Memory-steel can reinforce existing buildings at a reasonable cost

So far, the steel reinforcements in concrete structures are mostly prestressed hydraulically. This requires 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 alternative 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.

The development of memory-steel began in the early 2000s. In the previous decades, Empa had already 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.

Memory-steel reinforcement bars