MOISTURE CURLING OF CONCRETE SLABS

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MOISTURE CURLING OF CONCRETE SLABS FOR AIRFIELD
APPLICATIONS
PIs David A. Lange Jeffery R. Roesler RAs Chang
Joon Lee Yi-shi Liu Benjamin F. Birch November,
2005
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OUTLINE

• Objective of the Project
• Computer Modeling
• Laboratory Tests for FAA Material
• Prediction of NAPTF Single Slab
• Technology Transfer of Results
• Future Works

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OBJECTIVE OF PROJECT

• To develop a better understanding of concrete
  material behavior that leads to moisture curling
• To develop guidelines for future concrete
  materials selection for airport pavement
  applications.

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COMPUTER MODELING
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WHY IS OUR MODELING CONCEPT USEFUL?
ABAQUS DIANA ICON
Gradient excitations YES YES YES
Aging concrete properties NO YES YES
Hygrothermal model for shrinkage NO NO YES
Aging effect on creep NO SIMPLE SOLIDIFYING
NOTE Assessments are based on the built-in
functions of the codes
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Material Models
Concrete is an Aging Material
Instantaneous response - Static
Linear Elastic Continuum
Delayed response - Creep
Solidification Theory Bazant 1977
Hygrothermal Model
Hygrothermal response - Shrinkage Thermal
Expansion
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Stress is a function of porosity and humidity
Drying shrinkage is a mechanical response of
porous microstructure to the capillary pressure
due to internal humidity reduction
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Capillary pore pressure as a function humidity
Kelvin-Laplace Equation relates RH directly to
capillary pressure

• surface tension
• r mean pore radius
• RH Relative humidity
• R Universal gas constant
• T Temperature
• v molar volume of water

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Two concepts for hygrothermal models
Stress ApproachInternal stress based
hygrothermal model
Strain ApproachStrain based hygrothermal model
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Internal stress based hygrothermal model
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Average stresses in porous mediaConverts pore
pressure to average bulk stress!
Pc 9 saverage 90.1psi
Pc 16.3 saverage 162.8psi
Pc 22.5 saverage 225.2psi
pore pressure 1000psi,
saverage p x pc (pore pressure) x (porosity)
NOTE saverage average hydrostatic stress
assuming that out-of-plan behavior of the porous
medium shows the same behavior with the in-plan
behavior
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Stress in concrete for a given humidity porosity
As applied to Concrete
Where,
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Finite Element Analysis for a free drying prism
Aging Material properties (Porosity, Elastic
Creep response)
Humidity History at different depth from drying
surface
1/8 model
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Deformation and stress distribution in a free
drying prism
1/8 model, stress in z direction at age of 30days
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Free drying shrinkage of prism
Best fit with the parameter Pcal
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Strain based hygrothermal model
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Strains in a solid with spherical pores under
negative pore pressure(A linear elastic solution)
Grasley et al., 2003
P
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Saturation factor (Approximation)Bazant Kim,
1991
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Fit to experimental data (RH, T, shrinkage)
NOTE simple linear model for shrinkage ?
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LABORATORY TESTS TO CALIBRATE MODELFOR FAA
HIGH-FA CONCRETE
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Lab Test Strength Development Rate
Uniaxial Compressive Strength
Split Tensile Strength
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Lab Test Stress-strain Youngs modulus
Youngs modulus
Uniaxial compressive test with axial lateral
strains
Stress-strain
Stress-lateral dilation
28 days
28 days
7 days
7 days
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Lab Test Temperature, RH shrinkage
Drying shrinkage
Free drying shrinkage test internal temperature
relative humidity
Drying
Internal humidity
Internal temperature
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Lab Test - Creep
Sealed test
Exposed to ambient
Drying
Total deformation
Basic creep
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PREDICTION OF NAPTF SLAB
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Material Models for Prediction
Instantaneous response - Static
Linear Elastic Model
Delayed response - Creep
Bazants Solidification Theory Const. creep
Poissons ratio
Shrinkage Thermal Expansion
Strain based Hygrothermal Model for Shrinkage
Different shrinking expanding rates for drying
wetting
Linear relation for thermal expansion
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INPUTS Finite Element Mesh Boundary Conditions
¼ modeling using symmetric boundary conditions
7.5ft
7.5ft
11 in.
Non-linear spring for base contact
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INPUTS Material Parameters from Lab. tests
ELASTIC MODULUS
Parameters for the material model set were
calibrated based on the Lab. material test
results.
BASIC CREEP
SHRINKAGE
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INPUTS Internal Temperature RH from NAPTF test
Internal humidity and temperature measured at
the NAPTF were applied to the FE model
TEMPERATURE
RELATIVE HUMIDITY
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OUTPUTS - Deformation Stresses
A
B
234 psi
Max. Principle stress
Deformation map
Age 68days, Mag. 100x
Age 68days
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Deformation Comparison
Lift-off displacement
VD-1
CL-2
A
VD-4 CL-3
VD-5 CL-4
VD
CL Clip gauge
CL
VD Vertical Displacement Transducer
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Deformation Comparison
Lift-off displacement
VD-2
B
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TECHNOLOGY TRANSFER OF RESULTS
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Finite Element Analysis Code
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Finite Element Analysis Code
ICON ver 0.1.0

