Swiss researchers have proposed an ambitious solution to one of the most pressing challenges of climate change: storing the vast amounts of carbon that needs to be removed from the atmosphere. Their answer lies in an unexpected place—the concrete beneath our feet.
Scientists at Empa, the Swiss federal laboratory for materials science and technology, calculate that by converting captured carbon dioxide into building materials, specifically concrete aggregate, we could potentially eliminate all excess carbon from the atmosphere by the end of the century.
“These calculations are based on the assumption that after 2050 there will be enough renewable energy to remove carbon dioxide from the atmosphere, which is an energy-intensive task,” explains Pietro Lura, head of Empa’s Concrete and Asphalt Laboratory. “This hypothesis allows us to use different scenarios to analyze how realistic and efficient our concept of ‘mining the atmosphere’ plan is.”
scale of challenge
The numbers are staggering. To return atmospheric carbon dioxide concentrations to their 1988 levels of 350 parts per million, the threshold considered safe by climate scientists, about 400 billion tons of carbon would have to be removed from the atmosphere. This is equivalent to about 1.5 megatons of carbon dioxide.
Current carbon capture and storage methods typically focus on underground injection, but this approach faces significant challenges, including potential leakage risks and limited suitable locations. The Empa team’s proposal offers a different route: converting captured carbon dioxide into solid materials that can be used in construction.
From air to concrete: the new carbon cycle
The process begins by using renewable energy to capture carbon dioxide from the air and convert it into basic chemicals like methane or methanol. These materials are then converted into solid carbon materials that can be incorporated into concrete as aggregates (components of sand and gravel, which make up about 70% of concrete’s volume).
Researchers have identified two promising approaches. The first involves creating porous carbon aggregates that can replace up to 10% of traditional concrete materials. The second, more ambitious option is to use silicon carbide (SiC), an extremely hard material containing 30% carbon that has the potential to replace all traditional aggregates in concrete.
Carbon Neutrality Timeline
According to the team’s calculations, if implemented on a large scale after 2050, this approach could sequester about 1 billion tons of carbon per year. In the most optimistic scenario, using mainly silicon carbide aggregates, excess carbon in the atmosphere could be eliminated in about 50 years.
“Silicon carbide has huge advantages because it can bind carbon almost permanently and has excellent mechanical properties,” Lula points out. “However, its production is extremely energy-intensive, posing one of the biggest challenges both in terms of cost-effectiveness and sustainable implementation.”
economic opportunity
Unlike traditional carbon capture and storage, which is purely cost-effective, this approach can generate economic value. The captured carbon can be used to produce a variety of high-value materials, from polymers to carbon fibers and nanotubes, potentially helping to offset the cost of carbon removal.
The proposal also addresses another growing challenge: the global shortage of natural sand suitable for concrete production. By using captured carbon to create synthetic aggregates, the construction industry can reduce its reliance on natural resources while helping to combat climate change.
future challenges
Researchers acknowledge that significant obstacles remain. The whole concept depends on having abundant renewable energy after 2050.
The team stresses that this approach should be seen as part of a wider strategy to combat climate change. “Nonetheless, our goal should be to remove as much carbon dioxide from the atmosphere as possible every year, combined with other measures, to achieve 350 ppm CO2 emissions in a realistic time frame,” Lura said. “At the same time, it is vital to keep reducing emissions so that the recovery process is not in vain.”
The research was published in the journal Resources, Conservation and Recycling.
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