Executives talk best practices in crumb rubber

AKRON—While using crumb rubber with asphalt is not a new technology, it is increasingly being used around the U.S., as states take an active voice in the ways to mix and lay rubberized asphalt.

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.

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

Rubberized asphalt takes the place of something else, such as a polymer.

“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.

The use of rubberized asphalt began in 1966 as a patching material, Carlson said. Charles McDonald worked for the city of Phoenix as an engineer and was interested in using tire buffings from a local retreading plant to use as a patching material with asphalt. The mix was about 30 percent rubber at the time.

He tracked the performance of the road, Carlson said, and in some cases, the patch performed better, and in some areas, ended up as the only thing left on the road. Carlson said McDonald then started looking for other opportunities to use this material, especially in Phoenix, where the dry environment can cause materials to crack easily. This led to this material being used as chip seals, and the industry later started making machines that could spray the hot, rubberized asphalt.

Previously, rubber cost more than asphalt. In August of 1990, Carlson said, asphalt cost about $100 a ton, 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 rubberized asphalt, the product needs to be recyclable, he said, in order to prevent problems downstream. While rubberized asphalt has not always been able to meet these objectives, Carlson said it finally does.

For instance, Liberty Tire Recycling collects tires from around the country from tire dealers, etc. Either the company goes out to pick these tires up, or they send someone to pick them up and bring them back to Liberty's plants so it can shred the tires.

“A lot of people just think, ‘Well it's no big deal. You just throw rubber into asphalt, right?' No, no. It's not that at all. There's a lot of science that goes into it,” Carlson said.

He related it to baking cookies, where it is all the same basic formula. A person can still combine flour, butter, etc., “but you tweak some of the ingredients a little bit, and you get a different result.

“It is an engineered material, and you can't just throw waste product to asphalt and expect a good performing pavement,” Carlson said.

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.

A myth about rubberized asphalt is that it only works in hot climates, Carlson said.

“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.

It must be placed at 45° Fahrenheit or warmer.

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.

He said there are a few “asteroids that are approaching this market.”

A new generation of environmental regulations will come into the tire manufacturing industry that are going to spill over into the tire recycling industry, Clark said. Additionally, some fundamental changes will impact the U.S. economy as well as the global economy.

“So when we talk about climate change, you have to understand that climate change really isn't just climate change,” Clark said.

“It is a recognition that sustainability now has got to be a part of every corporation's ethic in operations.”

Clark said the population is growing so much that a city the size of Chicago could be “built every three weeks for the next 35 years to keep up with what's already in the cards for population development.”

As the global middle class continues to rise, demand will increase on all the environmental systems, he said. Sustainability initiatives recognize that the world cannot tolerate growth as it is occurring and limits carbon fuel.

This will impact the tire manufacturing industry because carbon fuels are going to make for lighter cars, Clark said, which means the tires are going to last longer.

“It is going to change where tires go when they are done,” he added.

The supply side of the tire industry will be affected, as well as the waste disposal and recycling side.

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.

“We have to find a way to make these systems work and find a way to get them adopted by a large number of states,” he said.

Clark said that learning what the customer wants is important. One large customer of the rubberized asphalt market is the state departments of transportation.

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 rubberized asphalt works are over. As long as some guidelines are followed, the compound will be successful.

“The markets … tell us what we're doing right, and what we're doing wrong,” he said.

For instance, the state DOTs can dictate what processes can be done on the roads. Clark said in California, the state has decided that rubber should be used in asphalt, period. Other states agree, while others have decided to let the market sort it out.

In 2006, Florida's DOT decided to use rubber in asphalt, Clark said. It recommended using the wet process, but rubber or a polymer-modified asphalt could be used. The program has worked well, he said.

“As far as Florida is concerned, the roads have been getting steadily better,” Clark added.

Users have begun to realize that rubber can be more difficult in the wet process. Whereas the mixture used to be 2/3 rubber and 1/3 polymer, those ratios were reversed in 2013.

This is why it is important to understand each market, Clark said. For instance, rubberized asphalt is performing better in Georgia, Clark said, but Georgia DOT is allowing the dry process to be used.

While some states still may be hesitant to use rubberized asphalt, it is becoming more popular.

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 rubberized 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.

While making the product, the manufacturer must ensure certain customer qualifications are met. For instance, Hitti said the qualifications for PG material are different among the states, such as California, Nevada, Arizona, etc. The mix may need to be tweaked based on historical performance, he said.

Paramount Petroleum performs theses tests to ensure it is an approved supplier, he said. The company submits weekly samples and other paperwork when necessary. In the case of a grant, the company may have to document exactly where the crumb rubber came from and the percentages in the batches.

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

A common misconception is that rubber must be used in certain aggregates, he said. In reality, the pavement is the combination of the asphalt, which is the glue, and the rubber. Any application can be used, be it a prime coat or layering.

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