Ultra high strength concrete

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Ultra High Performance Concrete (UHPC; English Ultra High Performance Concrete , common abbreviation UHPC ) or ultra high-performance concrete is a type of concrete, which is characterized by particularly high density and strength. A common, but not generally recognized, distinction from normal concrete is a compressive strength of over 150 N / mm² and a w / c value <0.25.

Components and manufacturing principles

Gärtnerplatzbrücke in Kassel, first UHPC construction in Germany
Walser bridge in Oberstdorf with balustrades made of UHPC, design by Dr. Schütz engineers

The most important component of concrete is the cement stone matrix, which is essentially produced from the binding agent cement and water. The cement paste envelops the aggregates such. B. natural aggregates and glued them together. The denser and more pore-free the cement stone matrix, the denser, stronger and more stable the concrete will be.

Usually a binder mixture of Portland cement , blast furnace slag or fly ash is used. The cement stone matrix can be further improved by a granulometric optimization of the fine materials below 0.063 mm grain size. Cement grains have an average grain diameter of around 30 to 80 micrometers. The addition of significantly smaller and hydraulically active substances with a diameter in the single-digit micrometer range or nanometer range fills the interstices between the cement grains and leads to a compaction of the structure. The most widespread substance is silica dust , but aluminosilicates, metakaolin, finely ground cements or industrially produced nanosilica are also used. In the range of 60 to 125 micrometers, i.e. above the cement grain, ground, graded rock powder is used to precisely define the grading curve , see also high-strength concrete .

A second measure is to reduce the water content to a w / c value of 0.3 to 0.2 ( water-cement ratio ). On the one hand, this minimizes the water film and thus the distance between the cement grains. On the other hand, due to the lack of water, the cement grains only react on the surface and approx. 70% of the cement grain remains as high-strength aggregate. In order for the concrete to be flowable or self-compacting, large quantities of high-performance superplasticizers based on polycarboxylate ether (PCE) are required.

With the two measures described, one can produce concrete with a cylinder compressive strength of 100 to 150 N / mm² using conventional aggregates such as quartz or basalt. With such test specimens, the concrete no longer fails around the aggregate, but the crack runs through them. Further increases in the mechanical characteristics require additional measures. On the one hand, the usual grains can be replaced by aggregates of high strength and density such as. B. corundum or other natural or industrially manufactured abrasives are replaced. Second, by adding steel fibers (up to over 3% by volume or 250 kg / m³), ​​additional high-strength components are introduced ( steel fiber concrete ). These steel fibers, often as a fiber cocktail, not only lead to ductile behavior, but also significantly increase the compressive strength of the concrete. In the case of concretes with silica fume, as a third measure, thermal treatment in the first week leads to an accelerated hydraulic reaction of the silica with a further improvement in mechanical characteristics ( pozzolanic reaction ).

Alternative names

Shrimp breeding tank made from UHPC
Volksbank Krefeld with white facade panels made of UHPC
Weir system in Zabeltitz with UHPC protective layers against abrasion

Other terms for UHPC that define components or isolated properties more precisely or come from other language areas are:

  • UHSC "Ultra high strength concrete"
  • UHPFRC "Ultra high performance fiber reinforced concrete"
  • UHPdC "Ultra high performance ductile concrete"
  • DFRCC "Ductile fiber reinforced cementitious composite"
  • SHCC "Strain hardening cementitious composite"
  • ECC "Engineered cementitious composite"
  • UHP-HFRC "Ultra high performance hybrid fiber reinforced concrete"
  • HPFRCC "High performance fiber reinforced cementitious composites"
  • RPC "Reactice powder concrete"
  • UHFB "Ultra high-strength concrete" (German)
  • UHFB "Ultra-High-Performance Fiber Concrete" (Switzerland)
  • UHFB "Ultra-high-strength fiber composite building material" (Switzerland)
  • UHLB "Ultra High Performance Concrete" (German)
  • BFUB "Béton fiber à ultra-hautes performances" (French)
  • BPR "Beton de Poudres Réactives" (French)

history

The development of ultra-high strength concrete began in Denmark in 1967 with Hans Henrik Bache (Aalborg Portland Cement). This year he published the development of smaller material samples in which the binder was compressed to a strength of 350 MPa. In 1970 superplasticizers were used for the first time in further development. In 1978 a material strength of 280 MPa is achieved due to the development of a mixed binder with approx. 30% ultrafine fillers. Aalborg Portland Cement and Hans Henrik Bache received the patent for this high-strength binder system this year. In 1981 DENSIT a / s was founded in Aalborg Denmark, DENSIT a / s developed and produced further ultra-high-strength binder systems based on the first patent. PCE superplasticizers were first developed in Japan in the 1980s, and microsilica from Elkem in Norway became generally available in the 1990s. After Densit's patents expired, a handful of companies in Europe and Japan began producing ultra-high-strength binders. In 2002, the cement manufacturer Lafarge registered the European patent EP 1315683 "High-strength, highly ductile fiber-reinforced concrete".

