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What is Asphalt Rubber? What is RAC

What is Asphalt Rubber? What is RAC. San Jose Asphalt Rubber Design and Construction Workshop February 20, 2002. Do you know of a material that can be recycled more economically than the production of a similar virgin material?. Did you know?.

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What is Asphalt Rubber? What is RAC

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  1. What is Asphalt Rubber?What is RAC San Jose Asphalt Rubber Design and Construction Workshop February 20, 2002

  2. Do you know of a material that can be recycled more economically than the production of a similar virgin material?

  3. Did you know? • The federal government figures roughly one tire per capita is discarded annually.

  4. Asphalt-Rubber uses over 2,000 TIRESper lane-mile on a typical 2” overlay.

  5. ASTM D 8 Standard Definitions of Terms Relating to Materials for Roads and Pavements Asphalt Rubber – 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 asphalt cement sufficiently to cause swelling of the rubber particles.

  6. Components Of The Binder • Asphalt modifier • Asphalt cement • Crumb rubber modifier

  7. ADDITIVES Sometimes used in conjunction with crumb rubber to aid or help produce a desirable property. Some additives include: Extender oils - aid in the reaction of the crumb rubber by providing aromatics which are absorbed by the rubber, and help with dispersion by chemically suspending the rubber in the asphalt. Anti-stripping agents - used to increase or improve adhesion. High natural rubber - used to improve adhesion and flexibility. Polymers Asphalt Rubber Binder

  8. Asphalt Modifier • Resinous high flash point aromatic hydrocarbon compound (2.5 - 6.0 %) • Variable viscosity requirements, “x” value +/- 3 and must be between 19 - 36 cst, once set it can’t be changed without a new binder design

  9. Paving Asphalt • AR 4000 asphalt (80 +/- 2 %) • Conform to Section 92 “Asphalts” of the Standard Specifications

  10. Crumb Rubber Modifier (CRM) • Scrap tire CRM (75 +/- 2 %) • High natural CRM (25 +/- 2 %) • Max. 0.01 % wire (by wt. Of CRM) • Max. 0.05 % fabric (by wt. Of CRM) • Max. 3 % calcium carbonate or talc • Specific gravity 1.1 - 1.2 • Chemical requirements

  11. Binder Properties Are Influenced By: • Asphalt Cement • Amount of Rubber • Gradation of Rubber • Reaction Temperature and Time

  12. Laboratory Binder Design • Asphalt heated to 415 F • Asphalt modifier added to asphalt • Crumb rubber blended into asphalt/asphalt modifier blend • Reacted for 45 minutes • Agitated (stirred) frequently during reaction period • Properties tested

  13. Asphalt Rubber Binder Properties • Cone penetration • Resilience • Field softening point • Viscosity

  14. APPARENT VISCOSITY • Measurement is achieved by a rotational viscometer and presented in centipoise (cP) or Pascal Seconds (Pa-s). • Brookfield Viscometer • Haake Viscometer • Monitors fluid consistency of asphalt rubber binder to ensure pumpability, to identify binder changes which might affect hot mix placement and compaction. • If the Brookfield is the required method for acceptance, then the Haake viscometer should be calibrated and corrected to the Brookfield measurement for field use.

  15. RESILIENCE • ASTM D5329 • Measures the elastic properties of the asphalt rubber binder and is expressed as a percentage of rebound for the binder. • Resilience is one of the most important properties in the specifications and is a more reliable measure of elasticity.

  16. SOFTENING POINT • ASTM D36 • AASHTO T 53 • Measurement is achieved by the ring and ball method and presented in °F or °C and is an indicator of material stiffness. This shows the tendency of the material to flow at elevated temperatures.

  17. DUCTILITYASTM D113 AASHTO T 51 • Measurement is achieved by pulling a sample apart at a specified rate and temperature until fracture. This is one measure of the tensile properties of the asphalt rubber binder. • Ductility should not be considered a reliable measure of ductile properties for an Asphalt Rubber Binder. The crumb rubber particle interference within the reduced area of the test specimen is most likely to cause premature failure

  18. FIELD AGING EFFECTS ON THE FATIGUE OF ASPHALT CONCRETE AND ASPHALT-RUBBER CONCRETE Lutfi Raad Professor of Civil Engineering Director, Transportation Research Center University of Alaska Fairbanks Fairbanks, Alaska 99775 fflr@uaf.edu Ph: (907) 474-7497 Fax: (907) 474-6087

  19. UAF – RAAD Conclusions ARHM-GG exhibited lower stiffness at 22oC and –2oC, than CAC-DG, for both aged and original conditions. The increase in stiffness of ARHM-GG as a result of aging is minimal (less than 6 percent) at both test temperatures. Aging increased the stiffness of CAC-DG by about 30 percent for testing at 22oC. The average stiffness of CAC-DG for tests conducted at –2oC was 12 percent smaller for aged specimens than for original specimens.

