A Introduction to Rubberized Asphalt Paul W. Wilke, P.E., Principal Engineer.

Introduction to Rubberized AsphaltPaul W. Wilke, P.E., Principal Engineer

Expanding the Realm of Possibility

Presentation Outline

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


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


How Asphalt Rubber Works

22,937,600

rubber

particles per

ton of mix

help fight

cracking


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


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


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


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


Environmental Benefits Reduces waste tire stockpiles 1,000 tires per lane-mile per 1inch asphalt layer

(Caltrans 2006 Asphalt Rubber Usage Guide)


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


Limitations & Challenges (cont’d)

Lower workability makes handwork difficult Limited contractor experience (would be overcome

with more PA projects)


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)


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


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


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


Rubberized Asphalt Manufacturing

Rubber Modified Asphalt Technical Manual Ontario Tire Stewardship October 2012


Rubber Is Loaded into Weigh Hopper


Size of CRM particles



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 (?)


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


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)


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


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


Mix Design

Conventional mix design procedure used with slight modifications

Increased mix & compaction temperatures


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)


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

temperature


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)


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


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


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


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


Questions?

Contact Info:

Paul W. Wilke, P.E.Principal EngineerApplied Research Associates, Inc.Phone: 717-975-3550Email: [email protected]

mailto:[email protected]


CRM Sizes Rubber is delivered in different systems with supper

sacks very prevalent. CRM comes in different sizes.

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A Introduction to Rubberized Asphalt Paul W. Wilke, P.E., Principal Engineer.

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