Smart steel heated to 392°F doubles bridge strength in retrofit tests

Swiss researchers at Empa have developed a novel bridge retrofit system combining ultra-high-performance fiber-reinforced concrete (UHPFRC) with iron-based shape-memory alloy (Fe-SMA) steel bars that contract when heated to about 392°F (200°C). This smart steel tightens itself upon heating, closing cracks and doubling the structural strength of concrete bridge slabs. The system was tested on full-size damaged slabs, where it successfully restored cracks and significantly improved load-bearing capacity without requiring complex tensioning devices. The Fe-SMA bars generate internal stresses as they attempt to return to their original shape but are restrained by the concrete, enabling self-healing and strengthening of aging infrastructure. The hybrid retrofit outperformed conventional reinforcement methods under typical traffic conditions and offers a compact, effective solution for extending the service life of bridges, especially those built before the 1980s that are nearing the end of their design life. Although Fe-SMA materials are currently costly, the researchers suggest targeting severely damaged structures initially,