Block 6 SP 14

Asphalt Binder Modified Binders 1

Modified Asphalt Binders

Senior/GraduateHMA Course

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Why are Modifiers Used?• Mitigate both traffic- and environmentally

induced HMA pavement distresses– Rutting resistance

•Stiffer asphalt binders at warm temps– Thermal cracking

•Inhibit crack propagation– Internal elastic network (polymers)–Crack pinning (solid particles)

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Types of Modifiers• Polymers

– Plastomers– Elastomers

• Fillers– Gilsonite– Mineral fillers– Misc.

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Polymers• Plastomers

– Quick early strength but with little ability to strain without brittle failure

– Any strain tends to be permanent•Little elastic behavior

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Plastomer Product Examples

Trade Manufacturer Type ChemistryNameNovophalt Novophalt Copolymer LDPE

Elvax DuPont Copolymer EVA

Polybuilt Exxon Copolymer EMA or EVA

Starflex Carraux Copolymer EVA

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Polymers• Elastomer

– Resist permanent deformation by an ability to stretch and recover shape once load is removed

– Only contribute to tensile strength when stretched

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Elastomer Examples

• Natural Rubber• Synthetic Rubber

– Styrene-Butadiene Rubber (SBR)•Random block

• Thermoplastic Rubbers– Styrene-Butadiene-Styrene (SBS)

•Triblock copolymer that form network

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Elastomer Product Examples

Trade Manufacturer Type ChemistryNameDownright DOW Random SBR

Copolymer

Kraton Shell Block SBSCopolymer

Styrelf Koch Block BlendedCopolymer

Vector Exxon Block SBSCopolymer

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Common Polymer Terms

Straight Chain or Linear

Radial

Polymer with Branches

Crosslinked

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SBS Polymers in Asphalt Binders

Step 1

Step 2

Step 3

Polymer Polymer in hot AC

Polymer in cool AC

StyreneButadiene

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Traditional Testing for Modified Asphalt Binders

• Vacuum viscosity– Asphalt Institute tubes

• Ductility– Elastic recovery

• Softening Point– Increases with polymer concentration

• Toughness and Tenacity• Separation

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TEM Microphotographs

2% Linear SBS 4% Linear SBS

White area = Asphalt Binder and Black area = polymer

500 nm 500 nm

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TEM Microphotographs

6% Linear SBS 10% Linear SBS

500 nm1 m

White area = Asphalt and Black area = polymer

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TEM MicrophotographsWhite area = Asphalt Binder and Black area = polymer

4% Radial SBS

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NCHRP Report 459

Characterization of Modified Asphalt Binders in Superpave Mix Design

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Topics Covered

• Storage stability of modified asphalt binders• Shear-rate dependency of viscosity• Strain dependency of rheological response• Effect of mechanical working• Loading-rate dependency and time-temp

equivalency

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Modified Asphalt Binders• Simple asphalt binders

– Do not violate assumptions of Superpave rheological tests

• Complex asphalt binders– Behavior (characteristics) violate one

or more assumptions

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Simple Asphalt Binders

• <2% by vol of additives retained on No. 200 sieve– PAT with toluene

• Stable for 2 or more days at mix/compact temps– LAST

• Reasonably linear over range of stress and strain• Insensitive to cyclic damage during testing

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Particulate Additive Test (PAT)

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Laboratory Asphalt Stability Test(LAST)

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Other Topics• Researchers addressed

– Effect of traffic volume– New procedures for low temperature

cracking prediction models

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QUESTIONS?