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24 January 2020

As the most widely-used building
material in the world, it’s no surprise that making cement is one of the single
biggest contributors to our carbon emissions problem. MIT researchers now claim
to have developed a new method that can clean up the cement production process,
removing most of the carbon emissions without affecting the resulting product.

Portland cement, the most common type, is made by
grinding up limestone, mixing it with sand and clay then cooking it at
extremely high heat – up to 1,450° C. Not only does the energy used to heat the
mixture produce huge amounts of carbon dioxide, but the greenhouse gas is also
released by the limestone itself during this process. In all, that means about
1 kg of CO2 is released for every kilogram of cement produced, which
adds up to a staggering 8% of global CO2 emissions.

While it’s been argued that concrete eventually sponges up much of the CO2 emitted during
its production, it still wouldn’t be a bad idea to try to clean up the
manufacturing process. Researchers have experimented with changing ratios of ingredients, developing new ‘geopolymer’ recipes,
or replacing cement with environmentally-friendly composite binders.

The problem with all of those ideas is that the end
result is a different type of concrete. And the building industry may be
reluctant, at least at first, to start using a different material. So the
researchers on the new study focused on improving one step of the regular
process, making plain old cement greener without having to change the material

Rather than heating the ground-up limestone, the
new process uses an electrolyzer, where electrodes split water molecules into
oxygen and hydrogen. Doing so creates an acid at one electrode and a base at
the other. The limestone is dissolved in the acid, and calcium hydroxide is
created at the other end, in solid flakes. These flakes of lime can then be
harvested to produce cement.

Of course, carbon dioxide is still produced during
the process, as the limestone dissolves. But it isn’t released into the air –
instead, it can be captured and because it’s pure, used for other purposes,
such as making liquid fuels or carbonating drinks. The team even says that it can be combined with oxygen produced by the
same system, and burned to fuel the rest of the new cement-making process.

The researchers demonstrated the technique in the lab, and showed that it worked on a small scale. The team says it could be scaled up quite easily, but it is still just one part of the larger process of making cement. More work needs to be done before it can be implemented in the real world, but it’s a promising step.https://newatlas.com/materials/cement-electrolysis-technique-no-carbon-emissions/

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