Presentation delivered March 4, 2015 by Amir Ghavibazoo, Ph.D., at the California Asphalt Pavement Association joint Los Angeles-High Desert Technical Committee meeting in Fontana.

2. Terms and Glossary
Asphalt Rubber Binder (ASTM D8 – 13b):
“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 particles”
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3. Terms and Glossary
• Asphalt Rubber Interaction:
– The act of physical blending of CRM in asphalt at elevated
temperature which results in swelling of CRM particles and develops
physical properties of asphalt
• Interaction/reaction Temperature:
– The temperature at which the CRM and Asphalt are blended
• Mixing Temperature:
– The temperate of mixing aggregate and binder
• Compaction Temperature
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4. Caltrans Specification-Composition
Typical proportion of Asphalt Rubber per Caltrans:
•80% Asphalt binder
•2% Asphalt modifier (extender oil)
•18% CRM
Proportion of CRM
•75% CRM from scrap tiers (100% passing
No. 8 sieve)
•25% High natural rubber CRM (100%
passing No. 10 sieve)
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5. Caltrans Specification-Interaction
Interaction Temperature Profile
•Mixing temperature
•Asphalt rubber binder: 375°F – 425°F
•Aggregate: 300°F-325°F
•Compaction temperature
•290°F - 320°F
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•Per Caltrans, interaction
temperature is: 375°F – 425°F for
first 6 hours
•Temperature drops to 275°F after 6
hours for another 18 hours

6. How the temperature
tolerance(interaction and mixing)
affects the property development
of asphalt rubber
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7. Property Development of Asphalt
Rubber
• Dynamic Shear Rheometer (DSR)
– Plate Geometry: 25 mm
– Gap Size: 2 mm
– Temperature: 147°F (64°C)
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8. Property Development of Asphalt
Rubber
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Property development of asphalt
rubber is time and temperature
dependant
These trends are independent from
material type and concentration

9. Disintegration/Dissolution Test
• Sieve #200 (75µm) was used
• Passing CRM particles considered as dissolved/disintegrated
• Asphalt binder was dissolved into TCE and drained through sieve #200
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10. CRM Status in Asphalt
•CRM dissolves in asphalt
•Dissolution is almost independent from
CRM concentration
•Dissolution of CRM highly depends on
interaction temperature
•At 420°F, CRM dissolution can reach to more
than 60% within 4 hours
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11. Property Development Vs. CRM Status
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•Physical properties of asphalt is
mainly governed by status of CRM
particles
•Swelling improves the physical
properties
•Dissolution deteriorate physical
properties

12. CRM particles status in asphalt
Swelling process
Disintegration/Dissolution process
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MagdyAbdelrahman,TRB2006

13. Is the mechanism of
dissolution/disintegration the
same for all interaction
temperatures
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14. Disintegration/Dissolution Process
•Dissolved portion of CRM changes the
properties of the binder
•Mechanism of dissolution is temperature
dependant
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15. Effect of Mixing Temperature on
Oxidization
•For conventional asphalt:320°F
•For asphalt rubber: 375°F to 420°F
•Addition of CRM to asphalt reduces its aging susceptibility and prevent it from
oxidization
•BUT, increasing the interaction temperature significantly increases the
oxidization level of the asphalt binder
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16. Conclusion
• Asphalt rubber has a very dynamic nature
• Its properties are highly temperature dependant
• By regulating the interaction temperature, it is possible to satisfy specification’s
requirements, using almost any type of binder
• Better controls on interaction time and temperature will lead to better consistency
of the construction process and long term performance of the roads
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17. 17
Thank you!