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Recycled thermoplastic materials for bridge

posted Apr 18, 2012, 5:55 AM by Radiance Calmer   [ updated Mar 23, 2014, 10:31 PM by Chang-jin Kang ]

Civil Engineering, the magazine of the American Society of Civil Engineers published an article about bridges built with recycled thermoplastic composites in the issue of April 2012. The three authors, V. Chandra, J.S. Kim and T. Nosker, are coming back on the history of plastic materials for road applications, then, they are introducing the last thermoplastic railroad bridges built in Virginia, USA.

                First road elements in recycled plastic were constructed in the early 1990s. Even if the U.S. Department of Transportation promoted the use of this durable and environmentally friendly product, the material suffered from a low elastic modulus as well as significant creep. However, since then, thermoplastic fabrication technology has greatly improved and the use of the material has expanded from small elements to majors structures as bridges. The list of thermoplastics advantages is very long! From structural properties equivalent to classical materials to the main criterion of recycling, this product is environmentally safe, no carcinogens or chemicals. Not only does it resist to extreme weather conditions, to fire, moistures and insects, but also its lightweight property lends itself to accelerated construction. Thermoplastic composites meet requirements formulated by the American Association of State Highway and Transportation Officials, moreover for seismic design applications.

Last thermoplastic structures were built in Reston, Virginia to replace too old timber bridges in 2010.  Bridge No. 3 is a 38 ½ ft long, four span continuous structure supported by two end bents and three intermediate bents. The spans vary from 8 ft to 9 ½ ft. The structure consists of six vertical piles at the end bents and six intermediate bents. Bridge No. 7 is an eight-span structure 84 ft long supported by two end bents and seven intermediate bents. The spans vary in length from 9 to 11.5 ft. Each pier of each bridge has a total of six 12 in. diameter piles made of thermoplastic. Tests were performed before the opening of the bridges to confirm the safety. Pile testing was performed with a pile capacity estimated on the basis of the end bearing and skin friction. The maximum elastomeric bearing pads deflection was around 0.02 in. Live-load testing was also performed, using three different live loads. Beam deflections were measured at various locations. For Bridge No. 3 the maximum deflection was 0.21 in. and for the bridge No. 7, it was 0.32 in. These two values are very close to the maximum calculated deflections by structural analysis programs. As bridges meet the specification code requirements and with all the advantages of thermoplastic materials, this kind of bridge will be developed, research and development efforts improving. Given that consumers around the world discard 100 million tons of plastics annually, there will be no shortage of raw material for future applications of this virtually maintenance-free structural solution.

For more information, please refer to the article Recycled routes, V. Chandra, J.S. Kim and T. Nosker, Civil Engineering, April 2012.