Perpetual Pavement Design

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Perpetual Pavement Design
Perpetual Pavement Open House Ashton,
Iowa October 5, 2005
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Overview

• Pavement design background
• Layered elastic theory
• Perpetual pavement design philosophy
• Design basics

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Goal of Perpetual Pavement Design

• Design the structure such that there are no deep
  structural distresses
• Bottom up fatigue cracking
• Structural rutting
• All distresses can be quickly remedied from
  surface
• Result in a structure with Perpetual or Long
  Life

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Surface Distresses Only
Top Down Cracking
Non-Structural Rutting
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Materials
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1
2
3
After Loading - Same Size as Before Loading
Before Loading
During Loading
Figure 1. How an Elastic Material Behaves.
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D
DD/2
s
Dl
l
el Dl/l
E s/e
et DD/D
m el/et
Figure 1. Definitions of E and m.
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Dynamic Modulus Test
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Witczak Equation for E

• cum. retained on 19-mm sieve
• cum. retained on 9.5-mm sieve
• cum. retained on 4.76-mm sieve
• passing the 0.075-mm sieve

• bitumen viscosity (dynamic shear rheometer)
• loading frequency
• air voids
• effective bitumen content

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HMA Modulus VersusTemperature
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Soil Modulus Testing
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Dynamic Cone Penetration
Mass
Rod
Reference
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Effect of Moisture Content
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FWD Testing
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Backcalculation
E f(Load, Pressure, Deflection, Distance)
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Traffic
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Single Tire
Dual Tire
Tandem
Tridem
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Tire has a total load P, spread over a
circular area with a radius of a, resulting in a
contact pressure of p.
Pavement Reactions
Layer 1 HMA E1
Deflection (d)
No horizontal boundary, assume layers extend infi
nitely.
h1
Tensile Strain (et)
Layer 2 Granular Base E2
h2
Layer 3 Subgrade Soil E3
Compressive Strain (ev)
No bottom boundary, assume soil goes on
infinitely.
Figure 2. Layered Elastic Model Representation of
a Pavement.
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400
Test Section 21
Mn/ROAD Measurements
300
me
200
Transverse Strain,
Layered Elastic Results
100
0
20
30
40
50
60
Wheel Load, kN
Figure 4. A Comparison of Measured Strains and
Computed Strains at Mn/ROAD. (After Timm et al.,
1998, Development of Mechanistic- Empirical
Pavement Design, Transportation Research Record
No. 1629, Transportation Research Board,
Washington, DC.)
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Thickness vs. Tensile Strain
HMA Tensile Strain
HMA Thickness
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Modulus vs. Tensile Strain
HMA Tensile Strain
HMA Modulus
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Thickness vs. Compressive Strain
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Traditional M-E Design
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Perpetual Pavement Design
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Transfer Functions
et
ev
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Miners Hypothesis

• Provides the ability to sum damage for a specific
  distress type
• D ? ni/Ni ? 1.0
• where ni actual number of loads
  during condition i
• Ni allowable number of loads
  during condition i

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Probabilistic Design Monte Carlo Simulation
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Below Threshold

• Design should have high below threshold

f
Below Threshold
Pavement Response
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Damage Computation

• For responses exceeding threshold, compute N
  using transfer function
• User defined
• Calculate damage accumulation rate
• Damage / MESAL

f
Below Threshold
Damage MESAL
Pavement Response
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Estimated Long Life

• Convert damage rate into an estimated life
• Use traffic volume and growth
• Calculate when damage 0.1
• Use for Low Vol. Roads (t 30 yrs.)

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PerRoad 2.4

• Sponsored by APA
• Developed at Auburn University / NCAT
• M-E Perpetual Pavement Design and Analysis Tool
• Help File is the Users Manual
• Press F1 at Any Time for Help File

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Deterministic Output
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Probabilistic Output
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Design Criteria Recommendations
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PerRoad is available for freeatwww.AsphaltAllian
ce.com
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P.S.

• TxDOT intends to incorporate PerRoad in its next
  generation design procedure.
• One-day workshop is available at the request of
  Iowa Asphalt Paving Association - Work out the
  dates with Mike.