The development of memory steel began in the 2000s and it found almost immediate applications in medicine. Now, scientists at Empa, the Swiss Federal Laboratories for Materials Science and Technology, have found a way to make a type of memory steel that is sufficiently inexpensive to be used on a much larger scale in the construction industry and on civil engineering projects. [M. Shahverdi et al., Construct Build Mater (2018) 173: 586; DOI: [10.1016/j.conbuildmat.2018.04.057]
Empa's memory-steel could be used to reinforce new and existing concrete structures. It requires a one-off heating to pre-stress it automatically. This is in complete contrast to most pre-stressed steel reinforcements used in concrete which must be treated hydraulically requiring ducts for guiding the tension cables, anchors for force transfer, and oil-filled hydraulic jacks. Hydraulic pre-stressing is a cumbersome and heavy-weight process and generally not plausible with old structures that require reinforcing.
It has taken Empa scientists some fifteen years to find an alternative in their research into iron alloys that have the shape memory properties that could sidestep the complexities of conventional pre-stressing. They show that heating using a brief electric current or infrared device is sufficient to have a marked effect on the characteristics of the alloy. The Empa team and spin-off company re-fer AG have already initiated several successful pilot projects. For example, a strip of memory steel can be fastened under a ceiling slab using dowels and then heated to stress it or the reinforcement can be first set in concrete by milling a groove into the slab.
The scientists explain that In the future, memory-steel could also be used for manufacturing precast concrete parts with novel geometries. The hydraulic pre-stressing used up to now creates friction in curved structures, which greatly limits the use of this method. By embedding the memory-steel in concrete, even highly curved constructions could be possible. When the structure is heated, the profile contracts uniformly over its entire length without friction losses and transfers the stress to the concrete making it stronger.
The team's cost-effective memory steels are based on an iron alloy containing a small proportion of manganese, silicon, chromium, nickel, vanadium, and of course, carbon. The team provides full details of the formulation in the research paper. Not only is this a relatively inexpensive alloy but it is also cheaper to manufacture than nickel-titanium alloys, the team reports.
David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase.