It is in our roads, in wind turbine masts, nuclear power stations, skyscrapers, in social housing blocks, in both modestly-priced housing estates and upmarket architectural houses … it is everywhere. Every second, close to 150 tonnes of concrete is poured in the world. In just one year that would be enough to cover the whole of France in a grey layer.
The environmental cost of this huge production of concrete is colossal. Concrete suffocates the soil, clogs up rivers, destroys habitants, pollutes the air and erodes beaches. It is also one of the main producers of greenhouse gas emissions after coal, oil and gas. The image often used is that if concrete were a country it would be the third biggest emitter of CO2 after China and the United States.
For a long time the leading manufacturers of concrete were not much concerned about their carbon footprint. “Recent decades in France have been marked by a certain wait-and-see attitude on the sector's part,” said The Shift Project, a think tank run by engineering consultant and academic Jean-Marc Jancovici. But with the climate crisis growing the pressure has increased on major CO2 emitters and they have accordingly stepped up the number of public pronouncements about their willingness to help the environment.
In October 2021 the Global Cement and Concrete Association unveiled its road map to reach zero carbon by 2050. The French cement industry had done the same thing a few months earlier. Its leading names have competed with each other in their promises to save the planet. The multinational Lafarge, for instance, has boasted of being the “first construction material company to commit itself to Net Zero” and the vast majority of the announcements made by its communications team now concern its decarbonisation efforts.
Enlargement : Illustration 1
Concrete is made from water, sand, gravel and cement and it is the cement which is responsible for close to 90% of its carbon footprint. So decarbonising concrete means in effect decarbonising cement. Making cement involves a mixture of clay and chalk being heated for hours at high temperatures to produce what is called 'clinker'. This material makes up 80% to 100% of Portland cement, the most commonly used type. This production method produces a lot of CO2: when it is burnt the chalk gives off large quantities of the gas and this process represents two thirds of cement's carbon footprint.
“To improve cement's carbon performance there's therefore no choice other than to reduce the quantity of clinker in its composition,” writes Florent Dubois, who is in charge of sustainable construction at Lafarge, in his recent book Béton écologique et construction durable ('Ecological Concrete and Sustainable Construction') published by Eyrolles in January 2022 and which supports the potential of “green concrete”.
Like other producers, Lafarge is capable of making cement with less clinker or even none at all. That is, for example, what the company HoffmannGreen does at their ultra high-tech plant in west France. “We only use waste and by-products from industry, which is mixed cold with our activators,” said the firm's president Julien Blanchard.
Another start-up firm has shown what it can do in the world of green cement: Ecocem. It has two sites in France that result from a joint venture with the global steel giant Arcelor-Mittal. At the bottom of the group's blast furnaces in Dunkirk in the north and Fos-sur-Mer in the south of France there is a waste product called slag, an off-white powder. Rather than throw it away, it can be used to replace some of the clinker used to make cement.
The slag-based cement from Ecocem will be used to build the Olympic Village for the Paris Games in 2024 and the tunnels for a new metro line – line 18 – in the capital. The building sites for the Olympic Games and this major new transport route – which are about to use millions of tonnes of concrete, not all of it so responsibly sourced – have thus been able to show off some green construction credentials. However, this is no environmental revolution.
Niche market
Many of these 'low carbon' products were discovered a long time ago, in particular blast furnace slag. They were already used the end of the 19th century to build the Paris metro. In other words, the use of slag-based cement to build the new metro line does not represent a major turning point.
“These alternative cements are struggling to get pass the niche market stage because of their cost, their different properties and the available of the raw materials which they need,” says the French environment agency ADEME. For example, according to the World Steel Association 97% of blast furnace slag is already recovered and reused. “If you wanted to increase the quantity of slag to produce more low-carbon concrete you'd need to produce more steel … an industry that emits almost as much [carbon dioxide] as the cement industry … You then fall into an environmental absurdity of polluting more to make less polluting materials at the end of the chain,” said Matthias Dreveton, a structural engineer and specialist in low-carbon concrete.
Another problem is that anyone who ventures into the tortuous and opaque world of carbon calculations quickly discovers that the carbon performance claimed by the majority of 'green cements' is not always reliable. To start with, there is no official definition of 'low-carbon cement': and no rule about which cement to compare it with, nor over the threshold at which a cement becomes 'green'.
So when Société du Grand Paris, the state enterprise building the new underground line in Paris, pats itself on the back and states that “70% of the new metro will be made with low-carbon concrete” it is the company itself that has set its own rules. “By that we mean a concrete that produces 40% fewer CO2 emissions than an equivalent concrete made with CEM1 cement [editor's note, which contains 100% cement], the one that emits the most,” it states. But it could equally well have set the bar differently.
Is a low-carbon concrete really low carbon? You can't say that..
Just to make it even more confusing, cement makers have the right to keep their formula secret and the carbon footprint on the labelling of their product is hard to verify. In January this year the French group Vicat unveiled a 'carbon-negative cement'. But how is it made and of what? Questioned about it at the time, Vicat declined to say more, referring to the need to protect its intellectual property rights.
Few companies ultimately opt for complete transparency by publishing their data, for example, on the INIES database – which provides environmental and health data on construction products and equipment – which has a verification programme. Even here there can be controversy, in particular over the methods used to make the calculations.
