Scientists have designed a “skin” that senses when concrete structures are damaged

Image: Bittbox via Flickr, reproduced under creative commons.

Concrete is pretty great, isn’t it? It’s strong, it’s cheap, it’s easy to use. Let’s hear it for concrete!

On the downside, though, it’s also prone to cracking – if there are swift changes in temperature, for example, or if it’s bearing too much weight. Cracks in concrete structure are annoying at the best of times, but if said structure is holding, say, nuclear waste, they can also be disastrous.

So a team of scientists from North Carolina State University and the University of Eastern Finland have developed plans for a “skin” that would flag up cracks or damage to the concrete’s surface. Their idea involves installing electrodes at the edges of a structure, then applying electrically conductive copper paint across the concrete. The electrodes would emit a constant, low-level current across the surface of the painted “skin”, monitored by a computer. If the surface was weakened, cracked or damaged, the paint would become less conductive, and the computer would sense a change in the signal. You can even analyse the data to produce a map of the damage.

Here’s a cracked piece of concrete, alongside a computer rendering of the damage:

Image: Aku Seppänen.

So far, the researchers have only tried the method out on small, 1m long pieces of concrete, but they’re hoping to test on bigger areas. Dr Mohammad Pour Ghaz, one of the paper’s co-authors, said the team were keen to show the method could work on “real-world structures”.

 
 
 
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Glowing roads, Halloween pop-ups and London's national park

The business of Halloween. Image: Turnkey Events.

Some of the city stories we enjoyed elsewhere this week.

  • Designer Dan Roosegaarde, of glowing tree streetlights fame, has used glow-in-the-dark paint on a stretch of highway in the Netherlands to create road markings. Unlike cats' eyes, the markings don't rely on reflecting light, making them safer for cyclists and easier to follow for cars. Once the markings have been tested in the Netherlands, they may be rolled out in other countries, including the UK. 

This video shows them in action:

  • This piece at How We Get To Next, the site accompanying the science and futurism TV series of the same name, follows the attempt of one Londoner to turn the city into a National Park. This may sound bonkers, but Daniel Raven-Ellison argues that London is actually one of the greenest urban areas in the world, and should be recognised as such. Here's one of his promotional graphics, which shows London's land categorised by use:

Raven-Ellison told the site: 

There’s a sense that somehow the wild has to be pristine to be valued. But if you’re an individual flower, or pigeon or fox, you’re no less wild. There are just fewer of you, and you’ve learned to be in a city better than maybe other things. But that doesn’t make you any less valuable.

  • CityLab has taken an unusually economics-based approach to their Halloween coverage in the form of this piece on Halloween pop-up stores. The stores, which appear one day in August stuffed with masks and capes, then disappear just as suddenly on 1 November, have suffered as the economy's improved and as rents have inched upwards. To save on overheads, some now operate from giant tents in shopping centre car parks:

That Halloween pumpkin tent might look silly. (I would say "delightful.") But more of them could be a telltale heart—no, sign—of a slow but steady economic rebound. And what could be less scary than a robust national retail sector?

  • And finally, forget skeletons and pumpkins - it's  UN World Cities Day. The Guardian is marking the major international holiday by hosting 12 minute pitches of city ideas from all over the world. Meanwhile, we're mostly unwrapping gritty urban gifts and cracking open the port. 
 
 
 
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