EYHajj Characteristics of the Loading Pulse for the FN Test€¦ · Characteristics of the Loading Pulse for the Flow Number Performance Test Elie Y Hajj Alvaro Ulloa Raj Siddharthan

Characteristics of the Loading Pulse for the gFlow Number Performance TestElie Y Hajj Alvaro Ulloa Raj Siddharthan Peter E SebaalyElie Y. Hajj, Alvaro Ulloa, Raj Siddharthan, Peter E. Sebaaly

Association of Asphalt Paving Technologists Annual MeetingMarch 7-10 , 2010, Sacramento, California

Introduction

A h l L B h iAsphalt Layer Behavior

Stress State Loading Rate Temperature

Lab test that simulates field conditions

Flow number (FN) test( )

0.1 s 0.9 s

Flow number (FN) testPermanent deformation CharacterizationPermanent deformation Characterization

Objectivej

FN Test FN Test variables

Triaxial state Testing Loading Wave Pulse iTriaxial state of stresses

Testing Temperature

Loading Wave Form

Pulse Duration Rest Period

Provide recommendations for the characteristics of the deviator loading pulse in the flow number testdeviator loading pulse in the flow number test

Pulse duration prediction

Barksdale 1971Barksdale, 1971Brown, 1973McLean 1974McLean, 1974MEPDG, 2002Al-Qadi, 2008Al Qadi, 2008…

Tire directly above PVehicle direction y

xσzzP

xz

σyy

σxx

Pavement response histories for a single circular tire…..

0 τxyσzz

0 Timeσyy

Time

xy

Time0

σxx0 τyz

0τxz

0

Question: What stress pulse shape to use in triaxial test?Time Time Time

Stress State in the Triaxial FN Test

σy

σzMoving loads

Pavement responses histories

RLT / FN

σxσ3

σd

σ3 σ3

Database of pavement stresses time-historieshistories

60 mph without braking40 mph without braking40 mph without braking20 mph without braking2 mph with braking10 mph with braking20 mph with braking HMA layer temp:

104 F, 122 F,104 F, 122 F, 140 F, and 158 F

3D-Move Model

Complex surface Complex surface loadings

in all three directions.

3D3D--Move Move ModelModel

Moving loads of Moving loads of any shape

(braking forces)

Visco-elasticVisco elasticproperties

Semi-trailor Truck

dynamic load transfer vertical loads on tires additive (+ or -) to static load

Braking = f(deceleration “a”, braking forces)

Semi-trailor Truck

• Load Distribution During 6000 4250 4250

4250 4250g

Braking: 14 Unknowns– 11 equilibrium equations

3 characteristic equations:– 3 characteristic equations:

Application (treadle output) vs. actuation (brake

8480 4395 286051203340

chamber) pressure/axle

Brake force vs. actuation pressure on each axle.

2161 2968 2968 2561 2561

p

Dynamic load transfer coefficient.

Equivalent deviator and confining stresses time-historiestime-histories

σd & σc were analyzed under Single and Tandem axlesd c y gfor every:

pavement structurepavement structure

mixture type

pavement temperature

braking and non-braking conditions.g g

Equivalent deviator and confining stresses time-historiesSingle vs Tandem AxlesSingle vs. Tandem Axles

130140

ving

110120130

ss fo

r Driv

psi)

8090

100

rtical Stres

Axles (p

607080

60 70 80 90 100 110 120 130 140

Max Ver

60 70 80 90 100 110 120 130 140Max Vertical Stress for Steering Axle (psi)

Non‐Braking Conditions Braking Conditions

Equivalent deviator and confining stresses time-historiesSingle vs Tandem Axles (Non-braking)

90

Single vs. Tandem Axles (Non braking)

σd Si gl = 81 psi 75 i

50

70

90

iator an

d tress, psi

σd-Single 81 psi σd-Tandem = 75 psi

σc-Single = 49 psi

30

50

ximum

dev

finem

ent s σc-Tandem = 37 psi

‐10

10

Max

conf

0.25 0.28 0.30 0.33 0.35 0.38 0.40Time, sec

Deviator stress single axle Confinement stress single axleDeviator stress tandem axle Confinement stress tandem axle

Equivalent deviator and confining stresses time-historiesSingle vs Tandem Axles (Braking)

120

Single vs. Tandem Axles (Braking)

