Reinforced concrete structures, like bridges and high-rise buildings, must handle heavy loads, vibrations, and other stresses over time.
Regular inspections are essential to check the health of these structures and prevent dangerous failures.
However, traditional methods, such as manual hammer tapping to find cavities, are time-consuming, expensive, and sometimes require closing bridges.
Now, researchers have developed a new ultrasound-based monitoring method called coda wave interferometry (CWI).
This technique allows for continuous, detailed monitoring of concrete structures, making it easier to detect problems early and avoid costly repairs or unexpected closures.
How does CWI work?
CWI uses ultrasonic waves to identify small changes in concrete and reinforced concrete. These waves are sensitive enough to detect stress and early signs of damage before they become serious.
The method can provide a clear picture of the material’s condition, helping engineers take action before issues get worse.
The CoDA research group, which includes scientists from the Technical University of Munich (TUM), BAM, Ruhr-Universität Bochum, and Bochum University of Applied Sciences, is testing CWI on real-world structures.
Since 2021, researchers have been using ultrasonic sensors on the Gänstor Bridge, a 96-meter-long structure connecting Ulm and Neu-Ulm.
They started similar tests in 2022 at the Scheidplatz subway station in Munich, where the sensors track stress caused by streetcar traffic above.
The sensors, which are small tubes about 7.5 cm long, are placed inside the concrete or in small holes drilled into the structure. These sensors continuously collect data on stress, aging, and damage in the concrete. The data is then sent to a computer system for analysis.
The signals collected by the ultrasonic sensors don’t directly show where or how severe the damage is. Machine learning helps analyze this data, identifying changes in material properties like stiffness. It can also pinpoint the exact location of damage.
This system enables remote monitoring, meaning engineers can oversee multiple structures from a central location without needing to visit each site.
“This method allows us to monitor large structures with minimal disruption,” says Christoph Gehlen, a professor at TUM and leader of the CoDA project.
By accounting for factors like temperature and humidity, the research team has refined CWI into a reliable tool for long-term monitoring.
This breakthrough could revolutionize how we maintain bridges and other critical infrastructure, making them safer for everyone.
