Carbstone

” Each year Belgium’s (stainless) steel industry produces over 500,000 tonnes of steel slag as a by-product. Specialists – such as Orbix – process this slag on behalf of the steel industry and, in doing so, recover residual steel. “In the 1990s, the slag was dumped after the ore had been removed. These days, we turn it into bricks or so-called carbstones .”

In 2004, the recycling company Orbix discovered that the finest residual particles of slag can be hardened with CO₂ and water. “This is a natural process, based on the so-called carbonation of calcium oxide, leading to the creation of calcium carbonate”, explains Dirk Van Mechelen, head of Research and Development at Orbix. “Calcium carbonate is a binding agent and can fill pores. This allows us to create an effective and hard building material, with which bricks, paving stones, tiles and roof tiles can be made.”

Onto the market

Research and development in partnership with the Flemish Institute for Technological Research (VITO) led to the development of a patented process and the foundation of Carbstone Innovation in 2009. “The carbonation process is very simple, but it still took us almost ten years to refine the basic technology. In 2013, we built a pilot plant in Farciennes, near Charleroi, in order to be able to produce large blocks. Small blocks do not convince industry.”

In 2016, Carbstone Innovation signed its first deal, with the Dutch company RuwBouwGroep CRH. “We just supply the raw materials. The RuwBouwGroep do the stone production themselves in their own factories. The building market is very competitive, which is why we are using a company with the right expertise to launch the carbstone onto the market.” Van Mechelen anticipates a snowball effect on a commercial level.  “In 2017, we aim to set up a production installation for the Belgian market. At the same time, we will develop a licence model to commercialise the technology across the globe.”

No loss of quality

The quality and characteristics of carbstones match those of existing bricks. “Customers experience no difference”, emphasises Van Mechelen. “However, carbstone is naturally much better for the environment. We not only recycle all remaining steel slag, we also capture the greenhouse gas CO₂. The carbon footprint of carbstones is approximately 600 kilograms CO₂/tonne less than conventional concrete.”

“Innovation is, of course, influenced by economic motives. It costs a lot to send waste to landfill. So we went out looking for a suitable application. Carbonation is carried out without the addition of precious binding agents such as cement, which means there is a significant cost saving.”

Infinite list of applications

Carbstone Innovation has not been idle over the last few years. “Besides carbstone, we have also developed various other uses”, claims Van Mechelen. “We use the residue of steel slag in the top layers of asphalt roads, as a filling instead of ground limestone and as granulates in concrete. We are also in the final phase of our research into its use in plastic. With such a variation of end products, we can use 100 per cent of the residual fraction. In the last ten years, we have not needed to send a single tonne to landfill. We are currently looking at whether carbonation technology can be used on other raw materials, such as bottom ash, non-ferrous slag, and other waste minerals.”