Cities can be built with volcanic ash

Cities can be built with volcanic ash

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The researchers report that, by replacing a certain percentage of traditional cement with volcanic ash, they can reduce a concrete structure's embodied energy, or 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

MIT engineers working with scientists in Kuwait have found that volcanic rocks, when pulverized into a fine ash, can be used as a sustainable additive in concrete structures. The researchers report that, by replacing a certain percentage of traditional cement with volcanic ash, they can reduce a concrete structure’s embodied energy or the total energy that goes into making concrete. According to their calculations, it takes 16 per cent less energy to construct a pilot neighborhood 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 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 resulting structure’s embodied energy. 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. They say engineers can use this relationship as a blueprint of sorts to help them choose, for instance, the percent of cement they would want to replace with volcanic ash to produce a given structure.

Volcanic ash has several sustainable advantages as an additive in manufacturing concrete: 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, ôpozzolonicö 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.

According to the researchers, replacing 50 percent of traditional cement with volcanic ash with an average particle size of 17 micrometers can bring down concrete’s embodied energy by 16 per cent. However, at this particle size, volcanic ash can compromise concrete’s overall strength. Grinding the ash down to a particle size of about 6 micrometers significantly increases concrete’s strength, as smaller particles provide more surface area with which water and cement can chemically bind.

(Source: MIT News)