Rubber pavement progresses
The Rubber Pavements Association
(RPA) has been a strong advocate
for use of tires in asphalt concrete
mixes for highway construction
in the United States and its
advocacy efforts are paying dividends.
American Recycler recently spoke
with Doug Carlson, executive
director of the RPA, to learn
the latest on technological developments
and what more can be done to
have the road construction industry
play a greater role in the recycling
What type of technological advances
have been made in terms of the
use of rubber from tires in asphalt
Carlson: There are two sides
to the industry, tire recycling
and asphalt-rubber manufacturing.
Generally speaking, the whole
tire processing industry is still
relatively new, having gone “mainstream”
in the mid 1990s, and there has
been some good advances.
On the asphalt side, material
property tests and standard specifications
used by the city, county and
state paving agencies have better
defined the technology to generate
consistent performance of the
pavements in the field.
The common usage today is about
20 percent tire rubber and 80
percent asphalt cement used as
a binder for asphalt concrete
(8 percent binder and 92 percent
rock) surfaces in the top one
to two inches on a roadway.
The blending equipment used to
combine the solid tire rubber
particle and the liquid asphalt
cement has advanced tremendously
since the 1970’s when the first
roads in Arizona were paved.
Computer controls have been a
great help and more accurate
meters, scales and heating efficiency
have boosted the quality for
mass production and large-scale
A new technology used to measure
tire/pavement noise called On
Board Sound Intensity (OBSI),
where a microphone is mounted
to a vehicle and tuned to a tire
as it drives on the highway,
has really demonstrated the long-term
performance of rubber pavements
with respect to overall traffic
noise. At speeds of 45 mph and
greater, the tire noise on automobiles
can be over 75 percent of the
total traffic noise.
This new technology gives the
pavement maintenance engineer
an effective tool to control
and lower traffic noise impacts
on the community along the entire
length of the highway instead
of hundreds of spot checks along
the side of the road, which is
the current technology.
Is the use of tires in various
mixes of asphalt concrete increasing
Carlson: The use of tire rubber in asphalt is increasing. The very positive field performance of roads constructed using the proven standard specifications has caught the attention of many engineers outside of Arizona, California, and Texas where tire rubber has been routinely used for 10 to 40 years.
Growth in the United States has been about 10 percent each year, but outside the United States it has been much higher. For example, the market in China five years ago had little or no producers and now there are reportedly over 20 blenders in that country (the United States has about 30).
Is government helping or hindering
the campaign to promote the
use of tires in highway construction?
Carlson: I don’t see anyone
hindering the process, but
policies such as the Noise
Policy are very slow to change.
If the United States policy
were to change and allow states
to use rubber to control noise,
every state would use it within
What is being done to lobby
highway construction companies
to use tires in their mixes?
Are they lobbying for the increased
use of tires as material?
Carlson: Most highway construction
companies spend most of their
time just building what the
paving agency specifies in
the construction contract.
They would use tire material
if a project specified it for
use. So the key is the specifier,
or designer of the project.
Individual companies that have
invested in the asphalt-rubber
blending equipment often do
valued engineering proposals
for projects that are not currently
specifying tire rubber. The
value engineering proposal
shows either the cost saving
upfront, through a reduced
thickness application, or a
life cycle cost savings where
the road maintenance can be
reduced by $20,000 per mile
over twenty years because the
tire material is so effective
at stopping cracks.
Highway construction is an
extremely competitive business
and those that see the advantages
of using tire rubber and how
the market can grow in their
area can grab the public domain
technology and really run with
it and have a competitive advantage.
However, those companies that
don’t want to invest may wish
to push the potential rubber
Some asphalt refining companies
have created asphalt materials
where the tire rubber is completely
dissolved in the liquid asphalt
and they have done some damage
to new markets creating much
confusion in the engineering
community. Engineers are expecting
asphalt-rubber, but get something
Should government introduce
legislation to set quotas for
the use of tires as road construction
material? What type of tax
incentives and credits should
Carlson: The RPA advises against
mandates or quotas and has
dedicated the last 10 years
or more to training and education
for engineers so that they
voluntarily choose to use asphalt-rubber.
An engineer out of Texas once
told me that “the best way
to build a road is to keep
the water out of the base material
and the politics out of the