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.
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.
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.
All over Europe, energy is recovered by incinerating trash, generating steam for heating apartment complexes in towns and cities and/or generating electricity. This works very well, greatly reducing the volume of material that needs to be buried in landfills.
Thank you for the nice article. These materials are quite different from Trex in many regards, and this is recyclable after the end of life. As for static/Dynamic considerations, the tank bridges were designed to have a tank parked on the bridge for 25 years and then drive off and have the bridge recover its' shape. The Scotland bridge was a more modest 10 year loading.
I recommend a couple of videos to those interested:
These materials have higher specific strength than mild steel, and we have a handle on the most important issue for thermoplastics- the creep issue.
As for cost, I'll let other speak. The Army has just completed a full 2 year constant study of the first takn bridge at Bargg, and came through perfectly. Listen to the video on the tank bridge opening ceremony very carefully. He says 3 important things- one referring to maintenance, one referring to degradation, and one referring to a ROI.
Thanks for the link, Ann. From what I can tell in the Fort Bragg bridge, the Elastic Modulus was somewhere above 350 ksi, which would be very low compared to steel. Ultimate bending strength is 2,300 psi, which again would be much lower than steel. I think steel bridges are designed for 36,000 psi in bending. My guess is that this wouldn't give you the long unsupported spans that steel would but it's very impressive nonetheless and obviously has supported some high loads in short spans.
Chuck, thanks for sifting through the specs and making comparisons with steel. Sounds like, at least for now, this material competes with steel on the lower-end apps in terms of strength and length. But at least it's been done at all--it's a start!
Thanks for the info Charles. I'm amazed that they were able to get the specs to be that good, actually. Whilel this is not necessarily a material that you would want to use for long-term, high-weight traffic, it might be a great option for lower cost pedestrian bridges in a park, for example.
Actually, this material is being used for heavy-duty bridges built to take heavy traffic. The Fort Bragg bridge Chuck references was made for military vehicles, such as Army tanks, and the bridge I reported on, in Scotland, is built to take heavy equipment loads. The same material is used to build railroad bridges, including ties. Pretty amazing stuff. And it looks like the materials supplier, Axion, is increasing its production capability with at least one manufacturing facility:
An efficient way of using those plastic bottles, thus great thought of waste management. Recycling plastic is the easiest way of making our earth cleaning and free from plastic landfilling. We at Replas encouraging for the same concept of plastic recycling as we manufacturing plastic recycled products like plastic profiles, plastic deck, bollards, furniture etc.
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.
The reference to the M1 ABRAMS tank crossing a bridge @ Ft. Bragg begs the question regarding static & dynamic loads. Was the tank in motion or sitting mid-span? If in motion, the calculations for acceptable load vs. deflection take on a different posture than if the tank was sitting mid-span w/ engine running while the summer sun baked down on the bridge structure. While I'm convinced that the designers did their "homework" regarding allowable loads, did they also consider ambient temperature and/or chemical decomposition from UV rays, etc.? The installation of a short-span bridge in Scotland, which see much cooler average temperatures & wetter climate conditions than many parts of the U.S. etc. also should be a factor in determining suitability of installation. The initial cost of installation should not be high on the list of priorities, given the elimination of periodic maintenance, especially in light of the fact that maintenance costs are not fixed over time. It would seem to me that they are probably more exponential in nature.
Good story, Ann. I'm impressed. It's one thing to fill a car seat with this material, but a weight-bearing bridge is quite something else. It pretty much takes the ceiling off for this material. Imagine, infrastructure made from landfill material. Now I don't feel so bad about drinking bottled water.
This is a great use of recycled material. A major portion of steel bridge maintenance is the on-going sandblast / paint cycle. Using plastic for the bridge span is great. Using recycled plastic is even better.
If the materials are the least expensive installed cost, don't require maintenance like steel, and last longer because they are impervious to rot, chemicals, etc, then it looks to me like the total cost of ownership would be lower than steel. If the materials cost is the same as steel, or even somewhat higher, this lower COO is likely to offset that cost. The simple fact that the Army is paying for it tells me this is highly likely.
I'd be surprised if it's impervious to fire--I don't know any plastic that is.
Did you listen to the Army video I gave the link for? There is a 34:1 ROI on the bridges. There is a totally safe component in the material that retards fire. There are also coatings we have developed to render the material totally fireproof.
Thanks for the fire-retardant info. What exactly is the "totally safe component in the material that retards fire"?
Regarding the 34:1 ROI, to be honest that's one of those phrases that tends to sound like PR or marketing, at least without enough contextual info for comparisons. ROI on exactly what? Compared to what? Those are the questions I usually ask a vendor. In any case, what readers have been wanting to know, and so have I, is the relative costs of this material vs the traditional ones, and that information doesn't seem to be available. Hence my guess that the material must be relatively inexpensive by now--or at least the comparative COO with steel must be relatively low, if the Army has been willing to pay for it.
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