1. Introduction to Rubberized Asphalt
Paul W. Wilke, P.E.,
Principal Engineer
Pavement Preservation and Maintenance

2. Presentation Outline What is Rubberized Asphalt?
Advantages & Limitations/Challenges
Design & Construction Considerations
Experience from Other States
PennDOT Initiatives

3. 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

4. How Asphalt Rubber Works
22,937,600 rubber particles per ton of mix help fight cracking

5. 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

6. 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

7. (DOT Spec or Special Provision)
States Where RTR Can Be Used in Performance Graded Asphalt and Superpave Mixes
(DOT Spec or Special Provision)
New Hampshire
Washington
Vermont
Maine
Montana
North Dakota
Minnesota
Oregon
Massachusetts
New York
Idaho
Wisconsin
South Dakota
Wyoming
Michigan
Rhode Island
Connecticut
Iowa
Pennsylvania
New Jersey
Nevada
Nebraska
Ohio
Delaware
Indiana
Utah
Illinois
Colorado
West Virginia
Washington, D.C.
Kansas
Maryland
Virginia
California
Missouri
Kentucky
Tennessee
North Carolina
Oklahoma
Arizona
Arkansas
New Mexico
South Carolina
Mississippi
Georgia
Alabama
DOT with Permissible PG Spec or Special Provision for RTR
Texas
Alaska
Louisiana
Not using rubber or unknown
Florida
DOT has indicated they would use PG Rubber if it were supplied
Hawaii
Doug Carlson, Liberty Tire

8. 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 bumped to PG
Performance Benefits
Increased resistance to cracking (reflective, fatigue, low-temperature) & rutting
Better noise attenuation

9. Environmental Benefits
Reduces waste tire stockpiles
1,000 tires per lane-mile per 1inch asphalt layer (Caltrans 2006 Asphalt Rubber Usage Guide)

10. 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

11. Limitations & Challenges (cont’d)
Lower workability makes handwork difficult
Limited contractor experience (would be overcome with more PA projects)

12. 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)

13. 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

14. Wet Process- 2 Types “High” & “Low” Viscosity Binders
High Viscosity (“Asphalt Rubber”)
Meets requirement of ASTM D 6114
Rotational viscosity > ºF
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

15. 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

16. Rubberized Asphalt Manufacturing
Rubber Modified Asphalt Technical Manual Ontario Tire Stewardship October 2012

17. Rubber Is Loaded into Weigh Hopper

18. Size of CRM particles

20. 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 (?)

21. 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

22. 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)

23. 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

24. 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

25. Mix Design
Conventional mix design procedure used with slight modifications
Increased mix & compaction temperatures

26. Structural Design (Pavement Thickness)
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
Surface
Base / Subbase
Subgrade
A1 = 0.44
A2,3 = 0.40, 0.11
Non-Destructive Data Collection

27. Warm Mix Asphalt Works Well with Rubberized Asphalt
WMA decreases temperature required for compaction
Alleviates concerns for rubberized asphalt compaction temperature

28. 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
°F (air & AC surface 55-64°F)
°F (air & AC surface > 64°F)

29. 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

30. Comparative Cost
SBS polymer modified binder $75-150/ton more than conventional unmodified asphalt
PG rubber modified similar cost to polymer modified (anticipate decrease in rubber modified over time)
Green benefits to use of rubber

31. 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 premium mix for high traffic applications

32. Summary
Rubberized asphalt provides superior mix to reduce rutting & cracking
Similar to polymer modified PG (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

33. Questions?
Contact Info:
Paul W. Wilke, P.E.
Principal Engineer
Applied Research Associates, Inc.
Phone:
The feature of the road surface that ultimately determines most of the tire/road interactions including wet friction, noise, splash and spray, rolling resistance, and tire wear is pavement texture. Pavement texture is typically divided into categories of microtexture, macrotexture, and megatexture based on wavelength and vertical amplitude characteristics.
Microtexture is the surface “roughness” of the individual coarse aggregate particles and of the binder, and contributes to friction through adhesion with vehicle tires.
Macrotexture refers to the overall texture of the pavement (controlled by coarse aggregate type and size in flexible pavements and by surface finish in rigid pavements), which is intended to serve as escape channels for the surface water at the pavement-tire interface.
The Committee on Surface Characteristics of the World Road Association (PIARC) proposed the following more detailed definitions of the texture categories:
Microtexture—wavelengths of 1 mm to 0.5 mm ( to 0.02 in) with a vertical amplitude ranging between 1 and 0.2 mm ( to in). Microtexture is the surface “roughness” of the individual coarse aggregate particles and of the binder, and contributes to friction through adhesion with vehicle tires (wavelengths of 1 to 0.5 mm [ to 0.02 in]). This level of texture makes it possible to characterize a surface which is more or less rough, but is generally too small to be observed with the naked eye.
Macrotexture—wavelengths of 0.5 mm to 50 mm (0.02 to 2 in) with a vertical amplitude ranging between 0.1 and 20 mm (0.004 to 0.8 in). Macrotexture refers to the overall texture of the pavement (controlled by coarse aggregate type and size in HMA pavements), which is intended to serve as escape channels for the surface water at the pavement-tire interface (wavelengths of 0.5 mm to 50 mm [0.02 to 2 in]). This level of texture gives wavelengths of the same order of magnitude as those of the rubber strips of the tread of the tires which intervene in the tire-pavement contact.
Mention that there is also something called Megatexure—wavelengths of 50 mm to 500 mm (2 to 20 in), with a vertical amplitude ranging between 0.1 mm and 50 mm (0.004 to 2 in). This level of texture is generally a characteristic or consequence of deterioration of the surface.
Wavelengths longer than the upper limit (> 500 mm [20 in]) of megatexture are defined as “roughness.”

34. CRM Sizes
Rubber is delivered in different systems with supper sacks very prevalent.
CRM comes in different sizes.