Develop Epoxy Grout Pourback Guidance and Test Method to Eliminate Tensioning Anchorages

Develop Epoxy Grout Pourback
Guidance and Test Method to Eliminate
Thermal/Shrinkage Cracking at PostTensioning Anchorages
Project Manager
Rick Vallier
Investigators:
Irtishad Ahmad, Florida International University
Nakin Suksawang, Florida Institute of Technology
Khaled Sobhan, Florida Atlantic University
John A. Corven, Corven Engineering Inc.
Outline
• Full-Scale Testing
• Finite Element Analysis
• Preliminary Conclusion
Full-Scale Testing
• 2 sets of pourback with different geometry
were tested.
– Set 1 consists of irregular shaped pourbacks found
on the Le Roy Selmon Expressway
– Set 2 consists of rectangular shaped pourbacks.
• Three v/s ratios (0.26, 0.32, 0.37) were selected
based on possible ratios of actual pourbacks. It
is highly unlikely that actual pourbacks would
exceed these ranges.
Experimental Plan (Set 1)
S2
S2.5
S3
S2
S2.5
S3
3
6
6
ECI 6-7
ECI 6-12
ECI 6-19
D
h
7.40
8.66
10.24
4.17
4.90
5.63
Volume of caps (ft3)
0.31
1.00
1.61
Pourback height (in)
Pourback width (in)
Clear cover (in)
H
B
38.00
24.00
2.33
61.75
39.00
2.10
73.00
46.00
2.37
4.44
11.77
16.41
6.8
11.04
13.22
6.50
7.00
8.00
8.12
18.21
25.22
2.09
5.86
9.33
0.26
0.32
0.37
Specimens
Equation
Number of grout caps
n
Type ECI grout caps
Grout caps diameter (in)
Grout caps height (in)
Area of face surface(ft2)
Length of free edges (ft)
Thickness (in)
Exposed surface (ft2)
Volume (ft3)
Volume/surface ratio
c
A
L
t
S=A+(L . t)
V=(A .t) - Vc
V/S
4
Full Scale Pourbacks
Experimental Plan (Set 2)
R2
R2.5
R3
R2
R2.5
R3
3
6
6
ECI 6-7
ECI 6-12
ECI 6-19
D
h
7.40
8.66
10.24
4.17
4.90
5.63
Volume of caps (ft3)
0.31
1.00
1.61
Pourback height (in)
Pourback width (in)
Clear cover (in)
H
B
38.00
16.00
2.33
45.00
29.50
2.10
52.00
35.00
2.37
4.22
9.22
12.64
6.33
7.50
8.67
6.50
7.00
8.00
7.65
13.59
18.42
1.98
4.38
6.82
0.26
0.32
0.37
Specimens
Equation
Number of grout caps
n
Type ECI grout caps
Grout caps diameter (in)
Grout caps height (in)
Area of face surface(ft2)
Length of free edges (ft)
Thickness (in)
Exposed surface (ft2)
Volume (ft3)
Volume/surface ratio
c
A
L
t
S=A+(L . t)
V=(A .t) - Vc
V/S
6
Instrumentation Plan (Typical)
S2
S2.5
S3
Number of
Thermocouples
12
12
12
Number of
Vibrating gauges
2
2
2
Time
48 hours
(Record at 10 minutes
time interval
continuously for 48
hours period after the
casting)
7
Formwork Preparation
Mixing Epoxy Grout
Casting Full-Scale Pourbacks
Temperature History
Note: Peak Exothermic Temperature based on
ASTM D2471 is only 60C (Specimen size is 12 by
12 by 3 in)
Cracked Pourbacks
S3 Model
R3 Model
S2.5 Model
Actual Pourback Cracked Location
13
Finite Element Analysis (FEA)
• FEA was
performed
using ANSYS by
first performing
thermal analysis
followed by
thermal stress
analysis.
Flow Chart showing Thermal and
Stress Analysis
Start
1.
A.


