Published: September 07, 2008 03:49 pm      

Bone-cement inventor widens his scope to benefit all

Says he has invented a green cement that could eliminate huge amounts of carbon dioxide

Palo Alto, Calf — Back when Stanford Professor Brent Constantz was 27 he created a high-tech cement that revolutionized bone fracture repair in hospitals worldwide. People who might have died from the complications of breaking their hips lived. Fractured wrists became good as new.

Now, 22 years later, he wants to repair the world.

Constantz says he has invented a green cement that could eliminate the huge amounts of carbon dioxide spewed into the atmosphere by the manufacturers of the everyday cement used in concrete for buildings, roadways and bridges.

His vision of eliminating a large source of the world's greenhouse CO2 has gained traction with both investors and environmentalists.

Already, venture capitalist Vinod Khosla is backing Constantz's company, the Calera Corp., which has a pilot factory in Moss Landing, Calif. churning out cement in small batches.

And Carl Pope, executive director of the Sierra Club, says it could be "a game changer" if Constantz can do it quickly, on a big scale and at a decent price.

"It changes the nature of the fight against global warming," said Pope, who has talked with Constantz about his work.

That might sound like hyperbole, but the reality is that for every ton of ordinary cement, known as Portland cement, a ton of air-polluting carbon dioxide is released during production. Worldwide, 2.5 billion tons of cement are manufactured each year, creating about 5 percent of the Earth's CO2 emissions.

When Constantz learned about the high CO2 levels, he thought he could do better. After all, the majority of his 60 patents have to do with medical cement.

He claims his new approach not only generates zero CO2 but has an added benefit of reducing the amount of CO2 power plants emit by sequestering it inside the cement.

To make traditional cement, limestone is heated to more than 1,000 degrees Celsius, which turns it into lime -- the principal ingredient in Portland cement -- and CO2, which is released into the air.

Constantz uses a different approach, the details of which remain secret pending publication of his patent.

At his pilot factory, a former magnesium hydroxide facility that made metal for World War II bombs, magnesium crunches underfoot as Constantz outlines how the process works.

He pointed to two enormous smokestacks billowing flue gases full of carbon dioxide next door at Dynegy, one of the West's biggest and cleanest power plants.

Constantz takes that exhaust gas and bubbles it through seawater pumped from across the highway. The chemical process creates the key ingredient for his green cement and allows him to sequester a half ton of carbon dioxide from the smokestacks in every ton of cement he makes.

Constantz says his cement would tackle global warming on two fronts: eliminating the need to heat limestone (which releases CO2) and siphoning away harmful emissions from power plants to lock them into the cement.

The same process can also be used to make an alternative to aggregate -- the sand and gravel -- that makes up concrete and asphalt, which would sequester even more carbon dioxide from power plants.

Constantz estimates his cement would retail for $100 a ton versus roughly $110 for Portland.

Portland cement has a track record of more than 100 years, and any new material would have to get incorporated into building codes, noted Rick Bohan, director of construction and manufacturing technology for the Portland Cement Association in Skokie, Ill.

And Tom Pyle, a Caltrans engineer who serves on the cement subgroup of Gov. Arnold Schwarzenegger's Climate Action Team, acknowledged that the technology is possible, but he still wants to examine Constantz's cement.

Constantz is confident he will prove himself, first by mixing his cement with the traditional, then easing a conservative industry into a new product. He will speak about Calera cement at their annual World of Concrete in Las Vegas next February.

Constantz envisions building cement factories next to power plants the world over. A team is scouting out U.S. locations. While Dynegy has supplied Constantz with some flue gas, it hasn't entered into a formal agreement. Dynegy spokesman David Byford says his company is "very interested."

It could be good for business. California has mandated emissions reductions. And Congress is working on legislation that would allow high polluters to buy credits from those with low emissions. Power plants would have a huge incentive to sequester their CO2 in cement.

But even if Constantz succeeds, the world would still need to do much more to fight CO2 emissions, said Chris Field, director of the department of global ecology at the Carnegie Institution for Science at Stanford. "It's a big, long complicated game," he said.

Constantz's idea for bone cement began during a televised football game, when he was reading an osteoporosis article in the New England Journal of Medicine. Three weeks later, as he studied a coral reef, it occurred to him he could maybe synthesize coral skeletons in human bones.

His new cement mimics how coral reefs form, too. Coral uses the magnesium and calcium present in seawater to create carbonates much as he's using CO2 and seawater to make carbonate.

This latest invention took 18 months to conceive and execute. He says it's one of the most important things he's ever done.