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The Critical Role of Chemistry in Asphalt Paving and Pavement Preservation
International HighwayTechnology Summit
Shanghai, PRCApril 21-23, 2015
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Outline of Topics
Review of materials in asphalt pavementsChemistry of componentsBitumen emulsions and emulsifiersAdhesion mechanismsProperties imparted through chemical selectionSummary
WMA Operations & Baghouse Mangement / June 7, 2012
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What Goes Into Building a Road?
Most hot mix asphalt roads are:• 95% Aggregate (rock)• 5% Binder (ie. bitumen or other additives)• Laid down in “lifts” or layers of 5 to 20 cm
90% of all paving is hot mixPavement preservation techniques are used to maintain service life of the road or repair damage from aging/wear.• Hot mix overlays (~5 cm)• Slurry / Micro surfacing (~6 to 12.5 mm)• Seals (3 to 12.5 mm coating)
5% Binder
8% Binder
5-30% Binder
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Where Does Chemistry Play a Role? Bitumen or Asphalt Aggregate Chemical Additives
Adhesion Promoters / Anti-Stripping Additives
Warm mix additives Emulsifiers Performance additives Polymers
WMA Operations & Baghouse Mangement / June 7, 2012
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Chemistry of BitumenComposed of crystalline particles generally classified as asphaltenes suspended in an oily liquid continuous phase generally classified as maltenes. Other resins are also dispersed in the maltene phase. •Maltene fraction is further classified as saturates and aromatic oils.
WMA Operations & Baghouse Mangement / June 7, 2012
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Bitumen Variability
• Crude source / type – naphthenic vs. paraffinic
• Refinery processing
• Processing additives – caustic treatment
WMA Operations & Baghouse Mangement / June 7, 2012
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Bitumen composition directly affects performance of pavements and pavement preservation processes
Adhesion / moisture susceptibility. Long-term pavement life. Emulsion quality.
Viscosity Stability Mixing / setting / curing
characteristics
WMA Operations & Baghouse Mangement / June 7, 2012
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Aggregate Chemistry
Minerals have surface chargesThe charges on the asphalt particles interact with the stone’s
charges“Opposites attract” – longer lifeSilicates and slags – generally “–”Limestones – generally 0 or “+”HCl can help identify
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Aggregate
Definition – A mass of distinct things gathered into a total or whole
Hornblende – Ca2(Mg,Fe,Al)5(Al, Si)8O22(OH)2
1010
Where in the road?
New Construction & Recycling
Preservation
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Pavement Preservation
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Pavement Preservation Products
Micro SurfacingSlurry SealSeal Coat / Chip Seal
/
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Bitumen Emulsions
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What is an Emulsion?
Colloid or emulsion• A homogeneous mixture of two
insoluble substances• Particles of one substance
(dispersed phase) are surrounded by molecules of the other substance (continuous phase)
• Examples:– Milk, butter, mayonnaise– Latex paint– Bitumen emulsion
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Why emulsify bitumen?Viscosity reduction and safer use at lower temperaturesAbility to haul longer distances“Water based” system has better environmental impactReduced energy use, worker exposure, burn hazard, and job site odorProperly formulated emulsion systems provide long term performance benefits!
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Bitumen Emulsion
Hot Bitumen
EmulsifierSolution
+
Colloid Mill
Bitumen Emulsion
Bitumen Emulsion
- TRB circular E-C102
Human hair (50 microns)
Bitumen particle (5 microns)
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Emulsifier Chemistry
CH3 CH2CH2 CH2CH2 CH2CH2 CH2
CH2 CH2CH2 CH2CH2 CH2CH2 C
O
CH2 CH2NH2
CH2 CH2NH2
NHTail group
Head group+/-
“Short hand” picture
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Emulsifier Orientation at the Bitumen/Water Interface
+/-
Bitumen particle surface
Emulsifier solution
Micelle
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Emulsifier Orientation at the Bitumen/Water Interface
Opposite charges attract and same charges repel
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Emulsion Performance – How does the emulsion act in the presence of aggregate?
- --- - - - ---- - - -- -
+
+
+ +
+
++++
+
+ +++ +
+
++++
++
++
+ + + +
++
+
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Adhesion – A Simplified Model
Benefits• Reduced susceptibility to water damage• Greater resistance to pavement deformation• Reduced raveling or chip loss• Increased pavement life
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Adhesion – Oxide Mineralogy (Granite, Trap Rock, Basalt, Slag…)
-- + - -- +++ + ++++ -+ -- + --- ------
Asphalt film Asphalt film
StoneStone
Cationic EmulsionOpposite charge interaction
produces a tight bondAnionic Emulsion
Similar charge interaction produces a weak bond
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Adhesion – Carbonate Mineralogy (Limestone, Dolomite, Marble…)
++ + + -- +++ + ++++ ++ +- + -+- ------
Asphalt film Asphalt film
StoneStone
Anionic EmulsionOpposite charge interaction
produces a tight bondCationic Emulsion
Similar charge interaction produces a weak bond
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Adhesion – The Real World
Aggregates are never a single pure mineral
Adhesion is really development of “enough” water insoluble “glue” at the binder/aggregate interface to meet a specification
Remember the hornblende?
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Adhesion – The Real World
One emulsion must work with a variety of aggregates in a region.
Formulations are developed that perform over the range of variation anticipated.
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Other performance properties optimized through chemical selection
Particle size distribution
Storage and transport stability
Viscosity
Mixing characteristics
Rate of set and cure
WMA Operations & Baghouse Mangement / June 7, 2012
Emulsion Additives
Polymers (rubber)• Water based latex polymers may be incorporated in the
emulsion water phase or solid polymers incorporated into the binder
• Polymers provide low temperature flexibility, high temperature stiffness, moisture resistance and improved pavement durability
• Lower life cycle cost by extension of pavement life
Polymers
Dried emulsion residues (coalesced bitumen particles)
Unmodified asphalt Latex modified emulsionEmulsion of polymer modified asphalt
Bitumen rheology only Improved binder properties•Improved low temperature fatigue properties•Reduced rutting at high temperature•Improved early strength development
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Summary
Chemical composition of paving materials is diverse and affects performance.
Chemical additives can be selected to achieve optimum performance and deliver successful projects.
Bitumen emulsions are a fundamental part of many Pavement Preservation technologies.