The best-documented example is the use of blast-furnace slag in the majority of 'green cements'. Its CO2 footprint is considered to be nil in carbon calculators. “But that doesn't represent reality,” said Matthias Devreton, who has written a study on the issue. “In the end it allows cements made with slag to label themselves as having exceptional environmental performance but their real impact is three times higher than the actual calculations,” he said.
This bias is well known within the scientific community. “It's been an underlying issue since 2004,” said Adélaïde Féraille, a researcher at the École des Ponts science, engineering and technology institute. “Two years ago the government took up the issue by putting together a group of experts. A conclusion was reached but there were disagreements so it dragged on. This issue of the carbon footprint of slag also arises for other by-products used to make low-carbon cements,” added the researcher, who said the rules are due to change on September 1st.
“Is a low-carbon concrete really low carbon? You can't say that,” concludes Guillaume Jarlot, CEO at Nooco, an online software platform that measures the environmental impact of building projects.
To summarise this with a real example, consider the case of a bag of PLANET® cement marketed by Lafrage as the “most eco-responsible available on the French market”. This product has not been declared on the INIES database so instead one has to go by the data supplied by the manufacturer.
Reading the product information sheet, one quickly realises that it is not carbon neutral but has less carbon; the neutrality is achieved thanks to carbon-offsetting strategies. One also learns that it is made of slag whose carbon footprint is not counted. The result is that this cement probably produces less carbon but is certainly not carbon neutral – contrary to how it is marketed.
The risky gamble on carbon capture technology
Green cement is not a miracle solution and the manufacturers are fully aware of this. According to projections from the industry trade body the Syndicat Français de l’Industrie Cimentière, carbon neutrality in this sector will mainly be reached thanks to what is touted as a new saviour technology, the capture and storage of CO2.
The idea is to capture the carbon produced during the making of the clinker and then store it either offshore or inside the cement itself. This last option is regularly cited by manufacturers who note that concrete can, like trees, store carbon dioxide. “The manufacturers are very engaged with these technologies that avoid having to deal with the issue at the moment of production,” said Léa Mathieu-Figueiredo from the climate network Réseau Action Climat. But it is a risky gamble.
In a report published in July 2020 the ADEME agency listed the main limitations of these technologies. For example, they will produce no results in the medium term because they are not yet mature technologies. Another problem is that while they reduce carbon emissions at a site, they can cause other environmental impacts there: increased water contamination, higher emissions of nitrogen oxides (a pollutant), the production of waste amines (a dangerous waste product) and so on.
What happens to the carbon dioxide once it is captured? If it is re-injected into the cement – which does not last forever – it will return to the atmosphere one day. If it is stored offshore, then what legacy does this leave for future generations? “The deployment of these technologies is restricted by the limited storage possibilities, which make just 20% of French cement makers potentially eligible and at a non-negligible cost,” says ADEME.
Lobbying for the status quo
Once the drawbacks with green cement and carbon capture become apparent there is little else that can be done to save the planet other than to stop using concrete altogether. The most carbon-neutral concrete is the concrete that is never poured. If the miracle technology of carbon capture promised by manufacturers does not materialise in France then the country will have to cut the amount of concrete it uses by half to reach net zero by 2050, according to ADEME's own calculations. This reduction will come in part from demographic change and developments in construction but also from “a very restrictive regulatory framework in order to fight against the concreting over of the land and reducing new construction”, it says.
The problem is that this kind of restraint is not really on the manufacturers' agenda. “Concrete is a lucrative, conservative and very capitalistic business. The manufacturers have invested in their quarries, their manufacturing tools, it's not at all in their interest for things to change,” said HoffmannGreen's Julien Blanchard. It is true that the sector is now making announcements and promises and investing real money in climate issues. “But it remains insufficient and there are still lots of gaps. There's movement but nothing very restrictive,” said Léa Mathieu-Figueiredo from Réseau Action Climat.
Whenever the government tries to tighten the vice a little more the construction industry lobby groups immediately protest. Most recently the new environmental regulation RE2020 led to some particularly strong clashes within the opaque world of technocrats, far removed from the glare of the media. This regulation sets the carbon thresholds that must not be exceeded when constructing a building. The thresholds are staged, with a first level in force from January, a second one set for 2025 and a final one for 2028. It was published in January this year after two years of delay and lots of lobbying.
The result was a huge slab of new regulations which is not really going to change things. “The lobbying in favour of the status quo worked very well,” said Thierry Rieser of the association négaWatt, part of the expert groups who were consulted during the drawing up of these regulations. “We saw a gap grow between our proposals and the first draft of the text following the phase of consultation with the manufacturers. In the end the mountain gave birth to a mouse,” he added.
Engineering firm Bastide Bondoux carried out a study into the impacts of RE2020 on the concrete sector. The study was based on plans for a concrete-built multi-unit residential development that was representative of the market and constructed without any particular environmental demands. “It could pass the first threshold of RE2020 without changing anything,” said the engineer who carried out the study, Hala Rochdi. And for it to meet the next threshold in 2025 very few changes would be required, for example a modification to the design of the skirting board. Concrete, it seems, still has a future.
-----------------------------------------------------------------------
- The original French version of this article can be found here.
English version by Michael Streeter