Carbon reinforced concrete construction involves a closed material cycle. In the very extensive investigations along the entire material cycle, until now no respirable fibre fragments within the size range of the WHO definition have been found for the carbon used in carbon reinforced concrete. Therefore, no measures extending beyond the usual occupational safety provisions are required.
Production of carbon
To produce reinforcement, a pyrolysis process is used to merge many individual carbon fibres to form a yarn. The material carbonitriding – or PAN for short is solely used as the raw material for the yarns used in construction. The carbon fibres are produced worldwide, for construction particularly in Asia, North America and Europe. On an industrial scale, more than 150,000 tonnes carbon fibres (as of 2017) worldwide per year can be produced and then processed, of which 5,410 tonnes are currently used annually worldwide and 400 tonnes are used in Germany – with the trend increasing.
Among others, the following institutions are available for the production of carbon reinforced concrete: Hexcel Composites GmbH, SGL Carbon SE, Solvay GmbH, Teijin Carbon Europe GmbH, Carbon Fiber Division (MCCFC; USA) and ZOLTEK Corporation (Toray + Zoltek; USA)
Production of reinforcement
The carbon yarns are processed in textile technological processes to form reinforcement welded mesh (mats) or bar material and are impregnated with a polymer matrix. Accordingly, carbon reinforced concrete construction does not describe a construction method in which short fibres are used. Such reinforcement is preferably produced in Europe.
Among others, the following institutions are available for production of reinforcement: solidian GmbH, Hitexbau GmbH, Sika Deutschland GmbH, thyssenkrupp Carbon Components and WILHELM KNEITZ Solutions in Textile GmbH
Production of structural members
New structural members made of carbon reinforced concrete are primarily produced off-site in precast concrete element plants. If existing steel reinforced concrete structures are strengthened or repaired with carbon reinforced concrete, this takes place on-site, directly on the construction site. Carbon reinforced concrete construction is characterised by the fact that up to 80% material can be saved, compared to the use of steel reinforced concrete. Regardless of this, the reinforcement made of carbon accounts for less than three percent of the mass (weight) of a structural member. The constructions made of carbon reinforced concrete are therefore flexible in their design and require fewer resources.
Among others, the following institutions are available for the production of structural members: Betonwerk Oschatz GmbH, Beton- und Naturstein Babelsberg GmbH, GOLDBECK Ost GmbH, Hentschke Bau GmbH, Hering Bau GmbH & Co KG, Klebl GmbH and Weber Betonwerk GmbH
Erection of structures
The ceiling slabs, sandwich walls, beams/girders, bridge segments and much more produced in the concrete factory are transported to the construction site with little effort, are joined and can be used to erect a complete structure. The precast elements made of carbon reinforced concrete are treated like the usual precast elements and are integrated into the construction processes.
Use of carbon reinforced concrete
The drilling, sawing, cutting, breaking or other type of machining of the structural members made of carbon reinforced concrete can be carried out using standard tools throughout the entire use phase.
Demolition and dismantling
The usual equipment and machinery can also be used without limitation for the dismantling and reuse of structural members made of carbon reinforced concrete, as well as their demolition and crushing.
Crushing and sorting
The demolished material can be crushed using conventional crushing technology. The reinforcement is successfully separated from the concrete. The subsequent sorting can be carried out using a sensor-based sorting plant, which is also used to sort plastics.
Among others, the following institutions are available for crushing and sorting: Caruso Umweltservice GmbH, H. Nestler GmbH & Co.KG and Nordmineral Recycling GmbH & Co. KG, STEINERT GmbH and TOMRA Sorting GmbH
Treatment of the reinforcement
To recycle and use the recovered carbon material, the polymer matrix must be removed, among other things by thermal decomposition (pyrolysis) of the carbon. To this end, the carbon is fed into a pyrolysis or solvolysis process.
Among others, the following institutions are available for treatment of the reinforcement: Abfallentsorgung Stadt Burgau, carboNXT GmbH, GESA Engineering und Apparatesysteme GmbH and ELG Carbon Fibre Ltd. (GB)
Thermal recycling of the reinforcement
A small part of the recovered concrete, whose fibres are too short (smaller than 40 mm) for further processing, is currently still used in thermal recycling (waste-to-energy). This requires temperatures above 800 °C and a dwell time of 60 minutes. These conditions exist, for example, in the calcium carbide process.
Among others, the following institutions are available for thermal recycling of the reinforcement: Alzchemie Group AG
Production of recycled products
In construction, by adding new thermoplastic fibres, the treated carbon can be used to produce new reinforcement in the form of welded mesh (mats) and bars. Further applications in non-construction sectors include, among other things, the production of front spoilers and rear aprons for cars, frames and attachments for bicycles and non-woven materials.
Among others, the following institutions are available for the production of products from recycled materials: carboNXT GmbH, Institut für Textilmaschinen und Textile Hochleistungswerkstofftechnik der TU Dresden, ITV Denkendorf Produktservice GmbH, Sächsisches Textilforschungsinstitut e. V., WIPAG Süd GmbH & Co. KG/WIPAG Nord GmbH & Co. KG and ELG Carbon Fibre Ltd. (GB)
Although the carbon reinforced concrete material cycle already occupies every step, among other things, the latest research and development work of the more than 140 partners in the C³ project promise further alternatives for action – so that the sustainability of the concrete construction method will increase still further. With the economical recovery of recycled carbon, Germany is able to occupy a global leader role in the rapidly growing market worldwide – and not only in construction.
The film: “The carbon reinforced concrete material cycle” is available in our Download area.