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REPORT
This report is an archived publication and may contain dated technical, contact, and link information
Publication Number:  FHWA-HRT-14-090    Date:  October 2014
Publication Number: FHWA-HRT-14-090
Date: October 2014

 

Bond Behavior of Reinforcing Steel in Ultra-High Performance Concrete

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FOREWORD

With the ever increasing congestion and deterioration of our nation’s highway system, a need exists to develop highly durable and rapidly constructed infrastructure systems. Durable bridge structures that would require less intrusive maintenance and would exhibit longer life spans thus maximizing the use of the facility are highly desirable. Expediting bridge construction can minimize traffic flow disruptions. Ultra-high performance concrete (UHPC) is an advanced construction material which affords new opportunities to envision the future of the highway infrastructure. The Federal Highway Administration has been engaged in research on the optimal uses of UHPC in the highway bridge infrastructure since 2001 through its Bridge of the Future initiative. This report presents results of a study aimed at assessing the potential of using UHPC-class materials to anchor or lap splice deformed reinforcing bars in field-cast connections.  This concept could potentially allow for the simplification of connection details in some prefabricated bridge systems, and may also allow for the development and deployment of expedited construction techniques.

This report corresponds to the TechBrief titled “Bond Behavior of Reinforcing Steel in Ultra-High Performance Concrete” (FHWA‑HRT-089). This report is being distributed through the National Technical Information Service for informational purposes. The content in this report is being distributed “as is” and may contain editorial or grammatical errors.

 

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document.

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers’ names appear in this report only because they are considered essential to the objective of the document.

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TECHNICAL REPORT DOCUMENTATION PAGE

1. Report No.
FHWA-HRT-14-090
2. Government Accession No. 3 Recipient's Catalog No.
4. Title and Subtitle
Bond Behavior of Reinforcing Steel in Ultra-High Performance Concrete
5. Report Date
October 2014
6. Performing Organization Code

 

7. Author(s)
Jiqiu Yuan and Benjamin A. Graybeal
8. Performing Organization Report No.

 

9. Performing Organization Name and Address Office of Infrastructure Research & Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296
10. Work Unit No. (TRAIS)

 

11. Contract or Grant No.
12. Sponsoring Agency Name and Address
Office of Infrastructure Research & Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

13. Type of Report and Period Covered
March 2013 – March 2014

14. Sponsoring Agency Code
HRDI-40
15. Supplementary Notes
This document was developed by research staff at the Turner-Fairbank Highway Research Center. Portions of the work were completed by PSI, Inc. under contract DTFH61-10-D-00017. Jiqiu Yuan of PSI, Inc. is a contract researcher on FHWA's structural concrete research efforts and Ben Graybeal of FHWA both manages the FHWA Structural Concrete Research Program and leads the Bridge and Foundation Engineering Research team.
16. Abstract

Ultra-High Performance Concrete (UHPC) is a relatively new class of advanced cementitious composite materials, which exhibits high compressive [above 21.7 ksi (150 MPa)] and tensile [above 0.72 ksi (5 MPa)] strengths. The discrete steel fiber reinforcement included in UHPC allows the concrete to maintain tensile capacity beyond cracking of the cementitious matrix. The combination of the matrix and fiber performance allow for a reduction on the development length of reinforcing bar, thus providing the potential for a redesign of some structural systems such as field-cast connections between prefabricated bridge elements. The bond behavior of deformed reinforcing bar in UHPC is investigated in this study by conducting direct tension pullout tests. Over 200 tests were completed and the effect of embedment length, concrete cover, bar spacing, concrete strength, bar size and type on bond strength were investigated. It was found that the development length of embedded reinforcement in UHPC can be significantly reduced. Guidance on the embedment of deformed reinforcing bars into UHPC is provided.

This report corresponds to the TechBrief titled “Bond Behavior of Reinforcing Steel in Ultra-High Performance Concrete” (FHWA-HRT-089).

17. Key Words

Ultra-high performance concrete, UHPC, fiber-reinforced concrete, reinforcing bar, bond strength, anchorage, development length, splice length

18. Distribution Statement

No restrictions. This document is available through the National Technical Information Service, Springfield, VA 22161.

19. Security Classif. (of this report)
Unclassified
20. Security Classif. (of this page)
Unclassified
21. No. of Pages
78
22. Price
N/A
Form DOT F 1700.7 (8-72)Reproduction of completed page authorized

