Rubber Modified Binders and Mixtures

Transcription

1 Rubber Modified Binders and Mixtures Presented by: Gaylon L. Baumgardner Paragon Technical Services, Inc. and Ergon Asphalt and Emulsions, Inc. 56 th Annual New Jersey Asphalt Paving Conference 5-6 March 2013

2 Introduction

3 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

4 Asphalt/Asphalt Grades

5 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.

6 Useful Temperature Interval (UTI) SuperPave Made Simple

7 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.

8 Useful Temperature Interval 98 C 86 C 74 C

9 UTI of Performance Grade Asphalts A PG would have a UTI of 86 C A PG 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

10 Modification of Asphalt Binders

11 Methods of Modification: addition extending agents, chemical additives, air blowing, polymer addition.

12 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.

13 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...

14 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.

15 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

16 GTR Modification of Asphalt

17 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.

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

19 Critical Factors Asphalt Chemistry - Source Rubber Composition Chemistry Rubber Particle Size Processing Parameters Time and Temperature Optimization

20 Asphalt Binder Source/Composition

21 Petroleum Administration for Defense Districts (PADDs) East Coast 2 - Midwest 3 - Gulf Coast 4 - Rocky Mountain 5 - West Coast 3

22 Bitumen Compositional Analysis 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

23 True Grade Range vs. Composition

24 Asphalt Chemistry vs. GTR Loading

25 GTR Polymer Modifier

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

27 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

28 Tire Compositions by Weight Passenger Tire Natural rubber 14 % Synthetic rubber 27% Carbon black 28% Steel 14-15% Fabric, fillers, accelerators, antiozonants, etc % 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 % Average weight: New 120 lbs., Scrap 100 lbs.

29 Compatibility Factor C f = Polyisoprene/Acetone Extract + Ash

30 Time and Temperature

31 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 C)

32 Time and Temperature

33 Increasing Processing Time Isoprene SB SBS Linear SBR SIS SBS High Vinyl SBS Radial GTR Time

34 MIXTURES

35 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

36 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)

37 Mixture Preparation Mixtures with PG67-22, GTR Wet and PG 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.

38 Binder Test Data at 76 C (except PG67) Original Binder Extracted Binder Material G* (kpa) δ (deg) G*/sinδ (kpa) Material G* (kpa) δ (deg) G*/sinδ (kpa) PG GTR Wet GTR Dry GTR Wet PG Aged Binder RTFO Residue G* δ (kpa) (deg) PG PAV Residue G* (kpa) Material G*/sinδ δ G*sinδ Stiffnes (kpa) (deg) (MPa) s m PG GTR Wet PG Extracted binder testing indicates that dry addition of GTR may not incorporate GTR into the binder well

39 Rut testing APA 64 C dry

40 Rut testing HWTD 50 C wet

41 Non-Recoverable creep compliance - J nr Non-recovered Creep Compliance/Recovery (RTFO binder tested at 64 C) 0.1 kpa Shear Stress % Recovery J nr, kpa 3.2 kpa Shear Stress % Recovery Binder J nr, kpa PG GTR Wet PG PG76-22 = PG64VH-22 GTR wet = PG64H-22 fails recovery

42 Repeated Creep Cycles/Strain Slope Tertiary Flow Failure (TFF) Normalized Strain Flow Number (FN) Normalized Parameter Time, seconds

43 Repeated Creep Repeated Creep Data 34 kpa 64 C Binder Time to 2% Strain (sec) Time to 5% Strain (sec) Flow Number (Fn) (sec) Tertiary Flow Failure (TFF) (sec) 1/Slope Dense Mixture PG GTR Dry GTR Wet PG SMA Mixture GTR Dry GTR Wet PG

44 Repeated Creep Repeated Creep Cumulative Strain for Dense Mixtures

45 Repeated Creep GTR Dry GTR Wet PG Normalized Strain Time, seconds Repeated Creep Cumulative Strain for SMA Mixtures

46 AMPT Flow Number Average Flow 64 C, 600 kpa, 10 psi confining pressure

47 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.

48 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

49 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

50 Thank You!