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

Emulsions• Definition of emulsion:

Suspension of small droplets of liquid in a second liquid with which 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 water-resistance of the original asphalt cement

• Asphalt particle size = 4Asphalt particle size = 4mm• #200 sieve = 75#200 sieve = 75mm• Grain of salt = 500Grain of salt = 500mm

Emulsifying agent• Surface-active agent, or surfactant• Keeps asphalt droplet in stable suspension• Controls breaking time• Determines classification

• Rapid Set RS• Medium Set MS• Slow Set SS

• 1 or 2, relative viscosity• “h” indicates harder asphalt

Cationic “C”, positively (+) charged

Anionic,negatively (-) charged

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

• Polymers

Emulsion Grade AC 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

PassFail

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

• 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

Don'ts

Do’s

Handling Emulsions

• 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

Don'ts

Do’s

Handling Emulsions

• 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

Don'ts

Do’s

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