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Concrete accounts for the largest share of worldwide building material use and waste generation, with cement production being responsible for approximately 9% of global anthropogenic CO2 emissions. A currently untapped strategy to significantly reduce these environmental impacts consists in reusing reinforced concrete (RC) elements in new load-bearing applications. This paper presents a new design-and-build concept to reuse cast-in-place RC wall and slab elements sourced from obsolete buildings. The applicability of the proposed paradigm is demonstrated through a prototype: a 10-m spanning post-tensioned segmental arch made of 25 reclaimed concrete blocks. The paper illustrates the complete workflow, including the sourcing of the blocks through sawing and the prototype assembly. A comparative Life Cycle Assessment shows that the prototype structure has a significantly lower environmental impact than equivalent designs made of new material.

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.

A travers une revue de la littérature, ainsi que 32 études de cas et des entretiens avec des praticiens, ce recueil: › synthétise les principes fondamentaux des deux approches; › documente et diffuse les retours d’expériences et les bonnes pratiques; › apporte aux entrepreneurs/entrepreneuses, concepteurs/conceptrices et maîtrises d’ouvrage des références techniques; › procure aux parties prenantes un bagage théorique à la pointe et détaillé ainsi qu’une série de référence pour aller plus loin; › esquisse les perspectives d’évolution et opportunités applicables au bâti suisse.

As the most widely used construction material worldwide, concrete is the main cause of greenhouse gas emissions, material depletion, and waste generation by the construction industry. Typically, concrete waste is crushed and, at best, reclaimed into recycled aggregate or used as gravel. This process is energy-intensive and results in a reduction in material properties. In contrast, the direct reuse of concrete elements from obsolete structures offers great potential for significantly reducing the environmental impact of new constructions. To be reused, concrete elements are carefully sawn out of soon-to-be-demolished buildings. Elements are then used without other major transformations for another service cycle in a new assembly. This paper analyses two recent projects in Switzerland that showcase innovative applications of concrete reuse: a post-tensioned segmented arch footbridge and a parking pavement. Both projects reuse blocks extracted from cast-in-place concrete buildings undergoing transformation or demolition. In this paper, environmental and economic analyses provide a comprehensive understanding of the alleviations and costs involved. Results are compared to those of alternatives with conventional construction methods. The two projects reusing concrete globally showcase a drastically lower environmental impacts for comparable or higher construction costs, hence calling for future developments of such new circular construction strategies.

Le centre pour la redistribution et la recherche sur les matériaux de réemploi est un programme nouveau qui participe à l’économie circulaire. Distinct du recyclage, le réemploi conserve la forme, l’énergie, le savoir-faire, la technologie et la part culturelle contenus dans un matériau pour l’utiliser une nouvelle fois sans le modifier fortement. Le “hub de réemploi” répond aux difficultés spécifiques, normatives, économiques, culturelles ainsi que de synchronisation entre chantiers. Ces nouveaux lieux de partage, qui certifient et revendent ces matériaux, forment un réseau actif pour l’innovation et la diffusion de la pratique. A Ecublens, le “hub” pour la Suisse romande est un bâtiment “low-tech” qui valorise la topographie et les infrastructures existantes. Conçu avec des matériaux de réemploi, il est organisé en plan selon deux L: l’un permet l’arrivée de marchandises par le train et l’autre par la route. A l’intérieur, des volumes chauffés reçoivent une part des activités didactiques, de recherche et de remise en état. Dans une logique vertueuse, le centre pourra s’agrandir par étape avec son propre stock, en parallèle au développement de la filière. En plus de compléter une jonction écologique, le projet veut valoriser les mobilités douces, consommer une quantité minimum de matériaux et proposer une stratégie énergétique positive. Le choix des matériaux, développé dans une série de détails constructifs, repose sur des éléments d’occasion régulièrement destinés au recyclage et typiques des rejets de la déconstruction régionale.

Concrete is the most ubiquitous construction material worldwide but also a major source of waste and CO2 emissions. Worse, it is too often crushed down prematurely for recycling or filling. Can’t we do better? We seek to reuse concrete from demolition sites by carefully sawing reinforced walls and slabs, hence generating a new circular supply chain. Reclaimed components come with their own history, their own imperfections and irregularities. Yet, they are a fully reliable construction material, amply capable of new structural feats. We designed and built the RE:CRETE footbridge, a unique post-tensioned arch that spans 10 meters, with 25 reused concrete blocks. The joints are made with regular mortar before post-tensioning. Loaded up to 1.8 tons, and deflecting less than 1.15mm, the footbridge performs just as any other one. This bridge is built out of concrete… without pouring any concrete. It opens up new pathways to drastically cut waste and CO2 emissions.

