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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Urban leopards, moving islands and America's largest homeless camp

Christmas Island: future location tbc. Image: NASA.

Our round-up of city stories we enjoyed elsewhere this week. 

  • OK, we know we never shut up about devolving powers to UK cities, but it’s always interesting to see the issue from a different perspective. This week, American urbanist Richard Florida summed up the issue as he sees it for Citylab. And, it seems, we’re doing pretty well in the context of other world cities:

The notion that national governments have become inert and dysfunctional while cities power the global economy has become a bit of a mantra among urbanists… Yet for all the talk, even the largest cities and most powerful urban leaders in the United States and around the world remain highly dependent upon higher levels of government.

But in the United Kingdom, at least, the scales may finally be tipping in favor of cities. Spurred on by the ill-fated Scottish independence movement, Labour Party leaders in [other cities] began agitating for greater powers… In early November, 10 regional councils decided to allow Greater Manchester to elect its first metro mayor, who will oversee the area's transportation, social welfare, housing and police budgets.

It all sounds quite exciting when you put it like that, doesn’t it?

  • The bad news: climate change and rising sea levels will have the most serious effects on small islands. The good news: rather than sinking, some smaller islands made of sand and gravel may rise with water levels, with some sediment joining other islands and the rest forming higher elevations on the original island.

Adele Peters at Fast Company magazine reports that some islanders are calmly developing plans and new types of housing to prepare for this terrifying prospect:

It's possible that if development on Kiribati [islands] radically shifted to a more mobile design, people could move as the islands evolve. A more distributed population could also help. The dense population in places like South Tarawa strains current resources like limited water supplies. Groundwater is threatened by rising sea levels—but also by pollution and mismanagement.

  • This piece and video from the National Journal  tells the story of America's largest homeless camp, just outside San Jose, California. It's populated by those who made their fortunes as Silicon Valley boomed - in construction or electronics, for example - but lost their jobs in the dotcom boom in 2000. Rents in Silicon Valley are now some of the highest in the country, and the result is this enormous camp of the homeless and often unemployed, known as "The Jungle".

Helpfully, the city's planning to bulldoze the camp in December (as it has done many times in the past). Officials say they'll subsidise the residents' rents in accomodation nearby, but only for a year or two; making it likely the camp will pop up again soon.

 

  • And finally, this month, the Guardian’s Cities section has been hanging around Mumbai, reporting on the city and how it works. This fascinating piece traces the history of Mumbai’s 21 leopards, who live in a national park which is also home to 250,000 people:

The presence of leopards living alongside humans is a case of two highly adaptable species sharing space, says Athreya, who calls the animals “living ghosts” for their ability to be elusive.

The very idea that the leopard shouldn’t live near humans is a completely urban construct, she says. “If you got to rural India, people know leopards have always been around. Theadivasis [ethnic and tribal groups of India] have always lived with them and see the animal as part of their cultural identity.”

Call us cowards, but we still wouldn’t be keen. 

 
 
 
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