Summary

Swiss researchers at Empa have developed an innovative reinforcement system for old reinforced concrete bridges that combines shape memory steel with ultra-high-performance fiber concrete for the first time. The material contracts when heated and automatically prestresses concrete structures – without elaborate tensioning devices. Large-scale tests show that the system restores already damaged bridges, closes cracks, and doubles load-bearing capacity.

People

Topics

  • Bridge renovation and infrastructure
  • Shape memory steel (Fe-SMA)
  • Ultra-high-performance fiber concrete (UHPFRC)
  • Materials science and building materials technology

Clarus Lead

Many Swiss bridges from the 1970s are approaching the end of their service life. An Empa research team has now developed a novel reinforcement system that reactivates damaged structures without elaborate tensioning devices. The combination of shape memory steel and ultra-high-performance concrete makes it possible to close existing cracks and lift sagging structural elements – by simply heating to approximately 200 degrees Celsius. For infrastructure decision-makers, this represents a more cost-effective alternative to conventional renovation methods, once material costs decline.

Detailed Summary

The research team led by Angela Sequeira Lemos and Christoph Czaderski replaced conventional steel reinforcement in their system with iron-based shape memory alloys (Fe-SMA). These materials possess a unique property: after heating, they "remember" their original shape and generate internal stress forces that are transferred to the concrete structure. The process is elegant in its simplicity – the bars are anchored, heated, and do the rest on their own.

In extensive tests in the Empa building hall, the team tested five concrete slabs, each five meters long, simulating cantilever bridge decks. One slab remained unreinforced as a reference, while the others were equipped with either conventional reinforcement or Fe-SMA bars. Crucially: the slabs were deliberately cracked to simulate realistic renovation conditions. During activation of the shape memory steels, cracks visibly closed, and deformations reversed completely. State-of-the-art measurement methods – including fiber-optic sensors that function like fiber optic cables – continuously monitored deformations inside the structure.

The results show clear advantages: both conventional and new reinforcement at least doubled the load-bearing capacity of an unreinforced slab. Under everyday conditions (normal road traffic), however, the shape memory steel system proved superior – it makes bridge slabs stiffer, delays permanent deformations, and can repair existing damage.

Key Findings

  • First-time combination: Shape memory steel is combined with ultra-high-performance fiber concrete for the first time, enabling automatic prestressing without external tensioning devices.

  • Doubled load-bearing capacity: Tests show at least doubled load-bearing capacity compared to unreinforced slabs; under everyday conditions, the new system is superior.

  • Crack closure and lifting: The system can close existing cracks and lift sagging structural elements – ideal for already damaged bridges.

  • Simple application: The process requires only anchoring, heating to ~200°C, and concrete overlay – significantly less effort than conventional methods.

  • Costs and scope of application: Material costs are currently high; the system is primarily suitable for severely deformed or damaged bridges where conventional methods reach their limits.

Critical Questions

  1. Long-term behavior under traffic load: How do Fe-SMA steels behave over decades under cyclic loading from real road traffic? Were fatigue tests conducted, or are the statements based only on static tests?

  2. Cost reduction and scalability: The press release mentions "relatively expensive" materials. What concrete cost targets does the team have, and on what basis is cost reduction expected through increased demand – are there market studies or industry contracts?

  3. Comparability with established methods: Were the costs (material + labor) of the new system quantitatively compared with conventional renovation methods (e.g., external prestressing, fiber composite reinforcement), or is the comparison purely qualitative?

  4. Practical implementation and quality control: How is it ensured that heating on construction sites occurs precisely at ~200°C? What tolerances are permissible, and how is the quality of prestressing verified?

  5. Environmental balance and recycling: How sustainable is the Fe-SMA alloy in manufacturing and disposal? Can the steels be recycled after their service life, or do disposal problems arise?

  6. Interface with existing standards: Are the materials and procedure already integrated into Swiss building standards (SIA), or must new standards be developed before practical application is possible?

  7. Long-term tightness and corrosion: The text mentions that UHPFRC is particularly resistant to water. How does the bond between Fe-SMA and concrete behave long-term against freeze-thaw cycles and chloride exposure (de-icing salt)?

Bibliography

Primary Source: New Reinforcement System for Reinforced Concrete Bridges: Bridge Renovation with "Smart" Steel – Empa Press Release, February 19, 2026

Participating Institutions:

  • Empa (Swiss Federal Laboratories for Materials Science and Technology)
  • Eastern Switzerland University of Applied Sciences OST
  • Empa spin-off re-fer
  • Association of the Swiss Cement Industry cemsuisse
  • Innosuisse (Funding)

Verification Status: ✓ February 19, 2026

This text was created with the support of an AI model. Editorial responsibility: clarus.news | Fact-checking: February 19, 2026