T d L L ti P tTowards Long Lasting Pavement Design: Pavement Response toDesign: Pavement Response to

Actual Loading

Imad L. Al-QadiUniversity of Illinois at Urbana-Champaign

Fl ibl P tFlexible Pavement

Direction of Travel

Free WaterAggregate Base

Deflection

Free Water Wedge

Hydrostatic Pressure

Subgrade Deflection

Factors Affecting Flexible PavementFactors Affecting Flexible Pavement Performance

Hot-Mix Asphalt (HMA) characteristicsHot-Mix Asphalt (HMA) characteristicsAggregate size, shape, texture and gradationBinder stiffness and contentAir void content

Loading conditionsVehicle speedVehicle speedTire type, load and pressure Traffic wandering

Pavement structural designLayer thickness and stiffnessInterface conditionInterface conditionBase and subgrade support

Environmental factorsEnvironmental factorsTemperature Moisture

C t MEPDG A l i A hCurrent MEPDG Analysis Approach• Poisson’s Ratio• Complex Modulus, E*

IDT St th• IDT Strength• Thermal Contraction• Creep PropertiesCreep Properties

P t RPavement Response

Analysis Engine(LEA/ FE) After MEPDG

Sh t i f C t A hShortcomings of Current ApproachVehicular loading:Vehicular loading:

Static and stationary circular loading Uniform vertical contact stresses

Hot-Mix Asphalt Properties:p pElastic properties corresponding to single temperature and loading ratetemperature and loading rate

Damage transfer functions:Rutting: compressive strain onlyFatigue: tensile strain onlyNeglecting effect of shear strain

S l tiSolutionsUnderstand real vehicle loadingUnderstand real vehicle loading

Moving load, surface contact stresses, dynamic ff teffect …

Utilize advanced finite element approaches

Appropriate material characterization andAppropriate material characterization and interface bonding condition

OutcomeOutcomeCritical pavement responses for pavement damage predictiondamage prediction

M h i ti F kMechanistic FrameworkD l t fDevelopment of

3D Finite Element Models

Loading PatternSimulation

Mod

Material and Interface Constitutive Modeling

el Adjusg

FE Model Validation

stment

Using Field Measurements

Pavement Response Prediction

3D FE P t M d l3D FE Pavement ModelPavement Design In-Plane Dimension (mm) Infinite Domain

Boundary Condition EffectBoundary Condition Effect

D i A l iDynamic AnalysisSt t d d i l diStructure response under dynamic loadingdepends on the ratio of load frequency to

t l f f th t tnatural frequency of the structureFlexible pavement natural frequency = 6-14HzV hi l l di f 0 10HVehicle loading frequency = 0-10Hz

Dynamic analysis considers mass inertia and damping forces effect on pavement responses due to a moving load

Implicit dynamic analysis is selected

Ti C t t St M tTire Contact Stress MeasurementThree Horizontal Data Triggering Points in a TreadThree Horizontal Data-Triggering Points in a TreadCover Whole Longitudinal Contact points

Tire Rolling

3D Ti P t C t t St3D Tire-Pavement Contact Stresses1 001.00

s

Entrance Part of Tire Imprint Exit Part of Tire Imprint0.70

act S

tress

es

Vertical StressLongitudinal Stress

0.40

aliz

ed C

onta Transverse Stress

0.10Nor

ma

-0.20

0 100 200

Longitudinal Contact Length Data not available

Moving direction

Moving Load SimulationMoving Load SimulationT diti l th dTraditional methodTriangular, trapezoidal, rectangular amplitude in g , p , g pconstant loading areaPavement at different depths have same loading timeImpulsive loading (hammering)

Continuous loadingContinuous loadingLoading area changes as tire movingL di lit d li l i d ith ti fLoading amplitudes are linearly varied with time for the entrance and exit parts of tire imprint

Loading Amplitudes (Entrance/ Exit)Loading Amplitudes (Entrance/ Exit)

HMA C l M d lHMA Complex ModulusExperiment setup: uniaxial or indirect tensile

Using Sigmoidal function for master curve

( )⎬⎫

⎨⎧

⎥⎤

⎢⎡

⎟⎞

⎜⎛−⎟

⎞⎜⎛Δ

−+

−+=

11)log(*)log(

aEt

MaxEγβ

δδ⎭⎬

⎩⎨ ⎥

⎦⎢⎣

⎟⎠

⎜⎝

⎟⎠

⎜⎝

+

+ 25.295T14714.19)log(

1t

eγβ

1000 T=1/fσ=σ0sin(ωt)

where,E* = complex modulus;t = loading period;600

800

0.E+00

5.E-05

1.E-04

Δtε=ε0sin(ωt-Φ)

σ σ0sin(ωt)

t loading period;T = temperature in ° Rankine; ΔEa,δ, β and γ = fitting parameters; andMax = limiting maximum modulus.

