Categories: Innovation

Replacing Cement with Belterra Clay

German and Brazilian scientists have proposed a climate-friendly alternative for cement called Belterra clay, which is just as stable as traditional Portland cement. 

The clay alternative is the outcome of a collaboration between Martin Luther University Halle-Wittenberg (MLU) in Germany and the Brazilian University of Pará.

Considered to be an unused overburden from bauxite mining, Belterra clay could almost halve CO2 emissions produced by the cement industry.

This is significant as cement is responsible for around 8% of man-made CO2 emissions. In 2020 alone, nearly six billion tonnes of cement were produced worldwide, even with the pandemic raging on.

According to MLU professor Herbert Pöllmann, Portland cement is the most dominant construction material used everywhere.

It is traditionally made using using various raw materials, including limestone, which are burned to form so-called clinker.

But in the process of calcium carbonate being converted into calcium oxide, large quantities of carbon dioxide are released.

One promising solution is calcium sulphoaluminate cement, in which a large portion of the limestone is replaced by bauxite.

However, bauxite is a sought-after raw material in aluminium production and not available in unlimited quantities.

The MLU team and their Pará colleagues have now come up with an ‘alternative for the alternative’ by using an overburden of bauxite, Belterra clay.

“This layer of clay can be up to 30 metres thick and covers the bauxite deposits in the tropical regions of the earth, for example in the Amazon basin,” says Pöllmann.

“It contains enough minerals with an aluminium content to ensure good quality cement. It is also available in large quantities and can be processed without additional treatment.”

Another advantage of Belterra clay is that it has to be removed anyway, so it does not have to be extracted only for cement production. 

Even though cement cannot be entirely produced without calcium carbonate, at least 50% to 60% of the limestone can be replaced by Belterra clay, says Pöllmann.

The process also has another environmentally relevant advantage: the burning process only requires 1,250°C – 200°C less than for Portland cement.

Moreover, the new method not only releases less CO2 during the chemical conversion, but also when heating the rotary kilns. 

Image and content: Pau Barrena-Bloomberg/MLU

Aruna Urs: Aruna is an industrial journalist. He writes on innovations that emanate at the intersection of science and engineering having a profound impact on the manufacturing sector.

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