Innovation That Matters

Corrosion detection | Photo source Samuel Zeller on Unsplash

Microwaves used to sniff out corrosion deep inside concrete


Researchers use microwaves to detect iron and steel corrosion deep inside concrete structures.


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Doctors regularly use forms of electromagnetic radiation such as x-rays to detect broken bones and internal damage inside the human body. Now, researchers at the US National Institute of Standards and Technology (NIST) have developed a similar technique that can search for signs of corrosion of iron and steel located deep inside concrete.

Corrosion in iron and steel is caused when water and oxygen combine with the metals to produce iron oxide products. The two most common are the minerals goethite (brown rust) and hematite. Researchers have demonstrated that terahertz radiation – electromagnetic waves with frequencies 10 to 100 times higher than the microwaves we use to cook food – can detect both goethite and hematite in the early stages of formation.

Previous methods used microwaves to detect corrosion through changes in the thickness of the metal, and could only detect corrosion once it was well under way. Earlier methods also relied on baseline data on the thickness of iron and steel beams that was not available for many of the nation’s older bridges and buildings.

The new method was first conceived in 2009 by the late William Egelhoff, a NIST fellow and pioneer in the field of magnetic materials, and is described in a paper published in the journal Applied Magnetic Resonance. It can detect very small amounts of corrosion through 25mm of concrete, polymer composites (such as pipe insulation), paint and other protective materials. The NIST team hopes to soon boost this to penetrate up to 50mm of concrete – the thickness used in most steel-reinforced concrete structures.

We have recently seen the development of sensor technology that can tell us whether our food is organic, alert us when undersea pipes are not fully operational, and let us know how much vitamin D we are exposed to. What else in our environment can we use sensors to sniff out for us?




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