Assess the improvement of the life cycle through four point bending test on prismatic beams reinforced at the bottom with a geo-composite interlayer

• at 5°C;• at 10 Hz;• two different type of load curve.

PET

PPPE

Sfor

zi [G

Pa]

0 5 10 15 20 25 30 350.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Fibra di vetro

Allungamento [%]

Polypropylene

• Un-reflective behavior: to retard the occurrence of reflective cracking

• Increasing the resistance to the shear stress;• To resist moisture intrusion into the underlying pavement

structure.

Tensile strength 100/100 kN/mE modulus of 73000 MPa

A Glass fiber grid Continuous filament nonwoven

1. Determination of the optimal methodology to realize the beam;

2. Tuning and validation of the UTM instrumentation for the four point bending test execution;

3. Tests execution and analysis.

REAL SCALE FIELD

ROLLER COMPACTOR METHOD

METALLIC MOLD METHOD

POSITIVE ASPECTS:Reduced influence of human factor

Compaction energy completely different from the real one

NEGATIVE ASPECTS:

Border effects quite influence

Reduced variation of the beam thicknessHigh productivity (one slab every 3/4 h)

Through the control of the thickness and amount of material voids content

ROLLER COMPACTOR METHOD

5,4% 5,1% 5,1% 5,2%

5,1% 4,9% 5,1% 5,0%

5,3% 5,2% 5,2% 5,4%

ROLLER COMPACTOR METHODAnalysis done on the plates create by the Roller Compactor to test the accuracy of the method

The life cycle improvement it has been determined performing the four point bending test over the beams

realized with roller compactor

The proof condition at 5°C (mechanical characteristics

of the material)

Proportional (P) Integrative (I)Derivative (D)

Controller

Need oftuning

Asphalt mixture: 0/12 mm mixture according to the SocietàAutostrade standard

Bitumen: Ordinary bitumen 50/70

Comparison between: Beam n. 1 REINFORCED (R)Beam n. 3 UN REINFORCED (NR)

Beam n. 2 SPARE BEAM

3

12

First phase: Sinusoidal waveform

Fatigue test were performed in controlled strain mode (250 µε) at the temperature of 5°C using a sinusoidal waveform at a frequency of 10 Hz on beams reinforced/un reinforced

Sinusoidal waveform

The sinusoidal waveform produces at each cycle the maximum strain either at the bottom side and on the surface

With this configuration it’s possible that, in the case of Reinforced beam, the crack starts on the surface – the side not reinforced with geo-composite

Deflection

Deflection

Reinforced side

Macro-crack propagation

In that case the fatigue behavior of the two beams could be the same or even better for the un-reinforced and rehabilitation with reinforcement becomes useless

Sinusoidal waveform

Second Phase: Haversine waveform

In light of the fact that traffic loading induces the maximum tensile strain at the bottom of the layer…is justified the will to reproduce with laboratory tests this type of solicitations:Haversine waveform in strain control mode at 350 µε

Deflection

Haversine waveshape:

Haversine waveshape:classical approach

0

25 000

50 000

75 000

100 000

125 000

150 000

175 000

200 000

225 000

22-1 22-2 23-2 24-2 28-2 29-2 30-2 33 Media

Cyc

les

Comparison R e NR

NRR

Couplesn. cycles

NRn. cycles

RRatioR/NR

22-1 73'560 154'280 2.1022-2 93'320 120'180 1.2923-2 39'800 124'450 3.1324-2 66'060 80'040 1.2128-2 45'700 141'790 3.1029-2 32'520 135'930 4.1830-2 113'500 199'000 1.7533 81'690 206'530 2.53

Mean 68'269 145'275 2.41Dev. St. 29'660 36'171 1.11

Nf. Cycles of reinforced (R)

Nf. Cycles of un-reinforced (NR)

Haversine waveshape: energy ratio approach

What happen if we investigate only the part of the life cycle where the macro cracks start and begin to

propagate?

nnn

n

iiii

nRφεπσ

φεσπ

sin

sin0∑==

It’s plausible to consider that the geo-composites begins to work after the macro-crack has started and so the contribute of the geo-composite can be observed after that point

Indicates the beginning of crack propagation phase (Ni)

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

0 20000 40000 60000 80000 100000 120000 140000 160000

Rn

N. di cycles

Comparison NR e R

28-2 NR

28-2 R

36000

100000

RL-R

RL-NR

Residual life of the beam (RL)

The part of the life cycle that begins with the manifestation of the first macro crack and lasts until the end of the test

(Nf-Ni)

Ni Nf NfNi

Haversine waveshape: energy ratio approach

couples Nf Ni RL=Nf-NiRatio

RL r/nr

1 22-1 NR 73560 50000 23560 4.001697822-1 R 154280 60000 94280

2 22-2 NR 93320 80000 13320 5.719219222-2 R 120180 44000 76180

3 23-2 NR 39800 28000 11800 4.444915323-2 R 124450 72000 52450

4 24-2 NR 66060 36000 30060 1.864271524-2 R 80040 24000 56040

5 28-2 NR 45700 36000 9700 4.308247428-2 R 141790 100000 41790

6 29-2 NR 32520 20000 12520 4.467252429-2 R 135930 80000 55930

7 30-2 NR 113500 82000 31500 3.714285730-2 R 199000 82000 117000

8 33 NR 81690 50000 31690 3.677185233 R 206530 90000 116530

Mean value 4.03Dev. St. 1.08

RL of reinforced (Nf-Ni)R

RL of un-reinforced (Nf-Ni)N R

• A more proper evaluation of the reinforcement efficiency in terms of life cycle increase could be done investigating only the phase of macro-cracks initiation and propagation (Nf-Ni)

• The use of the geo-composite reinforcement as rehabilitation method allowed to implement, on average, 4 times the fatigue life during the spread of the macro-cracks

• Carrying on the comparison at different temperatures;

• Repeat the tests at different value of controlled strain to determine the fatigue laws for the reinforced/un reinforced material.