In late 2020, the French Regional Department of the Environment, Planning and Housing (DREAL) for the Auvergne-Rhône-Alpes region, project owner for the upgrade of the Rondeau interchange, awarded a contract to the consortium led by Campenon Bernard Centre Est, a VINCI Construction subsidiary, to build a 300 ml tunnel and develop two new 500 ml ramps, along with the construction of crossings.
For the project, VINCI Construction’s concrete laboratory developed an innovative, highly specialised concrete solution in partnership with the concrete department of the Technical and Operational Resources Division from the Centre-Est Civil Engineering Delegation and the ready-mix concrete manufacturer VICAT.
As Grenoble is classified as a “mountain” area, the site is subject to freeze/thaw conditions and frequent salting. As a result, XF4 Gel + Sel (G+S) concrete was used, in accordance with section 65 of France’s concrete standard and with the “Recommendations for the durability of hardened concretes subjected to frost”. These high-cement concrete formulations (385 kg of cement/cu. metre of concrete) are usually made with CEM I 52.5 PMES cement, which has a very high carbon footprint.
However, the team from VINCI Construction’s Centre-Est Civil Engineering Delegation wanted to develop technical solutions that would make it possible to use low-carbon concrete on this type of infrastructure project and to test them on the worksite for the Rondeau cut-and-cover tunnel. The goal is to standardise these solutions for future structures meeting the same criteria in all “mountain” areas.
The engineering concrete mixture developed limits the use of CEM I 52.5 cement and stays within the low-carbon threshold of the EXEGY matrix, with a carbon footprint of 239 kg of CO2 equivalent per cu. metre (i.e. 26% lower than the CEM I formula).
The formula was approved in the spring of 2024 by the project manager and the external inspector. The three concrete plants that supply the site are currently manufacturing the product, and implementation has been a success. In 2024, some 10,000 cu. metres of XF4 G+S concrete will be used on this project.
