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Combatting Carbon With Activated Clay

Published by , Editorial Assistant
World Cement,


As the world grapples with climate change, the pressure to decarbonise the cement industry has never been more intense. One promising avenue for reducing CO2 emissions is the use of activated clays, like metakaolin, as supplementary cementitious materials (SCMs).

Activated clays and other SCMs are used in various cement types, including OPC, Portland Pozzolana Cement (PPC), Portland Slag Cement (PSC), and Limestone Calcined Clay Cement (LC3).

The role of activated clays in the cement industry

The global cement market is projected to reach US$682.3 billion by 2025, driven by rapid urbanisation and extensive infrastructure development across emerging and developed economies. However, the industry’s growth is tempered by stringent environmental regulations and the urgent need to reduce carbon emissions. The Paris Agreement and various national policies aim to limit global warming to well below 2°C, with efforts to limit it to 1.5°C. To achieve this, the cement industry must reduce its carbon emissions by at least 16% by 2030 and achieve net-zero emissions by 2050. Such ambitious CO2 reduction targets have compelled the cement industry to innovate and adopt greener technologies, leading to a CAGR for the activated clay market of 8%.

In developed markets like Europe, CEMBUREAU (the European cement association) has been at the forefront of promoting sustainable cement manufacturing practices. The European Union’s Emissions Trading System has set a cap on CO2 emissions, motivating companies like Holcim and Heidelberg Materials into investing in the development of LC3 and other low-carbon cements. For example, Holcim’s ‘Green Cement’ initiative aims to reduce CO2 emissions by 25% by 2030 using SCMs, including activated clays. Similarly, in North America, the Portland Cement Association has committed to a roadmap for carbon neutrality by 2050. The US Environmental Protection Agency has also established the ENERGY STAR programme for the cement industry, encouraging the adoption of energy-efficient technologies. Companies like CEMEX USA are exploring the use of metakaolin to produce more sustainable cement products. Research initiatives in collaboration with universities are focused on optimising the performance of activated clays in cement.

The emerging markets in the Asia-Pacific region are led by China and India, as the largest producers and consumers of cement. Both countries are implementing policies to curb CO2 emissions. China’s Ministry of Ecology and Environment has set stringent emission standards, pushing the industry towards cleaner technologies. The Indian government’s National Action Plan on Climate Change promotes the use of blended cements like PPC and PSC. Indian cement companies such as UltraTech Cement and ACC are actively incorporating metakaolin and other SCMs to meet these standards. In Latin America, emerging countries like Brazil and Mexico are taking steps to reduce their carbon footprint in the cement industry. The Brazilian National Cement Industry Association has initiatives aimed at promoting the use of alternative materials. Companies like Votorantim Cimentos are investing in the production of LC3 to achieve sustainability targets.

The use of activated clays necessitates advanced analytical techniques like x-ray diffraction (XRD), to analytically enable this decarbonisation strategy. Activated clays are gaining traction as sustainable alternatives to traditional clinker. The use of SCMs like metakaolin can significantly reduce the clinker factor in cement, thereby lowering CO2 emissions and production cost (Figure 1). For instance, LC3 cement, which combines limestone and calcined clay, can reduce CO2 emissions by up to 40% compared to OPC, while also being 10% cheaper. The adoption of PPC and PSC, which incorporate pozzolanic materials and slag respectively, also contribute to CO2 reduction. Both have similar cost levels compared to LC3 and, in some cases, can be even cheaper. In this context, ensuring the quality and performance of these alternative materials is crucial, and this is where routine XRD analysis becomes indispensable.

What are activated clays and why are they beneficial?

Activated clays, such as metakaolin, demonstrate significant potential within the cement industry. The production of these materials generally involves the calcination of various types of clay at temperatures between 600°C and 900°C, where they decompose and form amorphous aluminosilicates. This process can be optimised to enhance their reactivity and pozzolanic activity. During this process amorphous aluminosilicates are formed, which have a high pozzolanic reactivity. Several studies have examined the impact of different activated clays on the properties of cementitious composites. For example, research has shown that replacing 10 – 20% of Portland cement with activated clays can significantly enhance the compressive strength and durability of concrete. This improvement is attributed to the pozzolanic reaction between the activated clays and the calcium hydroxide produced during cement hydration, which results in the formation of additional calcium silicate hydrate (C-S-H) gel.

Moreover, activated clays have been found to improve the resistance of concrete to chemical attacks, such as sulfate and chloride ingress. This is particularly important for structures exposed to aggressive environments, as it extends their service life and reduces maintenance costs. Metakaolin, as one specific example of activated clay, has been extensively studied and has shown considerable promise in these applications. However, the broader category of activated clays continues to offer significant opportunities for enhancing the performance and sustainability of cementitious materials.

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Read the article online at: https://www.worldcement.com/special-reports/18122024/combatting-carbon-with-activated-clay/

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