Some Plastics are Made to Last Forever

Recycled plastic building materials

stone bridgeWhile most petroleum-based plastics can last almost forever, sometimes that is exactly what we need. One such application is bridges. In the (really) old days, we had stone bridges, and we still do. Roman bridges still exist in Britton and Rome that are now 1500 years old, and many are still used!

Wood was cheaper, but they are gone! Iron then steel replaced wood but iron rusts, and steel needs maintenance too. This is the current status of over 143,000 bridges in the US today.

So if plastic can last as long as stone, why not build our bridges out of recycled structural plastic? The cost of recycled plastic (or thermoplastic timber) is half as much as steel, weighs less, and lasts much longer[1].

Some applications, it appears, really benefit from the toughness and longevity of plastic. Recycling plastic it turns out can supply even better materials for some applications than other existing materials; wood, concrete, steal or even virgin plastic[2].

Some will expect that the “plastic” bridges would not be as strong as steel bridges. But existing bridges are already proving they will stand up to weight as well as the weather. The first plastic bridge built by Rutgers University leads the way, and currently two bridges are on public roads. They support cars, trucks and military tanks!  With over five years of service they are proving to be as expected. Imaginge having a bridge stay in-tact for centuries without maintenance!

Structural plastic naturally has many other uses.

Railroads have a major expense replacing railroad ties. Plastic rail ties are now replacing wood and concrete railroads ties at lower cost after just the second replacement[3] with traditional materials. This promises to be another significant improvement in construction and it uses our pre-used PET bottles and HDPE and automotive bumpers.

Projects are faster to construct because the weight is less. This reduces heavy equipment use and costs less to transport. Further, no pesticides or chemicals are used to protect ties from ground contact saving the environment from toxicity that must be used today to prevent rotting. This makes environmentalists happy because toxic material is not necessary for plastic preservation.

Most people are aware of “composite” decking, the recycled wood and plastic alternative to wood decking for outdoor patios and decks. The benefits of composite decking includes, durability like structural plastic and low-maintenance because its does not need periodic stain or paint[4].  The deck will last much longer than most types of wood decks, because they are new the real life is not yet known but some expect a lifetime of service[5]. The vulnerability may really be the structural wood beams used as structural beams to attach the decking to. We expect structural plastic beams will soon pair up with composite decks for a very long-lasting deck, fence and railing system. We’ll probably tire if them before they wear out!

It is argued by some that fewer trees will be used in the future by using our trash to make synthetic alternatives to wood, concrete and metal resources. If plastic is used for structures that we intend to last for well over a hundred years, and store CO2 all that time, could it be argued that plastic is more environmentally friendly than rotting wood in a forest? In any case the frontier for recycled plastic structural material and other external weather facing materials looks like a win-win for all.

See more on this subject:

Video Railroad bridges https://www.youtube.com/watch?v=2srE7muq-Hk

Plastic ties

https://plastics.com/plastics-into-rail-ties/

Plastic bridge materials- long term costs vs initial cost  http://theinfrastructureshow.com/audio/downloads/Worlds-First-Thermoplastic-Bridge.pdf

http://earthtechling.com/2013/06/100-recycled-plastic-bridge-holds-strong-in-ohio/

Videos

https://www.youtube.com/watch?v=rPQvn2LuNmQ

https://www.youtube.com/watch?v=OQxaWZBjSfs

https://www.youtube.com/watch?v=ZxsXUbnlDEM

 

[1] World’s First  Thermoplastic Bridges Abstract, Vijay Chandra, P.E., Director of Structures, Parsons Brinckerhoff Inc. Dr. John S. Kim, Ph.D., P.E., Supervising Bridge Engineer, Parsons Brinckerhoff Inc. Dr. Thomas J. Nosker, Ph.D., Professor, Rutgers University George J. Nagle, P.E., Manager of Engineering, Axion International, Inc.   Table1. http://theinfrastructureshow.com/audio/downloads/Worlds-First-Thermoplastic-Bridge.pdf

[2] Ibid.

[3] Ibid, Table 2

[4] The Enterprise Magazine, online. https://www.davisenterprise.com/features/five-advantages-of-composite-decks/

[5] Fence Authority Website, http://blog.fenceauthority.com/how-long-will-my-deck-last/

 

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