ACI-SP-201-2001.pdf

Fracture Mechanics for Concrete Materials: Ø- Testing and Applications Editors: C. Vipulanandan W. H. Gerstle international SP-201 COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services Fracture Mechanics for Concrete Materials: Testing and Applications Edztors C. Vipulanandan W. H. Gerstle international SP-201 COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services DISCUSSION of individual papers in this symposium may be submitted in accordance with general requirements of the AC1 Publication Policy to AC1 headquarters at the address given below. Closing date for submission of discussion is December, 2001. All discussion approved by the Technical Activities Committee along with closing remarks by the authors will be published in the MarcWApril 2002 issue of either AC1 Structural Journal or AC1 Materials Journal depending on the subject emphasis of the individual paper. The Institute is not responsible for the statements or opinions expressed in its publications. Institute publications are not able to, nor intended to, supplant individual training, responsibility, or judgment of the user, or the supplier, of the information presented. The papers in this volume have been reviewed under Institute publication procedures by individuals expert in the subject areas of the papers. Copyright O 2001 AMERICAN CONCRETE INSTITUTE P.O. Box 9094 Farmington Hills, Michigan 48333-9094 All rights reserved including rights of reproduction and use in any form or by any means, including the making of copies by any photo process, or by any electronic or mechanical device, printed or written or oral, or recording for sound or visual reproduction or for use in any knowledge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors. Printed in the United States of America Editorial production: Bonnie L. Gold Library of Congress catalog card number: 2001091922 ISBN: 0-8703 1-039-9 COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services PREFACE Fracture mechanics concepts are increasingly used in designing concrete structures and also in understanding the fundamental behavior of concrete-like materials. Fracture mechanics concepts have the potential for use in designing concrete-FRP composites and in repairing concrete structures. To review and discuss the current state-of-applications of fracture mechanics concepts to concrete materials, AC1 Committee 446 sponsored two sessions at the AC1 Spring 2000 Convention held in San Diego, California. One objective of this conference and the resulting publication is to provide an update on the use of fracture mechanics concepts to cement concrete, polymer concrete, and FRP- concrete materials. This conference also provided an effective means of sharing recent technological advances, engineering applications, and research results among practitioners, researchers, and potential users from many parts of the world. Selecting the testing method to determine the fracture properties of concrete materials for various applications is an issue confronting the profession and was discussed during the sessions. This publication contains the papers that were presented at the AC1 Annual Convention held in San Diego, California, March 27,2000. Also, some additional papers are included in this Special Publication. All the papers in this Special Publication were peer reviewed by at least two reviewers for content, quality, and for possible publication. All papers are eligible for discussion in the ACI Materials Journal. The editors would like to thank the authors for their papers and the reviewers for the constructive and timely reviews of the papers. Thanks to the AC1 staff for their role in completing this AC1 Special Publication. Editors C. Vipulanandan Center for Innovative Grouting Materials and Technology (CIGMAT) University of Houston and W. H. Gerstle Department of Civil Engineering University of New Mexico COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services AC1 Committee 446 Walter H. Gerstle Chairman Voting members: Zdenek P. Bazant Manuel Elices Masoud Ghandehari James H. Hanson Neil M. Hawkins J. Woody Ju Christian Meyer Sidney Mindess Klaus A. Rieder Surendra P. Shah C. Vipulanandan Zhishen Wu Fracture Mechanics Associate members: Nemkumar Banthia Maria del Mar Lopez Steven L. McCabe Consulting members: Ignacio Carol B. L. Karihaloo Pere C. Prat Barzin Mobasher Secretary David Darwin Barry D. Fehl Vellore S. Gopalaratnam Toshiaki Hasegawa Anthony R. Ingraffea Neven Krstulovic-Opara Hirozo Mihashi Kamran M. Nemati Victor E. Saouma Wimal Suaris W. Jason Weiss Sungchul Yang Lennart G. Elfgren Arup K. Maji Tibor J. Pataky Luigi Cedolin Mohammad Taghi Kazemi Hans W. Reinhardt IV COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services CONTENTS PREFACE Simplification of the Testing and Analysis Procedure for the Two Parameter Fracture Model by D. C. Jansen, W. J. Weiss, and S. H. F. Schleuchardt . 