Modeling materials flow of waste concrete from construction and demolition wastes in Taiwan

Material flows of concrete from construction and demolition (C&D) waste in Taiwan have grown considerably over the last two decades, Hsiao et al. (2001). This increased flow puts pressure on limited national disposal capacity and has indirectly caused ecological damage to domestic riparian zones used as sources of natural aggregate. Using existing statistics and literature sources for C&D waste generation in Taiwan we have developed a dynamic model of domestic material flows of concrete waste and employ statistical analyses to obtain projections of future material flows. Our major findings are: (1) Taiwan’s rate of waste concrete generation in 2001 for the residential and commercial construction industry was approximately 2.4 Million Metric Tons (MMT) per year, averaging 0.11 metric tons of waste concrete generated annually by each Taiwanese; (2) Around the year 2009, the national rate will more than triple to exceed the spike in C&D concrete waste generation that occurred after the Chi Chi earthquake 9/21/99, 8.5 MMT. (3) Aside from pilot-scale development of waste concrete utilization technology, nationwide recycling rates remain negligible. Without resource recovery, the volume of C&D waste generation by 2009 is projected to occupy nearly 7% of all existing and planned domestic landfill capacity. A target is established to raise resource recovery rates for waste concrete to 50% by 2005 and a 100% nationwide recycling rate by 2009.     

Decisions on recycling: Construction stakeholders’ decisions regarding recycled mineral construction materials

Construction and demolition (C&D) waste, being already the largest waste fraction in industrialized countries, is expected to increase in the future. C&D waste recycling has been considered to be a valuable option not only for minimizing C&D waste streams to landfills but also for mitigating primary mineral resource depletion. Even though the use of recycled mineral construction materials (RMCM) is regulated and successful application examples are available, construction stakeholders do not yet broadly apply them. Although various criteria hindering a transition towards a broader application of RMCM have been identified, it is yet unknown how these criteria differ among decisions, stakeholders and applications. We therefore analyze construction stakeholders’ behavior, and decision-making regarding RMCM for the construction material market in Switzerland. Stakeholders’ decision-making was quantified with the analytical hierarchy process (AHP) in a survey in combination with their behavior. The results demonstrate the importance of stakeholder interaction, i.e. most stakeholders decide which material to apply based on interaction with other stakeholders e.g., recommendations and specifications. However, the initial general specification by awarding authorities that construction should be sustainable has little relevance to the subsequent material decisions. On the contrary the role of the recommendation of engineers, have a high impact on the subsequent decisions by the other stakeholders. Results also confirm that RMCM are broadly accepted in civil engineering (CE), whereas in structural engineering (SE) RMCM are still a niche product. The good alignment of the outcome of decision modeling with observed behavior shows the usefulness of analyzing decision-making with AHP.     

A model for estimating construction waste generation index for building project in China

The increasing construction and demolition (C&D) waste causes both cost inefficiency and environmental pollution. Many countries have developed regulations to minimize C&D waste. Implementation of these regulations requires an understanding of the magnitude and material composition of waste stream. Construction waste generation index is a useful tool for estimating the amount of construction waste and can be used as a benchmark to enhance the sustainable performance of construction industry. This paper presents a model for quantifying waste generation per gross floor area (WGA) based on mass balance principle for building construction in China. WGAs for major types of material are estimated using purchased amount of major materials and their material waste rate (MWR). The WGA for minor quantities of materials is estimated together as a percentage of total construction waste. The model is applied to a newly constructed residential building in Shenzhen city of South China. The WGA of this project is 40.7 kg/m², and concrete waste is the largest contributor to the index. Comparisons with transportation records in site, empirical index in China and data in other economies reveal that the proposed model is valid and practical. The proposed model can be used to setup a benchmark WGA for Chinese construction industry by carrying out large-scale investigations in the future.     

Mechanical recycling of EOL concrete into high-grade aggregates

Recycling End of Life (EOL) concrete into high-grade aggregate for new concrete is a challenging prospect for the building sector because of the competing constraints of low recycling process cost and high aggregate product quality. A further complicating factor is that, from the perspective of the environment, there is a strong societal drive to reduce bulk transport of building materials in urban environments, and to apply more in situ recycling technologies for Construction & Demolition Waste. The European C2CA project investigates a combination of smart demolition, grinding of the crushed concrete in an autogenous mill to increase the liberation of cement mortar from the surface of aggregates and a novel dry classification technology called ADR to remove the fines. The feasibility of this recycling process was examined in a demonstration project involving 20,000 tons of EOL concrete from two office towers in Groningen, the Netherlands. Results show that the +4 mm recycled aggregate compares favorably with natural aggregate in terms of workability and the compressive strength of the new concrete, showing 30% higher strength after 7 days.     

