Sustainable Engineering and GGBS
In the ever-evolving landscape of sustainable construction practices, Engineers are constantly seeking solutions to reduce the environmental impact of building materials.

One such solution that has been used since the nineteenth century due to its ability to improve concrete’s durability is Ground Granulated Blast Furnace Slag (GGBS). GGBS, a by-product from the blast furnaces used to make iron and steel, possesses unique properties that can enhance the performance of concrete while simultaneously reducing its environmental impact.

Concrete in Construction
Concrete is the most widely used construction material globally; in the UK alone, it is estimated that around 37.5 million cubic metres are used in the construction industry each year. However, concrete has long been associated with significant carbon emissions during its production. The process of manufacturing traditional Portland cement, a key component of concrete, releases substantial amounts of carbon dioxide into the atmosphere.

Using GGBS to Reduce Carbon Emissions
One of the primary advantages of GGBS is its ability to replace a portion of the cement content in concrete mixes, leading to a decrease in overall carbon emissions. By replacing a percentage of cement with GGBS, Engineers can achieve concrete mixes with improved durability, reduced heat of hydration, and enhanced resistance to aggressive environments.

GGBS - a Limited Resource
However, a recent paper from the Institution of Structural Engineers highlights that GGBS is in fact a limited resource and has almost been fully exploited around the world. Although global supplies should continue to be utilised where technically needed, such as for durability or for temperature and crack control, beyond these alternative options should be considered.

If other cement substitutes are available locally these should be used in place of GGBS. With the introduction of the new British Standards for Concrete (BS8500-1:2023 and BS8500-2:2023) in November 2023, the range of low carbon options permitted has increased to aid with optimising the use of GGBS and to enable GGBS to be primarily used where required for technical reasons. The most significant change to the Standards has been the introduction of the use of multi-component cements, also known as Supplementary Cementitious Materials (SCMs). As an example, GGBS and limestone or pulverised fly ash and limestone can be used in combination with a cement replacement. The revised BS8500 now permits up to 65% cement replacement, whereas with the previous standards this was limited to 35%.

Further research is also being carried out into the use of alternative materials such as calcined clay. This could mean that future updates to British Standards allows for additional options to reduce the cement content of concrete, leading to a reduction in carbon emissions.

Our Approach
As Engineers we fully understand our role in helping to reduce the impact of Portland cement in construction.

When presented with a project, we will assess whether GGBS is required for technical reasons or if there are alternative concrete mixes that can be provided. By having an in-depth understanding of the latest British Standards, we are up-to-date on the current alternative concrete mixes that are available to best inform our clients of how the carbon emissions associated with concrete can be reduced.