Rubber Modified Binders and Mixtures Presented by:

Gaylon L. Baumgardner Paragon Technical Services, Inc.

and Ergon Asphalt and Emulsions, Inc.

56th Annual New Jersey Asphalt Paving Conference

5-6 March 2013

Introduction

Rubber Modified Asphalt

Asphalt Rubber or rubber modified bitumen/asphalt is the largest single market for recycled tires and consumes an estimated 12 million tires annually.

Ground Tire Rubber (GTR) is separated into two particle sizes by class “ground” (2000μm and less) and “coarse” (greater that 2000μm)

Rubber produced from ground whole tires contains ~ 30% reactive material for asphalt modification

Functional yield is dependent of tire composition and directly proportional to rubber particle size

There is no “Magic” to GTR modified asphalt, another way to modify asphalt.

Terminal blending can be an operations challenge

Asphalt/Asphalt Grades

Definition - Asphalt

a high molecular weight, thermoplastic hydrocarbon constituent, found in a large number of petroleum crude oils. Although some asphalts do occur naturally, asphalt as we know it, and as discussed herein, is derived from fractional distillation of petroleum crude oil.

Useful Temperature Interval (UTI)

“SuperPave Made Simple”

Useful Temperature Interval

Simply put, the “useful temperature interval” (UTI) of an asphalt is the differential, or spread in C , between the high temperature grading and the low temperature grading.

Useful Temperature Interval

74 C°

98 C°

86 C°

UTI of Performance Grade Asphalts A PG 64-22 would have a UTI of 86 C A PG 58-28 also has a UTI of 86 C If we needed a PG 76-22, which has a UTI of 98 C -

how is this accomplished? As a “rule of thumb”, to achieve a UTI of >92 C , the

asphalt has to be “modified”. Depending on crude source, some binders with more

narrow UTI’s of 86 and 89 C may also require modification

Modification of Asphalt Binders

Methods of Modification:

addition extending agents, chemical additives, air blowing, polymer addition.

Addition of Extending Agents Additives sometimes referred to as “extenders”, or

“extending agents” are materials added to asphalt to improve or “extend” asphalt properties. In the past, asbestos was one of the more popular

additives used to improve the strength and longevity of asphalt.

Today, due to safety hazards attributed to asbestos, other materials are utilized to include, cellulose fibers, and synthetic fibers.

Chemically Modified Asphalt Some asphalt binders may be modified chemically by

the addition of selected chemicals which enhance or improve the properties of asphalt. These chemical additives might include: Sodium Hydroxide, and other materials of alkaline

nature. Phosphorous Pentoxide, and other acids Sulfur, or sulfur donning materials. Tall Oil, etc...

Air Blown/Air Rectified Asphalt

Air blowing is a process in which an asphalt flux is heated to 490/500 F and contacted with air. This process is sometimes referred to as “oxidizing” with the finished product being called “oxidized asphalt.” Since very little oxygen is added, the most accurate description would be “blowing” and “blown asphalts.”

Polymer Modified Asphalt Addition of polymer additives to asphalt to provide

improved performance is known as polymer modification. These asphalts are also sometimes referred to as PMAC. The most common polymers used in PMAC are

from the family of synthetic polymers, to include: SBR Synthetic and Natural Latex Styrene-Butadiene Block Copolymers Ethylene Vinyl Acetate Reclaimed Rubber, GTR is a Polymer

GTR Modification of Asphalt

Ground Tire Rubber (GTR) Modified Asphalt

Ground Tire Rubber (GTR) is a post consumer polymer fractionally beneficial in modification of asphalt binders.

Benefits of modification of asphalt with GTR are similar to those achieved with virgin synthetic polymers with the exception GTR loadings are typically higher.

Knowledge and technology for processing GTR modified binders are just as critical as with synthetic polymer modified binders e.g. SBS

In the US, Asphalt Rubber or rubber modified bitumen/asphalt is the largest single market for recycled tires and consumes an estimated 12 million tires annually.

