Materials research conducted at MIT, Kuwait Institute for Scientific Research and Kuwait University indicates that communities with abundant volcanic ash supplies can use this rocky resource to replace some of the Portland cement used in manufacturing concrete. Such use can reduce the embodied energy of concrete structures.
The energy costs of concrete begin with 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. Environmental impacts are also incurred, as Portland cement production accounts for about five percent of global carbon dioxide emissions.
Volcanic ash offers several sustainable advantages as an additive in manufacturing concrete. It is naturally available and some forms have pozzolonic properties - in powder form, the ash with a reduced amount of cement can naturally bind with water and other materials to form cement-like pastes.
The researchers manufactured small samples of concrete in the laboratory with volcanic ash percentages of 10-50 percent. Standard strength tests were applied to these materials and to samples made only of Portland cement.
In weighing each sample’s strength against its calculated embodied energy, they observed that 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 percent. However, at this particle size, volcanic ash can compromise concrete’s overall strength. Grinding the ash down to a particle size of about six micrometers significantly increases concrete’s strength, as smaller particles provide more surface area with which water and cement can chemically bind.
Next the researchers examined how structures made partly with volcanic ash would affect concrete’s embodied energy at the scale of entire buildings and neighborhoods. They analyzed images from drone surveys of a Kuwaiti neighborhood with 13 residential and 13 commercial buildings, all made with traditional Portland cement, as well as data provided by local authorities.
The conclusion is in accord with laboratory results: a neighborhood’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 percent volcanic ash.