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How low can you go?

10 Oct 23 In the increasingly urgent quest to find low-carbon construction materials, scientists are exploring a wide – and often unexpected – range of possibilities.

Carbonaide chief executive Tapio Vehmas (right) with chief operating office Jonne Hirvonen with samples of their ‘carbon-negative’ concrete products
Carbonaide chief executive Tapio Vehmas (right) with chief operating office Jonne Hirvonen with samples of their ‘carbon-negative’ concrete products

It is estimated that at least 8% of global carbon emissions caused by humans come from the cement industry alone – although the source of that statistic remains tantalisingly elusive.

But whatever the exact percentage, there is no doubt that cement production is a major contributor to global warming. The industry itself acknowledges the fact and consequently it is pouring money and resources into finding ways to decarbonise.

This article was first published in the May 2023 issue of The Construction Index Magazine. Sign up online.

Scientists all over the world are now collaborating with cement producers, governments and technology start-ups to develop new and often surprising alternatives to traditional cement and concrete.

In Finland, a new company called Carbonaide, has recently secured €1.8m (£1.6m) of seed funding from concrete producer Lakan Betoni and power generator Vantaa Energy to develop a method of producing what it claims will be “carbon-negative” concrete.

The company will use the money, supplemented with public loans and contributions from other investors and concrete companies, to build a commercial production line using new CO2 curing technology at a precast concrete factory in Hollola, Finland.

Carbonaide hopes that the factory-scale pilot unit will be able to mineralise up to five tonnes of CO2 per day and increase production of its carbon-negative concrete products 100-fold.

Carbonaide’s production technique uses a carbonation method that binds carbon dioxide into precast concrete using an automated system at atmospheric pressure. The technology is said to be able to halve the CO2 emissions of traditional Portland cement concrete by reducing the required cement content and mineralising CO2 into concrete.

The process uses industrial by-products, such as industry slags, bio-ash and green liquor dregs from paper production, instead of normal cement, to bind the aggregate together. The result is concrete with a negative carbon footprint, claims Carbonaide.

This article was first published in the May 2023 issue of The Construction Index Magazine. Sign up online.

While industrial by-products such as pulverised fuel ash and ground granulated blast-furnace slag have long been used as cement substitutes in concrete mixes, Carbonaide’s method differs in that CO2 is permanently stored and removed from the carbon cycle.

The CIRCLE project has trialled shellfish concrete at several sites, including the Euroveloroute V4 in France
The CIRCLE project has trialled shellfish concrete at several sites, including the Euroveloroute V4 in France

“We have demonstrated in the pilot unit that our technology is capable of reducing the CO2 emissions of conventional concrete by 45%,” says Tapio Vehmas, chief executive of Carbonaide.

“Last autumn, we demonstrated lowering our products’ carbon footprint to -60 kg/m3 by replacing Portland cement with slag. Our first pilot unit had limited capacity, so we’re grateful to our investors for the chance to upscale our technology to a factory-sized pilot and demonstrate the technology full-scale.

“Our goal at Carbonaide is to create a more sustainable future with cutting-edge tech that doesn’t just reduce the carbon emissions of construction materials like concrete, but that traps more CO2 than they emit throughout their lifetime. It is very natural that the constructed environment becomes a CO2 sink as it is the largest volume of man-made material,” adds Vehmas.

With governments introducing carbon taxes, emission trading mechanisms and renewable energy targets, and consumers willing to pay a premium for low-carbon products, material producers and construction companies are increasingly drawn to such innovations, says Juho Hiltunen, chief executive of Lakan Betoni.

“As new innovations take ground, the demand for low-carbon products will likely increase. New technologies, such as Carbonaide, provide the means for the industrial-scale production of affordable low-carbon products,” he says.

“We’re happy to support Carbonaide to scale up its production and realise the world’s first CO2 curing integration to a fully automated precast concrete production line.”

Matti Wallin, business director at Vantaa Energy, adds: “Avoiding carbon dioxide emissions should always be the primary mechanism to foster biodiversity. However, carbon capture and permanent storage of unavoidable CO2 emissions are needed to enable a sustainable carbon cycle, for example in the waste-to-energy sector.

“Carbonaide technology is an excellent example of how to both reduce and utilise existing CO2 in new products and permanently store carbon from the cycle,” continues Wallin.

This article was first published in the May 2023 issue of The Construction Index Magazine. Sign up online.

Carbonaide now plans to open 10 production lines for carbon-negative concrete in the Nordic countries by 2026. If successful, by 2050 these plants could bind up to 500 million tonnes of carbon dioxide annually, the equivalent of almost 20% of the concrete market’s carbon emissions.

The project has been part of VTT LaunchPad, a science-based spin-off incubator, where VTT researchers and technology are brought together with entrepreneurs and investors to drive industrial innovation.

Meanwhile, closer to home, scientists at the University of Strathclyde have discovered that crushing rock in the presence of carbon dioxide gas can result in trapping carbon in a stable, insoluble form, thus reducing emissions.

