The ready-mixed concrete sector presents its solutions to decarbonize construction

Concrete, an essential link in construction since the beginning of the 82th century, is found in 74% of collective housing in France, 50% of tertiary buildings, and around 80% of individual houses. Knowing that ready-mixed concrete (BPE) represents 39% of concrete production in France, this means that it has a considerable weight in our industrial landscape (3 million m2023 produced in mainland France in XNUMX) .

Concrete is by nature a material that meets today's challenges: its 100% recyclable nature in the form of aggregates, its ability to trap CO2, its ability to build at height and therefore to limit urban sprawl, its role key in the energy transition as a constituent of wind turbine bases, dams, soft transport infrastructure, etc. are real assets.

While the 2020 Environmental Regulations (“RE2020”), which came into force in January 2022, reinforce the requirements for results in terms of building design, comfort and energy consumption, the ready-mixed concrete sector ( BPE) does not rely on its intrinsic strengths. She was one of the pioneers in terms of approaches and sharing of environmental data, and continues to mobilize to meet the objectives set by RE2020.

The BPE sector is part of a logic of sobriety and innovation, both to decarbonize or even capture carbon, but also to respond to comfort issues. The idea is to build better with less, to live better, move around better, live better, while preserving the planet.

The national ready-mixed concrete union, the SNBPE, takes stock a year and a half after the entry into force of RE2020, and presents its solutions to go even further, during a conference of press organized at La Maison des Centraliens, Tuesday September 19, 2023.

Ready-mixed concrete: a material that meets current construction challenges

Ready-mixed concrete is a 100% recyclable material

If 80% of demolition concrete is now recovered, the sector has set itself the objective of increasing the recycling of deconstruction concrete into concrete.

The commitment of stakeholders in the sector has resulted in the evolution of the normative context with the revision of the following standards:

aggregate standards NF EN 12620 of June 2008 and NF P18-545 of September 2011 which specify the characteristics and properties of recycled aggregates;
concrete standard NF EN 206-1/CN of December 2012 which authorizes the use of recycled aggregates from deconstruction for the manufacture of concrete.

This normative development now makes it possible to construct buildings with recycled concrete. A new step was even taken in 2023 with the construction of the first fully recycled concrete building in Genevilliers! A first which could open the way to a new constructive mode.

Ready-mixed concrete is a Co2 trap

The ability of concrete to trap carbon dioxide is linked to the natural phenomenon of carbonation. Throughout the life of a structure, atmospheric CO2 penetrates the concrete from its surface. It is absorbed by its cement matrix which then transforms into limestone. Carbonation makes it possible to capture 15 to 25 kg of CO2 per cubic meter of concrete during the life of a structure. The concrete of existing structures therefore permanently traps millions of tonnes of CO2. When the structure reaches the end of its life and at the time of its demolition, the crushing of the concrete multiplies the surface area offered to CO2. Thus, the capacity of concrete to capture carbon can lead to carbon-negative concretes, that is to say made from recycled concrete aggregates having previously been enriched with CO2 (permanent carbon sink); the national Fastcarb project exploits this property through several demonstrators.

Ready-mixed concrete helps combat urban sprawl

By its properties, concrete lends itself to the verticality of works, and to the creation of infrastructures. Underground and high-rise construction limits urban sprawl and the artificialization of land by densifying the urban fabric.

Ready-mixed concrete enables the energy transition

The bases of wind turbines, dams, transport infrastructures and the development of soft mobility rely on the resistance properties and mechanical performance of concrete.

A BPE sector committed for a long time to the decarbonization of construction

A desire for absolute transparency on environmental impacts since the 2000s

The best way to design more environmentally friendly constructions is to know the ecological impacts of their components. The FDES, documents presenting the results of the Life Cycle Analysis of a product (as well as health information) are there for that.

However, in the case of ready-mixed concrete, the default data is not enough to optimize the design; it is essential to use the most precise environmental data possible, truly corresponding to the concretes and reinforcements used.

This is why the SNBPE has developed the BETie configurator for ready-mixed concrete, making it possible to integrate the data most suited to the situation of a project. Thus, the eco-design of the structure upstream can lead towards solutions allowing significant gains: use of the right exposure classes, rationalization of reinforcement rates, implementation of constructive solutions (thickness, solid elements vs. hollow elements, etc.).

The BPE sector was a pioneer in this area, carrying out its first FDES in the early 2000s. The work of the SNBPE has largely contributed to the global database, and the FDES are easily identifiable in the Environmental Guide for Major Works (GEGO). ) offered with free access.

This absolute transparency on environmental impacts, and more particularly on the carbon footprint, is not only an incentive to comply with the regulations in force, it also constitutes a very valuable tool for project managers who now have all the cards in hand to eco-design their sites and constructions.

