Fatigue damage of bituminous mixes

Sylvie Yotte et Mohsen Ech

Centre de Développement des Géosciences AppliquéesUniversité de BordeauxFrance

Contents

● Pavement design and fatigue test● Damage model● Specimen simulation● Test simulation● Conclusion

Pavement design

Fatigue cracking is one of the degradation mode of pavements

Many laboratory fatigue tests existsAmong them LCPC fatigue test (standard in France)

Fatigue test

Xmsin(t)

Trapezoidal specimen subjected to a two point bending testSpecimen size : Bases : 25 mm and 56 mm – height : 250 mm

Result of the test

Experimental fatigue test

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Cycles

Stif

fnes

s

Simulation of the test

The stiffness loss is due to

•An increase of temperature due to viscoelasticity

•Thixotropy

•Damage

Assumptions :

•The temperature increase is neglected (stiffness loss of 3%)

•Elastic damage (we are interested in the final state of the specimen)

Simulation of the test

)10 DEE

3

1

12

)(1ln

DFD

NDF a

1

1

22IIIa

kk

kIIkIkk

lcr

a S

Sei

224

2

2

Three parameters damage test

1 = 50 – 2 = 5 – 3 = 3

= 0,5

r = 4mm

lc = 3mm

a is the weighted mean of the strain for elements which are within a circle of r radius of the examined element

Specimen simulation

Image creation

Image meshing

Scale : 1 mm = 1 pixel

Specimen simulation

gr3 gr2 gr1

aggregates 74.1 % 88.8% 90.1%

deviation=0.9% =0. 8% =1.3%

Simulation • 3 granulometries :

0

20

40

60

80

100

120

0 10 20 30 40 50 60

diameter (mm)

frequ

ency

granulometry 1

granulometry 2

granulometry 3

Results granulometry 1

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cycles

stiff

ness

loss

mean

gr01 min

gr01 max

0

20

40

60

80

100

120

0 10 20 30 40 50 60

diameter (mm)

frequ

ency mean

max

min

16 specimens

Granulometry computed on the initial image

Results of the simulation

Results granulometry 2

9 specimens

Granulometry computed on the initial image

Results of the simulation

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gr02 min

gr02 max

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diameter (mm)

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max

min

Results granulometry 3

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0 5 10 15 20 25 30 35

diameter (mm)

frequ

ency

mean

max

min

8 specimens

Granulometry computed on the initial image

Results of the simulation

70,00

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Cycles

Stiff

ness

loss

meangr03 mingr03 max

Comparaison of the 3 simulations

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cycle number

stiff

ness

loss

gr01 min gr01 max gr02 mingr02 max gr03 min gr03 maxreal real realreal

Results granulometry 4

9 specimens

Results of the simulation

5 % of asphalt mastic element were weak :

Eb = 9Mpa instead of 90 Mpa60,00

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stiff

ness

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0 10000 20000 30000 40000 50000 60000 70000

Cycles

Stiff

ness

mean

max alea

min alea

Discussion

Granulometry does not explain the dispersion

The introduction of 5 % aleas in the asphalt mastic phase increases the brittleness

The model with the chosen parameters cannot modelize the localization

Possible causes :

There are more then 5% feeble points in the mastic phase.

The damage program favors the damage on one side of the specimen

Localization begins sooner in the second phase of the test

Perspectives

● Identification method to set● Simulations with more aleas in the mastic phase● Healing simulation ● Multiscale simulation