Removal Technology Spotlight — Concrete Mineralisation

Welcome to our ‘Spotlight’ series. We’re on a mission to make the process of addressing residual emissions as transparent and accessible as possible for companies across all sectors. This is why we’re launching our ‘Spotlight’ series in which we’ll be profiling a broad range of nature-based projects and carbon removal technologies.

In each edition, we’ll give you a useful overview of how a given project or technology works, its features and benefits, as well as some of the challenges that it presents. We’ll also interview one of our partner project leaders to help bring the project or technology to life. 

As of 2017, the carbon footprint of the cement industry accounted for approximately 7% of the world’s CO2e emissions. The reduction of cement carbon emissions poses a major challenge, as over 60% of them are closely linked to its production. This environmental impact cascades down to the manufacturing of concrete, of which cement is a key ingredient. But scientists have found a solution to decarbonise this value chain by using recycled concrete or similar waste materials as a CO₂ sequestration media. In this edition of our ‘Spotlight’ series, we’ll explore the process of concrete mineralisation and speak to one of our partners who specialises in mineralisation as a negative emissions technology.

What is carbon mineralisation?

Carbon dioxide mineralisation is a process in which CO₂ reacts with alkaline compounds to form solid carbonate minerals. CO₂ mineralisation removes carbon dioxide from the air and stores it permanently in a range of possible locations: e.g., within underground rocks or concrete (as described below). There are various sources of alkalinity that can be used, including naturally occurring silicate materials, or waste materials from industrial or mining operations.

What is concrete mineralisation?

Carbon mineralisation in concrete is a technique which involves injecting the captured CO₂ into fresh or recycled concrete, thus permanently removing it from the atmosphere.. 

The process happens in 3 stages: 

  1. CO₂ is removed from the atmosphere through direct air capture (DAC) or by harvesting it from biogenic treatment processes such as biogas production.

  2. The liquefied CO₂ is transported to a concrete mineralisation plant. 

  3. At the plant, concrete is injected with the captured CO₂. 

What are the benefits of concrete mineralisation? 

The CO₂ is irreversibly bound to the concrete

The major advantage of this approach over natural carbon sinks (e.g., ocean, trees) is that the embodied carbon in concrete has no chance of returning into the atmosphere. In other words, carbon dioxide is permanently stored inside the concrete.

It reduces the need for cement in fresh concrete

Another additional benefit of carbon mineralisation is an increase in the concrete strength, which is a property given by cement. This translates into a reduced demand for cement in fresh concrete, thus slashing the carbon emissions of its manufacturing. 

It does not impact concrete workability 

Studies have demonstrated that even with 8% less cement, concrete can reach the same workability without changing the setting time. 

Concrete Future’s Roadmap — scaling concrete mineralisation

The Global Cement and Concrete Association (GCCA) has released a roadmap that outlines its actions towards a net zero future. Here, carbon capture utilisation and storage (CCUS) is highlighted as a key strategy. The association is planning to work with policymakers and investors to help de-risk and scale the technology. To reduce the carbon footprint of concrete, GCCA aims to develop 10 CCUS commercial plants across the world by 2030. While concrete mineralisation is a proven process, its industrial use is not yet widespread. With Pledge, you can help scale this technology-based carbon removal as we provide access to these projects. On top of that, you’ll be able to address your residual emissions.

Spotlight on our partner: neustark

neustark prides itself in enabling permanent CO₂ storage in concrete - and being one of the first to roll out this negative emissions technology in both a commercially and ecologically viable manner. In 2020, the company pioneered the market with their modular plants, enabling producers to capture CO₂ in recycled concrete. Today, neustark’s technology as well as its value chain from source to sink to carbon dioxide removal (CDR) client already helps remove significant amounts of CO₂ .

We spoke to Lisa Braune, who leads neustark’s CDR activities, to find out more about their work

You use reclaimed concrete materials in your processes. Why is this beneficial?

The benefits are two-fold: Our primary goal is to capture and store permanently CO₂ in recycled concrete thanks to our mineralisation technology. These emissions would have otherwise gone into the air, and since the source of the CO₂ is biogenic, we’re not offsetting the emissions, but rather removing them. As an add-on, through the injection of CO₂ in the demolished concrete, producers that we partner with can reduce the amount of cement needed to make concrete.

What is the source of your CO₂, and why is this important?

