Swiss researchers have developed a strengthening system to retrofit damaged bridges, combining ultra-high-performance fibre-reinforced concrete with memory steel. The latter, alloyed with manganese, silicon, and chromium, among other elements, contracts after being heated, thus prestressing concrete structures.
Researchers at Swiss construction engineering institute Empa have replaced conventional steel reinforcement with iron-based shape memory alloy (Fe-SMA) bars – a “smart” material that can remember its original shape. After installation, the bars are heated to around 200°C. As they attempt to contract but are restrained by the concrete, internal stresses develop. These internal forces can close cracks, lift deformed elements, and extend the service life of a bridge, Kallanish learns.
The Fe-SMA (iron-based shape memory alloy) bars are manufactured like normal ribbed reinforcing bars and are delivered to the construction site in a pre-stretched condition. They are then positioned and anchored in the existing reinforced concrete structure, heated, and then covered with concrete.
The materials used by the Empa team are rather expensive, the researchers note. “The system is therefore particularly suitable for heavily deformed or already damaged bridges – in other words, where conventional reinforcement methods reach their limits.”
