Empa Introduces Shape Memory Steel Solution to Modernize Bridge Rehabilitation and Extend Infrastructure Lifespans

Finest fibers: The cracks formed during the experiment reveal the reinforcing fibers in the ultra-high-performance concrete. Image: Empa

(IN BRIEF) Empa researchers have developed a novel bridge retrofitting system that integrates ultra-high-performance fiber-reinforced concrete with iron-based shape memory alloy reinforcement to strengthen aging concrete bridges. When activated by heat, the smart steel generates internal prestressing forces that close cracks, restore deformation, and significantly improve structural stiffness without requiring complex tensioning equipment. Large-scale laboratory tests demonstrated that the method can more than double load-bearing capacity while outperforming conventional strengthening techniques under everyday traffic conditions. The technology is particularly suited to heavily damaged infrastructure and is now being prepared for its first real-world application through collaborations with academic and industry partners.

(PRESS RELEASE) DÜBENDORF, 20-Feb-2026 — /EuropaWire/ — Researchers at Empa have introduced a new strengthening approach for reinforced concrete bridges that combines ultra-high-performance fiber-reinforced concrete with shape memory steel, offering a promising method to rehabilitate aging infrastructure. The innovation is particularly relevant for Switzerland, where many bridges built before the 1980s are nearing the end of their intended service life.

Traditional retrofitting methods typically involve applying a protective layer of ultra-high-performance fiber-reinforced concrete to bridge decks and embedding conventional reinforcing steel to enhance structural capacity. The Empa research team, led by Angela Sequeira Lemos in collaboration with Christoph Czaderski from the Structural Engineering laboratory, has advanced this concept by replacing standard reinforcement with iron-based shape memory alloy bars, a material capable of returning to its original shape when heated.

Once installed, the Fe-SMA bars are heated to approximately 200°C. Because the bars are anchored within the concrete and cannot freely contract, they generate internal prestressing forces. These forces help close cracks, reduce deformation, and strengthen the structure without the need for complex mechanical tensioning systems, simplifying the retrofitting process.

Large-Scale Testing Demonstrates Practical Benefits

To validate the concept, the researchers first examined how well the shape memory steel bonded with the fiber-reinforced concrete, particularly after thermal activation. They then conducted full-scale experiments in Empa’s construction hall using five-meter-long concrete slabs designed to replicate cantilever bridge decks.

The slabs were intentionally cracked to simulate real-world deterioration before being strengthened. Some were reinforced using conventional techniques, while others incorporated the new Fe-SMA system. After activation through heating, the smart steel generated prestress within the structure, immediately closing cracks and eliminating residual deformation.

Enhanced Stiffness and Structural Performance

Advanced monitoring methods were used throughout testing to track structural behavior. Digital imaging systems observed crack development, while embedded fiber-optic sensors measured strain distribution along the reinforcement. These sensors allowed researchers to detect minute deformations by analyzing light signals reflected within the fibers.

Results showed that both strengthening approaches doubled the load-bearing capacity compared to unreinforced slabs. However, under everyday service conditions such as traffic loads, the system combining fiber-reinforced concrete with shape memory steel delivered superior performance. It increased stiffness, delayed permanent deformation, and actively counteracted existing structural damage, effectively revitalizing compromised bridge elements.

Targeted Application for Heavily Damaged Structures

Although the materials currently involve higher costs, the solution is particularly suited to bridges that are already significantly deformed or where traditional reinforcement reaches its limits. The technology may also be applicable to building construction, including balconies and flat roofs, where compact reinforcement and improved sealing properties are beneficial.

The project, funded by Innosuisse and carried out in collaboration with the University of Applied Sciences of Eastern Switzerland, the Empa spin-off re-fer, and the Swiss Cement Industry Association cemsuisse, is now moving toward real-world implementation. The research team is seeking a suitable bridge for its first field deployment, with the expectation that broader industry adoption could drive costs down and transform bridge rehabilitation practices.

How Shape Memory Steel Enables Self-Prestressing

The Fe-SMA bars resemble conventional ribbed reinforcement but are delivered in a pre-stretched condition. When heated after installation, the alloy’s atomic structure reverts to its original configuration. Because the bars are fixed within the concrete, this recovery process produces internal stresses that prestress the structure, sealing cracks and slightly lifting deformed components.

This behavior is made possible by a specially engineered iron alloy containing elements such as manganese, silicon, and chromium, which enable the reversible phase transformation responsible for the shape memory effect.

How shape memory steel works

The Fe-SMA (iron-based shape memory alloy) bars are manufactured like normal ribbed reinforcing bars and are delivered to the construction site on a pre-stretched condition. They are then positioned and anchored in the existing reinforced concrete structure, heated, and then covered with concrete. When heated, the steel “remembers” its original shape and tries to recover it. By being restricted to move, it develops internal forces instead which are transferred to the concrete via the anchor zones.

This shape memory effect is made possible by a special iron alloy that contains manganese, silicon, and chromium, among other elements. By initially stretching the bars, the atomic crystal structure is altered. When heated to around 200°C, the atomic structure reverts back. Since the steel is fixed in place, the resulting forces prestress the existing structure, closing existing cracks, and lifting deformed elements.

Media Contacts:

Angela Sequeira Lemos
Structural Engineering
Phone: +41 58 765 3989
angela.lemos@empa.ch

Dr. Christoph Czaderski
Structural Engineering
Phone: +41 58 765 4216
christoph.czaderski@empa.ch

Manuel Martin
Communications
Phone +41 58 765 4454
redaktion@empa.ch

SOURCE: EMPA