An energetic life cycle assessment of C&D waste and container glass recycling in Cape Town,South Africa

This study presents the results of a comparative life cycle assessment (LCA) on the energy requirements and greenhouse gas (GHG) emission implications of recycling construction and demolition (C&D) rubble and container glass in Cape Town, South Africa. Cape Town is a medium sized city in a developing country with a growing population and a rising middle class, two factors that are resulting in increased generation of solid waste. The City is constrained in terms of landfill space and competing demands for municipal resources.The LCA assessment was based on locally gathered data, supplemented with ecoinvent life cycle inventory data modified to the local context. The results indicated that recycling container glass instead of landfilling can achieve an energy savings of 27% and a GHG emissions savings of 37%, with a net savings still being achieved even if collection practices are varied. The C&D waste results, however, showed net savings only for certain recycling strategies. Recycling C&D waste can avoid up to 90% of the energy and GHG emissions of landfilling when processed and reused onsite but, due to great dependence on haulage distances, a net reduction of energy use and GHG emissions could not be confidently discerned for offsite recycling. It was also found that recycling glass achieves significantly greater savings of energy and emissions than recycling an equivalent mass of C&D waste.The study demonstrated that LCA provides an important tool to inform decisions on supporting recycling activities where resources are limited. It also confirmed other researchers’ observations that strict adherence to the waste management hierarchy will not always result in the best environmental outcome, and that more nuanced analysis is required. The study found that the desirability of recycling from an energy and climate perspective cannot be predicted on the basis of whether such recycling conserves a non-renewable material. However, recycling that replaces a virgin product from an energy-intensive production process appears to be more robustly beneficial than recycling that replaces a product with little embodied energy. Particular caution is needed when applying the waste management hierarchy to the latter situations.     

Reverse logistics in the Brazilian construction industry

In Brazil most Construction and Demolition Waste (C&D waste) is not recycled. This situation is expected to change significantly, since new federal regulations oblige municipalities to create and implement sustainable C&D waste management plans which assign an important role to recycling activities. The recycling organizational network and its flows and components are fundamental to C&D waste recycling feasibility. Organizational networks, flows and components involve reverse logistics. The aim of this work is to introduce the concepts of reverse logistics and reverse distribution channel networks and to study the Brazilian C&D waste case.     

Best practice measures assessment for construction and demolition waste management in building constructions

Currently the construction and demolition (C&D) waste collection system in Spain is managed in a decentralized manner by each sub-contracted company. This lack of comprehensive strategy for C&D waste management causes a confusing and sometimes individual attitude regarding the different measures for C&D waste. Therefore effective waste management should be enforced. Construction stakeholders have wide range of best practices in C&D waste management that can be implemented, so they need to be assessed for their effectiveness.The aim of this research study is to assist construction stakeholders in making a decision on C&D waste management. This paper carries out a survey conducted among the construction agents in order to evaluate the effectiveness of 20 best practice measures regarding C&D waste management, identifying the most suitable types of building constructions to implement these practices and also the advantages and drawbacks of their performance in a building construction project.Results of this study show that among the highly effective best practices are: the use of industrialized systems and the contract of suppliers managing the waste. In addition, distributing small containers in the work areas is also another high valued practice, although only 36% of respondents usually implement this measure in their works.     

Management and recycling of waste glass in concrete products: Current situations in Hong Kong

Disposal of more than 300 tonnes waste glass daily derived from post-consumer beverage bottles is one of the major environmental challenges for Hong Kong, and this challenge continues to escalate as limited recycling channels can be identified and the capacity of valuable landfill space is going to be saturated at an alarming rate. For this reason, in the past ten years, a major research effort has been carried out at The Hong Kong Polytechnic University to find practical ways to recycle waste glass for the production of different concrete products such as concrete blocks, self-compacting concrete and architectural mortar. Some of these specialty glass-concrete products have been successfully commercialized and are gaining wider acceptance. This paper gives an overview of the current management and recycling situation of waste glass and the experience of using recycled waste glass in concrete products in Hong Kong.     

