Carbon reinforced concrete is a composite material consisting of two high-performance materials. The innovative combination of carbon fibre fabrics or bars with fine-grained concrete simultaneously enables significantly more varied shapes and a high load-bearing capacity. Due to the corrosion resistance of the fabrics and rebars, the concrete cover and thus the use of resources can be reduced to a minimum. Carbon reinforced concrete can be used for sustainable, resource-saving, less material-intensive and lighter construction.
Photos © Ansgar Pudenz, DZP 2016 (mats); CARBOCON (rods)
Since its introduction, steel reinforced concrete as a load-bearing building material has made possible the construction of important buildings, and that in a very short time and in robust designs. However, due to their susceptibility to corrosion, the service life of steel reinforced concrete structures falls far short of earlier expectations. Many buildings are hardly older than the people who use them. With more than 100 million cubic metres used in construction each year, steel reinforced concrete is the most important building material in Germany.
The use of concrete as the world's most frequently used building material after water has always led to a high consumption of raw materials and energy. In addition, steel is subject to enormous price fluctuations due to its versatile use in construction and other industries.
This is exactly where the new carbon reinforced concrete technology comes in. It reduces the total consumption of materials and replaces steel with carbon. Since carbon does not rust, less concrete is required to protect the steel from corrosion. Carbon reinforced concrete can be used for sustainable, resource-saving, less material-intensive and lighter construction.
The advantage lies in the approx. 50,000 individual fibres, which are much thinner than a human hair. These fibres are combined into a yarn, processed to form a grid structure and coated. Compared to steel, carbon is four times lighter with six times more load-bearing capacity. Carbon reinforced concrete not only makes it possible to create much slimmer and more delicate new structures, but also to strengthen and repair existing structures, which then have a much longer service life. Architecturally, versatile building geometries can be realised that are difficult to achieve with steel reinforced concrete. 'Lightweight construction' and 'concrete' are no longer a contradiction in terms, but a concept for the future.
The origins of concrete
Concrete is more than 10,000 years old. Archaeological finds show that concrete-like building materials were used even 10,000 years ago. These building materials were found in millennia-old buildings on the territory of present-day Turkey and on the pyramids in Egypt. The next stage of development was the use of opus caementicium in ancient Rome, as in the construction of the Pantheon, for example.
Concrete in the Age of Industrialisation
Steel reinforced concrete since the middle of the 19th century (1867 patent by Joseph Monier) to compensate for the low tensile strength of concrete with the high tensile strength of steel.
Notable advantages: non-combustible/high fire resistance; available everywhere, cheap, can be formed into any shape
Notable disadvantages: less delicate and high dead weight; corrosion of the reinforcing steel necessitating concrete covering; high use of resources and materials
Introduction of the term steel reinforced concrete
Around 1900 emergence of the term "steel reinforced concrete" and around 1920 first experiments with pre-stressed concrete: Prestressed concrete is a further development of steel reinforced concrete whereby an axial force is introduced by prestressing the steel before concreting. This prestressing allows longer spans for beams and girders with the same ceiling height due to lower deformations.
Beginnings of textile reinforced concrete
In the 1990s, researchers from Dresden worked for the first time on a composite material made of textile fibres and high-performance concrete. Textile fibre enables a weight reduction due to the elimination of the concrete covering required in steel reinforced concrete to protect the steel.
Crucial basic research
Between 1999 and 2011, under the initiative and leadership of Prof. Curbach and Prof. Hegger, more in-depth research into textile reinforced concrete has been carried out in two Collaborative Research Centres of the Deutschen Forschungsgemeinschaft in Dresden and Aachen. From 2000 onwards, the standards of textile reinforced concrete technology made of fibreglass have been further developed through the use of new materials such as carbon and basalt. An initial summary is given under the general term 'carbon concrete'.
First pilot applications in practice
In 2005, the planning, design and construction of the first bridge made of textile reinforced concrete took place as part of the State Horticultural Show in Oschatz/Saxony. In 2006, following the planning and approval processes, the first reconstruction using carbon concrete on an existing structure took place - here on the Schweinfurt hyperdome.
