'Absolute miracle' breakthrough provides recipe for zero-carbon cement

'Absolute miracle' breakthrough provides recipe for zero-carbon cement
Old concrete can be recycled in furnaces used to recycle steel, in a new method that drastically reduces the CO2 emissions of both
Old concrete can be recycled in furnaces used to recycle steel, in a new method that drastically reduces the CO2 emissions of both
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Old concrete can be recycled in furnaces used to recycle steel, in a new method that drastically reduces the CO2 emissions of both
Old concrete can be recycled in furnaces used to recycle steel, in a new method that drastically reduces the CO2 emissions of both

Concrete and steel production are major sources of CO2 emissions, but a new solution from Cambridge could recycle both at the same time. Throwing old concrete into steel-processing furnaces not only purifies iron but produces “reactivated cement” as a byproduct. If done using renewable energy, the process could make for completely carbon-zero cement.

Concrete is the world’s most used building material, and making it is a particularly dirty business – concrete production alone is responsible for about 8% of total global CO2 emissions. Unfortunately it’s not easy to recycle back into a form that can be used to make new concrete structures.

Scientists have of course been investigating ways to make concrete greener. That can include changing the recipe to switch out the most polluting ingredients – specifically limestone – or designing concrete so that it absorbs more CO2 from the air after it’s laid. For the new study, Cambridge researchers investigated how waste concrete could be converted back into clinker, the dry component of cement, ready to be used again.

“I had a vague idea from previous work that if it were possible to crush old concrete, taking out the sand and stones, heating the cement would remove the water, and then it would form clinker again,” said Dr. Cyrille Dunant, first author of the study. “A bath of liquid metal would help this chemical reaction along, and an electric arc furnace, used to recycle steel, felt like a strong possibility. We had to try.”

An electric arc furnace needs a “flux” material, usually lime, to purify the steel. This molten rocky substance captures the impurities, then bubbles to the surface and forms a protective layer that prevents the new pure steel from becoming exposed to air. At the end of the process, the used flux is discarded as a waste material.

So for the Cambridge method, the lime flux was swapped out for the recycled cement paste. And sure enough, not only was it able to purify the steel just fine, but if the leftover slag is cooled quickly in air, it becomes new Portland cement. The resulting concrete has similar performance to the original stuff.

Importantly, the team says this technique doesn’t add major costs to either concrete or steel production, and significantly reduces CO2 emissions compared to the usual methods of making both. If the electric arc furnace was powered by renewable sources, it could essentially make for zero-emission cement.

The technique has already been trialed in furnaces that produce a few dozen kilograms of cement, and the researchers say the first industrial-scale trials are underway this month, where it would be producing about 66 tons of cement in two hours. The researchers say that the process could scale up to produce one billion tonnes of "electric cement" by 2050.

"Producing zero emissions cement is an absolute miracle, but we’ve also got to reduce the amount of cement and concrete we use," said Professor Julian Allwood, who led the research. "Concrete is cheap, strong and can be made almost anywhere, but we just use far too much of it. We could dramatically reduce the amount of concrete we use without any reduction in safety, but there needs to be political will to make that happen.

"As well as being a breakthrough for the construction industry, we hope that Cambridge Electric Cement will also be a flag to help the government recognize that the opportunities for innovation on our journey to zero emissions extend far beyond the energy sector." A patent has been filed for the process, as the first step towards commercialization.

The research was published in the journal Nature. The team describes the work in the video below.

The world's first process for making zero emissions cement

Source: Cambridge University

Since cement absorbs CO2 as it cures, doesn't heating it back into cement release that CO2? Hardly zero-carbon.
Joshuaa Zev Levin, Ph.D.
Maybe this should be called "EZE Concrete", for Electric Zero-Emission. After all, if my middle name can mean "Zero-Emission Vehicle", then that isn't a stretch.
Joshuaa Zev Levin, Ph.D.
I understand that Roman concrete lasts for so long, even millennia, because it also contains quicklime (CaO), or calcium oxide. Would adding this have any effect on this process, either in the input stage (what goes into the pot), or the output state (the final product).
This sounds too good to be true, but this could also be huge.
I never thought I would see a concrete breakthrough that reminds me of Einstein's & every other physicists/chemists adage E=MC2ed. As it matter can be either created nor destroyed, it just exists in a different form. Nice! Not to belabor your synopsis, for it shows promise for our future with rampant CO2 based climate change - what say these scientists about the need to bring the concrete to the electric arc furnace with a liquid metal bath and the logistics of that process? Yes we need to reduce our usage of new concrete, but if we can recycle concrete without producing more CO2, releasing more CO2, and at the very least, continuing to sequester the current CO2, will it produce a substance with equal building capacities and strengths? As in actually proving to naysayers the zero-carbon processes?
Let's remember that the Three Laws of Thermodynamics make "net zero carbon" a scientific impossibility. As for using renewables to reduce GHGs, I strongly doubt that the start to finish carbon footprint for them is measurably lower that that of a fossil fuel produced at an advanced technology US refinery. Ethanol for instance contains only 67% of the energy per unit as gasoline. And the corn raw material requires fertilizer derived from natural gas. Why gas? It's the most efficient and cost effective way.
Does this new process mean that you would not have to spend the large polluting effort of heavy machinery to separate the re-bar from the concrete?
@Karmudjun, chemical reactions aren't so much an example of Einstein's mass-energy equivalence as a much earlier law. "The Law of Conservation of Mass dates from Antoine Lavoisier's 1789 discovery that mass is neither created nor destroyed in chemical reactions." Einstein's succinct formula shows this is an approximation; "However, as Max Planck pointed out, a change in mass as a result of extraction or addition of chemical energy, as predicted by Einstein's theory, is so small that it could not be measured with the available instruments and could not be presented as a test of special relativity." Radioactive decay and nuclear fission and fusion demonstrate the principle.

@CLH8712, life cycle analyses confirm the common sense view: building solar or wind once and then it sits there intermittently generating energy for 25+ years, has far less overall greenhouse gas emissions than continually mining, refining, shipping then BURNING fossil fuels in a thermal plant every hour it generates electricity. Yes, biofuels like ethanol don't have the same low greenhouse gas emissions per kWH.
Treon Verdery
Even though they are engineered for efficiency, refractory brick lined liquid metal alloy makers and cement plants might be even more efficient with more warmth retaining insulation. I think its possible to make refractory brick with internal bubbles or tubes that have IR retroreflecting smooth-reflective metallic glaze at their perimeter. The size of the mirrored bubbles, from tiny to big could be optimized with nonsentient genetic algorithms to find the very most insulative forms at a multirefractorybrick finite element analysis model. There is even a metamaterial thing called a "perfect mirror", just easy to pressmold titanium oxide columns that can reflect like IR back towards the liquid metal or cement. doubling the insulative capacity of refractory brick could save 40-70% of the warming energy, thus reducing pollution.
"If renewable energy is used", Yeah sure that's done so well in the energy sector, right! Zero carbon joke!