• ICON is a FEA code written in C for deformation
  and stress prediction.
• ? OOP (Object Oriented Programming)
• ? Effective in code maintenance, update
• ICON is specialized for aging concrete time
  dependent excitations
• ? Material properties as functions of time
• ? Internal humidity temperature as functions
  of time
• ? Loads BCs, as functions of time
• 3. ICON is a Standalone code
• ? Previous version required MATLAB engine for a
  sparse matrix solver.
• ? Current version uses TAUCS( a library for a
  sparse matrix solver).
• ICON can be run as a standalone
  program.

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Finite Element Analysis Code
ICON ver 0.1.0

• ELEMENTS
• 20-node solid element
• 8-node solid element
• 2-node spring
• 2-node bar-element

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Finite Element Analysis Code
ICON ver 0.1.0

• MATERIAL
• Linear elastic
• Solidifying material model for creep
• Internal stress based hygrothermal model
• Strain based hygrothermal model

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Structure of ICON input file
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Structure of ICON input file
1. NODE section ? nodal coordinates 2. ELEMENT
section ? element connectivity, properties 3.
GROUP section ? group info. (node element set)
for easy access to the model 4.
MATERIAL section ? material info. 5. CONDITION
section ? loads, BCs, RH, temperature, age 6.
ASSIGN section ? CONDITIONs are ASSIGNed to
GROUPs 7. CONTROL section ? analysis duration,
time interval, convergence criterion,
etc.
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Input file format

• NODE
• lt of nodesgt
• ltnode_idgt ltxgt ltygt ltzgt
• ltnode_idgt ltxgt ltygt ltzgt
• ELEMENT
• lt of elementsgt
• ltelement_idgt ltelement_typegt ltnode_idgt
  ltnode_idgt
• ltelement_idgt ltelement_typegt ltnode_idgt
  ltnode_idgt
• GROUP
• lt of groupsgt
• ltgroup_idgt ltgroup_labelgt ltid_typegt
• lt of ids in this groupgt ltidgt
  ltidgt
• ltgroup_idgt ltgroup_labelgt ltid_typegt
• lt of ids in this groupgt ltidgt
  ltidgt

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Input file format
MATERIAL lt of materialsgt ltmaterial_idgt
ltmaterial_typegt ltmaterial_property_setgt
ltmaterial_property_set, VAR_SET gt for
ltmaterial_type_ELgt lt E gt lt nu gt
ltmaterial_property_set, VAR_SET gt for
ltmaterial_type_SLDFBgt ltfc28gt
ltft28gt ltE28gt ltnugt lta_Tgt lta_HTgt
ltb_HTgt lt of KMgt ltTugt ltAugt
ltmgt ltalphagtltq4gt CONDITION lt of
conditionsgt ltcondition_idgt ltcondition_typegt lt
of time stepgt lttimegt ltcondition_value_se
tgt lttimegt ltcondition_value_setgt
ASSIGN lt of assignsgt ltassign_idgt
ltassign_typegt ltmaterial _id or condition_idgt
ltgroup_idgt ltassign_idgt ltassign_typegt
ltmaterial_id or condition_idgt ltgroup_idgt
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Input file format
CONTROL lt of controlsgt ltcontrol_idgt
ltanalysis_durationgt
ltanalysis_time_stepgt
ltmax_iterationgt ltconvergence_creteriongt
ltnum_monitor_nodegt ltnode_idgt ltnode_idgt
ltnum_monitor_elementgt ltelement_idgt
ltelement_idgt ltmonitor_writing_freq
uencygt
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Modeling Procedure
MSC.Patran- modeling geometry
Generate mesh data for ICON
Add materials other conditions(BC, RH, T)
model.inp
Read input file
ICON Finite Element Analysis
Write analysis results
model.res
Read result file
MSC.Patran- graphical postprocessing
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Modeling Procedure
MSC.Patran- modeling geometry
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Modeling Procedure
model.inp
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Modeling Procedure
ICON Finite Element Analysis
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Modeling Output File
model.res
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Modeling Results
MSC.Patran- graphical post-processing
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FUTURE WORK
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FUTURE WORK
Lab Tests Drying/Wetting test Scale-down
single slab test Computer Modeling Modeling
Twin slabs Application with the models using
various drying scenario Technology Transfer of
Results Users Manual for ICON Anticipated
Completion Summer 2006 Future
Features? Prediction of internal temperature
humidity Graphical pre- and post-processor user
interface