31/01/2022 By acomputer 726 Views

Low-carbon concretes: solutions to reduce greenhouse gases

Batirama.com 21/06/20210

The search for "low carbon" concretes leads players to use all innovative solutions throughout the production process: cements, aggregates, construction, etc.

Announcements relating to the low-carbon strategy in building and RE 2020 lead the concrete sector to highlight its R&D work in terms of CO2* reduction. Two topics emerge: the production of cement and the choice of aggregates.

Here are the initiatives of the Ecocem and Hoffmann Green Cement manufacturers. Ecocem focuses attention on cements based on iron and steel slag. For Rory Mc Neill, commercial and market development director for Ecocem France, ground blast furnace slag proposed as a substitute for clinker in various cements and concrete solutions is “a fatal product resulting from the production of cast iron. This material shows 17 kgCO2/t. To be compared to the 765 kgCO2 kgCO2/t of a CEM I.

The company works in a joint venture with Arcelor Mittal, supplier of the raw material. Ground, activated and mixed, these cements are incorporated by its customers into concretes and mortars. Ecocem has doubled its activity in two years and sells 2.5 Mt of its cement in Europe, 1.5 Mt in France.

The Hoffmann Green Cement Offensive

Hoffmann Green Cement, created in 2015, offers low-carbon cements produced cold in reactors. The basic materials are blast furnace slags, clays, biomass ash. With a fundraising of €75M, the company built a first unit of 50,000t/year in 2017 in Bournezeau (Vendée).

The manufacturer is planning a second of 250,000t/year in Vendée, and another of the same size in the Paris region. “In 2025-2026, the company is aiming for 550,000 t of cement sold per year, i.e. the entire production capacity of its three sites, announces David Guglielmetti, development manager”.

Get rid of fossil fuels

For Mouloud Behloul, Innovation and Sustainable Construction Director at Lafarge Ciment, all the levers are activated to achieve the objectives of -40% CO? in 2030 – i.e. 475kgCO2/t of cement – and to carbon neutrality in 2050. He speaks of the “five Cs: clinker, cement, concrete [concrete], construction and carbonation. »

To reduce carbon of fossil origin during the production of clinker, the idea is to use 80% of waste in the fuel against 40-45% today. Added to this is the improvement in “clinker firing efficiency”, referring to the new kiln at the Martres-Tolosane cement plant (Haute-Garonne), which will reduce energy consumption by 25%.

Next comes the incorporation of cement additives – fillers, slags, fly ash – to reduce the clinker by 10 to 15%. On site, parsimony would become the rule: "Use the right concrete in the right place, without overdosing on cement", explains Mouloud Behloul.

Review the entire production chain

“These cements already reduce the carbon weight of the products in our FDES** by 35 to 40%,” recognizes Côme Lesage, strategic marketing and international strategy manager at ‎Rector, who works with Ecocem.

At the end of 2022, Rector will present ranges of low-carbon pre-slabs and beams. KP1 has started a technical collaboration with Hoffmann Green Cement since 2019. "We have to demonstrate the effectiveness of cement based on 65 criteria", explains Christophe Pacqueau, concrete and process manager at KP1.

The end of the end remains the substitution of the aggregate by materials of vegetable origin. At Alkern, Christophe Lagrange, director of the offer, pays attention to miscanthus within the framework of the Biomis G3 project carried out in Île-de-France. Alkern and Ciments Calcia are working on a plant block project. Alkern also follows research work on stabilized raw earth.

* RE 2020: low-carbon specifiers present solutions for concrete on Batirama.com, December 9, 2020.

** Environmental and health declaration sheets

Technical solution 1: Lightweight, low-carbon and high-comfort floor slabs

This constructive system presents technical interests – integration of networks –, acoustic, environmental and acoustic.

Seacoustic by Seac

What is the composition of this system?

This alternative to the full floor slab is inspired by the ground floor floors of individual houses. They include prestressed beams filled with wooden or polystyrene slabs or interjoists, all covered with a reinforced compression slab. It is also possible to integrate underfloor heating. The underside is loaded with mineral wool insulation protected by a plasterboard.

What type of construction is it intended for?

This thermo-acoustic solution is proposed for small collectives and establishments open to the public, with a maximum of R+3.

What is the point of this solution?

