Cities of the future could be constructed from volcanic ash

Concrete is the most abundantly used material in the world, second only to water, but the energy needed to make it creates a significant environmental footprint.

Now, MIT engineers have discovered they can make stronger structures using less energy by adding volcanic ash to traditional cement.

According to the engineers’ calculations, it would take 16% less energy to construct a neighbourhood with 26 concrete buildings made using 50% volcanic ash, compared with the energy it takes to make the same structures entirely of traditional Portland cement.

“Cement production takes a lot of energy because there are high temperatures involved, and it’s a multistage process,” said Stephanie ChinChin of MIT’s Department of Civil and Environmental Engineering (CEE).

“That’s the main motivation for trying to find an alternative. Volcanic ash forms under high heat and high pressure, and nature kind of does all those chemical reactions for us.”

Constructing structures, at least in part, from volcanic ash has several advantages.

The rocky material, which lies in ample supply around active and inactive volcanoes around the world, is naturally available; it is typically considered a waste material, as people typically do not use it for any widespread purpose; some volcanic ashes have intrinsic, “pozzolonic” properties, meaning that, in powder form, the ash with a reduced amount of cement can naturally bind with water and other materials to form cement-like pastes.

Image courtesy of MIT

MIT engineers tested various ratios of concrete to volcanic ash and came to the conclusion that the correct ratio is dependent on the structure being built.

“You can customize this,” says Oral Buyukozturk, professor in MIT’s Department of CEE.

“If it is for a traffic block, for example, where you may not need as much strength as, say, for a high-rise building. So you could produce those things with much less energy. That is huge if you think of the amount of concrete that’s used over the world.”

The engineers found a mixture of finer volcanic ash and Portland cement produced stronger concrete structures, compared with those made from cement alone.

However, the process of grinding volcanic ash down to such fine particles requires energy, which in turn increases the energy that goes into making concrete, also known as the “embodied energy”.

Experiments in the lab revealed a neighbourhood’s infrastructure can be made with considerably less energy if the same buildings are built with concrete made from a cement mixture that is 30% volcanic ash.

“What we’ve found out is that concrete can be manufactured with natural additives with desired properties, and reduced embodied energy, which can be translated into significant energy savings when you are creating a neighbourhood or a city,” Buyukozturk says.

Semiconductor breakthrough paves way for “inexpensive and nearly invisible” solar panels

Scientists have achieved a breakthrough in organic solar panel technology that could allow the power source to become a ubiquitous presence in our lives, with the ability to be churned out cheaply by manufacturers and laminated to almost any surface you can think of.

Organic solar cells, while far cheaper than the more widespread inorganic equivalents that are most commonly seen in stores and rooftops today, have traditionally had very poor conductivity, meaning they can only generate small amounts of power.

However, engineers at the University of Michigan have changed that, by developing a way to make the electrons found in organic solar cells’ semiconductors travel far further, greatly improving their conductivity and thus their ability to generate power.

As a result, the breakthrough could make organic solar cells a viable alternative to inorganics for the first time, with the added benefit that they are far cheaper to manufacture, meaning they could see far more widespread use than is currently the case.

The research, which was published today in Nature, initially began as an experiment by Stephen Forrest, the Peter A. Franken Distinguished University Professor of Engineering and Paul G. Goebel Professor of Engineering at the University of Michigan, into organic solar architecture using a technique called vacuum thermal evaporation.

This involved Forrest and his team applying a thin film made up of 60 carbon atoms – known as a fullerene layer – over an organic cell’s power-producing later, where the sun’s photons displace electrons from their associated molecules, forming the basis of the power supply. On top of this they added another film of carbon atoms, which was designed to keep the electrons from escaping.

But this action produced a rather unexpected result. Instead of behaving as predicted, the electrons were moving at random through the material, even beyond the confines of the power-generating area, something that had never been observed in organic cells before.

This became the focus of their research, and after months of work they determined the cause: the layer of electrons was creating an area of low energy known as an energy well where negatively charged electrons could not recombine with the power-producing layer, and so moved far further than was normally the case.

“You can imagine an energy well as sort of a canyon–electrons fall into it and can’t get back out,” said Caleb Cobourn, a graduate researcher in the University of Michigan Department of Physics and an author on the study. “So they continue to move freely in the fullerene layer instead of recombining in the power-producing layer, as they normally would. It’s like a massive antenna that can collect an electron charge from anywhere in the device.”

said Quinn Burlingame, an electrical engineering and computer science graduate researcher and author on the study, with the original experiment. Image courtesy of Robert Coelius/Michigan Engineering, Communications & Marketing

While the research is still in the early stages, this breakthrough is hugely significant, and could be used to develop ultra-cheap, near-invisible solar panels in the future.

“This discovery essentially gives us a new knob to turn as we design organic solar cells and other organic semiconductor devices,” said Quinn Burlingame, an electrical engineering and computer science graduate researcher and author on the study. “The possibility of long-range electron transport opens up a lot of new possibilities in device architecture.”

It could even eventually play a vital role in the shift to renewable energy supplies.

“I believe that ubiquitous solar power is the key to powering our constantly warming and increasingly crowded planet, and that means putting solar cells on everyday objects like building facades and windows,” Forrest said. “Technology like this could help us produce power in a way that’s inexpensive and nearly invisible.”