How to decarbonise the world’s cement

We have several options. Can any compete on price?

I recently wrote about the impact that a “green premium” on cement and steel would have on the price of final goods, such as buildings and cars.

In that analysis, I used a fairly standard estimate of the extra cost that comes from adding carbon capture and storage (CCS) to cement production.

That, of course, assumes that CCS is the option we have. 10 years ago, that looked like it might be a given. There weren’t many other solutions for how to achieve low-carbon cement. But this is no longer the case. It might actually be possible to produce “green cement” for the same price, or cheaper.

After writing that post, I promised a few readers that I would do a deeper dive into cement and how we might decarbonise it. 

It seemed like the perfect time to do so. Last week I was at Gates’ Breakthrough Energy Summit, where there were a bunch of innovative companies trying to solve these problems. I got to speak to a few working on low-carbon cement, and ask some questions about the barriers to scaling these solutions.

So, here it goes. A short tour of global cement and what our decarbonisation options are.

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It’s impossible to produce traditional cement without CO₂ emissions

The world produces about 4 billion tonnes of cement every year. This production is unlikely to slow down much: incomes in low- and middle-income countries are going to grow, and billions of people globally are going to shift from rural to urban areas over the next few decades. The world is going to build a lot of stuff.

The cement industry is responsible for around 7% of the world’s CO₂ emissions. Or around 5% if you’re including all greenhouse gases.

This CO₂ is produced in two ways. 40% of emissions come from the demand for heat. Cement is produced from limestone at very high temperatures. Currently, fossil fuels are used to generate those high temperatures. That is a problem of decarbonising industrial energy.

The other 60% comes directly from the process itself. To understand this, we need to look at the chemical formula and conversions that take place in the reaction.

To make cement we take limestone, which is calcium carbonate (CaCO₃). We churn it up at very high temperatures – around 1500°C – to get two products. Calcium oxide (CaO), which is the core ingredient in cement, and CO₂ as a by-product.

So we have the following:

It is simply not possible to do this process – use limestone to make cement – without emitting CO₂ as a by-product.

This is the fundamental climate challenge with cement.

Knowing this, there are three main buckets of solutions to reduce emissions from cement. We either:

1. Use less cement

2. Keep the current process, but handle the CO₂ at the end of the chain

3. Find a new process for making cement.

Let’s look at the prospects for each.

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Option 1: Use less cement and more supplementary cementitious materials (SCM)

“Use less cement” could be interpreted as “build less stuff”. While there’s maybe some scope for that, I’m not here to dictate how many buildings, bridges, roads, wind turbines and other infrastructure the world should have.

Like it or not, the world is going to use a lot of cement over the next 50 years, so we need to find another way to decarbonise.

You can, however, build the same amount of stuff using less cement. That’s because we really build stuff out of concrete, not cement. It’s easy to use these terms interchangeably, but they’re not the same. Cement is an ingredient. Mix it with water, sand, gravel and other materials, and you get concrete.

These other materials are often referred to as “supplementary cementitious materials” (SCMs).

We would use less cement in our concrete and bulk it up with these other materials instead. What’s interesting is that countries already use different concentrations of cement. Europe and the United States tend to use more than other countries, without big gains in strength as a result.

This won’t get our emissions all the way to zero since we’ll still be using some cement. But it could cut them substantially. The Alliance for Low-Carbon Cement & Concrete looked at the impact of reducing the concentration of cement in concrete in Europe from 78% in 2020 to 60%, 50% or 40% by 2050. This would cut CO₂ emissions by 28%, 40%, or 52%.

The biggest barrier here is construction regulation and building codes. The industry (rightly) has strict rules around what materials can and can’t be used to make sure buildings, bridges and other infrastructure are safe. There are regulations on what concentration and mix of cement has to be used in concrete.

To use these new concrete mixes, countries would need to see a change in building codes. Of course, safety needs to be the top priority, but if these companies can prove that lower cement concentrations are just as strong as what we use today, then it could be an almost immediate solution that cuts emissions a lot. This could be an ideal way to limit the sector’s emissions while zero-carbon solutions take time to scale.

Ecocem is one company that’s trying to drive this forward.

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Option 2: Carbon capture and storage (CCS)

The next solution keeps the current process that we have today but captures the CO₂ at the end of the chain. You can then either transport and store it underground, so doesn’t get into the atmosphere. Or reinject it back into cement, where it’s stored. A company called CarbonCure is innovating on this last solution.

