In June, a tanker truck full of gasoline caught fire and exploded under a six-lane bridge that carries traffic along a busy section of Interstate 95 in Philadelphia, killing driver Nathaniel Moody in the ensuing inferno. The heat was so intense that a northbound section of the I-95 overpass collapsed and the southbound lanes were so damaged they could no longer safely support the weight of the 160,000 vehicles using this crowded artery each day.
With a rebuild of the overpass estimated to take many months, commuters and other drivers braced for endless traffic jams and delays. But thanks to an innovative approach that empowered public officials and private enterprise to explore unconventional solutions, I-95 reopened on June 23, 2023, not even two weeks after the destruction, with glass playing a starring role in the miraculous repair. The shocking turnaround was hailed by US President Joe Biden and PA Governor Josh Shapiro as an example of functional government, the power of private-public partnerships, and American can-do-ism. It was also the first time many (including this writer) heard of "foamed glass," the key to the rapid reopening used to fill in the underpass rather that rebuild the bridge. The name itself evoked wonder and skepticism “How the heck will foam and glass hold up a highway that supports thousands of semis each day?” It turns out the technology has been in development since the in the 1930s and has been used successfully for many building and construction applications for decades.
What is foamed glass? Put simply, this substance is essentially powdered glass that is heated along with a foaming agent such as calcium carbonate to about 1500 degrees F. In the resulting material the glass is suffused with gas bubbles. The hero-manufacturer in the I-95 reopening,AeroAggregates of North America is located in Eddystone, PA, a mere 25 miles from the construction site (and also just off I-95). Their grey and opaque Ultra-Light Foamed Glass Aggregate looks not unlike limestone chips but is approximately 85% lighter. Some 2000 tons of the material was used as a base for the temporary highway sections that were built atop. While the construction endeavor was substantial, it is a temporary fix and other lanes will be constructed around this stopgap—when the new lanes open, the temporary lanes will be replaced with a permanent section of highway that once-again allows traffic to pass beneath.
The material itself is just as arresting as this story of its use. The foamed glass made by AeroAggregates is comprised of 99% recycled glass and the company says that each of its three plants (Eddystone, Pennsylvania; Dunnellon, Florida; and Modesto, California) diverts from landfills the equivalent of 140 million glass bottles each year. In addition to this green profile and light weight, the load- bearing material is non-combustible, water resistant, chemically inert, thermally insulating and resists frost heaving.
Foamed glass (also called closed cell glass or porous glass) is prevalent in construction in Europe because of the above properties, and especially because the closed-cell bubbles are ideal for insulation and soundproofing. The aggregate described above is the result of the fracturing that occurs from not annealing the material. With annealing, the material can be shaped into blocks, slabs and custom forms. Owens Corning makes a wide range of products for insulation, corrosion resistance, and fire protection under the FOAMGLAS trademark.
The applications for foamed glass aggregate, such as substrates for green roofs and layering beneath foundational slabs at construction sites may not be glamorous, but as the US turns towards energy efficiency this material is used more and more as it’s lightweight, load bearing and insulating. AeroAggregates has been operating since 2017 and another company, Glavel (get it?) opened its manufacturing facility in Essex, Vermont, in 2021.