Mn/DOT Flexible Pavement Design Mechanistic-Empirical Method Pavement Design Systems and Pavement Performance Models March 22-23, 2007 - Reykjavik, Iceland Bruce Tanquist Assistant Pavement Design Engineer Minnesota Department of Transportation www.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)
ROADENT
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
Climate
Seasons MnROAD Cell 21
Modulus (ksi)
10,000
Asphalt Base Soil
1,000
100
10
1
0
50
100
150
200
Day of Year
250
300
350
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
Ti ∑ 2 i =1 Di T = n 1 ∑ 2 D i =1 i
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.
Structure
Material Properties • New Asphalt • Existing Asphalt (overlay design) • Aggregate Base/Subbase • Soils
Witczak Equation log E = a0 + a1p200 + a2 (p200 )
2
Vbeff + a3 p4 + a4Va + a5 Vbeff + Va
a6 + a7 p4 + a8 p3 / 8 + a9 (p3 / 8 ) + a10 p3 / 4 + 1 + e (a11 +a12 log f +a13 2 logη ) 2
Where: E = 10-5 x Dynamic Modulus (psi)
f = Load frequency (Hz)
η = 10-8 x Dynamic Viscosity (cP)
Vbeff = Effective binder content (% by vol.)
Pb = binder content (% by wt. of mix)
p3/4 = Cumulative % retained on 3/4” sieve
Va = Air voids (% by volume)
p3/8 = Cumulative % retained on 3/8” sieve
Pba = Absorption (% by wt. of aggregate) p4 = Cumulative % retained on No. 4 sieve Gb = specific gravity of binder Gsb = Bulk specific gravity of aggregate
p200 = Percent passing No. 200 sieve
Thompson (ILLI-PAVE) Equation log10 E AC Where:
⎛ AREA ⎞ ⎛ AREA ⎞ ⎟⎟ + 0.26⎜⎜ ⎟⎟ = 1.48 − 1.76 log10 ⎜⎜ ⎝ D0 ⎠ ⎝ TAC ⎠ ⎛ 2 D1 2 D2 D3 ⎞ ⎟⎟ AREA = 6⎜⎜1 + + + D0 D0 D0 ⎠ ⎝
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 load D2 = Deflection at 24 in. (610 mm) from center of load D3 = Deflection at 36 in. (914 mm) from center of load
Cell 20 Modulus Comparison 1994-2003 Witczak and Thompson Equations 10,000
HMA Modulus (ksi)
7.8” 120/150 Pen. (PG 58-28)
1,000
100
1994 1997 2000 2003
10
20
30
1995 1998 2001 Witczak 40
50
1996 1999 2002
60 70 80 90 HMA Temperature (°F)
100
110
120
Modulus Reduction Factor – Modulus Ratio (R ) • R= E*(near crack)/E* (between cracks)
MnROAD Class 5 Moduli 1994-1996
250
40
Backcalculated E (MPa)
30 150
25 20
100 15 10
50
5
Cells 21, 28 0
0 0
30
60
90
120
150
180
Days from Spring Thaw
210
240
270
300
Backcalculated E (ksi)
35
200
Unsaturated Properties 100%
CL3 est. CL 5 est. CL 3 measured CL 5 measured
90% 80%
CL 4 est. CL 6 est. CL 4 measured CL 6 measured
Saturation
70% 60% 50% 40% 30% 20% 10% 0% 0.001
0.01
0.1
1
10
Suction (kPa)
100
1000
10000
Statewide HMA Deflections 1994 - 2005
Subgrade Modulus Superimposed on Soil Map
Subgrade Modulus Predictions Hogg (FWD) Predicted 85th % 15th % MEPDG High MEPDG Low MnPAVE 5.2
Esubgrade, MPa
200
150
Epredicted = eµ+σ
2
2
µ = -7.74(CLAY2SILT2) + 0.694(e-CLAYe-SILT) + 3.86 σbest fit = 0.34 (range: 0.11 to 0.47)
35 30 25
COV = 34% 20 15
100
10 50 5 0
0 Silty Clay
Silty Clay Loam
Clay
Clay Loam
Silt
Silt Loam Sandy Sandy Sandy Loamy Sand Loam Clay Clay Loam Sand Loam
Esubgrade, ksi
250
Traffic
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
Repetitions
Steer Tandem Single Tridem
0
10,000
20,000 30,000 Axle Weight (lbs)
40,000
Vehicle Type 8
Repetitions
Steer Single Tandem Tridem
0
10,000
20,000 30,000 Axle Weight (lbs)
40,000
Burnsville I-35E (Feb. 1 - Mar. 1 1992) 10,924 AADT
Single Tandem
Repetitions
Tridem Steer
WIM MnPAVE
0
10,000
20,000
30,000
Axle Weight (lbs)
40,000
50,000
Output
Questions www.dot.state.mn.us