Innovation: Concrete recycling technology „reCO₂ver“

Sika has developed a new recycling process for old concrete in which the recycled material is made available in a higher quality than this is possible when using conventional recycling methods. In this process, old concrete is decomposed into the constituents gravel/chippings, sand and powder, and in which, in addition, about 15 kg CO₂ per ton crushed concrete demolition material can be bound. Under the brand name „reCO₂ver“, this innovation makes a considerable contribution to minimizing the ecological footprint of the construction industry and makes circular economy of concrete components possible for the first time.

For this purpose, Sika has built a pilot plant in Weiach near Zurich/Switzerland. The plant consists of four modular units, which have the size of an overseas container, as well as an upstream conveyor system and a downstream sieve module. Old concrete pre-crushed to a maximum of 40 mm is delivered in Big Bags and is transported via a conveyor belt system into the core component of the plant – the ball mill. There, the crushed old concrete is further crushed with the aid of metal balls using the principle of gravity, while hardened cement paste adhering to sand and coarse aggregates is rubbed off. Subsequently, the material is carried out of the mill automatically. The treated material is then separated in the sieving plant according to the requested grain size. In addition, the deriving powder is extracted from the mill and fed into prepared containers in an airtight system.

The recycled aggregates derived from the plant exhibit a considerably lower content of adhering hardened cement paste and a remarkably lower water requirement than conventional concrete chippings, and can therefore be used for a wide range of applications. The grain size distribution of the recycled material is much closer to the distribution of the starting material than is the case with previous processes. In addition, tests conducted by Sika have revealed that the derived powder can be used for the production of concrete, thus making a reduction of the used cement possible, while lowering the carbon footprint of the new products.

Along with the high quality of the recycled material, the plant provides the possibility of carbon sequestration. For this purpose, CO₂ is added to the derived powder and is carbonating. The tests carried out so far on a laboratory scale have revealed that an absorption of 50-60 kg of CO₂ per ton of powder can be realized.

The practical use of the „reCO₂ver“ technology was proved in two tests carried out at manufacturers of concrete components in 2023:

1. On the initiative of the German trade association of concrete sewer systems (FBS -Fachverband Betonkanalsysteme), new DN 500 reinforced concrete pipes were broken down to the required grain size of 40 mm at Röser II GmbH and were delivered to the „reCO₂ver“ plant. The recycled aggregates derived from the plant were used at Röser for the production of pipes of the same type. Here, 100 % of the normal aggregates were replaced by the „reCO₂ver“-recycled aggregates.

2. Kronimus AG supplied crushed paving blocks to the „reCO₂ver“ plant. The recycled aggregates derived from the „reCO₂ver“ process as well as the powder were completely reused in new products, according to information given by the company.

The findings gained with the pilot plant were incorporated in the upscaling by the machine manufacturing company, so that the „reCO₂ver“ plant can be ordered now according to the required throughput capacity.