ROAD SCIENCE: Part One: Asphalt Modifiers
RoadScience
by Tom Kuennen Contributing Editor
A
SPECIAL
SERIES
The Chemistry
of Road Building
Materials
Asphalt a
la Carte
Modifiers Control
Mix Performance
P
etroleum (literally, rock oil) is one of the
most important gifts of the union of carbon
and hydrogen. But instead of being a simple
compound (like water), petroleum is a natural product, a complex “soup” of thousands of hydrocarbon
compounds, the mix varying according to source. The
never-ending variance of the makeup of petroleum
challenges the refiner, who must adjust the refining
process to optimize extraction of the valuable components of petroleum.
16 April 2012 Better Roads
Liquid asphalt binder might be thought of as the
sludge left over from petroleum after higher-revenue
products such as gasoline, plastic feed stocks, kerosene
and petroleum distillates have been removed. About 3
percent of a barrel of petroleum (42 gallons) winds up
as liquid asphalt.
“Asphalt literally is the bottom of the barrel,” says
Codrin Daranga, Ph.D., technical manager, Blacklidge
Emulsions. “It is the waste left over at the bottom of
the distillery after more valuable hydrocarbons have
been extracted. At one time refineries would give away
the liquid asphalt for the price of transportation, just
so they would not have to deal with it. Now there is
such a need – with so little liquid asphalt available –
that we pay top dollar for it.”
As the demand for gasoline and plastics have increased, refineries have gotten better at removing those
“light” products from the source crude. As those valueadded products are removed, the “richness” of what’s
left over as liquid asphalt is diminished.
“The industry has gotten better at refining petroleum,” Daranga says. “It stands to reason that more
valuable product has been extracted than ever before,
and there is less in the remaining liquid asphalt. But
it depends on the refinery. Some refineries are geared
almost entirely to making gasoline; that’s what they’re
designed to do. There will be very little asphalt from
those plants, and it won’t be very good. For them
asphalt is a waste and they will do everything they can
to minimize that waste.
“But there is another kind of refinery that is geared
only toward making asphalt,” Daranga says. “Its business model is to make asphalt, so that end product will
be quite good.” Such a dedicated refinery in Louisiana
is scheduled to come online this year.
“Without a doubt, over the last 20 to 30 years,
refiners have gotten better at extracting all the highvalue materials they can out of the source crude,” says
Bob Kluttz, senior scientist, research and development,
Kraton Polymers. “This includes a variety of technologies, different distillation and extraction techniques as
well as coking. You can take asphalt that once was $100
to $200 a ton, and turn it into light ends and gasoline
which sell for much more.”