2010 FAA Worldwide Airport Technology Conference

Atlantic City, New JerseyApril 20 – April 22

2

Analysis and Design of Airfield Pavements Using Laboratory Tests

and Mechanistic – Empirical Methodology

Lorina Popescu, P.E., UCPRCRita Leahy, P.E., APACACarl Monismith, P.E., UCPRC

3

Outline Introduction Establish mix design criteria for taxiways

using Simple Shear Test Estimate permanent deformation using

laboratory tests and M-E methodology Airfield pavement design example using

long-life performance concepts Construction considerations & concluding

notes

4

Introduction

SHRP developed tests Simple Shear Test (AASHTO T-320, ASTM D-

7312) RSST-CH Flexural Fatigue Test (AASHTO T-321, ASTM D-

7460) SHRP tests and new analysis methods

adapted to evaluate HMA performance with large commercial aircraft loading

5

Establish Mix Design Criteria for Taxiways Using the Simple Shear

Test

6

San Francisco International AirportProject outline

Distresses observed shoving and rutting in AC turn areas of

taxiway - slow moving and sharp turning rutting distortions (dimpling) under static

loading Different trial mixes to mitigate

rutting problem Cores extracted from distressed areas

7

San Francisco International AirportProject outline

AC mixes in full compliance with FAA mix design

Enhancements to FAA mix design to reduce observed rutting

High Stability mix SHRP Simple Shear Test primary tool

used to evaluate mix rutting performance

8

Simple Shear Test (SST)

Evaluate the permanent deformation characteristics of FMFC cores;

9

Simple Shear Test (SST)

Sample size: D=6 in, H=2 in;

Shear stress: 10 psi (69kPa)

Loading time 0.1 sec; 0.6 sec rest period;

Test temperature 122F (50C);

11

RSST test results on field extracted cores

1

10

100

1,000

10,000

100,000

1,000,000

10,000,000

0 2 4 6 8 10 12

Air-Void Content

Re

petit

ions

to 5

% S

hear

Str

ain

High Stability Mixes

AR 8000 Mixes

95% reliability (5% probability of failure)

80%

10%

50%

12

Binder content selection

1.0E+03

1.0E+04

1.0E+05

1.0E+06

Asphalt content (percent)

Re

pe

titi

on

s t

o 5

pe

rcen

t s

he

ar

str

ain

(lo

g)

Design asphalt / binder content

N = 100,000 at 80 %

Each point is the average of 3 test results

13

Notes

Stiffness alone is not sufficient for mix design

Repeated loading used to arrive at design binder content

14

Estimate Permanent Deformation Using Laboratory

Tests and M-E Methodology

15

Estimate rutting performance - NDIA project outlook

New Doha International Airport – due to open July 2011;

All HMA TW/RW Built partially on

reclaimed land; Two parallel

runways; 40 gate terminal;

16

NDIA project outlook

Environment - Desert

Avg temperature –> 40C (104F)May - Sep

Avg Annual Rainfall –70mm (2¾ in)Oct - Mar

17

NDIA Project outlook

Typical aircraft loading 51,250 to 56,000 lb/tire

Tire pressure 215 to 220 lb/in2

18

Rutting Susceptibility Laboratory Tests

Hamburg Wheel Tracking Device Captures the combined effects of rutting

and moisture damage; Mixture was both moisture and rut

resistant

19

Rutting Susceptibility Laboratory Tests

RSST-CH Asphalt content: optimum & optimum “+”

for sensitivity analysis 122F (50C) 5000 load cycles;

20

Rutting Susceptibility Laboratory Tests

Shear Frequency Sweep test data Asphalt content:optimum & optimum “+” 3 temperatures (4C, 20C and 46C); 3 frequencies (0.1Hz, 1Hz and 10Hz);

Develop master curve to determine shear modulus with temperature and loading rate.

21

Performance tests results

10

100

1000

10000

1.0E-06 1.0E-03 1.0E+00 1.0E+03 1.0E+06

Reduced Frequency, Hz (20C Reference Temp)

Dyn

amic

Mo

du

lus,

k/i

n2

Optimum Optimum Plus

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 1000 2000 3000 4000 5000

Load Cycle

Per

man

ent

Sh

ear

Str

ain

, %

Optimum Optimum Plus

22

Rutting Susceptibility Mechanistic Empirical Approach

Mechanistic approach to determine the accumulation of plastic strain;

Rutting in AC is assumed to be controlled by shear deformation;

Time hardening principle applied to calculate cumulative plastic strain due to shear deformation;

i = f(, e,N)