200

400 -1.E-04

-5.E-05

0

200

0 5 10 15 20 25 30Time (s)

Li Vi l ti itLinear ViscoelasticityG li d M ll S lid M d lGeneralized Maxwell Solid Model: One spring and Maxwell elements in parallelRelaxation modulus:Converted from complex modulus and expressed as p pProny Series

∑−= −N /ti0 ))e-(1E1(EE(t) iτ

=1i

3D D i A l i Vi l ti Eff t3D Dynamic Analysis: Viscoelastic Effect

Stress under Transient Dynamic LoadingStress under Transient Dynamic Loading

FE M d l V lid tiFE Model ValidationBottom of the wearing surface (38 1mm)Bottom of the wearing surface (38.1mm)

105

150

n (µ

) MeasuredCalculated

15

60

105

nal S

trai

n Calculated

B tt f th HMA (188 )

-30

15

0 0.1 0.2

Long

itudi

n Bottom of the HMA (188 mm)

80

100

µ)MeasuredC l l t d-75 Time (sec)

L

40

6080

Stra

in (µ Calculated

200

20

0 0 1 0 2 0 3gitu

dina

l

-40

-20 0 0.1 0.2 0.3

Time (sec)

Long

P t D M h iPavement Damage MechanismFatigue crackingFatigue cracking

Tensile strain at bottom of HMA

Surface cracking (top-down or “near-surface”)

Tensile and shear strain Thermal stress and aging effect

HMA ruttingShear flowDensification

Subgrade permanent deformationSubgrade permanent deformation

St i Di t ib ti i D thStrain Distribution in Depth• Critical Strain within HMA

300400300250200

• Critical Strain within HMA• Strains from Surface to bottom of 150mm HMAOutside Rib Inside Rib

200200

300200

150

200100

0

100

in (µ

)

0

100

in (µ

)

0

100

ain

(µ)

50

100

in (µ

) 00 3 6 9 12 15S

train

(µ)

-100

00 3 6 9 12 15S

trai

200

-100

00 3 6 9 12 15St

rai

76mm Shear Strain-100

00 3 6 9 12 15St

ra

114mm Shear Strain

0

50

0 3 6 9 12 15

Stra

i

-100

-20038mm-Shear Strain38mm-Transverse Tensile Strain38mm-Longitudinal Tensile Strain

-300

-200 76mm-Shear Strain

76mm-Transverse Tensile Strain76mm-Longitudinal Tensile Strain

-200

114mm-Shear Strain

114mm-Transverse Tensile Strain

114mm-Longitudinal Tensile Strain-100

-50 150mm-Shear Strain150mm-Transverse Tensile Strain150mm-Longitudinal Tensile Strain

-200Surface-Shear StrainSurface-Transverse Tensile StrainSurface Longitudinal Tensile Strain

-300 Transverse Rib Position

38mm Longitudinal Tensile Strain-400

Rib Position-300

Transverse Rib Position-150 Rib Position

150mm Longitudinal Tensile Strain-300 Transverse Rib Position

Surface-Longitudinal Tensile Strain

0-500 -400 -300 -200 -100 0 100 200 300 400 500

Strain (µ)

Tensile vs Shear Strain

-500 -300 -100 100 300 500Strain (µ)

200

400

Dep

th (m

m)

Peak-horizontal

Tensile vs. Shear Strain

0

200

m)

600

800

D

Transverse StrainLongitudinal StrainVertical Shear Strain-Rib 1V ti l Sh St i Rib 5

Straining direction-change point

straining point

76 HMA400

600

Dep

th (m

Vertical Shear Strain-Rib 576 mm HMA

Longitudinal Strain (µ)

800Transverse StrainLongitudinal StrainVertical Shear Strain-Rib 1Vertical Shear Strain-Rib 5

E33

152 mm HMA

0

200

-500 -400 -300 -200 -100 0 100 200 300 400 500g (µ)

E21E31

E32

E12 200

400

Dep

th (m

m)

E13E11E23 E22

600

800

Transverse StrainLongitudinal StrainVertical Shear Strain-Rib 1Vertical Shear Strain-Rib 5

305 mm HMA Traffic Direction

Critical Strain300

400

500(µ

)Shear Strain Tensile Strain

HMA =76 mm Critical Strainin HMA Layer (25 ºC)

100

200

300

Stra

in (

035.5 kN 45.5 kN 53.4 kN

500 S S S

• Shear Strain: Critical value within HMA

300400500

n (µ

)

Shear Strain Tensile Strain• Maximum Tensile strain

at the bottom of HMA

HMA=152 mm

0100200

Stra

i

E31E32

E33

35.5 kN 45.5 kN 53.4 kN

400500 Shear Strain Tensile Strain

E21

E11 E23E22

E31

E12

HMA=305 mm

200300

400

Stra

in (µ

)