σd-Tandem = 104 psi 97 i

σd-Tandem = 109 psi

60

80

100

viator and

stress, psi σd-Single = 97 psi

σ = 44 psi

20

40

60

ximum

dev

finem

ent s

σc-Single = 44 psiσc-Tandem = 32 psi

σc-Tandem = 22 psi

‐20

0

4 5 5 0 5 5 6 0 6 5 7 0 7 5 8 0

Max

conf

4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0Time, sec

Deviator stress single axle Confinement stress single axleDeviator stress tandem axle Confinement stress tandem axle


•Tandem axle generates a more critical stress Tandem axle generates a more critical stress condition than the steering axle when the 3D state of stresses is analyzed.y

•Stresses evaluated under tandem axles at 2-inch Stresses evaluated under tandem axles at 2 inch below pavement surface.


Equivalent deviator stress pulse duration

• Loading pulse characterized using σd at 2 inches.• Best-fitting haversine wave shape.

100

si

Calculated by 3D‐MoveH i fit

60

80

ress, σ

dps Haversine fit

20

40

eviator Str

0

0.26 0.27 0.28 0.29 0.30 0.31

De

Time, sec

Equivalent deviator stress pulse durationunder tandem axle 2 inches below pavement surfaceunder tandem axle, 2 inches below pavement surface

PG64-22 Mix Non-braking0.1

lse

s)

20 mph40 mph60 mph

rsin

ePu

atio

n t p

(s

Pavement

0.01

Hav

erD

ura Pavement

structure: 4” HMA over 6” base

90 100 110 120 130 140 150 160 170Pavement Temperature, ºF

Equivalent tp at 2” below pavement surfaceNon-braking Conditions (20-60 mph, 104-158°F)Non braking Conditions (20 60 mph, 104 158 F)

0.080.090.10

on (s

ec)

T = asphalt layer temperature, ºC

0.040.050.060.07

ulse

Dur

atio p ,

S = vehicle travelling speed, mph.

0.000.010.020.03

Pred

icte

d P

0.000.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10

P

Calculated Pulse Duration (sec)PG64-22 (Non-braking) PG58-22 (Non-braking) PG52-22 (Non-braking)

Equivalent tp at 2” below pavement surfaceBraking Conditions (2-20 mph, 104-158°F)Braking Conditions (2 20 mph, 104 158 F)

T = asphalt layer temperature, ºC0.40

0.450.50

on (s

ec)

p ,S = vehicle travelling speed, mph.

0.200.250.300.35

ulse

Dur

atio

0.000.050.100.15

Pred

icte

d P

0.000.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

P

Calculated Pulse Duration (sec)PG64-22 (Braking) PG58-22 (Braking) PG52-22 (Braking)

Equivalent Deviator Stress Pulse Duration (tp) at 2” below pavement surfacebelow pavement surface

Non-Braking Braking

Speed 20-60 mph 2-20 mphSpeed 20 60 mph 2 20 mph

Equivalent Deviator stress pulse (tp) 0.016-0.069 sec 0.041-0.456 secstress pulse (tp)

< 0 1 sec typically applied to FN test< 0.1 sec typically applied to FN test(except for braking at 2 mph)

Equivalent deviator stress pulse durationBraking vs Non-braking at 20 mphBraking vs. Non-braking at 20 mph

0.075

sec)

0.065

0.070

‐Braking

(

0.055

0.060

e Duration

12% t 29%0.045

0.050

ading Pu

lse 12% to 29%

reduction in pulse time

0.040

0.040 0.045 0.050 0.055 0.060 0.065 0.070 0.075

Loa

Loading Pulse Duration ‐ Non Braking (sec)

pulse time

Equivalent Deviator Stress Pulse Duration (tp) at 2” below pavement surfacebelow pavement surface

Non-braking condition seems to result in a more critical diti th b ki diticondition than braking condition.

Evaluate the magnitudes of σd and σc under braking and non-braking conditions and non braking conditions

