DISSIPATED ENERGY STUDY OF

FATIGUE IN AIRPORT

PAVEMENTSPHD Candidate: Shihui ShenAdvisor: Prof. S. H. Carpenter

FAA Project ReviewNov. 9, 2005

INTRODUCTIONDissipated Energy (RDEC)– Unifying Concept

Load Modes, Gear Configurations, Load Pulse Duration, Load Levels

Fatigue Endurance LimitThick airport pavementsThickness below which no damage occurs

Healing is the Recovery from Damage Impacts total loads to failure

Damage Concept is Amenable to a Thickness Design Procedure

DISSIPATED ENERGY CONCEPT REVIEW

Ratio of Dissipated Energy Change (RDEC)

STRAINSTRAIN

STR

ESS

STR

ESS

Initial Load CycleInitial Load Cycle

Second Load CycleSecond Load Cycle

Different Dissipated Energy Between First And Second Load Cycle

RDEC REVIEW

IIIIII

IIIIII

Plateau Value

Ratio

of D

issip

ated

Ene

rgy

Chan

ge, L

og

Load Repetitions, Log

Dissipated Envergy Vs. Loading cyclesIDOT Mix 6-7-1A 1000 Microstrain

00.002

0.0040.006

0.0080.01

0.0120.014

0.016

10 510 1,010 1,510 2,010 2,510 3,010 3,510 4,010

Number of Load Cycles

DER

Plateau Value50% Stiffness

PV CALCULATIONIDOT03 mix 3N704B

DE vs. Loading cycles 800microstrain

y = 3.4255x-0.1638

R2 = 0.9512

00.20.40.60.8

11.21.4

0 1000 2000 3000 4000 5000Loading cycles

DE

Nf50

Slope f = - 0.1638

UNIQUE PV-Nf RELATIONSHIPy = 0.4428x -1.1102

R2 = 0.996

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08

loading cycles @ 50% stiffness reduction (Nf50), log

plat

eau

valu

e (P

V), l

og

Normal strain/damage

Data Points: 546Mixture types: 98Loading modes: 2Frequency: 0.5-10 HzRest period: 0- 0.4 sec.

UNIQUE PV-Nf RELATIONSHIP

1.E-36

1.E-31

1.E-26

1.E-21

1.E-16

1.E-11

1.E-06

1.E-01

1.E+04

1.E+00 1.E+04 1.E+08 1.E+12 1.E+16 1.E+20 1.E+24 1.E+28 1.E+32

loading cycles @ 50% stiffness reduction, log

Plat

eau

Valu

e, lo

g Normal PVLow PV

Nf=1.10E+7

PVL=6.74E-9

Fatigue Endurance Fatigue Endurance LimitLimit

Unique energy level at which no fatigue damage exists

APPLY RDEC IN HEALING STUDY

Researchers suggest healing can be better understood by carefully considering energy behavior and viscoelastic properties of an HMA PV, energy based, can provide a unique indication of the impact of a load pulse followed by a rest periodResearch hypothesis:

Rest periods promote healing effect and make it quantifiable through lab testHealing reduces the damageReduced damage produces a lower PV, which translates into a longer fatigue life

FATIGUE-HEALING TEST

Four Point Bending Beam (SHRP T321-03)Mode of Loading: Constant Strain @ 500 microstrainWave Shape: HaversineLoad Pulse Width: 100ms (10 Hz)Rest Period: 0~9 secondTemperature: 20℃

FATIGUE-HEALING TEST

ε

Loading time, second

No rest period, 0.1 second load pulse

1 second

3 second

9 second

Haversine Load Pulse Sequence A short rest period after each load pulse ~ to simulate rest between loads; An intermediate strain level, 500 microstrain, is used ~ relatively high damage level and shorter tests.

The whole nature of energy change during a test is still continuous, thus the dissipated energy and the PV can be obtained for each test to perform the RDEC analysis,

PV-Nf FOR HEALING TEST

395950

114700

21010

33070y = 0.4429x-1.1102

1.E-07

1.E-06

1.E-05

1.E-04

1.E+04 1.E+05 1.E+06

Nf 50 , log

PV, l

og

neat binder mix polymer binder mix

(RP=0 sec.)-neat

(RP=0 sec.)-polymer

Unique PV-Nf relationship for healing test With 9 second rest

period, the fatigue life is extended 5 times for neat binder mix and 10 times for polymer binder mix

neat

polymer

HEALING TEST ~ PV vs. (RP+1) FOR NEAT BINDER

70 microstrain

500microstrainPV = 1.018E-05(RP+1)-0.9069

R2 = 0.8944

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1 10 100 1000 10000 100000(RP+1), (second), log

PV, l

og

PVL

3127 741584 44600

HEALING TEST ~ PV vs. (RP+1) FOR POLYMER BINDER

500 microstrain

200 microstrain

500microstrain

y = 4.302E-06x-1.347

R2 = 0.7957

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1 10 100 1000(RP+1), (second), log

PV, l

og

PVL

121

1000 microstrain

800 microstrain

300 microstrain

399 5406

HEALING AND FELHealing study using RDEC approach helps to understand the existence of FEL

PV-IDE AT NORMAL STRAIN (DAMAGE)

y = 1.137E-05x2.416E+00

R2 = 7.934E-01

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

0 0.5 1 1.5 2 2.5 3Initial Dissipated Energy

Plat

eau

Val

ue, l

og

At normal strain/damage condition and continuous loading, the PV is found has good correlation with Initial Dissipated Energy (IDE).

