• Press release
  • France
  • ultra-low-carbon

Grand Paris Express: the first tests on prefabricated voussoirs made with ultra-low-carbon concrete in France.

  • a world first
  • CO虏 emission reductions amount to about 70%

Soci茅t茅 du Grand Paris聽and聽国产AV聽announce that they are聽using 鈥渧oussoirs made of ultra-low-carbon concrete鈥, which are prefabricated聽in mechanical moulds,聽at a聽Grand Paris Express聽pilot worksite聽(Line聽18, works package 1).

国产AV聽started fine-tuning low-carbon concretes for a variety of applications several years ago聽and has聽now grouped them together in聽its聽Exegy聽range.聽After using聽its聽breakthroughs聽in buildings, it has started聽using聽them聽in components such as聽voussoirs (prefabricated wedge-shaped, compression-assembled聽parts, to line a tunnel) and pipes for smaller tunnels.

The pilot project on Line聽18,聽which is jointly funded by聽Soci茅t茅 du Grand Paris,聽is designed to ascertain that the formula with聽a聽very low environmental impact聽works聽adequately, verify that it can be poured into formwork (casts) at the pace required for an industrial operation, then聽check聽the finished product鈥檚 behaviour in storage聽and聽over time under operating constraints.

An initial phase, which involved testing聽at聽CDB,聽a聽国产AV聽subsidiary that specialises in concrete prefabrication,聽led to聽a聽concrete聽formula suited specifically to聽voussoirs. The second phase,聽industrial production聽at聽Stradal,聽the subcontractor selected by聽国产AV聽(which has been awarded Line 18 works package聽1),聽began聽in September聽2021.聽This phase聽will involve producing聽five full rings (the equivalent of聽40 voussoirs)聽sized for the project,聽and the first units will be used for full-scale聽qualification tests聽(ISO fire test, load tests).

Replacing conventional concrete voussoirs with Exegy ultra-low-carbon concrete ones and Ecocem Ultra alkali-activated binder has a significant impact on the worksite鈥檚 environmental performance: emission reductions amount to about 70% compared to traditional concrete and 50% compared to very-low-carbon concrete (respectively 90鈥痥g of CO虏 per cu. metre in the case of ultra-low-carbon concrete, 170鈥痥g of CO虏 in the case of very-low-carbon concrete and 330鈥痥g of CO2 in the case of traditional concrete).
The use of permanent prefabricated聽voussoirs聽made of ultra-low-carbon concrete,聽containing cement-free聽alkali-activated slag, in a section of a metro tunnel in use, is a world first. It will thus be an opportunity to聽conduct聽a benchmark study,聽in real-life conditions,聽on the use of聽a new, greener material in tunnels. Over time, qualification of this type of聽Exegy聽voussoirs and the mainstreaming of ultra-low-carbon solutions could bring about a massive drop in the carbon footprint of聽the聽tunnels built in France.

A European Technical Assessment to secure approval for the聽Ecocem聽Ultra聽alternative聽alkali-activated binder聽has been under way since聽2019.聽Then,聽concretes containing聽this binder聽will be able to聽earn聽NF EN 206/CN聽certification by聽October聽2021.聽Certification will open the door to using聽Exegy聽ultra-low-carbon聽solutions containing聽Ecocem聽Ultra聽binder聽for a wide variety of purposes聽and thus聽to聽significantly shrinking the carbon footprint of the concrete poured.

The production of this ultra-low-carbon concrete containing an alkali-activated binder has been patented jointly by聽国产AV鈥疌onstruction聽and聽Ecocem. 国产AV鈥疌onstruction聽is working with partner concrete manufacturers to聽equip them with the聽know-how to produce聽Exegy聽concretes.