Building a Better World With Green Cement | Science | Smithsonian
Novacem plans to test its experimental cement (above: sample blocks) first in structures like doghouses and patios. (Alex Masi)

Building a Better World With Green Cement

With an eye on climate change, a British startup creates a new form of the ancient building material

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“You know, cement is everywhere,” Nikolaos Vlasopoulos, an environmental engineer at Imperial College in London, says while sitting in a brightly lit college conference room in a hulking seven-story building held up by the topic of conversation. “It’s all around us.”

Last year, the world produced 3.6 billion tons of cement—the mineral mixture that solidifies into concrete when added to water, sand and other materials—and that amount could increase by a billion tons by 2050. Globally, the only substance people use more of than concrete, in total volume, is water.

Cement’s virtues, Vlasopoulos says, have long been plain: It is inexpensive, pourable and, somewhat inexplicably, becomes hard as a rock. But one other important detail is seldom acknowledged: Cement is dirty. Not dirty as in it won’t come off your clothes—although that problem has dogged construction workers for centuries. The key ingredient is limestone, mostly calcium carbonate, the remains of shelled marine creatures. The recipe for making cement calls for heating the limestone, which requires fossil fuels. And when heated, limestone sends carbon dioxide gas wafting into the atmosphere, where it traps heat, contributing to global warming. Cement production is responsible for 5 percent of the world’s human-produced carbon dioxide emissions; in the United States, only fossil fuel consumption (for transportation, electricity, chemical manufacturing and other uses) and the iron and steel industry release more of the greenhouse gas. And with booming countries such as China and India using cement to construct their rise, cement’s dirtiness looms as one of the foremost downsides of globalization.

If cement’s enormous contribution to air pollution is largely overlooked by the general public, Vlasopoulos, 31, has been aware of it for some time. He grew up in Patras, a Greek port. His father was an engineer and his mother worked in a bank, and during Vlasopoulos’ summers home from Dimokrition Panepistimion Thrakis college, where he studied envi­ronmental engineering, he worked in a cement factory with his uncle. This was fortuitous. His job was to assemble the equipment that measured carbon dioxide emission levels. They were high; typically, a factory produces nearly a ton of carbon dioxide for every ton of cement. Vlasopoulos thought the work was interesting, but he didn’t see cement in his future. It was boring, it was old, it was dirty.

Then, one of his professors at Imperial College, where he was working on a master’s degree in engineering, received funding to examine a new type of cement made by an Australian company. The professor, Christopher Cheeseman, persuaded Vlasopoulos to collaborate on the project and earn a PhD. “This was a chance to do some nice work,” Vlasopoulos said in his typically understated manner.

People have been trying to build a better cement since just about the beginning of history. More than 2,000 years ago, the Romans devised a mixture of lime, volcanic ash and chunks of stone to form concrete, which was used to make harbors, monuments and buildings—the glue of early cities—including the Pantheon and the Colosseum. In the 1820s, in Leeds, England, about 200 miles from Imperial College, a stone mason named Joseph Aspdin invented modern cement. Aspdin heated a concoction of finely ground limestone and clay in his kitchen. After he added water, the mixture hardened. Voilà—the building block of the Industrial Revolution was born. Because the material looked like a popular building stone from the Isle of Portland, Aspdin called his invention Portland cement. The patent, issued in 1824, was for “an improvement in the mode of producing an artificial stone.”

The Australian developers had tried a new recipe, mixing Portland cement with magnesium oxide. They hoped to reduce carbon emissions because magnesium oxide can take the place of some of the limestone, and magnesium oxide does not have to be heated at such a high temperature. Limestone must be heated to 2,600 degrees Fahrenheit, but magnesium oxide can be prepared for cement at 1,300 degrees, a temperature that can be attained with biomass and other fuels that release less carbon, cutting down on fossil fuel consumption.

But Vlasopoulos quickly discovered that the blend did not reduce overall carbon dioxide emissions. In some tests, the emissions nearly doubled, because magnesium oxide itself is produced by heating magnesium carbonates, a process that releases carbon dioxide.

“I remember feeling very disappointed because when you see that the project you’re working on is not actually what you thought it was going to be, you lose motivation,” he said. “But we felt it was a very worthwhile project, a worthwhile idea, so we tried to find another way to solve the problem.”

At the time Vlasopoulos took up the question, in 2004, big cement firms around the world were looking for new ways to make Portland cement more environmentally palatable. The producers added steel byproducts, such as slag; coal residues, such as fly ash; and other materials, such as magnesium oxide, to bulk up the cement mixture, requiring less Portland cement. They experimented with mineral additives to reduce the temperatures needed to prepare the materials.


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