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Use of Asphalt Rubber in Pavements

Use of Asphalt Rubber in Pavements. PRESENTATION TOPICS. 1. ASPHALT RUBBER - RAC “101” HISTORY OF ASPHALT RUBBER RAC APPLICATIONS RAC USAGE GUIDELINES BENEFITS AND LIMITATIONS IMPLEMENTATION. 2. 3. 4. 5. 6. WHAT IS ASPHALT RUBBER ? Section. 1. AR 101.

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Use of Asphalt Rubber in Pavements

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  1. Use of Asphalt Rubber in Pavements

  2. PRESENTATION TOPICS 1 • ASPHALT RUBBER - RAC “101” • HISTORY OF ASPHALT RUBBER • RAC APPLICATIONS • RAC USAGE GUIDELINES • BENEFITS AND LIMITATIONS • IMPLEMENTATION 2 3 4 5 6

  3. WHAT IS ASPHALT RUBBER ? Section 1 AR 101 • ASPHALT RUBBERASTM D8 • 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 • RELATED SPECIFICATIONASTM D 6114 • Standard Specification for Asphalt Rubber Binder High viscosity material that typically requires agitation to keep CRM particles dispersed

  4. Asphalt Rubber Makeup 1 AR 101 • WET PROCESS • Adding graded rubber to asphalt and mixing and reacting-requires agitation • HIGH VISCOSITY – No Agitation • Adding fine rubber typically < #30 to asphalt at the terminal-generally little or no agitation. Often referred to as terminal blend • DRY PROCESS • Use CRM as substitute for 1-3% of Aggregate by mixing crumb rubber directly with aggregate • used for asphalt concrete

  5. Wet Process 1 AR 101 Method ofmodifying asphalt cement with CRM and other components • Most widely used in CA, AZ, FL & TX • Contains 18-22 % crumb rubber • Agency spec vary • Particle sizes # 8 to #10 top size Type 1 Asphalt Cement and tire rubber AZ, FL and TX Type 2 Asphalt, tire rubber, high natural CRM + extender oil (CA)

  6. Wet Process 1 AR 101 • Thoroughly mix CRM & other components with hot (400-425ºF) asphalt cement • Interact at 350-375ºF for designated period (typical minimums 45-60 minutes) • CRM particles swell, exchange oils with AC • Rotational Viscosity is discriminator for appropriate use

  7. No Agitation 1 AR 101 • Contains from <5%-15 % crumb rubber • Particle size ranges from 40 to 80 mesh top size • Can also contain polymers • Used in Arizona ,Florida, Texas, and California • Often referred to as Terminal Blend

  8. High Viscosity vs. No Agitation 1 AR 101

  9. Dry Process 1 AR 101 • Substitutes CRM for 1 to 3% of aggregate in hot mix • Not considered to modify binder, although some interaction with CRM may occur in place over time (absorbs light fractions) • CRM gradations have ranged from coarse (-1/4”) to fine (-#80)

  10. Asphalt Rubber Binder 1 AR 101 • Crumb Rubber (including HNR) • Asphalt Cement • Additives • Blended to meet specific specs COMPONENTS

  11. Crumb Rubber Modifier - CRM Grinding whole scrap tires Tread buffings Other waste rubber products. Crumb rubber comes in a variety of grades and designations presented by particular size and/or source. 1 AR 101 CRM Sources

  12. CRM Used For Wet Process 1 AR 101 CRM Product

  13. Asphalt Cements 1 AR 101 • Come in a variety of grades • Typically softer binders used for RAC than for conventional HMA

  14. Additives 1 AR 101 • Used in conjunction with the CRM to enhance interaction and produce desirable properties • Extender oils • Anti-strip agents • High natural rubber (HNR) • Polymers – typically limited to no agitation

  15. Interactions Depend On 1 AR 101 • Asphalt Cement Source & Grade • Rubber Type/Source • Amount Of Rubber • Gradation Of Rubber • Interaction Time • Interaction Temperature

  16. Advantages of High Viscosity AR Binder 1 AR 101 • Allows higher binder content and increased film thickness-resulting in increased durability (moisture resistance and aging resistance) • Improves aggregate retention • Minimizes drain-down problems • Increases resistance to fatigue and reflection cracking • Increases resistance to bleeding, flushing and deformation

  17. HISTORY OF ASPHALT RUBBER Section 2 History of AR Use • Used since the 1960’s • Use in chip seals, inter-layers, and HMA • Use extensively in CA, AZ, FL & TX • Design and construction guides now available from some agencies

  18. Caltrans Ravendale Project 2 History of AR Use • First CA project to use reduced thickness RAC when compared to the conventional AC design thickness • Different thickness test sections of RAC, dry process, and conventional AC mixes • Performance monitored for nearly 20 years

  19. CALTRANS Reduced Thickness Design 2 History of AR Use • CALTRANS developed the interim guidelines in 1992 • Based on laboratory and long-term field data (two decades) • Supported by research efforts

  20. Design Of RAC Overlays 2 History of AR Use • Uses a deflection based design method • Up to 50 % reduction in thickness compared to conventional AC design thickness • Over 200 reduced thickness projects

  21. History of AR Use 2 45mm AR over SAMI 16 yrs old 75mm AR over SAMI 16 yrs old SAM - Stress Absorbing Membrane

  22. Council on Scientific and Industrial Research - CSIR 2 History of AR Use • Caltrans conducted a research project with CSIR, UCB, and Dynatest Consulting to verify the reduced thickness theory for Asphalt Rubber pavements • The research used accelerated pavement testing (APT) using the heavy vehicle simulator (HVS) • The research included laboratory testing to support the field testing

