Re:Crete Footbridge

  • Building Type : Other building
  • Construction Year : 2022
  • Delivery year : 2022
  • Address 1 - street : Rte Cantonale / Rte de la Morge 1964 CONTHEY, Suisse
  • Climate zone : [Cfb] Marine Mild Winter, warm summer, no dry season.

  • Net Floor Area : 12 m2
  • Construction/refurbishment cost : 67 000 €
  • Cost/m2 : 5583.33 €/m2

Proposed by :

  • Primary energy need :
    kWhep/m2.an
    (Calculation method : )
Energy consumption
Economical buildingBuilding
< 50A
A
51 à 90B
B
91 à 150C
C
151 à 230D
D
231 à 330E
E
331 à 450F
F
> 450G
G
Energy-intensive building

The Re:Crete Walkway, designed and built by EPFL's Structural Xploration Lab (SXL), is a pedestrian walkway made of concrete blocks sawn into the walls of a building under renovation and reassembled into a prestressed arch. Initially produced as a research prototype, this footbridge demonstrates for the first time the feasibility of reusing non-prefabricated concrete elements in new load-bearing structures. Concrete is the most widely used building material in the world and is the major source of the construction industry's environmental impacts. Its reuse by sawing elements offers a new extension of life to obsolete concrete, thus avoiding its premature crushing, while promising a great potential for reducing greenhouse gases, demolition waste and extraction of raw materials.

In collaboration with the State of Valais, a site was found to install the prototype and make it accessible to the public. The structure was therefore equipped with guardrails, also made of reused materials, and set up for a period of 2 years on the Morge river in Valais (Switzerland). It is used for pedestrian mobility during the duration of the works on the bridge of the adjacent cantonal road.

The concrete blocks are extracted from the wall using a circular saw with a diamond blade, then cored to allow the passage of the prestressing cables. The blocks are then placed on a wooden hanger by passing the sheaths and prestressing cables through the core drillings. Before tensioning the cables and removing the handlebar, the joints are filled with mortar to ensure contact between each block. In order to make the footbridge permanent and suitable for outdoor use, the exposed reinforcing steels were covered with an anti-corrosion paint, a hydrophobic impregnation was applied to the concrete faces and the joints were covered with strips of tightness. However, the characteristic texture of sawn concrete, patchworks of aggregates and reinforcement spacers, is kept visible on the side faces of the arch. The materiality of the bridge expresses both the source of the material, with its own history preceding that of the bridge, and the technique used to implement it. Finally, the uprights and the handrail of the guardrail were made by recombining metal elements reused from an old marquee and the lattices are taken from old industrial shelves.

Besides providing a new design material for architects and engineers, the reuse of concrete elements is an effective solution to reduce the demand for cement, CO2 emissions and concrete waste. A detailed life cycle analysis shows that the Re:Crete footbridge has a lower environmental impact than similar solutions in reinforced concrete (-63%) or steel (-75%) and approximately similar to that of a solution in new wood (+9%).


If you had to do it again?

This pioneering experience of reusing concrete elements extracted from a cast-in-place structure validated a new way of designing structures. The technologies used (e.g. concrete sawing and prestressing) proved to be appropriate for the reuse of concrete blocks to design a new structure. Nevertheless, we have identified various points to further increase the environmental benefits of the approach:
- Minimization of transport distances for reused materials
- Verification of the properties of reused materials before their deconstruction or acquisition
- Minimization of the stages of preparation of the concrete elements to be reused
- Consideration of the durability aspects of reused concrete through adequate construction details

See more details about this project

 https://www.epfl.ch/labs/sxl/index-html/research/reuse-of-concrete/

Photo credit

Federal Polytechnic School of Lausanne (EPFL), Structural Xploration Lab (SXL)

Contractor

    Etat du Valais

    Jean-Baptiste Luyet (ingénieur Ouvrages d'art et Transports Exceptionnels)

Construction Manager

    Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratoire d'exploration structurale (SXL)

    Corentin Fivet (professeur et responsable du Laboratoire d'exploration structurale (SXL))

Stakeholders

    Company

    Diamcoupe SA

    Guillaume Mittnacht (chef de région, Suisse Romande)

    The Diamcoupe company supplied and prepared the concrete blocks. It sawed blocks in the walls of the source building and drilled cores for the passage of prestressing cables.


