Mn/DOT Flexible Pavement Design · Pavement Design Mechanistic-Empirical Method ... University of Minnesota (1996-1999) Dr. David Timm – Auburn University Dr. David Newcomb –

Mn/DOT Flexible Pavement Design

Mechanistic-Empirical Method

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

Bruce TanquistAssistant Pavement Design Engineer

Minnesota Department of Transportationwww.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

DDAREAWhere:

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

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 Deflections1994 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.dot.state.mn.us