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?
• The federal government figures
roughly one tire per capita is
discarded annually.
AsphaltRubber
uses over
2,000
TIRES
per lanemile
on a typical
2” overlay.
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.
Components Of The
Binder
• Asphalt modifier
• Asphalt cement
• Crumb rubber modifier
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.
Asphalt Rubber Binder
Polymers
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
Paving Asphalt
• AR 4000 asphalt (80 +/- 2 %)
• Conform to Section 92
“Asphalts” of the Standard
Specifications
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
Binder Properties
Are Influenced By:
•Asphalt Cement
•Amount of Rubber
•Gradation of Rubber
•Reaction Temperature and
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
Asphalt Rubber Binder
Properties
• Cone penetration
• Resilience
• Field softening point
• Viscosity
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.
Minutes of Reaction
60
90
240 360
2.7 2.8
2.8
2.8
2700 2800 2800 2800
Specified
Limits
1.5-4.0
1500-4000
Test Performed
1440
Viscosity, Haake at
2.0
177°C, Pa-s
2000
Centipoise cP
Resilience at 25°C, % 34
36
32 30 Minimum
Rebound (ASTM D3407)
Ring & Ball Softening 150.0 150.5 152.5 154.5 145.0
135
Point, °F (ASTM D36)
Minimum
Needle Penetration at 22
24
26 10 Minimum
4°C, 200g, 60 sec.,
1/10mm (ASTM D5)
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.
• 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.
DUCTILITY
ASTM 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
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
[email protected]
Ph: (907) 474-7497
Fax: (907) 474-6087
20000
18000
Flexural Stiffness, MPa
16000
14000
12000
10000
8000
6000
4000
2000
0
22 C
-2 C
Original CAC-DG
3700
18379
Aged CAC-DG
4800
16211
Original ARHM-GG
2350
11266
Aged ARHM-GG
2386
11960
FIGURE 1 Stiffness variation for original and aged mixes.
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 CACDG for tests conducted at –2oC was 12 percent smaller for
aged specimens than for original specimens.
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 unaged 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.
Quality Control
• Materials sampling and
testing
• Field binder testing - hand
held viscometer
• 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.
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
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
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
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
Asphalt Rubber
Specifications
• Rubberized asphalt concrete
Type “G”, Type “D”, Type
“O”, Type “O-HB”
• Asphalt rubber chip seal
Aggregate Gradation Comparison
Open Graded
Gap Graded
Dense Graded
Highlights Of
Specifications
Mix Design
• Mix design for asphalt rubber
mixes is similar to
conventional mix design, but
there are some major
differences
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
Mixing Aggregate
And Binder
• Make sure binder is brought
up to proper temperature
• Make sure binder is
thoroughly mixed before
adding to the aggregate
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
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
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
How Is VMA
Determined?
Important: in this test method
the apparent specific gravity is
used instead of the bulk specific
gravity.
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.
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.”
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
Asphalt Rubber
Construction
Practice
It is extremely important
that the specifications are
followed and that good
construction practice is used
The Three Most Important
Things In Construction
• Temperature
• Temperature
• Temperature
Asphalt rubber
is more temperature
sensitive than
conventional
AC mix
Differences During
Placement
• Keep windrows short
• Keep rollers right behind
paver
• Cover loads in cool weather
Placement
Requirements
• To help eliminate low temperature
placement problems changes
were made in the placement
requirements
• A two pronged approach was
implemented
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
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
Where have asphalt
rubber strategies been
used successfully?
US 70 Near Nashville, TN at one year and two years
ASPHALT-RUBBER