Micro-level Porosimetry of Virtual Cementitious Materials Structural Impact on Mechanical and Durability Evolution Luong Bao Nghi Le Micro-level Porosimetry of Virtual Cementitious Materials Structural Impact on Mechanical and Durability Evolution Proefschrift ter verkrijging van de graad van doctor aan de Technische Universiteit Delft, op gezag van de Rector Magnificus prof.ir K.C.A.M Luyben; voorzitter van het College voor Promoties, in het openbaar te verdedigen op maandag 19 oktober 2015 om 12:30 uur door Luong Bao Nghi LE Master of Engineering, Structural Engineering, Ho Chi Minh City University of Technology, Vietnam geboren te Da Lat, Vietnam -i- This dissertation has been approved by the promotor: Prof.dr.ir L.J Sluys Composition of the doctoral committee: Rector Magnificus chairman Prof.dr.ir L.J Sluys Delft University of Technology Independent members: Prof.dr V Mechtcherine Dresden University of Technology Prof.dr.ir N De Belie Ghent University Prof.dr.ir H.J.H Brouwers Eindhoven University of Technology Prof.dr.ir E Schlangen Delft University of Technology Prof.dr.ir K van Breugel Delft University of Technology, reserve member Other members: Dr.ir P Stroeven Delft University of Technology Dr.ir M Stroeven Delft University of Technology Copyright ©2015 by Luong Bao Nghi Le All rights reserved No part of the material protected by this copyright notice may be reproduced or utilized in any form or by any means, electronic, mechanical, including photocopying, recording or by any information storage and retrieval system, without the prior permission of the author ISBN: 978-94-6186-534-2 Author email: nghi.l.b.le@gmail.com Table of contents TABLE OF CONTENTS .III SUMMARY VII SAMENVATTING IX LIST OF ABBREVIATIONS XI CHAPTER INTRODUCTION 1.1 Concrete as a particulate and porous material at different levels of its microstructure 1.2 Pore characteristics and porosimetries 1.3 Virtual cementitious materials 1.3.1 Drawback of experimental porosimetries 1.3.2 Computational simulation of cementitious materials 1.3.3 Porosimetries applied to virtual cementitious materials 1.4 Objectives and outlines of this research work 1.4.1 Objectives of research 1.4.2 Outlines of research 13 CHAPTER MICROSTRUCTURAL SIMULATION OF HYDRATED CEMENTITIOUS MATERIALS 17 2.1 Introduction 18 2.1.1 Production and composition of cement 18 2.1.2 Particle size distribution and fineness of cement 19 2.1.3 Water to cement ratio 19 2.1.4 Cement hydration 20 2.1.5 Pozzolanic admixtures 22 2.2 Packing simulation of fresh (blended) cement paste 23 2.2.1 Generation of particles 23 2.2.2 Packing simulation by dynamic DEM 26 2.3 Hydration simulation of (blended) cement paste 27 2.3.1 Formation of eXtended Integrated Particle Kinetics Model 28 2.3.2 Equivalent mono-sized fine particles 35 2.3.3 Algorithmic aspects 36 2.3.4 Numerical estimation of the basic penetration rate of hydration front 39 2.4 Verifications 41 - iii - 2.5 Conclusions and discussion 45 CHAPTER COMPUTATIONAL POROSIMETRY FOR VIRTUAL POROUS MATERIALS 47 3.1 Pore characteristics 48 3.1.1 Porosity 48 3.1.2 Degree of connectivity 48 3.1.3 Specific surface area 49 3.1.4 Pore size distribution 49 3.1.5 Porosity gradient and interfacial transition zone 50 3.2 Pore size estimation 50 3.2.1 Star volume measure 50 3.2.2 Application of star volume measure to 3D virtual pore structure 51 3.2.3 Pore throat estimation 52 3.2.4 Enhancement of star volume measure 52 3.3 Random node structuring (RaNoS) 53 3.3.1 Algorithm 53 3.3.2 Characterization of pore structure by RaNoS 54 3.3.3 Localized and parallel computing 57 3.3.4 Examples 58 3.4 Summary 63 CHAPTER PERMEABILITY ESTIMATION FOR A VIRTUAL POROUS MEDIUM 65 4.1 Permeability 66 4.2 Stokes mixed FEM approach 66 4.2.1 Governing equations and weak forms 66 4.2.2 Boundary conditions 67 4.2.3 Mixed FEM Discretization 68 4.2.4 Admissible element 70 4.2.5 Solving the linear equation system 71 4.2.6 Examples 72 4.3 Double-Random Multiple Tree Structuring (DRaMuTS) 74 4.3.1 