Future cities may be built with volcanic ash

Boston

Fine volcanic ash can be used as a sustainable additive in concrete, and significantly reduce the energy spent in building infrastructure, a study has found.

Researchers at Massachusetts Institute of Technology (MIT) in the US found that, by replacing a certain percentage of traditional cement with volcanic ash, they can reduce a concrete structure's "embodied energy"—the total energy that goes into making concrete.

According to their calculations, it takes 16 per cent less energy to construct a pilot neighbourhood with 26 concrete buildings made with 50 per cent volcanic ash, compared with the energy it takes to make the same structures entirely of traditional Portland cement.

When they ground volcanic ash down to increasingly small particle sizes, the researchers found that a mixture of the finer powder and 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 resulting structure's embodied energy, researchers said.

There is, then, a tradeoff between a concrete structure's strength and its embodied energy, when volcanic ash is used.

Based on experiments with various concrete and volcanic ash mixtures, and calculations of the resulting structure's embodied energy, the researchers have mapped out the relationship between strength and embodied energy.

Engineers can use this relationship as a blueprint of sorts to help them choose, for instance, the per cent of cement they would want to replace with volcanic ash to produce a given structure, researchers said.

"If it is for a traffic block, for example, where you may not need as much strength as, say, for a high-rise building," said Oral Buyukozturk, a professor at MIT. "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," Buyukozturk said.

Concrete is the one of the most abundantly used material in the world.

The manufacturing of concrete involves first blasting rocks such as limestone out from quarries, then transporting the rocks to mills, where they are further crushed and treated under high temperature through various processes resulting in the production of cement.

Such energy-intensive processes create a significant environmental footprint; the production of traditional cement accounts for about 5 per cent of the world's carbon dioxide emissions.

Sustainable additives and alternatives to cement could help cut down these emissions.

Volcanic ash has several sustainable advantages as an additive in manufacturing concrete, researchers said.

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. PTI