Asphalt Rubber

FROM OLD TIRES COMES NEW PAVEMENT

Since its development in Arizona during the late 1960s, the process of adding ground tire rubber to asphalt has evolved into a widely used process. Over the past 20 years, blending and application equipment have been significantly improved. New compositions have been developed and introduced, and specifications for quality control and construction have been established.

Asphalt-rubber is blend of tire rubber and hot paving grade asphalt cement used as a binder in various types of pavement construction. This blend consists of 18% to 25% of select ambiently ground passenger and truck tire rubber by total weight of the blend.

When used as a binder in hot mixed asphalt concrete (either dense or open-graded) the mixture imparts tough, flexible characteristics to the hot mix. Lab tests and field results generally show the asphalt-rubber hot mix to be more resistant to thermal and reflective cracking than unconventional asphalt concrete pavements. In addition, thicker films on the aggregate are achieved on the asphalt-rubber due to the higher viscosity of the binder. The thicker films and high viscosity also allow for a higher percentage of binder to be used in the hot mix. Although asphalt-rubber paving products are approximately twice the initial cost of conventional asphalt products, they maintain their cost effectiveness by resisting oxidation and weathering by up to three times longer than conventional AC pavements. This is primarily due to the high percentage of carbon black, oils and resins formulated into tire rubber to prevent their deterioration.

Portions of Hwy 101 and I-880 were recently resurfaced with open-graded hot mix produced with asphalt-rubber binder at the Graniterock Peninsula Road Materials Plant in Redwood City. Caltrans found the rubberized open-grade to hold heat longer than conventional mix, thus allowing night placement at ambient temperatures as low as 50 degrees Fahrenheit. This equates to a cost savings passed on to the user agency since construction contracts requiring open-graded AC can now be completed on schedule.