Asphalt a la Carte

Modifiers Control Mix Performance

Petroleum (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.

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 value-added 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 high-value 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.”

Individual refiners also are using a wider variety of crudes, and this has led to increased variability of asphalt. “There are well over a hundred crude oil fields that are being accessed in North America, and each one is chemically a little different, so the asphalt you make out of it is chemically different,” Kluttz says. “They each will respond somewhat differently to modification. Consistency is the issue. The binder supplier’s concern is having that tanker show up day after day and having exactly the same material in it, month after month.”

One asphalt contractor was quite blunt about the situation. “The quality of the available liquid asphalt has changed,” he told Better Roads. “The asphalt is not as good as it used to be, in my opinion. That all changed as plastics evolved. We’re trading plastic water bottles for good asphalt, and now we’re adding plastic and rubber back to the mix.”

Polymer Modifiers for Asphalt

That contractor is describing the trend to add polymer modifiers to liquid asphalt to improve its performance.