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

• Definition of emulsion:

Grain 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 water resistance 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 • Rapid Set • Medium Set MS • Slow Set RS SS Anionic, negatively (-) charged • 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 • 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

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

• Use vertical tanks (less surface area)

Do’s

• Keep warm (check with supplier) • If over extended period, gently mix

Don'ts

• • • • Do not store for extended periods of time Do not contaminate Do not store at high temperatures Do not let freeze (>185ºF)

Handling Emulsions Do’s

• Heat slowly with indirect heat • Agitate slowly while heating • Follow supplier’s recommendations

Don'ts

• • • • • 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

• 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

Don'ts

• • 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