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Cutting the carbon out of concrete
The Radical Ceramic Research Group is pioneering potentially transformative alternatives to traditional concrete, the world’s second largest source of emissions.
Written by Amanda Ruggeri
Video Anna Berg
Photos Mikko Raskinen and Johannes Kaarakainen
One day in early 2023, doctoral researcher Ville Repo was in his laboratory testing clay from the region of Kainuu, eastern Finland. His goal: to see if, after being heated to 750° C and appropriately processed, it could replace the cement in concrete.
Half of the sample was kaolinite – a common, soft mineral, often white, that originates from the chemical weathering of certain minerals over millions of years. Kaolinite has been researched, and occasionally used, as a cement alternative around the world. After heating it, Repo cooled the clay, pulverised it, and mixed it with an alkaline solution to dissolve aluminates. The results of the strength test shocked him. Concrete made with the Finnish clay reached a strength of up to 74 megapascals. Regular concrete measures around 30 to 50.
The potential for a kaolinite mix to outperform concrete was exciting. The concrete industry is the second largest source of carbon emissions, accounting for 8% of the world’s total – a ‘horrendous amount of CO2’, says Repo, who studies mineral-based materials and mechanics at Aalto University. Most of the greenhouse gases are emitted when the limestone is processed and heated to around 1,450° C, and there are also emissions from transporting limestone and other materials over long distances for production.
Meanwhile, the world’s desire for concrete – or a material like it – is only growing. In 2020, about four billion tons of cement were used globally. That’s more than double the amount used just twenty years ago.
As a result, researchers like Repo are trying to find cement alternatives that can be produced using less energy and, ideally, local materials. Rocks rich in kaolinite, known as Kaolin, are common in most of the world, making kaolinite an ideal candidate. So for most researchers, those test results would have been a big win. But not for Repo.
That’s partly because kaolin isn't widely deposited in Finland, so Repo wants to find something more local. But there’s more to it than that. ‘We could have taken the easy way out and done cool stuff with just the kaolin,’ he says. ‘But we're trying to find something new, go a bit further.’
A radical approach
‘Going further’, pushing the boundaries of knowledge to pioneer new processes and materials, could be the unofficial anthem of an innovative new group at Aalto that Repo is part of.
Founded in 2022, the Radical Ceramic Research Group brings together researchers from very different disciplines – from arts to materials science, design to civil engineering – to share ideas, techniques, and even soil and clay samples. Their goal? To investigate how natural substances like clays could be used as geopolymers and alkali-activated materials. Geopolymers – polymers made of minerals that can be used in place of limestone-based cements – could be a greener alternative for everything from construction concrete to studio ceramics, both because they require less heat to produce and because they can be made from local materials, meaning less transportation.
Maarit Mäkelä, a professor of design in the group, is excited about the progress they’ve made so far. ‘We've already been able to make small-scale geopolymers that are the perfect, perfect shape – mainly cubes,’ she says.
In June, her team presented the research group's first official paper, highlighting their initial finding that geopolymers can be a lower-energy alternative to ceramics, which often need to be fired at temperatures of up to 1,300° C. The geopolymer mixes that her team used – which included mixes with raw Finnish clay, volcanic rock and even porcelain waste – didn't need to be fired at all. Instead, they were cured at just 80° C.
But geopolymers don’t just take less energy to make, the researchers say. They can also be made by re-using waste material which would otherwise go into landfills.
In Finland, clays tend to be too soft to directly build on, says Repo. ‘So when we’re building, we usually need to deal with the clays,’ he explains. ‘We have vast amounts of waste clays that are just dug out from construction sites and dumped in landfills. That also consumes quite a lot of energy because of how far the soils are transported.’ For example, in Helsinki alone, about 800,000 cubic meters of uncontaminated waste soils are transported an average 50km or more to landfills each year.
The researchers in the Radical Ceramic Research Group envision a different kind of future, one in which the clay dug out at a building site is mixed with cast-off shards of ceramics from a local factory, treated on-site, and used for construction right there.
According to Luis Huaman, a doctoral researcher in Civil Engineering at Aalto University, that vision isn't as far-fetched as it might seem. Like others in the research group, he was pulled into the world of geopolymers from a different background: in his case, geology.
