a introduction to rubberized asphalt paul w. wilke, p.e., principal engineer
TRANSCRIPT
Introduction to Rubberized AsphaltPaul W. Wilke, P.E., Principal Engineer
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Presentation Outline
What is Rubberized Asphalt? Advantages & Limitations/Challenges Design & Construction Considerations Experience from Other States PennDOT Initiatives
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What is Rubberized Asphalt?
Asphalt cement modified with crumb rubber, used in asphaltic concrete
Common source of crumb rubber modifier (CRM)- ground scrap tires
CRM used in lieu of polymers to increase PG grade of asphalt binder
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How Asphalt Rubber Works
22,937,600
rubber
particles per
ton of mix
help fight
cracking
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History of Rubberized Asphalt Use & Performance Use dates to 1960’s 1991 FHWA mandate led to widespread use Many early failures- mandate dropped 1995 Most failures associated with “dry process” Dry process- CRM added to aggregate before mixing
with asphalt binder (serves as partial aggregate replacement)
Wet process- finely ground rubber blended with hot asphalt binder
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Next Era of Rubberized Asphalt Many states continued research on AR usage Arizona, California, Florida continued to use
extensively (mostly wet process) Recently many cold climate states, Canadian
provinces & European countries reporting increased usage & good performance
PA neighbors using- NJ, Mass, Md,OH, Va
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South Carolina
Florida
North Carolina
Washington, D.C.
DelawareNew Jersey
ConnecticutRhode Island
Massachusetts
Maine
New Hampshire
Vermont
New York
Ohio
Kentucky
West Virginia
Pennsylvania
IndianaIllinois
Iowa
Missouri
ArkansasTennessee
GeorgiaAlabamaMississippi
LouisianaTexas
Oklahoma
Nebraska
Kansas
South Dakota
North Dakota
Virginia
New Mexico
Arizona
ColoradoUtah
Nevada
California
Alaska
Minnesota
Wisconsin
Michigan
Montana
Wyoming
Idaho
Oregon
Washington
Maryland
Hawaii
DOT with Permissible PG Spec or Special Provision for RTR
Not using rubber or unknown
States Where RTR Can Be Used in Performance Graded Asphalt and Superpave Mixes(DOT Spec or Special Provision)
DOT has indicated they would use PG Rubber if it were supplied
Doug Carlson, Liberty Tire
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Benefits of Rubberized Asphalt vs Conventional Asphalt
Improved “visco-elastic” behavior provides many benefits Increased elastic range (ductility at low temperature,
stiffness at high temperature) Typically “bumps” PG grade at least one PA commonly used PG 64 -22 bumped to PG 76 -22
Performance Benefits Increased resistance to cracking (reflective, fatigue, low-
temperature) & rutting Better noise attenuation
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Environmental Benefits Reduces waste tire stockpiles 1,000 tires per lane-mile per 1inch asphalt layer
(Caltrans 2006 Asphalt Rubber Usage Guide)
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Limitations & Challenges with Rubberized Asphalt
Mix sticks to roller during compaction (can be mitigated with use of detergents on roller)
Mix adheres to rubber tired rollers (use vibratory steel wheel rollers)
Higher placement & compaction temperature required due to stiffness of mix
Temperature management critical to success
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Limitations & Challenges (cont’d)
Lower workability makes handwork difficult Limited contractor experience (would be overcome
with more PA projects)
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Limitations & Challenges (cont’d)
Tendency for rubber & asphalt to separate during storage & hauling
Maintain heat & agitation or add chemical modifiers (enhance bond between asphalt & rubber)
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Limitations & Challenges (cont’d) Superpave spec requires
Dynamic Shear Rheometer (DSR) for high temperature PG grade verification
Rubber particles can influence test (mitigated by use of 2 mm gap between plates)
AASHTO working on alternative testing
DSR testing
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Wet Process- 2 Types“High” & “Low” Viscosity Binders
High Viscosity (“Asphalt Rubber”) Meets requirement of ASTM D 6114 Rotational viscosity > 1500 cPs @ 375ºF Typically 15-22% CRM (#10 to #8 sieve size) Requires agitation to keep CRM evenly distributed Sometimes called “field blend”, but can be made in
terminal or mobile field blender
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Wet Process- 2 Types “High” & “Low” Viscosity Binders
Low Viscosity (Crumb Rubber Modified Asphalt Binder) Finer CRM (< #50 sieve) Typically CRM-10% of binder Normal circulation in storage tank keeps dispersed Does not require subsequent agitation Sometimes called “No Agitation Binder” or “Terminal
Blend” but can be made in terminal or mobile field blender
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Rubberized Asphalt Manufacturing
Rubber Modified Asphalt Technical Manual Ontario Tire Stewardship October 2012
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Rubber Is Loaded into Weigh Hopper
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Size of CRM particles
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Suppliers Near Pennsylvania
Terminal Blends Seneca Petroleum (Toledo, OH) Blacklidge Emulsions (Tampa, FL)
Mobile Blenders All States Materials Ecopath, NJ Blacklidge Emulsions,Tampa, FL Bitumar, Baltimore, Md (?)
