block 3 sp 14

Asphalt Binder General Rheology 1

General Rheology

Senior/GraduateHMA Course

Asphalt Binders General Rheology 2

Rheology

• Rheology:– the study of flow and deformation

• Constitutive relations– fundamental relationships between

force and deformation


Rheometers

• Equipment used to measure rheology• Shear rheometers

– Drag flow– Pressure driven flows

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


Shear Rheometers


Drag Flow Rheometers

• Sliding plate


Schematic of Sliding Plate Viscometer

(not to scale)

Chart Recorder


Assumptions

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


Concentric Cylinder


RMi

Ri2 L

R

Ro - Ri

Narrow gaps: Ri / Ro > 0.99



• Cone and Plate

Similar triangles for shear flow

Homogeneous flow



• Parallel Plate

Shear flow varies with gap height and radius

Non-homogeneous flow


Assumptions

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


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


Elastic Viscous

TimeA

A

B

C

Strain

Strain in-phase = 0o

Strain out-of-phase = 90o


Viscous Modulus, G”

Storage Modulus, G’

Complex Modulus, G*

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


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


Equipment Example


Equipment Examples


25 mm Plate with Sample

Equipment Example


Pressure Driven Rheometers

• Vacuum Viscometer

Velocity Profile Shear Stress Profile


Viscometer Tube

• Asphalt Institute Tube


Stiffness and Strength Rheometers


Bending Beam Rheometer

Air Bearing

Load Cell

Deflection Transducer

Fluid Bath

Computer


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


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)


Direct Tension Test

Le

Stress = = P / A

Strainf

L

Load

f


Equipment Example

Cooling System

Fluid BathLoading

Ram


Direct Tension Test


QUESTIONS?

block 3 sp 14

Technology

laminar flow

flow pressure

flow rheometers cone

study of flow

rheometers equipment

rheology shear rheometers

flows rheometers

beam thickness