Researchers at Strathclyde University in Scotland have developed a paint that can detect microscopic faults in bridges, mines, and the foundations of wind turbines. The paint uses nanotechnology to sense movement in large structures.
Highly aligned carbon nanotubes that can carry an electrical current are combined with fly ash, an inexpensive recycled waste product, and mixed into a paint. When the carbon nanotubes begin to bend, their conductivity changes. These changes in conductivity are detected by electrodes incorporated within the structure that is coated with the paint. Any change in the flow of electrical current above a predetermined threshold can be interpreted as a sign of structural defect.
Changes in conductivity in highly aligned carbon nanotubes could help a new paint detect cracks in structures like the foundation of wind turbines, such as this one in Romania's Tihuta Pass. (Source: Rsocol/Wikipedia Commons)
The electrodes are attached to a battery, and wireless transmitters are placed throughout the structure. A master transmitter tracks changes in conductivity from all the structure's electrodes, which can be monitored remotely. The wireless communication nodes are powered in part by a battery, but they are also expected to rely on energy-harvesting methods where possible.
Most methods for checking large structures for defects use either a visual inspection (which requires an engineer to take a trip to the site) or time-consuming, complex, and expensive instrumentation. The paint can be sprayed on to any surface. With electrodes attached, it can detect structural damage long before failures occur.
When mixed, the paint is hard and durable, like cement. This makes it especially useful for coating structures that must withstand harsh environments, as well as those located where severe weather can make safety monitoring by human inspectors particularly difficult. Since fly ash is very inexpensive, the paint is expected to cost very little.
@Ann: One slight correction -- fly ash is a kind of coal ash, not the other way around. Fly ash means the light particles which are carried up with the flue gas; the heavy particles which don't float up are called bottom ash.
Fly ash contains very small quantities (less than 0.05%) of a number of harmful metals such as lead and cadmium. Given the small concentrations of these metals and the relatively small quantity of fly ash which is likely to be used in these coatings, I suspect that the chance of any significant environmental exposure from these coatings would be extremely low.
Of course, when you're talking about billions of gallons of coal ash in an impoundment, it's a different story. That's why I think it's unfortunate that EPA suspended its coal ash reuse program after the Kingston disaster. In my opinion, reuse helps prevent disasters by keeping coal ash out of impoundments and putting it into useful products.
Thanks for that observation, Chuck. Remote inspection/assessment/measurement/monitoring has been growing for some time in several areas. I thought it was kind of cool that this principle and the technologies are being applied to things like bridge inspection. It's interesting to find out that this smart paint isn't the only avenue of investigation.
I hadn't heard of fly ash before reporting this story. I think here the fly ash is being used to provide dimensionality (if that's the right word), bulk and strength to the paint: it seems to be the solid in the mix. That's interesting that coal ash, which is apparently one kind of ash classified as fly ash, is a waste product that needs a home, so to speak, although it sounds like it's also a possible polluting agent. I wonder if the fly ash becomes relatively harmless when it's mixed into the paint in the story? Or does repeated rain, and the effect of other elements slowly destroy the paint, releasing the pollutant into the atmosphere and ecosystem?
It's even more interesting that fly ash is being investigated for use in composites--thanks for that info, Dave, and all the links. And wouldn't it be cool if we could figure out how to re-use all kinds of industrial wastes.
This touches on what must be the fastest-growing, most innovative technical area in structural mechanics. For decades, bridges, buildings and other structures have been checked by inspectors. Lately, we've been seeing more remote monitoring and use of energy harvesting. And now here we have smart paint. And beyond that, the article mentions conductivity maps that can be used to create finite element models.
We often talk about how electronics is changing the consumer market, but we forget how civil engineering is being changed, too.
It's interesting to read about yet another beneficial reuse for fly ash. It sounds like the fly ash is being used to give strength to the coating, while the sensing strategy uses carbon nanotubes.
Believe it or not, there is actually a biannual conference called World of Coal Ash, which is all about (you guessed it) coal ash. Electric power generation produces so much coal ash that finding uses for it is a serious research topic.
The Kingston Fossil Plant disaster in 2008 -- in which over a billion gallons of coal ash slurry were spilled in Tennessee, destroying several homes and possibly contaminating local water supplies -- put a damper (deserved or not) on enthusiasm about beneficial reuse of coal ash. In response to the accident, the EPA suspended its Coal Combustion Products Partnership program, which up until that time had been a successful partnership with industry to investigate new uses for coal ash.
In fact, many people involved in beneficial reuse of foundry sand (where EPA also has had a successful industry partnership) were concerned that the accident would cast a shadow on all efforts to reuse industrial materials, even those which have nothing to do with coal. In 2009, EPA and USDA completed a draft risk assessment which essentially gave the green light to many kinds of foundry sand reuse, but the assessment has never been finalized -- possibly due to jitters from the Kingston disaster. In spite of this, industry efforts to reuse foundry sand seem to be moving forward.
Beth, the sensor itself should be quite inexpensive. In addition, sensor networks using the Zigbee standard can be quite inexpensive, low power and are self organizing.
This seems pretty cool. So by using this paint or coating on the structure, you get protection from the elements as well as a built-in way to detect structural problems and monitor integrity? While the paint/nanotechnology element is compelling and seemingly pretty cost-effective, what about the sensor and wireless infrastructure that has to be set up and maintained in order to monitor the feedback--is that pricey enough to take some of the utility out of this approach?
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