Algorithm 75 4.3.2 Extraction of main trunks from percolated trees 78 4.3.3 Flow estimation by ‘tube model’ 81 4.3.4 Examples 85 4.4 Summary 88 CHAPTER INVESTIGATION OF PORE CHARACTERISTICS AND PERMEABILITY OF CEMENTITIOUS MATERIALS 91 5.1 Existence of RVE on the aspect of pore characteristics of cementitious materials 92 5.2 Effect of rice husk ash blending 97 5.3 Experiments 98 5.3.1 Input parameters 98 5.3.2 Porosity evolution with hydration time 99 5.3.3 Porosity gradient 100 5.3.4 Pore size distribution 101 5.3.5 Permeability 104 5.3.6 Discussion 106 5.4 Summary 112 CHAPTER MICRO-MECHANICAL BEHAVIOUR OF CEMENTITIOUS MATERIALS 115 6.1 Methodology 116 6.1.1 Assessment of elastic moduli of matured cement pastes 116 6.1.2 2D representative specimen for mechanical tests 117 6.1.3 Tensile test configuration 120 6.1.4 Micro-macro transition 121 6.2 Existence of RVE in tensile damage response of cementitious materials 123 6.3 Parameter study results 125 6.3.1 Young’s modulus 125 6.3.2 Tensile damage response 128 6.4 Summary 135 CHAPTER CONCLUSIONS AND RECOMMENDATIONS 137 7.1 Conclusion 137 7.2 Recommendations 140 REFERENCES 143 ACKNOWLEDGMENTS 155 LIST OF RELEVANT PUBLICATION 157 CURRICULUM VITAE 159 -v- Summary Understanding the microstructure of cement paste is the basis of a study towards properties and behaviour of cementitious materials It is attractive exploiting modern computer facilities for this purpose, favourably competing with time-consuming and laborious experimental approaches This study aims at bringing material studies into virtual reality through a comprehensive computational framework that is composed of three parts as described below The first part deals with generating virtual representations of hardening cement composites at micro-scale, starting with producing a paste of randomly packed cement grains at the fresh state A DEM-based dynamic packing process is used for this purpose to obtain, not only paste with high density but also that with a wide particle size range The next stage involves simulation of the microstructure during hydration, based on an improved version of the well-known vector approach The proposed model denoted ‘eXtended Integrated Particle Kinetics Method’ (XIPKM) includes the following improvements: a multi-component particle model to take major cement compounds and the pozzolan into account, a numerical technique to capture the complex contact between expanding particles (a crucial issue in vector approaches), and finally a concept to avoid the extreme computational effort in generating a very large amount of fine particles Furthermore, a numerical procedure is proposed to obtain the basic penetration rates of different minerals instead of using a laborious calibration process commonly used in vector approaches In the second part, two computational porosimetry methods to explore the pore network characteristics are developed The first method denoted ‘Random Node Structuring’ (RaNoS) characterises the pore space, based on analysing the configuration of a system of random points dispersed in the pore space These random points are further employed, together with an enhanced version (for a more efficient size assessment of irregular pores) of the well-known stereological technique – star volume measure (SVM), to estimate the pore size distribution The second porosimetry method named ‘Double-Random Multiple Tree Structuring’ (DRaMuTS) is an enhanced version of RaNoS, whereby the topology of the pore structure is further efficiently explored by a system of concurrent virtual trees growing and branching randomly in pore space, configured by a robotics-inspired path planning algorithm Based on topological information attained by the tree systems, the pore space is then converted into a cylindrical tube network for directly estimating permeability Based on the pore configuration obtained by the porosimetry methods, 2D representative samples to study the tensile damage 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Stuttgart, 