The Mechanisms of Healing of Asphalt Pavement

By DingXin Cheng

For Dr. Lytton’s

Micromechanics Class

November 11, 2002

2

Outline

• Surface Free Energy Concept

• Fatigue and Healing Analysis

• Mechanical Testing Results

• Healing Mechanisms

3

Surface Free Energy

ABLW

2AB

Measurement of Asphalt-Wilhelmy Plate

Measurement of Aggregate

– Universal Sorption Device (USD)

6

lab

field

shiftfactor

K2f

K2I

Log Nf

Log

C

ALC

ULA

TE

D S

TR

AIN

Fatigue shift factor

7

Fatigue and Healing Model -(1)

• Fatigue model without rest period

nvJAdN

dc][ 0

)(,,,,,, 1 tWEmDfnA Rff

Where,

8

Fatigue and Healing Model -(2)

• Fatigue model considering the healing effect

dN

dhJA

dN

dc nv ][ 0

hThhhf ,,,

dN

dh2

.

1

.

9

Healing Curve

Rest Period

Hea

ling

Ind

ex

1

h2

h

1

h

2

h

10

R2 = 0.7797

4

6

8

10

12

14

16

1.5 1.7 1.9 2.1 2.3 2.5

Short Term Healing Rate

LW

Com

pone

ntShort-Term Healing Rate vs.

Non-Polar Component

11

R2 = 0.7445

0

1

2

3

4

5

6

0.2 0.3 0.4 0.5 0.6 0.7

Long-Term Healing Rate

Aci

d-B

ase

Com

pone

ntLong-Term Healing Rate vs

Polar Component

12

Summary of Effect of Surface Free Energy on Fracture Fatigue Healing

• Healing potential is promoted with

• Reduced LW

• Increased AB

LW and Healing Potential

0.005.00

10.0015.0020.00

Lif

shit

z-va

n d

er W

aals

com

po

nen

ts,

erg

s/cm

2

AB and Healing Potential

0.00

2.00

4.00

6.00

8.00

Aci

d-B

ase

com

po

nen

ts,

erg

s/cm

2

15

Testing Results and Healing Analysis- Aging Effect

0.002.004.006.008.0010.00

surf

ace

free

ene

rgy,

er

gs/c

m2

LW

AB

16

Asphalt Binder Fatigue Testing including Healing Effects

0

20

40

60

80

AAD-1 AAM-1 HCR

Asphalt Binder

Ave

rag

e p

erce

nt,

%

HPI (Healing Potential Index)

FLI (Fatigue Life Increase)

17

DMA Fatigue Data for AAM-1

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 2000 4000 6000 8000 10000

No. of loading cycles

No

rmal

ized

G*

without RP

with RP

Nf

18

DMA Data Fatigue for AAD-1

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 5000 10000 15000 20000

No. of loading cycles

No

rmal

ized

G*

with RP

without RP

Nf

19

Asphalt Mixture Healing Testing -by Si, et al.

0102030

405060

Different Mix Type

Ex

ten

sio

n In

de

x, %

20

Result Comparison Table

Healing Potential Level

AAD-1 AAM-1 HCR

Surface Energy

Low Median High

Binder Fatigue Test

Low Median High

Mixture Fatigue Test

Low Median High

21

Mechanisms of Healing

22

Acid-Base Components of Surface Energy

2

221

r

ezzFatt

- Acid-Base Intermolecular Force

23

Acid-Base Attracting Energy Potential

• Two Particles

r

ezzdr

r

ezzU

r

att

221

2

221

24

Attracting Energy Potential of One Mole Material

r

ezzANU att

221

25

Repulsion Due to Electron Orbital Overlap

91

r

NBU rep

26

Net Acid-Base Attraction Energy

9

221

r

NB

r

ezzANUUU repattAB

27

Potential Energy of Acid-Base Interaction Versus Inter-particle Distances

-10

-5

0

5

10

15

0 1 2 3 4

Distance, r

Po

ten

tial

En

erg

y, U

U-attraction

U-repulsion

U-Acid-Base

Umin

r0

28

Lifshitz-van der Waals Components

• London Dispersion Force

• Debye Induction Force

• Keesom Orientation Force

621

r

RUdispersion

621

r

QU indi

6

22

21 )(

r

PNU didi

29

Net Lifshitz-van der Waals Potential Energy

92

6

22

21

621

621 )(

r

NB

r

PN

r

Q

r

RU LW

30

Potential Energy of Lifshitz-van der Waals Interaction Versus Inter-particle Distances

-10

-5

0

5

10

15

0 0.5 1 1.5 2 2.5 3 3.5

Distance, r

Po

ten

tia

l En

erg

y, U

U-attraction

U-repulsion

U-LW

31

Comparison of AB and LW Potential Energy

Changing with Inter-particle Distances

-8

-6

-4

-2

0

2

4

6

8

10

0 0.5 1 1.5 2 2.5 3 3.5

distance, r

Po

ten

tia

l en

erg

y, U

U - Lifshitz-van derWaalsU - Acid-Base

32

Healing Mechanism

Microcracking

Van der Waals

Acid-Base Forces

33