Mn/DOT Flexible Pavement Design

Mechanistic-Empirical Method

Pavement Design Systems and Pavement Performance ModelsMarch 22-23, 2007 - Reykjavik, Iceland

Bruce ChadbournAssistant Pavement Design Engineer

Minnesota Department of Transportationwww.mrr.dot.state.mn.us

Acknowledgements

•

Icelandic Road Administration •

Haraldur Sigursteinsson

•

Nordic Road Association•

NordFoU Project

Pavement Design at Mn/DOT•

Current procedure–

Subgrade soil R-value, traffic, rule-of-thumb materials properties

–

Relates to ride•

MnPAVE procedure–

Modulus of all layers, base strength, repeated load damage in HMA and subgrade

–

Relates to structural distresses – cracking, rutting

Background

WESLEA•

Layered Elastic Analysis (5 Layers)

•

Developed at U.S. Army Engineer Waterways Experiment Station (Van Cauwelaert et al, 1986)

ROADENTROADENT

University of Minnesota (1996-1999)

Dr. David Timm –

Auburn University

Dr. David Newcomb –

NAPA

Dr. Bjorn Birgisson –

University of Florida

MnPAVE Pavement Design

•

Climate model•

More material types and default properties

•

Lab and field test results•

Updated performance models

ClimateClimate

MnROAD Cell 21

1

10

100

1,000

10,000

0 50 100 150 200 250 300 350Day of Year

Mod

ulus

(ksi

)

AsphaltBaseSoil

Seasons

Criteria for Determining the Beginning of MnPAVE Seasons

Season Criteria

Fall 3-day Average Temperature < 17 °C

Winter Freezing Index > 90 °C-days

Spring Thaw Thawing Index > 15 °C-days

Spring Recovery 2 Weeks After Start of Spring Thaw

Summer 3-day Average Temperature > 17 °C

Temperature Model

“Whiplash” Equation

∑

∑

=

== n

i i

n

i i

i

D

DT

T

12

12

1

5 Seasons vs. 52 Weeks•

Number of times the asphalt modulus (stiffness) is calculated.

•

Affects the calculation time.•

Wide range of pavements were simulated.

•

Design thickness differed by no more than 0.1 in.

•

Default MnPAVE procedure has 5 seasons.

StructureStructure

Material Properties• New Asphalt• Existing Asphalt (overlay design)• Aggregate Base/Subbase• Soils

Witczak Equation( )

( )( )ηlog2log

4/3102

8/398/38476

54432

200220010

1312111

log

afaa

abeff

beffa

epapapapaa

VVVaVapapapaaE

+++++++

+

++++++=

Where:

E = 10-5

x Dynamic Modulus (psi)

η = 10-8

x Dynamic Viscosity (cP)

Pb = binder content (% by wt. of mix)

Va = Air voids (% by volume)

Pba = Absorption (% by wt. of aggregate)

Gb = specific gravity of binder

Gsb = Bulk specific gravity of aggregate

f = Load frequency (Hz)

Vbeff = Effective binder content (% by vol.)

p3/4

= Cumulative % retained on 3/4” sieve

p3/8

= Cumulative % retained on 3/8” sieve

p4

= Cumulative % retained on No. 4 sieve

p200

= Percent passing No. 200 sieve

Thompson (ILLI-PAVE) Equation

⎟⎟⎠

⎞⎜⎜⎝

⎛+⎟⎟⎠

⎞⎜⎜⎝

⎛−=

ACAC T

AREAD

AREAE 26.0log76.148.1log0

1010

⎟⎟⎠

⎞⎜⎜⎝

⎛+++=

0

3

0

2

0

1 2216DD

DD

DDAREA

EAC = Modulus of the HMA layer (ksi)TAC = Temperature of the HMA layer (°F)D0

= Deflection at center of load (mils)D1

= Deflection at 12 in. (305 mm) from center of loadD2

= Deflection at 24 in. (610 mm) from center of loadD3

= Deflection at 36 in. (914 mm) from center of load

Where:

Cell 20 Modulus Comparison 1994-2003Witczak and Thompson Equations

10

100

1,000

10,000

20 30 40 50 60 70 80 90 100 110 120HMA Temperature (°F)

HM

A M

odul

us (k

si)

1994 1995 19961997 1998 19992000 2001 20022003 Witczak

7.8” 120/150 Pen. (PG 58-28)

Modulus Reduction Factor–

Modulus Ratio (R )

•

R= E*(near crack)/E* (between cracks)

MnROAD Class 5 Moduli1994-1996

0

50

100

150

200

250

0 30 60 90 120 150 180 210 240 270 300

Days from Spring Thaw

Bac

kcal

cula

ted

E (M

Pa)

0

5

10

15

20

25

30

35

40

Bac

kcal

cula

ted

E (k

si)

Cells 21, 28

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0.001 0.01 0.1 1 10 100 1000 10000Suction (kPa)

Satu

ratio

n

CL3 est. CL 4 est.CL 5 est. CL 6 est.CL 3 measured CL 4 measuredCL 5 measured CL 6 measured

Unsaturated Properties

Statewide HMA DeflectionsStatewide HMA Deflections 1994 1994 -- 20052005

Subgrade Modulus Subgrade Modulus Superimposed on Soil MapSuperimposed on Soil Map

Subgrade Modulus Predictions

0

50

100

150

200

250

SiltyClay

SiltyClayLoam

Clay ClayLoam

Silt SiltLoam

Loam SandyClayLoam

SandyClay

SandyLoam

LoamySand

Sand

E sub

grad

e, M

Pa

0

5

10

15

20

25

30

35

E sub

grad

e, ks

i

Hogg (FWD)Predicted85th %15th %MEPDG HighMEPDG LowMnPAVE 5.2 COV = 34%

μ = -7.74(CLAY2SILT2) + 0.694(e-CLAYe-SILT) + 3.86

σbest fit = 0.34 (range: 0.11 to 0.47)

2σμpredicted

2

eE +=

TrafficTraffic

Simplified Load Spectrum Input

•

Analysis of WIM data•

Mn/DOT and FHWA vehicle types

•

Axle distributions by truck type•

Assumptions about truck distributions

•

Route types

MnROAD 2001 WIM Data

0 10,000 20,000 30,000 40,000Axle Weight (lbs)

Rep

etiti

ons

SteerTandemSingleTridem

Vehicle Type 8

0 10,000 20,000 30,000 40,000Axle Weight (lbs)

Rep

etiti

ons

SteerSingleTandemTridem

Burnsville I-35E (Feb. 1 - Mar. 1 1992)

0 10,000 20,000 30,000 40,000 50,000

Axle Weight (lbs)

Rep

etiti

ons

SingleTandemTridemSteer

WIM

MnPAVE

10,924 AADT

OutputOutput

Questions

www.mrr.dot.state.mn.us