 |
| Locomotive on a bridge made of recycled plastics |
Transportation officials dismayed about the nation’s decaying bridges
are turning to the bottle to find relief. And it’s helping.
The solution isn’t what’s in the bottle, it’s what the bottles are
made of, where they came from, and what they’re capable of doing.
Discarded plastic beverage bottles, milk jugs, detergent containers, and
other household plastic trash can become, through the magic of
materials engineering, a totally green building material for new bridges
and other infrastructure upgrades.
:
Non-biodegradable thermoplastics are anathema to our nation’s
waste-management system. Improved recycling programs have reduced the
sheer volume of plastic in landfills, but there’s still the problem of
what to do with all of that recycled material. The supply of
second-generation plastic far outstrips the demand. Recycled structural
composites (RSCs) based on technologies developed at Rutgers University
and commercialized by Axion International, New Providence, NJ,
transform mountains of melted down and remolded plastic waste into an
all-green building material for heavy-duty infrastructural projects.
The U.S. Army was an early adopter of the new material, in part
because it has regulatory autonomy over the infrastructure on its bases.
Since 1998, the Army has been driving jeeps, tanks, and trains over
short-span plastic bridges at forts Leonard Wood, Bragg, and Eustis,
providing case data that is driving the technology’s acceptance in civil
projects in both the U.S and Europe.
In 2011, for example, the company completed the first plastic
vehicular bridge in Europe, a 90-foot span over the River Tweed near
Edinburgh. The pre-fabricated bridge was shipped in six sections to
Scotland, where crews rapidly reassembled them. “We were able to
complete construction on-site in just two weeks,” said Steve Silverman,
Axion’s president and CEO. Putting the pieces together, in fact, took
only four days out of that process, he said. “The remarkably fast
erection time for a 90-foot bridge is a major benefit.”
 |
| Assembling a plastic vehicular bridge over the river Tweed |
|
|
The degradation of the U.S. infrastructure is not a new problem, and
bridges are one of the areas of gravest concern because of the obvious
health and safety issues associated with a potential bridge collapse.
Although the nation’s bridges fared much better than schools, roads,
levees, and most other categories graded in the American Society of
Civil Engineers’ most recent Report Card for America’s Infrastructure,
they still only eked out a C. With one in four bridges either
structurally deficient or functionally obsolete, and a $17-billion
annual price tag for necessary improvements, there’s little question
that transportation officials will take interest in any technology that
offers a lower-cost alternative to traditional steel and concrete
construction.
Converting Garbage to a “Gar-Bridge”
The process of manufacturing the RSC materials is straightforward.
Axion receives giant bundles of sorted plastic – it has to be
high-density polyethylene, the kind stamped with a #2 recycling code.
The plastic is comingled with the other principal component, glass
fibers coated in polystyrene or polypropylene, generally scrap material
from the manufacture of car bumpers.
The raw materials are ground into tiny flecks, then subject to high –
but below melt point – heat. The precision of the heating process is
critical to getting the otherwise incompatible properties of various
polymers to work together to form a stronger material. The hot glop is
extruded through molds into its specified shape and allowed to cool.
The company forms its thermoplastics into standard construction
shapes such as I-beams, pilings, and boards, and also can pre-build an
entire bridge or boardwalk to a customer’s specifications. Thomas
Nosker, Ph.D., the Rutgers materials engineer who pioneered the
technology, has said the individual pieces “come together like a child’s
play set” to form bridges that are cost-efficient and easy to erect.
High-Performance Assemblies
Engineers have been experimenting with composite bridges made of
space-age carbon-fiber-reinforced polymeric materials since the
mid-1990s, and efforts have focused on high-performance assemblies
engineered for specific performance properties. Their performance,
however, suits them well toward applications in new construction and
retrofits in earthquake-prone
regions, harsh marine environments, or other situations where the
long-term durability will offset their higher first costs, according to
the U.S. Federal Highway Administration. But these advanced composite
structures require exotic raw ingredients and specialized fabrication
methods that drive the price up.
According to Axion, the lion’s share of the plastic bridge market is
on the nation’s secondary roadways where spans of 15 to 25 feet are
commonplace. From a performance standpoint in those applications,
thermoplastics won’t rot, rust, splinter, crumble, or attract bugs like
wood, steel, or concrete. They are lighter, don’t need to be painted,
and require no special tools or training to install. The initial cost of
building a plastic bridge is about the same as a similarly sized
traditional structure, but they are cheaper over their 50-year expected
lifespan because they avoid these costly ongoing maintenance
chores. State transportation officials concerned about the public
perception of plastic as a flimsy material are heartened by military
videos showing the bridges holding their own against 70-ton tanks and
120-ton locomotives.
Axion’s Silverman said the company is developing other infrastructure
applications for the STRUXURE components, including sound walls,
retaining walls, marinas, jetties and piers, culverts, and platforms.
The Container Recycling Institute counts approximately 1,755 thousand
tons of HDPE sold annually in the United States, meaning there is likely
to be a sustainable supply of raw materials for this emerging sector of
the sustainability market.
Source : http://www.asme.org/kb/news---articles/articles/construction-and-building/trash-bridges
