Reuse of construction materials : Environmental performance and assessment methodology
Abstract: Reuse is a measure for resource-saving materials and energy use, which is stressed in the concept of kretsloppsanpassning, or societal industrial ecology (SIE), as it will be termed in this thesis. Reuse is here used as a general term for any kind of reuse and divided into recirculation, upgrading and cascading, according to the degradation of the inner material structure. Reuse of construction materials in society is mainly done with the belief that any kind of reuse is environmentally beneficial. However, this assumption is seldom critically assessed.The aim of this thesis was to examine under which conditions reuse of construction materials in the Swedish building and transportation sectors is beneficial to the environment. In order to identify critical conditions, the environmental performance of actual building projects that to a large extent utilised reused building materials was assessed (Papers V-VI). To better understand the practice of SIE and how it was implemented, the transportation sector was studied (Paper I). In order to address the issue of assessing the environmental performance of construction material reuse, method development became an important part of this thesis. Methods and tools employed in this thesis were required to be able to simultaneously address different system boundaries and also involve simplification.Studying the implementation of SIE revealed the lack of a holistic approach in environmental management, though it is present in the overall objectives of the SIE concept (Paper I). This was concluded by studying the energy and material stocks and flows in a life-cycle perspective in the environmental management of the Swedish National Rail and Road administrations. The study showed that the SIE-related measures implemented were outflow oriented, while the material inflows were generally quantified. Overall, the management and use phases were addressed, while the construction and deconstruction phases were poorly considered.Studying environmental assessment methods showed that an important characteristic is the system boundaries, which to a large extent decide which issues could be addressed and what actually could be studied (Paper II). Environmental assessment methods applied to reuse of construction materials were organised in an assessment framework of four system levels: the material level, the local environment level, the narrow life-cycle level and the industrial system level. It was concluded that mainstream environmental assessment of construction material reuse that is performed in the process of development consent and also in research, mainly addresses the narrow scope of the material level. In order to apply a holistic approach to environmental assessments of reuse of construction materials, the system boundaries needed to be widened.When selecting system boundaries, methods and indicators, researchers indirectly decide on which environmental pressures we consider the most important (cf. Papers II - III). There are trade-offs between making broad or deep environmental assessments. To accomplish an environmental assessment wide in its scope requires abundant resources and is complicated to carry through. Simplifications of the complex reality are always needed. However, to counteract the risk of problem shifting, the simplified methods and indicators need to be balanced for environmental relevance and used with knowledge of what they reflect and what is left out (Paper III). One example of such method simultaneously environmentally relevant and capable to cope with wide system boundaries is the study of primary energy use in a life cycle perspective, applied to a material an energy use context (see Papers IV-VI).In searching for a tool to prioritise building materials in building research and environmental management of the building sector, the total amount of building materials present in the Swedish building material stock was multiplied by their embodied energy coefficients (Paper IV). This product was normalized for the building materials’ service life. The accounting resulted in an ordering of building material categories according to their energy intensity. These are, in decreasing order: wood materials, bricks and other ceramics, concrete and steel.After calculating energy use in a life-cycle perspective for the recirculation, upgrading and cascading of larger building reuse projects of concrete and clay bricks, it is not self-evident that reuse is beneficial for the environment (Paper V, VI). It mainly depends on the use of auxiliary materials and their embodied energy, but also the primary energy use for the reuse processes, such as transportation distance and mode between the deconstruction and construction sites. In order to improve the environmental benefits of reuse, primarily the auxiliary materials used in current reuse projects should be minimised. Otherwise, there is a risk that the energy use for these materials turns reuse into an unfavourable process for the environment. Furthermore, reuse should preferably be environmentally assessed with a wide scope before implementation. What is included in such environmental assessment is significant for the outcome and the pictured environmental performance.
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