Carbon concrete

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Carbon concrete (also carbon concrete written) is the reinforced concrete -like artificial construction and composite material . It consists of the two components concrete and a reinforcement made of carbon fibers (also called ' carbon (fibers) ' ) in the form of mats and rods. Due to the manufacturing process, the mat-like reinforcements are often referred to as textile and the concrete reinforced with them ( generic term ) as textile concrete .

The term carbon concrete includes mat-like and rod-shaped reinforcements made of carbon, but not alkali-resistant glass, basalt, etc. In contrast, the term textile concrete includes mat-like reinforcements made of alkali-resistant glass and carbon or basalt, but no rod-shaped reinforcements made of these materials. Thus carbon concrete is neither an umbrella term nor a subgroup of textile concrete. Rather, both areas intersect with the mat-like reinforcements made of carbon.

In contrast to reinforced concrete, in which the reinforcement is made of steel , the reinforcement in carbon concrete consists of continuous carbon fibers ( filaments ) processed into yarns or rods . The carbon reinforcement material used here has a tensile strength of approx. 3000 N / mm² and is therefore higher than that of the usual reinforcement steel (approx. 550 N / mm²), so that less reinforcement material is required in comparison. It is suitable for both the production of new and the reinforcement of existing components. Fine-grained concretes with a maximum grain size of <2 mm and concretes with a maximum grain size of <= 8 mm are used as concretes.

Technical textiles , usually non-woven fabrics, are used for textile concrete . Alkali-resistant glass and carbon fibers have proven themselves as fiber materials. Textile concrete has been developed mainly at the universities in Dresden and Aachen since the mid-1990s and its fundamentals have been researched within the framework of two special research areas of the German Research Foundation (DFG).

Carbon reinforcement is chemically inert to the stresses and strains in construction and, unlike steel reinforcement , does not have to be protected from corrosion by a concrete cover several centimeters thick . For components made of carbon concrete, material can thus be saved and made significantly thinner.

The carbon reinforcement is available in rod and mat shapes. Short carbon fibers are currently only of secondary importance and do not come under the term carbon concrete. Carbon rods are usually produced in a pultrusion process with round cross-sections in various diameters. The surface is often profiled in order to achieve good power transmission between reinforcement and concrete. The lattice-like mesh reinforcement is manufactured in a textile processing process, so that it is often also called reinforcement textile . The concrete reinforced with it is also known as textile concrete. The mesh reinforcement is offered with different yarn cross-sectional areas and grid widths. There are single-layer 2D fabrics and 3D reinforcement structures.

Carbon concrete (initially textile concrete) has been developed primarily at the universities in Dresden and Aachen since the mid-1990s and its fundamentals have been researched within the framework of two special research areas of the German Research Foundation (DFG). Since 2014, the further development has mainly been carried out in the C³ project funded by the Federal Ministry of Education and Research (BMBF).

history

Research into carbon concrete in Germany is based on research on textile concrete within the framework of two special research areas of the German Research Foundation (DFG) in Dresden and Aachen in the period from 1999 to 2011 - Collaborative Research Center 528 (focus on reinforcement, spokesperson: Manfred Curbach ) in Dresden and Collaborative Research Center 532 (Focus on new components, speaker: Prof. Josef Hegger ) in Aachen . The scientific knowledge gained was successively put into practice. The establishment of the German Textile Concrete Center, Tudalit e. V., TUDATEX GmbH and CarboCon GmbH are the result of this intensive work. Implementation in practice along the entire process chain - from the material to the finished component - has already begun and has been continued since 2014 in Germany's largest research project in the construction industry, "C³ - Carbon Concrete Composite". The C³ project is supported with 45 million euros in funding from the Federal Ministry of Education and Research BMBF as part of the funding initiative Twenty20 - Partnership for Innovation and has over 160 members (as of 2019).

Manufacturing process

The production of carbon concrete takes place mainly in the casting or lamination process; but spinning and printing are also possible. The casting process is mainly used for the production of new components. Here, the reinforcement is initially arranged in a vertical or horizontal formwork with the help of spacers. The component is then concreted in one step. This process is already known from the manufacture of reinforced concrete.
Production of a 5 m long carbon concrete beam in the casting process

The production of carbon concrete takes place mainly in the casting or lamination process; but spinning and printing are also possible. The casting process is mainly used for the production of new components. Here, the reinforcement is initially arranged in a vertical or horizontal formwork with the help of spacers. The component is then concreted in one step. This process is already known from the manufacture of reinforced concrete.

