.

A load-carrier perspective examination on the change of ecological environment carrying capacity during urbanization process in China.

Urbanization has prompted a dramatic social and economic development during the past decades in China. As a long-term national strategy, urbanization can only be implemented effectively with sufficient and sustainable ecological environment resources. By appreciating that the ecological environment carrying capacity (EECC) is a yardstick for guiding the practice of sustainable urban development, it is therefore pressing to examine the change of EECC adequately, so that the sustainable urbanization can be addressed appropriately. This paper develops a new method from load-carrier perspective to explore the change of EECC performance in the rapid urbanizing China. The EECC performance on water, land, atmosphere and overall perspectives were measured for 30 provinces in China based on the established method. The results show that most provinces in China are experiencing an improving EECC performance during the urbanization process, particularly with an obvious progress in land dimension. In referring to the spatial difference of overall EECC performance, the gap between 30 provinces has been narrowing during surveyed years. However, few provinces including Chongqing, Shandong and Jiangxi have undergone a degradation in overall EECC performance. The EECC performance in atmosphere dimension is still considered as a challenge faced by most provinces, evidenced by high level of PM2.5 concentration. These research findings provide valuable references not only for Chinese governments to formulate effective policy instruments and strategy measures for improving ecological environmental carrying status, but also for researchers to further study in the ecological environment carrying capacity in the context of other countries.

Methods for monitoring construction off-road vehicle emissions: a critical review for identifying deficiencies and directions.

The paper reviews the existing applications of sensing technologies for measuring construction off-road vehicle emissions (COVE) such as earthmoving equipment. The current literature presented different measurement methods and reported the results of utilisation of new technologies for measuring COVE. However, previous papers used different technology applications covering only a part of the monitoring process with its own limitations. Since technologies are advancing and offering novel solutions, there is an urgent need to identify the gaps, re-evaluate the current methods, and develop a critical agenda for automating the entire process of collecting emissions data from construction sites, and monitoring the emission contributors across cities. This paper systematically identifies relevant papers through a search of three key databases-Web of Science, Engineering Valley and Scopus-covering the publications in the last decade from 2008 to 2017. An innovative robust research method was designed to select and analyse the relevant papers. The identified papers were stored in a data set, and a thematic algorithm employed to find the clusters of papers which might be potentially relevant. The selected papers were used for further micro-thematic analysis to find key relevant papers on COVE, and the gap in the literature. A sample of relevant papers was found relevant to COVE and critically reviewed by coding and content analysis. This paper critically reviews the selected papers and also shows that there is a considerable gap in the applications of new technologies for measuring in-use COVE in real time based on real activities toward automated methods. This review enables practitioners and scholars to gain a concrete understanding of the gap in measuring COVE and to provide a significant agenda for future technology applications.

Construction debris becomes growing concern of growing cities.

How can growing cities be expanded in a sustainable way? Huge waste generation has become a major challenge in many growing cities, particularly in developing countries. China's annual C&D waste generation was and estimated 2.4 billion tonnes in the past decade, which is 15 times more than municipal solid waste generation. India has less C&D waste generation than China, yet still is as high as 530 million tons in 2013. However, only around 5% of C&D waste was reused in these countries and the rest largely ends up in dumping sites for disposal. As China and other developing countries continue to urbanize in the next decades, C&D waste management will continue to be a significant challenge for urban sustainability in terms of the environment, economics, and safety. We therefore critically reviewed the C&D waste generation, management, and challenges faced by the fast expanding cities in China and other developing countries. We also compared the current characteristics of key C&D waste systems in developing and developed countries. Recommendations for swift action are made for policy makers in growing cities.

Decoupling China's economic growth from carbon emissions: Empirical studies from 30 Chinese provinces (2001-2015).

The world has witnessed unparalleled economic development over the past decades, but accompanied by large amount of carbon emissions, which triggered the global warming. It is critical for the global sustainable development by decoupling economic growth from carbon emissions at country level, specifically for the largest emitter, China. This study conducts a decoupling analysis from the perspective of carbon intensity (CI), per capita carbon emissions (PC) and total carbon emissions (TC) with reference to 30 Chinese provinces, covering the period of 2001-2015. Based on the Log Mean Divisa Index (LMDI) method, the effects of energy structure (ES), energy intensity (EI), economic output (EO) and population size (P) on TC at provincial level are investigated. Results show that: (1) a strong decoupling relation between GDP and CI is found in most provinces except Hainan, Qinghai and Xinjiang, while there is large room for China to decouple completely from PC and TC; (2) EO and EI are the dominated inhibiting and promoting factors respectively for carbon emission reduction; (3) ES effect on increasing carbon emission changes between positive and negative, while P has a positive but insignificant effect on the increase of carbon emissions for most provinces. The results help local governments formulate measures to coordinate regional economic development and carbon emission reduction.