Two Basic Types of GTR Modified Asphalt Production Processes

Asphalt Rubber – also known as the “Wet Process” generally blended at the hot mix plant able to use larger particle size rubber, 15 – 20 mesh

Terminal Blend – blended and stored at the terminal or refinery typically uses 20 – 80 mesh rubber, performance yield is better with smaller particle size

Critical Factors

Asphalt Chemistry - Source Rubber Composition – Chemistry Rubber Particle Size Processing Parameters – Time and Temperature Optimization

Asphalt Binder Source/Composition

5

4 2

3 1 - East Coast 2 - Midwest 3 - Gulf Coast 4 - Rocky Mountain 5 - West Coast

Petroleum Administration for Defense Districts (PADDs)

1

ARCS - SARA Asphalt is deasphaltened according to ASTM Method D-3279

n-heptane in-soluble to yield asphaltenes “A” and maltenes or n-heptane soluble

Maltenes were further processed via an Iatroscan TH-10 hydrocarbon analyzer to yield composition in saturates “S” cyclics “C” and resins “R” n-pentane was used to elute the saturate species a 90/10 toluene/chloroform solution was used to elute the cyclics. the resins were not eluted and remained on the origin

Bitumen Compositional Analysis

True Grade Range vs. Composition

Asphalt Chemistry vs. GTR Loading

GTR “Polymer Modifier”

GTR is a Polymer – Vulcanized Rubber (Isoprene or SBR)

Typical Materials used to Manufacture Tires

Synthetic Rubber Styrene-Butadiene

Rubber Isoprene Butadiene Butyl Rubber Halogenated Butyl

Rubber Ethylene Propylene Diene

Monomer Natural Rubber Sulphur and sulphur

compounds Silica

Phenolic resin Oil: aromatic, naphthenic,

paraffinic Fabric: Polyester, Nylon, Etc. Petroleum waxes Pigments: zinc oxide, titanium

dioxide, etc. Carbon black Fatty acids Inert materials Steel Wire

Tire Compositions by Weight

Passenger Tire Natural rubber 14 % Synthetic rubber 27% Carbon black 28% Steel 14 - 15% Fabric, fillers,

accelerators, antiozonants, etc. 16 - 17%

Average weight: New 25 lbs, Scrap 20 lbs.

Truck Tire Natural rubber 27 % Synthetic rubber 14% Carbon black 28% Steel 14 - 15% Fabric, fillers,

accelerators, antiozonants, etc. 16 - 17%

Average weight: New 120 lbs., Scrap 100 lbs.

Compatibility Factor Cf = Polyisoprene/Acetone Extract

+ Ash

Time and Temperature

GTR and Polymer Modified Asphalt in General

Thermoplastic Elastomers/GTR used in asphalt modification “do not melt” SB SBS SBR etc.

Two Simultaneous Mechanisms Partial digestion Swelling (aromatic oils 180-230C)

Time and Temperature

Increasing Processing Time

Time

Isoprene SIS

SB SBS Linear

SBS Radial

SBR

GTR SBS High Vinyl

MIXTURES

Materials Four asphalt binders based on Conoco Phillips Wood River, IL

(CPW) PG67-22 Non-modified PG67-22 (referred to as PG67-22) CPW PG67-22 modified with pre-blended radial SBS to produce PG76-22 (referred to as PG76-22) CPW PG67-22 modified with pre-blended with 10 % GTR and

0.45% TOR (referred to as GTR Wet) Non-modified CPW PG67-22 co-mixed with dry added 10 % GTR

and 0.45% TOR in asphalt mixtures (referred to as GTR Dry) Granite aggregate from Rinker Materials meeting Georgia Department

of Transportation (GADOT) requirements

Mixtures Mixtures were prepared with all binders using:

GADOT 12.5mm nominal maximum dense graded SuperPave gyratory design with a target 5.1% binder content and nominal 6.0% voids (6.0 +/- 1.0% AASHTO T166)

GADOT OGFC 50 blow Marshall design with cellulose , a target 6.1% binder content and 20% voids (20 +/- 2.0% AASHTO T269)

GADOT SMA SuperPave gyratory design with a target 6.3% binder content and nominal 6.0% voids (6.0 +/- 1.0% AASHTO T166)

Mixture Preparation Mixtures with PG67-22, GTR Wet and PG 76-22 were produced at

171 C (340 F). Preheated aggregate was added to a 19 liter bucket mixer and dry mixed. A well was made in the middle of the dry aggregate to which the binders were added and mixed until the aggregate was coated. Mixtures were AASHTO R-30 short or long term aged as appropriate for testing

Mixtures produced with GTR Dry were produced at 171 C (340 F).

Preheated aggregate was added to a 19 liter bucket mixer and dry mixed, then GTR/TOR was added dry, the resulting dry aggregate plus dry GTR Dry mixture was then dry mixed again. A well was then made in the middle of the material to which the liquid PG67-22 binder was added and mixed until coated. The mixture was AASHTO R-30 short or long term aged as appropriate for testing.

