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Ultrasonic Wave Reflection Measurements on SelfCompacting Pastes and Concretes

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Ultrasonic Wave Reflection Measurements on Self�Compacting Pastes and Concretes ULTRASONIC WAVE REFLECTION MEASUREMENTS ON SELF-COMPACTING PASTES AND CONCRETES BY PRANNOY SURANENI THESIS Submitted in partial fulfillment of the requirements for the degree of Master of Science in Civil Engineering in the Graduate College of the University of Illinois at Urbana-Champaign, 2011 Urbana, Illinois Advisers: Professor Leslie J. Struble Associate Professor John S. Popovics ABSTRACT The objective of this study was to extend the use of combined longitudinal (P-wave) and shear (S-wave) ultrasonic wave reflection (UWR) to monitor the setting and stiffening of self- compacting pastes and concretes. An additional objective was to interpret the UWR responses of various modified cement pastes . A polymeric buffer with acoustic impedance close to that of cement paste, high impact polystyrene, was chosen to obtain sensitive results from the early hydration period. Criteria for initial and final set developed by our group in a prior study were used to compute setting times by UWR. UWR results were compared with standard penetration measurements. Stiffening behavior and setting times for normal cement pastes, pastes modified with mineral and chemical admixtures, self-compacting pastes, and concretes were explored using penetration resistance, S-wave and P-wave reflection. All three methods showed that set times of pastes varied linearly with w/c, that superplasticizer and fly ash delayed the set times of pastes, and that differences in w/cm, sp/cm, and fa/cm could be detected. Final set times determined from UWR correlated well with those from penetration resistance. Initial set times from S-wave reflection did not correlate very well with those from penetration resistance. Final set times from P-wave and S-wave reflection were roughly the same. Pastes with different chemical admixtures were tested, and the effects of these admixtures on stiffening were determined using UWR. Self-compacting concretes were studied using UWR, and their response and setting times were largely similar to that of corresponding self-compacting pastes. The P- wave reflection response was explored in detail, and the phenomenon of partial debonding and the factors affecting it were explained. Partial debonding is probably caused by autogenous shrinkage at final set, and was controlled and limited by water. The extent of partial debonding was higher with the transducers placed on the side as opposed to the bottom, and the S-wave ii transducer seemed to promote debonding in the P-wave reflection, whereas the P-wave transducer seemed to reduce debonding in the S-wave reflection. Simultaneous formwork pressure testing and UWR were performed; however, no clear correlation was seen between the two properties. Keywords: ultrasonic wave reflection, shear wave, longitudinal wave, setting time, self- compacting concrete, partial debonding. iii ACKOWLEDGEMETS “What a long, strange trip it’s been.” – The Grateful Dead, 1970. Starting the acknowledgements section with a quotation is surely clichéd, but the above quote so aptly describes the last three years of my life that I cannot deny its rightful place. This work has taken up the better part of those three years, and it has been a great learning experience for me. Several people have been a part of this trip along with me, and I take the opportunity here to thank them for that. I would like to thank Prof. Leslie J. Struble for her guidance in this project. Her experience, knowledge, and brilliance has helped me a lot (and hopefully rubbed off on me a bit). The Cement Center work that I did for Prof. Struble gave me an all round knowledge of construction materials, and I am thankful to Prof. Struble for giving me that opportunity. I also thank her for letting me be the teaching assistant for CEE501, and for her financial support through the project. I would also like to thank Prof. John S. Popovics. His knowledge of non-destructive testing has come in particularly handy whenever we have had issues with the project. I am also particularly thankful for his suggestions, many of which have helped guide me in the right direction. I would also like to thank Prof. David Lange for his insights on formwork pressure and underpressure. I appreciate the financial support provided by Prof. Lange. I would also like to thank Prof. Popovics, Prof. Struble, and Prof. Paramita Mondal for allowing me to be the teaching assistant for CEE300. I would like to thank Prof. Ravindra Gettu and Prof. Manu Santhanam at the Indian Institute of Technology Madras. I would never have been interested in construction materials if iv not for their beautiful presentation of the topic. I thoroughly enjoyed working for them during