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Greening cement production – Nature.com

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The cement industry is one of the world’s largest emitters of carbon dioxide.© Michael Milner/Moment/Getty
The cement industry annually produces around 3.5 billion tonnes of general Portland cement, the most common form, with emissions from the sector accounting for about 7% of total global anthropogenic GHG emissions. If the cement industry were a country, it would be the third largest emitter of carbon dioxide in the world with up to 2.8 billion tonnes produced annually.
Now, a team led by Ahn Ji-whan, director of the Carbon Mineralization Flagship Center at the Korea Institute of Geoscience and Mineral Resources (KIGAM), has developed a green cement production method that partially replaces limestone, a major component of cement and a raw material for carbon dioxide emissions, with industrial by-products. In addition, the team was able to produce this cement at a temperature about 200°C lower than the industry standard.
Moving past Portland
To produce Portland cement, limestone is mixed with raw materials such as siliceous stone and clay and is heated to about 1,450 °C. During this process, an intermediate product called ‘clinker’ is produced, and about 44 weight percent of the limestone is emitted as carbon dioxide.
The new green cement production technology, however, synthesizes a calcium sulfoaluminate (CSA) clinker by mixing a part of limestone into raw materials, such as coal ash and alumina by-product generated from thermal power plants.
The thermal energy required to produce 1 kilogram of green cement clinker is about 570 kilocalories, which is less than the general Portland cement heat energy of about 720 kilocalories. “This reduces energy consumption by 20% and carbon dioxide emissions by 2%,” explains Ahn.
“Moreover, our green cement performs twice as well as Portland cement for High Early Strength Concrete (on a 3-day strength basis, the compressive strength of Portland cement was 12.5 MPa, whereas green cement was 25 MPa) and expandability (Portland cement was 0.01% whereas green cement was 0.03%), so it can be applied to construction fields such as buildings and bridges. And thanks to its improved water-repellent characteristics, green cement will be able to be used as a fill material for abandoned mines, waste gas fields and waste oil fields in the future,” she adds.
Improving international standards
In October 2021, representatives from the South Korean government and leaders from nearly 200 nations met at the 26th meeting of the Conference of the Parties (COP26) to the UNFCCC in Glasgow, UK. COP26 was intended to accelerate actions towards achieving the 2015 Paris Agreement, which aims to limit average global temperature increases to below 2 °C by 2050 from pre-industrial levels. At the meeting, South Korea committed to reducing GHG emissions by at least 40% by 2030 from 2018 levels and committed to achieving carbon neutrality by 2050.

Ahn Ji-whan at the Korea Institute of Geoscience and Mineral Resources (KIGAM).© KIGAM

KIGAM’s green cement technology not only reduces greenhouse gases, but also meets one of the COP26 sustainable development mechanism goals – to reduce the use of limestone, a natural resource mineral, and overcome the deviation and harmfulness of industrial by-products. “About 88.7% of domestic mineral resource reserves are non-metallic ore, of which limestone accounts for nearly 72%, and most of these minerals are used in the cement industry,” explains Ahn.
Ahn Ji-whan at the Korea Institute of Geoscience and Mineral Resources (KIGAM).© KIGAM
In addition to the green cement technology, Ahn developed a new Clean Development Mechanism (CDM) methodology for use in the cement industry, which has many restrictions on carbon credits.
“The new CDM methodology is an international standard for estimating the greenhouse gas emissions that are reduced by specific activities, and it is necessary to certify the greenhouse gas reduction performance of our green cement production technology,” she explains.
The most challenging aspect of registering the technology under the CDM methodology was estimating the amount of carbon dioxide reduced by the cement production technology, recalls Ahn. She estimates that the cement developed with this technology releases 0.281 carbon dioxide emissions (tCO2) per tonne of produced cement fewer than that produced via general Portland cement.
“Take 2019 figures for example – if green cement comprised 5% (2,912,710 tons) of the total cement production in 2019, about 820,000 tCO2 of total greenhouse gas could have been reduced.”
The CDM methodology was approved and announced in October 2020 by the United Nations Framework Convention on Climate Change (UNFCCC). “This means our methodology has been recognized as an international greenhouse gas reduction technology standard for cement production,” she says.
And it’s this recognition as an international standard that Ahn believes will lead to greater impact. “Green cement technology not only has the potential to reduce domestic emissions from the cement industry in South Korea, but to also reduce greenhouse gas emissions in the cement industry through technology transfer at home and abroad based on the registration of a new CDM methodology.”
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