A concrete parking lot. Credit: Phil Roeder / Flickr Creative Commons
Making concrete is kind of like baking a cake. An giant, inedible, and extremely wasteful cake. Cement is the egg that binds everything together.
Franz-Josef Ulm, who directs MIT's Concrete Sustainability Hub, helps make that concrete cake. Now, when you think of concrete, you might imagine bulky industrial equipment...but Ulm uses a Kitchen Aid stand mixer. Exactly the kind you'd use for baking. Ulm's laboratory whips up small batches of experimental concrete in the hopes of creating a less wasteful concoction.
Ulm is part of a growing consensus among scientists and businesspeople who agree: It's time to build better concrete. Humans use a LOT of it. In fact, there is only one thing we consume more of—and that's water.
"What you're talking about in terms of total concrete laid down each year...it would be on the order of 2 tons for every man woman and child on the planet, laid down every year,” says Robert Courland, whose book Concrete Planet traces concrete's history from ancient Rome until today. He points out that Roman buildings lasted millennia. Today's industry standard—steel-reinforced concrete—crumbles after just 50 years.
Roman bridges are even supporting the weight of trucks and cars... and they were built 2000 years ago.
That's the visible waste. But there's even more invisible waste. Concrete—in our sidewalks and foundations and cinder blocks—produces a whopping 5 percent of global carbon dioxide emissions. Most of that comes from the cement that binds concrete together. Ulm puts it in perspective:
"Roughly each ton of cement which is produced amounts to one ton of CO2 released in the atmosphere.Now this is roughly the same amount of CO2 which is released by us breathing. It is quite substantial."
Two steps in the process are wasteful: Cement production takes place at 1000 degrees Fahrenheit, which means burning fossil fuels. And cement is made from limestone, which releases emissions during processing.
Ulm's MIT lab—which is partly funded by cement companies--aims to make concrete stronger, so we can use less of it. Before turning on the Kitchen Aid mixer, he and his colleagues use computer programs to experiment with cement's microscopic structure.
When they find a material that looks promising, they mix a batch. The samples are tiny half-inch squares that get tested for durability, using a knife to scratch just a bit of the surface. Scratches help Ulm's colleagues estimate the strength of each concrete sample. Their best result so far is twice as strong as standard Portland cement – the kind you usually see lining your sidewalks.
There are other strategies for making environmentally friendly cement. While Ulm refines existing concrete, some companies incorporate recycled materials to reduce waste. An architect named Ginger Dosier has taken an entirely different approach… inspired by her childhood hoarding of seashells.
Making concrete normally requires heating and processing. But 10 years ago Dosier started to wonder: If crabs and clams can make durable shells with biology alone, why can't humans borrow their approach?
"We heat, and we beat, and we treat materials to be able to construct with them. Quite a bit of energy goes into just making a product. Why can't we just try to grow it?"
So she founded a company: BioMason, which makes building materials at room temperature. They start by filling a mold with sand, nutrients, calcium, and special bacteria. As the bacteria consume the nutrients, the pH rises, which crystallizes the calcium into a form of cement. According to Dosier, it's "almost like if you were watering a plant."
After two days, you've got a brick—without needing huge kilns or cement mixing trucks. Fresh techniques like this could help us break out of the mold of old-fashioned concrete.
With all these ways to bake a better cake, the question is: Why did it take us so long to see concrete as a polluter? For one, concrete isn't glamorous, it's mundane. Corporations don't have big incentives to innovate, because they already make big profits on existing concrete. And a related problem: Cheap materials win out in construction projects. Courland thinks regulations should change this:
"When you go outside and look around, most of the buildings you see were done by the lowest bidder. And so until you level the playing field by saying you all have to use this and that, it's going to continue."
We probably won't find a replacement for concrete anytime soon, at least in Ulm's opinion. He believes that "concrete is the backbone material of our society for shelter, for infrastructure, for hospitals for schools etc etc. and as such, we cannot replace this material in the foreseeable future."
But small innovations will add up, precisely because humans gobble up so much concrete. Little improvements are multiplied by the trillions of tons we consume each year.
If we make concrete right, our great grandchildren could walk on the same sidewalks and inhabit the same buildings as we do. If we make it wrong, we'll go on rebuilding our built environment every half century.
Courland views concrete as a indelible part of the world humanity has created:
"If people were to vanish tomorrow, like world without people, our existence would be delineated hundreds of millions of years in the future by a crushed stone layer tinted red by iron oxide. And this layer would be the remains of steel reinforced concrete. There's that much of it."
Concrete is a legacy of the human race. It will take some serious changes to ensure that legacy doesn't crumble into dust.
Funding for Innovation Hub's environmental and sustainability reporting is provided by The Kendeda Fund: furthering the values that contribute to a healthy planet.