AsianScientist (Jan. 2, 2019) – Researchers in Japan have developed a non-destructive method to measure salt content in structures such as bridges, tunnels, and elevated roadways, which can suffer from degradation due to exposure to salt from seawater and other sources. They reported their findings at the 18th JSMS Symposium on Concrete Structure Scenarios.
The collapse of a bridge in August in Genoa, Italy, leading to the deaths of 37 people, has highlighted the danger posed by aging infrastructure. Japan, like many countries, faces major problems, as many of its bridges and tunnels constructed during the high economic growth period of the 1960s and 1970s are now suffering degradation.
However, structural inspections to gauge the salt content of cement structures is typically done by boring out a core—a time-consuming process that results in slight damage to the structure. To find a better way to analyze structural integrity, scientists at the RIKEN Center for Advanced Photonics, Japan, used a neutron beam that can penetrate quite far into metallic materials.
Neutrons are not affected by electric charge, although they occasionally interact with nuclei in the materials they penetrate, leading to the release of gamma rays that can be detected. The group used their compact neutron source, which generates neutrons by bombarding a beryllium target with protons, to irradiate a series of concrete blocks with salt mixed into the construction material.
They then measured ‘prompt’ gamma rays—gamma rays that are emitted immediately upon exposure to neutrons—using high resolution germanium detectors. Different elements within the concrete blocks can be detected by examining the energy of the gamma rays.
For example, chlorine—a component of salt—emits prompt gamma rays with energy peaks of 517 kiloelectron volts, 786 kiloelectron volts, 788 kiloelectron volts, 1,165 kiloelectron volts and so on. By recording these energy peaks, the researchers were able to demonstrate the presence of salt even when it was surrounded by 12–18 centimeters of concrete. Each measurement took about ten minutes.
“This is very exciting because Japan is suffering from serious infrastructure degradation, and it is impossible to predict when a major accident will happen,” said Dr. Yoshie Otake of RIKEN who led the study.
“Our feasibility study has shown that neutron beams can indeed be used to measure whether the salt content of a concrete structure is within the legal limits set by the government. Our next challenge is to build a compact neutron source that is small enough to be readily transported to various infrastructures to conduct measurements.”
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Source: RIKEN; Photo: Pexels.
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