Just one word: Plastics. Okay, make that two words, plastic bridges, and you just might have a green solution for the more than 65,000 bridges in the country that the Associated Press recently reported as being classified “structurally deficient”. The findings came from a recent AP analysis of the most recent federal National Bridges Inventory. In addition to the 65,605 “structurally deficient” bridges, another 20,808 were classified as “fracture critical” with 7,795 being classified as both “structurally deficient” and “fracture critical”. According to the AP report, “A bridge is deemed fracture critical when it doesn’t have redundant protections and is at risk of collapse if a single, vital component fails. A bridge is structurally deficient when it is in need of rehabilitation or replacement because at least one major component of the span has advanced deterioration or other problems that lead inspectors to deem its condition poor or worse.”
The technology for thermoplastic composite bridges was developed in the late 1980s at Rutgers University as part of a government-funded program to develop recycling systems for plastics. The composite polymer used to make the bridge components are 80 percent post-consumer high-density polyethylene (HDPE), think milk jugs and shampoo bottles, and 20 percent polystyrene plastics which are recycled from old automotive bumpers and dashboards. The bridge materials are manufactured by AXION International which are developed in conjunction with Rutgers University.
Currently there are only two bridges located on public roads in the United States that are made of 100 percent recycled plastics. The first was completed in December 2011 on Birch Hill Road in York, Maine. The second, with a span of 24.6-ft, is the longest in the United States and located on Township Road 174 in Logan County, Ohio. This bridge was opened to the public in December 2012 and was 80 percent funded by the Innovative Bridge Research and Deployment Program which is a federal program developed “to promote, demonstrate, evaluate, and document the application of innovative designs, materials, and construction methods in the construction, repair, and rehabilitation of bridges and other highway structures.”
The longest recycled plastic bridge is located in Peeblesshire, Scotland on private land spanning the River Tweed was made of 50 tons of recycled plastic. The bridge is 90-ft long and built to support up to 44 metric tons. Other examples of thermoplastic composite bridges include ones at Fort Bragg, North Carolina that were designed to bear the weight of a 71-ton M1 Abrams tank as well as two railroad bridges located at Fort Eustis in Virginia. The railroad bridges at Fort Eustis, one is 38.5-ft long and the other is 80-ft long, are engineered to support 130 tons.
Thermoplastic composite bridges boast a number of advantages over bridges made of steel, timber and concrete. The composite polymer the bridges are made out of won’t rot, rust or crack due to the elements and is a lot more eco-friendly than traditional bridge building materials. Unlike a timber bridge it won’t absorb moisture and is immune from insect infestations. These bridges require very little maintenance and have a life expectancy of over 50 years at which time they can be dismantled and recycled for some other purpose. In addition to being a part of the solution to one component of the nation’s failing infrastructure it would also eliminate thousands of tons of plastic waste that might otherwise end up in a landfill.