Develop Epoxy Grout Pourback Guidance and Test Method to Eliminate

Thermal/Shrinkage Cracking at Post-Tensioning Anchorages

Project ManagerRick Vallier

Investigators:Irtishad Ahmad, Florida International University

Nakin Suksawang, Florida Institute of TechnologyKhaled 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)

4

Full Scale Pourbacks

Experimental Plan (Set 2)

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 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 Flow Chart showing Thermal and Stress AnalysisStress AnalysisStartStart

1. PRE-PROCESSING1. PRE-PROCESSING

A. EXECUTION PARAMETERS Analysis Type (Transient thermal) Element Type

A. EXECUTION PARAMETERS Analysis Type (Transient thermal) Element Type

B. MATERIAL PROPERTIESConductivity (k)Specific Heat (Cp)Density (ρ)

B. MATERIAL PROPERTIESConductivity (k)Specific Heat (Cp)Density (ρ)

C. MODEL GEOMETRYMeshing

C. MODEL GEOMETRYMeshing

D. APPLICATION OF LOADSHeat GenerationHeat Convection (wood)Ambient Temperature

D. APPLICATION OF LOADSHeat GenerationHeat Convection (wood)Ambient Temperature

E. BOUNDARY CONDITIONPlacing TemperatureE. BOUNDARY CONDITIONPlacing Temperature

2. SOLUTIONInput total time and time step for the solution of temperature

2. SOLUTIONInput total time and time step for the solution of temperature

3. POST-PROCESSINGObtain and examine results (Time-Temperature Curve)

3. POST-PROCESSINGObtain and examine results (Time-Temperature Curve)

EndEnd

StartStart

PRE-PROCESSINGPRE-PROCESSING

EXECUTION PARAMETERS Analysis Type (Transient thermal) Element Type

EXECUTION PARAMETERS Analysis Type (Transient thermal) Element Type

B. MATERIAL PROPERTIESThermal Expansion (α)Elastic Modulus (E)Poisson’s ratio (υ)Density (ρ)

B. MATERIAL PROPERTIESThermal Expansion (α)Elastic Modulus (E)Poisson’s ratio (υ)Density (ρ)C. MODEL GEOMETRYMeshing

C. MODEL GEOMETRYMeshing D. APPLICATION OF LOADSThermal distribution from thermal analysis

D. APPLICATION OF LOADSThermal distribution from thermal analysis

E. BOUNDARY CONDITIONConstraints at Top, Bottom, Back and Formwork

E. BOUNDARY CONDITIONConstraints at Top, Bottom, Back and Formwork

2. SOLUTIONDefine Analysis option and Run2. SOLUTIONDefine Analysis option and Run

3. POST-PROCESSINGObtain and examine Stress results 3. POST-PROCESSINGObtain and examine Stress results

EndEnd

ANSYS ModelsANSYS Models

Material PropertiesMaterial Properties

Results from Thermal AnalysisResults from Thermal Analysis

ANSYS Experiment

Results: Contour with Maximum Results: Contour with Maximum StressStress

S3 Model R3 Model

Von Mises Stress at Different LocationsVon Mises Stress at Different Locations

Comparison of Actual Crack Comparison of Actual Crack Location and ANSYS ModelLocation and ANSYS Model

S2.5 Model

R3 Model

Comparison of Actual Crack Comparison of Actual Crack Location and ANSYS ModelLocation and ANSYS Model

Stress Analysis ResultsStress Analysis Results

Pourback S3 (V/S=0.37)

Preliminary ConclusionsPreliminary 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.