Resource Metabolism of the Construction Sector: an Application of Material and Exergy Flow Analysis

    Student thesis: Doctoral thesis

    Abstract

    This thesis aims to assess the resource consumption of the construction sector, and the wastes and emissions generated by the sector. This is motivated by the fact that the construction sector is responsible for large amounts of resource consumption and represents nearly 9% gross value added to the world’s gross domestic product. The assessment considers the life cycle perspective from raw material extraction, through construction product manufacturing, material transport, construction and demolition waste generation, to waste transport, treatment, and final disposal. The aim is to pinpoint the opportunities for improved material selection criteria, processing, reuse, and recycling for sustainable resource use. Due to the system complexity of buildings and infrastructure, composed of many interacting components, it is always challenging to undertake an accurate resource accounting within this sector. In this perspective, the concepts of material flow analysis (MFA), life cycle assessment (LCA), and exergy analysis (ExA) are discussed as resource accounting tools focusing on their applications in the construction sector. Apart from sectoral analysis, this thesis also analyzes the efficiency of manufacturing processes and products’ complete life cycle based on exergy. All the processes and products selected are relevant for the construction sector, and this analysis aims to provide deper insights into sectoral material use. Chapter 1 details the theoretical framework under which exergy and material flow analyses are used in assessing the resource metabolism of the construction sector highlighting the importance of this sector in terms of resource flows, and generation of waste and emissions. This chapter also introduces the exergy efficiency and exergetic life cycle assessment (ELCA) tools, explaining the limitations of energy analysis and LCA, and how the application of these exergy-based methods can provide better insights into resource use efficiency in manufacturing processes and throughout the products’ life, respectively. Industrial ecology (IE) is presented to introduce the systems-based approach and thermodynamic framework on which of the construction sector is analyzed in this study. Chapter 2 presents the results of material and exergy flow analyses of the Catalan construction sector for the year 2001. In 2001, Catalonia had an additional 52 million tonnes of material stock to the sector and generated 7 million tonnes of construction and demolition waste (CDW) of which only 6.5% were recycled or reclaimed. The study shows that manufacturing stage consumes the largest fraction of energy resources during the products’ whole lifecycle followed by material transport, accounting for 57% and 4% of exergy use, respectively. It is pointed out that improvement in material selection, manufacturing technologies, and design for disassembly lead to sustainability of the sector delivering improved resource use efficiency. In chapter 3, the exergetic efficiency of the production processes, both primary and secondary (recycling) production process, of construction materials is calculated in order to assess material quality, exergy losses, and process improvement potentials. This serves to quantify the improvement potentials for present manufacturing processes addressing the manufacturing inefficiencies of nine major non-renewable construction materials: aluminum, steel, copper, cement, concrete, ceramic, glass, polypropylene (PP), and polyvinyl chloride (PVC). Exergy efficiency based on the second law of thermodynamics is determined in order to compare the theoretical exergy efficiency and the real-process exergy efficiency. The large difference between theoretical and empirical exergy requirements in manufacturing processes suggests that opportunities for better industrial exergy utilization still exist but require design and/or technology improvements. The results demonstrate that resources are utilized more efficiently in recycling processes compared to primary manufacturing processes. This thesis has presented an effort (chapter 4) to pinpoint how efficiently resources are used in the construction applications, using exergetic life cycle assessment methodology in a cradle-to-grave life cycle approach. This included raw material extraction, resin manufacturing, and end-of-life waste management life-cycle stages. The irreversibility during the complete life cycle allows to evaluate the degree of thermodynamic perfection of the production processes and to conduct the assessment of the whole process chain. Overall life cycle exergy efficiency of PP and PVC is quantified 27.1% and 9.3%, respectively, characterized by a low efficiency of manufacturing and recycling processes for both materials. From resource conservation point of view, mechanical recycling has been suggested as the viable option for end-of-life plastic waste management, since it loops materials back directly into new life cycle and reduces primary resource inputs in the production.
    Date of Award24 Jul 2013
    Original languageEnglish
    SupervisorXavier Gabarrell Durany (Director), Gara Villalba Mendez (Director) & Cristina Sendra i Sala (Director)

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