It makes it possible to practically divide by 3 the consumption of concrete for the creation of floor slabs: it also reduces the consumption of reinforcement. The savings in materials reduce site nuisances: noise, dust and waste. In the case of underfloor heating, certain solutions make it possible to avoid the floating slab. It is also compatible with the installation of a thermal break at the interface of the slab and the balcony. Its simplicity makes it a system suitable for implementation by small masonry companies.

Advantages : This type of slab makes it possible to choose the level of thermal resistance between floors according to the thickness of the insulation. Its construction method makes it an interesting solution for construction sites where a reduced carbon footprint is sought.

Limits : it is reserved for small collectives or for the construction of terraced houses.

Technical solution 2: Build with an all-concrete solution

It is possible to produce constructions with concrete block walls charged with concrete foam insulation, with roof insulation of the same type.

Airium concrete foam

What is this system made of?

It includes concrete blocks filled with a concrete foam, which has the property of creating insulation distributed around the perimeter of the exterior walls. The level of thermal insulation is optimal. The insulation of non-convertible attics is ensured by the same foam, poured out at the pump and to a thickness adapted to the projected thermal resistance.

What are its properties?

They are structural, thermal and environmental. The envelope in the same concrete material makes it possible to better control the continuity of insulation of the envelope. In addition, the material is resistant to fire, rodent and traditional aging of mineral wool materials related to moisture loading. By nature, the concrete material has an inertia which promotes a long phase shift and improves both insulation in cold periods and comfort in summer. This system can be implemented by all construction companies. The recycling of end-of-life constructions is simplified by the fact that it is not necessary to separate the components.

Advantages : This product is available in the catchment areas of the concrete plants authorized to formulate it.

Limits : It is essentially intended for individual houses and small collectives.

Standardization: pending the new version of NF EN 197-1

Under discussion for years, the new version of the European harmonized standard is promised for next summer. It conditions the development of low-carbon concretes.

While the revision work has been underway for more than five years, cement professionals - and, in fact, concrete - are still awaiting the release of the European Commission regarding the publication in the Official Journal of the European Community of the new version of the harmonized standard NF EN 197-1.

The latest announcements report a publication in July 2021. Text by definition unique for all European countries, it must revise the compositions of existing formulations, from CEM I to CEM V, and must create the new class of CEM VI, known as ternary cements.

Two cement families impacted

Two families of cements should be particularly impacted by the new standards, the main effect of which is to pave the way for "low carbon" concretes: CEM II/CM and CEM VI, both called ternary cements, i.e. say mixing three components: clinker, blast-furnace slag, limestone or pozzolan or other (see table).

They have the advantage of displaying an estimated carbon weight 50% lower than that of CEM I, given for 850 kgCO2/t, and 35% lower than the average of all the cements used (established at 650 kgCO2/t) .

This expectation of the standard also leaves time for research. From the mid-2010s, the idea of producing alternative cements for concrete with a very high level of mechanical strength (50 to 70 MPa) – therefore for public works – emerged, with only 50% of clinker and 30% clays calcined at low temperatures (450 to 650°C): LC3, an acronym for Limestone Calcinated Clay and Clinker Cement, to be translated as cement of calcined clays and crushed limestone.

An alternative to Portland cement, this mixture was developed by researchers at the construction materials laboratory of the École polytechnique fédérale de Lausanne (Switzerland). It would also display a carbon weight 50% lower than the Portland. Given the delays in discussing the new NF EN 197-1 standard, this new category of cement could also be included.

The composition of CEM II to CEM VI cements

Cement	Kind	Clinker	blast furnace slag	Natural or calcined pozzolans; siliceous fly ash	Limestone
Portland slag cement	EMC II/AS	80-94%	6 to 20%	-	-
EMC II/BS	65 to 79%	21 to 35%	-	-
Portland cement compound	CEM II/CM (S, P, V, L)	50 to 64%	16 to 44%	6 to 20%	6 to 20%
↔
CEM II/CM (P, V, L, LL)	50 to 64%	-	16 to 44%	6 to 20%
Blast furnace cement	EMC III/A	35 to 64%	36 to 65%	-	-
EMC III/B	20 to 34%	66 to 80%	-	-
EMC III/C	5 to 19%	81-95%	-	-
Slag pozzolanic cement	EMC V/A	40 to 64%	18 to 30%	18 to 30%	-
EMC G/B	20 to 38%	31 to 49%	31 to 49%	-
Compound cement	EMC VI (S, P, V)	35 to 49%	31 to 59%	6 to 20%	-
EMC VI (SL)	35 to 49%	31 to 59%	-	6 to 20%