Adhesive Anchors in Concrete Under Sustained Loading Conditions (2009)

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TRANSPORTAT ION RESEARCH BOARD WASHINGTON, D.C. 2009 www.TRB.org N A T I O N A L C O O P E R A T I V E H I G H W A Y R E S E A R C H P R O G R A M NCHRP REPORT 639 Subject Areas Bridges, Other Structures, and Hydraulics and Hydrology • Materials and Construction Adhesive Anchors in Concrete Under Sustained Loading Conditions R. A. Cook E. P. Douglas and T. M. Davis UNIVERSITY OF FLORIDA Gainesville, FL Research sponsored by the American Association of State Highway and Transportation Officials in cooperation with the Federal Highway Administration

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CRP STAFF FOR NCHRP REPORT 639 Christopher W. Jenks, Director, Cooperative Research Programs Crawford F. Jencks, Deputy Director, Cooperative Research Programs Edward Harrigan, Senior Program Officer Eileen P. Delaney, Director of Publications Ellen M. Chafee, Editor NCHRP PROJECT 20-07/TASK 255 PANEL Field of Special Projects Alan D. Rawson, New Hampshire DOT, Concord, NH (Chair) Marcus H. Ansley, Florida DOT, Tallahassee, FL Alexander K. Bardow, Massachusetts Highway Department, Boston, MA Derrick Castle, Kentucky Transportation Cabinet, Frankfort, KY David Kuniega, Pennsylvania DOT, Harrisburg, PA Ronald Reese, California DOT, Sacramento, CA John P. Weisner, Maryland State Highway Administration, Hanover, MD Masha Wilson, Washington State DOT, Tumwater, WA Joey Hartmann, FHWA Liaison AUTHOR ACKNOWLEDGMENTS The research reported herein was performed under NCHRP Project 20-07/Task 255 by the Department of Civil and Coastal Engineering at the University of Florida (UF). Dr. Ronald A. Cook, P.E., Professor of Civil Engineering at UF, was the Project Director and Principal Investigator. The other authors of this report were Dr. Elliot P. Douglas, Associate Professor of Materials Science and Engineering at UF, and Todd M. Davis, Research Assistant at UF. The work was done under the general supervision of Professors Cook and Douglas at UF. C O O P E R A T I V E R E S E A R C H P R O G R A M S

This report presents a test method recommended to determine an adhesive anchor’s abil- ity to resist sustained tensile loads. The report will be of immediate interest to public- and private-sector engineers with responsibility for the specification and use of adhesive anchor systems. Adhesive anchor systems are commercial adhesives—often, but not exclusively, epoxy adhesives—used to anchor threaded metal rod and rebar into concrete. In many applica- tions of these systems, the adhesive anchor is under a sustained tensile load, mandating the use of adhesives with strength and creep behavior appropriate to the load and expected ser- vice life, the anchor installation details, and the environmental conditions at the anchor. The objective of this research was to develop a test method to determine the ability of adhesive anchors to resist sustained tensile load. This test method would build on current methods from AASHTO, ASTM, state departments of transportation, and other sources and would consider (1) the creep characteristics of the adhesive over the expected life of the structure, (2) site-specific ultimate strength requirements, and (3) the effects of tempera- ture and moisture. The research was performed by the University of Florida, Gainesville, Florida. The report fully documents a review and analysis of the highway engineering literature, agency speci- fications, and existing test methods applicable to the use of adhesive anchors under sus- tained tensile load and presents the results of a laboratory testing program to develop a rec- ommended test method based on the stress versus time-to-failure approach. The recommended test method, which is presented in Appendix A in the form of a draft AASHTO standard, is under consideration for possible adoption by the AASHTO Highway Subcommittee on Materials. F O R E W O R D By Edward Harrigan Staff Officer Transportation Research Board

C O N T E N T S 1 Summary 2 Chapter 1 Background 2 Introduction 2 Behavior/Design of Anchors 4 Factors Influencing Bond Strength 8 Test Standards Related to Sustained Loads on Adhesive Anchors 14 Product Evaluation Standards Related to Sustained Loads on Adhesive Anchors 22 Other Structural Adhesive Standards Related to Sustained Loads 24 Testing Adhesive Alone 27 Factors Related to AASHTO Applications 30 Possible AASHTO Test Methods for Evaluation of Sustained Tension Loads on Adhesive Anchors 33 Proposed AASHTO Test Method for Sensitivity of Adhesive Anchors to In-Service Moisture 34 Recommendations Resulting from the NCHRP Panel Review 34 Summary and Conclusion 35 Chapter 2 Research Approach 35 Overview of Test Procedure 36 Test Apparatus 38 Specimen Preparation 39 Instrumentation 39 Environmental Control 40 Data Management and Acquisition 41 Installation Procedure 41 Specimen Conditioning 42 Testing Procedure 43 Recommendations 45 Chapter 3 Findings and Applications 45 Static Load Test 55 Sustained Load (Creep) Test 60 Recalculation for Adhesive B Based on Incremental Load Rate Tests 62 Stress versus Time to Failure 64 Recommendations 66 Chapter 4 Conclusion and Recommendations 66 Recommendations 67 Benefits of the Stress versus Time-to-Failure Test Method 67 Implementing the Test Method 67 Further Research 68 References

A-1 Appendix A Draft AASHTO Test Method—Standard Method of Test for Evaluation of Adhesive Anchors in Concrete Under Sustained Loading Conditions B-1 Appendix B Test Graphs C-1 Appendix C Photographs