Decarbonising construction with calcined clay
One of the ways Holcim is decarbonising construction is by increasing the use of calcined clays to further develop the company’s ECOPlanet low-carbon cements and enable large-scale low-carbon construction. The first ECOPlanet calcined clay cement was launched in La Malle, France, in 2021, with multiple additional product launches planned in 2024. By Amith Kalathingal and Rémi Barbarulo, Holcim Innovation Center, France.
Calcined clay: the most reactive and most scaleable new mineral component (© Holcim)
With 70 per cent of the global population expected to live in cities by 2050, the world needs to build the equivalent of New York City every month. ECOPlanet, the world’s broadest range of low-carbon cement, aims to tackle this challenge sustainably by reducing emissions from cement by at least 30 per cent (compared to ordinary Portland cement) while delivering similar performance.
With Holcim’s formulation expertise, ECOPlanet’s sustainability profile is driven by innovative low-emission raw materials. The company uses calcined clay and recycled construction demolition materials in its next-generation ECOPlanet formulations to reduce building CO2 footprints by up to 50 per cent. By leveraging alternative fuels Holcim is further decarbonising the ECOPlanet production process. Moreover, it is harnessing advanced carbon capture, utilisation and storage (CCUS) technologies to produce ECOPlanet Zero fully-decarbonised cement as early as 2030.
The potential of calcined clay
The current practice of predominantly using slag and fly ash to make low-carbon cement and concrete is not sustainable because they are becoming scarce, able to supply less than 15 per cent of current cement production and set to drop to below 10 per cent. A new material is needed to replace clinker, the main source of carbon emissions in cement production.
Calcined clay under the microscope (© Holcim)
Calcined clay is a highly-reactive pozzolanic material produced by heating locally-sourced natural clays to 700-800°C, making it a scalable alternative to clinker. Moreover, as the composition of most clays is carbon free, the CO2 emissions from calcined clay production mainly come from the fuel used in the heating process. Calcined clay emits less than 200kg CO2/t based on the fuel used, which is only a quarter of clinker’s 680-800kg CO2/t. The high reactivity and low CO2 footprint of calcined clay complement its role as a significant decarbonisation tool, especially in conjunction with the deployment of CCUS technologies.
Holcim is committed to further reducing the carbon footprint of calcined clay production through innovative processes. For example, the Saint-Pierre-la-Cour plant in France will produce calcined clay with nearly zero CO2 emissions, using 100 per cent biomass-based alternative fuels and waste heat recovery systems. This facility, supported by the French government, is set to deliver calcined clay cement in the 4Q24.
Calcined clay can replace clinker or conventional additions (© Holcim)
Product, application and value proposition
Calcined clay cements can be used like any other conventional cement. They are currently applied in small- to large-scale construction for mass concrete, structural, precast, masonry and architectural applications in Europe, Latin America and North America. Holcim’s first ECOPlanet calcined clay cement was launched in La Malle, France, (with 32 per cent less CO2 when compared with OPC) in 2021, followed by Merone, Italy, (53 per cent less CO2) in 2022 and Macuspana, Mexico, (50 per cent less CO2) in 2023, with multiple product launches planned in 2024.
The key value drivers for its customers in France and Italy are low CO2 emissions with similar performance, excellent durability, low heat of hydration, and suitability for mass concrete applications.
ECOPlanet CEM V/A (S-Q) 42.5 N, produced in La Malle, France, demonstrates excellent resistance to aggressive environments, making it ideal for marine construction, sewage treatment plants and concrete applications in animal husbandry and agricultural works.
Structural concrete work with CEM V/A (S-Q) 42.5 N PM ES cement,
La Malle, France (© Holcim)
In Italy ECOPlanet CEM IV/B (V-Q) 32.5 N is produced using ground calcined clay from lightweight aggregates. This process enhances circularity while maintaining good resistance and high durability in structural works exposed to aggressive environments, including chloride and sulphate resistance. Additionally, calcined clay cements offer exceptional chloride resistance and a much lower risk of alkali-silica reaction. They also boast low heat of hydration, making them well-suited for mass concrete applications.
In France Holcim’s customers are leveraging the lower emissions of ECOPlanet calcined clay cement to comply with the RE2020 standard, which regulates building-level emissions per square metre. Beyond CO2 savings, customers in Mexico benefit from enhanced stability in fresh mortar/concrete, a better surface finish, and a distinctive earthy colour.
Apart from the strength development and durability that makes calcined clay cement extremely suitable for a wide range of applications, the higher surface area of calcined clay offers greater stability and cohesion in the plastic stage against segregation and bleeding, which makes it ideal for high workability concrete applications, including self-compacting concrete. The product is well-suited to masonry applications as well thanks to its favourable setting time and adhesion. The cement is also often associated with its better surface finish.
Masonry mortar produced with calcined clay cement in Macuspana, Mexico
(© Holcim)
Scaling up
Low-carbon cements are becoming more popular as governments and industry seek to reduce their environmental impact. Some countries offer incentives and subsidies to encourage the use of sustainable building materials. ECOPlanet calcined clay cement meets these requirements and aligns with the global goal of fighting climate change while future-proofing low-carbon construction by ensuring the availability of new minerals other than slag and fly ash. Its physical availability has increased the confidence of the construction industry, while its unique vibrant colour spectrum from pink to earthy tones acts as the stamp of proof that it is different from the conventional grey cement that the construction industry is used to. Morover, precise colour control allows for the production of the traditional grey hue if desired.
Holcim’s near-zero CO2 calcined clay production line
in Saint-Pierre-la-Cour, France (© Holcim)
Holcim’s introduction of the first ECOPlanet calcined clay cement took approximately three years. This timeline included research activities such as identifying raw clay sources, evaluating production technologies for capital expenditure investment, building and commissioning plants, conducting market research for product design, obtaining product certification, customer testing, and product launch. With the experience gained, Holcim is accelerating the launch speed, planning a global scale-up with 12 advanced projects by 2030 and more in the pipeline.
To accelerate the scale-up of ECOPlanet calcined clay cement, multiple stakeholders must collaborate: government agencies need to develop building standards that allow calcined clay cements in construction while incentivising low-carbon construction, and it needs to become a common practice that developers specify it in their procurement standards and architects specify it in their designs. Actors across the construction value chain need to work together to change the paradigm.
This article was first published in International Cement Review in August 2024.
