Illinois DOTFrom the AASHO Road Test

To 20 Years of Mechanistic Pavement Experience

……and Counting

David L. Lippert, PEBureau of Materials and Physical Research

Illi i D t t f T t tiIllinois Department of Transportation

Transportation Research Board87th Annual Meeting87 Annual Meeting

January 13, 2008

Outline• AASHO Road Test History• Illinois Adoption of MechanisticIllinois Adoption of Mechanistic • Current Updating Efforts

60708090

100

0102030405060

0 10 20 30 40 50

Probabilityof Failure, %

9-in CRCP without DC9-in CRCP with DC

0 10 20 30 40 50Cumulative ESALs, million

“AASHO Road Test”AASHO Road Test

LoadingLANE 1 LANE 2

Loading

LOOP

3 4 1 124 6 18 18

6 24 249 32 32

5 6 22 226 9 30 30

9 40 4012 48 486 9 30 30 12 48 48

2 Years = 1.1 Million Axle Loads

Rigid Profile 0

8

Rigid Profile

10”

8

310

312 5 612 8 912 11 121220”

THICKNESS

PCC

MATERIAL

0 3 6 9SANDY GRAVEL subbase

Flexible Profile0

3

Flexible Profile3

6

10”

8

ASPHALT surface 65432MATERIAL THICKNESS 20”

CRUSHED STONE base

SANDY GRAVEL subbase 16

128409630

6

TrafficTrafficAASHO – Static Weights – Dynamic Loading

Pavement PerformancePavement Performance PSR = 0 0?PSR 0.0?

PSR = 0 0?PSR 0.0? A l L d Fl Ri id Fl Ri idESAL’s18,000 Pounds

Axle LoadPounds

FlexSingleESAL’s

RigidSingleESAL’s

FlexTandemESAL’s

RigidTandemESAL’s

ESAL s

80 PSI2,000 0.0002 0.0002 0.0000 0.0001

6,000 0 010 0 01 0 001 0 0026,000 0.010 0.01 0.001 0.002

12,000 0.189 0.176 0.014 0.026

18 000 1 00 1 00 0 077 0 13318,000 1.00 1.00 0.077 0.133

24,000 3.03 3.36 0.260 0.444

30 000 7 00 8 28 0 658 1 1430,000 7.00 8.28 0.658 1.14

36,000 13.9 17.1 1.38 2.43

42 000 25 6 32 2 2 51 4 5542,000 25.6 32.2 2.51 4.55

Illinois Method of Calculating ESAL’sESAL s

• Collect static weight data from enforcement scalesscales.

• Load spectrum by axle/vehicle type. – Single.g– Tandem. – Triple.S f &• ESAL factor by FHWA vehicle class & road

type.– Class I – Interstate and multi lane– Class I – Interstate and multi lane.– Class II – Two lane over 2000 ADT.– Class III - 750 to 2000 ADT.– Class IV – Under 750 ADT.

• Summarize into PV, SU and MU groups.

PV SU and MUPV, SU and MUPassenger Vehicles (PV)

CarsSingle Unit (SU)

ClassCars

Light Trucks

Buses 4Class 2

Class 3

2 Axle 5

3 A l 6

Multiple Unit (MU)

3 Axle 6

4 Axle 74 Axle 7

Class 8 to 13

Traffic MapsTraffic MapsTotal ADT MU ADTTruck ADT

PV = Total ADT –Truck ADT SU = Truck ADT – MU ADT

Current ESAL Factors (Flex)Current ESAL Factors (Flex)Road Class

PV SU MUClass

Class I 0.0004 0.394 1.908

Class II 0.0004 0.372 1.554

Class III 0.0004 0.355 1.541C ass 0 000 0 355 5

Class IV 0.0004 0.350 1.523

Design Minimums: Interstate – 1,500 MU, 500 SU

N I 900 MU 300 SUNon Interstate – 900 MU, 300 SU

Rigid Nomographg g p

C SS

SOIL

AFF

IC

KN

E

TRA

THIC

T

Flexible Nomographg p

C

.N.

AFF

IC SOIL

S

TRA

4.75

AASHO AdvancesAASHO Advances

•Equivalent 18K Single Axle Loads (ESALs)

•Thickness Designs for both Flex & PCC

•“Equivalent” Pavements

•Cost Allocation•Cost Allocation

AASHO LimitationsAASHO Limitations

•One Set of Materials.

•Two Years of Weathering.

1 1 Milli A l•1.1 Million Axles.

•Totally Empirical – need to extrapolateTotally Empirical need to extrapolate to 100’s of millions of axles.