The lamination process is preferred for the reinforcement of buildings. First, a 3–5 mm thick layer of fine concrete is applied to the substrate (an existing structure or formwork). The first layer of textile reinforcement is slightly pressed into this layer. Then the steps of applying concrete and inserting textile reinforcement are repeated until the desired number of layers is reached. A thin layer of fine concrete forms the end. The fine concrete can be applied manually or by spraying. Spacers to secure the position are not necessary.
Repair of an old railway arch bridge using the lamination process

The lamination process is preferred for the reinforcement of buildings. First, a 3–5 mm thick layer of fine concrete is applied to the substrate (an existing structure or formwork). The first layer of textile reinforcement is slightly pressed into this layer. Then the steps of applying concrete and inserting textile reinforcement are repeated until the desired number of layers is reached. A thin layer of fine concrete forms the end. The fine concrete can be applied manually or by spraying. Spacers to secure the position are not necessary.

The spinning takes place in a similar way to reinforced concrete. Here, the reinforcement is usually arranged in a cylindrical formwork, which is then filled with concrete. The centrifugal process creates a tube-like cross-section.

The printing of concrete components is currently still part of research and is not yet / rarely used in construction practice. Arranging the concrete and reinforcement at the same time when printing is challenging. One solution is to lay down carbon yarns during the printing process.

Applications

The first known applications of carbon reinforcement in practical projects go back to the 1990s. Here u. a. bar-shaped carbon reinforcements are used in parts of bridges in Canada and Japan. In the USA, bar-shaped carbon reinforcements have been used in bridge construction, especially in the last 10 years. In Germany, the focus of applications so far has been on mat-like / textile reinforcements made of carbon. The area of ​​application is divided into new construction and renovation / reinforcement.

New building

Most practical projects can be found in the field of facades, cladding and wall constructions. Concrete slabs with reinforcement made of carbon and / or glass and thicknesses of only 10 to 30 mm offer an alternative / supplement to the already established reinforced concrete solutions, whose component thicknesses are usually well over 70 mm. The large slabs, with slab sizes of up to 3 × 5 m, are mainly reinforced with carbon. In addition to the facade area, the concrete slabs are also used to clad other structures. One example is the cladding of the world's tallest bridge pylons, the Yavuz Sultan Selim Bridge over the Bosporus in Istanbul.

The bridge, reinforced exclusively with carbon for the first time, was built in Albstadt-Ebingen. The bridge has a width of 3 m, a span of 15 m and a weight of approx. 14 t. The roadway is 9 cm thick and the balustrade is 7 cm thick. The bridge can be driven over with a clearing and gritting vehicle with a weight of up to 10 t.
Trough bridge made of carbon concrete in Albstadt-Ebingen

The bridge, reinforced exclusively with carbon for the first time, was built in Albstadt-Ebingen. The bridge has a width of 3 m, a span of 15 m and a weight of approx. 14 t. The roadway is 9 cm thick and the balustrade is 7 cm thick. The bridge can be driven over with a clearing and gritting vehicle with a weight of up to 10 t.

As part of the renovation of two further road bridges in Albstadt (districts of Margrethausen and Pfeffingen), the existing reinforced concrete components of the two old bridges were replaced by filigree and durable carbon concrete components. Both bridges with different geometries are based on the same support system. In the longitudinal direction, the load is transferred via steel girders and for the transverse direction, two carbon concrete plates are used, which are only 14 cm thick at the thinnest point. The thin elements are laid on the steel girders and transfer the vertical and horizontal loads into the steel substructure. The 5.7 m wide and 6.5 m long bridge in Margrethausen is approved for a load of up to 24 t. The sister bridge in Pfeffingen is almost 4 m longer and around 2 m narrower and has a permissible total load of 40 t.

