As part of the expedited replacement of the I-95 Cottman Avenue Exit Ramp in Philadelphia (that succumbed to a fuel oil tanker truck fire underneath it June 11th), six inner lanes will be temporarily supported from underneath with a lightweight engineered material that has been hiding in plain sight for a couple decades…and the material geek in many of us can’t stop talking about it.
Going by names like ultra-lightweight foam glass aggregate (we’re just going to call it foam glass and let the haters hate), the material being used for the I-95 bridge is made by Aero Aggregates in Eddystone, Pennsylvania and has been used in an array of different projects where low unit weight, stability, high permeability, or insulating characteristics were priorities.
The University of Delaware’s Professor Chris Meehan was on the cutting edge (hey, we had to go there) several years ago when he was interacting with Aero to better understand how the material could be used to advantage in transportation infrastructure, so we’ve been tossing around a piece of the stuff since back in the day. They say the material weighs only 15% of quarried aggregate and our sample suggests that’s true. That is a real advantage when a project rests on soft soils or underlying infrastructure (pipelines, sewers, and such) could be damaged by traditional quarried fill. The next time you’re in Scandinavia, ask them about it; they love the stuff because their whole region frost heaves.
Clearly, another attractive feature of the material is that its primary ingredient is recycled container glass, potentially breathing a whole new life into that part of the municipal waste diversion strategy. Glass bottles are ground to something like a powder and then foamed, heated, and formed into long sheets that cool and then crumble off the line into chunks that can be subsequently crushed to the desired nominal size. The end product is not really “foamy” at all and can withstand a substantial crushing force.
Will a high-profile project like the I-95 bridge elevate this type of material to increased infrastructure project applications? It certainly could (thank you, Captain Obvious), but moreover, it is a local example for us to observe and study to better understand how it might be used in non-emergency projects in our area. So, we’ll be keeping an eye on the bridge repairs just up the road to learn what we can from this unfortunate necessity.
We talked in our June e-newsletter about Environmental Product Declarations (EPD), the so-called nutrition label for construction materials and an Every Day Counts initiative. While we’ll need to see more details about the material manufacturing process, it stands to reason that these foam glass materials may compete well with quarried aggregate in the environmental impact landscape.
But wait…there’s more. Glass is fitting in nicely with other applications these days.
Processed glass aggregate (and materials by similar names) have been embraced by local agencies, particularly in the northeast. Here, discarded glass bottles are ground to about half an inch nominal size (12.5 mm for our European readers) and despite what you would expect, aren’t a cutting hazard; reportedly, you can gather the ground aggregate up in your hands and move it back and forth without needing a bulk order of gauze pads. Public works directors are finding that the material can be an excellent drainage layer for roadways and as bedding for pipes. See what a number of them have to say about it in this video from the Northeast Resource Recovery Association. When you consider that the use of so called PGA (let it go, golfers) reduces the use of virgin aggregate, diverts waste from the municipal landfills, potentially saves money, and probably does well on one of those cool new EPDs, maybe this is something we’ll see more commonly in the future?