Structural Number ConceptStructural Number Concept444” = 1 76.444 = 1.76

9.25” = 3.05.33

= 4.81Subgrade

1958 Materials vs. Modern Materials

Why Illinois Pursued MechanisticWhy Illinois Pursued Mechanistic• AASHTO design produced excessively

thi k t f hi h l f ilitithick pavements for high volume facilities.• New materials very difficult to relate back to

d t t f l ffi i troad test for layer coefficient.• Modern facility traffic well beyond road test

t ffitraffic. • Valid procedure??

M h i ti D iMechanistic -

Mechanistic DesignMechanistic

“Concerning the Relationships Between Applied Forces and Material Responses.”Material Responses.

i iBasic Premise -

Low Deflections = Long LifeLow Deflections = Long Life

Mechanistic EngineeringMechanistic Engineering

IL-AAHSTO vs MechanisticIL AAHSTO vs. Mechanistic30

es

20

25

s, I

nche

10

15

Thic

knes

s

AASHTOMech

Perpetual HMA Design

5

10

HM

A T

00 20 40 60 80

Traffic ESAL'sTraffic, ESAL s

Illinois Mechanistic-Empirical D iDesign

• Research completed in 1987Research completed in 1987.• Load spectrum discussed – dismissed.

D i b d 18K ESAL’• Designs based upon 18K ESAL’s.• Results very complex. • Many designer inputs.• Policy decisions needed to simplifyPolicy decisions needed to simplify.

Fatigue Theory

High Strain = Short Lifeg

Low Strain = Long Life18K

Fatigue Life

Fatigue Cracking

Repeated Leads topBending

e ds oFatigue Cracking

Fatigue Cracking

Repeated Leads topBending

e ds oFatigue Cracking

Illinois Mechanistic Loop pPavement Model

18,000 Pounds

80 PSI

100Performance Calibration

405060708090

100

Probabilityof Failure, %

i i h

Load Model0

102030

0 10 20 30 40 50Cumulative ESALs, million

9-in CRCP without DC9-in CRCP with DC

Why Load Spectrum Not Used

• Data reliabilityData reliability.– Calibration.

Maintenance of equipment– Maintenance of equipment.• Limited data collection ability.

– Expense.– People – Head count limits.

• Data fit into performance calibration??• Department understanding of ESAL’s.p g

Inputs – Full-Depth AsphaltInputs Full Depth Asphalt• TrafficTraffic.• Soil Support (Eri).

L ti (t t / d l l ti )• Location (temperature/modulus relations).• Asphalt grade.• Mix air voids and gradation.• Crack initiation at bottom of HMACrack initiation at bottom of HMA.• Reliability.

Inputs – Jointed ConcreteInputs Jointed Concrete• Traffic.Traffic.• Soil support (k).• Joint spacing• Joint spacing.• Joint load transfer.

Ed t• Edge support.• Drainage conditions.• Concrete strength .• Slab cracking.• Reliability.

Decisions Decisions Decisions!Decisions, Decisions, Decisions!• Policy decisions:

T i lif d i– To simplify design.– To limit sophisticated data collection or

testingtesting.– Insure design assumptions are built into

pavement.p• Maintain “off-the-shelf” or current inputs.

– 18K ESAL and related traffic data collection.– Current material test.

Example:Example:• Simplified correlation for soil inputs.

– Not going to run subgrade resilient modulus (Eri) for every project.

– Not going to determine “k” values.– Correlated to Corp of Engineers soil triangle

( i i l i ) t th(grain size analysis) to three common support levels.

Soil Input 100p

27% Clay45% Silt

“Poor”y28% Sand

50

Fair

Poor

0

PoorGran

Percent Sand

Impacts of Soil InputsImpacts of Soil InputsSoil Rating Full-Depth HMA Concrete

Granular - 5%k = 200

13.75 9.25

Eri = Stress DependentFair - 5%k 100

14.00 9.75k = 100Eri = 5 ksiPoor - 90% 14.25 10.25k = 50Eri = 2 ksiFor 2000 trucks/day in design lane – moderate volume Interstatey g

Pavement PerformancePavement Performance• Keys to long term performance:Keys to long term performance:

– Design.• Thickness• Thickness.• Cross-section.

– MaterialsMaterials.– Construction.– Maintenance– Maintenance.