Quantifying the effects of general waste reduction on greenhouse-gas emissions at public facilities.

Global municipal solid waste (MSW) amounts to approximately 1.3 billion tons per year and is expected to increase to approximately 2.2 billion tons per year by 2025. The greenhouse gas (GHG) emissions from landfills contribute to global climate change. Emissions from this sector contribute around 3% of total net emissions in Australia. Although responsible for a minor portion of Australia's emissions, the sector provides the opportunity for low-cost sources of abatement. This research study aimed to identify new opportunities for reducing GHG emissions from the landfill waste stream in public facilities in Blacktown City in New South Wales, Australia. For this purpose, two public facilities of different types were selected, a library and an aquatic center. The results of the study show that removing organic food waste from the landfill stream at 10 public facilities of the Council could reduce GHG emissions compared with landfilling the food waste by about 0.805 tCO2e/year. However, separately transporting that waste would emit 7.13 tCO2e/year. Therefore, the separated food waste would need to be processed on-site, for example, through worm farms. Removing coffee cups from the landfill waste stream could reduce the associated landfill GHG emissions by around 0.275 tCO2e/y for the 10 public facilities. The study also recommended separating plastic bags from the landfill waste stream of these facilities to reduce 1.10 tonnes of plastic bags from landfill each year. Implications: Potential opportunities for general waste reduction and GHG emission mitigation in public facilities has been studied in this paper. Removing coffee cups and organics food from the waste stream are the main potential opportunities for reducing general waste with possible GHG emission reduction of 0.275 tCO2e/y and 0.161 tCO2/y respectively for 10 public facilities. Removing plastic bags from the waste stream would offer another solution for waste reduction by jointing with the large program running in Australia and creating a collection point for them with 1.1 tonne/y mitigation in general waste at 10 studied public facilities.

Assessing relationships among properties of demolished concrete, recycled aggregate and recycled aggregate concrete using regression analysis.

Recycled demolished concrete (DC) as recycled aggregate (RA) and recycled aggregate concrete (RAC) is generally suitable for most construction applications. Low-grade applications, including sub-base and roadwork, have been implemented in many countries; however, higher-grade activities are rarely considered. This paper examines relationships among DC characteristics, properties of their RA and strength of their RAC using regression analysis. Ten samples collected from demolition sites are examined. The results show strong correlation among the DC samples, properties of RA and RAC. It should be highlighted that inferior quality of DC will lower the quality of RA and thus their RAC. Prediction of RAC strength is also formulated from the DC characteristics and the RA properties. From that, the RAC performance from DC and RA can be estimated. In addition, RAC design requirements can also be developed at the initial stage of concrete demolition. Recommendations are also given to improve the future concreting practice.

On the effectiveness in implementing a waste-management-plan method in construction.

The increasing awareness of waste management concerns from construction and demolition waste has led to the development of waste management as an important function of construction project management. The Hong Kong government started employing the implementation of a waste-management-plan (WMP) method for all construction projects in 2003. During the trial period, the government received different version of feedback from the industry. It also came out that detailed descriptions of waste management procedures in the WMP method largely affect the productivity of companies. This paper investigates the effectiveness of the existing implementation of the WMP method in the Hong Kong construction industry. A questionnaire survey and structured interviews were conducted. The result showed that "Propose methods for on-site reuse of materials" and "Propose methods for reducing waste" are the main benefits gained from the implementation of the WMP method. However, "Low financial incentive" and "Increase in overhead cost" are considered as the major difficulties in the implementation. From that, "Use of prefabricated building components" is considered as the major effective measure to encourage the implementation of the WMP method.

Optimal aggregate testing using Vandermonde polynomials and spectral methods.