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Asphalt Rubber Mix Types Gap Graded
Missing some fine size fractions- stone on stone contact High viscosity AR feasible due to high void content Good elastic recovery (resists cracking & rutting) Most widely used AR mix
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Asphalt Rubber Mix Types Open Graded
Predominately 2-3 aggregate sizes; few fines Rapid drainage of surface water (good friction) Can use high viscosity AR but no agitation AR needed to
preserve drainage properties Less commonly used (recent MassDOT experience)
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Asphalt Rubber Mix Types Dense Graded
Aggregate continuously graded (dense matrix) Most widely used non- rubberized mix type Need CRMAB, low % rubber (8-12%) & #30 mesh max to
incorporate binder into dense matrix Less widely used AR mix
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Binder Design
Binder design to use same materials as those in production Material interactions = f(source & type of materials)
For high viscosity binder, “blend profile” required in addition to conventional design to meet PG grade
Binder tests at 45, 90,240,360,1440 minutes from start of reaction to develop “profile” Verify viscosity & other properties Purpose- verify stability over time
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Mix Design
Conventional mix design procedure used with slight modifications
Increased mix & compaction temperatures
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Surface
Base / Subbase
Subgrade
Structural layer coefficients same as PennDOT Pub 242 for conventional Superpave layers
Range= 1.5” to 2.5” thick Minimum governed by aggregate size If traffic warrants > 2.5” layer, use
conventional HMA below 2.5” max
rubberized layer
A2,3 = 0.40, 0.11
A1 = 0.44
Structural Design (Pavement Thickness)
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Warm Mix Asphalt Works Well with Rubberized Asphalt WMA decreases temperature required for compaction Alleviates concerns for rubberized asphalt compaction
temperature
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Construction Considerations
No special placement equipment Use steel drum roller; avoid rubber tire roller Temperature control during transport & placement
important (AR mixes stiffer) Laydown Temperature
290-350°F (air & AC surface 55-64°F) 280-325°F (air & AC surface > 64°F)
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Other States Experience
Arizona, California, Texas, Florida extensive experience Gap graded most extensively used mix MassDOT gap graded spec used as basis for PennDOT
recent pilot projects Dense graded used by 6+ states MoDOT substantial dense graded projects (840 tons/8yrs) Good performance reported
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Comparative Cost SBS polymer modified binder $75-150/ton more than
conventional unmodified asphalt PG 76 -22 rubber modified similar cost to polymer modified
(anticipate decrease in rubber modified over time) Green benefits to use of rubber
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PennDOT Initiatives Gap graded pilot projects constructed in 2012, 2013,
2014 and 2015 1st GG project- I-78 Berks County 1.5” wearing on 10” concrete after HMA milled Excellent performance thru 2014
Dense graded pilot projects planned 2015 & 2016 Special Provision specs developed Asphalt Rubber Usage Guide developed Ultimate goal- allow polymer or rubber modification to
achieve PG 76 -22 premium mix for high traffic applications
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Summary
Rubberized asphalt provides superior mix to reduce rutting & cracking
Similar to polymer modified PG 76 -22 (used in severe traffic situations)
Usage across US growing Cost in PA should decrease as more PennDOT
projects done (expect $ similar to polymer modified) Green benefits
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Questions?
Contact Info:
Paul W. Wilke, P.E.Principal EngineerApplied Research Associates, Inc.Phone: 717-975-3550Email: [email protected]
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CRM Sizes Rubber is delivered in different systems with supper
sacks very prevalent. CRM comes in different sizes.