What is Asphalt Rubber?What is Asphalt Rubber?What is RACWhat is RAC

San Jose Asphalt Rubber San Jose Asphalt Rubber Design and Construction Design and Construction

WorkshopWorkshop

February 20, 2002February 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.

Asphalt-Rubber uses over

2,000 TIRES

per lane-mile

on a typical 2” overlay.

ASTM D 8ASTM D 8Standard Definitions of Terms Relating to Materials Standard Definitions of Terms Relating to Materials

for Roads and Pavementsfor Roads and Pavements

Asphalt RubberAsphalt Rubber – – a blend of asphalt a blend of asphalt

cement, reclaimed tire rubber and certain cement, reclaimed tire rubber and certain

additives in which the rubber component additives in which the rubber component

is at least 15% by weight of the total is at least 15% by weight of the total

blend and has reacted in the hot asphalt blend and has reacted in the hot asphalt

asphalt cement sufficiently to cause asphalt cement sufficiently to cause

swelling of the rubber particles.swelling of the rubber particles.

Components Of The Binder

• Asphalt modifier

• Asphalt cement

• Crumb rubber modifier

WHAT IS ASPHALT?WHAT IS ASPHALT?

Asphalt consists of two main fractions –“asphaltenes”which arethe hard brittle component, insoluble and not affected by oxidation and the highly reactive sub-fractions called “maltenes”. These maltenes are oily and resinous in appearance.

Asphalt Rubber Binder Asphalt Rubber Binder

ADDITIVESADDITIVES

Some additives include:

Extender oilsExtender oils - aid in the reaction of the crumb - aid in the reaction of the crumb rubber by providing aromatics which are absorbed rubber by providing aromatics which are absorbed by the rubber, and help with dispersion by by the rubber, and help with dispersion by chemically suspending the rubber in the asphalt.chemically suspending the rubber in the asphalt.

Anti-stripping agentsAnti-stripping agents - used to increase or improve - used to increase or improve adhesion.adhesion.

High natural rubberHigh natural rubber - used to improve adhesion and - used to improve adhesion and flexibility.flexibility.

PolymersPolymers

Sometimes used in conjunction with crumb rubber to aid

or help produce a desirable property.

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 Binder Properties Are Properties Are Influenced By: Influenced By:

•Asphalt CementAsphalt Cement

•Amount of Rubber Amount of Rubber

•Gradation of RubberGradation of Rubber

•Reaction Temperature and Reaction Temperature and

TimeTime

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 APPARENT VISCOSITYVISCOSITY

• Measurement is achieved by a rotational viscometer and Measurement is achieved by a rotational viscometer and presented in centipoise (cP) or Pascal Seconds (Pa-s).presented in centipoise (cP) or Pascal Seconds (Pa-s).

• Brookfield ViscometerBrookfield Viscometer• Haake ViscometerHaake Viscometer• Monitors fluid consistency of asphalt rubber binder to Monitors fluid consistency of asphalt rubber binder to

ensure pumpability, to identify binder changes which ensure pumpability, to identify binder changes which might affect hot mix placement and compaction.might affect hot mix placement and compaction.

• If the Brookfield is the required method for acceptance, If the Brookfield is the required method for acceptance, then the Haake viscometer should be calibrated and then the Haake viscometer should be calibrated and corrected to the Brookfield measurement for field use.corrected to the Brookfield measurement for field use.

RESILIENCERESILIENCE

• ASTM D5329ASTM 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 POINTSOFTENING POINT

• ASTM D36 ASTM D36 • AASHTO T 53AASHTO 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.

DUCTILITYDUCTILITYASTM D113 ASTM D113 AASHTO T 51AASHTO 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 FIELD AGING EFFECTS ON THE FATIGUE OF ASPHALT CONCRETE FATIGUE OF ASPHALT CONCRETE

AND ASPHALT-RUBBER CONCRETEAND 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

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

Fle

xura

l Stif

fne

ss,

MP

a

FIGURE 1 Stiffness variation for original and aged mixes.

Original CAC-DG 3700 18379

Aged CAC-DG 4800 16211

Original ARHM-GG 2350 11266

Aged ARHM-GG 2386 11960

22 C -2 C

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.

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.

Quality Control• Materials sampling and

testing

• Field binder testing - hand held viscometer

• QUALITY CONTROLQUALITY 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

Open GradedOpen Graded Gap GradedGap Graded Dense GradedDense Graded

Aggregate Gradation ComparisonAggregate Gradation Comparison

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

“On the Road Again”