The latest bridge constructions use prefabricated, pre-stressed, 4 cm thick carbon concrete slabs. These large-format panels are cut to size and used for both the bridge deck and the side members. The combination with longitudinal beams made of wood and beam beams are also shown for this system, see:

Renovation / reinforcement

Carbon concrete has been used for the renovation and reinforcement of several listed shell and dome structures for 10 years. One of the first applications is the reinforcement of a hypar shell in Schweinfurt from 1960. The reinforcement of a barrel roof in Zwickau from 1903 can also be mentioned in this context. In both reinforced concrete structures, which are only 8 cm thick, the existing load-bearing capacity was increased to the level required today with approx. 1–2 cm thick carbon concrete layers. Above all by applying very thin layers, one can do justice to the wish of the monument protection - to keep the original appearance.
Listed barrel roof after the renovation
In addition to the area of ​​monument protection, carbon concrete is mainly used for the classic reinforcement of reinforced concrete floor slabs. Among other things, the ceilings in a newly built residential and commercial building in Prague were reinforced. The point-supported reinforced concrete slabs are 30 m × 70 m in size and 23 cm thick. The ceilings showed deflections of up to 15 cm and insufficient load-bearing capacity. The reinforcement was done with carbon concrete on the underside.
Ceiling reinforcement with carbon concrete in a newly built residential and commercial building in Prague

Carbon concrete has been used for the renovation and reinforcement of several listed shell and dome structures for 10 years. One of the first applications is the reinforcement of a hypar shell in Schweinfurt from 1960. The reinforcement of a barrel roof in Zwickau from 1903 can also be mentioned in this context. In both reinforced concrete structures, which are only 8 cm thick, the existing load-bearing capacity was increased to the level required today with approx. 1–2 cm thick layers of carbon concrete. Above all by applying very thin layers, one can do justice to the wish of the monument protection - to keep the original appearance. In addition to the area of ​​monument protection, carbon concrete is mainly used for the classic reinforcement of reinforced concrete floor slabs. Among other things, the ceilings in a newly built residential and commercial building in Prague were reinforced. The point-supported reinforced concrete slabs are 30 m × 70 m in size and 23 cm thick. The ceilings showed deflections of up to 15 cm and insufficient load-bearing capacity. The reinforcement was done with carbon concrete on the underside.

Furthermore, carbon concrete has already been used to renovate two silos . The first cylindrical reinforced concrete silo has a capacity of 20,000 t of sugar, an outside diameter of approx. 30 m and a height of approx. 45 m. The inside of the silo showed numerous cracks with large crack widths. The second silo with a capacity of 80,000 tons of sugar was damaged on the inside by a fire. The surfaces of both silos were renovated with a carbon concrete layer.

The renovation of a single-span bridge in 2012 and the renovation of a multi-span bridge in 2014 can be named as the first major carbon concrete application in the renovation of road bridges. Both reinforced concrete bridges were given a carbon concrete layer that could be driven over directly. In a railway arch bridge from 1910, the arches, which were up to 19 m wide, had cracks with large crack widths. These had to be refurbished and reinforced with reinforcement. The renovation was carried out with a full-surface carbon concrete layer on the underside of the arches

advantages

A significant advantage of carbon reinforcement compared to steel reinforcement is its corrosion resistance, which initially enables the concrete structures to have a significantly longer service life. Since the carbon reinforcement does not have to be protected from corrosion like the steel reinforcement, the concrete cover, which is several centimeters in reinforced concrete, can be reduced to a few millimeters. Significantly thinner constructions and material savings of over 50% are possible. Facade panels that are made of reinforced concrete with a thickness of 7–8 cm are only 2–3 cm thick with carbon concrete. Reinforced concrete layers for reinforcement of structures are also approx. 7 cm thick - carbon concrete is only 1–2 cm thick.

Compared to reinforcing steel, carbon is four times lighter (density 1.8 g / cm³ instead of 7.8 g / cm³) and five to six times more load-bearing (3,000 N / mm² instead of 500 N / mm²). Carbon is therefore more than 20 times more efficient than reinforcing steel. Significantly less material is required, which must be taken into account when comparing prices.

