If concrete were a country, it would be the third largest emitter of greenhouse gases on Earth, behind China and the United States.
How to make this material, essential for habitat, construction and global infrastructure, less damaging to the planet?
How bad can it be?
Cement is the most widely used material on Earth, consumed to make concrete at a rate of around 150 tonnes per second.
According to the Global Cement and Concrete Association (GCCA), approximately 14 billion cubic meters of concrete are poured each year.
Cement production alone accounts for up to 7% of global CO2 emissions, or three times the emissions produced by aviation.
“This is more than all the emissions of the European Union or India, just behind those of China and the United States,” Valérie Masson-Delmotte, a key contributor to Groupe d, told AFP. intergovernmental experts on climate change from the UN.
And with ever increasing rates of urbanization in Africa and Asia, the global impact of this basic building material will only increase.
How does cement emit CO2?
Cement is the main binder that holds pebbles and stones in concrete together. It is mainly composed of clinker, a residue produced by firing clay and limestone in a kiln.
When heated, CO2 is produced.
In order to make one ton of cement, the 1400C firing process produces about one ton of CO2.
This chemical reaction, which has remained unchanged since the manufacture of cement more than 200 years ago, is responsible for 70% of the sector’s emissions.
The remaining 30% comes from the energy used to light the ovens themselves.
How to reduce emissions?
The concrete industry has said it wants to be carbon neutral by 2050. In October, it set itself the goal of reducing its emissions “by an additional 25%” by 2030.
This would save around five billion tonnes of CO2 over the decade.
Purging the sector of CO2 emissions relies heavily on technologies such as carbon capture and storage (CCUS), which have yet to be deployed on a significant scale.
But it also offers changes such as recycling old concrete and replacing hydrocarbons in its blast furnaces with biofuels.
State-run giants such as the China National Building Material Company have pledged to “play their part” in decarbonizing the industry.
At the other end of the scale, several startups are offering new ways to cut emissions.
The American company Solidia plans to capture the CO2 and use it to dry out the concrete mix, thereby minimizing the amount of water needed for production.
In Canada, CarbonCure is exploring how to inject liquefied CO2 into concrete and store it there.
Perhaps more importantly, the industry is banking on the development of new “green” cements, made from recycled materials.
In Britain, 26% of concrete is already made this way, according to the GCCA.
In May, France, home to several large concrete companies, issued new regulations on cement production.
Starting next year, all new buildings will be subject to carbon restrictions for their lifetime, from construction to demolition.
Is “green” cement the future?
As it stands, most green cements are made by new producers; traditional manufacturers say it will take time to modernize their existing machines.
One of these start-ups, Hoffman Green Cement, manufactures cement in France from industrial waste: clay sludge, blast furnace slag and fly ash, which are a by-product of coal combustion.
Even with a price of 25 € more expensive per square meter, demand is strong, explains founder Julien Blanchard.
“The cement industry plans to phase out its emissions by 2050,” he said. “With our revolutionary solutions, we can get them started now.”
The stakes for the planet are high: the UN estimates that three quarters of the world’s infrastructure by 2050 remains to be built.