  20. UAF – RAAD Conclusions Aging reduced the beam fatigue life of CAC-DG for the testing conditions used in this study. The reduction was essentially more significant for tests run at –2oC than at 22oC. Although the average stiffness for aged CAC-DG at –2oC was slightly smaller than the un-aged specimens, the reduction in fatigue life was quite significant. In case of ARHM-GG aging had negligible effect on fatigue life for tests conducted at 22oC. At –2oC, the reduction in fatigue life for ARHM-GG became more evident, but remained less significant than CAC-DG.

  21. Quality Control • Materials sampling and testing • Field binder testing - hand held viscometer

  22. QUALITY CONTROL • Begins with pre-job testing to set the standard from which field testing can be compared. • The asphalt rubber blend design evaluates the compatibility of the components to economically produce a binder that meets the project specifications. • The design profile is a good tool to indicate appropriate testing for monitoring the project. This profile establishes a target viscosity for field testing. • Monitoring: Significant fluctuation in viscosity (even if still meeting project specifications) can cause challenges with the hot mix placement or suggest that other specifications such as resilience, softening point, etc. are no longer being met.

  23. Materials Sampling • Asphalt rubber binder must be sampled from a point that will provide a representative sample • Crumb rubber must be sampled from various points in the bag in order to obtain a representative sample

  24. Hand Held Viscometer • Haake viscometer or equivalent • Viscometer must be calibrated • Viscosity range 1500 - 4000 cp @ 375 F • Target viscosity for hot mix binder is about 2500 - 3500 cp • Viscosity is a very good indicator of other binder properties

  25. Asphalt Rubber Specifications • Specifications have evolved over a period of years • Latest specifications are a product of a CT / Industry Task Force • Current specifications are the best ever developed

  26. Extremely Important • Specifications must be followed to obtain satisfactory results • Asphalt rubber mixes are more temperature sensitive • Compaction must be achieved at higher temperatures • Hand work must be done early

  27. Asphalt Rubber Specifications • Rubberized asphalt concrete Type “G”, Type “D”, Type “O”, Type “O-HB” • Asphalt rubber chip seal

  28. Aggregate Gradation Comparison Open Graded Gap Graded Dense Graded

  29. Highlights Of Specifications

  30. Mix Design • Mix design for asphalt rubber mixes is similar to conventional mix design, but there are some major differences

  31. Mix Design • Stability requirement is lower (23 min.) • Mix and compaction temperature is higher (300 F, and 290 F) • Waxed specific gravity is used (CT 308 Method “A”) • The air voids content varies depending on climate and traffic

  32. Mixing Aggregate And Binder • Make sure binder is brought up to proper temperature • Make sure binder is thoroughly mixed before adding to the aggregate

  33. Mixing And Compaction • Aggregate temperature should be between 300-325 F • Compaction temperature of the mix should between 290-300 F • After compaction make sure spacer is placed under the mold to support the mix during the cooling period to 140 F

  34. Optimum Binder Content (OBC) • Minimum 7.0% and maximum 9.0% • If the OBC is 8.5% recommend a range of 8.2 - 8.5% • If the OBC is 7.0% recommend 7.0% with no range • If the OBC is outside the 7.0 - 9.0% allowable OBC range then reject the mix design

  35. Voids In Mineral Aggregate (VMA) • Parameter not normally used by Caltrans • The requirement makes sure that the mix has adequate void space for the binder • Asphalt Institute mix design, MS - 2 Manual

  36. How Is VMA Determined? Important: in this test method the apparent specific gravity is used instead of the bulk specific gravity.

  37. Aggregate Requirements • Type “A” aggregate is required • High quality aggregate is required because of the reduced thickness design • Requirement for loss at 500 rpm in CT 211 is 40% max.

  38. Definition Of A Crushed Particle CT 205 is amended: “Any particle having 2 or more fresh mechanically fractured faces shall be considered a crushed particle.”

  39. Aggregate Gradation • Use of asphalt rubber allows for higher binder contents and thicker film thickness • For dense graded mixes - 20% higher (6.5 - 7.5%) and for gap graded mixes - 40% higher (7.5 -8.5%) • Limits of proposed gradation tolerances much tighter

  40. Asphalt Rubber Construction Practice

  41. It is extremely important that the specifications are followed and that good construction practice is used

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