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!
Top Related