Carbon-capturing Celour paint allows anyone to "participate in CO2 removal in their daily lives"

Design graduate Kukbong Kim has developed a paint made from demolished concrete that is capable of absorbing 20 per cent of its weight in carbon.

Called Celour, the paint can sequester 27 grams of CO2 for every 135 grams of paint used.

"That is the same amount of carbon dioxide that a normal tree absorbs per day," Kim said.

The indoor-outdoor paint is made of waste concrete powder, a cement-based residue from concrete recycling that is normally buried in landfills, where it can alkalise the soil and have a detrimental effect on local ecosystems.

Celour is a carbon-capturing paint that comes in three colours

Through a chemical process called mineral carbonation, which takes place when the paint reacts with the CO2 in the surrounding air, Kim says Celour can reabsorb a significant part of the emissions that were generated by producing the cement in the first place.

Eventually, she hopes to optimise the capturing capacity of the paint so that it completely negates the carbon footprint of the cement it is made from.

"I think it is too early to describe Celour as carbon neutral," Kim said. "It needs further study but I want to make it a carbon-negative product. That is my goal."

"It's not enough if we just stop emissions, as we already have high levels of CO2 in the air," she added. "We need to participate in CO2 removal in our daily lives."

Concrete naturally reabsorbs some of the carbon it emits

Cement is the most carbon-intensive ingredient in concrete and is responsible for eight per cent of global emissions.

But when concrete is recycled, only the aggregate is reused while the cement binder is pulverised to create waste concrete powder and sent to landfill, where it can disturb the pH balance of the surrounding soil.

"Waste concrete powder is high in calcium oxide," Kim explained. "And when it is buried and comes into contact with groundwater or water in the soil, it turns into calcium hydroxide, which is strongly alkaline."

The waste concrete powder is filtered, pulverised and mixed with a binder, water and pigments

With her graduate project from the Royal College of Art and Imperial College London, the designer hopes to show the usefulness of this industrial waste material by maximising its natural ability to capture carbon.

Studies have shown that cement already reabsorbs around 43 per cent of the CO2 that is generated in its production through the mineral carbonation process.

This is set off when concrete is cured by adding water, which reacts with the calcium oxide in the cement and the CO2 in the air to form a stable mineral called calcium carbonate or limestone.

A traditional concrete block continues to cure throughout its life but because this process is reliant on exposure to air, only its outer layers will react with the CO2 while its core will remain uncarbonated.

Celour could store carbon for thousands of years

But Kim was able to improve the material's carbon-capturing capabilities by turning the waste concrete pounder into a paint, mixed with a binder, water and pigments.

This is spread thinly on a surface so that more of the material is exposed to the air and can carbonate.

In addition, the coarse powder was further filtered and pulverised to increase the relative surface area of the particles while a polyvinyl alcohol (PVA) binder creates small gaps for air to enter.

"I have done a lot of experiments with different ingredients to maximise carbon absorption by increasing the surface area that comes into contact with carbon dioxide in the air," she explained.

"Graphene, which can capture lots of carbon thanks to its structure, was also considered as a binder but excluded because it is currently priced high and cannot be mass-produced."

The paint can be used both indoors and outdoors

Cement has long been used to create traditional paint, which is also capable of sequestering CO2. But Kim hopes to harness these carbon-capturing benefits while keeping a polluting waste material out of landfills and avoiding the emissions associated with making new cement.

How long the paint is capable of storing carbon is dependent on what happens to it after it is no longer needed. But Kim says it could be locked away for thousands of years unless exposed to extreme heat, which would alter the chemical structure of the carbonate.

As part of our carbon revolution series, Dezeen has profiled a number of carbon capture and utilisation companies that are working on turning captured CO2 into useful products from bioplastic cladding to protein powder and concrete masonry units.

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