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Carbonaide’s first pilot plant in Hollola, Finland. The company now plans to scale up commercial production
Carbonaide’s first pilot plant in Hollola, Finland. The company now plans to scale up commercial production

A paper published in the journal Nature Sustainability says that almost no additional energy would be required to trap the carbon.

More than 50 billion tonnes of rock is crushed worldwide every year and current crushing processes – widely used in construction and mining – do not capture CO2.

Previous work has explored trapping carbon into single minerals by the same method, but the research at the University of Strathclyde shows this is unstable and the CO2 dissolves out of the mineral when placed in water. 

The paper documents how a larger proportion of carbon dioxide can be trapped in a stable, insoluble form in rocks composed of multiple different minerals by grinding it in CO2 gas. The resulting rock powders can then be stored and used in the environment for construction and other purposes.

The abstract for the paper, called Mechanochemical processing of silicate rocks to trap CO2, reads: “Polymineralic rocks such as granite and basalt, whether high or low in carbonate-forming metals, are more efficient at trapping CO2 than individual minerals. This is because the trapping process is not, as previously thought, based on the carbonation of carbonate-forming metals.

“Instead, CO2 is chemically adsorbed into the crystal structure, predominantly at the boundaries between different minerals. Leaching experiments on the milled mineral/rock powders show that CO2 trapped in single minerals is mainly soluble, whereas COtrapped in polymineralic rocks is not.

“Under ambient temperature conditions, polymineralic rocks can capture >13.4 mgCO2 g−1 as thermally stable, insoluble CO2. Polymineralic rocks are crushed worldwide to produce construction aggregate. If crushing processes could be conducted within a stream of effluent CO2 gas (as produced from cement manufacture), our findings suggest that for every 100 Mt of hard rock aggregate sold, 0.4–0.5 Mt CO2 could be captured as a by-product.”

Scientists at Strathclyde University have found that carbon can be captured by crushing rocks such as granite and basalt in a stream of effluent CO2 gas
Scientists at Strathclyde University have found that carbon can be captured by crushing rocks such as granite and basalt in a stream of effluent CO2 gas

Principal investigator Rebecca Lunn, a professor in the University of Strathclyde’s Department of Civil & Environmental Engineering, says: “The hope is that the sector could reduce the emissions by adapting the current set-ups to trap carbon from polluting gas streams such as those from cement manufacture or gas-fired power stations.”

“If the technology was adopted worldwide in aggregate production, it could potentially capture 0.5% of global CO2 emissions – 175 million tonnes of carbon dioxide annually. Future research can pin this down, as well as optimise the process to trap more carbon.”

Co-investigator Dr Mark Stillings says: “Now we know that CO2 trapping in most hard rock can be done in a lab, we need to optimise the process and push the limits of how much can be trapped through the crushing technique. We then need to understand how this process can be scaled up from the lab to industry, where it can reduce global CO2 emissions.

“If this process was applied, the CO2 footprint associated with building houses and public infrastructure could be greatly reduced, helping to meet global objectives to combat climate change.”

Professor Lunn adds: “In the future, we hope that the rock used in concrete to construct high-rise buildings and other infrastructure such as roads, bridges and coastal defences will have undergone this process and trapped CO2 that would otherwise have been released into the atmosphere and contributed to global temperature rise.”

The work was part-funded by the Engineering & Physical Sciences Research Council, whose deputy director Dr Lucy Martin comments: “This breakthrough research from the University of Strathclyde, which EPSRC has proudly played a part in funding, is truly revelatory. It points to a new process for the construction industry that could significantly reduce global carbon emissions and help us meet our net zero goals.”

While crushing rock is not the most obvious method of reducing carbon emissions in the construction process, an even more unexpected process is at the heart of the CIRCLE project, an Anglo-French research programme investigating the use of shellfish waste to produce a sustainable permeable concrete product.

This article was first published in the May 2023 issue of The Construction Index Magazine. Sign up online.

The project, which began three years ago, is led by French organisation Builders for Society (Ecole d’ingénieurs), with materials company Eqiom (part of the CRH group), Communauté d’Agglomération des Deux Baies en Montreuillois, the University of East Anglia (UEA), the University of Central Lancashire (UCLan) and French local authority Golfe du Morbihan.

Over the past three years the partners have established that shellfish waste can successfully substitute for traditional aggregates to reduce and preserve non-renewable components.

Simultaneously, the use of shellfish waste tackles another environmental issue by recycling waste materials from the fishing industry.

The final CIRCLE event – presentation of the findings – took place at UEA in Norwich at the end of February when researchers presented their results on optimising the concrete formulations and from monitoring the durability of the material and its draining properties over the seasons.

Speakers presented case studies of the concrete trialled at several pilot sites, particularly the Eurovéloroute V4 pilot site and the Ostreapolis project, both in France.

Research carried out at UEA’s Norwich Business School is now focusing on business models that can support the adoption and marketing of this new concrete product.

Using seashells in concrete can also recycle waste from the fishing industry
Using seashells in concrete can also recycle waste from the fishing industry

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