Smart paint detects tiny faults in structures such as bridges

The paint is formed using fly ash and highly aligned carbon nanotubes, which are capable of carrying an electrical current.

David McGahon, a researcher on the project who initiated the work as part of his PhD, said: ‘When these carbon nanotubes start to bend, the conductivity in them will change.’

The bending is detected by electrodes incorporated within the structure and therefore any significant change in the flow of electrical current can be interpreted as a sign of a structural defect.

When the paint is mixed, it has a cement-like property, which makes it particularly useful in harsh environments.

‘The electrodes will be attached to a small battery and small wireless transmitters placed throughout the structure,’ said McGahon. ‘There will be a master transmitter as well that will receive and communicate the whole structure’s responses.’

The wireless communication nodes will be powered in part by a battery but are also expected to rely on energy-harvesting methods where possible.

‘If you’re in a tunnel, you can use the vibrations of cars or trains going past to harvest power. If you’re on a bridge, you could maybe use a solar panel,’ said McGahon. ‘The idea is to make it more sustainable so you’re not running out to your bridge or structure to change the battery all the time.’

He added that most current structural defect inspections are made visually and therefore require an engineer to come out to the site. Alternatively, complex and expensive instrumentation is used.

So far, a prototype has been developed and the product is undergoing testing. ‘What we’ve done to date is to try to find the exact percentage of carbon nanotubes we need to make it cost effective. We’ve also done bending tests using strain sensors,’ said McGahon.

The team is also looking at the possibility of incorporating electrical impedance tomography (EIT) technology into any selected structures.

‘It creates a conductivity map so if a crack appears you will be able to see on a finite element model where exactly in the structure it is,’ said McGahon.

The first tests for this are expected to begin in the next two months.