Wow, this is so cool. I'm assuming more construction efforts are made from recycled materials--it's just that I'm not as aware as when clothes or smaller products are marketed and sold that way.
Ann: Do you have a sense of how widespread this practice is and if there are limitations in terms of how big and how traveled a bridge has to be in order to leverage these recycled materials? How about pricing? Is it more expensive? Given that we have a surplus of small bridges that need repair throughout the U.S., this would be a great opportunity to spend tax dollars on infrastructure repair and environmental stewardship and kill two birds with one stone!
Ann, thanks for another interesting article. I read some one of the whitepapers on Axion's website to get a better idea of how these materials are made. It looks like this technology is based on the concept of immiscible polymer blends. The two formulations which were mentioned were a blend of high-density polyethylene with polystyrene, or a blend of high-density polyethylene with glass-reinforced polypropylene. In both cases, since the two plastics don't mix (like oil and water), you get a complex microstructure incorporating both stiff and pliable segments -- similar to the structure of many natural materials. For example, in natural wood, the stiff segments are lignin and the pliable segments are cellulose.
Beth, according to the whitepaper, when this material was first introduced in the late 1990s, the initial costs were more expensive than traditional materials. However, the authors claim that this was offset by lower lifetime maintenance costs. They claim that now both the initial investment as well as the maintenance costs are lower than traditional materials.
As far as load-bearing capacity, they have a photo of an M1 Abrams tank driving across a bridge made out of this material at Fort Bragg.
I wonder if this material could have applications beyond infrastructure. It seems to me that a lightweight, strong, tough, environmentally-sustainable material would be a winner in many applications.
This is great. There is a lot of valuable material bound up in all that trash we generate. This is one way to get that out and resue it. As far as plastics go, that material is hydrocarbons (either from oil or natural gas), which are worth recovering. It also sounds like these structures can be reused again. If you look at the long term energy input from making the original bottles and the bridge materials, this will, over time, lower our energy footprint without any deterioation of our way of life.
We have started to generate electricity from methane gas captured from landfills. There is much more to do in that area. Trash to steam did not work, but digester technologies to produce electricity are promising. And they leave the recycleable plastics intact.
Beth: you have a good point about the number of bridges and other such structures that are in need of repair. One of the reasons they are in such need is the materials used. If this material is as advertised, it is a better fit for those structures.
Finally, this is a great example of cooperation between academia and industry. We need more of that in this country. We have incredible resources in our universities. This is especially true of our technical universities. I would like to see more of this kind of coorperative development. I think most companies just see the universities as a source of educated employees. I often see great ideas that might be published in a paper and then, maybe picked up by someone reading that paper. We can do better.
Ann- It's great to see this trend strengthening. My first impression is, "What took us [human-kind] so long?" As was mentioned by both Naperlou and Dave Palmer, the recycle composite technology had been introduced long ago but is only now getting improved visibility in bigger applications that previously seemed unreachable.A load bearing bridge-?Really?I'd seen composites used for picnic tables and picket fences (think they'll lasts forever-?) but that garden-variety application has been sourly under-utilized. Broadening the horizon of use-cases into commercial applications like this is fantastic.More, please.– JimT.
Thanks for all the feedback. I agree, this is totally cool! And why the heck we haven't done this before, I don't know. Once I realized it was basically a form of Trex, not necessarily chemically, but in its function, I wondered the same thing. I suspect it's like a lot of other materials innovations--it just takes time to work out the kinks in performance, cost and manufacturing processes. Bearing the weight of heavy machinery--which this specific bridge was designed to do--is pretty different from bearing the weight of a few picnic tables and people on your home's deck. Note that this company also makes similar materials for railroads, so they've focused on solving problems in this particular app area.
Dave, thanks for sifting through those whitepapers and giving us a good summary of what they say regarding the materials details. I suppose the material may be used for other purposes, but the whole point of it, and of this app, is the structural performance characteristics. It's a parallel problem that is being solved in composites for aircraft, for example, the Boeing 787. Load-bearing structural materials made from plastic of any kind, let alone recycled plastics, is a Holy Grail of sorts.
It's amazing what's going on out there in both R&D and in actual commercial apps.
Great article, Ann. I've wondered for years when this would finally happen. Do we know how it compares to standard steel alloys, such as A36 steel, in terms of bending capacity and shear? I'm also surprised to see that it's being used for piles, which suggests high compressive strength.
I wonder how survivability of this plastic bridge compares to steel and other legacy materials. How well does it resist gasoline or a chemical spill? What if a vehicle or spilled fuel catches fire on the bridge? Is the material self-extinguishing or will it support and propigate combustion?
That is an interesting question regarding how this material stands up to things other than impact. Specifically, I'm wondering about its ability to withstand heat, i.e., fire. If this material could fare better than steel, for example, think of the ramifications for city buildings where safety and environmental issues are both a concern. The big one that comes to mind for me is that iconic image of the World Trade Center--could this type of material fared any better after the tragic plane impact? Afterall, it was the intense heat and fire--not the impact--that ultimately brought the buildings down.
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