Asphalt Gets a Hot, Green Makeover

Green road-construction methods got the star treatment at this year's Transportation Research Board conference

Cement Truck

iStockPhoto

Just back from the Transportation Research Board conference and meetings (http://www.trb.org/calendar/), Carolyn Whelan, a New York-based freelancer focused on alternative energy, climate change, trade, and travel, guest blogs for PopSci.com, focusing on new fossil-fuel emissions cutting technologies for infrastructure and transport which will (hopefully) play a prominent role in the Obama administration.

As the globe went ga-ga for Obama on the eve of his inauguration, builders and pundits at the recent transportation conference in Washington were angling for a piece of the green stuff Obama's pledged – and some eco street-cred, too.

Making rock-and-tar-like mixes like asphalt gobbles up energy and spews out C02 and other noxious fumes from plant smokestacks. And that's before the rocks and stinky, steamy stuff are trucked from distant quarries and plants to highway- and bridge-building sites. Those oil-hungry processes have made traditional road building both expensive and unpopular among environmentalists.

Enter Obama's economic stimulus package, which promises a big chunk of his up-to-a- trillion economic rescue proposal for 'shovel-ready' projects. He hopes upgrading our aging infrastructure will help engage the country's idled construction workers, engineers and architects, boost U.S. R&D and jumpstart our stalled economy. Emissions-friendly construction processes are also likely to earn respect – and federal dollars.

"Unglamorous, proven (and even old) technologies need to be employed quickly for the economy to benefit," said Dan McNichol, author of The Roads That Built America and The Big Dig, over e-mail from China. "Think paving, repaving, maintenance work and bridge repairs."

Cement isn't exactly sexy. But some new and not-so-new innovations presented at the TRB (Transportation Research Board) meeting suggest that a little science and technology can help cut building costs, and emissions, big-time, making the subject a lot more interesting.

Take aggregates, or rock-based materials that go into gravel (as well as other compounds). Aggregates are ground and glued together at high temperatures with liquid bitumen, a byproduct of the oil refining process, to pave our trails and highways. Typically, roads are built by piling a layer of aggregates, on rocks of various sizes, shapes, weights and mineral properties that are collected at quarries, sorted and sifted through 'screeners', trucked away for remix with rocks from faraway places to meet the best specs, and topped with asphalt or concrete– and voila! You've got a new road! When oil prices nudged the stratosphere as they did last year, scientists and industry leaders raced to find ways to cut costly aggregate production and transport costs, as well as ways to address occasional aggregate shortages.

One solution has been implemented near Ft. Myers, Florida, where aggregate pieces that would normally be discarded or languish as rejects in quarries replaced, as the bottom layer of a two layer road paving experiment, now known as 'econoconcrete', the bulk of the premium aggregates that would normally have been trucked in. Today, 12 of 33 sections over that 6.5 mile bonded, two-layered concrete pavement stretch, which sustains heavy traffic, still impress the experts with their performance.

"These 'substandard' pavement materials should have failed in the 80s, but in 2009 some sections are performing exceptionally well," crowed panelist Jamshid Armaghani, of the Florida Concrete and Products Association.

In Europe, where some governments have mandated 100% reuse of old road-building materials in new road construction, Viennese road builders are using roadside computer-controlled cement trucks to accurately measure grades for mixing recycled concrete, asphalt, and a base used in upgrading or widening roads.

The really big road-building buzz at TRB – a meeting of over 10,000 civil engineers, transportation department bureaucrats and other construction firm practitioners – was around warm mixed asphalt. The process, pioneered in Europe a decade ago (and still new-ish stateside), uses lower temperatures (250 degree Fahrenheit versus the normal 300 degrees or so for hot-mix), a foam mixture, and water, to coat the aggregates with liquid bitumen to make asphalt. 'WMA's attributes include lowering overall costs, using up to 30% less fuel, and emitting about a third less dust and C02 than the mainstream process does. These benefits helped lure a near-capacity crowd, at the conference, to hear about US and European warm mixed-asphalt trials.

Today, as the industry scrambles to cut its carbon footprint, 'warm mix' is the evolving new norm, with most of Western Europe and roughly 40 states – including a stretch of Yellowstone Park and I-70 near the Continental Divide - testing warm mix asphalt on highways, or at least a mix of hot and warm.

Concerns about WMA's efficacy center around its need for further testing for enduring performance, particularly over routes travelled regularly by heavy trucks. But the early signs look good, and most experts see an inevitable shift to warm mix over time.

As Adam Hand of Granite Construction commented, "If Al Gore has a say in an Obama administration we'll all be using warm mix regularly."

Read more of Carolyn's work, from ScientificAmerican.com, Fortune, Newsweek, the International Herald Tribune, and more.