In his native Peru, Huaman worked with Professor Joseph Davidovits, the world-leading pioneer of modern geopolymers. Huaman was especially interested because of the many ways the technique could be used in Peru. Mining is common in the country, and separating out the ore typically results in by-products – usually toxic – that are stored in earth-filled dams called tailing dams. Tailing dams are not only environmentally disruptive but can also be unsafe, with failures relatively common and sometimes deadly.
‘There’s a need to reduce the amount of tailings and the amount of residues that are stored in the dams. Currently, there are no green uses for them, and in some cases they can be dangerous,’ Huaman says. He realised that some of these residues were silicates – which could be used as fillers for geopolymers.
With the right materials, the process to make a geopolymer is actually ‘very simple’, he says. First, sodium, potassium silicate or sodium hydroxide are mixed with materials like kaolin or fly ash. Then fillers – such as sand or the leftover silicates from mine tailings – are added to the mixture. The material is left to dry at room temperature or cured in an oven. A day later, the mix is hard enough to be used. Not only is the resulting material as strong, or stronger, than concrete but some mixtures have additional benefits, like being fire-resistant.
‘That's one thing that caught my attention about geopolymers: they’re not difficult to produce. You can actually make them in a kitchen,’ he says. ‘Bringing an industrial process to isolated locations is difficult, but if you develop something that’s easy to make on-site, then that’s more suitable for our needs.’
Ancient to contemporary
While these innovations feel cutting-edge, it may be more correct to think of them as revitalising ancient practises, notes Mäkelä. Davidovits has theorised that 1,400-year old megalithic structures made of volcanic tuff at Tiahuanaco, Bolivia, used geopolymers; others have pointed to ancient Roman concrete, a mixture of volcanic ash and quicklime. ‘This work is really revisiting old techniques,’ she says. This is part of what intrigues her so much about the topic. ‘I conceive of myself very much as the kind of craftsperson who believes that, because of the state of the planet, we should go back and look at the traditions and materials we used to use, which are much more sustainable.’
When we speak, Mäkelä is getting ready for her sabbatical. She will be living near Nuorgam village in North Finland, next to the Teno River, where around half of inhabitants are Sami. While familiarising herself with local craft traditions, she found indications of the use of local clay; she will be living near where locals presumably dug up clay and made their own tiles. ‘The Sami are seen as an innovative people, because historically, it has sometimes been quite difficult to get materials that aren’t local’ – and, as a result, they've had to come up with other methods, she says.
On a global, industrial scale, using local materials is less common. ‘It's no secret that the construction industry is really conservative, so there’s not much of a driver coming from individual companies,’ says Repo. So far, the largest project using geopolymers was Brisbane West Wellcamp Airport in Australia, completed in 2014 with about 40,000 cubic metres of geopolymer concrete.
Still, Repo sees reasons to be optimistic. ‘I’ve seen changes in the mindsets of concrete and cement manufacturers. They're aware that they’re producing an enormous amount of CO2 emissions, and they’re really keen to lower them,’ he says. A few companies around the world already produce geopolymers. In Finland, the materials technology company Betolar produces a cement-free concrete which they claim reduces CO2 emissions by up to 80%.
In his lab, Repo continues to test new clay samples, some of which he has access to via the other researchers in the Radical Ceramics group. He hasn't found a silver bullet to replace kaolin yet, but he’s hopeful. ‘Our clays have what we call mica minerals – these really soft, sheet silicate minerals. And some of them have some analogies with kaolinite in their layered structure and chemical composition, like similar ratios of aluminates and silicates,’ he says.
But the research is very much at the experimental stage, and he knows it may come to little at all. ‘There's a high possibility of failure,’ he says. ‘But if it works, it could be a game-changer’ – not just for Finland, but for the rest of the world, too.
Want to see the beautiful work of the Radical Ceramics group live? Welcome to our Designs for a Cooler Planet exhibition!
This year the projects aim to shed light on the hidden and noteworthy. Fascinating prototypes, experiments, and perspectives on display can transform the way we see, think and act.
Come and explore the Invisible through over twenty creative and experimental research-based projects that encourage us to look beyond the surface and consider what lies beneath.
The exhibitions are free and open for everyone.
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