IDE, initial energy capacityPV, total effect of fatigue behavior (material fatigue resistance and load effect)

Under normal condition, load effect is dominant, while healing is negligible

PV-IDE FOR WHOLE LOADING RANGE

y = 38.221x0.3288

R2 = 0.7947

1.E-03

1.E-02

1.E-01

1.E+00

1.E+01

1.E-41 1.E-36 1.E-31 1.E-26 1.E-21 1.E-16 1.E-11 1.E-06 1.E-01 1.E+04PV, log

IDE

, log

Normal damage low damageNf LowHigh

PVL

Normal DamageLow Damage

With decreased damage level, the role of healing becomes more significant: healing starts to dominate the performance comparing to damage

At low damage level when PV reaches threshold PVL, the PV-IDE curve start to flatten, leading to extended fatigue life

PV, combined healing effect, can no longer be represented by initial loading status, IDE, starting from the endurance limit, PVL

PAVEMENT DESIGNRequires Relation to Standard ParametersLoad LevelSpeedRepetition IntervalMix VariablesAsphalt Grade

PRELIMINARY PV PREDICTION MODELBased on 19 IDOT mix Including neat binder and polymer binder mix; various gradations; 2 air voids levels; Rich bottom binder mixes are included

2.6812.6763.7505.3295 C)VbAV

AV(Sε104.598PV

Where:ε: controlled tensile strainS : the flexural stiffness of HMA mix, MPa AV : the air voids of mixtureVb : the asphalt content by volumeC : the aggregate gradation parameter, C=(PNMS-PPCS)/P#200PNMS : the percent of agg. passing nominal maximum size sievePPCS : the percent of agg. passing primary control sieve (PCS = NMS * 0.22)P#200 : the percent of agg. passing #200 sieve

PV PREDICTION

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02

PV tested

PV p

redi

cted

Line of equality

R2 = 0.902

BINDER FATIGUE TEST - DSR

DSR Testing Geometry Schematic Gemini 200 Dynamic Shear Rheometer

TYPICAL BINDER DE-Nf CURVE

50 Pen Bitumen with 65% limestone, 1% Controlled strain

50% complexmodulusreduction

0.E+00

2.E+07

4.E+07

6.E+07

8.E+07

1.E+08

0 50000 100000 150000 200000 250000

Loading Cycles

DE

0.00E+00

4.00E+03

8.00E+03

1.20E+04

1.60E+04

2.00E+04

G*

G*DEI

III

II

TYPICAL BINDER RDCE CURVE

50Pen Pure Bitumen, 15% Controlled Strain

0

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

0 50000 100000 150000 200000 250000 300000loading cycles

RD

EC

Plateau StageFailure Point

Plateau Stage, IIIII

COMPARE PV-Nf CURVES FOR BINDER AND MIXTUREBinder (Mastic):y = 1.7663x-0.9598

R2 = 0.9819

Mix: y = 0.5787x-1.101

R2 = 0.988

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1000 10000 100000 1000000 10000000Nf @ 50% stiffness reduction

Plat

eau

Val

ue (

PV)

Binder: con-strain Binder: con-stress Mixture

CONCLUSIONSRDEC provides a successful way to study HMA, fatigue, healing, and its role on fatigue endurance limitHealing does exist and its effect on fatigue behavior can be observed through lab accelerated fatigue-healing test:

CONCLUSIONS (cont.)The occurrence of healing is highly related to the level of damage; healing effect can be dominant under low load damage condition.Healing under the low damage condition is a key to understand the existence of a fatigue endurance limit (FEL).

Healing potential exceeds damage potential for any one load cycle.

RECOMMENDATIONSPV can be predicted based on material properties, which can be integrated into pavement structural design.

Combine this with PVL, the energy based FEL established before, provides a simple way to estimate the strain level that can reach “unlimited” fatigue life.

The fatigue-healing test can be extended to different temperature, load levels, and more diversity of mix types.Asphalt binders’ energy recovery rates and healing capacity can be studied using the RDEC approach. It should provide an insight of the healing kinetics derived from the existing fatigue-healing study for mixture.

THANK YOU !!

QUESTIONS ?