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Building the future: decarbonising concrete and cement

Steve Merritt looks at the problem of decarbonisation of concrete and cement production, and outlines some potential solutions.

Frazer-Nash recently responded to a call for evidence from the Department for Business, Energy and Industrial Strategy (BEIS) on the UK’s position in relation to advanced materials and concrete and cement. In this White Paper, Steve Merritt looks at the problem of decarbonisation of concrete and cement production, and outlines some potential solutions.

The concrete and cement industry is vital to our society – much of our critical national infrastructure depends upon these construction materials. But concrete and cement production is responsible for at least 8% of global CO2 emissions, so as the UK strives to play its part in the global drive to achieve Net Zero by 2050, radical changes are needed to reduce the industry’s emissions.

Some of these changes are already in progress: improvements have been made in distribution networks, cleaner fuel alternatives are being used, and greener formulations prepared. In fact, since 1990, concrete and cement emissions have reduced by 53%, with a total of 1.5% annual CO2 emissions from concrete and cement – a notable reduction relative to the global average of 7%. But emissions from these materials are only half the story. There has been a global increase of 200%, since 1990, in CO2 emissions directly related to the concrete and cement industry[i]. To achieve Net Zero by 2050 there needs to be further improvement, both in the UK and globally: CO2 intensity needs to decrease by 3% per annum, starting immediately, and continuing until at least 2030.

So how can the UK concrete and cement industry further reduce its carbon footprint? We envision that this could be achieved through providing further support to the development and commercialisation of:

  • Carbon capture, usage and storage (CCUS)
  • Self-healing concrete and
  • Additive manufacturing of engineered cement composites (ECCs)

Below, we outline some of the opportunities and challenges of these approaches.

Collaboration between UK industry and research institutes could deliver not only reductions in emissions, but could lead to the development of consultable techniques and exportable materials, supporting the UK government’s ambition to become a global science superpower.

Carbon capture, usage and storage (CCUS)

Cleaner fuel alternatives account for 43% of fuel burned in the UK, replacing an equivalent of 0.5megatons (Mt) of coal per annum. However, the burning of fuel sources emits 2.2Mt CO2, with a further 4.4Mt of CO2 emissions originating as a by-product of the calcination process that produces ‘clinker’, an essential ingredient in concrete. Funding the development of CCUS technology under its ‘Plan for Growth’ may help government to achieve the targeted capture of 10 million tons of CO2 by 2030, reducing emissions whilst creating new jobs and producing novel patentable materials for next generation CCUS. This could potentially place the UK at the forefront of emission reduction and CCUS technological capability.

There is a key opportunity to make a substantial leap forward in reaching Net Zero goals by 2050, through the implementation of advanced materials in CCUS technologies to capture the flue gases generated in carbon and cement production. CCUS, a broad umbrella of technologies including techniques such as chemical absorption, physical separation and membrane separation, prevents CO2 from being released into the atmosphere by capturing it, then utilising it or injecting it into geological formations for permanent storage.

Capturing cement flue gas through membrane separation does present a number of challenges, which will need to be overcome. These include its high temperature – usually between 85-105°C and 150-180°C depending on the process used – gas composition, and the size distribution of its particulate matter. The flue gas needs to be cooled before it can be separated, otherwise it may cause damage to the membrane. This ‘waste’ heat, however, could be used as a source of energy and/or heating for the CCUS or concrete production facility, helping to offset its energy-based carbon footprint.

It is desirable to reach carbon capture rates of over 80%, this may be achieved using advanced materials. By incorporation of nano-scale fillers that increase the membrane's CO2 'attraction' or by surface modification of the membranes with materials that reversibly bind the CO2 allowing for latter extraction.

Self-healing concrete

Two of the greatest problems, when working with concrete, are its natural cracking and its cracking due to poor workmanship. When concrete damage reaches a destructive level, there is currently little to be done beyond demolishing the structure and recycling the concrete as aggregate for a fresh batch of concrete. As we develop more infrastructure, and as our existing infrastructure ages, the annual cost of maintaining it increases. The introduction of self-healing concrete could help to reduce maintenance costs

The advanced materials which are used in self-healing concrete may include:

 

  • Microcapsules, which disperse within the cement. These are loaded with healing agents that rupture when cracks propagate, releasing the healing agent into the crack
  • Bacterial spores and nutrient sources which, again, randomly disperse within the cement, creating calcium carbonate deposits on crack surfaces
  • Flow networks – small diameter hollow networks loaded with healing agent. Dispersed within the concrete, these rupture and release their healing agent into the cracks
  • Shape memory polymers (SMP): these are strands of polyethylene terephthalate (PET) within the cement, which shrink in response to heat or an electric current. The resulting shrinkage closes cracks in the concrete and allows for nano/micro scale healing.

