University of Massachusetts Amherst ScholarWorks@UMass Amherst Masters Theses Dissertations and Theses March 2015 Nano-Scale Investigation of Mechanical Characteristics of Main Phases of Hydrated Cement Paste Shahin Hajilar University of Massachusetts Amherst Follow this and additional works at: https://scholarworks.umass.edu/masters_theses_2 Part of the Structural Engineering Commons Recommended Citation Hajilar, Shahin, "Nano-Scale Investigation of Mechanical Characteristics of Main Phases of Hydrated Cement Paste" (2015). Masters Theses. 151. https://scholarworks.umass.edu/masters_theses_2/151 This Open Access Thesis is brought to you for free and open access by the Dissertations and Theses at ScholarWorks@UMass Amherst. It has been accepted for inclusion in Masters Theses by an authorized administrator of ScholarWorks@UMass Amherst. For more information, please contact [email protected]. NANO-SCALE INVESTIGATION OF MECHANICAL CHARACTERISTICS OF MAIN PHASES OF HYDRATED CEMENT PASTE A Thesis Presented by SHAHIN HAJILAR Submitted to the Graduate School of the University of Massachusetts Amherst in partial fulfillment of the requirements for the MASTER OF SCIENCE IN CIVIL ENGINEERING February 2015 Civil and Environmental Engineering Structural Engineering and Mechanics © 2015 Copyright by Shahin Hajilar All Rights Reserved NANO-SCALE INVESTIGATION OF MECHANICAL CHARACTERISTICS OF MAIN PHASES OF HYDRATED CEMENT PASTE A Thesis Presented by SHAHIN HAJILAR Approved as to style and content by: __________________________________ Behrouz Shafei, Chair __________________________________ Alice Alipour, Member __________________________________ David M. Ford, Member _______________________________ Richard N. Palmer, Department Head Civil and Environmental Engineering ACKNOWLEDGMENTS I would like to thank all those who have helped me along the way to finishing this Master’s degree program. Including everyone would require several pages of text, so a summary will have to do. First and foremost, I would like to thank my advisor, Dr. Behrouz Shafei, who always gave me useful suggestions and orientation, and always encouraged me to challenge the deeper exploration throughout my research project at University of Massachusetts Amherst. Additionally, the perspective and commentary provided by my thesis committee members, Dr. Alice Alipour and Dr. David M. Ford, are gratefully acknowledged. I would like to thank my parents and siblings for their endless support that was crucial to my success. Knowing that they are proud of my academic accomplishments is one of my biggest inspirations. I would be remiss if I did not give a big thank to the graduate students with whom I worked on a daily basis: Dena, Ameh, Rose, Mark, Alex, Omer and David. The time here was accentuated by my relationships with each of you. Lastly, special thanks go to all my instructors and all staff (Jodi Ozdarski, Kelly Ives, Jennifer Pease, and others) in the Department of Civil and Environmental Engineering of University of Massachusetts Amherst. iv ABSTRACT NANO-SCALE INVESTIGATION OF MECHANICAL CHARACTERISTICS OF MAIN PHASES OF HYDRATED CEMENT PASTE FEBRUARY 2015 SHAHIN HAJILAR, B.S., UNIVERSITY OF TEHRAN M.S.C.E., UNIVERSITY OF MASSACHUSETTS AMHERST Directed by: Behrouz Shafei Hydrated cement paste (HCP), which is present in various cement-based materials, includes a number of constituents with distinct nano-structures. To understand the mechanical characteristics of the HCP at the nano-scale, a comprehensive set of crystalline structures that represent the main HCP constituents is developed for Molecular Dynamics (MD) simulations. The elastic properties of the HCP phases are calculated using the static methods. The accuracy of estimated values is verified by comparing them with the results from experimental tests and other atomistic simulation methods. The outcome of MD simulations is extended to predict the elastic properties of the C-S-H gel by rescaling the values calculated for the individual crystalline structures. To take into account the contribution of porosity, a detailed microporomechanics study is conducted on low- and high-density types of C-S-H. The obtained results indicate that MD simulations are capable of capturing the elastic properties of the C-S-H gel. This is further verified by comparing the rescaled values with the predictions from nanoindentation tests. To investigate the mechanical strength and performance of the HCP under external loads, the atomic structures of the main HCP crystals are generated at the nano-scale in the current study. Through an extensive set of MD simulations, the mechanical behavior of the HCP crystals is examined under uniaxial tensile strains. From the stress-strain curves obtained in the three v orthogonal directions, elastic and plastic responses of the HCP crystals are determined. A comprehensive chemical bond and structural damage analysis is also performed to characterize the failure mechanisms of the HCP crystals under high tensile strains. The outcome of this study provides detailed information about the nonlinear behavior, plastic deformation, and structural failure of the HCP phases and similar atomic structures. vi TABLE OF CONTENTS Page ACKNOWLEDGMENTS …………………………………………………….. iv ABSTRACT …………………………………………………………………….. v LIST OF TABLES …………………………………………………………..… xi LIST OF FIGURES …………………………………………………………... xii CHAPTER 1. INTRODUCTION ............................................................................................. 1 1.1 Objectives ............................................................................................................................. 1 1.2 Hydrated Cement Paste (HCP) .............................................................................................. 3 1.3 Need for Atomistic Simulation ............................................................................................. 3 1.4 Outline ................................................................................................................................... 4 2. CONSTITUENTS OF HYDRATED CEMENT PASTE ............................... 7 2.1 Hydration Reactions of the Cement Components ................................................................. 7 2.1.1 Tricalcium Silicate (Alite) ................................................................................................ 8 2.1.2 Dicalcium Silicate (Belite) ............................................................................................... 8 2.1.3 Tricalcium Aluminate (Celite) ......................................................................................... 9 2.1.4 Aluminoferrite (Ferrite) .................................................................................................. 10 2.1.5 Sulfate Attack ................................................................................................................. 10 vii 2.2 Hydration Products ............................................................................................................. 11 2.2.1 C-S-H Gel....................................................................................................................... 11 2.2.1.1 Tobermorites ........................................................................................................... 14 2.2.1.2 Jennite ..................................................................................................................... 15 2.2.2 Portlandite ...................................................................................................................... 15 2.2.3 Ettringite ......................................................................................................................... 16 2.2.4 Kuzelite .......................................................................................................................... 17 2.2.5 Hydrogarnet .................................................................................................................... 18 3. OVERVIEW OF ATOMISTIC SIMULATION METHODS ..................... 23 3.1 Introductory Statistical Mechanics ...................................................................................... 24 3.1.1 Method of Ensembles ..................................................................................................... 24 3.1.2 Ergodic Theorem ............................................................................................................ 24 3.2 Monte Carlo Techniques ..................................................................................................... 26 3.3 Molecular Dynamics Method .............................................................................................. 27 3.3.1 Forcefields ...................................................................................................................... 28 3.3.1.1 COMPASS .............................................................................................................. 28 3.3.1.2 Universal ................................................................................................................. 29 3.3.1.3 Dreiding .................................................................................................................. 29 3.3.1.4 ClayFF .................................................................................................................... 30 3.3.2 Energy Minimization ...................................................................................................... 31 3.3.3