What you don’t know about rubberized asphalt by Mike Breslin
Today, recycling tires by grinding them down to crumb
rubber and mixing into asphalt formulations is finding
wider acceptance by more state Departments of Transportation
(DOT). And, as the price of oil goes up, so does the
interest in A-R.
A-R is defined by ASTM (American Society Testing Materials)
as a blend of hot paving grade asphalt cement, reclaimed
tire rubber and additives where rubber content is at
least 15 percent by weight of the liquid asphalt binder,
and has reacted sufficiently to cause swelling of the
rubber particles. Rubberized asphalt has less than
15 percent by weight rubber content. Both terms are
used interchangeably in this article.
Proponents of using old automobile tires to make A-R
claim that the practice is better than landfilling,
and cleaner than burning the tires as a fuel. Used
A-R can also be recycled endlessly by milling it off
roads and adding it to new asphalt mixes. According
to the Rubber Pavements Association (RPA), a 2-inch
thick overlay of A-R hot mix will consume about 2,000
tires per lane mile. In the spray applied method for
seal coats, about 500 tires are used in a lane mile.
Approximately 18 million tires are recycled annually
in paving applications.
One of the predominant uses of A-R is in Asphalt-Rubber
Open Graded Friction Course (AR-OGFC) To appreciate one
of AR-OGFC’s most outstanding qualities, you have to
drive on it. It’s much quieter than conventional asphalt
“A few years ago, we did a project that was a 7-mile
section on Interstate 95 near our Ewing offices. We received
dozens calls from drivers asking what is that stuff?
It’s great, the noise is less. People driving on it can
tell the difference over regular asphalt and they say,
‘Wow! What a big difference.’ It’s very unusual for us
to get that kind of positive public reaction,” said Eileen
Sheehy, manager of New Jersey’s DOT Bureau of Materials.
Mike Harrington, sales manager for CRM told a similar
story. His company has been supplying crumb rubber for
asphalt for over 20 years and is the largest crumb rubber
producer in the western United States. “Several years
ago, they paved about a quarter mile of Loop 101 in Phoenix
with rubberized asphalt. The people who lived next to
the freeway said things like: ‘What happened, it’s so
quiet?’ Then, the people in the next community asked
why they didn’t have it. There was such an outpouring
of demand, that over the next few years the state wound
up having to pave the whole thing.”
“With rubberized asphalt, we were getting about a three
decibel reduction in noise over conventional asphalt,
but over concrete you may get up to a ten decibel reduction.
And, that’s really significant,” said Sheehy.
According to NJDOT, tires on concrete pavement generate
between 100 and 110 decibels of sound, depending on the
age and surface texture. On conventional asphalt the
noise is in the high 90s to low 100s. Rubberized open-graded
friction courses are in the 95 to 97 decibel range.
Doug Carlson, executive director of RPA put it this way
– “Sound reduction largely depends on what method is
used to measure the sound. There are many different ways.
From feedback we have received from numerous wayside
data sources, noise reductions can be in the 40 to 70
percent range, depending on the preexisting surface type
A-R helps reduce noise emanating from tires at higher
speeds. At speeds over 35 mph, the predominant noise
is made by the tires. At lower speeds much of the sound
comes from the engine, exhaust and rattles. The quietness
of A-R is largely due to its smoothness. A Texas DOT
study found that ride quality improved by 61 percent
on A-R. Because this pavement lasts longer and cracks
less over time, smoothness is maintained. WesTrack, a
Nevada road test facility built under a grant from the
Federal Highway Administration, found a 4.5 percent fuel
efficiency increase riding on smoother pavements.
“What we are really trying to do is cut the noise at
the source,” said Sheehy. New Jersey has completed most
of the sound walls and barriers mandated by federal requirements
to mitigate noise pollution. Sound walls and other types
of barriers are expensive, costing between $200 to $400
dollars per linear foot. In many urban areas there is
not enough space to build them. “Now we are dealing with
what we consider nuisance noise – noise not high enough
for mandated sound barriers, but nevertheless bothersome
to residents. That’s why we put rubberized asphalt on
Route 280, because of noise complaints. It’s also useful
in areas where it’s very hilly, because we can’t always
build sound barriers tall enough,” Sheehy said.
“The noise benefit has been the unsung hero. It’s kind
of a perfect marriage between the business and the environment.
Here is something that is ecological viable and technologically
sound so it really turns out to be a win-win,” said CRM’s
According to the United States Environmental Protection
Agency (EPA), rubberized asphalt is the single largest
consumer of ground rubber. California and Arizona use
the most in highway construction, jointly accounting
for over 70 percent of crumb rubber used.