The CO₂ that we source is biogenic. Biogenic carbon emissions are those that originate from biological sources such as plants, trees, and soil. Burning biomass emits carbon that is part of the biogenic carbon cycle (as compared to burning fossil fuels, which releases carbon that has been locked up in the ground for millions of years). In other words, the carbon absorbed by the plants while growing simply returns to the atmosphere.

When neustark’s technology injects CO₂ into concrete, it is permanently stored there and removed from where it would otherwise land, i.e., in the atmosphere. And since the CO₂ is biogenic, this sequestering process generates negative emissions. Neustark’s first and principal source partner is the biogas plant Arabern in Switzerland. We are soon launching partnerships with various other biogas plants to capture and transport their CO₂ to our local sink sites.

How much CO₂ are you able to store in the concrete? How does this compare to a tree?

Currently, we can store 10 kg of CO₂ per m3 of concrete – and we’re working on the optimisation of this figure. In terms of speed, our latest plant stores 220 kg of CO₂ per hour in concrete granulate. As a comparison, fast-growing pine trees absorb about 20 kg of CO₂ per year. So one neustark plant can do in one hour what 11 trees need a whole year for. Or, in other words, within 24 hours, one neustark plant can store the same amount of CO₂ in concrete granulate as the CO₂ that is on average emitted by two single-family homes heated with oil in Switzerland in a year.

Is the CO₂ released back into the atmosphere once a building built with neustark concrete is demolished?

No. The mineralisation process, which is the core of neustark’s technology, enables permanent CO₂ storage. Permanent means that the fraction of carbon dioxide stored through mineral carbonation that is retained after 1,000 years is virtually certain to be 100%. Even if the concrete in which the CO₂ is injected gets demolished again and again, the CO₂ will not be released into the atmosphere. There are many negative emission technologies that are in theory, and an increasing amount in practice, viable. They all certainly have their benefits, but mineralisation is one of the few technologies that warrants permanent carbon removal.

Could you tell us a little about the additional benefits of your concrete mineralisation process?

Our primary goal is to sequester CO₂ ,but there’s another benefit for the recycled concrete producers that we work with. The CO₂ that is permanently bound through the mineralisation process turns into limestone. Limestone is a key ingredient in the production of cement, which is in turn a key element of concrete. And the production of cement is the carbon-intensive part of the process. As they need less cement, concrete producers will generate less emissions. So, aside from storing captured CO₂ ,our technology also helps to reduce the one emitted by concrete manufacturing.

What are your growth plans? And are you facing any challenges with scaling?

In 2030, we aim to permanently store 1 million tons of CO₂. And we’re scaling up accordingly to deliver that amount of carbon removal. In 2020, we tested the technology and process with our pioneer plant. In 2021, we rolled out our first stationary site, and in 2022, had four sites up-and-running in Switzerland - and storing CO₂ successfully, around 300 tons to date. 2023 is the year of international expansion and when we’re starting to massively scale up our operations. In 2023, we aim to store at least a tenfold of the amount we stored in 2022, and the exponential growth path only continues from there!

Of course, that brings some challenges. Scaling up requires significant financial investments and a fast-growing team and network of partners in various locations to manage. What’s more, the carbon removal market is relatively new and rapidly evolving, so we need to observe and help shape the market – also from a policy point of view.

How is neustark different from other projects using similar technology?

The technology is not the trickiest part – though further optimisation is always possible and needed. It’s rolling it out and keeping all pieces together that’s complex. And neustark was one of the first to prove that the business model is both ecologically and commercially viable.

We cover the whole process, the whole value chain, not just part of it like various other players. We work with biogas plants to source our CO₂and install a technology at their existing plant to capture and liquify the emissions. We then transport the liquified CO₂ to our partner concrete recyclers. We’ve installed our technology as add-ons to their site, injecting the liquified CO₂ into the demolished concrete granulate during the recycler’s production process. Doing so, we’re permanently storing the CO₂ into the recycled concrete produced by our partner.

And last but not least, we work with companies that have ambitious net-zero strategies and are looking for partners to achieve their goals. Most companies cannot achieve net-zero by just reducing their emissions, they also need to tap into carbon removal. So they can acquire neustark’s CDR – and hence indirectly invest into our company and the scale-up of our facilities. And ultimately, the impact we can deliver – it's a win-win-win, for our partners, our CDR clients and, most importantly, all generations on our planet!

Thank you Lisa

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