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Re: conversion of disposed tires into energy



Here's another use for waste tires (courtesy the NPS Info list server).
Kelly Moran
TDC Environmental
___________________________
::: Arizona State University Research Finds Recycling Cure For Used
Tires
  Source: Arizona State University News Release , September 13, 2001.
Imagine for a moment seeing 5 million worn tires heaped up in a pile:
That
is roughly the number that Arizonans produce each year-one tire for
every
man, woman and child. How to dispose of all those used tires without
causing
serious environmental hazards used to have state officials scratching
their
heads, but one ASU researcher believes has an answer. Civil and
Environmental Engineering Assistant Professor Han Zhu says adding a
small
amount of the inexpensive crumb rubber to fresh concrete can improve
strength and durability. Crumb rubber is the end result of grinding used
tires into one-millimeter chunks. One tire produces about 10 pounds of
crumb
rubber and sells commercially for less than 20-cents per pound.
  While Zhu is not the first researcher to experiment with adding the
tire
bits to Portland cement concrete or PCC, he does own rights for the
first
"real world" application, a section of sidewalk on the ASU Main Campus
in
Tempe. "This is my baby," says Zhu of the sidewalk between the Memorial
Union and the campus bookstore. He bends down to get a closer look.
Black
flecks of rubber sparkle in the morning sun. "I have been coming out
here to
examine this sidewalk for two years. Most people think I am just a guy
looking for pennies," he jokes.
  Zhu began to explore uses for crumb rubber in 1998 with a grant from
Arizona Department of Environmental Quality. His research, however came
to a
screeching halt soon after because he could not find a natural
environment
as an experimental site, a critical step in testing new materials prior
to
certification. The researcher said few people were interested in using
the
new material because there was no guarantee of success. As luck would
have
it, Zhu found a test site in his own backyard.
  In February 1999, Zhu personally added 200 pounds of crumb rubber to
the
concrete mixture being prepared for the ASU site. He says the ratio of
crumb
rubber added to the mixture equated to about 8 percent of the cement
weight.
  Prior to Zhu's research, similar lab studies were not encouraging for
the
waste product. Earlier research showed that adding crumb rubber to
concrete
would lower the overall compressive strength, the major criterion used
in
designing PCC. Contrary to earlier research, Zhu's study showed adding
the
crumb rubber into PCC actually produced several benefits that would
compensate for the loss in compressive strength, particularly for
projects
that are not considered loadbearing. These benefits include reductions
in
thermal expansion, also known in Arizona as Summer Fatigue, along with
reductions in drying shrinkage and brittleness. The recycled rubber also
shows promise in ending the crumbling associated with freeze and thaw
damage
in colder climates.
  Zhu says these benefits alone significantly improve the overall
durability
and serviceability of PCC. More recently, the researcher made new
advances
in restoring the compressive strength level of crumb rubber PCC to
specifications by simply adding a small amount of gypsum to the mix.
Grounds
Construction Supervisor Andy Castillo said from his own observations of
the
ASU project, the crumb rubber PCC appeared to avoid cracking better than
its
original counterpart. "I'd be willing to use it again in another campus
project," he said.
  According to the Arizona Cement Association, within the Phoenix metro
area, some 12,000 cubic-yards of PCC are produced each day. By
conservative
estimates, if just 20 pounds of crumb rubber per cubic yard of fresh PCC
were added, all 5 million scrap tires produced annually statewide could
be
recycled into stronger and more pliable PCC for use in sidewalks,
parking
lots and concrete floors. This past May, Arizona Department of
Transportation used the new PCC technology to constructed a 12-foot by
12-foot parking lot at its Phoenix Division site using 50-pounds of
crumb
rubber per fresh cubic feet of PCC. Quality monitoring is still in
progress,
but Zhu says, so far so good. "It appears crumb rubber deserves public
attention and more crumb rubber PCC structures should be built. This
way,
time and nature can help determine additional benefits this technology
can
bring to our communities," Zhu said.