A model for cost-benefit analysis of construction and demolition waste management throughout the waste chain

Economic instrument is indubitably perceived as effective for encouraging or forcing contractors to conduct environmentally friendly construction practices. Previous studies in relation to this topic mainly put emphasis on economic analysis of construction and demolition (C&D) waste management from a static point of view, which failed to consider its dynamics nature by integrating all essential activities throughout the waste chain. This paper is thus intended to highlight the dynamics and interrelationships of C&D waste management practices and analyze the cost-benefit of this process using a system dynamics approach. Data related to concrete and aggregate of a construction project in Shenzhen was collected for the application of the proposed model. The findings reveal that net benefits from conducting C&D waste management will occur, but a higher landfill charge will lead to a higher net benefit, as well as an earlier realization of the net benefit. In addition, the general public under a higher landfill charge will suffer from a higher environmental cost caused by illegal dumping. The simulation results also suggest that current regulation in Shenzhen should be promoted to facilitate a dramatic increase in net benefit from the implementation of C&D waste management. This research is of value in facilitating better understanding on the dynamics of C&D waste management activities throughout the waste chain, as well as providing a tool for simulating the cost-benefit of C&D waste management practices over the project duration.     

A system dynamics model for evaluating the alternative of type in construction and demolition waste recycling center - The case of Chongqing, China

This paper presents a system dynamics computer model to evaluate alternative type of recycling center under different policy and economy environments through comparison on the economic feasibility of recycling centers and ratio of savings to costs in C&D waste management. A case study for the City of Chongqing, China is selected. Simulated results show three key factors can contribute to the economic feasibility of recycling and the ratio of savings to costs in C&D waste management: (a) profit; (b) unit recycling cost; (c) extra revenue from location advantage (It was assumed that the mobile centers can attain extra revenue from the location advantage compared with fixed recycling centers). The sensitive analysis and comparison on ratios between public and private sector indicate that to achieve the optimum ratio of savings to costs, design of recycling centers and selection of governmental instruments are determined by the priority list: (1) low extra revenue from location advantage; (2) low profit; (3) low unit recycling cost. Meanwhile, the fluctuation of the three factors must be prior to achieve economic feasibility of corresponding recycling centers.     

Evaluation of alternative landfill cover soils for attenuating hydrogen sulfide from construction and demolition (C&D) debris landfills

Hydrogen sulfide (H(2)S) generated from C&D debris landfills has emerged as a major environmental concern due to odor problems and possible health impacts to landfill employees and surrounding residents. Research was performed to evaluate the performance of various cover materials as control measures for H(2)S emissions from C&D debris landfills. Twelve laboratory-scale simulated landfill columns containing gypsum drywall were operated under anaerobic conditions to promote H(2)S production. Five different cover materials were placed on top of the waste inside duplicate columns: (1) sandy soil, (2) sandy soil amended with lime, (3) clayey soil, (4) fine concrete (particle size less than 2.5 cm), and (5) coarse concrete (particle size greater than 2.5 cm). No cover was placed on two of the columns, which were used as controls. H(2)S concentrations measured from the middle of the waste layer ranged from 50,000 to 150,000 ppm. The different cover materials demonstrated varying H(2)S removal efficiencies. The sandy soil amended with lime and the fine concrete were the most effective for the control of H(2)S emissions. Both materials exhibited reduction efficiencies greater than 99%. The clayey and sandy soils exhibited lower reduction efficiencies, with average removal efficiencies of 65% and 30%, respectively. The coarse concrete was found to be the least efficient material as a result of its large particle size.     

Evaluation of life cycle inventory data for recycling systems

This paper reviews databases on material recycling (primary as well as secondary production) used in life cycle assessments (LCA) of waste management systems. A total of 366 datasets, from 1980 to 2010 and covering 14 materials, were collected from databases and reports. Totals for CO₂-equivalent emissions were compared to illustrate variations in the data. It was hypothesised that emissions from material production and the recycling industry had decreased over time due to increasing regulation, energy costs and process optimisation, but the reported datasets did not reveal such a general trend. Data representing the same processes varied considerably between databases, and proper background information was hard to obtain, which in turn made it difficult to explain the large differences observed. Those differences between the highest and lowest estimated CO₂ emissions (equivalents) from the primary production of newsprint, HDPE and glass were 238%, 443% and 452%, respectively. For steel and aluminium the differences were 1761% and 235%, respectively. There is a severe lack of data for some recycled materials; for example, only one dataset existed for secondary cardboard. The study shows that the choice of dataset used to represent the environmental load of a material recycling process and credited emissions from the avoided production of virgin materials is crucial for the outcome of an LCA on waste management. Great care and a high degree of transparency are mandatory, but advice on which datasets to use could not be determined from the study. However, from the gathered data, recycling in general showed lower emission of CO₂ per kg material than primary production, so the recycling of materials (considered in this study) is thus beneficial in most cases.     

