A surprising contributor to climate change: concrete
What’s the material of the future? Titanium? Silicon? Maybe some rare metal used in electronics? Those materials will no doubt play increasingly larger roles in our lives. But arguably, the most important substance in the development of civilization has been — and will continue to be — concrete.
Take China, for example. It has poured more concrete in the past six years than America poured in the past 300.
Making concrete takes a ton of energy. As much as 10 percent of global CO2 emissions come from the production of concrete. So scientists and engineers are looking to reduce its environmental impact.
It’s really just one ingredient that’s responsible for its high carbon emissions: cement.
“The cement is just the glue that holds the other elements together,” says Robert Courland, the author of “Concrete Planet.” To make cement, limestone and a few other ingredients are put into a big kiln, and the temperature is fired up to about 2,700 degrees Fahrenheit, which produces lots of CO2.
“It’s been estimated, that producing one ton of cement generates one ton of CO2,” Courland says. “Since we are producing around 4 billion tons of concrete cement per year worldwide, that’s very, very troubling.”
Concrete is the most common man-made material on earth. So if its CO2 emissions could be reduced by even a tiny fraction, the environmental impact would be huge. A group of scientists at MIT announced in a recent paper they’ve found a way to reduce CO2 emissions of cement by more than half.
“We have developed a set of experiments measuring the mechanical properties at the sub-micron or big-nano level,” says Roland Pellenq, one of the authors.
His cement research is like a Russian doll, Pellenq says, the kind where a tiny doll rests inside a larger doll which rests inside a larger doll, etc. Pellenq and his colleagues study the properties of cement at the atomic level — the smallest possible doll. They do atomic-simulations, basically experimenting with different ratios of the elements in cement. Then they scale up those simulations until they have a new recipe.
This idea came from scientists at Corning who used a similar approach to invent Gorilla Glass — the super tough, scratch resistant glass often used for screens on smartphones.
“So here we tried to do the same approach for cement,” says Mathieu Bauchy, who also worked on the MIT paper.
Bauchy recently moved from Cambridge to Los Angeles to work at UCLA. In a basement lab below his office, engineers and chemists use Bauchy’s atomic-scale simulations to make concrete cubes that they measure, weigh and smash.
UCLA student Gabe Falzoni takes a gray cube of concrete, about the size of a Rubik’s Cube, and puts it in a cage. He lowers a metal cylinder on top of the cube and slowly ratchets up the pressure. When a cube breaks, it can be so loud that it jars the people in the office on the other side of the wall.
The display on the machine shows the pressure in kilonewtons. It climbs steadily 20kN…40kN…70kN…90kN…100kN… brace myself waiting for a violent explosion. And then, the cube crumbles sadly and quietly, like an Egyptian pyramid deteriorating slowly over hundreds of years.
“That happens sometimes,” says Falzoni, removing the shattered bits of concrete from the cage.
The final number: 121 kN, about seventeen and a half pounds per square inch. I ask Falzoni if he would drive on a bridge that strong. “If it was designed right,” he answers.
The goal of these experiments is two-fold: to develop cement that uses less limestone, which is the easiest way to cut concrete emissions, and to create stronger concrete. Stronger concrete means builders could use less of it — also cutting CO2 emissions.
But for builders to use concrete developed by this lab, it has to have another very important quality. It has to be cheap.
“That’s really the key,” Bauchy says. “You cannot expect the industry to change to a greener material if this greener material is not the same price, or cheaper than original material.”
The only way to make new concrete competitive is to take into account the cost of the CO2 released and charge a carbon tax on it, Bauchy says, or government could mandate the use of greener materials. Those policies would be politically difficult to enact. Greener concrete is not high on the priority list of voters, especially in developing nations where progress is often measured by the amount of freshly poured concrete.
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