Swiss researchers are developing a way of strengthening reinforced concrete bridges by retrofitting them with a system involving two high-tech materials.
At Empa, the Swiss federal laboratory for materials science and technology, researchers Angela Sequeira Lemos and Christoph Czaderski are working in the structural engineering lab to combine ultra-high-performance fibre-reinforced concrete (UHPFRC) with shape memory steel (Fe-SMA).
Shape memory steel is a smart material that “remembers” its original shape. Bars installed within concrete can be heated so they contract, closing cracks and lifting deformed elements. The Empa team is for the first time, investigating the interaction between memory steel and UHPFRC.
They tested the system in Empa’s lab using cracked 5m concrete slabs to represent damaged cantilevered bridge decks. One slab was used as a control, while the others were strengthened using various combinations of UHPFRC, conventional reinforcement and Fe-SMA. The researchers tracked deformation using digital cameras for the surface, and fibre optics within the slabs.
Both strengthening systems improved the load-bearing capacity; but the UHPFRC Fe-SMA combination was shown to delay permanent deformation, close existing cracks and lift slightly bent components. Lemos and Czaderski are now looking for a real-life bridge to try the system on. Lemos said: “If we can reinforce a real bridge with our system, interest from industry is likely to grow rapidly. And as demand increases, material costs are also likely to fall – then this technology could bring a lasting change in bridge renovation.”