Recycling inorganic domestic solid wastes: results from a pilot study in Dar es Salaam City, Tanzania

Solid waste recycling and recovery approach can be a sustainable and effective waste management system in many growing cities of the least developed countries. In the course of achieving proper solid waste management, a lot of efforts in these countries have, however, been focused more on collection and disposal and ignored waste recycling which can result into income generation, employment creation and reduction of the waste quantities that will finally require disposal in the existing municipal landfills or disposal sites. This paper reports the findings of a study on solid waste recycling in a selected semi-planned settlement in Dar es Salaam City, Tanzania. The objective of the study was to describe the existing solid waste management in the study area with a view to identifying the waste generation rates, types of the wastes and determine the amount of waste from the settlement that can be recycled for the purpose of income generation and reduction of the total amount of waste to be disposed of. Findings from this study revealed that waste generation rate in the study area was 0.36 kg per person per day, and that out of the 14 600 kg of recyclable waste generated per year, 8030 kg or 55% can be recycled and generate a per capita income of Tsh 834 000 for waste recyclists which is more than twice the official minimum annual wage (Tsh 360 000) in Tanzania at the time of the study. The study also revealed that effective waste recycling in the study area would result in the reduction of the total waste that need to be transported for final disposal by 11%.     

Balancing durability and environmental impact in concrete combining low-grade recycled aggregates and mineral admixtures

This paper investigated the effect of various amounts of low-grade recycled aggregates in concrete containing mineral admixtures at three different water-binder ratios on mechanical and environmental performance. The balance between durability and environmental impact for a given strength level similar to normal-use concrete was also examined using analytic hierarchy process. Results showed that increasing the water-binder ratio and volume of recycled aggregates reduced compressive strength and increased air permeability and drying shrinkage relative to normal aggregates. However, compared to normal-use concrete similar or better performance could be achieved, which was attributed to improvement of low-grade recycled aggregate performance when combined with fly ash. Similarly, CO₂ emissions and volume of raw materials were lower than the normal-use concrete for all mixes. Concrete mixes with low air permeability and low CO₂ footprint had the best balance of durability and environmental impact, as decreasing raw material volume tended to more greatly reduce durability.     

Evaluation of recycling efforts of aircraft companies in Wichita

The number of manufactured aircraft has been continuously increasing worldwide because of the high demand for airline transportation. During manufacturing, many advanced materials and devices are used to build various sizes and shapes of aircraft. However, most of these materials and devices require considerable energy and labor to produce, so reusing these at any life stage of the aircraft offers many economic and environmental benefits, and is considered lucrative and environmentally responsible. Several recyclable materials—composites, metals and alloys, wires, wood, paper, plastics, electronics, and avionics—emerge as waste streams during the manufacturing of aircraft. Many aircraft companies have been recycling these materials to remanufacture aircraft parts or other products for more sustainable production. In the present study, we evaluated the recycling efforts of local aircraft companies in Wichita, KS. These efforts were considered in terms of recycling efficiency/rate and environmental benefits. These included cradle-to-gate (CTG) life-cycle inventory analysis of the materials, carbon dioxide emissions, virgin material replacement with recycled materials, and natural resources usage. Our findings show that there exists a significant potential for contributions to sustainability as well as environmental and health benefits in the region from recycling by aircraft manufacturing plants.     

