special thanks to

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• special thanks to
• Joe Mahoney

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Topics

• Background
• Early-age behavior
• Scenarios and examples

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Background

• FHWA sponsored research project
• State and industry involvement
• Guidelines for fast-track jointed concrete
  pavements
• High performance concrete paving

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Background

• Assist engineer and contractor
• To understand 72-hour behavior
• To predict 72-hour behavior
• Can also be used for long-term performance
• Process has been validated through field trials
  in a number of states

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Why is early-age behavior important?
Distress Type
Critical stress locations
Critical period
Plastic shrinkage cracking
First 3-12 hours or until curing method
application
Thermal cracking
First 72 hours
Plan View
Cross section
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Paving Operations
800 AM
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Paving Operations
810 AM
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Curing
PCC Temp
Time
830 AM
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Environmental Influences
PCC Temp
Time
Overcast Conditions
Solar Radiation
Convection due to wind speed
Relative Humidity
Air temperature
Heat Conduction to/from the subbase
900 AM
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Heat of Hydration
PCC Temp
Time
Generated Heat from Hydration
1100 AM
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Set Time
PCC Temp
PCC Set Time
Transition from plastic to hardened state
Time
1200 AM
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Peak Concrete Temperature
Slab tends to expand from set time up to the
maximum PCC temperature
PCC Temp
Time
400 PM
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Cooling Begins
PCC Temp
PCC slab tries to contract
Time
600 PM
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Joint Sawing
PCC Temp
Time
Saw cut joints
Saw cut joints
700 PM
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Curling
PCC Temp
Thermal difference through the slab
Time
Cold
Warm
1100 AM
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Curling
PCC Temp
Bottom expands top contracts slab tends to curl
Time
Cold
Warm
900 PM
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Curling
PCC Temp
Slab weight restrains vertical movement
DT
Time
Slab Weight
900 PM
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Subbase Restraint
PCC Temp
Axial and curling restraint lead to crack
formation at joints
DT
Time
Formation of cracks at joints
Formation of cracks at joints
1200 AM
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Excessive Restraint
PCC Temp
As temperatures decrease, PCC contraction
continues
DT
Time
200 AM
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Early-Age Failure
PCC Temp
DT
Time
Mid panel thermal crack occurs
500 AM
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HIPERPAV II Approach

• Integrates
• Design parameters
• Material properties
• Environmental conditions
• Construction activities

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Stresses (first 72 hours)

• Estimates applied stresses
• When applied stress exceeds the estimated PCC
  strength
• A crack is predicted to form

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Long-term Predictions

• Joint faulting (inches or mm)
• Percent of transverse cracking
• Percent of longitudinal cracking
• Ride (IRI) (inches/mile or m/km)
• Serviceability (PSI)

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Download

• Free of charge
• http//www.fhwa.dot.gov/pavement/pccp/hipemain.cfm
  
• File size 75 MB

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User Manual

• Help tab on the software toolbar or
• Download at http//www.tfhrc.gov/pavement/pccp/pub
  s/04122/04122.pdf
• File size 5.1 MB

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Examples
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Example 1

• Interstate 405 in the vicinity of Bellevue, WA.
• Paving date is July 11, 2006
• The pavement is JPCP
• Slab 12 inches thick
• Dowel bars at transverse contraction joints
• Most of inputs will be default values contained
  in the software

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This information is simply a visual verification
of the rainfall data for Seattle.
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Dowels WSDOT uses a 1.5 inch diameter dowel. The
other values shown for dowels are default values
from the software.
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WSDOT typically places PCC on an HMA base (about
4 inches thick). The default values were adjusted
to reflect this.
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We will assume that Type I cement will be used.
If this was a time critical projectthen Type III
might be considered. Additionally, if the
chemical composition of the cement is known or
unique, the click on User-Defined Bogue
Compounds. Clicking on the yellow question
provides more insight as to why such information
is needed.
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The default PCC mix design was used for this
example. If you know the weights of the mix
ingredients, it is better to enter them under
Batch Proportions (lb/yd3) rather than use
default values.
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This screen requires an estimate of 28-day cure
strength of the PCC mix being considered. Since
WSDOT uses the 3rd point flexural strength
testthat one was used (the default test is
splitting tensile). Further, the typically
specified WSDOT flexural strength is 650 psiso
that value was used as well. All other needed
parameters can be estimated by the software.
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The software will estimate from the prior inputs
how the PCC will gain strength with timeoryou
can input your own Maturity data. For this
example, the default strength gain was selected.
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Example 2

• Change sawcutting from 7 hours to 24 hours after
  paving
• Scenario where the contractor does not sawcut the
  joints in a timely manner

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You can save Example 1 by clicking on Strategy
in the toolbar and selecting copy. Then change
the inputs on the copy for Example 2.
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For Example 2, the Sawcutting was changed from
Optimum Time to User-Defined Sawing Age. The
selected time was 24 hours following placement of
the PCC slabs.
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Example 3

• Change slab depth from 12 inches to 8 inches thick

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For Example 3, the only change from Example 1
that was made was the PCC slab thickness was
reduced from 12 to 8 inches.
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A Few More Details

• Requires mean values of strength
• Requires tensile strength
• Correlations exist with flexural strength and
  compressive strength
• Why is tensile strength used?
• The primary mode of PCC failure during early-age
  behavior is tensile stress

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A Few More Details

• The sensitivity of the stress calculations to
  modulus of elasticity (E) is low to modest
• Software does not check the PCC mixture
  proportioning nor the input estimates of
  strengthso you can input nonsense
• Chemical admixtures are considered based on
  average dosage rates (dosage rate is not an
  input)
• As applied in HIPERPAV, chemical admixtures have
  only a moderate effect on hydration rates
• Type IV cement is not considered in HIPERPAV
  since it is not a widely used portland cement

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A Few More Details

• Air entrained PCC is currently not considered
• The wind speed input is assumed to be constant
  over the 72 hour period
• Why is early-age behavior defined for a 72 hour
  period?
• Experience suggests that most potential problems
  associated with early age behavior occur within
  the first two to three days after placement of
  the PCC.
• HIPERPAV has been modeled to handle up to 12 inch
  thick slabs. Results for thicker slabs should be
  OK

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Questions?