Characterisation of Bitumen Using Rheological Means

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• Characterisation of Bitumen Using Rheological
  Means

Glynn and Irina Holleran
Customer Driven Highways NZIHT/NZTA
Rotorua November 2009
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Bitumen comes from crude oil
OR OTHER SOURCES
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Outline

• Specifications
• Bitumen Chemistry
• Rheology
• Bitumen Variability and Measurement
• Modification
• Field Performance

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"Everything should be made as simple as possible,
but not one bit simpler." Albert Einstein US
(German-born) physicist (1879 - 1955)
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Specifications

• Bitumen is a moveable feast, it is both shear and
  temperature dependant. It will change its
  response depending on how its loaded
• Traditional specifications measure points and
  join them up
• PG Specifications measure the physical properties
  in the range of interest and correlates them to
  field performance

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Source Exxon-Mobil
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Types of Performance Specification

• The Bitumen chemistry determines the Structure
  and Performance, especially in adhesion and water
  resistance
• The Bitumen rheology is determined by its
  structure and thus chemistry. Structure is
  produced by molecular associations, polar type
  interactions
• Both may be used in specifications and in
  deciding what performs best

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Polar Molecules have higher Volumes Create more
bulk
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Bitumen Chemistry

• Complicated! Many sources of crude and blend
  materials and different processing

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Making Bitumen Chemistry Easier to Cope with

• Break it up into bits- fractionation
• Model the bits
• Compare to real life
• Fractionation
• Different methods
• Asphaltenes/Maltenes
• SARA
• SARAB

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Structure in bitumen is a result of polar
molecular associations
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Iatroscan FH Method

• This method gives four peaks for the SARA(B)
  analysis
• Saturates
• Aromatics
• Resins
• Asphaltenes ( Resins B)

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Reproducibility
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Triangular Diagram
0
100
60/70 Light Imports or blends
80/100 Light Imports
80/100,180/200,60/70,40/50 New route Heavy crudes
NZRC
Blown 40/50 NZRC
Resins A
Resins B
Crude/Processing Shift
100
0
100
0
Oils
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Models Colloidal

• Colloidal
• Microstructural

High Gaestal Index
ARRB
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Models Microstructural
Colloidally unstable High Gaestal index
AFM Picture
Saudi- Arab Heavy Bitumen 15umX15um
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Bitumen composition 4 broad chemical types
100000
Adhesion
10000
Flexibility
Molecular weight
1000
Strength
Low Temperature
100
Saturates
Aromatics
Resins
Asphaltenes
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Example Of Composition Change
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Compositional Change with Grade
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Rheology

• Simply how the bitumen reacts to stress and
  strain
• Characterises real materials parameters compared
  to say penetration or softening point

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DSR
tmax gmax
B
Stress
Time
A
A
A
Strain
C
d
Bitumen in the Middle
Elastic
Viscous
Strain in-phase ? 0o
Strain out-of-phase ? 90o
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• Unaged and aged samples
• Temp range sub zero to 140C
• Measures a range of rheological parameters
• Prelim work based on AASHTO T315 looking at
  premature failures
• Very reproducible

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Repeatability- Control
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Phase angle shows structure
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Stiffness at High Temperature shows temperature
and shear susceptibility
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Stiffness- Intermediate to Normal Temperature
shows likelihood of ravel or stone loss
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The same effect is repeated for all bitumens e.g.
60/70
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Stiffness - High Temperature 60/70
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Stiffness- Intermediate to Normal Temperature
60/70
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Modified Materials can be characterised e.g. PMB
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Blending may be done to rheological targets
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How do we Know it works?- A few Examples

• Round About and Approaches- Heavy Traffic
• Mix design acceptable
• QA on site and in plant acceptable
• Shoved and flushes/Bled in two months

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Phase angle comparison
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Stiffness at High Temperatures
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Wheel Tracking
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Heavy Traffic Full Depth Asphalt

• Mix tender and tended to flush
• Hard to compact
• Adjustments improved but did not solve problem
• Bitumen blending to rheologically desirable form
• Problem solved- job met completion date

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Phase angle comparison
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Other

• Sealing cutbacks stone retention at low
  temperatures
• Sealing emulsions
• Emulsion stability
• All explained and successfully addressed using
  rheological and compositional analysis
• A future PG specification is possible for NZ in
  both Asphalt and Sealing

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Conclusions

• This work indicates that bitumen variability is
  an issue that needs attention.
• The work shows that rheological examination and
  compositional analysis can uncover potential
  issues not covered in empirical specifications.
  The work needs to be extended into very low
  temperatures using Bending Beam or Direct Tensile
  testing.
• Field correlation has been observed and a degree
  of predictability. At present this appears to
  eliminate the problem materials, but whether this
  also eliminates materials that will be acceptable
  is not known.
• A performance graded specification for all
  applications needs to be developed.
• The good performance of existing and past NZRC
  based materials has illustrated that TNZ M1 is
  adequate for this stable supply, but testing has
  also shown that variability can create issues.
  Import bitumens that meet TNZ M1 may still have
  issues and a performance approach can
  differentiate between satisfactory materials and
  those which may require attention and
  modification.