Recycled aggregate (RA) has been used in various construction applications around the world mainly as sub-grade, roadwork and unbound materials, but not in higher-grade applications. The major barrier encountered is the variation of quality within RA, which causes lower strength, and poorer quality. This work studies the relationships among six parameters describing the characteristics of RA: (i) particle size distribution, (ii) particle density, (iii) porosity and absorption, (iv) particle shape, (v) strength and toughness, and (vi) chemical composition. Samples of RA from 10 demolition sites were obtained with service life ranging from 10 to 40 years. One additional set of samples was specifically collected from the Tuen Mun Area 38 Recycling Plant. The characteristics of these eleven sets of samples were then compared with normal aggregate samples. A Vandermonde matrix for interpolation polynomial coefficient estimation is used to give detailed mathematical relationships among pairs of samples, which can be used to work out redundant tests. Different orders of interpolation polynomials are used for comparison, hence the best-fit equations with the lowest fitting errors from different orders of polynomials can be found. Fitting error distributions are then studied by using spectral methods such as power spectra and bispectra. From that, the best equations for result estimations can be obtained. This study reveals that there is strong correlation among test parameters, and by measuring two of them: either "particle density" or "porosity and absorption" or "particle shape" or "strength and toughness", and "chemical content", it is sufficient to study RA.

A closed-loop life cycle assessment of recycled aggregate concrete utilization in China.

This paper studies the potential environmental impact of recycled coarse aggregate (RCA) for concrete production in China. According to the cradle-to-cradle theory, a closed-loop life cycle assessment (LCA) on recycled aggregate concrete (RAC) utilization in China with entire local life cycle inventory (LCI) is performed, regarding the environmental influence of cement content, aggregate production, transportation and waste landfilling. Special attention is paid on the primary resource and energy conservation, as well as climate protection induced by RAC applications. Environmental impact between natural aggregate concrete (NAC) and RAC are also compared. It is shown that cement proportion and transportation are the top two contributors for carbon dioxide (CO2) emissions and energy consumption for both NAC and RAC. Sensitivity analysis also proves that long delivery distances for natural coarse aggregate (NCA) leave a possible opportunity for lowering environmental impact of RAC in China.

A system dynamics-based environmental performance simulation of construction waste reduction management in China.

A huge amount of construction waste has been generated from increasingly higher number of construction activities than in the past, which has significant negative impacts on the environment if they are not properly managed. Therefore, effective construction waste management is of primary importance for future sustainable development. Based on the theory of planned behaviors, this paper develops a system dynamic model of construction waste reduction management at the construction phase to simulate the environmental benefits of construction waste reduction management. The application of the proposed model is shown using a case study in Shenzhen, China. Vensim is applied to simulate and analyze the model. The simulation results indicate that source reduction is an effective waste reduction measure which can reduce 27.05% of the total waste generation. Sorting behaviors are a premise for improving the construction waste recycling and reuse rates which account for 15.49% of the total waste generated. The environmental benefits of source reduction outweigh those of sorting behaviors. Therefore, to achieve better environmental performance of the construction waste reduction management, attention should be paid to source reduction such as low waste technologies and on-site management performance. In the meantime, sorting behaviors encouragement such as improving stakeholders' waste awareness, refining regulations, strengthening government supervision and controlling illegal dumping should be emphasized.

Cross-cultural comparison of concrete recycling decision-making and implementation in construction industry.

Waste management is pressing very hard with alarming signals in construction industry. Concrete waste constituents major proportions of construction and demolition waste of 81% in Australia. To minimize concrete waste generated from construction activities, recycling concrete waste is one of the best methods to conserve the environment. This paper investigates concrete recycling implementation in construction. Japan is a leading country in recycling concrete waste, which has been implementing 98% recycling and using it for structural concrete applications. Hong Kong is developing concrete recycling programs for high-grade applications. Australia is making relatively slow progress in implementing concrete recycling in construction. Therefore, empirical studies in Australia, Hong Kong, and Japan were selected in this paper. A questionnaire survey and structured interviews were conducted. Power spectrum was used for analysis. It was found that "increasing overall business competitiveness and strategic business opportunities" was considered as the major benefit for concrete recycling from Hong Kong and Japanese respondents, while "rising concrete recycling awareness such as selecting suitable resources, techniques and training and compliance with regulations" was considered as the major benefit from Australian respondents. However, "lack of clients' support", "increase in management cost" and "increase in documentation workload, such as working documents, procedures and tools" were the major difficulties encountered from Australian, Hong Kong, and Japanese respondents, respectively. To improve the existing implementation, "inclusion of concrete recycling evaluation in tender appraisal" and "defining clear legal evaluation of concrete recycling" were major recommendations for Australian and Hong Kong, and Japanese respondents, respectively.

