Research that improvises on a conventional application, making it more accurate and easier to use, is a significant value addition. A research team from IIT-Bombay, led by Prof Siddharth Tallur and Prof Sauvik Banerjee, has developed a compact ‘probe’ that can gauge the extent of corrosion of steel reinforcement bars in concrete structures.

The probe simply needs to be placed on the surface of a concrete structure to determine the corrosion in its reinforcement steel bars or rebars. This is not only easier but also more accurate than existing methods.

One of the current methods, for instance, involves drilling a hole in a structure to expose a portion of the rebar and recording the voltage difference created in the corroded and non-corroded regions. Non-intrusive testing methods involve embedding a sensor in the concrete during casting to detect corrosion levels. Another non-intrusive method uses acoustic emission sensing, which records the sound waves created when cracks form on the rebar. However, these methods either have low sensitivity or do not detect early corrosion.

The probe developed by the IIT team uses the ‘pulsed eddy current’ method. Explains Prof Tallur: “Pulsed eddy current systems are commonly used for inspection of pipelines in the oil and gas industry. These sensors are placed on robotic systems that crawl along the length of the pipe while scanning it to identify defects. Such techniques are, however, not used for inspection of steel rebars in reinforced cement concrete (RCC) buildings.”

The reason for the non-use is the need for high-power circuits to drive large current in a coil, which makes such systems bulky and expensive. “Since we wanted to invent a hand-held scanner for structural audit and inspection of buildings, we had to redesign a compact and lightweight system. The probe we developed is smaller than a water bottle, and we are currently working to make a fully integrated hand-held unit, much like a barcode scanner,” says Tallur.

The pulsed eddy current method works on the principle that when current is passed through a coil it creates a magnetic field. When such a coil is placed near a metallic sample, the magnetic field induces eddy currents in the sample. The eddy currents generate a secondary magnetic field that opposes the original magnetic field produced by the coil. The strength of the eddy currents varies with the thickness of the metallic sample. Since corrosion causes material loss in steel, and the production of non-conducting rust, it causes a change in the eddy currents and is detected by the sensor as a change in the secondary magnetic field.

The IIT team has patented its probe and a prototype will soon be ready. The research was partially funded by the Department of Science and Technology and an industrial partner, Sanrachana Structural Strengthening Pvt Ltd. “We are working with our industry partner to evaluate the market readiness of our technology. We are considering launching a start-up venture to commercialise this technology,” says Tallur.

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