2011 [160] D'Addetta, G.A., Kun, F and Ramm, E., On the application of a discrete model to the fracture process of cohesive granular materials Granular Matter (2002) 77-90 Acknowledgments The research presented in this dissertation has been carried out in the framework of the PhD programme in the Computational Mechanics group in the Faculty of Civil Engineering and Geosciences of Delft University of Technology, the Netherlands First of all, I would like to express my deep appreciation to my promotor Prof Bert Sluys for his great encouragement, support and guidance throughout my studying, especially in difficult situations I wish to express my extreme gratitude to my ‘daily’ supervisor Prof Piet Stroeven for his enthusiastic inspiration, great assistance and meaningful guidance Also, I am sincerely grateful to my co-supervisor, Dr Martijn Stroeven, for many valuable discussions and careful review of my manuscript I especially thank Frank Everdij for his willing help on my IT problems I would like to express my deep gratitude to Veronique van der Varst, Marjon van der Perk and Anneke Meijer for their thoughtful administrative support I would like to thank my colleagues Angelo Simone, Awais Ahmed, Mehdi Nikbakht, Mojtaba Talebian, Oriol Lloberas Valls, Prithvi Mandapalli, Zahid Shabir, Vinh Phu Nguyen, Frans van der Meer, Rafid Al-Khoury, Adriaan Sillem, Amin Karamnejad, Jitang Fan, Kai Li, Erik Simons, Marcello Malagu and Jaap Weerheijm for friendship and relaxing discussion My special thankfulness goes to Fandi Pawiroredjo for an excellent translation of my thesis’s summary I am also very thankful to my Vietnamese friends in Delft for a lot of joyful and relaxing activities, especially to my roommate Phan Hien Vu for his delicious meals and drinks The financial support by Vietnam Ministry of Education and Training, CICAT and Section of Structural Mechanics is gratefully acknowledged And last but not least, I would like to greatest gratitude to my parents and my sisters for their unconditional encouragement and support Le Luong Bao Nghi Delft, September 2015 List of relevant publication Article - letter to the editor Stroeven, P, Sluys, LJ, Le, LBN & He, H (2011) Porien in virtueel beton Cement: vakblad voor de betonwereld, 2011(4 |(juli)), 1-4 Le, LBN & Stroeven, P (2012) Strength and durability evaluation by DEM approach of green concrete based on gap-graded cement blending Advanced Materials Research, 450451, 631-640 Stroeven, P, Le, LBN & He, H (2012) Methodological approaches to 3D pore structure exploration in cementitious materials Key Engineering Materials, 517, 305-314 Stroeven, P, Le, LBN, Sluys, LJ & He, H (2012) Porosimetry by double-random multiple tree structuring in virtual concrete Image Analysis and Stereology, 31(1), 55-63 Stroeven, P, Le, LBN, Sluys, LJ & He, H (2012) Porosimetry by random node structuring in virtual concrete Image Analysis and Stereology, 31(2), 79-87 He, H, Le, LBN & Stroeven, P (2012) Particulate structure and microstructure evolution of concrete investigated by DEM Part 1: Aggregate and binder packing Heron, 57(2), 119-132 Le, LBN, Stroeven, M, Sluys, LJ & Stroeven, P (2013) A novel numerical multicomponent model for simulating hydration of cement Computational Materials Science, 78(October), 12-21 Le, LBN, He, H & Stroeven, P (2012) Particulate structure and microsstructure evolution of concrete investigated by DEM Part 2: Porosimetry in hydrating binders Heron, 57(2), 133-150 Li, K, Stroeven, P & Le, LBN (2015) Methodology for porosimetry in virtual cementitious composites to economically and reliably estimate permeability Image Analysis and Stereology, 34(2), 73-86 10 Stroeven, P, Li, K, Le, LBN, He, H & Stroeven, M (2015) Capabilities for property assessment on different levels of the micro-structure of DEM-simulated cementitious materials Construction and Building Materials, 88(July), 105-117 11 Le, LBN, Stroeven, P (2015) Effect of blending on properties of pore network