First national technical approval and largest construction research project in Germany
In 2013, on the basis of years of research and pilot applications, the German Institute for Building Technology issued the first national technical approval for the use of carbon reinforced concrete in strengthened concrete structures. In the same year, the responsible ministry of the Federal Republic of Germany approved the largest construction research project in Germany with the aim of implementing carbon reinforced concrete technology across the board in the construction industry.
Founding of CARBOCON as a leading supplier in the hotspot of Dresden
At the end of 2014, after a preparatory phase, CARBOCON GmbH was founded as a transfer service provider. The aim was to transfer the knowledge quickly, competently and professionally into construction practice and industry. More than 160 partners from industry, universities, public authorities and other stakeholders make up the competence network C³.
Future prize for carbon reinforced concrete
At the end of 2016, former Federal President Joachim Gauck awarded the German Future Prize to the Dresden carbon reinforced concrete researchers Prof. Manfred Curbach (shareholder of CARBOCON GmbH), Prof. Chokri Cherif and Prof. Peter Offermann of the TU Dresden.
Rebars made of carbon, basalt, glass or combinations of materials are used. CARBOCON develops the materials together with its partners and manufacturers and applies them specifically in construction projects. Rebars made of carbon fibre-reinforced plastic are among the high-performance materials and can withstand up to 6 times higher tensile forces than comparable steel rebars.
50,000 individual carbon fibres are combined in a special manufacturing process to form a yarn, processed into a lattice structure and impregnated. These fabrics or mats are characterised by a wide variety of properties in terms of load-bearing capacity, flexibility, formability and also resistance to temperatures. CARBOCON always selects the most suitable materials for a specific project.
Concrete has several functions in the composite material of carbon reinforced concrete. The selection of the right concrete type is therefore important. An example of a specially developed product and application is TF10 TUDALIT from PAGEL (grain size 0-1 mm). In addition to the special fabric, this fine-grained concrete is the central element for strengthening with carbon reinforced concrete according to the existing national technical approval.
The current state of the art and the requirements of bridge technology prompted CARBOCON developers and engineers to incorporate hybrid applications of different types of reinforcement into the projects. A combination of the fabrics/mats and bars offers a multitude of possibilities to achieve the best solution for the application.
What is fine-grained concrete?
Fine-grained concrete generally has a maximum grain size between 1–4mm. According to the standardised definition, all fine-grained concretes with a maximum grain size of less than or equal to 4mm are referred to as mortar. As the use of carbon reinforced concrete increased, however, the term fine-grained concrete was coined, since its properties usually correspond to those of high-performance concrete and the term fine-grained concrete therefore seemed more appropriate.
What is carbon concrete?
Carbon reinforced concrete is a composite material consisting of a (fine-grained) concrete and a non-metallic reinforcement in the composite, such as textile fabrics and rebars made of carbon, glass or basalt fibre.
How long has carbon reinforced concrete been available?
In the 1990s, researchers from Dresden worked for the first time on a composite material made of textile fibres and high-performance concrete. Textile fibre enables a weight reduction due to the minimisation of the concrete covering required in steel reinforced concrete to protect the steel.
Who researched carbon concrete in depth for the first time?
In Germany, between 1999 and 2011, under the initiative and leadership of Prof. Manfred Curbach, Prof. Peter Offermann, Prof. Chokri Cherif and Prof. Josef Hegger, more in-depth research into textile reinforced concrete was carried out in two Collaborative Research Centres of the Deutsche Forschungsgemeinschaft in Dresden and Aachen
CARBOCON is the leading partner when it comes to planning, developing and implementing carbon reinforced concrete projects. Due to our many years of experience in the field of carbon reinforced concrete and our broad network of industry partners, we can professionally master any challenge together with you in a direct contractual relationship or partnership.
Will carbon reinforced concrete replace steel reinforced concrete?
No, because that is not the aim of carbon reinforced concrete. CARBOCON wants to establish this high-performance, innovative and resource-saving composite material in the construction industry according to its potential and advantages. The current goal is to replace 20 % of steel reinforced concrete with carbon reinforced concrete in the near future.
What are the advantages of carbon reinforced concrete over steel reinforced concrete?
Carbon has several advantages over steel. In addition to corrosion resistance, it is mainly the lower density and higher load-bearing capacity that make carbon as a whole significantly more efficient than steel. Because carbon does not corrode, the components made of carbon reinforced concrete are also much more durable and at the same time allow for more slender designs. Since a concrete cover is no longer required for corrosion protection, there is also a high potential for saving on materials and resources.
