Scientists have developed a new form of shape memory alloy which can be activated at reduced temperatures and incorporated into conventional building materials.
Shape memory alloys (SMA) are metals which are capable of resuming their original shape following severe warping or deformation. The self-correcting function can occur either spontaneously or be activated following the application of high levels of heat.
This extraordinary ability to self-repair following bending or warping confers SMAs with a remarkable range of industrial applications and makes them the ideal materials for delicate technical devices such as micro-actuators, spectacles, stents and thermostats.
They also possess immense potential for usage as a construction material. While it is not possible to use SMAs to create self-repairing walls or ceilings, they can be incorporated into other components like concrete beams and then activated to pre-stress structures such as bridge spans.
This technique of pre-stressing using SMAs is much easier and more economical than conventional methods. It also has the potential to permit the pre-stressing of a far greater range of structures than is currently feasible using standard techniques, including column wrapping, near surface mounted laminates, short fibre concrete and ribbed armouring steel.
Such applications have thus far been hampered, however, by either high costs or the extremely high temperatures often required to trigger the self-correcting process in cheaper SMAs.
The nickel titan alloys which are typically employed to make smaller self-repairing devices, such as spectacles and stents, are too expensive for usage in the copious amounts required by large-scale engineering or building projects.
While SMAs made using iron are cheaper to source and process, they require extreme temperatures as high as 400 degrees Celsius to activate the their memory function, making them impractical for usage alongside conventional building materials such as concrete.
Researchers from the Swiss Federal Laboratories for Materials Science and Technology (Empa) have developed a new type of iron-based SMA which they claim can be activated at temperatures low enough to make its usage in the building industry viable while still remaining cost effective.
Christian Leinenbach of the Joining Technology and Corrosion Laboratory led the development of the material, which involved creating thermodynamic simulations of a variety of virtual alloys before manufacturing real versions of the best permutations of the metals and testing out their shape memory capabilities.
The result of their efforts has been the development of an iron-manganese-silicon SMA alloy with an activation temperature of just 160 degrees Celsius – low enough to permit its usage alongside conventional concrete.
According to a feasibility study financed by the Commission for Technology and Innovation, it should be possible to produce the new alloys on a mass scale for industrial applications, with the costs of the product expected to comparable to that of stainless steel based materials.
A start-up company, re-Fer AG, has already been established to engage in the manufacture and distribution of the new iron-based SMA for usage in the construction industry.