What is evoBuild low carbon GGBS?
Ground granulated blast furnace slag (GGBS) is a high-performance substitute for Portland cement in concrete. It significantly reduces the environmental impact of construction by lowering the CO₂ emissions associated with cement, and therefore, concrete production.
evoBuild low carbon GGBS is a proven supplementary cementitious material (SCM), recognised in British Standards BS EN 197-1 and BS EN 15167. It was discovered in the 19th century and has a long history of use in the UK. GGBS has much lower embodied carbon than Portland cement and can achieve the highest replacement levels in concrete of any SCM. In special applications, it can replace up to 90% of the cement content, with a typical replacement rate of approximately 50%.
GGBS is suitable for almost all concrete applications. Its specific properties also make it ideal for use in aggressive environments exposed to sulphate or chloride attack, such as sea defences, where it enhances the durability of concrete.
What is GGBS?
GGBS is a Type II addition manufactured from blast furnace slag, a by-product of the iron-making process. During iron production, molten slag is rapidly cooled or quenched to form granulated blast furnace slag (GBS). This granulate is then dried and finely ground to produce GGBS.
CO₂ emissions comparison
Portland cement
The production of standard CEM I Portland cement is highly energy intensive and emits a substantial amount of CO₂, typically around 800 to 900 kg of CO₂ per tonne. CEM I is manufactured by heating a mixture of calcium carbonates (such as limestone or chalk) with silica and aluminates (such as clay, marl, or shale) to approximately 1,450°C. During this process, calcium carbonate reacts to form calcium oxide and releases CO₂ as a by-product.
Heidelberg Materials has made significant investments to reduce the carbon footprint of cement production. This includes reducing reliance on fossil fuels, such as coal, by increasing the use of alternative fuels like solid recovered fuel (SRF) and meat and bone meal (M&BM). A notable milestone was the successful feasibility study using hydrogen as a fuel source at our Ribblesdale cement plant.
evoBuild low carbon GGBS
Compared to one tonne of Portland cement, evoBuild low carbon GGBS offers a significantly lower embodied carbon. According to our Environmental Product Declaration (EPD), the Global Warming Potential (GWP) of evoBuild low carbon GGBS is 155 kg CO₂e per tonne, compared to 804 kg CO₂e per tonne for our CEM I. This represents a substantial reduction in carbon emissions, supporting our commitment to developing low carbon concrete solutions that support developers, contractors, and specifiers in reducing the environmental impact of their projects.
Secure supply and sustainability
While domestic steel production in the UK continues, the closure of blast furnace operations at Port Talbot has reduced domestic availability of GBS. Despite this shift, we have maintained a safe, secure and consistent supply of slag for evoBuild low carbon GGBS production.
We source GBS from both UK and international steelworks, ensuring continuity and quality. This enables us to continue delivering evoBuild low carbon GGBS reliably across the UK.
How is GGBS made?
Slag is an inevitable outcome of producing iron in a blast furnace, where raw materials are melted to extract molten iron.
To optimise its cementitious properties and produce GGBS, the molten slag undergoes the following process:
- Discharge: The molten slag is tapped from the blast furnace.
- Quenching: It’s rapidly cooled with water to form granulated blast furnace slag, a glassy, granular material.
- Drying and grinding: The granulate is then dried and finely ground to produce the fine, off-white powder known as GGBS.
- Final product: The result is a high-performance cement substitute with similar binding properties to Portland cement.
Importantly, energy is only used in the drying and grinding stages of GGBS production. The energy required to melt the slag is allocated to the iron production process, making GGBS a more energy-efficient and sustainable material.
Environmental benefits of low carbon GGBS
evoBuild low carbon GGBS supports sustainable construction by reducing the need for virgin raw materials and lowering environmental impact. As a by-product of the iron-making process, it avoids the quarrying of new materials and helps divert slag from landfill.
Each year, we have the capacity to supply up to 1.5 million tonnes of evoBuild Low Carbon GGBS throughout the UK as a replacement for Portland cement. This contributes to:
- Saving approximately 2.03 million tonnes of quarried material
- Reducing primary energy use by around 1.2 million MWh
- Cutting CO₂ emissions by nearly 1.17 million tonnes
According to the Environmental Product Declaration (EPD) for UK Average evoBuild low carbon GGBS:
- The Global Warming Potential (GWP) is 155 kg CO₂e per tonne, compared to 804 kg CO₂e for Portland cement.
- The product is manufactured under ISO 9001, ISO 14001, ISO 45003, ISO 50001, and BES 6001 certified systems.
- The EPD is independently verified and valid until January 2030, ensuring transparency and reliability.
Case study: Using evoBuild low carbon GGBS at Hinkley Point C
Hinkley Point C is one of the UK’s most significant infrastructure projects. evoBuild low carbon GGBS has played a key role in reducing the environmental impact of this new nuclear power station in Somerset.
Since 2014, more than 230,000 tonnes of evoBuild low carbon GGBS have been supplied to the site from Heidelberg Materials’ Port Talbot facility. The material is rigorously tested both at the production site and upon delivery to ensure it meets the exacting standards required for nuclear-grade concrete.
By replacing a portion of Portland cement in the concrete mix, evoBuild low carbon GGBS has already helped save around 200,000 tonnes of CO₂. This contribution supports the project’s low carbon credentials while maintaining the durability and performance needed for such a critical structure.
GGBS milestone at Thames Tideway Tunnel
Decarbonise your construction project with evoBuild
evoBuild low carbon GGBS offers a wide range of benefits, from significantly reduced CO₂ emissions to enhanced durability and improved aesthetics. Whether you're working on infrastructure, commercial developments, or architectural projects, evoBuild can help you meet your sustainability goals without compromising on performance.
Webinar: Specifying sustainable concrete
Find out how Heidelberg Materials can support your journey toward low carbon construction. Our technical experts are here to help you specify the right solutions for your project.