What are the application areas for carbon reinforced concrete?
Carbon reinforced concrete can be used in the most diverse areas of construction, such as new construction, strengthening and reconstruction. Projects in bridge construction, structural engineering and prefabricated construction have already been realised. In the field of reconstruction, these include the strengthening of silos, bridges, canal structures and historical and listed buildings.
What is the difference between steel reinforced concrete and carbon reinforced concrete?
The main difference lies in a more efficient and corrosion-resistant reinforcing material, which enables lighter, more delicate and higher load-bearing constructions and a new variety of shapes.
How is a fabric/reinforcement mat made from carbon fibres?
Up to 50,000 carbon fibres are combined in one yarn and then processed and impregnated in a lattice structure. Both laying and warp knitting techniques are possible.
How is carbon reinforced concrete produced and how is it different to steel reinforced concrete?
Carbon reinforced concrete, like steel reinforced concrete, can be produced by classic casting or spraying processes. The application of a manual laminating process is also possible. Due to the reduced cross-sectional dimensions, smaller equipment can be used for reinforcing measures with carbon concrete.
How expensive is carbon reinforced concrete compared to steel reinforced concrete?
The more efficient raw materials (e.g., carbon, glass, fine-grained concrete) are more expensive than conventional steel reinforced concrete. But due to the many advantages (sustainability, resource savings, thinner cross-sectional dimensions, more efficient process flows and low transport costs), carbon reinforced concrete solutions are already highly competitive in the entire value creation process. In addition, the construction principle based on carbon reinforced concrete opens up fields of application that could not previously be realised with steel reinforced concrete.
How big are the savings on resources and materials when using carbon reinforced concrete?
Depending on the field of application and requirements, material and resource savings of up to 80% are possible.
Are there processes in place for recycling carbon reinforced concrete?
A separation of the two basic components - carbon and concrete - was achieved very early in the development of the technology. Later, large pilot studies were carried out simulating the recycling process. The recycled carbon is fed through the same processes known in the aerospace, automotive and sporting goods industries. The concrete recycling process is then carried out on the same line already established for steel reinforced concrete.
What is the future of carbon concrete?
Carbon reinforced concrete is the future in the construction industry. Increasingly scarce resources, the corrosion of steel reinforcement and its consequences in steel reinforced concrete construction open up a large field of application for carbon concrete. Whether and to what extent carbon reinforced concrete can replace steel reinforced concrete will be seen in the future.
Where in Germany has carbon or textile reinforced concrete been used?
The use of this innovative technology has been successfully demonstrated in a large number of projects. CARBOCON is currently working on many construction projects and is planning, for example, the reconstruction and strengthening of existing bridge structures. In addition, we are working on development projects with industry partners of various kinds. Further information can be found under CARBOCON References.
The hypar shell in Magdeburg, built according to the plans of civil engineer Ulrich Müther, is one of the largest concrete shell constructions of its kind. The roof construction consists of four hyperbolic paraboloid shells. The hypar shell, a listed building, already showed structural damage years ago. In recent years these have become more prominent, so that a reconstruction concept has been sought. Based on an inventory analysis, it was decided to strengthen the shell construction with carbon concrete technology. The structure will be saved from demolition by applying a protective 10mm thin carbon reinforced concrete layer on the top and bottom of the concrete shell.
Foto: © CARBOCON
p>Naumburg is home to one of the oldest preserved steel reinforced concrete bridges in Germany – the Thainburg pedestrian bridge. The bridge, which is now under a preservation order, was built in 1892 and made of steel reinforced concrete, a new material at that time. In recent decades, the structure has suffered corrosion damage due to lack of maintenance and constructional sealing defects. The CARBOCON project team developed a strengthening concept and integrated this into the plans for approval. The innovative strengthening with carbon reinforced concrete was chosen for reasons of material efficiency and design.
Foto: © CARBOCON
The first carbon reinforced concrete road bridge in eastern Saxony is being planned as part of the '100-Bauwerke-Programm' of the Free State of Saxony. This bridge is located in the area of a state road and is therefore used by conventional road traffic. For the first time, carbon reinforcement bars and mats are being used in the design of the engineering structure. The carbon rods are developed and produced in the Free State of Saxony. The project is therefore regarded as an important milestone in bridge construction and application of the innovative composite material, carbon reinforced concrete, and is intended to demonstrate the durability of the material under real conditions.
