The increasing volume of Construction and demolition waste (CDW) associated with economic growth is posing challenges to the sustainable management of the built environment. The largest fraction of... Show moreThe increasing volume of Construction and demolition waste (CDW) associated with economic growth is posing challenges to the sustainable management of the built environment. The largest fraction of all the CDW generated in the member states of the European Union (EU) is End-of-life (EOL) concrete. The most widely applied method for EOL concrete recovery in Europe is road base backfilling, which is considered low-grade recovery. The common practice for high-grade recycling is wet process that processes and washes EOL concrete into clean coarse aggregate for concrete manufacturing. It is costly. As a result, a series of EU projects have been launched to advance the technologies for high value-added concrete recycling. A critical environmental and economic evaluation of such technological innovations is important to inform decision making, while there has been a lack of studies in this field. Hence the present study aimed to assess the efficiency of the technical innovations in high-grade concrete recycling, using an improved eco-efficiency analytical approach by integrating life cycle assessment (LCA) and life cycle costing (LCC). Four systems of high-grade concrete recycling were analyzed for comparison: (i) business-as-usual (BAU) stationary wet processing; (ii) stationary advanced dry recovery (ADR); (iii) mobile ADR; (iv) mobile ADR and Heating Air Classification (A&H). An overarching framework was proposed for LCA/LCC-type eco-efficiency assessment conforming to ISO standards. The study found that technological routes that recycle on-site and produce high-value secondary products are most advantageous. Accordingly, policy recommendations are proposed to support the technological innovations of CDW management. Show less
Zhang, C.; Hu, M.; Dong, L.; Xiang, P.; Zhang, Q.; Wu, J.; ... ; Shi, S. 2018
Rapid urbanization drives massive construction, which, in return, leads to ever increasing urban metabolism challenges on the provision of raw materials, as well as the disposal of construction and... Show moreRapid urbanization drives massive construction, which, in return, leads to ever increasing urban metabolism challenges on the provision of raw materials, as well as the disposal of construction and demolition waste. Due to its large volume, the transporting and processing of these materials cause considerable greenhouse gas emissions and land use change. With this circumstance, shortening the supply chains of urban construction by efficient recycling of construction and demolition waste becomes a frontier field for the circular transition of cities. It is particularly important in current China, where the concrete recycling is still rare. This paper aims to map the opportunities and potentials of concrete recycling on the mitigation of greenhouse gas emissions and land use change, with an integrated material flow analysis and life cycle assessment for the case study city – Chongqing, China. For the baseline year 2015, four scenarios representing various recycling routes in Chongqing have been explored: (1) improving brick manufacturing; (2) recycling on-site for road base filling; (3) recycling aggregate for prefabricated concrete component and (4) recycling concrete aggregate for structure use. Results highlighted that different technological routes have different potentials to increase recycling rates but all generate co-benefits on greenhouse gases mitigation and land transformation reduction. Recycling of stony construction and demolition waste for high value concrete aggregate has the biggest potential to bring the co-benefits on greenhouse gases mitigation and land use reduction. Besides, on-site recycling for road-base aggregates also presents a high performance, especially on greenhouse gases mitigation in transport. Based on the sensitivity analysis, policy implications were discussed, highlighting the necessity of to develop the recycling routes that substitute primary gravel with aggregates recycled from the stony waste; unlocking the existing recycling capacity and restricting landfilling. Show less
Tantalum, considered one of the critical elements by many countries, is a widely used metal in industries such as electronics, aerospace and automotive. The tantalum market has experienced several... Show moreTantalum, considered one of the critical elements by many countries, is a widely used metal in industries such as electronics, aerospace and automotive. The tantalum market has experienced several disruptions and subsequent price swings in the past, implying problems with its supply chain resilience and stability. In this study, we trace the entire value chain of the tantalum industry from mining to the intermediate and the downstream industries. Our interest is to see how dependent the tantalum supply chain is on specific countries and regions, how exposed primary production is to disruptions, and what mechanism counteracts disruption. This study assesses the tantalum supply chain from a resilience perspective rather than an investigation of any specific disruption in the system. We analyze several resilience-promoting mechanisms such as: (a) diversity of supply, (b) material substitution, (c) recycling and (d) stockpiling. We evaluate each of these mechanisms, and find that even though diversity of supply and stockpiling mechanisms have been decreasing for years, the tantalum supply chain has been flexible in its response to disruption. We find a much larger supply from unaccounted artisanal and small mining sources than expected based on official statistics, and estimate the unaccounted production in Africa, which shows an almost 250 percent increase from around 600 tons in 2004 to more than 2000 tons in 2014.. Besides flexible primary production from small-scale mining, we identfy rapid material substitution and increasing availability of waste and scrap as the main reasons behind the observed supply chain resilience. Show less
