Emulsions 101
Sponsored by:
Minnesota LTAP Center
Presented by:
Michael Marti, P.E.
SRF Consulting Group, Inc.
Dan Wegman, P.E.
SemMaterials
Why are there Emulsions?
• Asphalt is a semi-solid or solid at room
temperature
• For workability it must be in a liquid state
• It can be liquefied by:
– heating (HMA)
– adding petroleum solvents (Cutbacks)
– emulsifying in water (Emulsions)
Cutbacks
• Petroleum solvent (naphtha or kerosene) is
added to base asphalt to make fluid
• Solvent then evaporates restoring asphalt’s
binding properties
• Health and environmental concerns:
– Flammable: Working temps of 275-300ºF
– Hydrocarbon emissions into atmosphere
• Other concerns: expense, sensitive to bleeding
• Asphalt particle size = 4m
Emulsions
• #200
sieve =of75m
• Definition
emulsion:
of
small
droplets of liquid in a second liquid with which
• GrainSuspension
of
salt
=
500m
the first liquid will not mix
• Allows for handling at air temperatures.
• Consists of:
– asphalt
– water
– emulsifying agent (surfactant)
• “Breaking” occurs (separation of the asphalt and
water)
• Upon curing, the residual asphalt retains all
of the adhesion, durability, and waterresistance of the original asphalt cement
Emulsifying agent
•
•
•
•
Surface-active agent, or surfactant
Keeps asphalt droplet in stable suspension
Controls breaking time
Determines classification
Cationic “C”,
positively (+) charged
Anionic,
negatively (-) charged
• Rapid Set RS
• Medium Set MS
• Slow Set
SS
• 1 or 2, relative viscosity
• “h” indicates harder
asphalt
Factors Affecting Breaking/Curing
• Weather Conditions:
Temperature, humidity, wind
• Water Absorption
• Aggregate moisture content:
Although wet aggregate may facilitate coating, it
tends to slow the curing process
• Mechanical forces:
Roller pressure forces water from mix
• Surface area:
Excessive fines or dirty aggregate accelerate
breaking
• Surface chemistry
Advantages of Emulsions
•
•
•
•
•
•
•
Safer (Working temps 150º vs 275ºF)
Delivered at useable temperature (no need to heat)
No solvents released to environment
Will adhere to wet aggregates
Less expensive
Ability to control breaking process
Built in anti-strip (better adhesion)
Modifiers
• High Floats
Emulsion Grade AC
• Polymers
High Float Residue
High Floats
• Most emulsifiers are designed to have little
effect on the properties of the asphalt after
the emulsion has cured.
High Floats are the exception.
• High floats are designed to form a
networked “gel” structure with the asphalt.
– Gel structure, similar to Jell-O, keeps the
asphalt from flowing
Why use High Floats?
• Gel structure has little effect at low
temperature but keeps asphalt from flowing at
higher temperatures
(road surface on hot summer days)
• Allows the use of a softer base AC
– less brittle at lower temps
(reduces thermal cracking)
– less runny at high temps
(reduces bleeding)
When should High Floats be used?
• Very good for dirty aggregate
– Emulsion are designed to begin breaking when
they come in contact with aggregates
– High Floats set slow enough to soak through
dust/dirt and lock on to rock
– Dusty hand test
• Areas susceptible to bleeding
Why is it called High Float?
• Refers to passing the “float” test
– ASTM D139; AASHTO T-50
• Emulsion residue poured into aluminum float
• Placed in water bath (140ºF) for 20 minutes
Pass
Fail
Polymer Modification
• What is it?
– Made of many (poly) small molecules (monomers)
– Monomers chemically reacted to one another
• Why?
– Extra performance and durability
– Reduced life cycle costs
• How?
– Many different process
Benefits of Polymer Modification
• Early chip retention
• Better adhesion and elasticity at low
temperatures (pushed rocks will get pulled backed)
• Reduced bleeding and flushing
• Enables use of chips seals for higher
volume roads
• Retards aging process (more self healing)
Handling Emulsions
Do’s
Don'ts
• Use vertical tanks (less surface area)
• Keep warm (check with supplier)
• If over extended period, gently mix
•
•
•
•
Do not store for extended periods of time
Do not contaminate
Do not store at high temperatures (>185ºF)
Do not let freeze
Handling Emulsions
Do’s
Don'ts
• Heat slowly with indirect heat
• Agitate slowly while heating
• Follow supplier’s recommendations
•
•
•
•
•
Do not heat above 185ºF
Do not heat with steam
Do not heat for a long time
Do not heat too quickly
Do not allow to cool lower than 60ºF
Handling Emulsions
Do’s
Don'ts
•
•
•
•
Use pumps with proper clearance
Warm pumps before pumping
Fill pump with fuel oil to prevent seizing
Pump in and out of the bottom of the tank
• Do not splash material when pumping
• Do not pump excessively
Review
• What does CRS stand for?
– Cationic Rapid Set
• When would you use a high float emulsion?
– With dirty/dusty aggregates
– Areas susceptible to bleeding
• What factors effect curing/breaking?
– Temperature, humidity, wind, Water Absorption,
Aggregate moisture content, Mechanical forces,
Surface area, Surface chemistry