Can Paving America be Eco-Friendly?

Given that Obama's economic stimulus package is likely to include billions of dollars in road projects, how will he counteract the environmental toll? One idea, supported by the steel industry, is to funnel more of that money into rail, such as the $45-billion high-speed train between Los Angeles and San Francisco that was approved by the state's voters in November.

Another idea is to build those roads greener. Two new cement companies, one in Great Britain, another in Silicon Valley, claim to have discovered a new way to produce cement that not only emits no carbon dioxide, but also sucks much of it from the atmosphere.

This is no small feat. Cement production accounts for 5 percent of the world's CO2 emissions--more than the entire aviation industry. And a recent report by the French Bank Credit Agricole estimated that demand for cement will increase 50 percent by 2020.

The Silicon Valley company, Calera Corp, was founded by Stanford professor Brent Constanz, who in 1986 invented a medical cement that revolutionized the way hospitals repaired broken bones. Unlike conventional cement, which is made by heating up limestone or clay to around 1500 degrees C, his medical cement combined carbon dioxide and magnesium to mimic the way coral reefs are formed. His new eco-cement works much the same way, except the carbon dioxide comes from power plants that would otherwise spew it into the atmosphere. The British company, Novacem, uses a similar process.

Both companies claim their products are strong enough to work in roads, buildings, and bridges and are cost-competitive with conventional cement. The hard part will be to convince customers that the cements will endure the test of time when there's no real track record. Of course, using conventional cement will also be a gamble--in the form of some 450 million tons of yearly carbon emissions.