Environmental Benefits when Reusing Load-Bearing Components in Office Buildings: A Case Study.

This case study applies life-cycle assessment methods to the preliminary design of an office building in order to quantify the benefits achieved when reusing its load-bearing components. Results show that the production of the load-bearing system would account for 40% of the global warming potential indicator. The slabs are responsible for 65% of the environmental impacts among all structural elements and should be considered for reuse first. Compared to traditional constructions built from first-use material, a fictitious reuse of undamaged load-bearing components over three consecutive use cycles would reduce the global warming potential indicator by 25%. The global warming potential of reuse is eventually computed according to three repartition methods, highlighting the need to separate the life-cycle footprints related to production, use, and end-of-life more systematically.

Comparison of environmental assessment methods when reusing building components: a case study

Catherine Elvire L. De Wolf, Corentin Jean Dominique Fivet, Endrit Hoxha

The building industry is responsible for 35% of all solid waste in Europe and more than a third of greenhouse gas (GHG) emissions. To address this, applying circular economy principles to the building sector is crucial, for example by reusing building elements from demolition sites rather than extracting and producing new materials. However, most current life-cycle assessment (LCA) tools are not appropriate to evaluate the environmental impact of a building when its components originate from prior buildings and/or will be used in future unknown ones. Still, robust measurement is needed to demonstrate the benefits of reuse towards environmentally sustainable cities. This paper compares existing methodologies to quantify the global warming potential (GWP, expressed in kgCO2e/unit) of recycled/recyclable and reused/reusable products, selected within widely recognised standards, rating schemes, and academic studies, such as the cut-off method, the end-of-life method, the distributed allocation (PAS-2050) method, the Environmental Footprint method, the Degressive method and the SIA 2032 method. Based on these recognised approaches for assessing the GWP of products, new equations are written and applied to buildings with reused/reusable materials for each of the methods. The Kopfbau Halle 118 building (Winterthur, CH, 2021), which is designed with reclaimed elements from local demolition sites, is chosen as a case study. Discrepancies in LCA methods are highlighted by applying them to three different life cycles corresponding to the first, intermediate, or final use of building components. This paper shows that current quantification methods to assess reuse give wide-ranging results and do not address the full spectrum of the reuse practice, that their boundaries are too limited, and that a number of critical features are currently hardly quantifiable, such as embedded use value, versatility, storage and transformation impacts, user-owner separation, dis/re-mountability, or design complexity.

2020

Zürich Stadtspital Triemli Personalhäuser – Resource assessment of structural elements

Maléna Bastien Masse, Julie Rachel Devènes, Corentin Jean Dominique Fivet, Célia Marine Küpfer

The Triemli Personalhäuser are three equal 15-story buildings located on the Zürich Triemli Stadtspital campus and erected between 1964 and 1969. Cast-in-place reinforced concrete (RC) slabs and walls form the building cores and their surrounding corridors. The rooms are arranged around these cores. The load-bearing intermediate walls, made of prefabricated masonry, support thin precast slabs used as permanent forms. A RC layer is cast over these precast slabs and connects the room slabs with the cast-in-place slabs of the corridors and cores. The self-supporting facade consists of precast RC panels. The City of Zürich plans the deconstruction of these three buildings, thus making available a large amount of RC elements composing the structure and the facades of these buildings. Little-known and rarely implemented, the reuse of concrete elements from obsolete buildings in new projects is a sustainable approach that promotes a circular economy. When reusing, the components of obsolete buildings are carefully dismantled without being crushed. They are then cleaned, possibly repaired or trimmed, and reused without many transformations in a new project, maintaining their shapes, technologies, and mechanical properties. In addition to maintaining the embodied energy and history of the reused components, reuse allows the construction industry to reduce demolition waste, greenhouse gas emissions, and material consumption. This report is a preliminary resource assessment and aims at inventorying and assessing all structural elements of the Triemli Personalhäuser, focusing on their potential value for reuse. Both precast and cast-in-place RC elements are included. They are part of the load-bearing structure or are self-supporting such as the precast facade elements. The proposed methodology allows identifying all properties needed to evaluate the potential for reuse of an element: geometry, material properties, current condition, aesthetics, accessibility, resistance, future durability and environmental impacts. After reviewing available reports and drawings on the buildings, onsite visits are carried out to complete the information and visually inspect the structural elements. During the inspection, the elements are assessed with regards to their suitability for reuse and their condition is classified into a five-grade scale. The investigations are completed with destructive and non-destructive testing of the material properties. Together, Buildings A, B and C are made up of approximately 7 000 m3 of materials constituting their load-bearing system, with approximately 2 500 m3 of precast concrete, 3 400 m3 of cast-in-place concrete and 1 100 m3 of masonry. Of this total, approximately 4% of the volume is dropped from the analysis due to the bad condition of the elements, namely the balcony slabs, the roof slab, and the external stairs. The other elements are in a good or acceptable condition and ae inventoried and analysed in detail. The inventoried elements are divided into 5 categories: (1) facade elements; (2) slab elements; (3) wall elements; (4) column elements; and (5) staircases. Each of these categories are subdivided into a certain number of element types for which a complete factsheet is prepared, including pictures, drawings and useful information on their condition. The volume and weight of each element types are given, as well as their share of the total material volume. The embodied global warming potential (in kgCO2eq) for fabrication and demolition of the elements is also calculated. The results of the investigation on material properties confirm sufficient compressive strength for all elements. The carbonation depths measured on the cores are lower than the cover thickness of the reinforcement. Thus, the concrete is not carbonated in the reinforcement areas and the risk of corrosion is kept low, insuring a good durability of the elements. This document should serve as a base for designing and planning future reuse applications for the concrete elements extracted when deconstructing the Triemli Personalhäuser. The information presented here will help the planners to prioritize the reuse strategy on the elements in the best conditions, with the largest volume share and thus with the largest embodied global warming potential.

EPFL2022

The reuse of load-bearing components

Jan Friedrich Georg Brütting, Catherine Elvire L. De Wolf, Corentin Jean Dominique Fivet

Load-bearing systems of buildings are poorly valued when they reach functional obsolescence. Still, they contribute the most to the material weight and embodied impacts of buildings and infrastructures. The reuse of structural components therefore offers great potential to save materials, energy and resources. While historic and contemporary projects highlight the environmental, time or cost benefits of building with reclaimed elements, many technological challenges remain. This paper gives an overview of buildings that efficiently reuse structural components as well as a review of current research efforts addressing structural reuse. The first case study is the design process of an elastic gridshell made from reclaimed skis. This project demonstrates the potential of ensuring structural performance while working with uncharacterized and heterogeneous materials. In general, designing structures from a stock of reclaimed elements entails reversing the conventional structural design process. The synthesis of structures has to follow the availability of elements and their mechanical and geometric properties. Developed tools that facilitate such design from reused elements while minimizing embodied environmental impacts are presented in this paper. A second case study demonstrates the relevance of such tools through a conceptual train station roof made from electric pylon elements. Lastly, some key challenges related to the design of structural systems from reused elements are presented. These research initiatives constitute a first step to understand and support the design of load-bearing systems from reused elements and hence to bring the construction industry closer to circular economy.