Current research results show that after the end of their useful life, carbon and concrete can be separated again using technology that is already common today. A degree of purity of 97% is achieved. The concrete can then be recycled in concrete recycling and the carbon in carbon recycling - i.e. where sporting goods, cars, airplanes etc. are also recycled.

disadvantage

One disadvantage is the largely lack of automation in the manufacture of carbon concrete components. In precast factories, for example, the reinforcements are often cut by hand and there are hardly any robots (e.g. welding robots, such as those used for reinforced concrete). Another disadvantage of carbon concrete is the lack of experience with recycling. Even if carbon and concrete can already be separated and recycled, the construction industry (as in other industries) largely lacks products in which recycled carbon fibers are used. This will be a focus of research in the coming years.

Price-performance ratio

Carbon and steel are currently (as of 2019) priced at eye level in terms of performance. One kilogram of steel costs only around 1 euro, whereas 1 kilogram of carbon costs around 16 euros. However, the density of carbon is four times lower and its strength six times higher. So you get 24 times the performance for 16 times the price. Therefore, in purely mathematical terms, carbon would already be cheaper than steel today.

The significantly reduced use of materials has a positive impact on carbon concrete compared to reinforced concrete. Facade panels or reinforcement layers with carbon concrete, for example, are only about 2 cm thick instead of at least 8 cm, as is the case with reinforced concrete. This means that around 75% less material has to be manufactured, transported, installed and anchored. Since the production of reinforced concrete in the precast plant is now highly optimized and automated compared to that of carbon concrete, reinforced concrete parts are usually cheaper than the carbon concrete parts that are often still produced manually.

See also

Fiber concrete

literature

  • M. Dupke: Textile-reinforced concrete as protection against corrosion. 1st edition. Diplomica Verlag, 2010, ISBN 978-3-8366-9405-6 .
  • M. Curbach, F. Jesse: Reinforcing with textile concrete. In: concrete calendar. Volume 99, T. 1, Ernst & Sohn, Berlin 2010, pp. 457-565.
  • K. Bergmeister, J.-D. Wörner: Betonkalender 2005. Ernst & Sohn, 2004, ISBN 3-433-01670-4 .
  • W. Brameshuber (Ed.): Textile Reinforced Concrete: State-of-the-Art Report of RILEM Technical Committee 201-TRC: Textile Reinforced Concrete . Report 36, RILEM, Bagneux 2006, ISBN 2-912143-99-3 .
  • F. Schladitz, E. Lorenz, F. Jesse, M. Curbach: Reinforcement of a listed barrel shell with textile concrete. In: Concrete and reinforced concrete construction. Volume 104, No. 7, 2009, pp. 432-437.
  • D. Ehlig, F. Schladitz, M. Frenzel, M. Curbach: Textile concrete-executed projects at a glance. In: Concrete and reinforced concrete construction. Volume 107, No. 11, 2012, pp. 777-785.
  • M. Horstmanm, J. Hegger: Sandwich facades made of textile concrete - experimental investigations. In: Structural Engineering. Volume 88, No. 5, 2011, pp. 281-291.
  • HN Schneider, C. Schätzke, C. Feger, M. Horstmann, D. Pak: Modular building systems made of textile-reinforced concrete sandwich elements. In: M. Curbach, F. Jesse (Ed.): Textile reinforced structures. Proceedings of the 4th colloquium on textile reinforced structures (CTRS4), 3rd – 5th June 2009. Dresden, pp. 565-576.
  • A. Bentur, M. Ben-Bassat, D. Schneider: Durability of Glass-Fiber Reinforced Cements with different Alkali-Resistant Glass Fibers. In: Journal of the American Ceramic Society. Volume 68, No. 4, 1985, pp. 203-208.
  • Manfred Curbach, Chokri Cherif, Peter Offermann: Economical, gentle, beautiful - the fascinating material carbon concrete. In: Technology in Bavaria. 02.2017.
  • GW Ehrenstein: Fiber composite plastics. Materials - processing - properties. 2nd, completely revised edition. Hanse, Munich 2006.
  • J. Kortmann, F. Kopf, L. Hillemann, P. Jehle: Recycling of carbon concrete - processing on an industrial scale successful! In: civil engineer. 11/2018, annual edition 2018/2019 of the VDI Department of Structural Engineering, pp. 38–44. ISSN  0005-6650
  • J. Kortmann, F. Kopf: C³-V1.5 Demolition, dismantling and recycling of C³ components. In: Proceedings of the 10th Carbon and Textile Concrete Days , September 25 and 26, 2018. C³ - Carbon Concrete Composite eV and TUDALIT eV, 2018, pp. 84–85.
  • M. Lieboldt: Fine concrete matrix for textile concrete; Requirements - practical adaptation - properties. In: Concrete and reinforced concrete construction special. Volume 110, Issue S1, 2015, pp. 22-28.
  • F. Schladitz, M. Curbach: Carbon Concrete Composite. In: K. Holschemacher (Ed.): 12th Concrete Components Conference - New Challenges in Concrete Construction . Beuth Verlag, 2017, pp. 121-138.
  • K. Schneider, M. Butler, V. Mechtcherine: Carbon Concrete Composites C³ - Sustainable binders and concretes for the future. In: Concrete and reinforced concrete construction. Ernst & Sohn Verlag for Architecture and Technical Sciences, 2017.