Self-healing strategies are well-established in research and are already commercialised, but are more expensive than standard concrete – one producer has reported an increase in price of £25/m3. It is these upfront capital costs that are the undesirable factor for private construction ventures; maintenance costs are significantly lower, almost negligible, over the material’s life. An opportunity presents itself, however, if the UK can drive the cost of these self-healing additives down and scale up production.

Investment in partnerships between research and manufacturing would enable the establishment of self-healing additive research and manufactory centres, allowing the UK to produce both self-healing microcapsules and bacteria/nutrient mixes for the industry. This type of investment would ensure we are able to proactively reduce the cost of self-healing additives, whilst simultaneously providing the UK with a new marketable product.

Additive manufacturing of engineered cement composite (ECC)

Additive manufacturing of engineered cement composite (ECC) could enable the UK to capitalise national concrete production, reducing the requirement for imported materials – the UK produces 95% of its own concrete, with the average distance from supplier to client around 12 kilometres. Concrete is considered a material with high strength, however cracks form due to brittle concrete formulations limiting its tensile strength. Ductile concrete is created through the introduction of polymers, such as high-density polyethylene (HDPE), that are able to elongate without breaking but possess low strength. The development of advanced materials, which exhibit pseudo-ductility – the abilities of high strength and ductility (a high value of elongation) simultaneously – offer a solution. ECCs distribute polymer fibres within the cementitious matrix to achieve this solution.

In addition to maximising national resources, 3D printing of ECC (3DP-ECC) could potentially offer a viable route to tackle the rising cost of housing. Homes need to be built faster, and more affordably: using additive manufacturing could increase build speed via automation. One of the key benefits of working with 3DP-ECC is the potential to omit the need for a steel formwork, which can account for approximately half the cost of cast-in-place construction projects[ii]. By being able to build housing and offices faster, using less steel and with improved structure ductility, we will be able to accommodate for an ever-growing population with a lower construction cost and carbon footprint.

The price of 3D printing has decreased drastically in the last decade, with the average small household unit now costing only a few hundred pounds, and the technology offers a key opportunity for us to construct a net zero future. In 2018, a cost viability study of 3D printed houses in the UK identified that, technology pricing aside, it would be possible to 3D print houses 30% more cheaply than can be achieved through traditional construction methods.

There are, however, challenges for 3DP-ECC, in relation to materials, printers, design and construction. However, where there is a challenge there is also an opportunity: for a one-off investment to stimulate the development of 3D printed construction, through an academic partnership, similar to that established by the EPSRC for self-healing concretes, enabling the UK to cement its place (pun intended!) as an advanced construction scientific superpower. If UK Advanced Materials were able to fund collaborative research – similar to that of the EPSRC’s ‘Materials for Life’ (M4L) and ‘Resilient Materials 4 life’ (RM4L) projects – for self-healing materials, the UK could develop a suite of reliable ECC blends and 3D printing protocols that have the potential to revolutionise the way we build.

As with all the steps being taken on the journey towards Net Zero, there will be no single, magic bullet solution – it will take collaboration and a range of innovations in existing technologies and practices to reach our goal. Often, the greatest leaps forward humankind makes, are in the combination of technologies rather than a single material or idea, and the decarbonisation of concrete and cement production will require a similar approach.

 

References

[i] ‘CO2 Capture, Use, and Storage in the Cement Industry: State of the Art and Expectations’. Marta G. Plaza, Sergio Martínez and Fernando Rubiera. 2020, Energies.

[ii] ‘Vision of 3D printing with concrete — Technical, economic and environmental potentials’. Geert De Schutter, Karel Lesage, Viktor Mechtcherine, Venkatesh Naidu Nerella, Guillaume Habert, Isolda Agusti-Juan. s.l.:Cement & Concrete Research, 2018, Vol. 112.