“Over 90 percent of state highways in Arizona are paved
with it. In California it’s huge. They don’t have good
data, but of 65,000 miles of roadway I would say that
about 20 percent has been rubberized at one point or
another,” said Carlson. Florida uses A-R exclusively
on every state highway for friction courses. Among others,
Texas, Nebraska, South Carolina, New York, New Jersey,
New Mexico, Maryland, Massachusetts and Puerto Rico are
currently testing or using A-R. In Canada it’s being
used in British Columbia, Alberta and Saskatchewan.
Naturally, each state DOT must test and approve various
formulations before general use. This can take years,
and in some cases decades. Like many states, New Jersey
began testing rubberized asphalt in the early 90s in
response to the Intermodal Surface Transportation Efficiency
Act of 1991 (ISTEA)
The act suggested there would be mandates for states
to use one percent rubber in asphalt in order to receive
federal funds. Later, the mandate was dropped, but ISTEA
had the effect of getting many states to test A-R. “We
did some projects at that time to see how it would work.
Two projects were quite successful using asphalt rubber
in an open-graded friction course. There are benefits
with the open-graded friction course. It has a very open
texture so it drains very well. You don’t have as much
spray off the surface in rainy conditions. Because you
do not have as much water on the surface you don’t get
as much hydroplaning. So it’s safer in the rain. We identified
that as a very valuable asset for those areas that have
high wet-weather accidents,” said Sheehy.
New Jersey’s oldest project, a short test section of
Route 195, was constructed in 1992 and is scheduled to
be removed and replaced this year. Like conventional
asphalt, when a rubberized road reaches end of life,
it can be milled up and recycled into new mixes of A-R,
or into new mixes of regular asphalt. “We did a project
back in 1991 where we took an asphalt rubber road and
recycled it. We tested the emissions and properties of
the mix and found no problems with recycling. It can
go to an asphalt plant and be mixed in with unrubberized
asphalt. We are confident that the percentage in the
mix after reprocessing won’t make any difference at all,”
New Jersey uses between 15 to 20 percent crumb rubber
in the asphalt binder, which constitutes about 8 percent
of the overall pavement mix. The state uses conventional
asphalt plants and paving equipment, but out-of-state
blending units are currently being trucked-in to make
A-R. Sheehy said that New Jersey asphalt producers are
waiting to see how A-R develops before investing in equipment.
The A-R on Route 195 lasted 18 years as compared to the
average 12 year life expectancy of non-rubberized Open
Graded Friction Course. New Jersey is planning to use
more AR-OGFC because of its durability. Sheehy commented
on 195: “It’s lasted longer than expected. We have been
happy with that performance and believe it justifies
the increased cost.”
In Phoenix, A-R is only about 5 percent more expensive
per ton than conventional mixes. “An interesting thing
has happened as a result of recent economics. As the
price of asphalt per ton increases, the cost saving value
of recycled tire rubber in the asphalt increases. The
crumb rubber market has been steady and stable at about
$300 dollars per ton. Back in the late 90s, liquid asphalt
cost about $70 dollars a ton. Now it costs $500 a ton!
By using crumb rubber there is about a 20 percent displacement
of oil,” said Carlson.
Despite the higher initial cost in other states, RPA
claims other significant cost savings based on several
factors: longer life cycle, decreased maintenance, and
in many instances half as much material is required.
“[California Department of Transportation] has a layer
equivalency guideline for rubberized asphalt based on
almost 30 years experience. If the conclusion is to give
a roadway a 10 year service life, you can pave it with
four-inches of conventional asphalt, or use 2 inches
of rubberized asphalt and expect the same results,” said
CRM’s Mike Harrington.
There are climate and topography issues related to the
use and they can vary greatly from state to state. Each
area must test and evaluate which formulations best suit
their roadways and conditions. Warmer weather in Arizona,
California, Texas and Florida has undoubtedly led to
heavier usages there. But A-R has been tested and successfully
used in many cold regions.
Arizona routinely uses a combination of gap-graded A-R
hot mix and an open graded A-R friction course in the
Flagstaff area at elevations over 7,000 feet with winter
temperatures of 20 below zero. California has also successfully
used A-R in the high Sierra Nevada Mountains. “In 1992,
one of the very first California highways using rubber
was at Donner Pass. At over 7,000 feet elevation and
snow up to 30 feet, it has held up beautifully. It was
recently repaved using rubber,” Carlson noted.
New Jersey, however, is working on the issue of snow
and ice removal. They found that salt seeps into the
pores of the open-grade and does not stay on the surface
and continue to work. This resulted in the need for more
frequent salt applications. “Unless that issue is resolved,
we will probably see it only in areas that we identify
as either a wet weather problem, or a noise problem that
we want to mitigate. Our maintenance people are looking
at different snow and ice removal techniques. We are
also considering a slight change in the gradation, porous
enough to work well in wet weather, but not as porous
to work well in ice and snow.”
NJDOT has more asphalt rubber projects planned for 2010.
“Generally, we are optimistic about rubberized asphalt.
It has been performing well for us and I think we are
going to be using it more,” concluded Sheehy.