1 Using Fracture to Predict Restrained Shrinkage Cracking: The Importance of Specimen Geometry by W. J. Weiss, W. Yang, and S. P. Shah 17 The Fracture Surface Roughness of Concrete with Different Aggregate Sizes and Loading Rates by Y. S. Roh and Y. Xi 35 Controlled Crack Growth Tests for Optimization of Micro-Fiber Reinforced Cement Composites by N. Banthia and I. Genois 55 A Testing Procedure for Assessing the Uniaxial Tension of Concrete by H. Akita, H. Koide, D. Sohn, and M. Tomon 75 Punching Failure of Interior Slab-Column Connections-Influence of Material Properties and Size Effect by J. Oibolt, H. Vocke, and R. Eligehausen 93 On the Accuracy of Fracture Toughness Test Results for Concrete Using Different Size and Geometry Specimens and Data Reduction Methods by J. H. Hanson and A. R. Ingraffea . :. 11 1 ExperimentallAnalytical Study on Interfacial Fracture Energy and Fracture Propagation Along FRP-Concrete Interface by Z. Wu, H. Yuan, H. Yoshizawa, and T. Kanakubo . 133 Fatigue Crack Growth in Polyester Polymer Concrete by C. Vipulanandan and S. Mebarkia 153 Dimensional Factors of Bond Failure in Reinforced Concrete by M. Ghandehari, S. Krishnaswamy, and S. P. Shah 169 Tension Test of Stress Versus Crack Opening Displacement Using Cylindrical Concrete Specimens by L. R. Lenke and W. H. Gerstle . 189 COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services Determination of Crack Resistance Curves of Cementitious Materials from Measurements of a Wedge Splitting Test by K. A. Rieder 207 Tensile and Bending Tests on Very High Performance Concrete by L. Biolzi, S. Cattaneo, and J. F. Labuz . 229 Fracture Properties of Polyester Polymer Concrete with Chopped Graphite Fibers by J. Cao and C. Vipulanandan 243 FE Analysis on Cohesive Debonding and Cracking Behavior of FRP-Strengthened Concrete Beams by Nonlinear Fracture Mechanics by J. Yin, 2. Wu, and T. Asakura . 267 VI COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services SP 201-1 Simplification of the Testing and Analysis Procedure for the Two Parameter Fracture Model by D. C. Jansen, W. J. Weiss, and S. H. F. Schleuchardt Synopsis: This work describes a modification to the two-parameter fracture methods experimental procedure aimed at removing this operator/equipment dependence. With this method, three compliances are used to determine the focal point at which these compliances intersect. This focal point is then used to determine the slope of the unloading compliance that corresponds to the peak of the load vs. CMOD curve. The unloading compliance that corresponds to unloading at the peak load and initial compliance are then used to determine K c and CTODc as normally done with the Two Parameter Fracture Model. Use of this method makes it possible to remove operator and machine dependence, especially if the materials are extremely brittle, such as in pastes or high strength concrete, thereby permitting the loading and unloading to be programmed using testing software removing the need for manual operator loading changes. Tests on 15 mortar beams with 4 different notch lengths and initial unloading points ranging from 97% to 75% of maximum load are used to validate this approach. The experimental results are typically more consistent and better correlate to results from the peak load test method. These results indicate that utilizing the focal point correction typically reduces Klc and CTODC by 12% and 38% respectively for the mortar tested thereby causing the TPFM and peak load method results to coincide even more closely. Kevwords: compliance; concrete; cracking; effective crack; fracture mechanics; post-peak; test methods 1 COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services 2 Jansen et al. Daniel C. Jansen is an assistant professor in the Department of Civil and Environmental Engineering at Tufts University. He received a B.S. in Structural Engineering from the University of California at San Diego, and a Ph.D. from Northwestern University. His research interests include fracture of concrete, compression strain localization, and use of recycled materials. Jason Weiss is an assistant professor in the school of Civil Engineering at Purdue