New powder generation
Specifiers seeking lower-carbon concretes will very soon have a new tool at their disposal, with the addition of multi-component cements to the BS 8500 standard.
The 2022 update will permit more “ternary blends”, which can contain up to 20% limestone powder as a second cement replacement in addition to GGBS or fly ash. In the UK, limestone is an abundant resource that needs only to be ground up, a process that requires relatively little energy. When it is used in ternary blends, there is no reduction in strength or performance, only embodied carbon.
Portland cement is responsible for the characteristics that make concrete so widely used, but it also accounts for most of its carbon emissions, so the search is on to find cementitious replacements that offer the same benefits with a lower environmental impact. This is bearing fruit in the far greater choice now available to specifiers. There were 15 general purpose cements in the 2006 version of BS 8500 and 16 in the 2015 version. But by the time of the 2019 amendment this had increased three-fold to 48, and in 2022 it is set to more than double again to 112.
The explosion of new cements in the 2022 standard reflects the considerable efforts taking place to decarbonise concrete, but also the long process of testing that the performance, strength and durability of new mixes matches the concretes that we are used to relying on – today’s new cement blends have been in development for more than a decade. The Seratech scientists in Innovation represent many, many more working in laboratories across the UK and the world.
The good news for specifiers scratching their heads over the proliferation of lower-carbon options is that ternary blends will simply become the default within two or three years. Most concrete plants have two silos: one for Portland cement and one for GGBS or fly ash. Rather than investing in a third, suppliers will most likely just add limestone into their Portland cement, automatically lowering the embodied carbon of the concrete they produce. This is already the case in Ireland, where these kinds of ternary blend have been permitted for some years and “limestone cement” has become the default.
This shows the market driving carbon improvements in two ways: one, Portland cement is energy-intensive and therefore expensive to produce, so it makes commercial sense to reduce this component where possible. Two, concrete suppliers are responding to increasing demand for products that have a lower embodied carbon, reflecting the consumer power that specifiers can bring to bear.
So it’s well worth becoming familiar with the new standard – even if another update may follow hot on its heels. Because by informing themselves about the options and, crucially, asking for them, specifiers can continue to drive change across the built environment.
Jenny Burridge, head of structural engineering, The Concrete Centre