Researchers at the MIT say the cement produced by this formula has many advantages. Volcanic ash is widespread around both active and inactive volcanoes, and scientists have yet to find any practical use for it. It has convenient natural properties when it is combined with water and other materials to make a cement-like paste.
"It takes a lot of energy to produce cement because of the high temperatures involved," says Stephanie Chin of MIT's Department of Civil and Environmental Engineering. This is a multi-stage process. "It is the main motivation for seeking alternatives, and volcanic ash is formed under high temperature and pressure."
In exploring the potential of this new additive, Chin led a research team that began looking at existing data on the "implicit energy" of the different industrial processes involved in cement production. This is the total amount of energy used to crush rock, solidify cement, or make concrete. Using this data, the team calculated the overall energy of cement formulations containing different proportions of pozzolan, ranging from 10% to 50%. Then they produce some samples in the laboratory.
The researchers found that replacing 50% of conventional cement with volcanic ash, which has a particle size of 17 microns, reduces the implied energy of the resulting concrete by 16%, although this hinders the overall strength of the material. Reducing the pozzolana particles to a size of around 6 microns greatly increases its strength by creating more surface area for the water and cement to bond together.
They then intend to apply this knowledge to the real world, turning to a community of 13 homes and 14 commercial buildings made of traditional Portland cement in Kuwait. They use drones to fly over the structure, collect images and measurements, and combine with local authority data to calculate the implied energy of the neighbourhood.
Building on their earlier work, the scientists calculated how this implicit energy source could be altered by varying proportions of volcanic ash. They found that 30% was the best ratio they had set, and they thought it would greatly reduce the embodied energy.
"We found that concrete can be made with natural additives that have desirable properties and reduce the embodied energy, which can translate into significant energy savings when you build a community or city," said Oral Buyukozturk, a professor in MIT's Department of Civil and Environmental Engineering. The advantage of this approach is its flexibility. Engineers can adjust the recipe to vary the amount of ash used based on the current mission.
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