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.
In a paper published online in the Journal of Cleaner Production, 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 percent less energy to construct a pilot neighborhood with 26 concrete buildings made with 50 percent 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.
“You can customize this,” says Oral Buyukozturk, a professor in MIT’s Department of Civil and Environmental Engineering (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.”