24

Rutting Susceptibility Mechanistic Empirical Approach

Analysis assumptions: Aircraft operations uniformly distributed

throughout the year; Plastic strain accumulated during the

warmest months; Plastic strain accumulated 8 hrs/day; 50% of aircraft operations at max. weight No aircraft wander;

25

Accumulation of Inelastic/Plastic Strain "Optimum" and "Optimum + 0.5% Mixes"

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0 300 600 900 1200 1500Number of days (5yrs x 244 days/yr)

Cum

ulat

ive

Inel

astic

/Pla

stic

Stra

in

Cumulative inelastic strain AC optimum Cumulative inelastic strain Opt + 0.5%

26

Notes

RSST-CH test helped identify the target binder content and the construction control limits (±0.25%)

27

Airfield Pavement Design Example Using Long-Life Highway Design

Concepts

28

Pavement Structural Section Design for Wide-Bodied Aircraft

Lab test data from I-710, LA County – Long Life Performance concept; Carries traffic into and out of the Port of

Long Beach; ADT = 155,000 vehicles/day; 13% trucks;

29

Pavement Structural Section Design for Wide-Bodied Aircraft

Use of ME procedure Multilayer elastic program Laboratory flexural fatigue and stiffness

data

30

Estimate Elastic Modulus and Fatigue Life

Elastic Modulus PBA-6a*: E (ln stif) = 9.1116-

0.1137*Temp PG 64-16: E (ln stif) = 14.6459-

0.1708*AV-0.8032*AC-0.0549*TempFatigue Life PG 64-16:

E (ln nf) = -36.5184-0.6470*AV-6.5315*lnstn

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Analysis – Pavement Structure

4 in PBA-6a*(PG64-40), 4.7% AC, 6% AV, E = f(Temp)

12 inches AB

(TBD) PG 64-16, 4.7% AC, 6% AV

E=f(AV, AC, Temp)

3 in PG 64-16 RB, 5.2% AC, 3% AV

E = f(AV, AC, Temp)

SG

32

Data Analysis Factorial

Three wide-bodied aircraft types: Boeing 747-400 Airbus 380-800 Boeing 777-800

Design to strain levels at the bottom of the HMA layer: ~100, 200, 300 s

33

Data Analysis Factorial

Two climate zones: Desert area – Yuma, AZ Coastal region – San Francisco, CA

Temperature: Aug (hotter month) Jan (Yuma), Feb (SF) – colder month

Temperature at 1 in depth increments – EICM to determine layer stiffness for ME analysis

34

Yuma: Tensile Strain vs. Asphalt Layer Thickness

1

10

100

1000

10 15 20 25 30 35 40

Total AC Thickness (in)

Ten

sile

str

ain

(H

MA

bo

tto

m)

(mic

rost

rain

)

Yuma Aug-B777 Yuma Aug - B747 Yuma Aug - A380Yuma Jan - B777 Yuma Jan - B747 Yuma Jan - A380

35

Check Fatigue Resistance for 25in Asphalt Thickness

25in asphalt layer thickness: Aug: Avg t = 180 s, Nf=5*107

Jan: Avg t = 105 s, Nf=7*108

20 years: 5*106 operations 1.25*106 operations over 4 warmer

months 3.75*106 operations over 8 cooler months

36

Check Fatigue Resistance for 25in Asphalt Thickness

Apply linear summation of cycle ratio cumulative damage hypothesis – Miner criteria

Shell subgrade strain criteriav=2.8*10-2*N-0.25

37

Construction Considerations

38

Construction Considerations

NDIA project RSST-CH tests suggested tighter binder

content tolerances ±0.25% asphalt binder content

39

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.4 4.6 4.8 5 5.2 5.4

As-constructed average asphalt content (%)

Sim

ula

ted

ES

AL

s t

o 1

0%

ru

ttin

g (

15

mm

or

more

rut

de

pth

) exp

resse

d a

s f

ractio

n o

f ta

rge

t E

SA

Ls

0.114

0.19

0.266

As-constructed

standard deviation of

asphalt content (%)

Influence of As-Constructed Asphalt Content on Rutting Performance

40

Construction Considerations

Long Life Performance project AV 4% - 6% rut-resistant upper and

intermediate HMA layer; Desirable AV <=3% - rich bottom layer

Increased fatigue life – key for long life performance

Tack coat essential between lifts

41

Concluding Notes

Shear Test was useful for: HMA design Establishing performance criteria under

repeated trafficking on taxiways Examine materials response at more

than one binder content – more effective use of different quantities of binder (rich bottom concept)

42

Concluding Notes

Potential savings: More effective use of materials Ability to estimate long term

performance

THANK YOU!