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Asphalt Binder General Rheology 1

General Rheology

Senior/GraduateHMA Course

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Rheology

• Rheology:– the study of flow and deformation

• Constitutive relations– fundamental relationships between

force and deformation

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Rheometers

• Equipment used to measure rheology• Shear rheometers

– Drag flow– Pressure driven flows

• Rheometers for measuring stiffness and strength– Bending beam– Direct tension

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Shear Rheometers

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Drag Flow Rheometers

• Sliding plate

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Schematic of Sliding Plate Viscometer

(not to scale)

Chart Recorder

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Assumptions

• Steady, laminar flow, isothermal flow• No radial or vertical flow• Negligible gravity and end effects

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Concentric Cylinder

Drag Flow Rheometers

RMi

Ri2 L

R

Ro - Ri

Narrow gaps: Ri / Ro > 0.99

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Drag Flow Rheometers

• Cone and Plate

Similar triangles for shear flow

Homogeneous flow

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Drag Flow Rheometers

• Parallel Plate

Shear flow varies with gap height and radius

Non-homogeneous flow

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Assumptions

• Steady, laminar, isothermal flow• Negligible body forces• Cylindrical edge

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1 cycle

TimeAA

B

C

CA

B

Fixed Plate

Oscillating Plate

Test operates at 10 rad/secor 1.59 Hz

360o = 2 p radians per circle1 rad = 57.3o

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Elastic Viscous

TimeA

A

B

C

Strain

Strain in-phase = 0o

Strain out-of-phase = 90o

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Viscous Modulus, G”

Storage Modulus, G’

Complex Modulus, G*

Complex Modulus is the vector sum of the storage and viscous modulus

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Master Curves• DSR testing can be used to develop master

curves– Need range of temps and frequencies at

each temperature• Information

– Affect of loading time on asphalt binder stiffness

– Estimate of thermal coefficient of expansion

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Equipment Example

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Equipment Examples

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25 mm Plate with Sample

Equipment Example

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Pressure Driven Rheometers

• Vacuum Viscometer

Velocity Profile Shear Stress Profile

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Viscometer Tube

• Asphalt Institute Tube

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Stiffness and Strength Rheometers

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Bending Beam Rheometer

Air Bearing

Load Cell

Deflection Transducer

Fluid Bath

Computer

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Bending Beam Rheometer

• S(t) = P L3

4 b h3 (t)

Where:S(t) = creep stiffness (M Pa) at time, tP = applied constant load, NL = distance between beam supports (102 mm)b = beam width, 12.5 mmh = beam thickness, 6.25 mmd(t) = deflection (mm) at time, t

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Bending Beam Rheometer• Evaluates low temperature stiffness properties

– Creep stiffness– Slope of response (called m-value)

8 15 30 60 120 240

Log Creep Stiffness, S(t)

Log Loading Time, t (sec)

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Direct Tension Test

Le

Stress = = P / A

Strainf

L

Load

f

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Equipment Example

Cooling System

Fluid BathLoading

Ram

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Direct Tension Test

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QUESTIONS?