Plus que de tout autre matériau, le bâti suisse est fait de béton. Matériau aux nombreuses qualités, il est présent dans toute nouvelle construction, souvent en grande quantité. Malgré cela, des tonnes de béton sont quotidiennement démolies, pour des raisons plus proches de l'obsolescence des espaces qu'il crée que de sa propre dégradation. Ces démolitions exacerbent l'impact considérable de la mise en œuvre du béton sur l'environnement. Face à ce constat, un nouveau paradigme de construction permettrait de découpler obsolescence du bâti et demande en béton neuf : le réemploi d'éléments de béton, extraits par sciage des bâtiments voués à la démolition et réassemblés dans de nouvelles structures porteuses. L'approche n'est pas neuve, est déjà éprouvée, mais peine à se généraliser. Le territoire suisse rejette sans cesse du béton dévalorisé. Cette ressource sera-t-elle un jour exploitée à sa juste valeur ?

Diese Sammlung stützt sich auf eine Literaturrecherche sowie 32 Fallstudien und Interviews mit Fachkräften und: › fasst die Grundprinzipien beider Ansätze zusammen; › dokumentiert und gibt Erfahrungsberichte und bewährte Verfahren weiter; › liefert technische Referenzen für Bauunternehmen, Entwerferinnen/Entwerfer und Bauherrschaft; › bietet einen aktuellen und detaillierten theoretischen Hintergrund sowie Referenzen für die weitere Entwicklung; › skizziert die Möglichkeiten zur Weiterentwicklung und Umsetzung für Schweizer Bauten.

Le réemploi des composants se présente comme une stratégie de durabilité prometteuse pour l’industrie de la construction, mais sa généralisation est-elle à portée de main ?

The production of concrete, the most widely used construction material, detrimentally affects the environment. Obsolete reinforced concrete (RC) load-bearing structures, even when still in good condition, are today prematurely crushed and landfilled or recycled into new concrete mixes. Little known and rarely implemented, the reuse of RC structural components is an alternative strategy towards more circularity in the construction industry. Since 2021, RC component reuse has been implemented in a series of construction and deconstruction projects in Switzerland. This paper identifies existing process sequences for RC-reuse projects and proposes one that involves a new assessment procedure to evaluate the reusability of the components early on and facilitate their future reuse planning. The paper discusses the application of this procedure to three deconstruction projects. Results are encouraging with regard to the durability of RC components. Almost 90% of the RC components of a building could be reused for new purposes with the same stability and exposure as in the donor building.

Distinct from recycling, reuse maintains the shape, energy, know-how, technology and cultural part embedded in a component to use it beyond an initial use into a new project without strongly altering it. The "hub" for research and resale of reusable construction components is a building that participates in a more sustainable construction industry and circular economy. The “hub for reuse” program responds to specific normative, economic and cultural difficulties of reuse, as well as the challenge of synchronizing deconstruction and construction sites. These new places of sharing, where salvaged construction components are certified and resold, form an active network for innovation and implementation of the practice of reuse. In Ecublens, the "hub" for French-speaking Switzerland is a low-tech building that takes advantage of the existing topography and infrastructure. Designed to be built with reused components, it is organized in two Ls: one allows the arrival of goods by train and the other by road. Inside, heated volumes host part of the didactic, research and repair activities. In a virtuous logic, the center will be able to expand step by step with its own stock, in parallel to the development of the reuse sector. In addition to completing an ecological junction, the project aims to enhance soft mobility, consume a minimum amount of materials and propose a positive energy strategy. The choice of materials, developed in a series of constructive details, is based on second-hand components regularly destined for recycling and typical of the rejects of the regional deconstruction.

As floors typically account for the largest share of a building embodied carbon footprint, new strategies to build low-carbon floors must be developed and implemented. Among these strategies, the reuse of existing components is a promising circular approach in which components are carefully extracted from buildings undergoing transformation or demolition and reused into new buildings. Recent research reviewed built examples that mostly reuse prefabricated reinforced-concrete (RC) components but also revealed a lack of design explorations for floor systems that reuse pieces extracted from cast-in-place (CIP) RC structures. This paper presents two new floor systems reclaiming pieces cut from typical CIP structures. In the first one, cut pieces are as long as the new span. In the second one, cut pieces are smaller and supported by girders as long as the new span. The environmental footprint of each new system is compared to conventional ones through a life-cycle assessment (LCA) and for multiple design parameters. In addition, a procedure is introduced to estimate the maximum cutting length that allows the reuse of pieces as simply-supported slabs. Results show that these lengths correspond to those of the donor slab if it spans up to 5.6 meters, depending on the slab thickness, construction period, and design uses. LCA shows radical carbon-footprint reductions that average 85 % for all simulations. Overall, results show that discarded concrete is a valuable material source for building innovative, efficient, low-carbon floor systems combining existing (de-)construction tools.

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.