Foto: © CARBOCON
The Leopold Franzens University of Innsbruck is one of the leading universities in Austria. This is particularly true in the field of research and development. And this also applies to carbon reinforced concrete. The field of solid construction and bridge construction, headed by Prof. Dr Eng. Jürgen Feix, has been researching the practical application of carbon reinforced concrete for many years. In close cooperation with the Otto Mohr Labor in Dresden as a partner of CARBOCON, steel reinforced concrete girders were produced for Innsbruck, reinforced with carbon reinforced concrete and subsequently tested.
Foto: © CARBOCON
As part of the reconstruction of the Beyer Bau building complex on the TU Dresden campus, load-bearing deficits in beams and ceilings are to be eliminated by strengthening with carbon reinforced concrete technology. The deficits mostly result from increased usage requirements and the very slim design of the existing building. In a feasibility study, the use of carbon reinforced concrete was proven to be a good alternative to the demolition and new construction of the existing historic structure, and was favoured not only in terms of the protection of the existing structure but also from an economic point of view.
Foto: © CARBOCON
Within the scope of the conversion of an existing bunker in Bremen, the private client asked CARBOCON for support. Carbon reinforced concrete technology is to be used in order to increase the required load-bearing capacity of the ceilings with a small reduction of the room height in the areas of use of the bunker. The client also had special requirements with regard to the application temperature in the bunker system. Under normal operation, temperatures of up to 40°C are to be expected. Since the possibility of cooling failure cannot be ruled out, temperatures of up to 80°C are possible for short periods. Accordingly, a project-related approval must be provided.
Foto: © CARBOCON
As part of the total overhaul of the A3, the 'Landesbetrieb Straßen.NRW' is also involved in work on the Rottbach underpass. Based on an analysis of the existing structure, a new replacement structure was recommended, but this proposal was rejected. A preliminary design for a strengthening option was then suggested, with a 20 cm thick shotcrete shell of steel reinforced concrete as a replacement structure. However, this would cause a considerable narrowing of the cross-section of the structure and high costs for the construction logistics. Within the scope of a feasibility study, different options were examined. These resulted in several carbon reinforced concrete options which could be used as an alternative to the classic strengthening with steel reinforced concrete.
Foto: © Roads.NRW
In this project, carbon reinforced concrete technology is to be applied profitably within the construction industry. Based on the existing state of knowledge from research into carbon reinforced concrete, application-oriented potentials should be used to make this technology accessible to a broad specialist audience. The focus here is on being able to react quickly and flexibly to the needs and requirements of industry. In addition, "bridges should be built" in the interests of the construction industry, in order to compensate for the lack of certain expertise there and to be able to adequately answer the open questions and challenges in connection with new technologies.
Foto: © Ulrich van Stripriaan
The Augsburg State Building Authority plans to strengthen and repair an existing bridge over the Danube in Donauwörth (Bavaria). The aim is to achieve a remaining service life of at least 20 years. Due to various technical challenges, the planning team turned their focus to carbon reinforced concrete. It turned out that with carbon reinforced concrete strengthening the currently identified deficits of the bridge could be remedied within the scope of the reconstruction process. Furthermore, it was determined that a project-related approval was required for the innovative materials to be used and for the character of the pilot project in the federal state of Bavaria.
Foto: © CARBOCON
Hessen Mobil plans to renovate and repair a multi-span bridge in Hesse. The target is a remaining service life of at least 15 years. In the course of a recalculation of the existing structure, various deficits were identified which call for precautionary remediation with regard to future requirements and traffic loads. In this context, the strengthening of individual elements was envisaged. A feasibility study in cooperation with a planning project partner illustrated that strengthening with carbon reinforced concrete would be the only sensible approach.
Foto: © CARBOCON
Carbon reinforced concrete technology was used in the reconstruction of several sugar silos. Before the start of the project, during inspection and sampling, the silo walls showed severe damage in the form of deep cracks, spalling and reduced tensile strength. The aim was to permanently restore a uniform cross-section with a smooth and hygienic surface. The approximately 5,000 m² interior wall of the silo received a strengthening layer of textile reinforced concrete, which ensured both better load-bearing capacity and sustainable serviceability. In this situation the SiloSolution product was used.
