What is Crumb Rubber Modified Asphalt?

Redmond Clark, president of Asphalt Plus L.L.C. spoke at the 34th Clemson University Global Tire Conference in regards to the benefits of using Dry Process crumb rubber modified asphalt.

 “The window of opportunity is open, but it won’t remain open, because more aggressive industries will beat us to it,” said Redmond Clark.

 With more than 50 percent of all recycled rubber being used in non-sustainable markets, CRM using crumb rubber from recycled tires seems like a natural choice for all stakeholders, according to Clark. Nevertheless, only about 120 million pounds of recycled rubber is used for CRM every year—2 percent of the market potential. Clark said there are multiple reasons for this. CRM has never really lived down the debacle of the Intermodal Surface Transportation Efficiency Act in the early 1990s.

ISTEA required state highway agencies to use an increasing percentage of CRM in highway projects as a prerequisite of receiving federal highway funds.

However, states tried pilot projects without really understanding the technology, and the results were so disastrous that highway officials rebelled. The crumb rubber modified asphalt provisions of ISTEA were repealed after a few years. “Rubber has been burned with a black mark ever since,” Clark said.

The “terminal blend” CRM technology from ISTEA days remains unpopular with customers, according to Clark. “The mix sticks to their equipment, and they have trouble keeping the rubber particles suspended because they can’t melt,” he said. “Terminal blend asphalt can’t compete,” he said.
To get recycled rubber into asphalt, the rubber recycling industry needs to listen to the customers, according to Clark.

crumb rubber modified asphalt
Dry Process Project

To get recycled rubber into asphalt, the rubber recycling industry needs to listen to the customers, according to Clark.

“What the customer is saying is, ‘Give me pavement performance at least as good as SBS, make the material compatible with my plant, and charge less than SBS,’ ” he said.

Fortunately, dry process rubberized asphalt addresses those customer needs.

Clark said it uses a chemically engineered crumb rubber that is added like an aggregate during asphalt mix production. “Like a fine sand, the crumb rubber is blown into the process,” he said. “Plants see no difference in processing from regular asphalt.”


The dry process uses the heat from mix production to activate the rubber. The process improves the mix quality, eliminates the need for special handling, and is Dramatically less expensive than either terminal blend or SBS.

Among other things, dry process mix is more workable at low temperatures than other technologies, according to Clark. “We can extend the season when we can lay asphalt,” he said.

Dry process CRM has been in the field 15 years, approaching 4 million tons placed to date.

“We should be looking at ways for the tire industry to accelerate the adoption of this technology in the marketplace,” he said. “The specifications get changed because individual players band together and demand change.”

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Rubberized Asphalt Project