What is Asphalt-Rubber?

Seen above is a typical field blending plant.

Asphalt-Rubber (A-R) is a blend of approximately 75 - 80 percent asphalt and 20 percent (+/-2%) recycled scrap tire rubber that is field blended under a time-temperature formula to create a binder than can be used in hot mix or spray applications.

It is a non proprietary, non-patented public process that was developed in the 1960's by a City of Phoenix engineer and used routinely in Arizona, California, and Texas. It is also used on a limited basis in several northeastern states and is currently under review in Tennessee.

The blend has been used in countries on five continents. South Africa has been using it for over 15 years.

A-R is the only crumb rubber modified asphalt binder with an American Society for Testing Materials (ASTM) definition and specifications. It has also been researched and tested more than any other
asphalt binder available today.

The ASTM definition (D8-88), adopted in 1987, reads:

"Asphalt-Rubber is a blend of asphalt cement, reclaimed tire rubber and certain additives in which the rubber component is at least 15% by weight of the total blend and has reacted in the hot asphalt cement sufficiently to cause swelling of the rubber.

The crumb rubber is delivered in bags.

The binder specification can be found in the ASTM Standards D-6114097.

In hot mixes, the A-R allows for a higher binder content than unmodified asphalt. It is generally used in gap graded and open graded mixes.

The higher binder content (between 8 to 10%) allows for more coating on the aggregate and produces a longer lasting pavement. Smoother ride and noise reduction are two other major benefits of the A-R hot mix pavements.

The open and gap graded A-R hot mixes are often used together or in combination with an A-R membrane spray as an interlayer. The open graded mixes are used as friction or surfaces courses and have proven to be an extremely cost effective treatment for aging concrete pavement.

In spray applications, A-R binder is placed at .55 to .70 gallon PSY and followed by hot, precoated aggregate spread at 30 to 40 lbs. PSY. This chip seal application is called a Stress Absorbing Membrane (SAM). It is also used as an Stress Absorbing Membrane Interlayer (SAMI).

In addition, it is used with a type 2 slurry to form what is known as the Asphalt-Rubber Cape Seal. This application was pioneered in Cape Town, South Africa and is popular with agencies that want a durable pavement with a smoother surface than a chip seal.

Above, a hot mix paving operation in Phoenix. Below, a chip seal application.