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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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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Caltrans Specification-CompositionTypical 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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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

How the temperature tolerance(interaction and mixing) affects the property development

of asphalt rubber

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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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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

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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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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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

CRM particles status in asphalt

Swelling process

Disintegration/Dissolution process

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Is the mechanism of dissolution/disintegration the

same for all interaction temperatures

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Disintegration/Dissolution Process

•Dissolved portion of CRM changes the properties of the binder•Mechanism of dissolution is temperature dependant

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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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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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Thank you!