What is Asphalt Rubber? What is RAC

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What is Asphalt Rubber?What is RAC

• San Jose Asphalt Rubber Design and Construction
  Workshop
• February 20, 2002

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

• The federal government figures roughly one tire
  per capita is discarded annually.

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Asphalt-Rubber uses over 2,000
TIRESper lane-mile on a typical 2 overlay.
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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.
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Components Of The Binder

• Asphalt modifier
• Asphalt cement
• Crumb rubber modifier

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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
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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
  cant be changed without a new binder design

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Paving Asphalt

• AR 4000 asphalt (80 /- 2 )
• Conform to Section 92 Asphalts of the Standard
  Specifications

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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

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Binder Properties Are Influenced By

• Asphalt Cement
• Amount of Rubber
• Gradation of Rubber
• Reaction Temperature and Time

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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

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Asphalt Rubber Binder Properties

• Cone penetration
• Resilience
• Field softening point
• Viscosity

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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.

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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.

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• 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.

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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

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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_at_uaf.edu
• Ph [phone]
• Fax [phone]

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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.

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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.
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• 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.

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Quality Control

• Materials sampling and testing
• Field binder testing - hand held viscometer

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• 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.

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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

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Hand Held Viscometer

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

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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

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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

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Asphalt Rubber Specifications

• Rubberized asphalt concrete Type G, Type D,
  Type O, Type O-HB
• Asphalt rubber chip seal

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Aggregate Gradation Comparison
Open Graded Gap Graded Dense Graded
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Highlights Of Specifications
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Mix Design

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

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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

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Mixing Aggregate And Binder

• Make sure binder is brought up to proper
  temperature
• Make sure binder is thoroughly mixed before
  adding to the aggregate

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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

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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

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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

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How Is VMA Determined?

• Important in this test method the apparent
  specific gravity is used instead of the bulk
  specific gravity.

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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.

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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.

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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

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Asphalt Rubber Construction Practice
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It is extremely important that the specifications
are followed and that good construction practice
is used
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The Three Most Important Things In Construction

• Temperature
• Temperature
• Temperature

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Asphalt rubber is more temperature sensitive
than conventional AC mix
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Differences During Placement

• Keep windrows short
• Keep rollers right behind paver
• Cover loads in cool weather

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Placement Requirements

• To help eliminate low temperature placement
  problems changes were made in the placement
  requirements
• A two pronged approach was implemented

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Atmospheric and Pavement Surface Temperature 65
F or above

• Aggregate temperature 325 F or less
• Mix spread at not less than 280 F nor more than
  325 F
• First coverage of breakdown compaction performed
  not less than 275 F, and all compaction completed
  before 250 F

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Atmospheric and Pavement Surface Temperature is
below 65 F

• Aggregate temperature shall be not less than 300
  F nor more than 325 F
• All loads shall be covered
• Mix spread at not less than 300 F nor more than
  325 F
• First coverage of breakdown compaction performed
  not less than 280 F, and all compaction completed
  before 260 F

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Where have asphalt rubber strategies been used
successfully?
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US 70 Near Nashville, TN at one year and two years
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ASPHALT-RUBBEROn the Road Again