Researchers from the University of Cambridge, UK, have developed a method to produce very low-emission concrete at scale – an innovation they claim could be transformative in the transition to net zero.

The method uses the electrically-powered arc furnaces used for steel recycling to simultaneously recycle cement, the carbon-hungry component of concrete.

Concrete is the second-most-used material on the planet, after water, and is responsible for approximately 7.5% of total anthropogenic CO₂ emissions. A scalable, cost-effective way of reducing concrete emissions while meeting global demand is one of the world’s biggest decarbonisation challenges.

Concrete is made from sand, gravel, water and cement, which serves as a binder. Although it’s a small proportion of concrete, cement is responsible for almost 90% of concrete emissions. Cement is made through a process called clinkering, where limestone and other raw materials are crushed and heated to about 1,450°C in large kilns. This process converts the materials into cement, but releases large amounts of CO₂ as limestone decarbonates into lime.

The Cambridge researchers found that used cement is an effective substitute for lime flux, which is used in steel recycling to remove impurities and normally ends up as a waste product known as slag. But by replacing lime with used cement, the end-product is recycled cement that can be used to make new concrete.

The cement recycling method, reported in the journal Nature, does not add any significant costs to concrete or steel production and significantly reduces emissions from both concrete and steel, due to the reduced need for lime flux, claim the scientists.

Recent tests carried out by the Materials Processing Institute, a partner in the project, showed that recycled cement can be produced at scale in an electric arc furnace (EAF), reportedly the first time this has been achieved. Eventually, this method could produce zero emission cement, if the EAF was powered by renewable energy.

The Cambridge Electric Cement process has been scaling rapidly, and the researchers say they could be producing 1bn t/y by 2050, which represents roughly a quarter of current annual cement production.

New study offers a pathway for fossil fuel-burning operations to capture emissions
Meanwhile, a costly step in the process of taking CO₂ emissions and converting them into useful products such as biofuels and pharmaceuticals may not be necessary, according to University of Michigan researchers.

The presence of CO₂ in the Earth’s atmosphere is a key driver of climate change, with the burning of fossil-fuels accounting for 90% of all CO₂ emissions. New US Environmental Protection Agency (EPA) regulations introduced in April call for fossil fuel plants to reduce their greenhouse gas (GHG) emissions by 90% by 2039.

Researchers point out that carbon is needed to make many products we depend on daily, such as clothing, perfume, jet fuel, concrete and plastic. But recycling CO₂ typically requires that it be separated from other gases – a process with a price tag that can be prohibitive.

Now, new kinds of electrodes, enhanced with a coating of bacteria, can skip that step. While conventional metal electrodes react with sulphur, oxygen and other components of air and flue gases, the bacteria seem less sensitive to them, claim the University of Michigan researchers.

‘The microbes on these electrodes, or biocatalysts, can use smaller concentrations of CO₂ and seem more robust in terms of handling impurities when compared with electrodes that use metal catalysts,’ explains Joshua Jack, Assistant Professor of Civil and Environmental Engineering, and key author of the paper published in Environmental Science Nano. ‘Platforms that use metals seem to be much more sensitive to impurities and often need higher CO₂ concentrations to work. So, if you wanted to take CO₂ directly out of power plants’ emissions, the biotic catalyst may be able to do it with minimal cleanup of that gas.’

The analysis showed that by using waste gases or air directly, recycling CO₂ from dilute sources could become economically viable.

New metal-free porous framework with potential for nuclear and hydrogen applications.
Meanwhile, researchers at the University of Liverpool and the University of Southampton in the UK have used computational design methods to develop non-metal organic porous framework materials (N-MOFs), with potential applications in areas such as catalysis, water capture and hydrogen storage.

In a study published in the journal Nature, the research team says that the N-MOFs have yet to be fully explored but have already shown early promise for the capture of iodine, which is important in the nuclear industry.