σ3

σd

σ3 σ3

Maximum equivalent σd and σc stresses

95100105

Stre

ss, p

si 4-inch HMA layer - Tandem Axle

20 mph40 mph

95100105

Stre

ss, p


20 mph40 mph

95100105

Stre

ss, p


20 mph40 mph

60657075808590

Max

imum

Dev

iato

r S 40 mph

60 mph

60657075808590

Max

imum

Dev

iato

r S 40 mph

60 mph

60657075808590

Max

imum

Dev

iato

r S 40 mph

60 mph

60

90 100 110 120 130 140 150 160 170HMA Layer Temperature, ºF

60


60


50

, psi 4-inch HMA layer - Tandem Axle 50

psi 6-inch HMA layer - Tandem Axle 50

, psi 8-inch HMA layer - Tandem Axle

30

35

40

45

mum

Con

finin

g St

ress

,

20 mph40 mph60 mph

30

35

40

45

mum

Con

finin

g St

ress

, p

20 mph40 mph60 mph

30

35

40

45

mum

Con

finin

g St

ress

,

20 mph40 mph60 mph

PG64-22 Mix for non-braking conditions

25

30

90 100 110 120 130 140 150 160 170

Max

im

HMA layer Temperature, ºF

25

30

90 100 110 120 130 140 150 160 170

Max

im


25

30

90 100 110 120 130 140 150 160 170

Max

im


PG64 22 Mix for non braking conditions


130

135

140

Stre

ss, p


2 mph10 mph 130

135

140

Stre

ss, p


2 mph10 mph 130

135

140

Stre

ss, p


2 mph10 mph

100

105

110

115

120

125

Max

imum

Dev

iato

r S 10 mph

20 mph

100

105

110

115

120

125

Max

imum

Dev

iato

r S 10 mph

20 mph

100

105

110

115

120

125

Max

imum

Dev

iato

r S 10 mph

20 mph

100


100


100


50



ss, p


30

35

40

45

mum

Con

finin

g St

ress

,

2 mph10 mph20 mph

30

35

40

45

mum

Con

finin

g St

ress

,

2 mph10 mph20 mph

30

35

40

45

xim

um C

onfin

ing

Stre

s 2 mph10 mph20 mph

PG64-22 Mix for braking conditions

25

30

90 100 110 120 130 140 150 160 170

Max

im

HMA Layer Temperature, ºF

25

30

90 100 110 120 130 140 150 160 170

Max

im


25

90 100 110 120 130 140 150 160 170

Max


PG64 22 Mix for braking conditions


• Predictive Equations for:

d c

Predictive Equations for:Equivalent max deviator stress, σd

fEquivalent max confining stress, σc = σ3

at 2 inches below pavement surfaceat 2 inches below pavement surfaceBraking and Non-Braking Conditions

Function of AC layer thickness, T, E*, S, interaction terms

Equivalent Deviator & Confining Stresses at 2”Non-Braking ConditionsNon-Braking Conditions

Equivalent Deviator & Confining Stresses at 2”Braking ConditionsBraking Conditions

Equivalent Deviator & Confining Stresses at 2” Below Pavement SurfaceBelow Pavement Surface

Non-braking conditions: g–σd ranged from 69 to 102 psi –σc ranged from 27 to 47 psi σc ranged from 27 to 47 psi

Braking conditions:slight increase (5%) i

40% increase in σd

Braking conditions:–σd ranged from 108 to 132 psi –σ ranged from 30 to 47 psi

(5%) in σc

–σc ranged from 30 to 47 psi

Summary and conclusionsy

• Equivalent deviator stress pulse duration (t ) at 2”Equivalent deviator stress pulse duration (tp) at 2below the pavement is function of

vehicle speed and– vehicle speed, and– pavement temperature.

• Neither pavement thickness nor mixture propertiessignificantly impacted t at 2” below pavementsignificantly impacted tp at 2” below pavementsurface.


• Standard pulse time loading of 0 1 sec does notStandard pulse time loading of 0.1 sec does notsimulate actual traffic-induced deviator stress pulseduration.

• Braking conditions, though it generates interfaceshear stresses, leads to lower deviator pulse duration& higher amplitude.


• Amplitude of the equivalent triaxial deviator and Amplitude of the equivalent triaxial deviator and confining stresses are highly affected by:

– Mixture’s stiffness– Pavement effective temperaturePavement effective temperature– Vehicle speed.

Thank you for your attention!!!y y

•Acknowledgments•Acknowledgments

This work is part of the overall effort in the Asphalt – This work is part of the overall effort in the Asphalt Research Consortium (ARC) work element E2c: “Critically Designed HMA Mixtures.” Critically Designed HMA Mixtures. (www.arc.unr.edu)

– Authors gratefully acknowledge the FHWA support.

Documents

EYHajj Characteristics of the Loading Pulse for the FN Test€¦ · Characteristics of the Loading Pulse for the Flow Number Performance Test Elie Y Hajj Alvaro Ulloa Raj Siddharthan