3D Radar Reveals Defects Within Bridges

Imaging tech slips signals through steel mesh to uncover weaknesses in concrete

3 min read

A bridge in China spanning out over water
Xu Congjun/VCG/Getty Images

This article is part of our exclusive IEEE Journal Watch series in partnership with IEEE Xplore.

Many people around the world cross bridges on a daily basis without a second thought—but behind the scenes, engineers are conducting a battery of tests to ensure bridge safety. To support these efforts, one group of researchers in China has created a new radar device that can penetrate the concrete of bridges to create 3D images of its interior. The new tech, which was able to reconstruct detailed internal images of real-world bridges, is described in a study published 9 May in IEEE Sensors Journal.

Currently, there are several bridge-inspection techniques for assessing and monitoring the condition of bridge structures, including visual inspection, ultrasonic testing, infrared thermography, aerial inspection, and radar.

Radar is an especially good method for noninvasive testing of bridges, whereby electromagnetic signals are directed toward them. “These pulses penetrate the surface and bounce back when they encounter changes in material density, like defects or voids in the reinforced concrete of a bridge,” explains Xinghua Shi, a senior engineer at the China Research Institute of Radiowave Propagation and Ph.D. candidate at Xi’an Jiaotong University.

However, there are some challenges when it comes to using the technology to probe inside reinforced concrete. Due to the presence of steel mesh in bridges, low-frequency radar may not be able to effectively penetrate the steel mesh and detect defects below it.

To overcome these challenges, Shi and his colleagues sought to develop a novel 3D ground-penetrating radar device that works at frequencies of 1.3 gigahertz. It emits radar signals that emanate out at a wide range of angles. Although this approach produces background noise and scattered return signals, the researchers’ data analysis package translates the returning signals into 3D images of defects lurking behind the steel mesh.

An orange and black device with small wheels sits next to a tablet computer on a slab of concrete.This prototype 3D ground-penetrating radar system uses sophisticated software to discover potential bridge defects otherwise buried in concrete. Xinghua Shi et al./IEEE

Next, the researchers tested their device in the lab using a slab of reinforced concrete with known defects, which the system detected. “Our system produces detailed images of subsurface structures, allowing engineers to visualize defects, voids, and other anomalies within the reinforced concrete,” Shi says, noting that when his team went on to test the device on real bridges with prestressed concrete T-beams, its ability to detect defects was “outstanding.”

Despite the steel mesh in the bridge’s concrete structure, the system developed by Shi and his colleagues generates 3D images up to 60 centimeters deep, via a portable device that boasts real-time imaging.

Shi also notes that interpreting data from the team’s device still requires a high level of expertise. “Identifying and distinguishing between different types of anomalies in the radar images can be challenging,” he says. “[While] 3D imaging can provide a more intuitive visualization of steel reinforcement, other anomalies may require careful human judgment for identification.”

Therefore, he hopes to use deep learning to analyze the images and provide automatic classification of defects in future work.

“Reinforced concrete, being the cornerstone of bridge structures, plays a pivotal role in ensuring their quality and safety. It is imperative to introduce new, convenient, efficient, and accurate nondestructive testing technologies and equipment to identify defects and weaknesses in the reinforced concrete components of bridges,” he says.

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