SI* (Modern Metric) Conversion Factors

TABLE OF CONTENTS

CHAPTER 1. INTRODUCTION

CHAPTER 2. EXPERIMENTAL INVESTIGATION

CHAPTER 3. PULLOUT TESTS RESULTS

CHAPTER 4. DESIGN RECOMMENDATIONS FOR REINFORCING BAR EMBEDDED IN UHPC

CHAPTER 5. CONCLUSIONS

ACKNOWLEDGMENTS

REFERENCES

LIST OF FIGURES

Figure 1. Graph. Tensile stress strain response of reinforcing bars.
Figure 2. Photo. Reinforcing bar rib pattern.
Figure 3. Illustration. Overall configuration of test specimens.
Figure 4. Illustration. Pullout test specimens layout.
Figure 5. Illustration. Loading setup.
Figure 6. Photograph. Loading setup.
Figure 7. Photograph. Displacement measurement via three LVDTs.
Figure 8. Photograph. UHPC strip casting setup and orientation: (a) side pour setup; (b) side pour casting; (c) upright pour setup; and (d) upright pour casting.
Figure 9. Illustration. Conceptual bar stress versus slip response.
Figure 10. Equation. Average bond stress in reinforcing bar.
Figure 11. Illustration. Pullout tests: (a) forces on bars; and (b) crack patterns.
Figure 12. Photo. Crack patterns: (a) longitudinal splitting cracks to adjacent No. 8 bars; (b) splitting cracks to side face; (c) splitting cracks to side face and adjacent No. 8 bars; and (d) UHPC tensile failure with opened diagonal cracks.
Figure 13. Photo. Diagonal crack observation: (a) visual inspection; and (b) crack inspection with denatured alcohol.
Figure 14. Photo. Conical surface failure: (a) conical surface around the bar; and (b) conical surface extended to the side face.
Figure 15. Graph. Effect of embedment length: fs,max versus embedment length ld.
Figure 16. Illustration. Bond splitting cracks: (a) csi > cso; and (b) csi < cso.
Figure 17. Graph. Effect of side cover: bond strength µTEST versus side cover for specimens in Sets 1, 2 and 3. The csi is constant.
Figure 18. Graph. Effect of side cover: bond strength µTEST versus side cover for specimens in Sets 4 and 5. The csi is constant.
Figure 19. Graph. Effect of bar spacing: bond strength µTEST versus 2csi for specimens in Set 1. The cso is constant.
Figure 20. Illustration. Geometrical demonstration of lstan(θ) and 2csi.
Figure 21. Graph. Effect of bar spacing: bond strength µTEST versus 2csi for specimens in Set 2. The cso is constant.
Figure 22. Graph.Effect of bar spacing: bond strength µTEST versus 2csi for specimens in Set 3. The cso is constant.
Figure 23. Graph. Effect of bar spacing: bond strength µTEST versus 2csi for specimens in Set 4. The cso is constant.
Figure 24.Graph. Effect of UHPC compressive strength: bond (a) uTEST versus ƒ'c and (b) uTEST versus ƒ'c1/2 for specimens in Set 1.
Figure 25. Graph. Effect of UHPC compressive strength: (a) uTEST versus ƒ'c and (b) uTEST versus ƒ'c1/2 for specimens in Set 2.
Figure 26. Graph. Effect of UHPC compressive strength: (a) uTEST versus ƒ'c and (b) uTEST versus ƒ'c1/2 for specimens in Set 3.
Figure 27. Chart. Bond strength versus bar size.
Figure 28. Chart. Average bar stress at bond failure for different types of reinforcing bar.
Figure 29. Graph. Bar stress at bond failure versus embedment length for all tests with A1035 No. 5 bars.
Figure 30. Graph. Bar stress at bond failure versus embedment length for all tests with A1035 No. 5 bars and with a side cover ≥ 2.7 db.
Figure 31. Graph. Bar stress at bond failure versus embedment length for tests with A1035 No. 7 bars and epoxy coated No.8 bars.
Figure 32. Chart. Bar stress at bond failure for all A1035 No.5 bars with different design details. All specimens had a bar clear spacing between 2 db and lstan(θ).
Figure 33. Chart. Bar stress at bond failure for all epoxy coated and uncoated No.5 bars with different design details. All specimens had a bar clear spacing between 2db and lstan(θ).
Figure 34. Chart. Bar stress at bond failure for all A1035 No. 4 and No.7 bars and epoxy coated No. 8 bar with different design details. All specimens had a bar clear spacing between 2db and lstan(θ).

LIST OF TABLES

Table 1. Typical field-cast UHPC material properties.
Table 2. UHPC mix design.
Table 3. Properties of Reinforcing Steel
Table 4. Test Specimens – Effect of Casting Orientation.
Table 5. Test specimens – effect of embedment length.
Table 6. Test specimens – effect of side cover.
Table 7. Test specimens – effect of bar spacing
Table 8. Bond strength reduction for bar clear spacing out of the range of 2db < 2csi < lstan(θ).
Table 9. Test specimens – effect of UHPC compressive strength.
Table 10. Test specimens – effect of bar size.
Table 11. Test specimens – effect of bar type.
Table 12. Bond stress reduction between different types of reinforcing bar.

 

LIST OF ABBREVIATIONS AND NOTATION

ABBREVIATIONS

ABC Accelerated Bridge Construction
ASTM American Society For Testing and Materials
DOT Departments Of Transportation
FHWA Federal Highway Administration
LVDT Linear Variable Differential Transformer
PBES Prefabricated Bridge Elements And Systems
UHPC Ultra-High Performance Concrete
NOTATION
cso = side concrete cover for reinforcing bar
csi = one-half of the bar clear spacing
db = reinforcing bar diameter
ƒ’c = concrete compressive strength
ƒs,crack = bar stress at first observed crack
ƒs,max = maximum bar stress at bond failure
ld = embedment length
ls = lap spliced length
s1 = bar slip at bond failure
µTEST = average bond strength at bond failure
θ = angle between the diagonal cracks and testing bar

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Turner-Fairbank Highway Research Center | 6300 Georgetown Pike | McLean, VA | 22101