structure in blended cements studied in virtual reality Cement and Concrete Composites (submitted) 158 References Article in volume – proceedings Stroeven, P, He, H & Le, LBN (2011) 2D and 3D routes to investigating pores in concrete In s.n (Ed.), 13th international congress for stereology (pp 1-4) Beijing: Tsinghua University Stroeven, P, Le, LBN & He, H (2011) 3D exploration of percolated porosity in virtual concrete In s.n (Ed.), 13th international congress for stereology (pp 1-4) Beijing: Tsinghua University Stroeven, P, Le, LBN, Stroeven, M & Sluys, LJ (2011) Discrete element modeling approach to porosimetry for durability risk estimation of concrete In E Onate & DRJ Owen (Eds.), Particles 2011 (pp 1-12) Barcelona: IACM Stroeven, P & Le, LBN (2011) Studying percolated porosity in concrete by dem In A-M El-Batahgy & M Waly (Eds.), Processing, performance and failure analysis of engineering materials (pp 447-456) Luxor, Egypt: IQCMEA-ICF Le, LBN & Stroeven, P (2012) Porosity of green concrete based on a gap-graded blend In AM Brandt, J Olek, MA Glinicke & CKY Leung (Eds.), Brittle matrix composites 10 (pp 315-324) Cambridge: Woodhead Publishing Stroeven, P, He, H & Le, LBN (2012) Analogue simulation by dem of material structure for property estimation of cementitious materials In s.n (Ed.), International US-Poland workshop multiscale computational modeling of cementitious materials (pp 155-164) Stroeven, P, Sluys, LJ & Le, LBN (2012) Assessment of pore characteristics in virtual concrete by path planning methodology In AM Brandt, J Olek, MA Glinicke & CKY Leung (Eds.), Brittle matrix composites 10 (pp 200-207) Cambridge: Woodhead Publishing Stroeven, P & Le, LBN (2013) Evaluation by discrete element method (DEM) of gapgraded packing potentialities for green concrete design In C Goodier, M Soutsos, TT Le & VT Nguyen (Eds.), International conference on sustainable built environment for now and the future (pp 347-354) Hanoi: National University of Civil Engineering Stroeven, P & Le, LBN (2013) Porosimetry by DraMuTS applied to DEM-produced cementitious materials In H Uzoegbo & W Schmidt (Eds.), International conference on advances in cement and concrete technology in Africa (pp 277-284) 10 Le, LBN & Stroeven, P (2014) Packing issue in cement blending for sustainability developments - Approach by discrete element method In V Bilek & Z Kersner (Eds.), Proceedings of the international conference on non-traditional cement and concrete, ICNTCC2014 Vol International Journal of Research in Engineering and Technology (online) (pp 147-150) Brno: NOVPRESS 11 Stroeven, P, He, H, Le, LBN & Li, K (2014) Modeling possibilities of concrete structure for durability purposes In NB Barabash (Ed.), Proceedings of the international seminar on modelling and optimization of composites (pp 60-63) Odessa: Astroprint Curriculum vitae October 17th, 1983 born in Da Lat, Vietnam, as Le Luong Bao Nghi Sep 2001 – Mar 2006 Bachelor in Civil Engineering, Ho Chi Minh University of Technology Sep 2006 – Dec 2008 Master of Science in Structural Engineering, Ho Chi Minh University of Technology Mar 2010 – Mar 2015 PhD candidate in the Computational Mechanics group at the Faculty of Civil Engineering and Geosciences, Delft University of Technology [...]... by new porosimetry techniques that are applicable to the virtual porous materials, evaluation of the permeability of the materials by an economical pore-scale network model and investigation of the influence of pore characteristics on mechanical and transport properties of cementitious materials A new material model for the simulation of hydration and microstructural evolution of cementitious materials. .. applications Microstructural simulation of hydrated cementitious materials (Chapter 2) Investigation of pore characteristics and permeability of cementitious materials (Chapter 5) Computational porosimetries on virtual porous media (Chapter 3) Implication of microstructure and pore characteristics on elastic