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An ancient but forgotten application

Carbstone emerged from the synergy of our decades of experience as a manufacturer of building blocks, valuable research insights from the Vito, as well as the expertise provided by our partner Orbix. Carbonatation is the natural process by which Ca-containing materials react with carbon dioxide and transform into calcium carbonate. That calcium carbonate, better known as limestone, is found worldwide in the subsurface and is a major source of natural CO2 storage. Although the Romans already knew how to make clever use of this process, it disappeared into the background for a long time. Until recently, because of the demand for sustainable CO2 storage, there was renewed interest in it from industry.

In addition to CO2, a source of calcium oxide is needed, in this case steel slag. These slags are a byproduct of the steel industry and have been recycled for years to recover the metal and gravel. What remained had no industrial use until recently. However, thanks to this patented process, by adding CO2, it can now be used to produce high-quality and sustainable building materials.

Production Process

No magic, though it comes pretty close.

The manufacturing process of our Carbstone blocks consists of 6 steps, which we explain below in words and pictures.

Want to know more? If so, please do not hesitate to contact us. Our experts will be happy to assist you!

Production process Carbstone

In this video, we show you the manufacturing process of our circular and CO2-negative Carbstone building blocks. These are a durable, cement-free alternative to traditional concrete block and are available in numerous designs.


This slag is a waste product from the steel industry.


Through an upcycling process, the steel is separated and then recovered.


What remains is a mineral fraction. This forms the basis for the final product.


The mineral fraction is further supplemented to form a concrete-like composition without cement.


That composition is pressed into blocks or other products, which are automatically driven into the drying chamber.


Here they undergo a CO2 cycle. After 24h, they are fully cured and ready for transport and use on site.


Always further and better thanks to continuous development

Since producing our first batch of circular masonry blocks, we at Masterbloc have certainly not been idle. Soon Climasonoblocks, bondable blocks as well as our acoustic Soundblox – produced with Carbstone technology – rolled off the assembly line.

To this day, together with our partners, we remain fully committed to further development and optimization. We do this in our mobile test lab, where new developments and applications are first tested and fine-tuned on a small scale before being manufactured on an industrial scale in our high-tech, automated production environment.

Our goal? Defining the construction industry of tomorrow with innovative and circular products that reduce the impact on the environment, thus contributing our (CO2-negative) bit to the Flemish Concrete Agreement
and the European Green Deal. Our long-term ambition is to completely eliminate the use of cement, which accounts for some 10% of global CO2 emissions – from our production site; and to manufacture our entire product range including stacking blocks using this innovative and circular technology.