PRE-PROCESSING
EXECUTION PARAMETERS
Analysis Type (Transient thermal)
Element Type
B. MATERIAL PROPERTIES
Conductivity (k)
Specific Heat (Cp)
Density (ρ)
C. MODEL GEOMETRY
Meshing
D. APPLICATION OF LOADS

Heat Generation

Heat Convection (wood)

Ambient Temperature
Start
PRE-PROCESSING
EXECUTION PARAMETERS

Analysis Type (Transient thermal)

Element Type
B. MATERIAL PROPERTIES
Thermal Expansion (α)
Elastic Modulus (E)
Poisson’s ratio (υ)
Density (ρ)
C. MODEL GEOMETRY
Meshing
D. APPLICATION OF LOADS

Thermal distribution from thermal
analysis
E. BOUNDARY CONDITION

Placing Temperature
E. BOUNDARY CONDITION

Constraints at Top, Bottom, Back
and Formwork
2. SOLUTION

Input total time and time step for the
solution of temperature
2. SOLUTION

Define Analysis option and Run
3. POST-PROCESSING

Obtain and examine results (TimeTemperature Curve)
3. POST-PROCESSING

Obtain and examine Stress results
End
End
ANSYS Models
Material Properties
Concrete Slab
Standard Test
Thermal conductivity
Specific heat
ASTM E1269 -11
Heat-transfer film coefficient (air exposure)
Units
kJ/m.h.C
kJ/kg.C
kCal/m^2.h.C
Value
2.3
0.23
4.3
Density
Young Modulus
ASTM C580
Poisson’s ratio
Thermal Expansion Coefficient
ASTM C531
420 Epoxy Grout System
Standard Test
Thermal conductivity
Specific heat
ASTM E1269 -11
Heat-transfer film coefficient (wood forms)
Heat-transfer film coefficient (air exposure)
Kg/m^3
MPa
-m/m/C
Units
kJ/m.h.C
kJ/kg.C
kCal/m^2.h.C
kCal/m^2.h.C
2400
30000
0.18
1.0x10^-6
Value
2.3
0.23
8.5
4.3
Density
Young Modulus
Poisson’s ratio
Thermal Expansion Coefficient
Plastic End Caps
Thermal conductivity
Specific heat
Density
Young Modulus
Poisson’s ratio
Thermal Expansion Coefficient
Kg/m^3
MPa
-m/m/C
Units
kJ/m.h.C
kJ/kg.C
Kg/m^3
MPa
-m/m/C
1986
12000
0.4
5.4x10^-6
Value
0.68351
1.05
1400
3000
0.4
3.6x10^-5
ASTM C580
ASTM C531
Standard Test
ASTM E1269 -11
ASTM C580
ASTM C531
Results from Thermal Analysis
180
140
ANSYS
Experiment
120
100
80
60
40
20
0
0
10
20
30
40
50
60
160
Time, Hours
140
Temperaure, Celcius
Temperaure, Celcius
160
120
100
80
60
40
20
0
0
10
20
30
Time, Hours
40
50
60
Results: Contour with Maximum
Stress
S3 Model
R3 Model
Von Mises Stress at Different Locations
Stress
(MPa)
11
10
9
8
7
6
5
4
3
2
1
0
R3
S3
0
1
2
3
4
5
6
7
8
9
10
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
R2.5
S2.5
0
1
2
3
4
5
6
7
8
9
10
3.5
Location in model
3
2.5
Stress (kPa)
Stress (kPa)
Location in model
2
1.5
R2
1
S2
0.5
0
0
1
2
3
4
5
6
7
Location in model
8
9 10
Comparison of Actual Crack
Location and ANSYS Model
S2.5 Model
Comparison of Actual Crack
Location and ANSYS Model
R3 Model
Maxm Stress (MPa) in X-dirn
Stress Analysis Results
30
25
20
15
10
5
0
0.24 0.26 0.28 0.3 0.32 0.34 0.36 0.38
V/S Ratio
Tensile Strength Limit (24MPa)
S-type
R-type
Pourback S3
(V/S=0.37)
Preliminary Conclusions
•
•
•
•
The time-temperature curves predicted by the ANSYS finite
element model closely matched the data obtained from field
experiments.
Thermal stresses predicted by FEM around the vicinity of the
actual physical crack observed in the field showed close
agreement with the limiting tensile strength
Both the peak exothermic temperature and the maximum
thermal stress increased as V/S ratio increased.
For the S-type, the maximum thermal stress reached or
exceeded the tensile strength of 24 MPa at V/S ratio between
0.32 and 0.37. For the R-type, this limit was reached at V/S
ratio of about 0.37.