evaluation of fatigue performance at different temperatures · minhoto, pais, fontes 10. 1. for...

Minhoto, Pais, Fontes

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Evaluation of Fatigue Performance at Different Temperatures

M.J.C. Minhoto J.C. Pais L.P.T.L. Fontes

http://www.uminho.pt/default.aspx


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• possible discrepancies between the climatic chamber temperatureand the specimen temperature

• The temperature variation inside of specimen, during fatigue test

Objective

• Evaluation of the fatigue life of AC mixes at different temperatures

Based of the obtained results:Second objective


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temperature measurement

‐ During twelve months; ‐ every hour during the year‐ temperatures hourly recorded;‐ at seven different depths

Field Observations


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Temperature variation


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The stiffness and fatigue resistance evaluations were performed

• Test temperatures of ‐5 ºC; 5 ºC, 15 ºC and 25 ºC

• A conventional mix and an asphalt rubber mix

• 4PB test in controlled strain

Laboratory tests

For stiffness and the phase angle evaluation‐ frequency sweep test at (10; 5; 2; 1; 0,5; 0,2; 0,1 Hz) in 100 cycles

Flexural fatigue tests: according to the AASHTO TP 8‐94

Carried out at 10 Hz and specimens with 50 x 63 x 380 mm3

Fatigue failure: flexural stiffness reduced to 50 % of initial value.


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Frequency Sweep Tests results

Stiffness Modulus

Phase Angle

Conventional mix


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Asphalt Rubber mix Frequency Sweep Tests results

Stiffness Modulus

Phase Angle


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Flexural Fatigue Tests resultsConventional MixtureFatigue Laws T = ‐5ºC; 5ºC; 15ºC; 25ºC


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Flexural Fatigue Tests resultsAsphalt Rubber mixtureFatigue Laws T = ‐5ºC; 5ºC; 15ºC; 25ºC


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1. For test temperatures of 25ºC and 15ºC:• the decrease of the test temperature in the asphalt mixture

decreases its fatigue resistance;

2. for lower test temperatures of 5ºC and ‐5ºC:• the decrease of the test temperature in the asphalt mixture

increases its fatigue resistance;

Fatigue results analysis

The results allows to conclude:

must be a temperature value at which:below and above, the fatigue resistance shows a different behavior


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Shell model: ( )

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36.008.1856.0

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− ⎟⎟⎠

⎞⎜⎜⎝

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=mixb

t

SVN ε

Specimen Tempe-rature(ºC)

Strain(E-6)

Stiffness(MPa)

Fatigue lifetest

Fatigue lifeShell model

Error(%)

mcd-06

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448 3440 4.9E+04 4.4E+04 11mcd-01 858 3183 3.0E+03 2.0E+03 53mcd-02 820 3602 4.9E+03 2.0E+03 148mcd-03 916 2548 3.7E+03 2.1E+03 74mcd-05 422 4033 5.9E+04 4.4E+04 33mcd-05 479 2524 4.7E+04 5.5E+04 -15mcd-12

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448 5129 2.9E+04 2.1E+04 36mcd-07 913 5004 2.0E+03 6.4E+02 214mcd-08 882 6062 1.9E+03 5.4E+02 251mcd-09 904 5752 1.2E+03 5.2E+02 140mcd-10 424 7885 3.0E+04 1.3E+04 130mcd-11 443 6316 1.7E+04 1.6E+04 7mcd-18

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302 12443 1.2E+05 3.1E+04 280mcd-13 417 11322 3.8E+04 7.3E+03 420mcd-14 450 8473 4.7E+04 8.5E+03 457mcd-15 409 14029 4.8E+04 5.5E+03 771mcd-16 226 11982 1.2E+06 1.4E+05 754mcd-17 314 10777 1.6E+05 3.3E+04 391mcd-24

-5

424 10666 1.5E+05 7.6E+03 1905mcd-19 412 16536 2.2E+05 4.0E+03 5355mcd-20 520 15084 1.3E+05 1.5E+03 8738mcd-21 576 8238 2.0E+04 2.6E+03 650mcd-22 335 11428 6.0E+05 2.2E+04 2678mcd-23 341 10489 8.1E+05 2.3E+04 3395