my undergraduate years. I also have to thank my colleague Dr. Chul-woo Chung, whose project this is an extension of. Chul-woo was a mentor to me. Without him, I doubt I would have managed to get anything done at all. I would also like to thank Dr. Andres Salas for help with equipment and guidance in general. I wish to thank Ashna Chopra, Sravanthi Puligilla, and Eric Kim for many productive hours spent discussing research, and for their support, and encouragement. Thanks are also due to Paul Mockus, Jeffery Zhang, and Jorge Avalos who helped me in the lab. I also wish to thank my colleagues in the Civil Engineering Department for their suggestions and their friendship. Special thanks are due to the teaching assistants of CEE300, who made the job so much fun. I wish to thank my friends for being around when I needed them. I cannot imagine what I would have done without you guys. Thank you, Abhishek, Adi, Ani, Ashna, Jayanthi, Laavi, Rannesh, Rimpa, Sneha, Sravanthi, and Swati. Lastly I wish to thank my parents for everything. Mom, Dad, thanks for always being there, I do hope I have made you proud. v TABLE OF COTETS 1. INTRODUCTION...............................................................................................................1 2. LITERATURE REVIEW....................................................................................................3 3. EXPERIMENTAL PROCEDURES AND MATERIALS................................................12 4. PENETRATION RESISTANCE.......................................................................................23 5. ULTRASONIC SHEAR WAVE REFLECTION..............................................................40 6. ULTRASONIC LONGITUDINAL WAVE REFLECTION.............................................70 7. INSTRUMENTATION EFFECTS....................................................................................91 8. FORMWORK PRESSURE.............................................................................................104 9. SUMMARY AND KEY CONCLUSIONS.....................................................................115 10. REFERENCES .... ............................................................... ...... ............... .............. ..........117 vi 1. ITRODUCTIO Hydration and setting of cement paste have been widely researched and studied topics. Classically, penetration resistance tests have been used to determine the setting time of concretes. However, limited information is obtained from these tests, and they are laborious and time consuming. Additionally, they are not actually done on concrete, but on mortar extracted from concrete. Newer non-destructive testing methods have been developed to study stiffening of cement pastes, including electrical and acoustic methods. Much work on cement setting has been done with ultrasonic waves. Transmitted and reflected ultrasonic waves have both been studied, with reflected waves having the advantage of not needing two-sided access. Most of the work using reflected ultrasonic waves has focused on strength development; relatively little work has been done on setting and stiffening. Ultrasonic wave reflection (UWR) involves measuring the reflected wave energy at the interface of a buffer and a hydrating cementitious material. When the cementitious material is fluid, most of the incident energy is reflected back; whereas relatively more energy is transmitted with the material hardens. Changes in this reflected energy are monitored and plotted as a function of time. Shear and longitudinal waves have been used for this purpose, though rarely have they both been used in the same study. This work is a continuation of the Ph. D. work done by Chung at the University of Illinois [1]. Chung used combined shear and longitudinal (S- and P-wave) UWR with a low impedance buffer material, high impact polystyrene (HIPS), to obtain sensitive information about early age hydration of cement pastes. Both S- and P-wave UWR reflection data were collected, analyzed, and the wave responses were interpreted for normal cement pastes. Criteria 1 for initial and final set using UWR were developed. The partial debonding response observed with P-waves was broadly explained. The main objective of this study is to extend the application of combined shear and longitudinal UWR to self-compacting pastes and concretes. An additional objective is to understand the responses of various cementitious pastes using UWR. Pastes modified with mineral and chemical admixtures, fly ash-water pastes, geopolymers, and bacteria modified pastes were tested with UWR and their responses interpreted. The P-wave response is explained in detail, and instrumentation effects on the response are elaborated on. Setting times from UWR are compared with penetration resistance setting times. Combined UWR and formwork pressure tests are done in order to explore the relationship
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