Basic Emulsion Chemistry
AEMA Asphalt Emulsion Technologies Workshop November 14, 2011
Andrew Bickford Asphalt Innovations MeadWestvaco Topics
Wha t is an asph alt emul si on ? Emulsion chemistry Emulsion composition and performance What is an Emulsion?
Solution A homogeneous mixture of two substances Indivi dual m ol ecules of on e substa nce (sol ute) are surrounded by molecules of the other substance (solvent) Examples: What is an Emulsion?
Colloid or emulsion A homogeneous mixture of two insoluble substances Particles of one substance (dispersed phase) are surrounde d by mol ecu les o f the o ther sub st ance (continuous phase)
. What is an Emulsion?
Colloid or emulsion A homogeneous mixture of two insoluble substances Particles of one substance (dispersed phase) are surrounde d by mol ecu les o f the o ther sub st ance (continuous phase) Examples: What is an Emulsion?
AhltAsphalt Composed of crystalline particles generally classified as “asphaltenes ” Asphaltenes are suspended in an oily liquid continuous phase generally classified as “maltenes” The balance of composition determines asphalt physical properties such as rheology What is an Emulsion?
Why emuls ify aspha lt? Viscosity reduction and safer use at lower temperatures Change from “oil based” to “water based” system Reduced energy use, worker exposure, burn hazard and job site odor Properly formulated emulsion systems provide long term performance benefits What is an Emulsion?
Rotor
Gap
Stator What is an Emulsion?
Molten asphalt and emulsifier solution Rotor go in…
shear Time
Stator What is an Emulsion?
Molten asphalt and emulsifier solution Rotor go in…
shear Time Time
…and a water based Stator asphalt emulsion comes out What is an Emulsion?
Asphalt particle (5 microns)
Human hair (50 microns)
- TRB circular E-C102 What is an Emulsion?
The aspha lt particl es will stiktick toge ther (the emulsion will break) if only water and asphalt are used
The emulsifier is added to coat the asphalt particle surfaces and keep them from sticking together What is an Emulsion? What is an Emulsion?
Average 3-7 microns diameter Asphalt is usually 57-70% of the emulsion 1 gram of asphalt will form more than 10 billion particles The to ta l sur face area o f 1 gram of asphalt is 1-2 m2 OOene dopdrop of em useulsifier w oudould ssabetabilize 14 ft as much as 100 billion particles or 10- 20 m2 of asphalt particle surface area 14 ft Emulsion Chemistry
GlGeneral emulifilsifier chilhemical stttructures “Salt” formation Surface activity of emulsifiers Asphalt Emulsifiers Have in Common…
An oil sol u ble par t A water soluble part Some characteristic that allows the molecule to protect the surf ace of the asphalt droplet Elect ri cal charge… …or no charge, but large size Emulsifiers
CH3 CH2CH2 CH2 CH2 CH2CH2 CH2
CH2 CH2CH2 CH2 O Tail group (oil soluble) CH2 CH2CH2 C NH CH CH 2 2 2 NH NH CH CH 2 2 2 +/- Head group (water soluble) “Short hand” picture The Oil Soluble Part
In most cases bbdased in anima l or vegetable fats Cont ai ns chemi ca lly reac tive sites to allow attachment/modification of the water soluble part The Water Soluble Part
Pol ar sub s tituen ts (those tha t s hare bond electrons unevenly) are water loving Types incl u de oxygen, n itrogen and sa lts of O and N (full +/- electrical charges) CdCompounds contiitaining these atoms can be chemically attached to the acid end of the fatty acid molecule Anionic Emulsifier Molecule
CH3 CH2CH2 CH2 CH2 CH2CH2 CH2
CH2 CH2CH2 CH2 O CH2 CH2CH2 C Tail group OH
Head group Cationic Emulsifier Molecule
CH3 CH2CH2 CH2 CH2 CH2CH2 CH2
CH2 CH2CH2 CH2 O CH2 CH2CH2 C NH CH CH Tail group 2 2 2 NH NH CH CH 2 2 2 Head group Salt Formation
AiAnioni c =O =O - + R–C–OH + NaOH R–C–O Na + H2O Fatty acid Fatty acid sodium salt “R” = Hydrocarbon tail
Cationic =O =O + - R–C–NH2 + HCl R–C–N H3Cl Fatty amide Fatty amide hydrochloride salt Emulsifier Orientation at the Asphalt/Water Interface
Asphalt particle Emulsifier surface solution
+/-
Micelle The Emulsifier - Stability
The emulsifier coats the surface of asphalt droplets in the emulsion and makes them storage stable The Emulsifier - Performance
+ The emulsifier coats the surface of + asphalt droplets in the emulsion and + makes them storage stable
+ + + + +
+ + + + + Upon application, the emulsifier provides a predetermined breaking + + speed + Application
“Appli ca tion” usually refers to spraying the emulsion onto surfaces or mixing them with aggregates To understand emulsion performance, we need to know more about aggregate or other surfaces A Short Interlude - Aggregate
DfiitiDefinition – A mass of ditidistinc t things gathered into a total or whole
Hornblende – Ca2(Mg,Fe,Al)5(Al, Si)8O22(OH)2 Surface Properties of Rocks
Surface charge measurements (Zeta potential) show that general mineral categories fall in two zones This affects the rock’s interaction with asphalt emulsions Carbonates Silicates Aged asphalt surfaces Slag
positive negative 0 The Emulsifier - Performance+ + + + 1. Light weight, fast moving + surfactants interact with aggregate + + 2. Asphalt particle attracted to surface + + + + 3. Opposite char ges neutralize + each other and emulsion breaks + 4. Asphalt particles stick to + - - - - - each other and to the - - - aggregate Adhesion – Silicate Mineralogy (Granite, Trap Rock, Basalt, Slag…)
Cationic Emulsion Anionic Emulsion Opposite charge interaction Similar charge interaction produces a tight bond produces a weak bond
Asphalt film Asphalt film
+ + + + + + - - - - - + --- + - + ------+ - + Stone Stone Adhesion – Carbonate Mineralogy (Limestone, Dolomite…)
Cationic Emulsion Anionic Emulsion Similar charge interaction Opposite charge interaction produces a weak bond produces a tight bond
Asphalt film Asphalt film
+ + + + + + ------+ + + + - - + + + + - + + - + - Stone Stone Adhesion - Benefits
Red uce d susceptibility to water damage Greater resistance to pavement dfdeforma tion Reduced raveling or chip loss Increased pavement life Adhesion
Adhes ion can be achieve d through … …proper selection of emulsion and emulsifier type (cationic vs anionic) based on aggregate mineralogy, or… …through use of emulsion chemical additives Emulsion Additives Polymers (rubber) Water based latex polymers may be incorppporated 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 asphalt particles)
Emulsion of polymer Unmodified asphalt Latex modified emulsion modified asphalt
Asphalt rheology only Improved binder properties •Improved low temperature fatigue properties •Reduced rutting at high temperature •Improved early strength development
Content courtesy of BASF Questions??