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.
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?
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.
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.
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.
@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 the correction. The article I read for background was badly written and implied the opposite relationship. I'm glad to know that fly ash is relatively harmless, which was implied in the source materials for the smart paint story. I agree with you about reuse, and that's one of the reasons I like writing about recycling plastics into bridge materials, for instance. Sounds like a major problem is how to store fly ash in huge quantities without harm to the environment.
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.
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.
Tom, that's very interesting, that a similar concept has been used on brake springs. What exactly is similar? Do you mean a similar principle or method of fault detection, including remote wireless detection, or mixing with fly ash, or all of the above? Please let us know.
I know what you mean--when I first read about this paint's wireless monitoring and sensors, I thought, huh? But it is designed for applications where it's tough and/or expensive to send a human.
I think I've heard of the paint you describe, which clearly requires onsite inspection, something that makes more sense for brakes than for bridges.
I sure hope that paint stays put; iit's hell on auto paint and wafts for many miles. As every coal-fired power plant or factory can attest, the lawsuits and/or scrubbers are quite expensive.
As Dave Palmer pointed out below, lots of people in the US are nervous about fly ash/coal ash after the Kingston disaster. But the research in my story here is being done in Scotland. That's interesting because my impression is that Europeans are both more environmentally conscientious and either equally or more willing, or perhaps able, to do some of this alternative materials research. It would be interesting to find out if Europeans, or at least people in the UK, are similarly concerned about fly ash getting loose. The source materials implied that it would be a good thing to find a use for this waste substance, and that the mixed paint is like cement, making it useful in harsh environments. That implies that it's not likely to break down quickly.
Thanks, but those are two different concerns; ground/water pollution vs. ruining car paint, metal roofing, etc. from fly ash drifting on the winds. TVA, DuPont, etc. have had their disasters (often unpublicized by communities afraid to lose jobs).
You're certainly right that those are two different types of disasters, but my point was the more general one that the US problems have put a damper on research associated with reuse of this industrial waste. Versus wondering how the situation might be different in Scotland, the UK, and/or Europe. I'd sure like to know if any of our readers knows the answer to that question.
Nice article, Ann. Interesting that this involves self-charging batteries. We're seeing this on more and more remote sensors. they don't need powerful supply sources. So, any ambient disturbance -- cars driving down the freeway -- is sufficient to recharge. Pretty cool for hard-to-get-to sensors.
Rob, self-charging batteries on remote sensors makes a lot of sense, thanks for the input. I think what we're also seeing in this case, as well as the ones you describe, is more attention being paid to designing total systems that are simpler and more self-sustaining. Totally cool! And green without any "washing."
Yes, I was very surprised to learn that batteries could be charged by slight ambient vibration -- such as a truck going by on a nearby freeway, or cars traveling over a bridge. I would imagine this is possible in part because the sensors require very little energy.
I know next to nothing about how these self-charging batteries work, or what the actual energy harvesting techniques involve. I'd love to know more. It sounds like yet more sci-fi comes true.
I first learned about them while doing a story on remote sensors. Self-charging batteries are also being developed for medical applications for devices that are put into people's bodies. Those are chaged based on the temperature difference between the human body and the world outside.
Thanks, Rob. I have heard about the ones that work by harvesting energy from body movement and/or heat. Somehow that seems easier to immediately grasp than the ones that get charged by ambient vibrations. This article made the ambient vibrations method clear: it's piezoelectric, which makes total sense, and I should have guessed that. On top of my wood stove is a piezoelectric fan that creates electricity from the stove's heat and redistributes that heat faster throughout the room. The efficiency increase actually saves me a bit on firewood.
That makes sense, using it on the stove, Ann. Is that your sole source of heat? If so, does the fan distribute throughout the house or just the room with the stove?
The fan is designed specifically for woodstoves. There are a few different brands, but they seem to be practically identical. They all come in two sizes and I have the "large" size. The fan is designed only to distribute the heat in one room; it's not powerful enough for more than that. Most heat sources aren't, except for whole-house forced air furnace systems. I've always thought those were unnecessarily and ridiculously complex and expensive.
The woodstove is our major source of heat. It's unhelpfully located at one end of the (smallish) house's long axis (and not relocatable without great hassle and expense), so two small ceiling fans distribute the heat farther. But the farthest rooms tend to get cold in winter. About half way from the stove is a forced air propane wall heater for backup, but I rarely use it except on winter mornings before the woodstove cranks up. I hear that Vermonters adhere to the same principal as Scots and Brits: "put on a sweater!" Sounds like us here at my house.
Thanks for the links, Chuck. I see you were writing about this back in 2009. One interesting aspect is that some of this is made possible because of lower power needs from sensors and other devices. So the advances is not just greater ability to harvest energy, but also that not as much energy is required.
Chuck, thanks for the links and info on this form of energy harvesting. It's also interesting to hear that bridges are already being built with wireless sensor networks for detecting structural problems. This research was done in Scotland, though, and the study makes it sound like they don't have those installed there for remote fault detection.
This smart paint can be of great use in SHM ( Structural Health Monitoring) systems that can be implemented on aircrafts and other aerospcae structures. Smart paint with the WSN ( wireless Sensor Network ) can improve the maintenance operation and will be a boon to the aircraft industry
vimalkumarp, that's an interesting observation. It may be possible to adapt this paint to detection of cracks in aircraft. However, I'd guess that it's a different problem set with a different solution. That's seems to be true in the case of composite fault detection as I've reported on here:
yes i agree with you that it is a different set. But i was just trying to explore the possibilities of this smart paint in SHM applications, Thanks for the clear analysis and inputs
I'm with you--I like finding out about technologies that can be used for other applications. In this case, what I've learned about aerospace composites, specifically carbon fiber types, makes me hesitate to think this one can be applied to them, since fault detection seems so different with them.
Ann, do you know if this paint is currently being used on any bridges in the US? I can't remember the stats or which bridge, when the US last bridge collapsed a report indicated there were a lot of bridges that needed repair. This type of paint even if it is just in a testing phase would serve a good purpose. I would be most interested in the any report that would be created from data collected at the various test sites.
gsmith, this paint was developed in the UK, not the US, and when I reported this it was in a prototype stage, so I doubt if it's being used here. However, some of the comments in the message board below list a few articles by Charles Murray on various US attempts at detecting faults in similar structures using wireless sensor networks.
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