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Belgian manufacturers now stuff their building blocks with CO2

After development suddenly stalled, Flemish family businesses energetically picked up the carbstone technology. Their CO2-negative building blocks are now finding eager demand.

Björn Gubbels is unstoppable. The 44-year-old top executive of concrete manufacturer Gubbels is overflowing with enthusiasm about the carbon-negative building block his company launched late last year. The demand for his product now exceeds his production capacity, but that took a long road and substantial investment.

The making process required converting one of the drying rooms at the Maasmechelen plant into a so-called curing room. In it, the newly pressed, still soft concrete bricks are exposed to the greenhouse gas and fill up completely. Not only that: the CO2 reacts with the sand and gravel pellets used, which are a by-product of stainless steel production.

After 24 hours in the curing chamber, at atmospheric pressure and a temperature of thirty degrees, the blocks have reached their final strength and can go straight to the construction site. They don’t have to harden for weeks first. All without a drop of cement. The greenhouse gas causes the binding reaction. Each stone contains about one and a half kilograms of CO2.

CO2 negative is actually positive

Even if you include emissions for transportation and assembly, the end result of the masonry block wall is still generously CO2-negative, according to Gubbels. “So this is positive” he emphasizes. He himself prefers to talk about building blocks that store CO2. “That, of course, is much smarter than pumping the greenhouse gas into an empty gas field.”

The basis of the carbstone technology that Gubbels is working with comes from Orbix, a Flemish company that reprocesses residues from mainly the steel industry into usable raw materials. The materials have traditionally been common in road foundations and asphalt. Back in 2011, Orbix patented carbonatation technology, which involves calcium oxide reacting with CO2 to form calcium carbonate.

Björn Gubbels (left) leads around the curing chamber where rocks are saturated with CO2. Photo: Marco Mertens / Orbix

Around 2014, the company thought it had struck a major blow when Dutch sand-lime brick producer Calduran embraced the technology. With the daughter of multinational CRH on board, the whole world would open up, they thought at Orbix in Genk.

Expectations were also high at Calduran. A development process was established, leading to a variant of limestone in which the bricks were saturated with the greenhouse gas in an autoclave. In 2018, the two companies made it to the NOS news and other news bulletins, announcing the construction of a real factory for the offset stone.

But it never came, and the multinational withdrew. That was a huge bummer for Orbix development manager Dirk van Mechelen, he acknowledges. “We were really devastated for a time. Fortunately, in the background, parties such as brick manufacturer Vandersanden were also experimenting with the technology. The family business was keen on a CO2-negative facing brick and had already conducted promising trials at our pilot plant near Charleroi.”

In a pilot plant in Kloosterhaar, Calduran produced “compensation bricks” in 2016. Photo: Toma Tudor

Contacts with Gubbels had also existed for some time. The concrete manufacturer had been incorporating ground steel slag into their earth retaining Masterblocs since the 1990s. “We knew all too well how hard the stuff can get if you leave it in storage unused for too long,” the director recalled. “After a while you couldn’t get it off with the heaviest wheel loader.”

It was Van Mechelen, a geologist by trade, who pointed out to Orbix’s top in 2003 that this hardening comes from carbonation. A process underlying many natural rockformations. With his remark, Van Mechelen ignited a spark in the company.

"As a family business, we don't suffer from the short-sightedness of shareholders."

A seed was then also planted with the current Gubbels director. But only when CRH dropped out did he raise his finger. “Then we’ll do it,” he reflects. “As a family business, we don’t have to deal with short-sighted shareholders and can look much further into the future.”

Carbstone. The investment of the future

“Gubbels is really a pit bull, he has done an incredible amount of work,” says Van Mechelen. “He is now even managing to sell his products at a higher price than the classic blocks of cement. Maybe that’s temporary, but it allows him to recoup investment costs faster.”

Gubbels does not beat around the bush that he had made a big mistake. “When I raised my finger, I thought an investment of 300 K would suffice. Meanwhile, our counter stands at over 2 million euros.” Every time, something else had to be figured out, the top executive explains. “Then a pressure valve didn’t work, or it turned out another fan was needed to circulate the CO2 properly. It didn’t stop there. But now we can produce the bricks at atmospheric pressure and room temperature. With that, the footprint of our bricks is really much better than Calduran’s at the time. Even our solid bricks are completely saturated in 24 hours.”

Consequently, he has no regrets about the investment. The launch took place last year at a Besix transformation project. Afterwords they let us know that they known that it wanted to work with carbstone as much as possible from now on. Colruyt and other contractors followed.

'Demand exploded'

Gubbels notices this on a daily basis. “Demand exploded last year, exceeding our production capacity over twenty times. So we often have to say no. We are now busy scaling up production and converting another drying room. It won’t be the last one.” He considers this to be an extraordinary experience in a concrete market that has has collapsed by 30 percent.

Vandersanden, which has been in talks with Orbix for much longer and invested 30 million euros in a new factory, is also reaping the benefits of all the hard work. For example, the brick manufacturer modified the curing room based on Gubbels’ latest findings.

"We are not childish in sharing our findings. We want good products to come to the market."

When developing its CO2-negative facing bricks, Vandersanden paid close attention to aesthetics in addition to properties such as compressive strength and frost resistance, emphasizes program manager Dries Beyens. “The latter is crucial with façade materials. The Pirrouet, as we call the stone, offers designers plenty of variations in color, texture and masonry bond. And at the same time, it meets the most stringent European requirements for ceramic facade materials.”

The bricks recently adorned the facade of the new house of the future in Brussels and were still being produced in Orbix’s pilot plant. But next April its own factory will be operational. Then facade bricks roll off the conveyor belt every day, permanently storing sixty kilograms of CO2 per ton. Twenty million bricks a year.

On the facade of the new “house of the future” in Brussels, Vandersanden’s CO2-negative facing bricks adorn the building. Photo: Vandersanden.


And at Calduran? Are they working on a successor to the compensation stone there? The company would not comment on that. Van Mechelen of Orbix, however, thinks they are not sitting still there. He saw new patents come along in CRH’s name. Although he is still disappointed that the collaboration went awry, he welcomes this development. “It will only benefit the technology if more parties start using it.”

This is also how Gubbels sees it. The entrepreneur still sees an endless parade of products for which the technology is suitable. Armed blocks, for example. Not with steel, because that will rust because of the CO2, but with basalt reinforcement or plastic rods. Gubbels even muses on floors and bridge girders made of carbstone.


The only fear the concrete director has is that this growth market will attract cowboys who supply inferior products. If problems then arise with longevity or quality, it irrevocably affects all carbstone products. “This is another reason why we are not childish in sharing our findings. We want good products to come to the market. Vandersanden and Orbix are also very open. It’s the only way such pioneering, sustainable technology has a chance of succeeding.”

Source: Cobouw, Dec. 20, 2023