As the UK construction industry advances towards net zero, Supplementary Cementitious Materials (SCMs) are becoming essential in reducing the carbon footprint of cement and concrete. These materials partially replace clinker, the most carbon-intensive component of cement, helping to lower CO₂ emissions while maintaining or enhancing performance.
We are actively developing and trialing a range of SCMs, each offering distinct sustainability benefits, technical characteristics, and opportunities for innovation.
What are SCMs and how are they made?
SCMs are materials that exhibit cementitious properties when combined with Portland cement. They are typically derived from industrial by-products, natural minerals, or recycled materials. By replacing a portion of clinker, SCMs contribute to lower embodied carbon in concrete.
Ground Granulated Blast Furnace Slag (GGBS)
GGBS is produced by rapidly cooling molten slag, a by-product of iron production, and then grinding it into a fine powder. It is compliant with British Standards (BS) EN 15167 and BS EN 197-1, and has been used successfully in UK concrete for decades.
Carbon impact: GGBS has a Global Warming Potential (GWP) of approximately 155 kg CO₂e per tonne, compared to around 804 kg CO₂e per tonne for Portland cement (CEM I).
Replacement levels: Up to 70% in special applications; typically, around 50%.
GGBS has additional benefits including:
Enhanced durability
Improved workability
Reduced heat of hydration
Lighter in colour for aesthetics
Heidelberg Material’s evoBuild low carbon GGBS is still the best option for low carbon concrete production and has a safe and secure supply for projects across the UK.
Calcined Clay
Calcined clay is a type of clay that has been heated to high temperatures to activate its cementitious properties. This process breaks down the clay’s internal structure, allowing it to react with cement and contribute to strength development in concrete. Unlike clinker, calcined clay does not release CO₂ during chemical transformation, making it a lower-carbon alternative. Emissions are limited to the energy used in drying, calcining, and grinding, and emerging technologies such as flash calcination offer potential for near-complete electrification, further reducing environmental impact.
Heidelberg Materials UK is actively involved in research and partnerships to assess UK clay sources and trial calcined clay mixes.
We have successfully supplied two C32/40 concrete mixes with 30% calcined clay to projects in London. Both reported:
Excellent compaction
No delays in striking
Great overall performance
These results reflect the strength of collaboration across the supply chain and our commitment to delivering low-carbon concrete solutions that meet real-world performance expectations.
At our Greenwich ready-mixed concrete plant in London, we offer calcined clay as part of our evolving portfolio of cement substitutes. Lab trials have shown that up to 30% replacement of Portland cement with calcined clay achieves strength equivalency with Ground Granulated Blast Furnace Slag (GGBS) at 28 days. Beyond 30%, relative strength declines more sharply, helping guide optimal usage levels.
As demand grows, we are preparing to expand supply, including importing material from European sources for further trials and development.
Limestone Fines
Limestone fines are finely ground calcium carbonate. When used in small quantities or as part of a ternary blend, they contribute to early-age strength and modest carbon reductions. Their inclusion in BS EN 197-5 and BS 8500 makes them a reliable option for mainstream applications.
Natural Pozzolanas
These are volcanic or sedimentary materials that react with calcium hydroxide to form cementitious compounds. Used since Roman times, they offer long-term durability and chemical resistance. While not widely available in the UK, deposits in Iceland and Greece are being explored.
Fly Ash
Fly ash is a fine powder produced as a by-product of coal combustion in power stations. Traditionally, it has been used in concrete for its pozzolanic properties, which help improve durability and long-term strength. However, as coal-fired power generation declines in the UK, fresh fly ash supplies have become limited.
Recycled Concrete Paste (RCP)
RCP is obtained from crushed concrete and contains residual cementitious material. Through carbonation, its reactivity can be enhanced, allowing it to contribute to strength development and CO₂ capture.
Partnering for progress
SCMs are reshaping the future of construction. Whether you are designing for durability, sustainability, or circularity, our technical team is here to help you find the right solution.
