Shape memory alloys (SMAs), which when heated are able to return to their original shape after being severely deformed, have found their way into everything from spectacle frames to cars. Now researchers at Empa in Switzerland have developed a new type of SMA that could allow the material to find applications in the building and construction industries.
While nickel titanium SMAs are fine for small-scale applications, such as the aforementioned spectacle frames, the raw materials and processing costs makes them unsuitable for use in building and construction. For this reason, iron-based SMAs are much more attractive in terms of cost, but such materials currently used must be heated to temperatures of up to 400° C (752° F) for the memory effect to be activated. This is much too hot when other heat sensitive materials, such as concrete and mortar, are involved.
But now a research team, led by Christian Leinenbach of Empa's Joining Technology and Corrosion Laboratory, has developed a new iron-manganese-silicon SMA whose memory effect is activated at 160° C (320° F). This would make it more suitable for use alongside concrete, opening up potential applications in the building industry.
One example suggested by the researchers is in the reinforcement of bridges. Instead of conventional pre-stressing systems that rely on elaborate tensioning systems and jacket tubes, reinforcing rods of SMA material could be embedded within a concrete beam. By applying heat, the SMA within its concrete sheath would attempt to return to its original shape, thereby exerting a pre-stressing force on the beam.
Scaling things up, the researchers say this technique could be used to pre-stress a complete bridge span or other structure, with the necessary force able to be produced simply by heating up the SMA rods by passing an electric current through them. The team believes such an approach will prove simpler and cheaper than conventional pre-stressing techniques, including the use of short fiber concrete, near surface mounted laminates, column wrapping and ribbed armoring steel.
A manufacturing process for the material has been developed in collaboration with Austria's Leoben University (Austria), the Technical University Bergakademie Freiberg in Germany, and the German company G. Rau GmbH, with a feasibility study showing that it is possible to produce the new SMA at an industrial scale.
A start-up company, re-Fer AG has also been established to further develop a range of SMAs, which are expected to be comparable in cost to stainless steel based materials.