In Germany there was a priority program SSP1182 “Sustainable Building with Ultra-High-Strength Concrete” of the German Research Foundation, which was endowed with EUR 12 million and ran from 2005 to 2012 . In 2008 the German Committee for Reinforced Concrete (DAfStb) published a status report on construction methods as issue 561 . A successor in the form of a DAfStb guideline is in progress.

In Japan, the guideline of the Concrete Engineering Series 82 “Recommendations for Design and Construction of High Performance Fiber Reinforced Cement Composites with Multiple Fine Cracks (HPFRCC)” was published in March 2008.

In Switzerland, the SIA 2052 leaflet “Ultra-High-Performance Fiber Concrete (UHFB) - Building Materials, Design and Execution” was published in 2016.

France is a leader in the field of UHPC. In 2016, two construction standards were published that regulate dry premixes (ready-mixed mortar) and their use in construction.

  • NF P 18-470 Bétons fibrés à ultra-hautes performances - Specification, performance, production et conformité, AFNOR, Paris 2016
  • NF P 18-710 Calcul des structures en béton - Règles spècifiques pour les bétons fibrés à ultra-hautes performances (BFUB), AFNOR Paris, 2016

The following French standard was published in December 2018: NF-P 18-451 Bétons - Exécution des structures en béton - Régles spécifiques pour les BFUB

Today, some cement manufacturers offer special binders and formulations for the production of UHPC. Since these are optimized for certain applications and thus characteristics such as compressive strength, tensile strength, ductility, flow behavior, abrasion, damping, etc., no generally binding table on material behavior can be given.

Building approval

Cloakroom steles made of unreinforced and fiber-free UHPC in the Museum Bibelhaus in Frankfurt am Main

UHPC differs from conventional concretes in terms of strength, fine material content, ductility, etc. and does not correspond to the concretes regulated by the building authorities. For its use in the building industry in Germany, approval in individual cases or a general building inspection approval is required.

Applications in the German construction industry

Machine component made from UHPC
Concrete surface made of UHPC in mechanical engineering

Worldwide there are a large number of sometimes spectacular structures such as B. the National Museum in Qatar or the MuCEM in Marseille. There are extensive concepts and research reports in Germany, but apart from a few lighthouse projects, UHPC is not used. The main cause is the high price, which - depending on the fiber content - is between EUR 500 and EUR 1,500 per m³ and is thus 5 to 20 times higher than normal concrete. Another cause is the test and quality requirements to be expected with a building authority approval, which make the product uneconomical despite the clear improvement in quality. Executed objects are:

  • Niestetalbrücke foot and cycle path bridges
  • Gärtnerplatzbrücke Kassel foot and cycle bridge
  • Arched cycle path bridge near Leipzig
  • Company headquarters in Ferchau Gummersbach, facade panels for house 1 and 2
  • Volksbank Krefeld, white facade panels
  • Shrimp farm Grevesmühlen
  • Anchor heads at the Iffezheim lock
  • Railway bridge of the Tegernsee-Bahn near Gmund
  • Gutter filling at the connection to the foundation as well as tower structures for wind power plants
  • Thin, reinforcing surface layers on bridge structures such as the B27 overpass of the L3378 near Fulda-Lehnerz in 2017. Another example is the renovation of the Maxau Rhine bridge near Karlsruhe in winter 2018/2019. The construction method has been used successfully in neighboring European countries for many years. A European patent for the construction has been withdrawn.

Other applications outside the area regulated by the building authorities are cloakroom steles, stairs, furniture, design items, vaulted concrete and gap filling in vertical column joints of offshore wind turbines.

