NEVER HEARD OF PERPETUAL PAVEMENT?
BY FRED F. FRECKER, P.E.
Today's asphalt pavement already lasts a long time. With surface
maintenance it can last more than 30 years. In fact, no full
depth asphalt pavement on Ohio's highway system has ever needed
to be replaced. Commonly it is a failing joint in the base below
some asphalt pavements that leads to major rehabilitation. That's
what keeps the orange barrel manufacturers in business, and
the rush hour drivers clenching their fists.
"The problem is the industry has designed pavements to
fail," said Dr. Marvin Traylor, director of engineering
at the Illinois Asphalt Paving Institute. "We design a
pavement to handle X number of loadings before it will finally
need to be replaced. Perpetual Pavement will be designed never
to exceed a critical fatigue level and therefore never to fail.
With surface maintenance, these pavements will truly last a
lifetime, taking a significant bite out of traffic delay in
This increased durability will be accomplished through the
use of mechanistic design. In a mechanistically based pavement,
designers analyze how traffic strain will affect the pavement's
performance, taking into account material qualities and thickness.
By designing the pavement to keep strain below the critical
level, fatigue failure is avoided and perpetual performance
can be assured. Structural and aeronautical engineers have used
mechanistic design principals for years. It's only a matter
of time before it's the standard in the paving industry.
Through the use of mechanistic design, each layer in Perpetual
Pavement's 3-layer system will be tailored specifically to local
climate and traffic conditions. The base layer will be made
of flexible fatigue resistant asphalt, designed to resist bottom-up
fatigue cracking. The middle layer will be made of high modulus,
rut resistant asphalt, formulated to support expected traffic.
The surface layer will be made of SMA, OGFC or Superpave, and
will be designed to eliminate rutting, reduce splash and spray,
absorb noise and hold up to local weather and traffic conditions.
The combination of the three layers will force distress to
the surface layer, where it can quickly be maintained at a low
cost. The surface will be milled off, recycled, and replaced.
This means that improved surface mix design can be incorporated
into an existing Perpetual Pavement as it is developed over
Perpetual Pavement will also provide a consistently smooth
and quiet ride. As traditional pavements approach the need for
major rehabilitation the ride quality, or "serviceability,"
deteriorates into bumps and thumps, until the pavement needs
to be overhauled, once again delaying traffic. With Perpetual
Pavement, surface maintenance in off-peak hours will keep the
serviceability level close to perfect throughout the life of
the pavement, without traffic delay. This means drivers will
enjoy a perpetually smooth and quiet ride.
While there are currently no Perpetual Pavements in service
in Ohio, there are plenty of deep strength asphalt pavements
from which we can draw meaningful data, since Perpetual Pavement
is essentially an improvement on the existing deep strength
asphalt design. Flexible Pavements of Ohio commissioned a study
of adjacent deep strength asphalt and concrete pavements. The
selection of adjacent pavement sections ensured identical weather
and traffic conditions. The study found that the asphalt sections
had a lower life-cycle cost, required less maintenance and were
a better value to taxpayers. In fact, all of the asphalt pavement
sections studied are still in service, some for as long as 40
Deep strength asphalt pavements have been widely used in Europe
for years. A recent study conducted by the Transport Research
Laboratory in England concluded that in pavements thicker than
8 inches, rutting and cracking was confined to the top layer
- where it is easily milled off, recycled and replaced.
These reports show us two things: Thick pavements perform better
than thin ones; and when it comes to choosing a pavement that
will last a long time, asphalt is the answer. Studies of this
nature led the industry's top researchers to deep strength asphalt
as the starting point in designing Perpetual Pavement. By incorporating
mechanistic design and segmenting the pavement into three distinct
layers, Perpetual Pavement begins to take shape.
Engineers from the University of California at Berkeley constructed
a segment of Perpetual Pavement and, using an accelerated load
tester, were able to simulate years of traffic strain. The results
of these tests helped CalTrans engineers evaluate material qualities
and thickness for use in the rehabilitation of I-710, the Long
Beach Freeway. The partnership between these two organizations
led to the development of a strategy to convert this California
highway into a Perpetual Pavement.
Dr. Marvin Traylor of the Illinois Asphalt Paving Institute
assisted an Illinois Department of Transportation task force
in developing a strategy to make Illinois' existing deep strength
asphalt pavements perform perpetually. Dr. Traylor's research
and recommendations helped the task force develop design plans
for I-70 in Clark County and will be used as a road map for
other states building Perpetual Pavements. Construction of the
first Perpetual Pavement in Illinois is slated to begin in 2003.
Perpetual Pavement is not just a wild-eyed look into the future.
It's here today, with projects happening in California, Michigan,
Texas and Illinois. Discussions with the Ohio Department of
Transportation indicate that a pilot Perpetual Pavement project
in our own state may be a reality in the near future. Perpetual
Pavement's lifetime guarantee will take asphalt's advantage
in cost, convenience and comfort to the next level - something
the orange barrel manufacturers may not be so happy about.
Fred Frecker is a Professional Engineer, and is President and
Executive Director of Flexible Pavements of Ohio.
Back to the Top