A Laser-quick and Non-destructive Method to Detect Cracks in Concrete Structures

Brief 

Researchers in Japan have developed a nondestructive method for testing large concrete structures that involves the use of shockwaves from laser-induced plasma. “The advantage of using Rayleigh waves to detect defects is that fewer measurement points are necessary compared to measuring the natural mode,” said professor Naoki Hosoya from the Shibaura Institute of Technology.

Insight

Nothing is truly set in concrete, and this is especially true for structures made of concrete. When structures made of concrete like bridges, buildings, and tunnels are loaded repeatedly over long periods, they develop cracks that may progress and cause structural failure. Regular inspections are therefore needed to detect cracks before they become a cause for concern.

Conventionally, defects in concrete structures are detected using the acoustic test called the “hammering method” performed by certified building inspectors. However, these tests take time to complete and as with most skill-based techniques, the effectiveness of the test is dependent on the expertise of the inspector. Moreover, as the number of aging infrastructures continues to rise, a method of inspection that is fast and reliable is paramount for ensuring the safe operation and long-term use of the structure.

An alternative inspection method for testing involves generating shock waves near the surface of the concrete structure. The shock waves induce vibrations on the structure which can be analyzed to detect defects. However, in such tests, it is necessary to generate shock waves that do not damage the structure.

In this regard, laser-induced plasma (LIP) shock wave excitation has shown great promise. The technique has been used to detect defects in a variety of structures, ranging from pipes to fruit surfaces. In this method, the shock waves are generated by colliding laser-generated plasma with air.

In a new study, researchers from Shibaura Institute of Technology and the National Institutes for Quantum Science and Technology, Japan, tested the effectiveness of this method at detecting cracks in concrete structures.