Workers arrange glass foam backfill made by Aero Aggregates in Delaware County to build up an overpass at Montgomery Avenue and 29th Street in Philadelphia. (Aero Aggregates/Facebook)

Amid the excitement about I-95 reopening much sooner than expected, there’s been a small nagging question: What’s with the much-hyped “foam glass” used to build the temporary lanes? Is the material — a product of Delco “ingenuity,” per Gov. Josh Shapiro — really suitable for such an important job?

As PennDOT prepares to send traffic over the roadway again, just two weeks after the gas tanker explosion collapsed a critical Northeast Philly segment, some drivers are skeptical.

But the backfill is more than up to the job, experts say. 

In fact, you’ve probably driven over it already.

The material, officially called ultra-lightweight foam glass aggregate (UL-FGA), turns out to be rather worldly, having been pressed into action not only elsewhere in Pennsylvania, but also in Maine, Rhode Island, New Jersey, Virginia, and as far away as Arizona, according to Pa. Transportation Secretary Mike Carroll.

“Those states, like Pennsylvania, recognize the quality of the product and its uses in certain applications like this,” Carroll said at a Tuesday briefing, directly addressing any safety concerns. 

In Europe, where residents are extremely pro-recycling, foamed glass has been used for decades, said Archie Filshill, CEO of Aero Aggregates North America, the Delaware County company that produced the foam glass for I-95.

“It’s a brand new technology to North America, but it’s got a 30-year track record in infrastructure projects throughout Europe,” Filshill told Billy Penn. “There’s probably a good 25 to 30 years of experience under highways, behind bridge abutments — with all successful use, no reported failures or movements or settlements.”

Despite its name, the aggregate is not flimsy, like foam, or breakable, like glass. It’s made from grinding recycled glass bottles into a powder, which then undergoes cleaning, filtering, foaming, and heating processes, per The Inquirer. The material is also weatherproof.

That Aero’s aggregate is “ultra-lightweight” makes it slightly different from the version sourced from New York and the Carolinas, according to Filshill. Around 20 state transportation departments on the East Coast have UL aggregate under their roadways. 

While Shapiro’s I-95 rebuild plan uses the foam glass on a temporary basis, about 98% of Aero’s work is permanent, Filshill said. 

Where else can you find it? Here are some other places in Philly and beyond built using UL-FGA.

Dilworth Park Starbucks

Been to the Starbucks next to Philadelphia City Hall? Whether you’re thankful for its existence or cast aspersions, the cafe kiosk sits atop a bunch of foam glass.

The project, which was completed about three years ago, consisted of workers excavating soil from the deck of the park and filling it with UL aggregate to lessen the pressure of the structure on the subway tunnel running beneath it.

“The weight of the building and the foam glass weighed less than the heavy soil that they took out,” Aero CEO Filshill said.

Various Philly streets and highways

Foam glass already undergirds the interstate in some places, as well as other roadways in Philadelphia. 

The on-ramp at I-95 and Girard Avenue features about 30 feet of the aggregate and has been operating smoothly for about two years, per Filshill. About a year ago, contractors added foam glass underneath JFK Boulevard on the way to 30th Street Station, right near the PECO building. 

When I-95 collapsed on June 11, contractors were in the middle of a different Philadelphia backfill project, adding around 20 feet of aggregate to the retaining walls approaching the Amtrak lines on Montgomery Avenue near 29th Street, Filshill said.

And thanks to a project completed in 2017, a section of Langley Avenue by the Philadelphia Navy Yard is also made from the aggregate. 

A bonus property of UL-FGA: It’s not affected by other materials that may end up on roadways. “If there’s oil, salts, if there’s a gasoline spill, acid spill, salts, none of those chemicals affect foam glass aggregate,” according to Filshill.

Philadelphia International Airport

Worries over whether the foam glass can withstand the weight of cars and trucks should disperse when you hear it’s been holding up to traffic of the jet planes at Philadelphia International Airport.

In a project completed a little over a year ago, 6 to 8 feet of the aggregate was used across a 10-acre floor in the overnight parking lot for planes on the south side of the airport.

Contractors removed the soil previously there, replaced it with the foam glass, and then paved concrete over it, Filshill said. “The job at 95 is probably just under 10,000 cubic yards. That project in Philadelphia International was probably closer to 90,000 cubic yards,” he added.

RCA Pier Park

The pier-turned-park along the Jersey side of the Delaware River was originally built with soil stacked 17 feet high. But the 100-year-old pier wasn’t designed to hold that type of weight. 

Two or three years ago, Filshill said, most of the soil was replaced: “They did it all with foam glass and then capped it with soil.”

Hilton Garden Inn, Camden 

Completed around the same time as the park, the first floor of Hilton Garden Inn in Camden rests on three feet of the glass aggregate. 

Why use it as part of the foundation? Elevation to prevent any settlement, according to Filshill, who said it also provided extra benefits. “They also could eliminate all the styrofoam that was going to be underneath that concrete slab as an insulator, because the foam glass provided that insulation as well.”

Beyond the Delaware 

UL-FGA has been used up and down the East Coast. 

Contractors finished construction two years ago on two ramps leading to a highway embankment in Rhode Island. The project featured foam glass fill stacked 36 feet high inside the concrete wall on either side of the road.

“I had our guy drive over it the other day and send a video to kind of prove it’s not settling, it’s not moving,” Filshill said. “But yeah, it’s been functioning as designed for close to two years now.”

The material was also used in Charlotte, North Carolina on the I-485 Express Lanes, according to EquipmentWorld, a construction news website.

Filshill believes the foam glass aggregate being used on I-95 will help promote the use of the material in the future.

“This type of attention from a national level with a big news story and high profile,” Filshill said, “that’s doing a lot more work in a short period of time than we could ever do as Aero ourselves.”