Process engineering of functional metakaolin based geopolymers by Matteo Pernechele M.Sc., Università degli Studi di Padova, 2012 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF Doctor of Philosophy in The Faculty of Graduate and Postdoctoral Studies (Materials Engineering) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) April 2018 © Matteo Pernechele, 2018 Abstract Geopolymers (GPs) are a class of inorganic materials which can be used as construction and refractory cements and as functional materials for environmental applications. GPs are low CO2 emissions binders with high durability that can replace traditional cementitious materials. However the effects and interactions of processing parameters on the different stages of GP setting (“geopolymerization”) are still under scrutiny and the molecular mechanisms and rate limiting steps controlling the setting kinetics are unknown. The crystallization in GPs, which ultimately controls their performance in advanced applications such as water purification and toxic waste encapsulation, is a poorly investigated topic. This dissertation provides new experimental evidences on the role of chemical composition and curing process on metakaolin-based GPs. Steady state and dynamic rheological studies, contact angle tests, microstructural (SEM), structural (XRD and FTIR) and mechanical analyses lead to better understanding of the fundamental transformations occurring during geopolymerization. GPs were seeded with different oxides and zeolites to determine the rate limiting step, increase the reaction rate and control the crystallization. This work contributes to clarification the complex effects of soluble silica on the geopolymerization process. It is shown that soluble and colloidal silicates (such as Na4SiO4 and Na2SiO3) can act as seeding agents, changing the geopolymerization rate limiting step at temperatures T≥35°C. However, they also slow down the reaction rate, possibly by forming passivation layers on the metakaolin particles, thus producing a more chemically stable and mechanically stronger amorphous gel. Silicates also decrease the water requirement in GPs and thus the porosity. Under certain conditions silicates can increase the percentage of crystalline Faujasite in GPs, but the crystallization process requires higher curing temperatures and times (T>40°C and t>4 days, depending on the amount of silicates). The alkali metals have also a structure- directing role in crystallization of GPs in the form of zeolite, favoring Faujasite structure. Water has a templating effect in GPs, favoring the structure of zeolite LTA-type over hydrosodalite. This work also illustrates the compromises that need to be made when selecting appropriate processing parameters to tailor the rheology, structure and properties of geopolymers for specific applications. ii Lay summary This work studies reactions between inorganic clay-based materials with different alkaline solutions and additives to produce environmentally friendly cementitious materials, called “Geopolymers”. Such materials have both conventional and advanced applications, and in some areas may replace Ordinary Portland Cement. The characteristics of the resulting geopolymers were studied, in terms of their viscosity, chemical bonding, crystallinity and compressive strength. It was found that the chemistry of precursor solutions and the processing temperature have a profound effect on the reaction and on the nature of the final geopolymer materials. The use of processing additives brought light on the reaction mechanisms, thus enabling a deeper understanding of the resulting material. Guidelines were developed to tune the properties of the geopolymeric cement to specific applications. iii Preface This dissertation is original, unpublished, and independent work by the author. None of the text is taken directly from previously published articles. -M. Pernechele iv Table of contents Abstract ..................................................................................................................................... ii Lay summary ........................................................................................................................... iii Preface ..................................................................................................................................... iv Table of contents....................................................................................................................... v List of tables ............................................................................................................................ xi List of figures ......................................................................................................................... xiii List of abbreviations and symbols ........................................................................................ xxii Acknowledgements............................................................................................................... xxv Dedication ............................................................................................................................ xxvi 1. Introduction........................................................................................................................... 1 1.1. Role of geopolymers in sustainable development ......................................................... 1 1.2. Inorganic binders ........................................................................................................... 2 1.3. Motivation ...................................................................................................................... 7 2. Literature review ................................................................................................................... 8 2.1. Introduction to geopolymers .......................................................................................... 8 2.1.1. Geopolymers and their terminology ........................................................................ 8 2.1.2. Types of aluminosilicate geopolymers .................................................................. 12 2.1.3. Geopolymers properties and applications ............................................................. 15 2.2. Metakaolin - based geopolymers (MK-based GP) ....................................................... 20 2.2.1. Historical perspective ............................................................................................ 20 2.2.2. The solid precursors to GP: metakaolin ................................................................ 23 2.2.3. The alkaline solutions ............................................................................................ 24 2.2.4. Geopolymerization reactions ................................................................................. 28 v 2.2.4.1. Conceptual models for geopolymerization reactions ..................................... 29 2.2.4.2. Dissolution and precipitation reactions in cementitious systems ................... 32 2.2.4.2.1. Thermodynamic and kinetic of complex reactions ................................. 32 2.2.4.2.2. Heterogeneous reactions ......................................................................... 34 2.2.4.3. Metakaolin dissolution.................................................................................... 36 2.2.4.4. Aluminosilicates condensation in solutions ................................................... 40 2.2.4.5. Kinetic models of geopolymerization ............................................................. 43 2.2.4.6. Additives and Seeding .................................................................................... 46 2.2.5. GP technology development: composition and properties optimization.............. 48 2.3. Zeolites ......................................................................................................................... 51 2.3.1. Synthesis, structure and applications..................................................................... 51 2.3.2. Induction time and kinetics of crystallization of zeolites ...................................... 55 2.3.3. Synthesis of zeolites from metakaolin................................................................... 57 2.4. Advanced GP applications and geopolymer crystallinity ............................................ 59 3. Objectives ........................................................................................................................... 63 4. Approach and methodology ................................................................................................ 64 4.1. Materials, synthesis and preparation methods ............................................................. 64 4.1.1. Raw material and metakaolin characterization ..................................................... 64 4.1.2. Geopolymer synthesis ........................................................................................... 67 4.2. Analysis methods ......................................................................................................... 67 4.2.1. Rheological characterization ................................................................................. 67 4.2.1.1. Viscosity ......................................................................................................... 68 4.2.1.2. Steady-state measurements ............................................................................