Removing carbon with recycled concrete already today

The latest report by the IPCC has pointed out the urgency with which we have to fight climate change stronger than any report before. Moreover, it made one thing perfectly clear: our time is running out. If we want to reduce global heating to below 1.5°C, we have to start decarbonizing and reduce our emissions wherever possible. However, even after drastically reducing our emissions, there will remain unavoidable emission. We have to address this by developing and scaling permanent carbon removal technologies. And we have to do it fast.

Concrete is the world’s largest waste stream. Neustark’s vision is to turn this waste stream into a carbon sink. To achieve that, we provide a solution that mineralizes CO₂ and stores it in recycled concrete aggregate. In 2017, we started developing this process and in 2020 we commissioned a first mobile prototype. As of today, neustark can announce the scaleup of its system to a fully commercial level.

The project

The scaleup was achieved through an installation which has been built by neustark for the concrete producer Kästli Bau, who has operated it ever since March 2022. Concrete aggregate is produced by Kästli Bau by crushing demolition concrete for the subsequent reuse in road construction or the production of new concrete. After crushing, the concrete aggregate is transported via conveyor belts to silos where it is stored. Kästli Bau’s existing storage silos have been retrofitted with neustark’s technology to permanently store CO₂ in concrete aggregate through mineralization. Through the new installation, a reaction volume of 250m³ was created, which shows a scale up by a factor of 10 compared to Neustark’s existing mobile pilot. By increasing the reactor volume, the daily throughout capacity could be increased up to 750 tons of concrete aggregate.

The technology

At the heart of the patented process lies the online CO₂ measurement system, which is based on multiple CO₂ flow and concentration measurements. The system has been revised as part of the scaleup and the first months of operation show, that CO₂ losses are reduced and CO₂ uptake is simultaneously increased — all without compromising on the precision of the measurements.

The CO₂ flow comes from a nearby wastewater plant. The biogenic CO₂ produced by the plant — which was released into the atmosphere before — is captured from point source. A remote level control for the liquid CO₂ storage tank ensures that neustark can take care of a smooth and continuous CO₂ supply.

The captured CO₂ is mineralized in the concrete aggregate and thereby stored permanently. On top of that, the carbonated concrete aggregate increases the compressive strength of the concrete. As a result of that and with a clever mix design, Kästli Bau can reduce the cement content by up to 10%. Overall, the CO₂ footprint of its concrete is lowered by 10%.

Whenever possible the technology makes use of existing material storage infrastructure. If at specific site no such infrastructure is available, neustark can offer an efficient material box solution to integrate it neatly.

The technology

The scaleup of neustark’s technology has been realized in the framework of the project DemoUpCARMA which is led by the ETH Zurich. The project explores the implementation and scale-up of negative emissions technologies while taking into account economical, regulatory, political and societal factors. Funded by the Swiss Federal Office of Energy (SFOE) and the Federal Office for the Environment (FOEN) it brings together 24 partners from both academia and industry aiming at advancing urgently needed carbon removal technologies from R&D stage to market readiness.

Under DemoUpCARMA the operation of the plant will be scientifically accompanied for 15 months. The Swiss Federal Laboratories for Materials Science and Technology (EMPA) strives to develop new low carbon concrete mix designs based on carbonated recycled concrete aggregates. The Paul Scherrer Institute (PSI) will conduct a dedicated life cycle analysis which will take into account the operational data of the plant as well as its surrounding value chain for quantification of environmental benefits and potential adverse side effects of the new technology and mix designs.

Key Take Aways

• Concrete is the world’s largest waste stream.
• The Swiss company neustark is transforming this waste stream into a carbon sink.
• The technology can be integrated in existing infrastructures and processes and enables industrial partners like Kästli Bau to lower the emissions of their concrete already today.
• The project DemoUpCARMA brings together high-level partners from academia, industry and policy to enable and further develop low carbon removal based on neustark’s technology.
• neustark provides a commercial solution for CO₂ mineralization that can be integrated in existing concrete recycling processes and infrastructures.