Resource metabolism of the construction sector: an application of exergy and material flow analysis
- Autores: Mohammad Rashedul Hoque
- Directores de la Tesis: Xavier Gabarrell Durany (dir. tes.), Gara Villalba Méndez (dir. tes.), Cristina Sendra Sala (dir. tes.)
- Lectura: En la Universitat Autònoma de Barcelona ( España ) en 2013
- Idioma: inglés
- Tribunal Calificador de la Tesis: Lidia Lombardi (presid.), Alejandro Josa García-Tornel (secret.), Julia Martínez-Blanco (voc.)
- Materias:
- Enlaces
- Tesis en acceso abierto en: TESEO
- Resumen
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 deeper 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. This study demonstrates that 75% of the extracted minerals were used in construction applications either as direct consumption or as raw material to produce cement, concrete, mortar, ceramic, glass, and other mineral processed materials. In 2001, Catalonia had an additional 52 million tonnes of material stock to the sector and generated 6.8 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 life cycle followed by material transport, accounting for 57% and 4% of exergy use, respectively. The total exergy input in the sector was estimated to be 113.1 PJ, with chemical exergy of materials representing 48.5 PJ and the remaining 64.6 PJ from exergy of utilities. Net addition to stock accounted for 40.3 PJ of exergy, which is nearly 36% of the total exergy input in the sector. It was estimated that a total 72.1 PJ of input exergy was lost from the system. The results show that energy intensive materials such as bituminous mix products, ceramics, glass, metals, plastics, and wood products account for 69% of the total exergy input in the sector, while these materials represents only 15% by mass. 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 both primary and secondary (recycling) production processes 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 study shows that exergy resources are utilized very inefficiently in present industrial practices since energy intensity of most of the case study processes is significantly higher than the theoretical minimum determined by the second law analysis. Some of the present industrial processes, such as aluminum, copper, and ceramic tile are highly inefficient and theoretical exergy efficiency results suggests that a wide margin of process improvement potentials exist for both primary and secondary production processes but require design and/or technology improvements. The exergy efficiency results of primary production processes show that PP production is the most efficient (53.4%) among others followed by PVC (23.7%) and steel (16.3%) production processes. Even though plastic production shows relatively higher exergetic efficiency in their primary manufacturing processes, recycling benefits of plastics may not be the same compared to that of metals or glass. This is due to the fact that a number of additives are added with the plastic resins to obtain the desired mechanical and chemical characteristics of these materials, which are difficult to remove while recycling process. Metals or glass on the other hand are used in more pure forms in construction applications, making them easily recyclable after the end of the life span of buildings and infrastructure. 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 chain.
