Expert Q&A: Decarbonising concrete and cement

Cement and concrete underpin modern construction, but their associated carbon emissions are enormous, accounting for up to eight per cent of the global total. The Engineer quizzed an array of experts working on solutions to decarbonise the materials.

Meet the experts:

  • Gianluca Ambrosetti - CEO, Synhelion
  • Dr Philippa Horton and Sam Bell - Cambridge University & Materials Processing Institute, Atkins, CELSA Manufacturing, Balfour Beatty, Tarmac Cement and Lime, and Day Group
  • Dr Theodore Hanein and Dr Cecilia Pesce - FeRICH Project, Sheffield University, Department of Materials Science and Engineering
  • Andreas Sichert - CEO, Orcan Energy

How does your solution help reduce the carbon emissions associated with cement production?

AS: We turn the huge amount of waste heat from cement production into clean, affordable and reliable electricity. Waste heat is the largest unused energy resource in the world. Our modules can be installed wherever waste heat is generated. As the energy-intensive cement industry seeks to achieve climate neutrality, waste heat recovery (WHR) offers a key solution. We’re talking about a massive potential: recovering the waste heat from all cement plants worldwide with our second-generation Organic Rankine Cycle (ORC) modules would generate power of a yearly volume of around 67 TWh which represents the electricity demand of all private households of more than 40 million European citizens. Harnessing this clean energy potential would save approx. 30 million tons of CO2 (depending on the considered electricity mix).

For a zero-carbon future in cement production, the industry needs to adapt and reinvent itself.

PH: Despite exploration to reduce emissions in cement production, there is currently no viable strategy to reduce process emissions to zero. Cement is therefore one of the most challenging areas of decarbonisation faced by the developed world.
Cambridge Electric Cement does not aim to reduce carbon emissions from the process: it hopes to remove them entirely. It uses the process of electric steel recycling with old cement powder to create a product which is then ground to produce a conventional Portland clinker. This method, together with a grid supplied by non-emitting electricity, has neither process nor combustion emissions, and therefore would create the first truly zero-emissions alternative to existing cement production. The Cement 2 Zero project will trial this innovative product for the first time on an industrial scale.

CP: The way using iron-rich waste products from the steel industry reduces carbon emissions is threefold:

1. A smaller amount of calcined limestone is used as this is replaced by the iron-rich waste. In traditional cement production the calcination reaction of calcium carbonate releases the embodied carbon of the limestone into the atmosphere. When less of this is used, less CO2 is emitted.

2. Using a higher amount of iron lowers the burning temperature necessary to produce clinker - the key precursor in cement. Usually the high temperatures are almost exclusively achieved by burning fossil fuels.

3. Waste products available in large amounts are upcycled instead of being sent to landfill.
GA: During cement production, there are two main sources of CO2 emissions. Synhelion’s sustainable technology is applicable to mitigate both.

One part of the emissions stems from the burning of fossil fuels to heat the pyro-processing stage for clinker production. We can replace the use of fossil fuels with concentrated solar thermal (CST) energy, delivering sufficient high-temperature process heat beyond 1,500°C. The other part of the emissions is produced during the calcination process. We can recycle these unavoidable CO2 emissions for our solar fuel production. This solution further reduces the overall emissions of the cement production process.

What are the biggest technical hurdles you have encountered so far?

CP: So far the biggest technical hurdle came when we were studying the pure/solution ferrite phase at the clinkering temperatures of Portland cement (>1400C). This was because the samples would melt, react with the Pt crucible and become unusable for further analysis and characterisation. For now, we are working around this by firing samples below melting temperature, but in the future we might try quenching methods that allow us to retrieve ferrite samples fired at 1,450C from the crucible. However, we cannot normally quench cement in water, because cement reacts with water.

