Hey Reader,

Yesterday was our little one’s first birthday.

Nice party, way too much food, and obviously quite some preparation time in the past few days, including some bad nights of sleep.

For a lack of a smoother introduction, I’ll directly get into.

Today’s edition of the newsletter is about concrete. Again.

Some weeks ago I wrote about the circularity aspects of concrete. Now it is time to tackle the real challenge, reducing the CO₂-footprint.

It’s tough to get not too technical but I promise I’ll do my best for this introduction. In later editions I will be talking about start-ups and new products of existing suppliers.

Btw: this is edition #9 of Building Beyond Bau. Thanks for sticking around and all your great feedback! I wrote a short recap on LinkedIn.

Where does the impact of concrete really come from?

Let’s zoom out and take a look at how concrete is made. I used this before but it’s a great visualization.

You need:

• Cement: the glue
• Aggregates: sand and gravel
• Water: you know what water is
• Admixtures: chemicals that make concrete flow faster or slower, make it more frost-resistant,…

While aggregates make up most of the weight, they contribute only a small part of the carbon footprint.

Cement is a different story.

At a global level, cement is responsible for around 7% of global CO₂ emissions.

There are not a lot of cement factories in Europe and the majority is in the hands of four to six big corporates.

That means that for the decarbonization we rely on what these big corporates are willing to do.

Most major producers now commit to net zero by 2050.

But it requires billions in investment.

How is cement being produced?

Producing cement is an incredibly energy-intensive process.

Limestone is crushed and mixed with clay (and sometimes sand).

This mixture goes into a huge rotating kiln (basically a giant oven) where it is heated to over 1,400°C.

At that temperature, the raw materials merge and form small grey pellets called clinker.

Yes, heating the kiln to 1,400°C requires a lot of fuel. Traditionally coal, petcoke or natural gas.

But an even bigger part of the CO₂ comes from chemistry. I don’t have a PhD in chemistry and I don’t think that you have either so I will keep it really short.

Limestone is mainly made of calcium carbonate (CaCO₃).

When it is heated, it breaks apart into:

• Calcium oxide (CaO) which becomes part of the clinker
• Carbon dioxide (CO₂) which is released as a gas

CO₂ is an unavoidable part in the production process.

Normally, that CO₂ simply leaves through the chimney.

How can concrete be decarbonized?

To reduce the carbon footprint of concrete, we need to start with the cement.

Let me walk you through four steps that are having a major impact.

1. Use less clinker

Clinker is the carbon-heavy part of cement.

Here is an overview of commonly used substitutes for clinker that lets emissions drop

Clinker can be partially replaced by slag from steel, fly ash from coal plants, limestone or calcined clay. That lowers emissions immediately.

The issue: today’s “low-carbon cement” still depends heavily on by-products from fossil industries: coal power and blast furnaces.

As those sectors decarbonise, those substitute materials become scarcer.

Which means that the industry has to look for new substitutes. This is one of the reasons why calcinated clay is getting traction.

2. Clean up the energy

Making clinker requires a lot of heat.

Producers are now switching to:

• Alternative fuels (biomass, waste-derived fuels)
• Renewable electricity

About 40% of cement’s emissions come from fuel and energy.

The other ~60% comes from chemistry.

So even a fully renewable kiln does not make cement carbon-neutral.

3. Capture the CO₂

That’s the chemistry part again: When limestone is heated, CO₂ is released. That part cannot be avoided in the traditional process.

So what the heck is carbon capturing?

To make it super easy: it’s like putting a vacuum cleaner on the chimney.

Instead of letting the CO₂ leave through the chimney, it is captured, compressed, transported and stored deep underground. Often in empty gas fields under the North Sea.

Without capture, full decarbonization is nearly impossible in the current process.

Almost every cement companies’ net-zero roadmaps rely heavily on this step.

And I think it’s a necessary step.

But I’m worried.

These vacuum cleaners are extremely expensive. Companies are planning to invest between €250 and €600 million per plant. They get hundreds of millions in subsidies.

We’re in an economic climate where European industry is under pressure. It’s only natural that companies pause or reconsider massive investments. Like we’ve just seen with Holcim in Belgium.

That means many net-zero plans rely on a handful of mega-projects.

If those projects stall, so do the targets.

Don’t get me wrong. CCS is a huge opportunity.

For example, the Holcim project in Obourg alone could cut roughly 1% of Belgium’s total CO₂ emissions.

That’s huge.

But it also shows how concentrated and fragile the strategy is.

4. Use less cement

Reader, if you happen to not own a cement factory here are two other possibilities that you can use in your projects.

Avoid over-dimensioning

In Belgium, concrete is classified using national E-classes (”omgevingsklassen”) alongside the European exposure classes.

At the lowest end sits EI, which applies to indoor, dry conditions. Low exposure. Low durability demand. You can kinda compare it to XC1.

There is a big opportunity: According to Belgian federation FEDBETON, a large share of concrete used inside buildings could technically fall under EI.

This class allows lower cement content and therefore lower clinker. Less clinker means less CO₂ per cubic metre.

Yet projects often default to higher classes than necessary. Habit plays a role. So does risk aversion and copy-paste specifications.

Today, only around 2% of Belgian concrete is specified in the lowest indoor class (EI). FEDBETON suggests that it could be realistic to go up to 15% without affecting structural safety.

That principle is applicable for other countries as well.

Reuse structures and don’t demolish

This one seems simple: Don’t use new concrete at all.

You won’t find that in most industry roadmaps. Because then they’d lose volume.

Yet the potential is enormous. Retrofitting existing buildings avoids the biggest emissions of all.

Brussels is a great example. It’s almost impossible to get a permit to demolish a building. As a result dozens of large office reconversions are underway.

The structure stays.

Keep the foundations. Keep the floors. Keep the walls.

On large projects, that can mean saving several thousand m³ of concrete. Use what is there.

From a carbon perspective, this is the biggest lever.

If we are serious about staying within a carbon budget, renovation without demolition needs to move from niche to focus strategy.

What can you do in your projects?

• Prioritize renovation and keeping structures.
• Challenge your advisors and partners to not over-dimension the concrete.
• Choose concrete with low clinker content

TIP OF THE WEEK When my favourite company talks about biobased construction, there is no excuse. I have to watch. You might have seen it already, it's two years old. But hotter than ever. It's about a company from the US building houses with straw. Beautiful images, high-quality production and Patagonia's founder talking about sustainability in construction. What else do you need as inspiration to start the upcoming week?! ​

That's it for this week.

Enjoy the rest of this beautiful Sunday.

Best,

Simon