Foto: © CARBOCON
Romania has a large number of steel reinforced concrete poles which have been severely damaged by corrosion over time. With the help of repairs using carbon reinforced concrete, the load-bearing capacity and serviceability were to be restored. A significant increase in load capacity could be proven in the tests due to the textile reinforcement made of carbon. A careful condition analysis and conceptual design by CARBOCON showed that this would be a cost-effective reconstruction solution for the long-term preservation of the existing structure.
Foto: © CARBOCON
The historical arched bridge in the city of Naila, which is more than one hundred years old, showed extensive crack formation and cavities almost over the entire surface. Since the listed building has a sentimental value for the region, a reconstruction method had to be found that preserves the old appearance and geometry and at the same time ensures compliance with current requirements for structural integrity, road safety and durability. Strengthening with carbon reinforced concrete was not only an economically attractive solution, but was also convincing in terms of durability, fine crack distribution and the simple practical application of carbon concrete technology.
Foto: © CARBOCON
The aim of the construction project was the structural strengthening of steel reinforced concrete columns in an office building. The carbon reinforced concrete technology was introduced as part of the conceptual design and planning. The existing national technical approval provided the perfect conditions for this. First, the old concrete surface was prepared using a high-pressure water jet. The strengthening work was then carried out. Fine-grained concrete and carbon reinforcement were alternately applied to the surface. A few centimetres of cross-sectional expansion with carbon reinforced concrete were sufficient to significantly increase the load-bearing capacity of the columns (load increase of about 40 %).
Foto: © CARBOCON
The 40-year-old Arabella skyscraper in Munich was damaged by cracks, spalling and frost damage on some balconies and balustrade panels. These affected the durability and safety of the balconies and the building's surroundings. During the repair work, the complex geometry of the facade was to be maintained without scaffolding where possible while the building continued to be used. The ideal solution here was a covering of carbon reinforced concrete. The low material requirement allowed outdoor work by industrial climbers. A textile concrete layer of only 6 mm ensured both the preservation of the old appearance and long-term load-bearing capacity.
Foto: © CARBOCON
Material tests and trials were to be carried out to qualify and develop a fabric. These were then to be used to apply for inclusion of a process of strengthening steel reinforced concrete with TUDALIT (textile reinforced concrete) in the existing national technical approval. A three-stage test programme was set up for this purpose. The required material tests were carried out in the partner laboratories.
The industry partner Koch developed a strengthening layer of carbon reinforced concrete for multi-storey car parks, which, in addition to a structural bending strengthening also functions as active cathodic corrosion protection by means of a direct current. The carbon fabrics form the anode and conduct a current. In addition to preliminary trials, as part of this collaboration, CARBOCON is developing a test concept in order to investigate the durability of the carbon reinforced concrete in the present combination, taking into account the influence of the electric current applied to the carbon fabric.
The building on the Dresden University of Technology campus has a facade made of betoShell® panels. The panels are double-layered and reinforced with fibreglass. As part of the installation work, anchor systems were dismantled and replaced by new anchor systems. As part of his quality management concept, the principal requested comprehensive documentation and supervision of the installation work. The monitoring of contractors should incorporate experience with carbon reinforced concrete technology.
The building complex of the Klostermühlen Museum in Thierhaupten is about 500 years old. The venerable Benedictine monastery was once the dominant centre of the village for centuries. Over the years, the Benedictines built four mills for self-supply: a sawmill, an oil mill, a paper mill and a grain mill. After its closure, the listed building became increasingly dilapidated and seemed doomed. After extensive reconstruction, the monastery mill museum was opened in 1997. Within the scope of an upcoming reconstruction of the channel in front of the museum, various reconstruction technologies were tested in 2019.
The CARBOCON team is also at your disposal as a central contact partner with interdisciplinary expertise. In connection with our range of services, this enables us to take care of various customers with different requirement profiles.
CARBOCON supports the projects from the first analysis to the subsequent application. The spectrum of projects ranges from comprehensive consulting on strategic, operational and technical issues in the use of carbon reinforced concrete technology to 'classic' planning for the strengthening of bridges and other structures with carbon concrete.
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