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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.

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.

The addition of a thin overlay of reinforced UHPFRC (R-UHPFRC) to a reinforced concrete (RC) element creates a composite member which can be used for the strengthening of an existing structure and in the design of new structures. With its strain hardening and softening behavior and high resistance in tension, the UHPFRC layer serves as an external tensile reinforcement contributing to both flexural and shear resistance of the RC element. The main failure modes of a composite section were identified during previous experimental campaigns. In this paper, experimental results on a composite slab strip are presented to demonstrate how the layer contributes to the shear resistance. Using this example, an analytical model to predict the behavior and calculate the resistance of a composite member is presented and applied.

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 ?

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.

Located in Switzerland, Chillon viaducts are two parallel highway posttensioned concrete bridges built in the late 1960s. The concrete of the deck slabs of these bridges shows signs of early stages of the alkali-aggregate reaction (AAR), which will induce, in time, a decrease of the concrete strength. To insure structural safety for future traffic demands, it was decided to strengthen the slab by adding a layer of 40 mm of an Ultra High Performance Fiber Reinforced cement-based Composite (UHPFRC) material, reinforced with steel rebars. Strain-hardening UHPFRC, with its low permeability, is used as a waterproofing layer protecting the slabs from the water to reduce the rate of AAR. UHPFRC has excellent mechanical properties and also acts as an external tensile reinforcement for the slab, increasing its bending and shear resistance and extending the fatigue life. To investigate this increase in structural resistance, an analytical calculation is done using models previously developed based on extensive experimental campaigns. Finally, the choice of UHPFRC for strengthening was also the most efficient in terms of intervention duration and cost.

Reuse of reinforced concrete (RC) components reduces construction’s environmental impacts and waste. Rather than crushing the concrete of an obsolete structure, its components are saw cut and later reassembled in a new structure. The theoretical feasibility of this method is demonstrated through a case study: the design of a residential building structure that reclaims cast-in-place RC components from two 60-year-old office buildings scheduled for demolition. Parts of the source buildings are allocated to an optimal position in the target building using an algorithm that minimizes the need for strengthening. Construction details are developed for the slab-wall connections and the bracing system. An alternative conventional cast-in-place RC design is proposed for comparison, as well as a hybrid design balancing environmental and cost savings with technical readiness. The assessment of the designs confirms that reusing RC components allows saving up to 75% of greenhouse gas emissions for similar costs, as long as demolition and disposal of obsolete source material are considered.

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.