Cement and concrete production is mighty big business. Such is our dependence on Portland Cement (PC), for example, that annual global cement production now exceeds 4 billion tonnes, due to the rapid infrastructural growth of developing economies, according to a 2018 report published by the US Geological Survey. In the UK, the Mineral Products Association (MPA) boasts several hundred members, which, between them, account for around 90% of aggregates production, 100% of GB cement production, and over 70% of ready-mixed concrete and precast concrete production – with concrete the most consumed man-made material in the world.
However, concrete does have its drawbacks. From an environmental standpoint, the production of one tonne of PC is calculated to cause the release of almost one tonne of CO2 into the atmosphere, along with the subsequent climate change impact these levels bring with them. On a practical level, PC-based concrete’s high heat of hydration limits pour sizes significantly, due to the risk of thermal cracking from the heat it generates.
The MPA, for its part, pointed to environmental improvements across the industry in its 2019 sustainability report: “In 2018, direct emissions of UK Cement industry CO2 emissions were 51% lower than the 1990 Paris Agreement baseline [25% lower per tonne of cement from 1998]. Waste-derived fuels made up 43% of the thermal input with waste biomass fuels composing 17% of the thermal input to the cement manufacturing process.” Looking ahead, the MPA says it is leading a project looking at “innovative ways to fuel switch the cement kilns to fossil fuel-free energy”.
Others would argue there is a better way for some applications, most vocally the DB Group, which has developed and manufactured an ultra-low carbon alternative to traditional PC-based concrete, Cemfree, said to have all the structural characteristics of traditional concrete, while being more sustainable and resistant to chemical attack. It is also claimed by the company that Cemfree requires fewer construction joints and less crack-control steel when used within key structural elements.
As an example of Cemfree in action, a team from Jackson Civils, DB Group and Axtell (working on behalf of Connect Plus) achieved a claimed 77% reduction in CO2 by using volumetric mix trucks for a pour on the Woodford West Viaduct M25 pilot project.
“This was a big deal,” states DB Group’s Andrew Frost, group special projects manager, “as the entire supply chain came together to supply a low-carbon alkali-activated cementitious material [AACM] to a major client [Highways England] on live permanent works.”
He continues: “Delivering the concrete via a volumetric truck, where you are operating a mobile concrete batching plant, has several benefits. It allows binders like Cemfree to be supplied without tying up a silo at a ready-mix concrete batching plant; enables deliveries outside of their normal operating hours; allows for smaller quantities to be delivered; and ensures access to difficult sites, as the vehicle tends to be smaller.
“This initial application – a concrete hardstanding underneath the viaduct – amounted to 52 m³ of concrete, leading to a saving of 9.4 tonnes of CO2 when compared to using a conventional mix, greatly reducing the environmental impact. Cemfree removes the need for PC completely, using instead 95% ground granulated blast-furnace slag [GGBS] and a 5% alkali activator.” The CO2 value of Cemfree is given as 114 kg per tonne, 77% lower than conventional mixes.
While concrete has a fairly low carbon footprint, compared to many other materials, one element, PC, has a high embodied carbon. “Depending on the application, the mix design and amount of Cemfree binder required, we can go to around 80% lower than PC concrete of an equivalent design. Concrete using Cemfree as a binder carbonates, as PC concrete carbonates during its life and at end of life, when it is crushed for recycling. This takes back some of that carbon. Unlike many other manufacturers, we do not use offsetting to claim carbon neutrality, as we believe this is a last resort once all other emissions have been reduced as far as practicably possible.”
A BIG ROLE IN FUTURE
PC is not likely to disappear anytime soon, of course. Indeed, it will still always have a big role to play. AACMs like Cemfree are currently outside the British Standards for concrete. They can be used, but additional testing is required. “They are not suitable for all applications and there are applications where PC is the material of choice,” states Frost. “They perform extremely well in aggressive environments. Whilst construction gains knowledge, data, experience of and confidence in these materials, the applications should be low risk – eg, temporary works and precast applications. Concrete in aggressive ground remains an ideal environment.”
Meanwhile, the Global Cement and Concrete Association (CCCA) has recently revealed its plans for achieving carbon neutrality within 30 years (www.is.gd/denudi). “The 2050 Climate Ambition represents our industry’s commitment to further reducing emissions and ensuring that the vital product we provide can be delivered on a carbon neutral basis by 2050,” says Albert Manifold, GCCA president and chief executive of CRH. “There is a significant challenge involved in doing so and achieving alignment across our industry on a sustainable way forward is an important first step. We cannot, however, succeed alone and in launching our ambition statement we are also highlighting the need for our industry to work collaboratively with other stakeholders in support of…a more sustainable future.”
The CCCA believes it is possible to achieve this goal on the basis of progress already made in reducing emissions. “Since 1990, we have achieved an 19.2% reduction in CO2 emissions per tonne of cementitious material and delivered more than a nine-fold increase in alternative fuel use replacing conventional fossil fuels. Over time, it will be possible to significantly reduce the energy emissions in cement manufacturing through fuel substitution with other sources of energy,” it states.
In response to the myriad challenges around climate change now faced globally, the need for environmentally friendly concrete that serves as a genuine alternative to traditional concrete is growing all the time. On which note, DB Group’s Frost acknowledges how MPA members with a cement interest have indeed made significant steps in decarbonising their operations and reducing emissions. “Alternative fuels, such as green hydrogen from renewables, as long as they address the NOx emissions, will be an interesting development, as will alternative binder systems, such as calcined clays. I have significant reservations with CCSU [Carbon Capture, Utilisation and Sequestration] technologies that collect the CO2 produced from industrial processes playing an increasingly important role in addressing climate change, but fear these will be required.
“A key opportunity for the MPA will be supporting the education and training of construction professionals to be smarter with their concrete design and specification, as well as supporting the updating of current standards to ensure concrete structures are safe, but limits set are sensible. The concrete industry needs to support the principals of ‘designing for sufficiency’ – less is definitely more in a truly sustainable world.”