ASTM Considers Rubberized Asphalt at Summer Meeting

Proposals to change the definition of the term “asphalt-rubber” to include a wide variety of materials containing recycled tire rubber (RTR) took center stage at the American Society for Testing and Materials (ASTM) International summer meeting held in June in Indianapolis, IN.

A goal for some was to create an umbrella term for asphalt materials with an RTR component. However, the term asphalt-rubber conveys very specific meaning with respect to material properties that are described in “ASTM D6114 / D6114M – 09 Standard Specification for Asphalt-Rubber Binder,” committee members said. The creation of a new term “rubberized asphalt” was recommended by the committee.

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A primary distinguishing characteristic of asphalt-rubber is the minimum apparent viscosity of 1.5 Pascal seconds (1500 centipoise) at 175°C, George Way, President of the Rubberized Asphalt Foundation (RAF) said. Way attended the ASTM subcommittee D4.91 meeting along with RAF Directors Mark Belshe of the Rubber Pavements Association and Doug Carlson of Liberty Tire Recycling The addition of RTR to a heated binder causes a swelling and gelling of the rubber particles that thicken the binder, building viscosity. The high viscosity allows asphalt-rubber to be used as an engineering tool in asphalt paving systems to increase the application rate on spray-applied systems to build a thicker sealant membrane or to increase binder contents in mixtures that will resist drain-down during construction and placement in order to boost fatigue resistance or long-term performance, Way explained.

A consensus was reached to update terminology related to rubberized asphalt through the adoption of new standards for performance graded rubberized asphalt binders where RTR is used as a modifier to enhance high temperature performance and greater resistance to rutting under heavy traffic loading conditions. New standards for RTR additives in mixtures, types of modifications, mix performance testing, and quality control were also recommended.

Committee members Way and Belshe noted that much work still needs to be done to introduce and advance asphalt materials and specifications that beneficially use RTR. Volunteers are welcome to join ASTM to participate and help develop the needed standards, they said.

© Scrap Tire News, August 2013