Research and development in the sector: the concrete of tomorrow will be low, very low, or even ultra-low carbon

Although “low carbon” concrete does not yet have an official definition, nor a normative or regulatory framework – work is underway at the French and European levels – it is however understood that it corresponds to concrete which, “for properties, performances, qualities of use and durability equivalent to those of a reference concrete", generates lower greenhouse gas emissions.

Semantic characterization decided or not, the concept is well recognized. This involves optimizing the formulations traditionally applied to make concrete: better dosage of sand, gravel, cement, water and additives for greater performance and lower carbon weight. Careful R&D work has resulted in innovative solutions already available on the market, and low-carbon concrete is already widely used.

The SNBPE has also published a document proposing thresholds to be reached for representative parts of structures, depending on the exposure classes and the concrete strength class. The values of these thresholds are 15% lower than the average for traditional concretes.

Steps taken on production sites, construction sites and BPE transport

Reducing the carbon footprint also involves improving the energy efficiency of BPE production units, construction equipment and transport.

Substantial investments have made it possible to modify processes to make them less energy-intensive.

Concrete is a material produced and used locally thanks to a dense network of 1.900 concrete plants distributed as close as possible to construction sites. The distances between production sites and construction sites do not exceed 15 kilometers.

If the BPE travels over very short distances, the sector's efforts focus on:

increased use of river and rail transport to transport the raw materials necessary for the production of concrete,
the use of trucks with green engines which will reduce the concrete transport footprint to 0.

A mobilization of all stakeholders to build better

The BPE sector has been mobilizing for many years to work with all players in the construction sector to activate the many levers to reduce the carbon footprint of buildings.

Increasingly sophisticated tools for eco-designing projects from the outset

By carrying out more in-depth reflection from the design of works, and by using digital models (BIM) more frequently, it is possible to increase the precision, execution and quality of construction with the aim of sobriety and reduction CO2 emissions.

At the same time, the development of 3D printing allows more streamlined constructions, using less material and which can be built in shorter time frames. This greater flexibility opens up new possibilities for the construction sector.

Also, the use of the performance of ultra-high performance fiber-reinforced concrete (UHPFRC) offers innovative applications, particularly for very thin, perforated or perforated structures previously inaccessible to concrete material.

Better use of the material

Based on the principle of using “the right concrete in the right place”, many levers for reducing the carbon footprint of buildings are possible, including:

Optimization of the choice of concrete exposure classes: depending on the exposure or not to precipitation of the different facades or elements of a building, different classes of concrete can be used, making it possible to lower the carbon footprint . On the contrary, the use of a single class of concrete would increase the overall carbon footprint of the building.
The use of low-carbon concrete also makes it possible to reduce the footprint of structures.
The development of the use of prestressing by post-tensioning also represents an important lever for decarbonization. This technique is widely used abroad, particularly for slabs or floors.
The use of more resistant concrete for posts or beams will reduce their section, their volume and therefore their footprint.

The mix of materials reduces the carbon footprint while increasing performance

It has been proven that combining concrete and other materials for the structure and envelope of buildings only has advantages, whether in terms of a lower carbon footprint or final efficiency. The qualities of each material can be taken advantage of, and their defects erased.

For example, concrete offers excellent resistance to compression, but not to traction, while steel is particularly efficient in this area. The steel-concrete mix has thus largely proven itself. And all structural elements are concerned: posts, beams, mixed floors, thin walls, etc.

Material mix projects are also likely to develop considerably, depending on the works and the regions: concrete in the foundations, combinations of prefabricated concrete and wood/plaster, or even concrete or concrete blocks containing wood.

The already notable developments should continue beyond 2031 in a multi-criteria approach

There is no doubt that RE2020 has borne fruit, but given the difficulty in attaching a label to examples of works, due to a lack of references, it is desirable to put in place, thanks to the consultation of the stakeholders concerned and the collection of data, a reliable RE2020 State Label, with a solid benchmark.

This is the reason for Cap 2030: a series of technical works aimed at creating a common reference framework and broadening the current regulatory field to other environmental aspects (sustainable water management, circular economy , biodiversity, health, etc.).

If the SNBPE has always supported RE2020, it regrets the abandonment of the operation of the E+ C- observatory, as well as the choice of the simplified dynamic life cycle analysis method. And to go beyond 2031, in the sense of a multi-criteria approach, he calls for a Level(s) type approach, supported by the European Union, which uses the main sustainability indicators, tested with and by the building sector, to measure carbon footprint, materials, water, health and comfort, climate change impacts, life cycle costs and performance estimates.

Conclusion

The carbon neutrality objective is as noble as it is essential, it is above all achievable given the degree of mobilization of all players in the sector.

The SNBPE also organizes Regional Meetings bringing together players in the construction value chain, in particular to support design offices and architects. This involves presenting the profession of producer of ready-mixed concrete, demonstrating the interest of concrete solutions for construction, recalling the availability of the FDES BETie configurator approved by the State, sharing the good practices, and to discuss a local project.