Seyedmorteza Khatibmasjedi has a conflicted relationship with concrete.

"I was always thinking concrete is the best material in the world," says the University of Miami civil engineering Ph.D student. (He goes by Morteza Khatib.) "All those skyscrapers, all those high bridges -- all of them are made out of concrete."

"We make a kind of soupy material," Khatib says. "After 10 hours... it can hold two cars."

But, he says, "I was working on concrete without paying attention to the environmental impacts."

Concrete's strength and versatility make it a highly desirable building material. Khatib says there's roughly enough manufactured each year for every single person on the planet to get a three-foot-tall cube and still have about a billion cubes left over. Industry analysts routinely describe it as the second- most widely used material in the world, ranking only behind water.

And water is part of concrete's problem.

"It has to be basically the water that people can drink," Khatib says, adding that based on a 2004 Columbia University study, concrete production uses 180 billion gallons of freshwater per year. He says that water could be going to people who are suffering from water shortages.

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The problems with conventional concrete

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The ingredient list for concrete is short: sand, water, cement and coarse aggregate (which is basically rock). Builders like the simplicity of these materials, but collecting and preparing them for concrete can do serious environmental damage.

Superheating limestone to make cement burns fossil fuels and can release pollutants into the air, (although UCLA researchers have figured out a way to make cement production carbon-neutral).

Mining rivers for sand can interfere with freshwater supplies and damage fragile ecosystems.

And then there’s the massive amount of freshwater required for the concrete mixture.

Many concrete structures are constructed around steel rebar, and salt in the concrete could cause the steel to corrode. So the water used in conventional concrete has to be fresh, says Steve Nolan, a structures and designs engineer for the Florida Department of Transportation. He compares rebar corrosion to the rusting that occurs if you leave a paperclip in saltwater.

“What happens to the steel when it corrodes is it expands. Then as it expands, it puts force on the surrounding concrete, tends to crack the concrete,” Nolan says. “That just allows more saltwater to come in and you get this domino effect of accelerated deterioration.”

That’s why builders haven’t historically been able to use seawater when they make concrete. They can’t use recycled concrete because it could be contaminated by seawater or — in some parts of the country — the salt that’s put on roads. And they have to wash sand with freshwater before they can mix it in.

Khatib says each ton of concrete uses 18 gallons of freshwater to make. Columbia University researchers report the concrete industry makes more than 10 billion tons of concrete per year.

So each year, the world uses more than 180 billion gallons of freshwater — enough to fill more than 272,000 Olympic-sized swimming pools — to make concrete. That doesn’t include the freshwater used to wash the sand.

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"The problem is that lab durability and lab aging is not the same as real aging" - Francisco De Caso

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Simultaneously, 783 million people worldwide lack access to clean drinking water, according to the United Nations.

“There is enough water available to meet the world’s growing needs, but not without dramatically changing the way water is used, managed and shared,” staff from the World Water Assessment Programme wrote in a prologue to a 2015 UN report, “Water For A Sustainable World.” “This is where the bulk of the action is required in order to achieve a water-secure world.”

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