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Bessac rewarded: the 1st EXEGY ultra-low-carbon microtunnel

At the Public works awards, Bessac received a prize for the construction of the world’s first microtunnel made entirely of EXEGY by Bessac ultra-low-carbon concrete for the Bonneuil-en-France wastewater treatment plant project.

Bessac is proud to have been awarded the Public Works 2024 trophy in the “Implementation of low-carbon materials” category. This category rewards innovations by Public Works companies that enable the development and/or industrialization of materials whose “low-carbon” advantage is objectively assessed by LCA, and which are adapted to projects and the needs of users and customers.

Project history

At the end of 2021, the Syndicat Intercommunal pour l’Aménagement Hydraulique des Vallées du Croult et Petit Rosne (SIAH) awarded a design-build contract to a consortium comprising Bessac (leader), Soletanche Bachy Fondations Spéciales and Setec Hydratec, for the discharge of treated water from the new wastewater treatment plant up to its connection to the Garges-Epinay collector.

To build this structure, which will improve water management, Bessac achieved a world first by constructing the entire tunnel using ultra-low-carbon concrete pipes. The concrete formula has a carbon footprint 4 times smaller than concretes generally used for the prefabrication of pipes ramming. This project was carried out under the EXEGY by Bessac brand, which brings together all the expertise of the company and Soletanche Bachy in low-carbon concretes.

This technical feat was made possible by :

  • The nature of the design-build contract enabled us to develop a tailor-made formulation for the site, using locally available materials.

  • The SIAH’s commitment to a strong environmental approach.

  • Bessac’s certified expertise in both tunnelling and the design and prefabrication of pipes ramming.

  • The involvement of Soletanche Bachy’s integrated materials laboratory, which enabled the development of a specific concrete formulation.

  • Finally, the support of the Tunnel Factory, a catalyst for innovation in the field of tunnels for the various VINCI Construction entities.

Favoring a short circuit from design to construction


To further improve the project’s carbon footprint, Bessac opted to relocate pipe manufacturing to France: the choice of Capremib for prefabrication, with its plant located near Reims, helped reduce transport distances and hence their impact.

Finally, the carbon footprint of this project was significantly improved, with a saving of 197 tonnes of CO2 thanks to the use of these pipes.

Congratulations to the BESSAC teams on receiving this award!

A project in line with the environmental ambitions of VINCI Construction and Soletanche Bachy

  • VINCI Construction objective: 90% low-carbon Concrete on its sites in France and worldwide by 2030.
  • Soletanche Bachy objective: -20% of CO2 emissions on Scope 3 by 2030, which concerns indirect emissions linked mainly to concrete and steel.

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