Web links

Individual evidence

  1. ^ F. Schladitz, M. Curbach: Carbon Concrete Composite . In: K. Holschemacher (Ed.): 12th Concrete Components Conference - New Challenges in Concrete Construction . Beuth Verlag, 2017, p. 121-138 .
  2. ↑ K. Schneider, M. Butler, V. Mechtcherine: Carbon Concrete Composites C³ - Sustainable binders and concretes for the future. In: Concrete and reinforced concrete construction . Ernst & Sohn Verlag for Architecture and Technical Sciences, 2017.
  3. ↑ M. Lieboldt: Fine concrete matrix for textile concrete; Requirements - practical adaptation - properties . In: Concrete and reinforced concrete construction special 110 . Issue S1, 2015, p. 22-28 .
  4. ↑ Manfred Curbach, Chokri Cherif, Peter Offermann: Economical, gentle, beautiful - the fascinating material carbon concrete . In: Technology in Bavaria . February 2017.
  5. ↑ Collaborative Research Center 528. In: TU Dresden, Faculty of Civil Engineering, Institute of Concrete. Retrieved March 1, 2019 .
  6. ↑ DFG - GEPRIS - SFB 532: Textile Reinforced Concrete - Basics for the Development of a New Technology. Retrieved March 1, 2019 .
  7. ↑ Overview of the C³ partners - Carbon Concrete Composite eV Accessed on March 1, 2019 (German).
  8. ^ F. Schladitz, M. Curbach: Carbon Concrete Composite . In: K. Holschemacher (Ed.): 12th Concrete Components Conference - New Challenges in Concrete Construction . Beuth Verlag, 2017, p. 121-138 .
  9. ↑ A. Bentur, M. Ben-Bassat, D. Schneider: Durability of Glass-Fiber Reinforced Cements with different Alkali-Resistant Glass Fibers . In: Journal of the American Ceramic Society . tape 68 , no. 4 , 1985, pp. 203-208 .
  10. ↑ GW Ehrenstein: fiber composite plastics. Materials - processing - properties . 2nd, completely revised edition. Hanse, Munich 2006.
  11. ^ F. Schladitz, M. Curbach: Carbon Concrete Composite . In: K. Holschemacher (Ed.): 12th Concrete Components Conference - New Challenges in Concrete Construction . Beuth Verlag, 2017, p. 121-138 .
  12. ^ F. Schladitz, M. Curbach: Carbon Concrete Composite . In: K. Holschemacher (Ed.): 12th Concrete Components Conference - New Challenges in Concrete Construction . Beuth Verlag, 2017, p. 121-138 .
  13. ^ F. Schladitz, M. Curbach: Carbon Concrete Composite . In: K. Holschemacher (Ed.): 12th Concrete Components Conference - New Challenges in Concrete Construction . Beuth Verlag, 2017, p. 121-138 .
  14. ↑ Jan Kortmann, Florian Kopf, Lars Hillemann, Peter Jehle: Recycling of carbon concrete - processing on an industrial scale successful! In: civil engineer . 11/2018, annual edition 2018/2019 of the VDI Department of Structural Engineering, ISSN  0005-6650 , p. 38-44 .
  15. ↑ Jan Kortmann, Florian Kopf: C³-V1.5 Demolition, dismantling and recycling of C³ components . In: C³ - Carbon Concrete Composite eV and TUDALIT eV (Eds.): Proceedings of the 10th Carbon and Textile Concrete Days , September 25th and 26th, 2018 . 2018, p. 84-85 .