  23. History of AR Use 2 HVS

  24. Original Condition Of Pavement 2 History of AR Use South Africa

  25. 75 mm Conv. AC 28 mm ARHM 38 mm ARHM

  26. Findings 2 History of AR Use • Thickness of RAC rubber mixes can be reduced by a factor of 2 and still give the same performance for resistance to reflective cracking • Reduced thickness first incorporated into the Caltrans design process in 1992

  27. AR APPLICATIONS Section 3 AR Applications • Chip Seals • AR Interlayer (SAM and SAMI’s) • RAC Overlay with SAMI-R • Dense-Graded Hot Mixes (RAC-D) • Do Not Use With High Viscosity • Gap-Graded Hot Mixes (RAC-G) • Open-Graded Hot Mixes (RAC-O) • Open-Graded High Binder Hot Mixes • RAC-O, HB ASPHALT RUBBER

  28. AR Applications 3 AR Applications SPRAY APPLICATIONS • Chip Seals • AR Interlayers • Dense-Graded HMA (RAC-D) • (Use with no agitation only) • Gap-Graded HMA (RAC-G) • Open-Graded HMA (RAC-O) • Open-Graded High Binder HMA (RAC-O-HB) HOT MIX ASPHALT ASPHALT RUBBER

  29. AR Spray Applications 3 AR Applications CHIP SEAL – SURFACE TREATMENT • ARAM - Asphalt Rubber–Aggregate membrane • SAM - Stress Absorbing membrane • SAMI - Stress Absorbing Membrane Interlayer SAMI - R when rubber modified • ARMI - Asphalt rubber membrane interlayer INTERLAYER - CHIP SEAL SANDWICHED BETWEEN TWO PAVEMENT LAYERS Same equipment and general procedures are used for both applications

  30. Uses for AR Chip Seals and Interlayers 3 AR Applications • Use with High Viscosity AR Binders over severely cracked but structurally sound pavements • Interlayers may be covered with RAC, MB or conventional DGAC paving mixes

  31. Chip Seals Factors to Consider 3 AR Applications • Chip Seal Equipment • AR Spray Application • Chip Application

  32. Finishing 3 AR Applications • Rubber-tired Rollers • Sweeping • Flush coat • Compaction • Sweeping • Flush coat

  33. AR Interlayers 3 AR Applications • Used to prevent reflection cracking • Used in two or three layer systems • Used by several agencies

  34. AR Overlay with SAMI-R 3 AR Applications

  35. Rubberized Asphalt Concrete RAC 3 AR Applications • High viscosity AR binder • Most effective in Gap and Open-graded mixes • Used in upper 60 mm of pavement For resisting reflective cracking, Caltrans allows reduced thickness for gap-graded RAC overlays of structurally sound pavements

  36. Hot Mix Asphalt HMA 3 AR Applications USES GAP GRADED MIXES RAC-G • Only with no agitation binders • Used primarily in Arizona, California, Florida and Texas • Reduced thickness is allowed by some agencies OPEN GRADED MIXES RAC-O DENSE GRADED MIXES RAC-D

  37. Aggregate Gradation Comparison 3 RAC Applications Open Graded Gap Graded Dense Graded

  38. Dense-Graded HMA RAC-D 3 RAC Applications EARLY USE • Limited performance improvements vs. cost • Inadequate void space to accommodate sufficient • AR binder to modify behavior • Discontinued use with high viscosity binder

  39. Gap Graded Mixes RAC-G RAC Applications • Currently the workhorse mix in CA • 30 to 60 mm Thickness • Thickness reduction allowed when this mix is employed

  40. HOT MIXES RAC-O 3 RAC Applications Open-Graded • Widely used in California as surface course • Free draining with reduced splash and spray • Does not add any structural value

  41. HOT MIXES RAC-O-HB 3 RAC Applications Open-Graded High Binder • Widely used in Arizona as surface course • Also used by Caltrans as surface course • Not as free draining, but improved durability

  42. DESIGN PRODUCTION & EQUIPMENT CONSTRUCTION SAMPLING & TESTING AR USAGE GUIDELINES Section 4 RAC USAGE GUIDELINES A B C D

  43. Where and Why Used? 4 RAC USAGE GUIDELINES • Replaces conventional mixes where paving temperatures and haul distances are favorable • More resistant to cracking and fatigue Particularly Reflection Cracking

  44. AR Design Considerations Design 4 RAC USAGE GUIDELINES 1 BINDER DESIGN 2 STRUCTURAL DESIGN

  45. Asphalt Rubber Blend Profile Design 4 RAC USAGE GUIDELINES • Developed to evaluate compatibility between materials used • Checks for stability of the blend over time • Should be required for each project

  46. Binder Design Design 4 RAC USAGE GUIDELINES ASPHALT RUBBER

  47. Asphalt Rubber Tests Design 4 RAC USAGE GUIDELINES • CONE PENETRATION • RESILIENCE • R&B SOFTENING POINT • FIELD VISCOSITY

  48. Cone Penetration Design 4 RAC USAGE GUIDELINES • ASTM D 217

  49. Resilience Design 4 RAC USAGE GUIDELINES • ASTM D 5329 Formerly ASTM D 3407

  50. R&B Softening Point Design 4 RAC USAGE GUIDELINES • ASTM D 36

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