Low-carbon alkali cement paves the way to energy savings

Happy Drexel researchers at manual labor

The source of 5 percent of global carbon dioxide emissions is hiding in plain sight, in the sidewalk beneath our feet. It is cement, a key ingredient of concrete, the most widely used building material on the planet. And manufacturing conventional “Portland” cement releases nearly a ton of the greenhouse gas for every ton produced – some 3 billion tons in 2010…

Enter Drexel University materials scientists Alexander Moseson and Michel Barsoum. They’ve created a low-tech, low-energy, low-cost cement that they hope to move out of the lab and into the real world.

But they face huge hurdles: Entrenched industry, tough building codes, a mindset that says there’s only one way to lay a foundation or build a bridge – with Portland cement…

The problem with any bid to replace it…is that Portland cement enjoys economies of scale, which keep prices down. Introduced in the 19th century, it’s also familiar: Governments and builders have many decades of “use and comfort” with the product, he said. It is the benchmark for industry codes. “Officials have a duty to give taxpayers the best, most-durable road or bridge or whatever possible,” Steve Kosmatka of the Portland Cement Association said. “There’s risk to trying new things…”

Moseson and Barsoum are…mixing recycled iron slag or fly ash with readily available limestone. “We literally used a bag of garden lime from Home Depot,” Moseson said. Instead of a coal-fired kiln, they use a bucket with a spoon at room temperature…

Tests showed that the Drexel duo’s cement is as durable as Portland but emits 95 percent less CO2. “You’ve found a way to bake bread without the oven,” Moseson said one impressed investor remarked. That energy-saving trick means this cement could cost about 50 percent less to produce, according to their calculations…

But market issues, lack of environmental awareness, inconsistent ingredients, and limited knowledge of cement chemistry have restricted alkali cement to a niche market. The cement industry came up with viable alkali cements 20 years ago but found few customers, Kosmatka said. “It was a product ahead of its time.”

Now, proponents say, the time for more widespread application of alternatives may be right.

Governments in Asia and elsewhere are kick-starting green building industries, opening doors for alkali-activated and other green cements. China’s newest cement standards, for instance, require a 15 percent reduction in energy use. India’s green-building standard takes a life-cycle approach and emphasizes recycling and pollution reduction.

And in the United States…?

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