Parameters for assessing recycled aggregate and their correlation.

Construction and demolition (C&D) waste has consumed a large portion of the landfill areas in Hong Kong. Among them, concrete occupies more than 70% of the total C&D waste by volume. Thus it is necessary to recycle concrete waste to preserve landfill areas. Various governmental departments of the Hong Kong Special Administrative Region (HKSAR) are encouraging the use of recycled aggregate (RA) in the Hong Kong construction industry by issuing various guidelines and specifications. Owing to uncertainty in their properties, however, practitioners are sceptical in using it as a substitute. In this study, an attempt has been made to look at relations among six main parameters that describe the behaviour of RA: (1) particle size distribution; (2) particle density; (3) porosity and absorption; (4) particle shape; (5) strength and toughness; and (6) chloride and sulphate contents. RA samples were obtained from nine demolition sites with service lives ranging from 10 to 40 years and another set of samples was collected from the Tuen Mun Area 38 recycling plant. The behaviour of these samples was compared with that of normal aggregate samples. This study revealed that there is a strong correlation among various parameters, and by measuring three of them: either 'particle density' or 'porosity and absorption' or 'particle shape', and 'strength and toughness', and 'chloride and sulphate contents', it is possible to assess the behaviour of RA. This can significantly help by reducing RA testing time and cost before using it as recycled aggregate concrete.

On the prevailing construction waste recycling practices: a South East Queensland study.

Waste generated from construction and building demolition work constitutes about 68% of all solid waste generated each year in South East Queensland. Consequently, it has created a serious waste management problem. The State Governments of Victoria and New South Wales have been encouraging the use of recycled materials from construction and related waste; they have also promulgated specifications for their use. In Queensland, however, similar regulations are not anticipated in the near future, which explains the lack of funded research conducted in this important arena. This paper presents an evaluation of the prevailing waste recycling practices in Queensland. Nine sites were visited, including two construction sites, three demolition sites, three recycling plants and one landfill in South East Queensland. The difficulties encountered by the recycling programme operators and their associates at these sites are described and the benefits of recycling construction materials are presented. One of the major barriers is that the local councils disallow the use of recycled materials in new construction work. To help rectify these impediments to recycling, recommendations are given to increase the use of recycled construction waste in South East Queensland.

Physio-chemical reactions in recycle aggregate concrete.

Concrete waste constitutes the major proportion of construction waste at about 50% of the total waste generated. An effective way to reduce concrete waste is to reuse it as recycled aggregate (RA) for the production of recycled aggregate concrete (RAC). This paper studies the physio-chemical reactions of cement paste around aggregate for normal aggregate concrete (NAC) and RAC mixed with normal mixing approach (NMA) and two-stage mixing approach (TSMA) by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Four kinds of physio-chemical reactions have been recorded from the concrete samples, including the dehydration of C(3)S(2)H(3), iron-substituted ettringite, dehydroxylation of CH and development of C(6)S(3)H at about 90 degrees C, 135 degrees C, 441 degrees C and 570 degrees C, respectively. From the DSC results, it is confirmed that the concrete samples with RA substitution have generated less amount of strength enhancement chemical products when compared to those without RA substitution. However, the results from the TSMA are found improving the RAC quality. The pre-mix procedure of the TSMA can effectively develop some strength enhancing chemical products including, C(3)S(2)H(3), ettringite, CH and C(6)S(3)H, which shows that RAC made from the TSMA can improve the hydration processes.

The effectiveness of Hong Kong's Construction Waste Disposal Charging Scheme.

The Hong Kong Government introduced the Construction Waste Disposal Charging Scheme in December 2005 to ensure that disposal of construction and demolition (C&D) waste is properly priced to reduce such waste. The charging scheme is not only intended to provide an economic incentive for contractors and developers to reduce waste but also to encourage reuse and recycling of waste material thereby slowing down the depletion of limited landfill and public filling capacities. This paper examines the effectiveness of the charging scheme 1 year after implementation. A survey was conducted at Tseung Kwan O Area 137 and Tuen Mun Area 38, and daily C&D waste records were collected from landfills and public filling facilities between January 2006 and December 2006. The results of the survey show that waste has been reduced by approximately 60% in landfills, by approximately 23% in public fills, and by approximately 65% in total waste between 2005 and 2006. Suggestions for improving the scheme are provided.