ºÚÁÏÍø

Our built environment is by far the world’s largest source of greenhouse gas emissions – in Finland, it accounts for around one third of all emissions. Most of these arise from the energy used in buildings, but the construction process itself also contributes significantly: over five million tonnes of COâ‚‚ equivalents, which is more than a third of the total emissions from the built environment. 

New districts in Helsinki, such as Kalasatama and Jätkäsaari, vividly illustrate where much of this comes from: grey concrete. The main ingredient in concrete is cement, and cement production is the single largest source of anthropogenic carbon emissions globally. 

But emissions start to accumulate even before the first building blocks are laid. Much of Finland’s geological soil is weak and soft clay, and strengthening such soil and transporting the resulting clay waste is both expensive and carbon-intensive. 

One of the most common ground improvement methods is deep stabilisation, where layers of clay, silt, or peat are reinforced with a binder to make them load-bearing. The binder is injected into the ground with compressed air to form column-like structures that stabilise the soil. Traditionally, a mixture of lime and cement – known as lime-cement – has been used as the binder, and its production accounts for 95% of the emissions from deep stabilisation. 

The emissions from ground improvement – as well as from other infrastructure construction, like roads, bridges and courtyards – haven’t been studied much so far. The estimated total is over two million tonnes of COâ‚‚ equivalents – roughly equal to the annual carbon footprint of more than 200,000 Finnish residents. 

What if COâ‚‚ could be locked in the ground? 

At the same time as urbanisation accelerates and construction expands onto ever softer ground – clay soils and peatlands – emissions need to drop close to zero. Finland’s national carbon neutrality target is set for 2035, and the City of Helsinki aims to reach it even earlier, by 2030. On top of that, Finland’s new construction legislation and the EU’s carbon border adjustment mechanism are also pushing the building sector to cut its emissions. 

But what if carbon dioxide could be locked beneath our feet – into roads, sidewalks and other concrete structures? What if construction were no longer just part of the emissions problem but part of the solution? 

‘We saw an opportunity here: the construction industry is in urgent need of low-emission materials, and at the same time, there’s an abundant supply of clay that’s considered unusable. Combining these two challenges could lead to a completely new and more sustainable solution,’ says Assistant Professor of Geotechnical Engineering Sanandam Bordoloi. 

Bordoloi’s research group is the first in the world to develop a binder material based on biochar that can bind CO₂ gas in a stable, solid carbonate form within the cementitious clay layer.  Lab tests have even shown negative emissions. 

‘Biochar is a by-product of the biofuel industry – and in Finland, we have plenty of it thanks to vast forest and biomass resources. Using biochar instead of cement as a binder for soil stabilisation could cut emissions from binder production by up to 75 percent – without compromising the durability of the structures,’ Bordoloi explains. 

‘And biochar has one more critical feature: it can sequester carbon dioxide directly from the environment,’ adds postdoctoral researcher Mohamad Hanafi, a member of the research team. 

Turning waste clay into a resource 

Bordoloi and Hanafi explain that the technology they have developed is not only low-emission but also quite simple. And it makes it possible to turn waste clay into construction material – without heavy industrial processes or transportation. In Helsinki alone, 340,000 cubic metres of waste clay are transported every year. 

‘We basically make construction material directly on site by mixing the clay with a minimal amount of binder and biochar. This way we avoid transportation costs, save emissions and meet the construction sector’s need to cut its climate impact,’ Hanafi says. 

Solving problems like this in today’s world requires a multi-disciplinary and multi-faceted approach – which is exactly why both Bordoloi and Hanafi have found their way ºÚÁÏÍø University. Bordoloi is originally from India but has worked as a researcher at the Hong Kong University of Science and Technology and the University of Illinois – both top universities in engineering. 

‘I’ve always had a curious mind from the get go, and I like to have global challenges that we as researchers can tackle. Of course, multidisciplinarity is nothing new to other universities either, but Aalto was formed around that idea. And that’s exactly what provides a safe space for doing explorative and experimental research,’ Bordoloi says. 

Mohamad Hanafi agrees. He completed his doctorate in Turkey, but Aalto’s strong focus on environmental issues is what he most appreciates here. 

But in addition to helping the climate, the researchers’ innovation also eases costs for companies – provided that funding and partners can be found to scale it up. 

Carbonaide’s innovation turns COâ‚‚ into concrete 

So how does a carbon-neutral or even carbon-negative innovation break through and reach large-scale production? Tapio Vehmas, CEO of Carbonaide, knows this journey well. He spent years as a concrete researcher at VTT and, before that, worked in various roles in the concrete industry. 

‘I’m a concrete guy through and through – my whole career has revolved around concrete,’ Vehmas says with a smile. 

Carbonaide’s method locks captured carbon dioxide into concrete during the curing phase. Once the concrete is poured, it simply needs to rest for a while to harden. During this time, COâ‚‚ is injected into the concrete, where it reacts and turns the cement into limestone and silica. The silica further densifies the concrete’s microstructure, making it even stronger – and because of this, less cement is needed in production. 

Their concrete can be used just like any conventional product: for example, the paving stones and parking areas of the new retail site of Northern Karelia Cooperative Society (Pohjois-Karjalan Osuuskauppa, PKO) were built using concrete made with Carbonaide’s technology – right under our feet. 

Perhaps surprisingly, this kind of modern technology was actually tested decades ago. But it wasn’t simply dusted off from a drawer – instead, Vehmas says, they ended up ‘reinventing the wheel.’ 

Climate goals require research – and courage 

Bordoloi emphasises that his team’s work is still in its early stages. The construction industry is conservative – for good reason, he adds. Structures must last at least 50–70 years, so any new material is naturally met with caution. Research is needed to prove how well and how safely these new materials perform. 

‘Besides ground stabilisation, realistic applications could include sidewalks, paving stones or parking areas – places where the load-bearing requirements aren’t as high as in buildings, and the lifespan can range from 5 to 30 years,’ Bordoloi says. 

The group’s partner, Mirva Koskinen, remains optimistic, although she acknowledges it will take years of work before the team’s innovation can become a commercial product. â€˜Many companies are already interested in this. But now we need to gather enough data through research and testing so that commercial producers can some day start manufacturing ready-to-use binder mixes for the market,’ Koskinen explains. 

Everyone agrees that research is crucial to make change happen. Koskinen also finds it frustrating that the construction sector rarely gets recognition as a driver of change and that its research is not always seen as ‘real science’. But it is a huge sector, tackling issues of global scale. 

‘To cut emissions and costs, we need innovations. And there won’t be any without the contribution of universities and research. That’s simply a fact,’ Koskinen states firmly. 

Achieving change demands research, funding, and a touch of radical creativity. 

‘It’s perfectly logical to be sceptical or even dismissive of new ideas – but then you should also be able to offer something better instead. If we truly want to reach ambitious climate goals, we need radical thinking. We need the courage to do something outside the box,’ Bordoloi says. 

This article has been published in the (issuu.com), September 2025.