Mixed glass is the Rodney Dangerfield of recyclable materials. It gets so little respect that some communities, like Harrisburg, have stopped collecting bottles and jars in their curbside programs. It's cheaper to leave glass in the trash and send it straight to a landfill.

Enter AeroAggregates LLC, which opened a plant in a former Eddystone locomotive factory this year, where it produces lightweight construction material from this lonely stepchild of municipal recycling programs.

"We can take Philadelphia curbside glass and make a construction product that's going right back into the city of Philadelphia," said Archie Filshill, chief executive and cofounder of AeroAggregates, which has sunk about $10 million into its project. "It's post-consumer waste. That's something that hasn't been done before."

The material AeroAggregates manufactures is foamed glass aggregate, which resembles crushed rock and serves a similar purpose in construction projects. It might seem crazy to manufacture stone, since there is no shortage of naturally occurring rock. But foamed glass aggregate is not ordinary rock — it weighs 85 percent less than stone, and yet is still very strong.

In Europe, where the product was developed decades ago, it is used in road building and bridge abutments, where heavier fill materials would compress soft soils or crush underground utilities. Foamed glass also has insulating qualities, and potential applications in green roofs and gardens.

Filshill said Drexel University and Lafayette College researchers are exploring using foamed glass aggregate in concrete, creating a lightweight alternative for nonstructural applications, such as the poured-concrete floors of a high-rise.

But the big market is in highway projects, though foamed glass is virtually unknown in America. Filshill and cofounders Thomas McGrath, the company's president, and Robert Schoen, the chief financial officer, are experienced in construction, and deployed their knowledge and connections to introduce the material to state highway engineers.

So far, transportation departments in Pennsylvania, New Jersey, Maryland, Virginia, and New York have given a preliminary thumbs-up. PennDot used the company's aggregate under a section of the Langley Avenue reconstruction project at the Navy Yard, which is nearing completion.

Last week, PennDot broke ground on an I-95 ramp project at Cottman Avenue that will use AeroAggregates' product. The company is also under contract to supply 30,000 cubic yards of aggregate next year for the Wittpenn bridge project in Kearny, N.J.

PennDot follows a rigorous testing procedure for any new material and regards the Philadelphia projects as tests of the recycled-glass product, said department spokesman Rich Kirkpatrick.

"Since this is a totally new aggregate, we have to make decisions on how to make proper use of it," Kirkpatrick said. "We are open to its use, but our reviews are continuing."

The Pennsylvania Recycling Markets Center recently recognized AeroAggregates for innovation, and state Environmental Protection Agency Secretary Patrick McDonnell last week marked the first North American use of foamed glass aggregate at the Langley Avenue project.

"Here we have an innovation that is not only a manufacturing project, but also helps us build out infrastructure across the commonwealth," said McDonnell.

Glass separated by color can be recycled into new bottles, but most towns don't have the capacity to clean the glass to make it attractive to buyers. According to one study, municipal recycling programs spend about $150 million a year to dispose of unwanted glass.

New York and other cities tried mixing glass shards into asphalt, giving resurfaced streets a sparkle that caught the eye of then-Plaza Hotel owner Donald Trump. But "glassphalt" did not catch on more broadly, and fell into disfavor.

The Eddystone plant, which employs 14 people, could resolve the problem by converting mixed glass into an entirely new value-added product. "Mixed glass, colored glass is a very difficult processing problem here in the city of Philadelphia," Streets Commissioner Carlton Williams said at last week's Langley Avenue event. "But it's not an issue when you come up with opportunities to put it back into the market like AeroAggregates has done."

Filshill, 52, who has a long career in "geotechnical" construction, was introduced to foamed glass aggregate while pitching a project in Ireland a few years ago.

The recycled-glass product has advantages over competing materials used as lightweight fills, Filshill said: It is lighter and requires less energy to manufacture than expanded shale, a mined rock that swells up after being heated in a kiln. Contractors can also use polystyrene fill, though some engineers shun it out of fear it will dissolve if it comes in contact with spilled gasoline. "They don't want to take a chance of losing a lane because the road melted," he said.

Filshill joined with McGrath and Schoen to form AeroAggregates. They hired Herb Northrop, a veteran of recycling operations, to serve as chief operating officer, and Theresa Loux, an engineer who had worked with Filshill, as technical manager.

The company bought a 97,000-square-foot building on 10 acres that was part of the Baldwin Locomotive Works, which closed in 1972. Larger banks declined to support the untried business, but QNB Bank, with whom McGrath and Filshill had previous relationships, stepped up with debt financing.

From German firm SGGC, AeroAggregates licensed its process, in which glass crushed into a powder is mixed with silicon carbide, which acts as a "foaming agent." As the blended powder passes on a conveyor belt through a 60-foot-long gas-fired kiln at about 1,800 degrees, the material melts, and the silicon carbide produces carbon dioxide bubbles that make the mix rise like a baked cake.

After a 40-minute trip through the kiln, the stuff emerges in a continuous gray sheet. As it cools, it cracks into pieces about two inches wide, with visible cavities similar to that of volcanic pumice stone.

Each kiln can produce about 80,000 cubic yards of aggregate per year from about 12,000 tons of mixed glass, the equivalent of about 55 million empty beer bottles. "That's our way of giving back after drinking all that beer," Filshill said.

AeroAggregates has ordered a second kiln, to be installed early next year. The expansion was financed by Closed Loop Partners, an investment fund underwritten by $100 million in corporate money aimed at advancing recycling technologies.

Its cavernous Eddystone building can accommodate two more kilns after next year's expansion, but AeroAggregate's leadership is thinking bigger. "We have a blueprint now," said Filshill. "If we want to go to another city, we can take everything we've learned on this first plant, and then it's basically a cookie-cutter to go to other locations."