First circular footpath in Ghent

A raw material for sustainable building materials

These are made by allowing a residual product from the steel industry (steel slag) to react with CO₂. Because no cement and concrete products are used, this new method has a much lower impact on the environment. Besides, the technology makes it possible to produce products with the same technical properties as conventional concrete products. It was developed by VITO and Orbix.

The Flemish steel industry produces more than 700,000 tonnes of steel slag as a by-product every year. Worldwide, this amounts to as much as 200 million tonnes. By adding CO₂ they now become a raw material for sustainable building materials.

That three-step process is called carbonation

• Calcium-rich steel slags are grinded into an ultra-fine powder.
• The powder is mixed with water to create a homogeneous mixture and pressed into a given shape.
• The porous stones are placed in an autoclave and treated with CO₂. Carbon dioxide is absorbed and converted into calcium carbonate, a strong binder that replaces cement.

The result

A durable building block with the same qualities as a classic brick. The big difference: no new raw materials are used and CO₂ is permanently stored, not emitted into the atmosphere. For example, 1 m³ of carbstone bricks stores a net 350 kg of CO₂.

The Carbstone technology has many advantages

• It is a circular building material. For example, steel slag, a by-product of the steel industry, is reused: the metal goes back to the steelworks and the residual fraction is used to make facing bricks and other building materials.
• Carbstone is just as strong as traditional tiles and bricks.
• No cement is needed: this reduces the cost and increases sustainability.
• The carbstone technology captures CO₂ and contributes to achieving global climate targets.
• The technology can be applied to other materials