Applications in mechanical engineering

The most economically significant application in Germany is the substitution of epoxy resin-bonded polymer concrete or mineral casting in mechanical engineering. In addition to high tensile strength, the damping of the material against vibrations and thermal inertia in the event of thermal fluctuations are decisive in this area of ​​application. Machine components made of UHPC must be manufactured and remain crack-free. Fibers and reinforcement only take effect after cracks have formed that change stiffness and are therefore not helpful. The cement paste matrix of the unreinforced UHPC must be able to withstand all forces. Since the required accuracies of parallelism and evenness are in the range of up to 5 micrometers over a reference surface of several meters, a deformation of the material such as B. can be safely excluded by shrinkage.

literature

  • Michael Schmidt, Ekkehard Fehling, Susanne Fröhlich, Jenny Thiemcke: Sustainable building with ultra-high- strength concrete, results of the priority program 1182 funded by the German Research Foundation (DFG). (= Building materials and solid construction. Issue 22). kassel university press, Kassel 2014.
  • DAfStb: Ultra-high-strength concrete, status report. (= German Committee for Reinforced Concrete eV, issue 561). Beuth, Berlin 2008.
  • UltraHigh Performance-Concrete (UHPC) 10 years of research and development at the University of Kassel. (= Building materials and solid construction. Booklet 7). 2007
  • Bernhard Sagmeister: Machine parts made of cement-bound concrete. Beuth Verlag, Berlin 2017, ISBN 978-3-410-27186-4 . (Description Beuth Verlag) .

Web links

Individual evidence

  1. ↑ T. Hirata: Dispersant . JP patent 842,022 (S59-018338) 1981
  2. ^ Lafarge: Highly Resistant And Ductile Fiber Concrete . EP 1315683 [1]
  3. ↑ beuth.de
  4. ↑ dafstb.de
  5. ↑ [2]
  6. ↑ shop.sia.ch
  7. ↑ boutique.afnor.org
  8. ↑ boutique.afnor.org
  9. ↑ [3]
  10. ↑ qm.org.qa
  11. ↑ mucem.org
  12. ↑ Michael Schmidt, Kai Bunje, Ekkehard Fehling, Thomas Teichmann: Bridge family made of ultra-high-strength concrete in Niestetal and Kassel. In: Concrete and reinforced concrete construction. 101, 3, 2006, pp. 198-204.
  13. ↑ Michael Schmidt, Kai Bunje, Ekkehard Fehling, Thomas Teichmann: Bridge family made of ultra-high-strength concrete in Niestetal and Kassel. In: Concrete and reinforced concrete construction. 101, 3, 2006, pp. 198-204.
  14. ↑ R. Mellwitz, M. Richter, M. Reichel: Ultra-high-strength fiber-reinforced concrete for precast segment parts. In: Betonwerk International. BWI 03/2014
  15. ↑ Bernhard Sagmeister, Thomas Deuse: Concrete applications outside the building industry - applications of UHPC based on a special binder in building technology and mechanical engineering. In: Betonwerk International. BWI 01/2012
  16. ↑ Thomas Drössler: Innovative Application of UHPC in Germany: Ultra-High Performance Concretes for fair-faced Facades and Custom Elements with glued Connections. (= Building materials and solid construction. Issue 27). Kassel university press, Kassel 2016.
  17. ↑ Thomas Deuse, Christian Drössler, Thomas Drössler, W. Ritter: High-performance concrete with adhesive connection. In: Betonwerk International BWI. 06/2014
  18. ↑ Hermann Weiher, Christian Tritschler, Michael Glassl, Sebastian Hock: Hybrid anchors from the first UHPC application for the reinforcement of the Iffezheim Rhine lock with permanent strand anchors. In: Concrete and reinforced concrete construction. Volume 107, April 2012.
  19. ↑ [4]
  20. ↑ Pelke, E .; Berger D .: UHFB first application in road bridge construction Part 1: Project ASB 5424-824 Üf B27 of the L3378 near Fulda-Lehnerz ; Lecture at the Dreikönigstreffen at the Rhein-Main University of Applied Sciences on January 15, 2019 in Wiesbaden
  21. ↑ [5]
  22. ↑ Kaptijn, N; Blom, J: A new bridge deck for the Kaag bridges ; in Proceedings of the International Symposium on Ultra High Performance Concrete Kassel University, 2004, pages 49-57
  23. ↑ Denarié E .; Brühwiler E .: CAST-ON SITE UHPFRC FOR IMPROVEMENT OF EXISTING STRUCTURES - ACHIEVEMENTS OVER THE LAST 10 YEARS IN PRACTICE AND RESEARCH ; in 7th workshop on High Performance Fiber Reinforced Cement Composites , 1-3, June 2015, Stuttgart, Germany [6]
  24. ↑ EP 1 623 080 B1 Sandwich plate-like construction [7]
  25. ↑ durcrete.de
  26. ↑ Bernhard Sagmeister: UHPC concrete in mechanical engineering. beton 12/2018, Verlag Bau + Technik, Düsseldorf