•A closed-loop LCA on RAC utilization in China with entire local LCI is performed.•Comparative results on environmental impact between NAC and RAC is achieved.•Possible opportunity for lowering ...environmental impact of RAC is proposed.
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.
As more than 50% construction and demolition (C&D) wastes are composed of concrete debris in Hong Kong, recycling this debris into Recycled Aggregate (RA) for production of Recycled Aggregate ...Concrete (RAC) is an efficient way to alleviate the burden on landfill areas. Since RA is generated from concrete debris which has undergone years of services, the resulting RAC bears the weaknesses of lower density, higher water absorption, and higher porosity that limit them to lower-grade applications. Pinpointing to these weaknesses, Tam et al. 2005, Cement Concrete Res 35(6):1195-1203 developed the Two-Stage Mixing Approach (TSMA) for improving the strength of RAC, leading to the possibility in applying RAC for higher-grade applications. While the improvement in strength by TSMA has been proven in Tam et al.'s work 2005, Cement Concrete Res 35(6):1195-1203, the durability, in terms of deformation (shrinkage and creep) and permeability (water, air and chloride permeability), remains to be verified. In this paper, 0%, 20% and 100% of RA substitutions have been experimented to compare the durability performance of the Normal Mixing Approach (NMA) and the TSMA. Experiment results highlight that: (i) the higher the substitutions of RA, the weaker the performance of RAC; and (ii) the deformation and permeability of RAC can be enhanced when adopting TSMA. Therefore, it demonstrates that TSMA can help to improve the durability of RAC, on top of the previously verified strength improvement, and thus opening up wider applications of RAC.
•This paper develops a system dynamics model of construction waste reduction management at the construction phase.•Source reduction is an effective management measure in reducing 27.05% of total ...waste generation.•Construction waste reduction implementation can reduce 53.77% of landfill.•Illegal dumping problem is serious and it is necessary to strengthen government legislations.
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.
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.
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•Decoupling degree of three carbon indexes in 30 Chinese provinces is analyzed.•China has made great strides in decoupling economic growth from carbon emissions.•Improving energy efficiency is the most effective way to control carbon emission.•The understanding of impact factors offers references for emission mitigation.
•Growing cities are facing environmental and safety risks of construction debris.•Mismanagement has led to serious impacts, such as the Shenzhen and Chennai disasters.•Dumping dominated the disposal, ...and consumed considerable scarce scare land resources.•More research on construction debris reduction is essential.•Rethinking of urban planning to avoid large scale urban renewal is urgently needed.
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.
Solid waste arisen from construction activities is grave concern in many economies. Given its negative impacts to the natural environment as a public good, construction waste is often heavily ...regulated by authorities. Hong Kong is no exception to this; over the past decades, a series of construction waste management (CWM) policies including regulations, codes, and initiatives have been introduced by the Government and her executive arms. It comes to an opportune time to retrospectively examine the effectiveness of these policies with a view to providing insights for further improvement. The aim of this paper is thus to examine CWM policies and their effectiveness in Hong Kong by conducting a longitudinal study. The evaluation of the policy effectiveness is derived by triangulating empirical data collected from various sources including Hong Kong Census and Statistics Department, Civil Engineering and Development Department, Environment Protection Department, and Hong Kong Construction Association with the qualitative data gleaned from interviews and case studies in construction sites, waste sorting facilities, and landfills. It is found that Hong Kong is actively trying new CWM policies based on latest waste management philosophies available (e.g. reduce, reuse, and recycle principle, and polluter pays principle). These policies have formed an interlocking, and relatively effective policy framework for CWM in Hong Kong. However, new initiatives are desired if aiming to change the gloomy situation since 2006 when the construction waste disposal charging scheme was effectively implemented. This research provides insightful understanding of CWM policies and their effectiveness, which is often concerned policies makers, researchers, and the like.
With a rising tide of adoption of recycled aggregate (RA) for construction, investigation on ways to improve the quality of RA has been overwhelming. The adoption of RA brings benefits including ...savings in the limited landfill spaces and the use of natural resources. However, the poorer quality of RA often limits its utilization to low grade applications such as sub-grade activities, filling materials and low grade concrete. The major reason that affects the quality of RA is the large amount of cement mortar remains on the surface of the aggregate, resulting in higher porosity, water absorption rates and thus a weaker interfacial zone between new cement mortar and aggregates, which weakens the strength and mechanical performance of concrete made from RA. This paper attempts to study three pre-soaking treatment approaches; namely ReMortar
HCl,
ReMorta
r
H
2
S
O
4
and
ReMorta
r
H
3
P
O
4
in reducing the mortar attached to RA. The results show that the behaviour of RA has improved with reduction in water absorption, without simultaneous exceeding the limits of chloride and sulphate compositions after the treatment. This work has also compared the compressive strength, flexural strength and modulus of elasticity of concrete made from the approaches, which shows marked improvements in quality when compared with those using traditional approaches.
Owing to the shortage of space for land reclamation in Hong Kong, it is difficult to dispose of tons of masonry waste generated daily from construction activities. Adoption of recycled aggregate from ...concrete waste thus becomes a burning issue. The Hong Kong SAR Government has set-up a recycling plant in Tuen Mun Area 38 aiming at turning concrete waste into recycled aggregate with a practice note and specifications issued for controlling the quality of recycled aggregate. However, the use of recycled aggregate concrete to high-grade applications is rarely reported because of its poorer compressive strength and high variability in mechanical behavior. This paper proposes a new approach in mixing concrete, namely, “two-stage mixing approach (TSMA),” intended to improve the compressive strength for recycled aggregate concrete and hence lower its strength variability. Based upon experimental works, improvements in strength to recycled aggregate concrete were achieved. The effect can be attributable to the porous nature of the recycled aggregate, and hence, the premix process can fill up some pores and cracks, resulting in a denser concrete, an improved interfacial zone around recycled aggregate and thus a higher strength when compared with the traditional mixing approach.
There is an urgent issue on huge quantities of wastage generation in construction. There should not be lack of environmental support from construction stakeholders. The current implementation of ...prefabrication seems unable to provide satisfactory results to the construction industry. This paper provides a feasibility analysis in adopting prefabrication in construction activities. Advantages, hindrances and future development on prefabrication's applications are provided based on a questionnaire survey. The suitability in adopting prefabrication of various project types is also examined. Furthermore, a financial analysis is also investigated by a local case study. It found that wastage generation can reduce up to 100% after adopting prefabrication, in which up to 84.7% can be saved on wastage reduction.
•This paper investigated 10 different Chinese cities.•It investigated current status of C&D waste management in China.•Eight major challenges limiting the promotion of waste management were ...found.•Recommendations were provided for the policy makers.
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.
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