impact of healing - university of wisconsin–madison · pdf filerecall that the term ro,...

Self healing in bituminous materials

0

log N

Lab.Field

?

3.291 0,84518.3 *f tN C E

Impact of Healing

Step 1: Interfacial Wetting Step 2: Intrinsic healing

ba

dtXtd

, tRh

t

h ddt

XdtRR

,

The two processes are combined using the approach originally proposed by Wool and O’Connor as follows:

= fn (healing zone, bonding stress, creep compliance properties, work of cohesion)

fn (work of cohesion, self diffusivity)

Healing Mechanism

Work of cohesion: From surface energy

m

b

c

mb DW

kDa

dtXtd

1

0221 141,

Step 1: Interfacial Wetting

Crack closing speed

Healing process zone

Crack surface

ba

b

Viscoelastic property: Creep parameters from power law, (t)=D0+D1tm

Bonding stress: Indirectly dependent on the surface energy

= fn (healing zone, bonding stress, creep compliance properties, work of cohesion)

Healing Mechanism

Step 2: Intrinsic healing

Strength gain of wetted surfaces over time is defined using an intrinsic healing function: tRh

Strength gain is also a two step process:

1. Instantaneous adhesion due to surface energy

2. Time dependent self diffusion and randomization

Collectively, the intrinsic healing function can be modeled as:

rqth epRtR 10

Instantaneous healing proportional to work of cohesion

Time dependent healing proportional to self diffusivity

Healing Mechanism

rqth epRtR 10

Instantaneous healing proportional to work of cohesion

Time dependent healing proportional to self diffusivity

The approach used in polymers is based on the random walk approach

• requires detailed knowledge of the molecular structure of the material•more applicable to materials with chain like molecules

With asphalt binders, we do not have the luxury of either of theabove two….Instead we used a DSR to determine the intrinsic healing function of different asphalt binders

Healing Mechanism

Outline of the procedure

D1 = 25 mm

D = 18 mm

t ≈ 3.5 mm

t ≈ 3.5 mm

ω = 10 rad/sec

t1 = 7 mm

Two piece specimen of asphalt binder was brought into contact to obtain a “wetted” interface

G* was recorded intermittently at 0, 2, 4, 6, 8, 10, 15, 20, 25, 30, 40, 50 and 60 seconds after bringing the two specimens into contact with each other

Quantifying Intrinsic Healing

Outline of the procedure

The final results were normalized by repeating the test with a single specimen of the same asphalt binder and twice the thickness

D1 = 25 mm

D = 18 mm

t ≈ 7.0 mm

ω = 10 rad/sec

t1 = 7 mm


Images of the test being performed with the two piece specimen before and after the test


Data analysis


Replicate data


Results for the SHRP binders


Results for the SHRP binders

rqth epRtR 10

This data were fit to the functional form for intrinsic healing to obtain the relevant parameters

Recall that the term Ro, was due to the surface free energy or work of cohesion of the binder


t

h ddt

XdtRR

,

Properties related to intrinsic healing

Data Acquisition &

Force Data Acquisition &

Force

Validation of Model

t

h ddt

XdtRR

,

0.000

0.050

0.100

0.150

0.200

0.250

0.300

0.350

0.400

0.450

2.05 2.1 2.15 2.2 2.25 2.3 2.35

MMHC Ratio

Hea

ling

Inde

x

5 minutes10 minutes20 minutes40 minutes

S-20 F-20

W-40

-CH2/-CH3 = 3.9 -CH2/-CH3 = 3.3

-CH2/-CH3 = 2.1

Validation of Model

t

h ddt

XdtRR

,

Validation of Model

Total intrinsic healing at the end of 1 hour for RTFO and PAV aged binders at

different temperatures

Intrinsic Healing – Temperature and Age Dependency

o

time

Cyclic Rotation

Specimen Fabrication

Test Setup

Test Form

Quantifying Healing: DMA

Quantifying Healing: DMA

Healing: Convolution of Wetting/Intrinsic Healing

Damage evolution of the intact specimen

Extension in fatigue cracking life due to each

rest period


t

h ddt

XdtRR

,

Measured experimentally (FAM DMA fatigue)

Measured experimentally (DSR binder)

Elements of Micromechanical Model

m

b

c

mb DW

kDa

dtXtd

1

0221 141,

Wetting function obtained using overall healing curves with different

materials will be used to validate relationship to surface free energy and viscoelastic properties

Micro-damage Healing Evolution fn

Abu Al-Rub, Darabi, Little, and Masad (2010)

1

2

0

1 1 exp 1b

beffh

cr

Th hT

h

1 2&b b Model parameters related to history

Healing viscosity parameter (second-1) that controls how fast healing occurs, and increases as surface energy increases.

The maximum healing rate:max

hh

bah

1

02 21

1 24(1 )

mh

m b

G DD k

0 1, , , and :mD D m k Viscoelastic properties:G Surface energy: Size of the fracture process zone: Poisson’s ratio

Micro-damage Healing: Comparison with Experiments

0

1

2

3

4

5

6

7

8

9

0 200 400 600 800 1000

Axi

al st

rain

(%)

Time (Sec)

Experimental data

Model prediction without healing

Model prediction including healing

=1500kPaLT=120 sec, C

Uompression

T=100 sec =1500kPa

LT=60 sec, UCo

Tm

=1pr

00 ses

ecsion

0

1

2

3

4

5

6

7

8

9

10

0 500 1000 1500 2000

Axi

al st

rain

(%)

Time (Sec)

Experimental data

Model prediction without healing and damage


Model prediction with healing

LT : loading timeUT : Rest period (unloading time)


=1500kPaLT=60 sec, UC

Tompression

=1500 sec

0

2

4

6

8

10

12

14

0 5000 10000 15000 20000 25000 30000 35000

Axi

al st

rain

(%)

Time (Sec)

Experimental data



=300kPaLT 120 sec, UT 100 sTen o

ci n

es

0

1

2

3

4

5

0 200 400 600 800 1000 1200

Axi

al st

rain

(%)

Time (Sec)

Experimental data





0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 5000 10000 15000 20000 25000

Axi

al st

rain

(%)

Time (Sec)

Experimental data



0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 500 1000 1500 2000

Axi

al st

rain

(%)

Time (Sec)

Experimental data




ci n

es


ci n

es


Techniques: AFM Nano-indentation

Ref http://www.nanotech-now.com/Art_Gallery/antonio-siber.htm

Mechanical Properties and MorphologyAdditional Work


Ref: Allan Grover, Master’s Thesis

Mechanical Properties and Morphology

• Three‐dimensional depiction of phases (AAD unaged)


• Three‐dimensional depiction of phases (AAD aged)




Creep measurements before and after aging


impact of healing - university of wisconsin–madison · pdf filerecall that the term ro,...

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