Road Maintenance Solutions from One Source

G. Holleran, Vice President, Valley Slurry Seal Company, USA

Prepared For AEMA 2001 meeting San Diego 

Outline

Emulsion Basics

Test Methods and Emulsion types

Results

Conclusions

 Emulsion Basics

• Emulsions are dispersions of immiscible phases stabilized chemically
• Emulsions are NOT thermodynamically stable
• Emulsions settle due to density differences
• Emulsions flocculate and coalesce due to disruption and transport mechanisms
• This is time and temperature and handling dependant

What Do Emulsifiers Do?

• Create a surface charge at the interface of the asphalt and the water.
• Create Repulsion and storage stability.
• Provide wetting.
• Enhance adhesion (cationic).
• Gel the asphalt (high float).
• Control break and cure rate.

 Important Factors

• Charge size
• Molecular size
• Charge density
• HLB
• Double layer thickness
• Where is the emulsifier ?- equilibrium time
• Miscelle formation

Instability Mechanisms

• Water Inclusion
• Sedimentation
• Flocculation
• Coalescence
• Inversion
• Ostwald Ripening

 

• Basic emulsion testing equivalent to ASTM D244. Brookfield Viscometer used.
• Torsional recovery using Mobil method- (same as caltrans).
• Recovery using evaporation and CT331
• Microscopic technique visible developed at Mobil labs and done at Massey university N.Z
• Storage testing done using forced air ovens on 4 lt cans
• Stirring done every 24 hrs where appropriate
• Polymer micrographs done using UV fluorescence
• Lab Coarsening done using Brookfield viscometer and 100 rpm
• All formulations meet CRS-1 and CRS-2 basic Caltrans specs

 Sampling:

• Representative
• Not under pressure- e.g spray bar
• Discard first gallon (Minimum) ( T140)
• Gallon at least- Not smaller
• Transfer samples to avoid material broken on sides of sampling container
• Plastic or metal acceptable
• Sample must be preserved: new containers
• Protected from freezing

Chip Seal Process and Emulsion Properties - Stability
The emulsion must remain dispersed until sprayed and aggregate is applied.
Test Indication: 
Storage stability.
Shear susceptibility.
Important physical properties:
Particle size, particle size distribution, particle charge, emulsifier type, asphalt chemistry.

Chip Seal Process and Emulsion Properties - Sprayability

The emulsion must be able to be sprayed so that it will form an even fan and laterally distribute on the pavement.
Test Indication:
Sieve Content
Transverse Distribution Test
Important Physical Properties: 
Particle size, contamination, viscosity and viscosity profile, shear thinning, binder content.

Chip Seal Process and Emulsion Properties - Thixotropy

The emulsion must not run off the pavement and must form an even membrane on which to apply the chips.
Test Indication:
Binder content, field spray.
Shear thinning hysterisis loop.
Important Physical Properties:
Particle size and distribution, emulsifier type, binder type, binder content.

Chip Seal Process and Emulsion Properties - Mobility (Flow)
The emulsion must, after spraying, be able to coat the aggregate and pavement surface.
Test Indication:
Emulsion viscosity.
Important Physical Properties:
Particle size and distribution, emulsifier type, binder type, binder content.Chip Seal Process and Emulsion Properties - Wetting.

The emulsion be able to displace water from the surface of an aggregate and form a chemical bond.
Test Indication:
Coating, adhesion and stripping tests.
Important Physical Properties: 
Particle size and distribution, emulsifier type, binder type, binder content 

Chip Seal Process and Emulsion Properties - Breaking.

The emulsion must break on and between the aggregate particles slowly enough to allow bond and membrane formation but fast enough to allow traffic quickly.
Test Indication: 
Demulsibility, break tests. Zeta potential.
Important Physical Properties:
Particle size and distribution, emulsifier type, binder type, binder content. Aggregate type and condition, weather.

Chip Seal Process and Emulsion Properties - Curing.
The emulsion must be able to coalesce to form an even film and expel water from itself.
Test Indication: 
Water resistance, stripping tests, cure tests.(Vialit).
Important Physical Properties:
Particle size and distribution, emulsifier type, binder type, binder content.

 

Physical Properties of Binder

Rheological Properties:

penetration

Viscosity

Float Test

Ductility

Softening Point

Elastic Properties ( torsional, elastic)

Modulus/ phase angle

General

CRS-1 is 60% and is made to be stored and used at ambient.
CRS-2 (LM) is 65% asphalt and 3% latex and is made to be stored and used at 40 plus C. (AEMA)

Other Ways Emulsions Coarsen

• Pumping
• Dilution of cationic emulsions CRS type*
• Very low temperatures
• Boiling
• Low emulsifier contents

Purpose made low binder content tack coats are usually CSS or will have proportionately higher emulsifier contents based on asphalt

 

Conclusions

• Storage is a determinant of emulsion stability properties
• Storage effects dispersion of the polymer in the binder ie its morphology this affects viscoelastic properties
• Pen is largely unchanged (25C)