    Company

    Freyssinet SA

    Adrian Motte (directeur d'agence, Suisse)

    Freyssinet supplied the sheaths and prestressing cables. It proceeded with the tensioning of the cables and the injection of the sheaths.


    Environmental consultancy

    Bridgology SA

    Alexis Kalogeropoulos (fondateur et directeur)

    Bridgology carried out non-destructive measurements on the structure to determine the cover of the pre-existing reinforcing bars and check the condition of the concrete.


    Company

    Sika Suisse SA

    Cédric Chetelat (ingénieur conseil, Suisse Romande)

    The Sika company supplied the products applied to the footbridge to protect it from water (anti-corrosion paint, hydrophobic impregnation, sealing strips).


    Company

    Emil Egger Romandie SA

    Frédéric Marilley (chef de projet)

    Emil Egger transported the footbridge from its manufacturing site in Friborg (Switzerland) to its installation site in Conthey (Switzerland). It also carried out the lifting for the installation of the footbridge over the river.

Systems

    • No heating system
    • No domestic hot water system
    • No cooling system
    • Double flow
    • No renewable energy systems

GHG emissions

  • The calculation is made according to the LCA method and the Swiss KBOB database. The system considers all procedures related to deconstruction, preparation of elements, production of new materials, transport and construction works.

  • 25,00 KgCO2 /m2
  • 15,00 an(s)
  • 25,00 KgCO2 /m2
  • Only the bridge structure was evaluated. CO2 emissions related to the construction of guardrails are not included in this figure.

Life Cycle Analysis

    Comparison of the global warming potential between the Re:Crete footbridge and 4 variants: prefabricated recycled concrete block arch, recycled concrete monolithic arch, steel beam arch, wooden beam arch (Devènes et al., 2022).

Resiliency

    • Gel

    The concrete structure is exposed to rainwater and frost, which can accelerate its degradation.

    The concrete elements, as well as the sensitive parts of the structure, were protected from water by simple and common solutions in the industry. These make it possible to guarantee the durability of the structure for a longer period. The solutions implemented are as follows:

    • the cut rebars, visible on the cut faces of the concrete blocks, were protected with anti-corrosion paint;
    • the exposed concrete faces have been impregnated with a hydrophobe;
    • the sheaths of the prestressing cables were injected with mortar;
    • the joints were sealed with glued plastic strips.

Construction and exploitation costs

  • 67 000
  • 25 900
  • As the project was carried out within the framework of research activities of a university, the study costs have not been quantified. Financial aid comes from internal funding at EPFL as well as corporate sponsorship.
    Instead, reuse resulted in an additional cost of approximately 30% compared to a conventional variant in another material. However, we believe that this additional cost is mainly due to the novel nature of the approach. Optimization of the acquisition, assembly and maintenance process should provide a reduction in costs. It should also be noted that these costs are compared to a conventional variant whose aesthetics are not the same. Replicating an aesthetic similar to the Re:Crete Walkway with conventional materials would likely increase costs.

Urban environment

This project was initially designed as a prototype to demonstrate the feasibility of reusing concrete blocks. The width of the Morge river at the Cantonal Road site matched the span of the Re:Crete footbridge and this site was therefore an opportunity to adapt the prototype for outdoor use. Its implementation in the Swiss Alps allows a dialogue between the minerality of the slices of exposed cut concrete and the surrounding mountains.

Reuse : same function or different function

    • Structural works
    • Locksmithing-Metalwork

    Major work :

    • Concrete blocks: 2.43 m3
    • Sub-tie: 22 linear meters

    Locksmith-Metallery:

    • Steel posts and handrail: 40 linear meters
    • Trellis: 44 m²

    Big work :

    • Concrete blocks: sawn into the walls of a hotel basement undergoing transformation in the canton of Vaud, reused as the structure of the arch. Supplied by the sawing company.
    • Sub-tie rods: salvaged from an EPFL structural testing hall in Lausanne, reused.

