Axion International Holdings Inc. (New Providence, N.J.) has announced that it has built the first railroad bridges constructed from 100 percent recycled thermoplastic materials, at Fort Eustis, Va. Designed by Parsons Brinckerhoff (New York, N.Y.) the short-span bridges are based on Axion’s patented Recycled Structural Composite (RSC) system, which consists of nearly 100 percent recycled post-consumer and industrial thermoplastics and is developed in collaboration with researchers at Rutgers University. Axion International is the commercial spin-off and licensee of the RSC system, developed at Rutgers’ AMIPP Advanced Polymer Center. The bridge design and engineering work was supported by Reston, Va.-based Centennial Contractors Enterprises, the prime job order contractor for the project, and Parsons Brinckerhoff. The bridges can reportedly support a load of 260,000 lb (118 metric tonnes) and are approximately 12.2m/40 ft and 24.4m/80 ft long.
According to Axion, the capital cost is less than conventional concrete, steel or wood bridges. The composite bridges also require less maintenance while being more environmentally friendly. Parsons Brinkerhoff’s Vijay Chandra, principal-in-charge for the design of the two railroad bridges, offered his own perspective: “RSC material meets the country’s need for green, sustainable and durable competitive products, which are highly competitive initially and on a life cycle cost basis.”
The RSC system involves both plastic formulations and structural engineering design. The plastic is made by combining polystyrene and high-density polyethylene (two polymers that are ordinarily incompatible) in a melt blend, with fibers and nanoparticles in a proprietary blending process to achieve structural strength exceeding that of either polymer. The polymers come primarily from recycled plastic milk and laundry detergent bottles and automobile bumpers, says the company. Structural I-beams, railroad ties, and other components can be economically and effectively fabricated via extrusion. For the Ft. Eustis bridges, structural elements included 12-inch/3.7m diameter pilings and I-beams made by bolting two T-beams together, says Tom Nosker of Rutgers’ AMIPP’s group: “It would be difficult to cast an I-beam in one piece because of the way hot thermoplastic contracts upon cooling while still locked in a mold. The T-beam design proved feasible and structurally sound.”
Read about the design of Axion’s first RSC bridge in “Engineering Insights: Tough I-beam bridge for tank traffic,” link at right.