Pathways to decarbonising the cement industry

Cement production accounts for 7% of global greenhouse gas (GHG) emissions, making it one of the highest-emitting industries. Cement is also the most used building material – in fact, cement is the single most widely used man-made material – meaning decarbonising it is an urgent need.

Strategic approaches to novel materials and processes in cement production will be critical along the journey to net zero. We see five pathways to decarbonising the cement industry, each of which are necessary to address this hard-to-abate sector.

Why is cement decarbonisation so urgent?

Almost all cement in the world is “Portland cement.” It’s made from elements found in limestone, and is cheap because limestone is nearly ubiquitous. This is why we use it – not because it’s necessarily the best material for the job, but because today, it makes good financial sense. 

However, the production process of Portland cement is problematic. The material has a uniquely polluting chemistry. Most of its emissions come from an unavoidable chemical process known as calcination. Limestone is heated to about 900 degrees Celsius, separating into lime and CO2 as a result. 44% of the mass of limestone turns into CO2. These emissions, in addition to the emissions from burning fossil fuels to produce the required heat, work out to almost a ton of CO2 produced for every ton of cement. 

Unfortunately, it’s unlikely we can solve Portland cement with carbon capture. Its emissions are mixed together and come out hot, dirty, and unpressurised – conditions which aren’t exactly ideal for the carbon capture process.

In recent years, global cement production is just over 4 billion metric tons per year. If the industry were a country, it would be the third largest emitter in the world.

But this is a problem we can solve. In this article we’ll explore five key pathways to decarbonising the cement industry – a necessary precursor to achieving net zero. 

New technologies

We need new processes, new technologies, and new ways of recycling existing materials. Portland cement can no longer be the norm. There are already existing alternatives (engineered timber and geopolymers to name a few) that are more sustainable and transportable for the same structural virtues. But here we will focus on ways that might enable us to continue to produce the grey glue that holds our world together.

Electrochemical cement production

Electrochemical cement production is one solution. Sublime Systems has developed an electrochemical approach to producing lime, a key ingredient of cement that enables high water retention and low air content for increased bond strength. Their approach is done at room temperature, which does away with the traditional need for industrial heat to power kilns.

According to Clean Technica, cement emissions would fall by 70% if all limestone used today were put through Sublime Systems’ process. Additionally, their approach can use any material that includes lime, meaning industrial slag and recycled concrete are fair game. If 100% of concrete and EAF slag in the future were put through Sublime’s process (though the odds of this are unlikely), it might provide 10% of the world’s cement needs. 

This might not sound like a lot but it’s a powerful lever to pull.

New ways of recycling

Effective cement recycling could massively reduce its carbon footprint. A team of researchers from Cambridge University’s Department of Engineering is working to combine cement and steel recycling. Used cement can be reactivated when exposed to high temperatures. The idea is to prove it can be done by piggybacking on the heat generated by other industrial processes. In this case, it turns out the slag used in steel recycling is almost the exact same composition as that of used cement.

Of course, the process will need to be done in electric arc furnaces powered by renewable electricity. The hope is that this process will prove to be more economical because it uses what is essentially waste heat from the steel recycling process.

New ways of heating

Traditional cement production involves heating raw materials to temperatures upwards of 1,450°C. Today that heat is powered through burning fossil fuels. Decarbonising the cement industry requires that we implement new ways of powering this process. We see three possible pathways to replace fossil fuels in industrial heat.

Electricity. A techno-economic assessment of four electrified cement plants found that:

• Electrification is competitive under low-cost electricity scenarios

• Partial electrification (with combustion of alternative fuels) is more competitive

• Carbon capture should complement electrification
  

Hydrogen. Green hydrogen, which ‘emits’ only water, can be used in place of fossil fuels:

• The hydrogen must be pure

• It must be economical

• There must be an adequate supply

However, storing and transporting hydrogen is technically challenging. It’s worth considering placing electrolysers directly at cement plants.

Ammonia. Ammonia might serve as a more energy-dense and cost-effective source of hydrogen. Unlike hydrogen, it can be easily transported and stored:

• There are existing infrastructure and protocols in place

• It’s stable at normal temperatures and pressures

Cracking ammonia is energy intensive, but we’re making progress here. A recent breakthrough facilitates a photon-driven reaction that operates at lower temperatures and is as efficient as traditional thermal catalysts.

CO2 collection from the cement and clinker industry

We believe carbon capture could be economically viable in the cement industry under certain conditions. If limestone kilns are electrified, cement production emissions would be fairly pure streams of CO2. This would reduce capture costs significantly. Even better if plants are located beside sequestration plants, reducing the costs and risks of transport and distribution. 

The ideal scenario is to capture CO2 at the point of emission and sequester it into SPSE or DRC pipes. This way, it’s feasible to transport emitted CO2 elsewhere to be re-used in industrial processes such as plastics or biofuels.

Plants in better locations

Advantaged markets with access to cheap renewable power are our best bet for enabling lower-carbon clinker (the key material in cement made by heating limestone in a kiln). New net zero mega plants with carbon capture use and storage (CCUS) capabilities constructed in locations in Europe with CO2 sinks and renewable resources, and in the United States with the support of the Inflation Reduction Act (IRA) could reach a cost advantage of 60%.

Plants placed elsewhere could consider having electrolysers on site, partial electrification paired with alternative fuels, and the use of admixtures to reduce the amount of cement needed.

Displacement

Though global cement production volumes are expected to stay level through 2050, demand is falling. Affluent areas in the West have already built most of their infrastructure. China, too, is reaching the end of building cities. Moving forward, there will hopefully be more repurposing of existing buildings rather than today’s habit of destroying and beginning anew. Additionally, developing countries will likely build their infrastructure with far less materials than the west did, enabled by modern software. 

Cement prices are likely to increase significantly. The EU’s current budgetary guidance for the lifecycle costs of GHG emissions is €250 at a 4% discounting rate in 2030. At that carbon price, the cost of a ton of cement increases from €150 per ton wholesale to €350 per ton. In 2040 it would shoot up to €430 per ton.

One could infer that this rise of cost combined with reduced demand will lead to the displacement of cement for alternative materials. Especially if the previously explored pathways fail to meet scale up potential.

Wrapping up

Decarbonising cement isn’t just a necessary precursor to net zero; it’s also the only way forward that makes good business sense. Companies and countries that don’t decarbonise will be uncompetitive with the ones that do.

We’re particularly excited about the role ammonia will play in cement decarbonisation. On-site cracking of ammonia could be used to generate green hydrogen to power kilns, effectively solving the issue of industrial heat emissions in cement production. We’re excited for what’s to come.