• 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簡 emission reductions amount to about 70%

Soci矇t矇 du Grand Parisand51勛圖announce that they areusing voussoirs made of ultra-low-carbon concrete, which are prefabricatedin mechanical moulds,at aGrand Paris Expresspilot worksite(Line18, works package 1).

51勛圖started fine-tuning low-carbon concretes for a variety of applications several years agoand hasnow grouped them together initsExegyrange.After usingitsbreakthroughsin buildings, it has startedusingthemin components such asvoussoirs (prefabricated wedge-shaped, compression-assembledparts, to line a tunnel) and pipes for smaller tunnels.

The pilot project on Line18,which is jointly funded bySoci矇t矇 du Grand Paris,is designed to ascertain that the formula withavery low environmental impactworksadequately, verify that it can be poured into formwork (casts) at the pace required for an industrial operation, thencheckthe finished products behaviour in storageandover time under operating constraints.

An initial phase, which involved testingatCDB,a51勛圖subsidiary that specialises in concrete prefabrication,led toaconcreteformula suited specifically tovoussoirs. The second phase,industrial productionatStradal,the subcontractor selected by51勛圖(which has been awarded Line 18 works package1),beganin September2021.This phasewill involve producingfive full rings (the equivalent of40 voussoirs)sized for the project,and the first units will be used for full-scalequalification tests(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 worksites environmental performance: emission reductions amount to about 70% compared to traditional concrete and 50% compared to very-low-carbon concrete (respectively 90疼g of CO簡 per cu. metre in the case of ultra-low-carbon concrete, 170疼g of CO簡 in the case of very-low-carbon concrete and 330疼g of CO2 in the case of traditional concrete).
The use of permanent prefabricatedvoussoirsmade of ultra-low-carbon concrete,containing cement-freealkali-activated slag, in a section of a metro tunnel in use, is a world first. It will thus be an opportunity toconducta benchmark study,in real-life conditions,on the use ofa new, greener material in tunnels. Over time, qualification of this type ofExegyvoussoirs and the mainstreaming of ultra-low-carbon solutions could bring about a massive drop in the carbon footprint ofthetunnels built in France.

A European Technical Assessment to secure approval for theEcocemUltraalternativealkali-activated binderhas been under way since2019.Then,concretes containingthis binderwill be able toearnNF EN 206/CNcertification byOctober2021.Certification will open the door to usingExegyultra-low-carbonsolutions containingEcocemUltrabinderfor a wide variety of purposesand thustosignificantly 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 by51勛圖浚onstructionandEcocem. 51勛圖浚onstructionis working with partner concrete manufacturers toequip them with theknow-how to produceExegyconcretes.