    Locksmith-Metallery:

Sustainable design

    Reuse of concrete blocks

    The search for concrete blocks for the construction of the footbridge was carried out by contacting various demolition and sawing companies. The desired dimensions of the blocks were set with a certain tolerance in the preliminary design, to allow for adjustments once the source building was found. The 25 concrete blocks used for the construction of the footbridge were finally sawn directly to size from the basement walls of a building that was being converted. The small size of the blocks, 1.2 × 0.4 × 0.2 m, made it easy to transport them to the outside of the building without machinery.

    The blocks were then transported to the premises of Diamcoupe, which was able to drill the holes for the prestressing cables. Finally, they were delivered to the workshop where the footbridge was manufactured. These steps are described in Figure 1.

    Figure 1: Deconstruction and supply of the concrete blocks: (a) sawing of the walls, (b)-(c) drilling of the openings for the prestressing cables, (d) transport, and (e) storage.

    Once delivered to the site, the blocks were assembled on a wooden hanger while the prestressing tendons were threaded. The joints were then filled with mortar to ensure good contact between the blocks. As the dimensional tolerances for sawing and drilling the concrete blocks were not specified to the company, the usual industry tolerances were applied. The dimensions of the delivered blocks, including the position of the holes for the prestressing, therefore varied by ± 27 mm. By sorting the blocks, the differences between two adjacent blocks were reduced and the mortar joints were used to absorb the remaining variations. Once the mortar had set, the prestressing cables were tensioned by Freyssinet and the arch could be dismantled.

    The shape of the arch and the use of prestressing are particularly well suited to the reuse of sawn concrete blocks. Indeed, the arch makes it possible to take advantage of the best property of concrete, namely its compressive strength. Moreover, thanks to the prestressing, the arch remains compressed, regardless of the configuration of the payload.

    Thus, the project diverted 6 tonnes of concrete from the landfill and demonstrated the feasibility of reusing concrete. However, there is still room for improvement.

    Figure 2: Assembly of the prototype: (a)-(b) placing the blocks, (c) filling the joints, (d) prestressing.

     

    Re-use for railings

    The railings were designed from local reuse materials, namely metal tubes and wire mesh, from companies that recycle and sell second-hand industrial equipment.

    The uprights and handrail are tubular elements reused from an old circus tent structure. Once sawn to the desired length, the uprights were simply welded to anchor plates, while the handrail was also bent to follow the curve of the concrete arch. The wire mesh was taken from old industrial shelves and cut and bent to give it more rigidity and expressiveness. They are linked together with staples from the shipbuilding industry. The uprights and mesh are fixed to the edge of the concrete blocks with screwed connections via galvanised anchor plates. The handrail is also screwed to the uprights and fences using standard elements found in most guardrails. This makes it easy to dismantle, repair or reuse these custom-made railings. All welds and sawn surfaces have been treated with a galvanising spray paint to protect this metal addition from corrosion.

    The chosen solution allows for user safety while maintaining transparency and moiré play, also highlighting the sawn edge of the concrete blocks. In addition to the tectonic expressiveness, this solution meets the safety standards required for footbridge railings, through the manipulation of the intrinsic characteristics of the reused materials and the resistance of each existing element.


    Figure 3: Construction of the railings: (a)-(b) stock of reused materials, (c)-(d)-(e)-(f) preparation of the elements, (g)-(h)-(i) assembly of the elements constituting the railings.

    As demonstrated by its installation on site, the gateway can easily be transported in its entirety to another site for subsequent use. Furthermore, its current site is temporary and a permanent installation at another site is already in the planning stages.

    The guardrails have been designed to be easily removable since all the parts are screwed or bolted. It could therefore be easily dismantled if necessary, for maintenance, adaptation or installation on another structure.

Environmental assessment

    The re-use operation saved the equivalent of 22788 kilometres travelled by a small car, or 26 trips from Paris to Nice, 117 rectangular bathtubs filled with water and 15 years of household waste for a French person.