University. He earned a BAE degree from Penn State University in 1995 and his MS and Ph.D. degrees from Northwestern University in 1997 and 1999 respectively. His research interests include concrete durability, early-age cracking, fracture mechanics, and non-destructive testing. Stefan Schleuchardt is an engineer with Wörner und Partner in Frankfurt, Germany. In 1997, he was a visiting researcher at Tufts University during which time the experimental portion of this work was completed. He completed his Diplomingenieur in 1999 from Darmstadt Technical University. INTRODUCTION It is widely accepted that the fracture process zone that develops in cement- based materials is not typically negligible in comparison to the overall dimensions of the specimen tested. As a result, analysis using linear elastic fracture mechanics cannot be applied directly to cementitous systems and some modification is needed to account for the region of stable crack growth that occurs prior to the peak load. Over the last three decades several experimental procedures have been developed which provide a minimum of two parameters (i.e., Kic and CTODC, GF and cf, f ' , and G, etc .) which have been used to characterize the behavior of the cementitous system.'-7 Numerous testing procedures have been proposed for obtaining these parameters and research continues to develop a standard test procedure that is accurate, requires relatively few samples, can be accomplished in a relatively short time of testing, and does not require a great deal of specialty test equipment.' In 1985 Jenq and Shah proposed one such method to account for the precritical crack growth that occurs prior to the maximum load.2 This method, called the Two-Parameter Fracture Method (TPFM), is based on the simple premise that the change in compliance that occurs when the specimen is unloaded at the peak load can be used to calculate the precritical crack growth (ie., length of an effective crack). While this method is of great value since it can be used to determine fracture properties using one specimen it is logistically difficult to unload the specimens exactly at the peak load since the true peak load of a specimen is unknown before the test. For this reason it was recommended that unloading could be conducted when the specimen load decreased to 95% of its maximum load. This however is a frequently discussed as a point of concern citing that this introduces operator and machine dependence especially if the COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services Fracture Mechanics for Concrete Materials 3 materials are extremely brittle such as in pastes or high strength concrete. This paper will focus on a modification to the existing two-parameter model, currently a draft recommendation from RILEM: which will provide a systematic method for removing operator dependence and improving overall accuracy and reproducibility. BACKGROUND The Two Parameter Fracture Method The two-parameter fracture method (TPFM), proposed by Jenq and Shah in 1985, is an effective crack model in which the length of the stable crack growth at peak is characterized to provided a method to account for non-linearities that exist in smaller specimen sizes. To perform this test, the specimen is loaded and the compliance of the load versus crack mouth opening displacement (initial compliance, Ci) and initial crack length, a, are used to determine the elastic modulus, E, of the concrete as shown in Figure 1. The length of the effective crack length, a, can be determined at any time during the test by unloading the specimen and using load-CMOD response (unloading compliance, Cu) in combination with the elastic modulus. Theoretically, the TPFM approach can be used to determine the length of the effective crack at any point along the Load-CMOD curve, however it is of practical interest to determine the length of crack growth exactly at the time the crack would begin to propagate unstably (i.e., the critical crack length, a, that occurs at the peak load). The fracture toughness, Klc, and the critical crack tip opening displacement, CTODc, are determined from the critical crack length and the peak load. More detail of the analysis procedure along with the necessary equations is provided in Appendix A. Determining the unloading compliance exactly at the peak load is impossible from an experimental viewpoint since one needs to go beyond the peak to know that it has been reached. As a result, the RILEM recommendation9 suggests that the specimen be unloaded at 95% of the peak load in the post