The Mechanochemical Shift

Over the next 25 years, the cement industry is anticipated to undergo significant changes, particularly concerning the demand for cement and traditional constituents like clinker. According to the World Cement Association’s 2025 long-term cement and clinker forecast, as the world edges closer to 2050, there will be a noticeable decline in clinker demand, attributed largely to the global push for more sustainable building practices and carbon reduction. This decline underscores a critical need for supplementary cementitious materials (SCMs) that can fulfil the functional requirements of clinker without the associated environmental costs.

However, the availability of conventional SCMs in North America and Europe has declined significantly. Since its peak in 2006, the availability of fly ash and ground granulated blast furnace slag (GGBFS) in the US has dropped by an estimated 45% in 2022 – a reality not dissimilar to that in Europe. This material scarcity is compounded by ongoing geopolitical trade uncertainties that have the potential to disrupt global supply chains and inevitably increase material costs. Such challenges necessitate the development and adoption of new locally sourced and produced SCMs to ensure the resilience and sustainability of the cement industry.

Carbon Upcycling Technologies is a Canadian-based technology and project developer enabling localised SCM production from alternative feedstocks. Carbon Upcycling’s technology utilises point-source CO₂ from flue gas to enhance out-of-spec materials like ponded ash, steel slags, and low-kaolin clays into a drop-in SCM to fill the void left behind by traditional materials. In applicable chemistries, the CO₂ from flue gas may be sequestered into the feedstock material, further reducing carbon emissions. Carbon Upcycling achieves this through its proprietary mechanically assisted chemical exfoliation (MACE) process, an advanced form of mechanochemical activation.

Clay as a suitable SCM and conventional activation methods

Clay is abundantly available globally, making it a promising candidate for use as an SCM. However, using clay as an SCM is not without challenges. Clay is naturally inert and requires high-energy processing to unlock its potential. Its mineralogy can also vary significantly, often containing impurities that affect its performance consistency.

The current method for activating clays is through calcination. This process involves heating the clay at temperatures typically between 600 – 900°C. The intense thermal energy changes the clay’s physical and chemical structure to expose the silica and alumina content within it, which is essential for pozzolanic reactions in cement.

There are several considerations that must be taken into account with clay calcination. One significant limitation of the process is its dependency on high-kaolin clays. Calcination typically requires a clay source that contains more than 40% kaolinite. This is a mine-quality clay that is not as readily available or cost-effective to acquire globally. Calcination also demands a high amount of thermal energy, making it less energy-efficient than other SCM production methods. As well, the calcination of calcareous or limestone-rich clays can cause the release of CO₂ through the thermal decomposition of carbonates. Finally, cement containing calcined clays can exhibit an increased water demand compared to conventional ordinary portland cement (OPC) blends, which may affect the workability and hydration properties of the cement.

An ideal clay activation process would be one that is energy-efficient and effective regardless of a clay’s composition.

Mechanochemical activation of clays

Mechanochemical activation (MCA) uses mechanical energy to induce physical and chemical changes in a material’s structure, ultimately altering its properties. This can be achieved typically through intense grinding in high-energy mills (e.g. planetary ball mills, attrition mills, stirred media mills), often combined with chemical activators to create a synergistic mechanochemical effect. The mechanical forces disrupt the clay structure, while the chemical environment channels the disordered system towards a more reactive state. This process generates binding sites that would not exist otherwise.

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Read the article online at: https://www.worldcement.com/special-reports/19052025/the-mechanochemical-shift/