Industry executives discuss rubberised asphalt, recycled tires

Akron, Ohio — Industry executives have called for better use of crumb rubber taking an active voice in the ways to mix and lay rubberised asphalt.

The topic of crumb rubber was discussed at length during the International Tire Exhibition & Conference for manufacturers in Akron in September.

Historically, the cost of crumb rubber has been more expensive than using other polymer sets in asphalt, but the tide seems to be turning, and more benefits are emerging with the use of crumb rubber.

“In general, in order to convince a customer to move to a recycled content product, usually that product has to cost less, has to perform better and needs to be recyclable itself,” said Douglas Carlson, vice president asphalt products at Liberty Tire Recycling.

Previously, rubber cost more than asphalt. In August of 1990, Carlson said, asphalt cost about $100 a tonne, then gradually increased as the cost of oil, an ingredient in the asphalt, increased.

“So now it’s very economical to put rubber in asphalt,” he said. “Rubber costs about half of what asphalt costs today.”

When creating rubberised asphalt, the product needs to be recyclable, he said, in order to prevent problems downstream. While rubberised asphalt has not always been able to meet these objectives, Carlson said it finally does.

He continued to say that “a lot of science goes into” the rubberised asphalt technology, adding: “It is an engineered material, and you can’t just throw waste product to asphalt and expect a good performing pavement.”

With the process, there are keys to quality control, such as using a paving machine and a roller on the road. This prevents cracks, he added, and reduces maintenance on the road over time.

He also played down as “a myth” the idea that rubberised asphalt only works in hot climates, saying:

“The important part is just the temperature at the time you place the pavement,” he said. “You can’t place it when it’s really cold out,” he said.

New technology

Redmond Clark, CEO of CBL Industrial Services, said not an enormous amount of attention is being paid to recycling or moving the EPA’s hierarchy. It is more focused on getting problems out of the way, then letting the markets develop on their own.

Currently, about 57-60 million tires are being used for crumb rubber, domestically, Clark said, and of that, about 10 percent is being used in asphalt. He said other opportunities exist to push more rubber out of less green ways, such as disposing or burning applications, into more productive use.

There are two processes for using crumb rubber in asphalt—a dry and a wet process. The wet process involves mixing the rubber in the liquid asphalt before it’s mixed with the aggregate, and then it is treated, etc.

The dry process, known as the plant process, involves mixing the rubber and the asphalt together simultaneously. The mixture does not need to sit to digest any amount of time, Clark said.

With a wet process, he said, the higher the percentage of rubber, the stickier the product is, thus special equipment is needed to lay it down. However, if the amount of crumb rubber in the mix is reduced, standard application equipment can be used.

No special equipment is needed with the dry mix process, Clark said.

Clark said the days of wondering whether rubberised asphalt works are over. As long as some guidelines are followed, the compound will be successful.

Revolutionising the way

Edgard Hitti, director of asphalt technical services, Paramount Petroleum Corp., said that this process has been an evolution. It began more as an experiment, but it has grown to become more high tech than just blending two components together for pavement.

It has grown from a simplified processes, to using a performance-graded material that consists of engineered properties and uses computerized equipment.

Paramount produces its product in asphalt terminals. Hitti said his firm incorporates the tire into the binder so it creates 100 percent liquid for the rubberised asphalt. It takes the tire rubber, which is a solid component, and the liquid component together. This type of mix has opened a lot of doors, he said.

Hitti said it is imperative to recycle a tire, since it has many expensive components and so much technology is used in its production.

While rubberised asphalt is not yet the main source for recycled tires, experts say it is continuing to grow across the US, and they expect this trend to continue.