Materials

Cement made with volcanic ash can make cities stronger and greener

Cement made with volcanic ash ...
MIT researchers say volcanic ash has a number of advantages as an ingredient in the cement manufacturing recipe
MIT researchers say volcanic ash has a number of advantages as an ingredient in the cement manufacturing recipe
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MIT researchers say volcanic ash has a number of advantages as an ingredient in the cement manufacturing recipe
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MIT researchers say volcanic ash has a number of advantages as an ingredient in the cement manufacturing recipe

It is one of literal building blocks of modern civilization, and somewhat ironically plays a significant role in one of its largest looming threats. Producing cement is a hugely energy intensive process that accounts for around five percent of global CO2 emissions, so scientists are continually searching for greener ways of doing things. Now a team from MIT has found that pulverizing volcanic ash and adding it to the mix can not only make the process more environmentally friendly, but the resulting structures stronger as well.

Incorporating irradiated plastic bottles and tweaking calcium levels are just a couple of ways MIT researchers have looked to improve on cement production in the past. This time around they have turned to volcanic ash, which they say has a number of advantages as an ingredient in the cement manufacturing recipe. It is widely abundant around both active and inactive volcanoes, we don't currently have any real use for it, and when reduced to powder it has handy natural properties when it comes to binding with water and other materials to create cement-like pastes.

"Cement production takes a lot of energy because there are high temperatures involved, and it's a multistage process," says Stephanie Chin of MIT's Department of Civil and Environmental Engineering (CEE). "That's the main motivation for trying to find an alternative. Volcanic ash forms under high heat and high pressure, and nature kind of does all those chemical reactions for us."

In exploring the potential of this new additive, a team led by Chin and study co-author Kunal Kupwade-Patil began by poring over existing data on what's called the "embodied energy" of different industrial processes associated with the production of cement. This refers to the total energy used to do things like crush rock, cure cement or make concrete.

Using this data, the team calculated the total embodied energy for cement recipes containing different proportions of volcanic ash, ranging from 10 percent to 50. Then they took to the lab to produce some samples.

The researchers found that substituting 50 percent of the traditional cement with volcanic ash ground down to a particle size of 17 micrometers reduced the embodied energy of the resulting concrete by 16 percent, although this hampered the overall strength of the material. Reducing the ash down to a particle size of around six micrometers greatly boosted its strength, by creating more surface area for the water and cement to bind together.

They then looked to apply this knowledge to the real world, turning to a neighborhood in Kuwait consisting of 13 residential and 14 commercial buildings made from traditional Portland cement. They used drones to fly over the structures, collecting images and measurements, and combined that with data from the local authorities to calculate the neighborhood's embodied energy.

Building on their earlier work, the scientists then calculated how that embodied energy could be altered were the structures crafted with different proportions of volcanic ash, something that is widely abundant in the Middle East. Thirty percent was the number they settled on as the optimal amount, which they say would greatly reduce the embodied energy but still provide the necessary strength.

"What we've found out is that concrete can be manufactured with natural additives with desired properties, and reduced embodied energy, which can be translated into significant energy savings when you are creating a neighborhood or a city," says Oral Buyukozturk, a professor in MIT's Department of Civil and Environmental Engineering (CEE).

The beauty of this approach lies in its flexibility. Engineers can fine-tune the recipe, altering the amount of volcanic ash used depending on the task at hand.

"You can customize this," Buyukozturk explains. "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."

The team's research was published in the Journal of Cleaner Production.

Source: MIT

10 comments
Reece Agland
I'm not surprised I am sure I read somewhere, pretty sure on New Atlas that ancient Roman structures have stood the test of time because they incorporated local volcanic ash.
miker100
In other words thay have 'discovered' how the Romans managed to build structures that have stood the test of time. Only took them 2000 years to discover it. I suppose next we will see the 'discovery' that rice in the Great Wall of China made its mortar extra strong.
NitramNangap
The idea that M.I.T. deserves credit for this is odd. The idea of using volcanic ash in concrete is historically very old and today quite common. Many concrete projects in Chile and some in Hawaii have been using ash because the benefits have long been obvious.
CzechsterMarek
Ditto the other comments. This is really old news.
EcoLogical
Sweden just announced they are using Hydrogen (instead of coke/coal) to produce steel. The Hydrogen is made by electrolyzing water using clean, renewable energy. Could Hydrogen be used to produce cement?
Edward Vix
As others have noted, Romans mastered this and made far more durable concrete anyone has done since its relatively recent reinvention (first architectural use 1903 by August Perret).
Don Duncan
Where are the details? How much stronger is the optimal combination? What are the drawbacks? Curing time? Fire resistance? How does one crush the ash to the correct size? Does the size vary depending on the use? Can I use this for a DIY project? How does this compare to Grancrete, which is 5 times stronger than conventional concrete?
Wombat56
@Don Duncan Just doing a search on Google, grancrete looks like it may have been a scam or at least the backers overstated its properties.
MQ
Ditto Roman concrete. Re Portland cement, People focus on the energy taken to manufacture looking only at heating. For CO2 balance, don't forget that the burning (calcination) of limestone to produce quicklime in itself emits a load of CO2. @EcoLogical, iron can also be smelted using electrolysis (like aluminium, but to make steel one has to get the carbon from somewhere (often: coke, produced from coal) not all coal is just burnt for thermal energy.
highlandboy
Fly Ash from burning coal gives 90% less greenhouse gas than ordinary Portland cement at the same strength. There are millions of tonnes of it piled up. The down side is variability in the raw material that needs testing.