Life-Cycle Sustainability Analysis of Construction and Demolition Wood Waste to Achieve Circular Economy

A substantial amount of construction and demolition wood waste (CDWW) is generated during construction, renovation, and demolition. This wood waste contains untreated, treated, or engineered wood products and other contaminants from the construction and demolition waste stream, which is exceedingly difficult to repurpose. Around 20-30% of wood waste is generated during residential construction, and this amount of wood waste is mainly landfilled, contributing to severe environmental effects. In Australia, around 2.3 million tons of wood waste is generated annually, and the construction and demolition sector are the second largest contributor. This wastage can be utilised to produce value-added products, which will help reduce the pressure on virgin material and divert the waste from landfill disposal. Therefore, the reduction, reuse, and recycling of CDWW and promoting of a circular economy (CE) are urgent needs as they comprise waste minimisation and efficient recovery of resources for sustainable development. Although much research is found in the literature on CDWW end-of-life (EOL) management, most studies focus on an environmental viewpoint that ignores the social and economic aspects of the CDWW recycling processes, and research on CE implementation considering each life-cycle stage of CDWW is still scarce. Thus, this study aims to identify the best EOL for CDWW to implement CE and how to improve the recovery rate and waste management performance for CDWW in the Australian context. This research also explored the life-cycle stages of CDWW to achieve sustainable development by investigating the environmental, economic, and social impacts of the CDWW recycling process. The core contribution of this study is providing a life-cycle sustainability assessment model incorporating environmental, economic, and social assessments for CDWW end-of-life management. An extensive literature review was first conducted, where we endeavoured to integrate CE in CDWW to identify the waste management strategies involved in the life-cycle phases of CDWW. After that, a questionnaire survey was conducted to identify the waste management practices of wood waste in the Australian context and to compare the amount and sources of timber waste, current practices to minimise timber waste, and reusing or repurposing timber waste, obtained from the viewpoints of residential builders. Afterwards, a semi-structured interview was conducted with stakeholders involved in waste management to identify industry experts' perceptions of waste minimisation and collect environmental, economic, and social life-cycle assessment data. A total of 106 survey responses and 230 interviews were conducted for data collection. Again, 15 residential constructions were considered for a case study, from which waste generation data was collected. This study also developed a novel environment impact assessment model, economic assessment model, and social impact assessment model for CDWW in light of the CE value retention process model. The developed models are implemented through a case study, where five EOL scenarios were analysed, such as two engineered products (particleboard, glulam) and three non-engineered products (garden mulch, incineration, landfill disposal), considering mixed and separate bin collection methods. The multi-criteria decision-making technique is used in this study to integrate the environmental, economic, and social impacts of CDWW recycling for life-cycle sustainability assessment. The literature review revealed that CE for CDWW is essential and has more significant growth potential. The questionnaire survey results highlighted that the volume builders' (builds 51-100 or more houses/annum) timber waste management practices are more environment-friendly than medium (builds11-50 houses/annum) and small builders (1-10 houses/annum), and that small builders generate at least three times more waste than volume and medium builders. It has also been revealed that timber flooring construction is responsible for significant timber waste (18% of total timber flooring). In contrast, timber roof produces 2-3 % wastage (if prefabricated) and 10% wastage for wall framing. The interview results disclosed that the designers are the first contributors to waste minimisation if they use building information modelling in the pre-construction stage. It has also been revealed that subjective attitudes and personal reluctance to exercise waste mitigation strategies are key barriers to industry practices. The developed environmental, economic, and social impact assessment models can identify the environmental, economic, and social hotspots for CDWW EOL scenarios. The environmental impact assessment results revealed that material recovery is preferred over energy recovery for wood waste to promote CE. Suppose timber is collected in a separate bin during construction. In that case, the wood recovery rate is almost thrice that of a mixed bin collection, and it will significantly reduce landfill disposal by 72%. A separate bin collection method can reduce global warming potential by 169.4 kg CO2 eq (28% reduction/ ton) and 157.9 kg CO2 eq (25% reduction/ton) per ton of particleboard and glulam production compared to the mixed bin method. An 8626 kg of particleboard was produced using the separate bin collection method. In contrast, only 3834 kg of particleboard was obtained from the mixed bin method from 15 residential building constructions' wood waste. The life-cycle cost analysis revealed that the net profit margin for per ton particleboard production was 46.3%, utilising the separate bin method, which had the highest profit margin compared to other recycling scenarios. The social impact assessment result revealed that the separate bin collection and sorting method improves the social impacts, especially in health safety and security and labour rights sub-categories, by up to 50% compared to the traditional mixed bin collection method. For the integrated assessment, the life-cycle sustainability assessment model is capable of efficient decision-making considering the three pillars of sustainability. The study's outcome provides a scientific background for wood waste EOL management to implement a CE. The developed model in this study contributes to boosting the CE and sustainability for utilising wood waste generated from residential construction. The study demonstrates enhanced knowledge and understanding of timber waste management practices, strategies, solutions, and life-cycle sustainability assessment for residential construction. Developing a framework based on life-cycle sustainability assessment incorporating environmental, economic, and social studies will help improve the recycling process's material recovery and energy consumption rates. The developed models in this study can be utilised in other waste management scenarios in further research.<p></p>