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Rocks beneath our feet could be the key to carbon-neutral cement


Rocks beneath our feet could be the key to carbon-neutral cement

Engineers show how simple processing turns olivine, the most abundant mineral in the Earth’s mantle, into a greener formula for cement and other building materials
May 9, 2024

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A common mineral present just beneath the Earth’s crust could help to negate the carbon footprint of concrete, researchers report in the journal Royal Society Open Science. The study details a way to turn the mineral olivine, which also forms the green gemstone peridot, into an alternative for cement and other construction materials. The research team has launched a startup to commercialize their patented process.

Concrete, the most widely used material in the world, is a mix of cement, water, gravel and sand. The production of cement and concrete results in about 8 percent of the world’s carbon dioxide emissions.

Most of these emissions are generated when limestone is heated at high temperatures to produce powdery cement. The emissions come from burning fossil fuels for heat, but also from the chemical reaction itself.

Some manufacturers are reducing concrete’s emissions by replacing part of the cement with waste material such as fly ash and slag or adding other recycled materials. Studies have shown that this replacement does not reduce the strength of concrete.

Civil and environmental engineers at Imperial College London turned to olivine, a magnesium silicate mineral that is found in the rocks in the Earth’s upper mantle. The mineral naturally reacts with carbon dioxide from the air and turns into magnesium carbonate. But this process works at a very slow geological timescale.


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The team wanted to see if they could speed up this carbonate-forming process. They crushed olivine samples and mixed them into sulfuric acid. This separated the silica from the olivine and created magnesium sulfate. When they bubbled carbon dioxide gas through the mixture, it reacted with the sulfate to produce magnesium carbonate, resulting in the sequestration of carbon dioxide.

The silica can be used as a cement substitute in concrete to add strength. And the magnesium carbonate can be used as a binder or filler in other low-carbon construction products such as bricks, blocks and board, the team writes in the paper.

Replacing 35 percent of regular Portland cement in concrete with the silica would give carbon-neutral cement, the researchers write. Replacing more than that could would make concrete carbon negative.

Further, they add that the olivine processing is not energy intensive and could be done electrically using renewable energy.

Source: Barney Shanks et al. Carbon capture and storage in low-carbon concrete using products derived from olivine. Royal Society Open Science, 2024.

Image: Smithsonian National Museum of Natural History

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