CO2 intensity derived from cement production has increased by about 1.5 per cent annually between 2015 and 2021. -

GA: Together with CEMEX, we’ve already been able to introduce CST in the cement production process, achieving the first successful laboratory-scale demonstrative pilot in 2022 by producing the first-ever solar clinker. The process needs now to be scaled and developed further. Together with CEMEX and Sandia National Laboratories, we are investigating methods to maximise heat transfer to the raw cement mix and increase the efficiency of clinker formation using solar energy. In the next steps, we target continuous daytime production and a pilot facility at an industrial scale to demonstrate the robustness and economics of the process.

SB: The primary challenge of any innovation in this area is scalability. With electric cement recycling in particular, the technical challenge we face is scaling from production of 1kg of cement to 20 tons of cement – and finally to the volume required to supply all future demand. Cement 2 Zero is now taking its first steps on the journey to solving that challenge.

AS: Waste heat recovery with the ORC technology was a long-proven technology in geothermal power plant construction. But it couldn’t be applied to the broader field of industrial waste heat sources and lower temperatures in everyday industrial processes – where we see the bulk of energy. Instead, the traditional ORC plants could only harness big heat sources, a very limited scope. We managed to improve this technology and massively reduce its dimensions to make it more applicable. Consequently, we made waste heat recovery more cost-efficient and hence significantly more often commercially attractive. This widely applicable second-generation ORC can have a major impact on decarbonising the cement industry – starting right now.

Can cement and concrete production be truly zero carbon in the future?

GA: By 2050, the cement industry aims to reach the net zero carbon goal. Achieving this goal requires constant and relentless innovation. Speaking for Synhelion, we are willing to deliver a major part: our solutions will significantly help to pave the way towards net zero.  The successful adoption of our technology in cement manufacturing will allow for 100 per cent replacement of fossil fuels, which are responsible for approximately 40 per cent of the direct CO2 emissions of the production process. And we can recycle the remaining CO2 emissions from cement production during the calcination process. With a very effective and economical cement carbon capture technology available, we could use the emissions directly for the production of solar fuels.

PH: If we can prove that C2Z can be produced on an industrial scale through this two-year demonstrator project, then it is possible we could conceive a world in which cement production produces zero emissions. Together with our supply chain partners, we are at the beginning of this challenging journey, but by bringing the collective expertise of all the entire supply chain around the table, the cement, steel and construction sectors are better placed than ever to find the optimum solution.

AS: For a zero-carbon future in cement production, the industry needs to adapt and reinvent itself. To keep on track with a Net Zero Emissions by 2050 scenario, cement production needs to decline by 3 per cent annually until 2030. Some players have started to act, but overall, the industry is nowhere near achieving this target. CO2 intensity derived from cement production has increased by about 1.5 per cent annually between 2015 and 2021. That’s why we need solutions having an impact right now. We are ready to deliver our part with modular waste heat recovery systems, saving carbon emissions from day one and still being flexible towards new technologies and changes on the cement plants themselves.

Should we be looking for alternative, more sustainable building materials, alongside trying to decarbonise cement?

TH: Any action that contributes to reducing global emissions should be pursued. Developing new building materials that reduce carbon emissions, including those of cement, is important for a sustainable future. Additionally, reusing construction materials from old buildings, including concrete, can result in a lower carbon footprint than using new ones. However, as it stands, the production and use of cement will not be phased out in the foreseeable future, so any effort aimed at lowering its carbon emissions is valuable.

AS: As of now, cement is an integral part of our everyday lives – it is the second-most consumed product worldwide after potable water. Currently, the silver-bullet roadmap towards decarbonisation of the construction industry does not exist and the eventual route remains uncertain. We definitely need a joint effort to decarbonise the industry, open to all types of solutions. At the same time, we need to harness the solutions being feasible today. By integrating waste heat recovery facilities in plants, manufacturers can increase the electrical efficiency and alleviate emissions.

GA: There is no silver bullet to tackle climate change. In cement production – as in any other field – we should constantly be looking for diverse sustainable solutions and alternatives. As of now, it’s impossible to imagine a world without concrete. It’s one of the most resilient, affordable, and durable construction materials. We need it for almost everything we build, and more importantly concrete is a construction material that is versatile. That’s why we are helping the cement industry to decarbonise. To achieve net zero and meet global commitments, there is no shortcut.