Finely tuned asphalt mixes may reduce roadway wear
 n the 1950s, Route 66 set the standard for the
lazy, laid-back way in which travelers meandered from Chicago to Los
Angeles and points in between. At the same time, a landmark highway-pavement
study in Ottawa, Illinois, set design standards for the types of pavement
on which truckers and tourists traveled the country for years to come.
Now, nearly 60 years later, an ever-increasing army of car and truck
drivers pounds the pavement—less to have a good time than to make
good time—and highway pavement materials like asphaltic concrete
aren’t bearing that load.
“The conventional asphalts are not meeting
our needs—and the problem that we face is that the refineries
cannot easily produce better asphalts,” says Professor Hussain
Bahia. “There are limitations on their equipment, economics,
and their procedures that limit the capability of modifying asphalt
at the refinery.”
In response, an emerging secondary market now offers
a massive menu of asphalt modifiers designed, in theory, to boost the
performance of asphalt pavement. Bahia is an expert in determining which
additives work best. “There is a need, not only for evaluating
new materials for their initial performance, but also for how they resist
damage,” he says.
With funding from the Federal Highway Administration,
the National Cooperative Highway Research Program, the Wisconsin Department
of Transportation, and private industry, Bahia’s group draws on
laboratory simulation tools that, in a matter of hours, replicate years
of roadway wear and tear. “We bring the bigger world into our
lab and try to simulate the exact climate and traffic conditions and
give an assessment of how the material will perform,” he says.
The simulation tools enable his group to evaluate such pavement damage
as wheel-path rutting, fatigue cracking, and thermal cracking. “We
can show anyone who might be interested that additives can be used to
enhance resistance to all of these distresses that result in closing
the roads for replacing or maintaining them,” he says.
Key to this research is new National Cooperative Highway Research Program
software that enables highway engineers to analyze specific pavement
and additive choices and predict roadway response. “The demand
from climate and traffic and the new software is really opening the
opportunity for scientific advancement in producing better asphalts,”
says Bahia.
Bahia also studies ways that modified asphalt mixes can contribute to
safer driving conditions. For example, during a rainstorm, a porous
asphalt mix can drain water through the pavement, reducing the likelihood
that drivers will skid on slick, puddled roadway surfaces. Though porous
asphalts are not new, Bahia’s studies focus on “sustainable”
asphalt choices, or those that last longer and require less repair.
In addition, he and colleagues are studying how to use additives to
decrease asphalt production temperature—and cut down on noxious
fumes—during road construction. At room temperature, asphalt is
a semisolid. To build a road with it, construction crews need heat the
asphalt only to the point that they can roll it smooth. This new, more
environmentally friendly asphalt is called warm asphalt mix and the
UW-Madison group is helping to define the effects of certain additives
on the mix temperature.
Ultimately, Bahia’s research enables asphalt manufacturers to
develop new and improve existing asphalt additives. The results also
provide state departments of transportation the information they need
to customize asphalt specifications for specific conditions, like roads
with frequent heavy truck traffic or those that experience wide temperature
swings. “We give them very specific information about how we think
the material is improving the asphalt, and by how much,” he says.
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