It’s the same concept as carbon capture and storage (CCS) proposals for power generation. Can’t get rid of a coal or gas plant? Capture the CO₂ from the stack and stop it from being released into the atmosphere.

This should be technically feasible for cement, but they might not be able to capture all of the CO₂. Many CCS plants today are designed to capture 90%; getting to 100% can be incredibly expensive with large diminishing returns. Some other studies suggest that actual capture rates are even lower than 90%. Nonetheless, I think that cement plants will be able to capture the majority of their CO₂, even if they’re not doing so today.

The biggest barrier is cost.

Building carbon capture infrastructure onto an existing cement plant costs money. It’s almost impossible to make it cheaper than running a plant without it.

This is where the “green premium” comes from: the extra cost of the CCS equipment. Estimates from a few years ago had this premium at around 75%.¹ Some companies working in this space – such as Leilac² – say they have this down to $40 per tonne.³ The argument they make is that heat from the cement process itself can be recycled and used to drive some of the capture process. That should make it a bit cheaper than CCS from power generation. Until these plants are built, it’s hard to verify the true price tag.

CCS is arguably the most established technology for decarbonising cement today, but its downside is cost. Without a decent carbon price, it’s unlikely to be cost-competitive with traditional cement.

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Option 3: Using a different source rock

Some companies are tackling the cement problem in the opposite direction.

Rather than trying to clean up the problem at the end of the chain – once the CO₂ has been produced – why not try to stop it from being produced in the first place?

Using limestone (CaCO₃) for cement makes CO₂ inevitable. But maybe we don’t need to use limestone at all. If we use a source rock that doesn’t emit carbon, then there’s nothing to scrub up.

The company Brimstone is innovating by using basalt or other calcium silicate (Ca₂SiO₄) rocks as source. The good news is that basalt is the most abundant surface rock on Earth – there’s a lot more of it than than limestone – so there should be no concerns about shortages or supply chain risks, and it should be pretty cheap.

Calcium silicate produces calcium oxide – the same ingredient that’s used in traditional cement – but without any CO₂ by-product. That’s because there’s no carbon in there. Instead, it generates other products that are actually useful.

First, the “supple­men­tary cemen­ti­tious materials” (SCMs) that we talked about in Option 1. This would reduce dependency on inputs from other industries, such as steel or coal slag. Second, it produces magnesium compounds, which can actually absorb and remove CO₂ from the atmosphere. Brimstone claims its entire process would actually be carbon-negative. Let’s see if that holds true once these processes get running at scale.

Combine these benefits—an abundant source rock, no carbon to capture, and valuable co-products—and we might have a clean cement solution that’s cost-competitive, if not cheaper, than traditional cement. To me, this is the most promising option for producing low-carbon cement without any green premium.

It might have some regulatory barriers to overcome – we would be changing the cement process that has been used for well over 150 years. But in principle, the cement that’s produced should be chemically and structurally identical to traditional cement, so this should be fairly easy to overcome.

The main barrier here is scale. Brimstone has proven this technology at the lab scale. They’re now building a pilot plant, and it might be some time before they go commercial. Remember, the cement industry is on a billion-tonne scale, so even if they manage to produce a million tonnes in these early stages, it’ll still be a tiny slice of the pie.

This is no different from innovations in other sectors. It usually takes well over a decade to scale. But if you have an effective and affordable solution, though, it then starts to fly.

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We probably need multiple approaches

I’ve summarised these three options in the diagram below. Note that the companies and approaches I mentioned above are not exhaustive. I’m sure there are other innovators in this space developing slightly different solutions.

It’s tempting to pick a “favourite” or go all-in on one concept. That would be a mistake.  

It might be well over a decade before innovations like Brimstone are ready to hit the global stage. That doesn’t mean we should sit on our hands and wait for it to happen. In the meantime, we could drive down emissions by using lower concentrations of cement (option 1) or retrofit existing cement infrastructure with CCS (option 2).

Hand-picking one solution is a luxury we just don’t have.

Cement is one of the “hard-to-abate” sectors that makes people pessimistic about net zero. A decade ago it seemed like an insurmountable challenge. Not anymore. Hard, yes. But not impossible.

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1. https://www3.weforum.org/docs/WEF_Net_Zero_Tracker_2023_CEMENT.pdf

https://rmi.org/five-insights-on-the-concrete-and-cement-industrys-transition-to-net-zero/

https://www.breakthroughenergy.org/our-approach/the-green-premium/

2. This stands for “Low Emissions Intensity Lime And Cement”.

3. This is the estimate from Chris Goodall’s book Possible, after speaking to its CEO, Dan Rennie.