Indianapolis, Indiana – RAF Chairman George Way and Directors Mark Belshe of the Rubber Pavements Association and Doug Carlson of Liberty Tire Recycling attended the summer meeting of the American Society for Testing and Materials (ASTM) International to provide guidance on the use of recycled tire rubber (RTR) in asphalt materials.
The meeting started with a discussion on June 11 where the ASTM subcommittee D4.91 entertained member proposals to change the definition of the term “asphalt-rubber” to include a wide variety of materials containing RTR. 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” and the creation of a new term “rubberized asphalt” was recommended.
A primary distinguishing characteristic of asphalt-rubber is the minimum apparent viscosity of 1.5 Pascal seconds (1500 centipoise) at 175°C. 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.
A consensus was reached to update terminology related to rubberized asphalt through the adoption of new standards such as:
- 1. 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.
- 2. RTR additives in mixtures, types of modifications, mix performance testing, and quality control.
ASTM D04 Subcommittees:
- D04.20 Mechanical Tests of Bituminous Mixtures
- D04.21 Specific Gravity and Density of Bituminous Mixtures
- D04.22 Effect of Water and Other Elements on Bituminous Coated Aggregates
- D04.23 Plant-Mixed Bituminous Surfaces and Bases
- D04.24 Bituminous Surface Treatments
- D04.25 Analysis of Bituminous Mixtures
- D04.26 Fundamental/Mechanistic Tests
- D04.27 Cold Mix Asphalts
- D04.30 Methods of Sampling
- D04.31 Calcium and Sodium Chlorides and Other Deicing Materials
- D04.32 Bridges and Structures
- D04.33 Formed In-Place Sealants for Joints and Cracks in Pavements
- D04.34 Preformed Joint Fillers, Sealers and Sealing Systems
- D04.38 Highway Traffic Control Materials
- D04.40 Asphalt Specifications
- D04.41 Emulsified Asphalt Specifications
- D04.42 Emulsified Asphalt Test
- D04.43 Specifications and Test for Tar and Tar Products
- D04.44 Rheological Tests
- D04.46 Durability and Distillation Tests
- D04.47 Miscellaneous Asphalt Tests
- D04.50 Aggregate Specifications
- D04.51 Aggregate Tests
- D04.90 Executive
- D04.91 Terminology
- D04.93 Long Range Planning
- D04.94 Statistical Procedures and Evaluation of Data
- D04.95 Quality Control, Inspection and Testing Agencies
- D04.99 Sustainable Asphalt Pavement Materials and Construction
Much work needs done to introduce and advance asphalt materials and specifications that beneficially use RTR. Volunteers are welcome to join ASTM to participate.
You can also support RAF’s efforts at ASTM. RAF is a U.S.-based 501(c)3 research foundation dedicated to the science and practical use of recycled tire rubber in asphalt.