Mixed-unit hybrid life cycle assessment applied to the recycling of construction materials

Abstract

The construction industry contributes around 18% of greenhouse gas emissions, 40% of depletion of natural resources, and 25% of wastes globally. To reduce these impacts, construction industries can adopt low-carbon alternatives for construction materials and waste minimisation strategies, including the recycling of construction and demolition waste. However, a comprehensive understanding of the full life cycle carbon profile of low-carbon and recyclable construction materials is required to accurately assess the efficacy of decarbonisation strategies in the built environment. Despite recent progress in hybrid life cycle assessment (hybrid LCA) methods, some weaknesses remain with respect to the inherent uncertainty relating to price variations and aggregated sectors that are unable to provide detailed waste-specific information in hybrid LCA. Furthermore, attributional, hybrid LCA for a functional unit does not reflect the actual, economy-wide physical flows of materials in a real economy. In this study, a mixed-unit hybrid LCA approach based on a combination of process life cycle inventory, input-output, and material flow data is used to model the economy-wide potential use of recycled construction materials in Australia. A comparison between methods of life cycle emissions of geopolymer concrete revealed that the mixed-unit hybrid LCA approach produced a more accurate and Australian-specific result. The usefulness of the proposed mixed-unit IO model is demonstrated through quantifying the cradle-togate embodied emissions of recycled construction materials and by-products utilised in concrete and steel sectors in Australia. The results yield a 1% reduction when recycled concrete aggregate completely replaces natural aggregate in both ordinary Portland cement and geopolymer concrete. Greenhouse gas emissions reduction of 30% is quantified for geopolymer concrete using recycled concrete aggregate compared with ordinary Portland cement concrete utilising natural aggregate and 43% is estimated for electric arc furnace route using iron and steel scrap compared with basic oxygen furnace route. The method merges physical and monetary units of industrial systems related to low-carbon alternatives and recycled construction materials to enable the calculations of embodied carbon with improved accuracy. The results of this study can help inform decarbonisation strategies in the built environment sector.

Implementing hybrid LCA routines in an input–output virtual laboratory

“…This effort is beyond the scope of this paper and only pays off if the intention is to make the background IO system more product-specific (Suh 2006;Peters and Hertwich 2006;Acquaye et al 2011a). The present system therefore represents a tiered hybrid system, which, however, can be extended to a truly integrated system once the downstream cut-off matrix is populated with scaled process data, subtracted from the IO background system (see, e.g., Teh et al 2018).…”

The State of the Art of Material Flow Analysis Research Based on Construction and Demolition Waste Recycling and Disposal

“…Therefore, many scholars combine MFA and other methods to achieve an accurate economic and environmental assessment, which further extends the MFA applications. One of typical combination applications is the integration of MFA and LCA methods [2,11,18,53]. Zhang et al illustrated through the integration between MFA and LCA that the recycling of C&D waste can generate the co-benefits of land use reduction and greenhouse gases mitigation [18].…”

“…The construction and operation of buildings occupy almost 40% of the depletion of natural resources and 25% of global waste [1,2]. Construction and demolition waste has become a major source of urban waste and usually accounts for 10-30% of the total waste landfilled [3].…”

“…For a multifaceted assessment, MFA is combined with other analytical tools and optimal methods. The combination of MFA and Life Cycle Assessment (LCA) can accurately calculate embodied carbon or carbon emissions, and track material flows, which is helpful for estimating the potential impacts of the changes of urban metabolism [2,18,32,33]. An integration framework of MFA and LCA is presented to assess the potential impacts of concrete recycling and metabolism [18].…”

“…Dahlbo et al combined MFA, LCA, environmental life cycle costing (ELCC), and best available technology (BAT) approaches to assess the performance of the C&D waste management system [11]. Beyond all that, there are some other combinations for C&D waste processing, such as MFA combined with statistical analysis [35], MFA combined with eco-balancing methods [36], MFA combined with input-output analysis (IOA) [2,37], and so on. Although some C&D-waste-related review articles can be found, such as quantifying C&D waste [38,39], C&D waste management [40][41][42][43], and sustainable assessment of construction materials [44], a comprehensive analysis and summary about the state of the art of MFA based on C&D waste is required.…”