Energy and CO2 from high performance recycled aggregate production

The use of recycled concrete aggregates (RCA) in applications other than road sub-layers is limited by two factors: the high porosity of RCA in comparison with natural aggregates, and the restrictions set forth in standards and building codes. Research efforts aimed at alleviating these restrictions are focused on improving the quality of coarse RCAs by reducing the amount of adhered cement pastes, which is the weakest element in this system and influences the rheological behaviour.This paper presents an analysis of the environmental impacts of the recent mechanical and thermo-mechanical processing techniques which produce high performance RCA by reducing the volume of adhered cement paste. Based on published data, processing scenarios were established. These scenarios permit making rough estimates of energy consumption, CO₂ emissions, fines generation and product quality. Using these data and the available emission factors from several countries, an objective comparison was made between these innovating processes and conventional recycling.The production of fines increases from 40% up to as much as 70% as the volume of adhered cement paste on the RCA is reduced. Fuel fed thermo-mechanical process energy consumption, per tonne of recycled aggregate, varies between 36 and 62 times higher than conventional recycling processes. Mechanical processing, combined with microwave heating, increases energy consumption from 3 to a little more than 4 times conventional recycling. Consequently, CO₂ emissions released by conventional coarse aggregate production go from 1.5 to 4.5 kgCO₂/t, to around 200 kgCO₂/t, for that of fossil fuel fed thermo-mechanical treatments.Mechanical and mechanical/microwave treatments appear to have the greatest environmental potential. Notwithstanding, the further development of markets for fines is crucial for reducing environmental loads.     

Sustainable recycling model: A comparative analysis between India and Tanzania

Higher economic growth in developing countries has caused higher amounts of wastes. Local government authorities in these countries usually fail to provide adequate services to dispose the increasing amounts of waste, resulting in threats for both the population and environment health. There is therefore an urgent need for recycling as a form of waste management in order to stop the devastating effects of solid waste in developing countries. Using a qualitative method of analysis, this study presents a model to measure and rank the sustainability of recycling programs in India and Tanzania. The model consists of six main constructs including “production, economic, governmental, social, technological, and international factors”. The results showed that India outperforms Tanzania in sustainable recycling programs: per capita waste generated per day in Delhi is higher than in Dar es Salaam; the government of India focuses more on developing recycling plans and techniques as compared to the government of Tanzania where the country is not actively involved in the recycling process; and the solid waste management planning in India is being performed better than Tanzania.     

Determining the socially optimal recycling rate

What municipal recycling rate is socially optimal? One credible answer would consider the recycling rate that minimizes the overall social costs of managing municipal waste. Such social costs are comprised of all budgetary costs and revenues associated with operating municipal waste and recycling programs, all costs to recycling households associated with preparing and storing recyclable materials for collection, all external disposal costs associated with waste disposed at landfills or incinerators, and all external benefits associated with the provision of recycled materials that foster environmentally efficient production processes. This paper discusses how to estimate these four components of social cost to then estimate the optimal recycling rate.     

Ramifications of solid waste disposal site relocation in urban areas of developing countries: a case study in Tanzania

Sanitary landfilling is considered to be the most appropriate means of final disposal of solid wastes. Currently in Tanzania, the cheapest method of developing a landfill is by making use of natural depressions or former borrow pits and mine pits. This paper examines the impacts associated with the relocation of a waste disposal site from a crude disposal site at Vingunguti to a new landfill site at New MECCO quarry in Kunduchi area, both in Dar es Salaam, Tanzania. The paper focuses on the fate of scavenging and solid waste recycling which are currently taking place at Vingunguti site and mining as well as food vending activities at the proposed new landfill site. Scavenging and waste recycling were found to be important sources of income for some individuals in the city. Various items collected for recycling were found to be an important source of raw materials for some industries in Dar es Salaam. A total of 94% of all the miners were entirely dependent on stone mining and crushing as a sole means of income generation, and 68% of the miners had practised this activity for between 1 and 9 years. Finally the paper recommends that, selection of a waste disposal site should favour abandoned mines or borrow pits rather than operational ones. It also recommends that, waste recycling and scavenging be accommodated in other stages of the waste stream since they can not be practised at a sanitary landfill.     

建筑废弃物再生利用的可行性技术研究综述

建材行业的发展为城市化建设提供了重要保障,在我国城市化快速发展、建筑材料需求旺盛的带动下,建材行业发展强劲,但大多属于高能耗高污染行业,加之城市拆迁改造产生大量建筑废弃物,环境压力十分巨大,必须加强建筑废弃物的环境管理。对建筑废弃物再利用、再循环以及减少建筑废弃物是解决建筑行业环境问题的重要方式,实施这些仍有很大的提升空间。本文回顾了近年来建筑废弃物再生利用方面的各种可行性技术。主要是针对沥青、砖、混凝土、金属、玻璃等几种物质再生利用的可行性技术进行综述,为未来建筑废弃物再生利用领域提供参考。