Holcim and Sequens will build a residence in fully recycled concrete

It’s a world first“, according to Holcim France and Sequens. The cement manufacturer and the group’s subsidiary Housing action announce the construction of two buildings in entirely recycled concrete. This set of 76 housing units will be located in Gennevilliers (Hauts-de-Seine) and will be built from a concrete solution “unpublished“whose components are all made from recycled materials (cement, gravel, sand and water), with the exception of the various additives which represent around 2% of the weight of the concrete.

Material traceability

In detail, 100% recycled clinker, produced in 2022 in the Altkirch factory, in the Haut-Rhin, will be used. “The 2,000 tonnes of clinker produced saved around 3,000 tonnes of natural resources that would have been taken from the quarry. This clinker made it possible to produce, thanks to the addition of other recycled components such as slag, a standardized cement CEM III/A 42.5 N intended specifically for the project.“, explains Holcim France in a press release on March 28, 2023. “Although not prohibited by the standard, the manufacture of a completely recycled clinker-based cement has, for the moment, never been carried out beyond laboratory tests, and never been implemented to achieve everyday works. On the other hand, several standardized cements already include in their composition recycled additions from waste, such as slag fromindustry iron and steel or fly ash from thermal power stations.

Gravel and sand from Parisian concrete plants and various demolition waste from Ile-de-France make up the recycled aggregates. The rubble was transported to recycling platforms close to the future construction site, then sorted, crushed and screened. A laboratory was responsible for analyzing their properties to ensure proper compliance with the various normative thresholds. In total, nearly 2,200 tonnes of aggregates will be used for the Gennevilliers building.

As for the water, it is also recycled. It was previously used to clean equipment and infrastructure at the Gennevilliers plant. In case of additional need, rainwater stored in basins can be injected into the production.

Holcim concrete plant in Gennevilliers
Holcim concrete plant in Gennevilliers. © Holcim

“Push the limits”

A specific ATEx has been filed with the Scientific and Technical Building Center (CSTB) for the construction site. Through this approach, the two companies seek to “validate the test program for these new concretes and establish an initial database to advance knowledge of the behavior of recycled materials in concrete“.

Baptized “Recygénie”, this project will require the use of 1,600 m3 of recycled concrete to build the superstructure of five and six levels respectively. The two actors say they want “innovate to accelerate the development of concretes [dits] ecological“. For them, the goal of this project, “that pushes the known boundaries in terms of recycled concrete“, East “to deepen as much as possible the recovery of waste in the construction sector“. The two companies hope to do “progress“the uses of the sector in order to tend towards dwellings”more durable“.

Delivery scheduled for 2024

Cement and concrete experts from the Holcim group’s research and development center on Isle D’Abeau (Isère) and engineers and technicians from the national laboratory for the analysis of Lafarge France are working on this project which should be delivered at the end of 2024. The architecture firm A26 BLM, the design office Ingea, the desk Qualiconsult and the CSTB are also involved in “Recygénie”.

Holcim R&D Center
Aerial view of Holcim’s R&D center. © Holcim

Producing this first entirely recycled concrete is an unprecedented performance for which we have mobilized all our business expertise. […] We are proud of this construction start, which marks a decisive step for the ecological transition of all construction. This is just the beginning, recycled materials from demolition will occupy an increasingly important part in our products.“, said the general manager of Holcim France, François Petry.

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