In Iceland, carbon dioxide captured from the air is pushed underground. There, in less than two years, it turns into carbonate, a mineral hard as rock. It is bound in such a way that it no longer pollutes the atmosphere. The Finnish company Carbonaide, which emerged from a research center, uses exactly this process to produce cement-free components that are as hard as concrete.
Around eight percent of man-made carbon dioxide emissions are produced during cement production. Carbonaide CEO Tapio Vehmas wants to change that. In just a few years, ten factories will be running in Finland producing prefabricated components that do not require cement, i.e. without the CO₂ that is produced. In addition, the components also bind the climate-damaging gas that is extracted from the air. In a pilot plant that Carbonaide operates in Hollola, Finland, paving stones for the construction company Skanska Group are already coming off the assembly line fully automatically.
In concrete, cement acts as a binder between the aggregate sand and gravel. Carbonaide replaces the binder with a mixture of blast furnace slag, green liquor from pulp production, and bio-ash from, for example, thermal power stations that burn wood. From this, the company mixes a paste and fills it into moulds. During setting, additional CO₂ is stored and petrified in a carbonation process. As in Iceland’s subsoil, the gas reacts with the calcium or magnesium silicates that make up the main part of blast furnace slag. The new type of concrete absorbs 60 kilograms of CO₂ per cubic meter of finished material. The process is therefore more than climate-neutral, it relieves the atmosphere and, if used on a large scale, could be effective against climate change.
1.8 million euros for the first large-scale plant
At least that’s what’s planned. Carbonaide received 1.8 million euros from the Finnish state, strategic investors and the local concrete industry to set up the first large-scale plant for cement-free components. It is designed to remove up to five tons of CO₂ from the atmosphere every day. Other planned factories should reach millions of tons a year.
Two other methods of producing concrete, in which part of the cement is replaced, are not quite as effective. Researchers at Rice University in Houston, Texas, rely on fly ash from fossil fuel power plants, from which they previously remove the heavy metals. In doing so, they replace 30 percent of the cement, and they estimate the reduction in emissions at 30 percent. In addition, the strength and elasticity of the concrete increase.
Researchers at the Massachusetts Institute of Technology (MIT) near Boston are achieving similar savings in greenhouse gas emissions. They are divided between the phase in which the concrete is mixed, i.e. it has a mushy consistency and has not yet set, and the phase in which concrete captures CO₂ from the air over time. This is already happening today, but not only has positive consequences. The carbon dioxide indirectly causes corrosion of the steel reinforcement, for example inside bridges. The MIT scientists prevented this effect with an unusual addition: they mixed sodium bicarbonate into the mixture of cement, gravel and sand, which is concrete after it had set. You actually know that from the baker. They call it simply: baking powder.