Bridging The Gap Between Dissimilar Road Types With Foam

When you think of driving up or down an embankment, do you ever wonder how much foam you’re currently driving on? Probably not, because it hardly seems like a suitable building material. But as explained by [Practical Engineering] in the video below the break, using an expanded material to backfill an embankment isn’t as dense as it sounds.

In many different disciplines, mating dissimilar materials can be difficult: Stretchy to Firm; Soft to Hard; Light to Heavy. It’s that last one, Light to Heavy, that is a difficult match for roadways. A bridge may be set down in bedrock, but the embankments approaching it won’t be. The result? Over time, embankment settles lower than the bridge does, causing distress for cars and motorists alike. What’s the solution?

To mitigate this, engineers have started to employ less dirty materials to build their otherwise soil based embankments. Lightweight concrete is one solution, but another is Expanded Polystyrene (EPS) foam. Its light weight makes installation simple in anything but a strong breeze, and it’s inexpensive and durable. When used properly, it can last many years and provide a stable embankment that won’t settle as far or as quickly as one made of dirt. Because as it turns out, dirt is heavy. Who knew?

Aside from roadways and bespoke aircraft, EPS foam has also been used for making home insulation. What’s your favorite use for EPS foam? Let us know in the comments below.

27 thoughts on “Bridging The Gap Between Dissimilar Road Types With Foam

  1. i have repeatedly seen this idea that if you successfuly spread the weight out so it isn’t focused like a puncture then EPS can support huge loads. they did this for a small part of a bridge right by my house, they basically used the EPS as a part of the form for pouring the joints, and then left the EPS in as load-bearing after the concrete hardened. it’s not nearly as much bulk as the images in the article but it seems to be really common now.

    but mostly i just wanted to say “… less dirty materials to build their otherwise soil based …”. get it? dirty? soil based!!! lol thanks Ryan!

    1. The EPS ban is on per-use basis:
      In June 2023, packing peanuts and other void-filling packaging will be banned. In June 2024, portable coolers will be banned. In June 2024, food service products like containers, plates, bowls, clam shells, trays, and cups will be banned.

      There’s nothing banning the material altogether.

    2. Using it in large chunks like this is probably one of the least-bad uses for it, and compared to the volumes of it that get used disposably for packaging etc. this is a fart in a hurricane.

      I’m sure when they (eventually) dig it up they can easily recycle it too, as recycling is much easier when you know you’re digging up 100’s of cubic yards of one material.

  2. In the Netherlands, to cover the jump from bridge abutment to embankment (the latter will settle, the former will not) we use what’s called “stootplaten” (bump plates). Those are concrete “plates” (usually quite thick) that rest on one end on the bridge abutment, and on the other on a reinforced plate on the end of the embankment. If the embankment side settles, the height difference is spread out over the length of the stootplaat (a few metres) instead of immediately.

    It is mainly used in the Netherlands because of the exteme weakness of the underlying soil (basically peat bogs) where the heavy sand substrate would sink away. A layer of EPS with some sand to spread the load on top has a similar weight to the peat it displaced, so it won’t sink away.

    1. If it’s bad enough to affect the EPS below the asphalt there’s a high chance the section of road would need emergency re-surfacing anyway – plenty of chemicals damage / degrade asphalt too.

  3. For those in British Columbia’s lower mainland, you might find this as surprising as I did when I heard it from a road-building friend a few years ago (he supervised the Hwy 17 build). At the Hwy 17 exit off the number 1 (near Langley) they kept pouring in fill to build up the ramp but the bog underneath kept sinking so conventional aggregate (truckloads of heavy rocks) wasn’t going to work. So they built it up with foam blocks. In some places in that area, the foam is 12 meters (40 feet) thick under the highway!

    Side note* When the main portion of Hwy 17 was complete and free of equipment and workers and just before opening it up to the public, he and his co-worker took their Corvettes and “tested” the road “for areas of high speed concern”.

    1. Sounds like the swamp castle in “Monty Python and the Holy Grail.”

      “When I first came here, this was all swamp. Everyone said I was daft to build a castle on a swamp, but I built in all the same, just to show them. It sank into the swamp. So I built a second one. That sank into the swamp. So I built a third. That burned down, fell over, then sank into the swamp. But the fourth one stayed up. And that’s what you’re going to get, Lad, the strongest castle in all of England.”

  4. Seriously?? EPS is being buried in roadsides? My experience of EPS in packing is that it starts to become unstable over time and it’s structure loosens. If you have to inevitably dig it up it will just break into beads of EPS and be a pain to clean up. Eco nightmare!

    1. Something wrong with your childhood. *

      You mix EPA with gasoline to make homebrew napalm. Duh. Recycling!

      * Apologies if you’re a little kid, haven’t reached the ‘pyro’ and ‘explosive pyro’ development stages yet.

    2. It is not the same type of EPS as used for packing. Millions of houses have their concrete foundations poured on top of EPS foam. It is very stable and will keep shape at least as long as the concrete.

    1. I have never seen a gas station immediately adjacent to a bridge. Let alone a gas tank in the gas station close enough to a bridge for a leak to spread to anywhere near the bridge. The tank would have to be feet away from the bank being bridged over, and/or ridiculously close to the road and bridge. I call BS.

  5. I built a giant boot out of it and covered it with epoxy and fiberglass for L.L. Bean 20 years ago. Slabbed it off those very blocks with a hotwire, cut to shape from a 3D scan (home built naturally), then re-glued the slices together with weird blue contact cement that came in 20# propane looking tanks. Final shaping was with a wire brush on an angle grinder then an orbital sander. Goes slower than you might imagine and the dust is double extra horrible because of static and quantity.

    Google for final results. Would never do it again.

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