Félix E. Pérez JiménezRodrigo Miró Recasens

Adriana MartínezRamón Botella Nieto

Oscar Reyes OrtizGonzalo A. Valdés Vidal

Departamento de Infraestructura del Transporte y Territorio

IntroductionTest Materials Four point bending beam fatigue testThree point bending beam fatigue test Direct tensile fatigue testConclusions

Different criteria to determine the number of cycles to failure:

Classical criterionStress controlled: Cycles to total specimen failure.Strain or displacement controlled: Cycles to 50% initial modulus.

Damage-energy approachAnalysis of the Dissipated Energy Ratio (DER).

nn

n

iii

DERθπσε

θπσε

sin

sin1∑==

Studies carried out at Road Research Laboratory have shown that some specimens do not achieve failure even though their modulus has drop below 50% the initial value in the displacement or strain controlled tests.These results will be shown in this presentation, obtained in flexural fatigue tests using the three and four point bending beam machines.

Two mixtures were testedAC22 bin 80/100 S with 30% of RAP, 4.5%.AC22 bin 150/200 S with 50% of RAP, 4.5%.

Four point bending beam fatigue test (UNE-EN 12697-24)

)2sin(0 ftDD π⋅=

False fatigue failure detected when higher strain is applied.

Three point bending beam fatigue test (UNE-EN 12697, Annex C)

)2sin(0 ftDD π⋅=

0

100

200

300

400

500

600

Load

(N)

Number of Cycles

200 microstrains

AC22 bin 150/200 S 50% RAP

0.00000

0.00050

0.00100

0.00150

0.00200

0.00250

0.00300

0.00350

0.00400

0.00450

0.00500

Stra

in (m

m/m

m)

Number of Cycles

200 microstrains

AC22 bin 150/200 S 50% RAP

0

100

200

300

400

500

600

Load

(N)

Number of Cycles

200 microstrains 500 microstrains

AC22 bin 150/200 S 50% RAP

0.00000

0.00050

0.00100

0.00150

0.00200

0.00250

0.00300

0.00350

0.00400

0.00450

0.00500

Stra

in (m

m/m

m)

Number of Cycles

500 microstrains200 microstrains

AC22 bin 150/200 S 50% RAP

Critical Strain.

AC22 bin 80/100 S with 30% RAP

Critical Strain.

AC22 bin 150/200 S with 50% RAP

CTD (Catalonia Direct Tensile) testStrain and stress controlled test

2/)(2

)2sin(

minmaxmin

minmax0

0

FFFAFFF

AftFF

−+=−=

+⋅= π)2sin(0 ftDD π⋅=

CTD test under strain controlled conditions

-240

-200

-160

-120

-80

-40

0

40

80

120

160

200

240

0 100000 200000 300000 400000 500000 600000 700000

Number of Cycles

Load

(kg)

AC22 bin 150/200 S with 50% RAP

Strain amplitude ranges

CTD (Catalonia Direct Tensile) test under stress controlled conditions. Critical strain.

0.00000

0.00010

0.00020

0.00030

0.00040

0.00050

0.00060

0.00070

0 200000 400000 600000 800000 1000000 1200000

Number of Cycles

Max

Str

ain

- Min

Str

ain

(mm

/mm

)

Specimen 1 (10-200)

Specimen 2 (10-300)

Specimen 3 (10-250)

Specimen 4 (10-280)

Specimen 5 (10-220)

Specimen 6 (10-170)

Specimen 7 (10-200)

Specimen 8 (10-180)

Critical Strain

AC22 bin 80/100 S with 30% RAP

  ε

Mixture C Mixture A

A and B: Low Modulus Mixtures

C and D: High Modulus Mixtures

N

Critical Strain for mixes B and D

Critical Strain for mixes A and C

Mixture B Mixture D

Fatigue cracking of bituminous mixtures takes place when a certain strain level is reached, for each test type and temperature, independently of the applied stress.The higher the mixture modulus and critical strain, the better its fatigue behaviourWhen performing at strain controlled, flexural bending beam tests may yield false fatigue failure when highly deformable mixtures are tested.

Departamento de Infraestructura del Transporte y Territorio