Recycled Plastic Bridge Stands Up to M-1 Traffic – Twice….
By Dana Finney
An innovative thermoplastic composite bridge at Fort Bragg, North Carolina, is the first known structure of its kind to support military equipment loads exceeding 70 tons. On June 11, 2009, an M-1 tank safely crossed the newly built bridge, which is made from some 85,000 pounds of recycled plastics.
Click on 'play' (above) to watch an M-1 tank drive across a new thermoplastic bridge at Fort Bragg, North Carolina. Video courtesy of the Army Corps of Engineers Construction Engineering Research Laboratory in Champaign, Illinois.
“The first crossing was greeted with a big sigh of relief from some of us and a hardy round of applause from about 30 people in attendance,” said Richard Lampo, materials engineer with the Army Corps of Engineers Engineering Research and Development Center in Champaign, Illinois, who led the project. The tank’s foray across the bridge marked the completion of load testing and safety validation for the new structure, which was completed in May.
Since then, the Army has built a second bridge on base, and approved construction for a third. During a dedication ceremony for top Army officials and the media, Fort Bragg officials staged a similar demonstration on September 18, 2009, showing an M-1 tank moving across the same bridge.
Working with the Fort Bragg Department of Public Works and industry partners, the Corps of Engineers’ Construction Engineering Research Laboratory (CERL) designed and built the thermoplastic bridge to replace a dilapidated wooden bridge with a load limitation of 4.7 tons. The goal was to provide a low-maintenance, affordable structure using recycled materials and avoiding the use of any wood components that require chemical treatments to fight rot and insect attack as well as costly routine maintenance to repair or replace deteriorated members.
According to Ali Achmar, Army Transportation Infrastructure Program manager at Army Headquarters, Installation Management Command Public Works Division, “The Army has many timber bridges in use, often in remote training areas. Wood naturally degrades with environmental exposure, and this happens faster in harsh environments. The result of this degradation is a reduced load capacity or possible removal of the bridge, which can compromise critical training activities.”
The new recycled thermoplastic bridge at Fort Bragg will be equipped with sensors for remote monitoring to collect performance data. Photo courtesy of Army Corps of Engineers.
To date, thermoplastic composite lumber, commonly known as “plastic lumber,” has mainly been used in non-structural or low-stress applications such as park benches, picnic tables, and residential decking. But now structural-grade reinforced plastic lumber is an emerging technology for use in load-bearing construction. These materials do not contain any wood material and are inherently resistant to rot and attack by insects without the need for chemical treatments. Innovative plastic I-beam components were used to support the heavy loads and to provide a design that is cost-competitive to a treated-wood bridge designed to carry the same load.
We expect the advantages of the plastic lumber bridge will be lower maintenance costs and the ability to meet long-term training needs,” said Darryl Butler, civil engineer with Fort Bragg’s Department of Public Works. “The potential for this innovative material is only limited by the commander’s requirements and the mission.”
The DoD Corrosion Policy and Oversight Office program funded the plastic bridge’s design and the Army’s Assistant Chief of Staff for Installation Management paid for its construction and initial load testing. The DoD Corrosion Office also is funding continuous, remote monitoring for the load testing, the Army Bridge Inspection Team), along with its contractor Bridge Diagnostics, Inc., recorded measurements from various strain and deflection gauges mounted on the bridge. To complete the load testing, different types of vehicles, in addition to the M-1, crossed the bridge multiple times.
In addition to assessing the bridge’s structural performance under heavy loading, CERL is equipping the bridge with special sensors and video cameras to remotely monitor the durability of the thermoplastic materials for long-term use in such a bridge. This long-term remote-monitoring of the bridge is supported by funding from the DoD Corrosion Policy and Oversight Office program.
Achmar added, “A maintenance and repair budget is not always available to renovate deteriorated bridges. Also, if the same materials are used, the same degradation cycle begins all over again.”
“This thermoplastic bridge, able to withstand heavy loads with little to no maintenance, expected to last at least 50 years, is no longer the bridge of the future—it’s the bridge for today,” said Daniel J. Dunmire, OSD Director of Corrosion Policy and Oversight. “It also meets national environmental goals of being completely recyclable. This technology is not only good for DoD, but should be immediately transferred to state departments of transportation for use with short-span bridges wherever possible.”
Editor’s Note: A version of this article originally appeared in the ERDC Bulletin on July 3, 2009.