    In order to calculate the avoided impacts, the material "breeze block - with concrete filling" was used as an equivalent to concrete blocks. To compensate for the different densities and assumptions about the future of the materials, the amount of concrete was increased proportionally. It is therefore assumed here that the entire quantity of concrete blocks would have been eliminated if they had not been re-used.

Reproductibility and Innovation

    Reuse has been integrated since the genesis of the Re:Crete footbridge project , which serves as a demonstrator of the possibilities of reuse for structures and in particular the reuse of concrete. The project took advantage of well-known technologies from the construction industry, such as sawing, concrete drilling and prestressing . Such a gateway could therefore easily be reproduced for another site. The innovation stems from the idea of reusing initially poured concrete and design methods integrating reuse. Designing structures with reused materials presents several constraints that modify the project phases compared to a classic project. For a reuse project, the design must be resilient to the unknowns of the stock of materials (availability, quantity, mechanical performance, geometric and texture variability), as was the case for the footbridge project.

    The contribution of companies is also one of the keys to the success of this project. The search for reusable concrete blocks was done in a non-systematic way by contacting several concrete demolition and sawing companies not used to this kind of request, the search was not easy. The blocks were finally supplied by the Diamcoupe company, which understood the needs of the project and was able to identify a renovation site that could serve as a source for the footbridge project. The reuse of concrete creates a new value chain where concrete sawyers are no longer at the end of the life of the material, but become suppliers.

    The Re:Crete gateway has attracted considerable media attention in Switzerland and abroad since the inauguration of the prototype in October 2021. Here is a summary (status as of May 17, 2022 and available at https://actu.epfl .ch/news/the-recrete-footbridge-in-the-news/ ):

    On LinkedIn

    • Our October 23, 2021 post on building the prototype received over 1460 likes and was shared 164 times. The video was viewed more than 50,000 times.
    • Our May 5, 2022 post on the installation of the Re:Crete footbridge in the Swiss Alps received more than 370 likes and was shared 12 times.

    Media Switzerland

    In Switzerland, in addition to the main EPFL media, the Re:Crete gateway was published in the general local newspapers: La Liberté, Heidi News, La Gruyère, Le Nouvelliste and La Côte. As well as in specialized media: Espazium/Tracés, Baublatt, Batimag. The members of the Structural eXploration Laboratory (SXL) have been invited on two occasions to the Swiss National Radio: RTS CQFD, RTS Forum. Videos for television channels have also been produced for RTS nouvo on the RTS 2 and TV5 monde channels, and for Canal 9.

    Foreign media

    Abroad the Re:Crete gateway has been published in the United States for Popular Science and SlashGear, in England for RIBA journal, in France for Le Moniteur and Usine Nouvelle, in Germany and Austria for PresseText, in India for TimesNowNews, and in China.

Economic assessment

  • 19 200
  • 29 %

Reasons for participating in the competition(s)

The Re:Crete footbridge is an original project which integrates for the first time the structural reuse of concrete elements from an existing concrete building poured on site . It demonstrates the technical feasibility while using technologies known by the construction industry such as concrete sawing and prestressing. To guarantee the long-term durability of reused concrete elements, the structure was adapted, by simple methods, to outdoor use. The railings are also designed with recycled materials.

Confirming that sawn concrete is a new reusable structural material, this project extends the application of circular economy principles to the construction industry. A new field of activity is created, with the key to the reuse of sawn concrete elements for the construction of traditional buildings. In addition, this first prototype convincingly demonstrates that the approach can drastically reduce greenhouse gas emissions, construction waste and extraction of raw materials. Its generalization offers new perspectives to quickly contribute to the mitigation of global warming and increase the sustainability of the construction industry.

Building candidate in the category

Prix hors-cadre

Prix hors-cadre

Trophées Bâtiments Circulaires 2022

 2022 Circular Buildings Trophies
 materials and solutions
 building
 circular economy
 reuse
 waste
 recycling

Author of the page


  • Other case studies

    More

    Contest

    Trophées Bâtiments Circulaires 2022