properties and damage behaviours of cementitious materials (Chapter 6) Permeability estimation on virtual. .. saturation, flow path blocking by movement of loose particles under high pressure and swelling of the CSH gel due to re-saturation 1.3.2 Computational simulation of cementitious materials An overview of computational works on cementitious materials The fast and continuing advances of computing facilities nowadays promote doing research on virtual materials as a more economic and reliable option Several... investigate mechanical properties and fracture process of cement pastes at micro- scale [56-61] On the nano-scale, the focus is on modelling of the nanostructure of CSH gel and on its evolution during hydration of PC Several models [6,62-66] are proposed for description of CSH as colloid structure of jennite (CSH substance) and of the gel pores Modelling approaches The ‘vector approach’ and ‘discretization approach’... of pore characteristics on elasticity moduli and on tensile damage behaviour The differences in properties and damage evolution are investigated as a result of different pore size distributions, different porosities and pore structures in ITZ and bulk zone The effect of RHA blending is considered Finally, summaries, conclusions and recommendations are given in Chapter 7 Introduction 15 Introduction... in the microstructure of the cement paste The measurement of saturated permeability of cementitious materials is hampered by a time-dependent reduction of the flow rate because of the so-called ‘self-sealing effect’ (SSE) [18] This phenomenon is the consequence of changes in pore structure during the process due to dissolution and precipitation of ions along the flow paths, continuing hydration by water... (Chapter 4) Conclusion (Chapter 7) Figure 1.6 Flow chart of the thesis Chapter 2 Microstructural simulation of hydrated cementitious materials Since the microstructure of a hardened cementitious material continuously varies over a long period of time (i.e., couple of decades), performing experimental tests on specimens at different ages to record the microstructural developments is extremely time-consuming... been and are still being carried out to improve the performance as well as the economic aspects of the concrete material, at the same time meeting increasing environmental demands From the structural engineering point of view, concrete at macro -level is considered a continuous and homogeneous material, of which physical and mechanical features nonetheless originate from its underlying meso- and micro- structure... the solid particles at micro- level 1.2 Pore characteristics and porosimetries One of the most important challenges in concrete engineering and research is to acquire an understanding of the pore network structure and of its influence on the physical, mechanical and durability properties of concrete Indeed, the strength, elasticity properties and permeability are affected not only by the porosity but... Chapter 1 Introduction 1.1 Concrete as a particulate and porous material at different levels of its microstructure Though used in construction industry for centuries, concrete is still one of the most popular materials for buildings and infrastructures (Figure 1.1) The long-lasting use of concrete comes from advantages as to its economy, geometrical flexibility, high fire-resistance and durability, etc .. .Micro- level Porosimetry of Virtual Cementitious Materials Structural Impact on Mechanical and Durability Evolution Luong Bao Nghi Le Micro- level Porosimetry of Virtual Cementitious Materials. .. model and investigation of the influence of pore characteristics on mechanical and transport properties of cementitious materials A new material model for the simulation of hydration and microstructural... microstructural evolution of cementitious materials As afore-mentioned, the micro- numerical models for simulation hydration and microstructural evolution of cement are classified into the ‘discretization