Recycling of Portland Cement and Steel in Electric Arc Furnaces

The use of concrete and steel have both become the bedrock of modern-day construction, which of course also means that there is a lot of both which ends up as waste once said construction gets demolished again. While steel is readily recyclable, the Portland cement that forms the basis of concrete so far is not. Although the aggregate from crushed concrete can be reclaimed, the remainder tends to end up in a landfill, requiring fresh input of limestone to create more cement. Now a team of researchers from the University of Cambridge claim to have found a way to recycle hydrated Portland cement by using it as flux during steel production in electric arc furnaces (EAFs).

Not only does this save a lot of space in landfills, it also stands to reduce a lot of the carbon dioxide produced during cement and steel production, which is primarily from the use of limestone for cement and lime-dolomite for steel. The details can be found in the open access paper in Nature by [Cyrille F. Dunant] and colleagues. Essentially reclaimed cement paste is mixed with some fresh material to form the flux that shields the molten steel in an EAF from the atmosphere. The flux creates the slag layer that floats on top of the molten steel, with this slag after cooling down being ground up and turned into cement clinker, which is then mixed to create fresh cement.

The process has been patented by Cambridge, who call the product ‘Cambridge Electric Cement‘, with the claim that if using low-carbon power sources for the EAF like hydro and nuclear, it would constitute ‘no emissions’ and ‘no landfill’ cement. We have to see how this works out on an industrial scale, of course, but it would definitely be nice to keep concrete and cement in general out of landfills, while cutting back on limestone mining, as well as questionable practices like adding heavy metal-laden fly ash as filler to concrete.

Thanks to [cscott] for the tip.

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