Fatigue results vs Shell ModelConventional Mixture

Specimen Tempe-rature(ºC)

Strain(E-6)

Stiffness(MPa)

Fatigue lifetest

Fatigue lifeShell model

Error(%)

ar-gg-05

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485 1046 2.6E+06 1.7E+06 49ar-gg-06 454 909 2.4E+06 2.4E+06 1ar-gg-01 858 880 2.6E+04 1.0E+05 -74ar-gg-02 817 1111 3.7E+04 1.3E+05 -71ar-gg-03 472 1040 2.5E+06 2.0E+06 27ar-gg-04 824 1152 1.1E+05 1.2E+05 -7ar-gg-12

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573 1808 1.0E+05 2.7E+05 -61ar-gg-07 947 1853 4.7E+03 2.2E+04 -78ar-gg-08 897 1798 6.1E+03 2.9E+04 -79ar-gg-09 910 1829 5.1E+03 2.7E+04 -81ar-gg-10 437 1453 1.5E+06 1.0E+06 47ar-gg-11 562 2060 3.1E+05 3.0E+05 3ar-gg-18

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312 3698 3.1E+06 2.5E+06 25ar-gg-13 428 3346 2.5E+05 5.1E+05 -50ar-gg-14 459 3025 6.1E+04 3.6E+05 -83ar-gg-15 411 3748 1.7E+05 6.2E+05 -72ar-gg-16 225 2978 1.1E+07 1.3E+07 -15ar-gg-17 216 3047 1.2E+07 1.6E+07 -22ar-gg-24

-5

534 3881 3.1E+05 1.2E+05 157ar-gg-19 427 4094 8.6E+05 3.7E+05 133ar-gg-20 422 3722 6.5E+05 3.9E+05 66ar-gg-21 483 3640 5.7E+04 2.0E+05 -71ar-gg-23 593 3031 3.5E+04 7.1E+04 -52ar-gg-05 485 1046 2.6E+06 1.7E+06 49

Asphalt Rubber Mixture

small errors

bigger error

bigger error

small errors


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The Shell design method draws someconclusions: the decrease of thetemperature can contribute to anincrease of the fatigue life , suggestingthe occurrence of the phenomenonabove described

The report SHRP–A–404 allows concludingthe same behavior: that the fatigue lifedecreases as the temperature decreases dueto the visco‐elastic behaviour of thebitumen


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From the laboratory fatigue test results, identical relationships:

Conventional Mixture Asphalt Rubber mixture


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Contribution to the discussion

A series of 4PB fatigue tests was performed at 20ºC

Observation of the thermal behavior of typical test samples , during a fatigue test

Thermocouples were placed in each specimen:

tested strain levels: 800E‐6; 400E‐6; 200E‐6

The temperatures were obtained by a Data logger, to which all the thermocouples were connected,


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Conclusion: in the fatigue tests performed at a strain level of 800, an increase of the dissipated energy occurs when compared to the other test conditions

Test results ‐ dissipated energy


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Conclusion: discrepancies between the climatic chamber temperature and the specimen temperature were observed

Test results ‐measured temperature


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Comparing the graphs of the dissipated energy and the temperature:

larger strain levels are responsible for larger dissipated energy

larger strain levels may be responsible for the reducing of the stiffness and affects its fatigue response

Then, it seems important to highlight some key aspects:

Test results ‐ Analisys

larger strain levels are responsible for the increasing of the temperature inside the specimen

Development of relationships between the thermal state of the specimen and theevolution of the fatigue test, by profiling a function of internal energy generation(Q(x,y,z,t)), that’s ensure thermal equilibrium of the test system:


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• The characterization an generalized law to describe the evolutionof the thermal state of specimens during the test

CONCLUSIONS

• Clear differences were observed between the climatic chambertemperature and the specimen temperature.

Thus, it seems important to investigate some aspects, such as:

• The extent to which the temperature variation observed in thesample can affect the fatigue resistance results

A set of 4PB fatigue tests were performed in order to observe thetemperature inside of test specimens.


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evaluation of fatigue performance at different temperatures · minhoto, pais, fontes 10. 1. for...

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