“D” Cracked ConcreteD Cracked Concrete ESAL Survival of Original P S h ILPavements – South IL100

D-Cracking Comparisons

708090

30% More Life

40506070

Probabilityof Failure, %

203040

9-in CRCP without DC9-in CRCP with DC

010

0 10 20 30 40 500 10 20 30 40 50Cumulative ESALs, million

Keys to Pavement Performance Illi i-Illinois

Design (T)Design (D)MaterialsMaterialsMaintenanceConstruction

Summary of Pavement Life (No DC) ADC) – Age

Original 1st Thin OL 2nd Thin OL

45

50

year

s

Original 1st Thin OL 2nd Thin OL

Design

30

35

40

tile

Ag

e, y Tentative

10

15

20

25

50 P

erce

nt

0

5

10

10 in JRCP 10 in CRCP 12 to 17 in HMAC

5

10-in JRCP 10-in CRCP 12 to 17-in HMAC

Summary of Pavement Life (No DC) C l ti ESAL– Cumulative ESALs

Original 1st Thin OL 2nd Thin OL

140

160

mill

ion

Original 1st Thin OL 2nd Thin OL

100

120

e E

SAL

, mi

i

40

60

80

0 Per

cent

ile TentativeDesign

0

20

10 i JRCP 10 i CRCP 12 t 17 i HMAC

50

10-in JRCP 10-in CRCP 12 to 17-in HMAC

Traffic DataTraffic Data

Search for New Portable Equipment

• Safety of the worker• Quality and Quantity of data collected• Cost to the Department• Comply with new FHWA’s Traffic

Monitoring Guide (TMG) o to g Gu de ( G)

Nu Metrics Hi Star 97Nu-Metrics Hi-Star 97

PV SU and MUPV, SU and MUPassenger Vehicles (PV)

CarsSingle Unit (SU)

ClassCars

Light Trucks

Buses 4Class 2

Class 3

2 Axle 5

3 A l 6

Multiple Unit (MU)

3 Axle 6

4 Axle 74 Axle 7

Class 8 to 13

Axle Classification vs. Length Classification(data from permanent ATR locations)

F12

F13

F12

F13

(data from permanent ATR locations)

F09

F10

F11

F12

F09

F10

F11

F12

F06

F07

F08

F06

F07

F08

F02

F03

F04

F05

F02

F03

F04

F05

Single-Unit Multi-Unit

F01

F02

0 20 40 60 80

F01

F02g

Vehicle Length (feet)

Distribution of Vehicles by Length

90,000100,000

es

PV SU MU

60 00070,00080,000

,

Veh

icle

30 00040,00050,00060,000

er o

f V

10,00020,00030,000

Num

b

0,

4 10 16 22 28 34 40 46 52 58 64 70 76 82 88

V hi l L th (f t)Vehicle Length (feet)

Illi i M h i ti D iMinimum Designs:Illinois Mechanistic Design

Minimum Designs:

Former procedure:

Minimum thickness by facility type

Same statewide

Industry issues

New Minimums

Mi i b F ilit TMinimums by Facility TypeInterstates 2 Way ADT:

500 SU 1500 MU500 SU 1500 MU

Other State300 SU 900 MU300 SU 900 MU

UnmarkedActual Traffic

Mechanistic ExampleMechanistic ExampleMechanistic ExampleMechanistic Example

Given: TF = 4.27

AC = PG 58 – XX

Location = Springfield, IL

Soil Input 100

27% Clay45% Silt

“Poor”y28% Sand

50

Fair

Poor

0

PoorGran

Percent Sand

Illinois 2008 Mechanistic UpdateIllinois 2008 Mechanistic Update

• HMAHMA– New Fatague Equation– PG Graded Materials for Modules – Limiting Strain (Max thickness)

• PCC– Relook at Joint Spacing– Mechanistic CRCP

• Both– New Minimum Traffic (Lower)

ImplementationImplementationImplementationImplementation

Research start 1980Research start 1980–– 6 years6 yearsIndustry meetingsIndustry meetings–– Design ProceduresDesign Proceduresgg–– Selection ProcessSelection Process–– ImplementationImplementation–– 2 years2 yearsIssue Design 1989Issue Design 1989gg

Issues after Issues after ImplementationImplementation

Industry questionsIndustry questionsFHWA/IDOT reviewFHWA/IDOT reviewFHWA/IDOT reviewFHWA/IDOT reviewRevisions 1992Revisions 1992

Summary/SuggestionsSummary/Suggestions

• Review design.Review design.• Determine where performance gains

needed in your state.needed in your state.– Durability (materials)– DesignDesign– Other

• Determine merits of each design input andDetermine merits of each design input and worth of refinement.

• Involve industryInvolve industry

Challenges & IssuesChallenges & IssuesQuality Data

i d dSimplified Inputs

Quantity Needed? 100p p

50Fair

PoorGr

0Gr

Questions?

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