A new building material developed at Empa is about to be launched on the market: "memory-steel" can not only be used to reinforce new, but also existing concrete structures. When the material is heated (one-time), prestressing occurs automatically. The Empa spin-off re-fer AG is now presenting the material with shape memory in a series of lectures.
So far, the steel reinforcements in concrete structures are mostly prestressed hydraulically. This re-quires ducts for guiding the tension cables, anchors for force transfer and oil-filled hydraulic jacks. The space requirements of all these apparatuses created the geometric framework conditions for every prestressed concrete structure; the strengthening of older structures therefore sometimes fails due to the high space requirements of this proven method.
In around 15 years of research work, experts from Empa and re-fer AG have now brought an alter-native method to series production readiness: shape memory alloys based on iron, which contract during heating and thus permanently prestress the concrete structure.
Hydraulic prestressing can thus be avoided - it is sufficient to heat the steel shortly, for example by means of electric current or infrared radiators. The new building material will be marketed immediately under the name "memory-steel". Several pilot projects, such as the reinforcement of various reinforced concrete slabs, have already been successful.
Development of memory-steel
The development of memory-steel began in the early 2000s. In the previous decades, Empa had al-ready pioneered the strengthening of concrete with carbon fibre reinforced polymers (CFRP). This led to the idea of using shape memory alloys for prestressing concrete.
Initial tests with nickel-titanium alloys were positive. However, the material known from medicine is far too expensive for use in the construction sector. In 2009, Empa researchers succeeded in developing an iron-based shape memory alloy, which they also patented. In 2012, researchers around Julien Michels finally founded the company re-fer AG; Michels has been CEO of the young company ever since.
New opportunities for old buildings
memory-steel should first of all be used for the strengthening of existing buildings. As soon as, for example, new windows, doors or lift shafts are installed in the concrete structure of an old building, a new reinforcement of the load-bearing structure is often unavoidable. In industrial buildings, the load-bearing capacity of an old suspended slab sometimes has to be increased.
Thanks to memory-steel, such tasks can now also be easily solved in confined spaces: Either a strip of special steel is fastened under the ceiling using dowels and then heated with electricity or an infrared radiator.
Alternatively, the reinforcement can also be set in concrete: First a groove is milled into the surface of the concrete slab, then a ribbed reinforcement bar made of memory-steel is inserted in-to the groove and filled with special mortar. Finally, the profile is heated with the aid of direct cur-rent and thus prestressed. Another variant is to embed the reinforcement bar in an additional shotcrete layer.
Precast concrete elements with special geometry
In the future, memory-steel could also be a proven method for manufacturing precast concrete parts with a previously unknown geometry. The hydraulic prestressing used up to now creates fric-tion in curved structures, which greatly limits the use of this method.
With a memory-steel profile embedded in concrete, highly curved constructions are now also possible: when heated, the profile contracts uniformly over its entire length without friction losses and transfers the stress to the concrete.
Market launch of memory-steel
The ready-to-install memory-steel profiles are manufactured by Voestalpine Böhler Edelstahl GmbH & Co KG in Austria. The company is also working with re-fer and Empa to further develop the composition of the alloy.
The new building material memory-steel will be presented to interested building experts and archi-tects during four technical seminars. Contact persons include experts from re-fer, Empa researchers, concrete experts from Sika AG and concrete profile manufacturer Stahlton AG.
Dates of the symposia
30 October 2018 Empa, Dübendorf - 13.15 h to 16.45 h
31 October 2018 Empa, St.Gallen - 13.15 h to 16.45 h
5 November 2018 FH Luzern - 13.15 h to 16.45 h
7 November 2018 Kursaal Bern - 13.15 h to 16.45 h
Dr. Christoph Czaderski
Empa, Structural Engineering
Tel.: +41 58 765 4216
Dr. Julien Michels
Tel.: +41 58 765 4339
voestalpine BÖHLER Edelstahl GmbH & Co KG
Tel.: +43 3862 203 60 62
J Michels, M Shahverdi, C Czaderski; Flexural strengthening of structural concrete with iron-based shape memory alloy strips; Structural Concrete (2018); DOI: 10.1002/suco.201700120
Rainer Klose | Empa - Eidgenössische Materialprüfungs- und Forschungsanstalt
TU Graz researchers want to fundamentally improve concrete diagnostics
29.06.2020 | Technische Universität Graz
The digital construction site: A smarter way of building with mobile robots
02.06.2020 | Fraunhofer Italia
Solar cells based on perovskite compounds could soon make electricity generation from sunlight even more efficient and cheaper. The laboratory efficiency of these perovskite solar cells already exceeds that of the well-known silicon solar cells. An international team led by Stefan Weber from the Max Planck Institute for Polymer Research (MPI-P) in Mainz has found microscopic structures in perovskite crystals that can guide the charge transport in the solar cell. Clever alignment of these "electron highways" could make perovskite solar cells even more powerful.
Solar cells convert sunlight into electricity. During this process, the electrons of the material inside the cell absorb the energy of the light....
Empa researchers have succeeded in applying aerogels to microelectronics: Aerogels based on cellulose nanofibers can effectively shield electromagnetic radiation over a wide frequency range – and they are unrivalled in terms of weight.
Electric motors and electronic devices generate electromagnetic fields that sometimes have to be shielded in order not to affect neighboring electronic...
A promising operating mode for the plasma of a future power plant has been developed at the ASDEX Upgrade fusion device at Max Planck Institute for Plasma...
Live event – July 1, 2020 - 11:00 to 11:45 (CET)
"Automation in Aerospace Industry @ Fraunhofer IFAM"
The Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM l Stade is presenting its forward-looking R&D portfolio for the first time at...
With an X-ray experiment at the European Synchrotron ESRF in Grenoble (France), Empa researchers were able to demonstrate how well their real-time acoustic monitoring of laser weld seams works. With almost 90 percent reliability, they detected the formation of unwanted pores that impair the quality of weld seams. Thanks to a special evaluation method based on artificial intelligence (AI), the detection process is completed in just 70 milliseconds.
Laser welding is a process suitable for joining metals and thermoplastics. It has become particularly well established in highly automated production, for...
02.07.2020 | Event News
19.05.2020 | Event News
07.04.2020 | Event News
03.07.2020 | Life Sciences
03.07.2020 | Studies and Analyses
03.07.2020 | Power and Electrical Engineering