E13

E11HMA 305 mm

Traffic Direction

0100

35.5 kN 45.5 kN 53.4 kN

S Direction

I t f U i R l d M t i lImpact of Using Recycled Materials

RAP’s Binder Blending Scenarios @RAP s Binder Blending Scenarios @ 20% RAP

1E+4[ ]

1E+4Total

SET 4

s (k

si)

s (k

si)

binderRAPSET 3

1E+3

Mod

ulus

D1-SET1-20D1 SET2 20

1E+3

Mod

ulus

D4-SET1-20Total binder

ompl

ex D1-SET2-20

D1-SET3-20D1 SET4 20C

ompl

ex

D4-SET2-20D4-SET3-20

RAP

SET 2

1E+21E 1 1E+1 1E+3 1E+5 1E+7

C D1-SET4-20

1E+21E-2 1E+0 1E+2 1E+4 1E+6

C D4-SET4-20 Total binder

1E-1 1E+1 1E+3 1E+5 1E+7Reduced frequency (Hz)

1E 2 1E+0 1E+2 1E+4 1E+6Reduced frequency (Hz)

RAP’s Binder Blending Scenarios @RAP s Binder Blending Scenarios @ 40% RAP

[ ]1E+041E+041E+04 Total

SET 4

1E+041E+04

(ksi

)

1E 04

(ksi

)

SET 3

1E 04

(ksi

)

Total binder

RAP

1E 04

(ksi

) Actual Practice Specimen

1E+03

Mod

ulus

(

1E+03

Mod

ulus

(

Total binder

SET 3

1E+03

Mod

ulus

(

D4 SET2 401E+03

Mod

ulus

(

D4-SET1-40

Com

plex

M

D4-SET2-40 SET 2

Com

plex

M D4-SET2-40

D4-SET3-40

binder

RAP

Com

plex

M D4-SET2-40

D4-SET3-40

D4 SET4 40Com

plex

M D4-SET1-40D4-SET2-40D4-SET3-40

S1E+02

1E-02 1E+00 1E+02 1E+04 1E+06

C

Total binder

1E+021E-02 1E+00 1E+02 1E+04 1E+06

C S 3 0

1E+021E-02 1E+00 1E+02 1E+04 1E+06

C D4-SET4-40

1E+021E-02 1E+00 1E+02 1E+04 1E+06

C D4-SET4-40

Reduced frequency (Hz)Reduced frequency (Hz)Reduced frequency (Hz)Reduced frequency (Hz)

Complex Modulus Results

1E+041E+4

lus

(ksi

)lu

s (k

si)

1E+03

ex M

odul

D1-SET 1-001E+3

ex M

odu

D4-SET1-00

Com

ple

D1-SET 1-20

D1-SET 1-40Com

ple

D4-SET1-20

D4-SET1-40

1E+021E-02 1E+00 1E+02 1E+04 1E+06

1E+21E-2 1E+0 1E+2 1E+4 1E+6

D4-SET1-40

1E 02 1E+00 1E+02 1E+04 1E+06Reduced Frequency (Hz)

1E 2 1E+0 1E+2 1E+4 1E+6Reduced Frequency (Hz)

D bl B i Eff t M d lDouble Bumping Effect on Modulus

1E+41E+4

s (k

si)

(ksi

)

1E+3

Mod

ulus

1E+3

Mod

ulus

D4-SET1-40 w/ PG58-28

ompl

ex D1-SET1-40 w/ PG58-28

D1-SET1-00 w/ PG64-22D1-SET1-40 w/ PG64-22C

ompl

ex M

D4-SET1-00 w/ PG64-22

D4-SET1-40 w/ PG64-22

1E+21E 2 1E 0 1E 2 1E 4 1E 6

Co D1 SET1 40 w/ PG64 22

1E+21E 2 1E+0 1E+2 1E+4 1E+6

C

1E-2 1E+0 1E+2 1E+4 1E+6Reduced frequency (Hz)

1E-2 1E+0 1E+2 1E+4 1E+6Reduced frequency (Hz)

F t E / V i RAPFracture Energy w/ Varying RAP

1500

2000

/m2)

0 C -12 C

3

4

RAP-00 RAP-20 RAP-40

Temperature = 0 °C

1000

ure

Ene

rgy

(J/

2

Forc

e (k

N)

p

0

500Frac

tu

0

1

00 20 40

RAP %

0 2 4 6 8CMOD (mm)

As RAP ↑, Fracture Energy ↓

Summary30

SummaryAccurate pavement response prediction requiresAccurate pavement response prediction requires realistic loading simulation and appropriate material and interface modelingg

3D tire contact stresses (non-uniformity and tangential shear stress) may affect the prediction oftangential shear stress) may affect the prediction of top-down cracking, primary rutting, and occasionally fatigue damageg g

Shear strains at pavement near-surface are significant; fresh look into “NEAR SURFACE”significant; fresh look into NEAR SURFACE CRACKING” is needed in thick pavement

Find critical repose for each failure mechanismFind critical repose for each failure mechanism

Thank You