Binder Test Data at 76 C (except PG67)

Material G*

(kPa) δ

(deg) G*/sinδ (kPa)

PG67-22 1.21 86.8 1.22 GTR Wet 1.88 79.1 1.92

PG76-22 1.09 67.3 1.18

Material RTFO Residue PAV Residue

G* (kPa)

δ (deg)

G*/sinδ (kPa)

G* (kPa)

δ (deg)

G*sinδ (MPa)

Stiffness m

PG67-22 2.96 83.2 2.98 6363 44.4 4452 192 0.300 GTR Wet 4.20 70.0 4.47 5168 39.8 3307 138 0.292 PG76-22 2.40 62.6 2.71 4165 45.8 2986 145 0.328

Material G*

(kPa) δ

(deg) G*/sinδ (kPa)

GTR Dry 1.57 84.0 1.58

GTR Wet 6.85 76.5 7.07

PG76-22 2.88 62.8 3.24

Original Binder Extracted Binder

Aged Binder

Extracted binder testing indicates that dry addition of GTR may not incorporate GTR into the binder well

Rut testing

APA Rutting @ 64°C dry

Rut testing

HWTD Rutting @ 50°C wet

Non-Recoverable creep compliance - Jnr

Binder

0.1 kPa Shear Stress

3.2 kPa Shear Stress

Jnr, kPa %

Recovery Jnr, kPa %

Recovery PG67-22 4.973 0 5.363 0 GTR Wet 0.636 37.1 1.072 9.6 PG76-22 0.349 78.0 0.399 75.1

Non-recovered Creep Compliance/Recovery (RTFO binder tested at 64°C)

PG76-22 = PG64VH-22 GTR wet = PG64H-22

fails recovery

Repeated Creep

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 500 1000 1500 2000 2500 3000 3500

Nor

mal

ized

Par

amet

er

Time, seconds

Cycles/Strain Normalized StrainSlope Flow Number (FN)Tertiary Flow Failure (TFF)

Repeated Creep

Binder

Time to 2%

Strain (sec)

Time to 5%

Strain (sec)

Flow Number

(Fn) (sec)

Tertiary Flow Failure (TFF)

(sec) 1/Slope

Dense Mixture PG67-22 70 460 1120 2410 209.5 GTR Dry 320 1740 4500 6000 933.2 GTR Wet 590 3090 3670 9900 1579.7 PG76-22 260 1840 7500 9900 1107.0

SMA Mixture GTR Dry 45 170 1040 1215 84.5 GTR Wet 115 455 2000 2710 195.3 PG76-22 85 430 6850 8225 663.6

Repeated Creep Data 34 kPa stress @ 64 C

Repeated Creep

Repeated Creep Cumulative Strain for Dense Mixtures

Repeated Creep

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

Nor

mal

ized

Str

ain

Time, seconds

PG76-22GTR WetGTR Dry

Repeated Creep Cumulative Strain for SMA Mixtures

AMPT – Flow Number

Average Flow Number @ 64°C, 600 kPa, 10 psi confining pressure

Summary Rubber produced from ground whole tires contains ~ 30%

reactive material for asphalt modification. There is no magic to GTR modified asphalt production,

that makes it any better or worse than other modifiers, improved performance modified asphalt can be produced with most all modifiers as long as proper engineering and evaluation is performed.

Asphalt source and chemistry directly effect rubber loading and the end properties of GTR modified asphalt.

Processing parameters Time/Temperature/Processing are important factors e.g. Typical processing temperature should be above 180 C, high shear not always beneficial.

Summary GTR chemistry and particle size greatly effects the

efficiency of modification as well as long term performance. Typically smaller particles yield better performance and easier processing.

Addition of ground tire rubber (GTR) to asphalt is an accepted practice in HMA production

Modification of liquid asphalt binders with GTR is well established and can provide high performance pavements which aid in reduction of the number of waste tires deposed of in landfills and elsewhere

Dry addition of GTR to asphalt mixtures prompts concern as to detrimental effects on long term mixture performance

Problems with GTR Modified Asphalt

Separation/Settlement Current SBS systems are not ideal for GTR Generally should use ~10% more AC and gap grade

mix increases cost of mix – hybrid addresses this issue

Cannot use standard SuperPave tests for rubber without changing DSR gap setting to 2mm for all test, ETG recommending changes to AASHTO and developing new method for large rubber particle sizes e.g. 15 mesh

Thank You!