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Asphalt Binder Modified Binders 1
Modified Asphalt Binders
Senior/GraduateHMA Course
Asphalt Binder Modified Binders 2
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?
