A laser-quick and non-destructive method to detect cracks in concrete structures
Scientists analyze vibration patterns resulting from laser-induced shock
waves to detect defects in concrete structures

Date:
February 24, 2022
Source:
Shibaura Institute of Technology
Summary:
Large concrete structures need to be regularly tested for defects
that may compromise their stability. While acoustic tests performed
by certified inspectors are usually the inspection method of
choice, these tests take longer to perform as the structure's size
increases. In a new study, scientists developed a new method to
identify defects using shock waves generated by laser-induced
plasma. The new method is faster, completely non-destructive,
and allows for timely evaluation of concrete infrastructure.



FULL STORY ========================================================================== 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. "We used LIP shock waves as a non-contact, non-destructive
impulse excitation. This allows for remote and completely non-destructive detection of defects in concrete structures," explains Naoki Hosoya,
a Professor at the Department of Engineering Science and Mechanics at
Shibaura Institute of Technology and the corresponding author of the
study. Their findings have been published in the International Journal
of Mechanical Sciences.

To evaluate the new method, the researchers exposed a concrete block
that had an artificially created defect to a shock wave generated by a high-power pulsed laser. The vibrations were then analyzed at multiple
points on the concrete surface inside and outside the defect area. The
analysis revealed the presence of Rayleigh waves at the site of the
defect. These are surface waves that move at a faster velocity than
other shock waves. The researchers were able to successfully determine
the defect areas by detecting the points where these Rayleigh waves
were reflected. "Defects in the concrete specimen can be detected and
the location of the approximate boundary can be determined using the propagation of Rayleigh waves," explains Prof. Hosoya.

By visualizing Rayleigh waves, defects in a structure can be detected
much faster than with other telemetric methods which analyze vibrations,
making it a useful method for non- destructive testing of concrete
structures. "The advantage of using Rayleigh waves to detect defects
is that fewer measurement points are necessary compared to measuring
the natural mode. Additionally, the time required for defect detection
can be shortened. Visualizing Rayleigh waves propagation has potential
for practical detection of the configurations and defects in concrete," elaborates Prof. Hosoya.

In conclusion, the use of LIP shock waves to assess cracks in concrete structures is a safe and rapid method that can be used to maintain infrastructure and prevent structural failure.

========================================================================== Story Source: Materials provided by
Shibaura_Institute_of_Technology. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Sho Wakata, Naoki Hosoya, Noboru Hasegawa, Masaharu
Nishikino. Defect
detection of concrete in infrastructure based on Rayleigh
wave propagation generated by laser-induced plasma shock
waves. International Journal of Mechanical Sciences, 2022; 218:
107039 DOI: 10.1016/ j.ijmecsci.2021.107039 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220224140837.htm

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