Renens, avenue des Paudex 10-12, dans la périphérie résidentielle et tertiaire de l’ouest lausannois, 64 appartements regroupés en deux barres de logements coopératifs sont en cours de démolition pour être remplacés par 86 nouveaux appartements qui répondent aux « standards » et normes actuelles. Voici l’illustration concrète du procédé démolition-reconstruction largement mis en œuvre aujourd’hui lors du renouvellement urbain. A l’heure où l’impact environnemental néfaste de cette pratique est avéré, ce travail de master est un contreprojet qui explore le potentiel de transformation des deux barres existantes. Celui-ci repose sur le constat que la substance principale du projet est déjà là : des logements traversants est-ouest, spacieux, lumineux et dotés chacun d’une loggia privative. La conception d’origine était basée sur la simple répétition d’unités d’habitation indépendantes ; la nouvelle intervention propose quant à elle de régler l’articulation entre les logements à l’échelle du palier, de l’étage et de l’implantation urbaine, par l’introduction d’une structure légère glissée sur et entre les deux barres. Cette structure, conçue comme une couche vivante et active qui participe au concept énergétique global du bâtiment, dégage en outre des espaces extérieurs partagés. In fine, le projet veut montrer qu’il existe dans l’acte de Projeter la transformation un vrai potentiel architectural et une alternative pour sortir de la pratique actuelle basée sur la démolition.

Depuis 2019, des pluies exceptionnelles ont touché plusieurs régions du Soudan du Sud, provoquant le débordement anormal de certaines rivières. La ville de Pibor, dans le comté de Jonglei, a été complètement submergée par les eaux, ce qui a entraîné la destruction des habitations déjà précaires, l’inaccessibilité aux infrastructures publiques et la perte des récoltes. Afin d’apporter une réponse à ces phénomènes dont la fréquence ne cesse d’augmenter, le projet vise l’adaptation à ces changements environnementaux et la garantie d’accès aux ressources essentielles par la mise en place de hameaux d’agriculture communale. Chacun de ces nouveaux centres de production est entouré d’une digue. Cette digue est conçue comme un support pour un système d’abris à fonction publique, ainsi que pour un grenier à grain, dans lequel les réserves sont stockées puis redistribuées. À travers la construction et l’utilisation collective de ces hameaux, le but est de transmettre des solutions résilientes, basées sur l’utilisation de matériaux locaux et l’usage de techniques vernaculaires, qui pourront, par la suite, être reproduites à l’échelle de l’habitation familiale.

Garde-enrobe est un projet qui s’implante sur un parking en plein air dans la zone sportive du quartier des Vergers à Meyrin. Il propose l’extension du centre sportif avec l’ajout d’une zone dédiée aux sports urbains (skatepark, pumptrack, basket 3x3, danse urbaine, street workout, échecs, etc.) ainsi qu’un bâtiment accueillant des dortoirs, un restaurant, des espaces destinés aux associations sportives et un centre de réparation pour deux roues non motorisées. Ce parking date de la fin des années 1970 ; son utilité est remise en question par le projet de renaturation du Nant’Avril qui longe la parcelle au Nord-Ouest, la construction de trois parkings souterrains à proximité ainsi que le développement des transports publics de ces dernières années. Il offre ainsi l'opportunité d’utiliser la surface d’enrobé bitumineux existante, telle quelle, pour un nouveau programme. Pour le bâtiment, les matériaux biosourcés et locaux, les assemblages mécaniques ainsi que des techniques diminuant les besoins en énergies non-renouvelables sont privilégiés. Il est surélevé par rapport au sol créant ainsi une plateforme en bois, recouverte par endroit d’ombrage, qui sert à la fois de circulation et d’espace de flâneries. Cette même logique de plateforme est utilisée pour les mobiliers urbains permettant ainsi d’unifier les interventions. Les espaces dédiés aux sports urbains sont quant à eux essentiellement composés de dessins au sol exploitant la surface plane et imperméable existante.

Dans un environnement construit considéré immuable, les changements fréquents de besoins et d’usages rendent nombre de bâtiments obsolètes, alors même que leurs composants conservent majoritairement leur valeur intrinsèque. L’une des conséquences visibles de ce manque d’adaptabilité est incarnée par l’imposante et vétuste raffinerie Tamoil en Valais, dont l’empreinte physique, sociale et environnementale sur le territoire reste lourde pour les populations locales. En envisageant de nouvelles vies pour les composants de la raffinerie à travers la conception de projets versatiles et réversibles, les 2ème et 3ème cycles proposés redéfinissent ainsi un environnement bâti capable de s’adapter à de nouvelles conditions, au-delà d’un horizon temporel prévisible. Accueillant les matériaux de réemploi consciencieusement analysés comme source de projet, l’architecture des bâtiments receveurs gagne en expressivité par la célébration structurelle et tectonique de stratégies non-destructives, favorisant ainsi le développement d’une image tangible d’une grande adaptabilité pour l’architecture.