Departments
4MAT - BATir
Contribution to the development
of an additive for bulk waterproofing
of cement-based materials
Dissertation presented in order to obtain the title of
Docteur en Sciences de l’Ingénieur et Technologie
Nenad MILENKOVIĆ
Thesis Supervisor: Prof. Marie-Paule DELPLANCKE Co-Supervisor: Prof. Stéphanie STAQUET
Academic year: 2017/2018
Members of the Jury:
Chairman:
Prof. Bernard Espion Université Libre de Bruxelles, Belgium
Supervisor:
Prof. Marie-Paule Delplancke Université Libre de Bruxelles, Belgium Co-supervisor:
Prof. Stéphanie Staquet Université Libre de Bruxelles Belgium
Members:
Prof. Hubert Rahier Vrije Universiteit Brussel, Belgium
Dr. Jean-Paul Lecomte DOW CORNING, Belgium
Prof. Özlem Cizer KU Leuven, Leuven, Belgium
Contact:
Nenad MILENKOVIĆ, PhD Researcher ÉCOLE POLYTECHNIQUE DE BRUXELLES Departments 4MAT-BATir
50 av. F.D. Roosevelt - CP165/63 1050 Bruxelles, Belgique
Email : nemilenk@ulb.ac.be
Acknowledgements
Herewith, I would like to express my gratitude and acknowledgements to the people who contributed to the work presented in this thesis.
First of all, I would like to express my sincere gratitude to my thesis supervisor, Professor Marie-Paule Delplancke-Ogletree. I profoundly appreciate your scientific guidance and constructive discussions regarding my work. During more than 4 years I was honoured to share the passion for science with you, to learn and to broaden my horizons. You gave me the opportunity to meet wonderful people in 4MAT and to live in an amazing city of Brussels. Also, thank you for all your friendly support during my difficult moments.
I would also like to acknowledge my co-supervisor, Professor Stéphanie Staquet, for discussions and scientific guidance during my work in BATir. Your friendly approach and constructive advices regarding my work with new testing methods, motivated me to explore the world of construction materials. Thank you for giving me the opportunity to work on the latest characterization methods. Moreover, I appreciate all the help from Brice Delsaute and Jérôme Carette during my experimental work in BATir.
Hereafter, I would like to thank Mr. Jean-Paul Lecomte and his team from Dow Corning for supporting my work on the NISHYCEM project. I appreciate for giving me the opportunity to enter the world of R&D of silicones and to work in the labs of Dow Corning. Thank you for being always available for clarifying my doubts and for sharing your expertize. Special thanks to Marie-Jo Sarrazin for the assistance in laboratory work in Dow Corning. Your friendly approach and valuable experience have made my days in DC very interesting.
Furthermore, I acknowledge Mr. Christian Pierre and his team from CRIC-OCCN for their participation to the characterization of mortars and electrical resistivity tests. I enjoyed discussing our ideas that led us to essential findings that contributed to the interpretation of the phenomena of the delayed release. Thank you Michel, Geraldine and Alain, for your help in experimental work.
I express my deepest gratitude to the jury members, Prof. Bernard Espion, Prof. Hubert Rahier, Prof. Özlem Cizer and Dr. Jean-Paul Lecomte for reviewing my thesis. Many thanks to the VUB MACH-FYSC team for their help in low-temperature DSC analyses, and Sam Dehaeck from the ULB TIPs for the surface tension measurements.
This work would not be possible without enormous energy and friendliness of the whole team of 4MAT. Your skills, professional attitude in the labs and friendly talks in the offices motivated me to work more and to enjoy better! Tiriana, Gilles and Patrizzio, I have spent many hours with you in order to properly assess numerous analyses. Your knowledge, precision and positive energy was a valuable factor that contributed to the quality of the data presented in this thesis.
Much love and gratitude goes to my dear friends, Miss Pati, Mr. Pouya, Meba and Guoxing with whom I was sharing daily life in our offices, discussing about life and making plans for the future. My days in 4MAT were full of joy and good atmosphere thanks to all my colleagues in 4MAT. Special thanks for all-time support goes to Shain Ismail.
I dedicate this thesis to my family and my Dunja, who supported me with love, care and understanding for my ambition. Thank you all for giving me the wind in my back to find my path. Love you all!
I also wish to dedicate this thesis to my friend Jelena, who, although not anymore with us, continues to motivate me to fight and never give up.
Table of contents:
ACKNOWLEDGEMENTS ... I TABLE OF CONTENTS ... III LIST OF TABLES ... VII LIST OF FIGURES ... IX ABSTRACT ... XVII RÉSUMÉ ... XVIII TABLE OF ACRONYMS AND ABBREVIATIONS ... XX PUBLICATION LIST ... XXI
CHAPTER - I: INTRODUCTION ... 1
GENERAL INTRODUCTION ... 2
MOTIVATION FOR THE RESEARCH ... 3
AIM OF THE RESEARCH ... 5
METHODOLOGY ... 6
CHAPTER - II: BULK HYDROPHOBIC TREATMENT OF CEMENTITIOUS MATERIAL .. 9
CEMENT ... 10
II.1.1. Classification of cement ... 11
CEMENT PASTE AND MORTAR ... 12
II.2.1. Cement hydration ... 13
C3S - tricalcium silicate (3CaO.SiO2)... 13
C2S – dicalcium silicate (2CaO.SiO2) ... 14
C3A – calcium aluminate (3CaO.Al2O3) ... 14
C4AF – calcium alumoferrite (4CaO.Al2O3.Fe2O3) ... 15
II.2.2. Cement hydration ... 16
Stage I – Initial hydration ... 17
Stage II – Dormant phase (low hydration reactions) ... 18
Stage III – Acceleration phase ... 18
Stage IV – Deceleration phase ... 19
Stage V – Curing ... 19
II.2.3. Cement particles interaction during early age hydration – cohesion ... 20
II.2.3.1. Electric double-layer forces ... 20
II.2.3.2. Rheology of cement paste ... 20
II.2.4. Setting and hardening ... 21
CHEMISTRY OF SILANES AND SILOXANES.INTERACTION WITH CEMENT ... 22
II.3.1. Silanes and siloxanes ... 22
II.3.3. Silane admixture... 24
HYDROPHOBIC TREATMENT OF CEMENTITIOUS MATERIALS ... 24
II.4.1. Reaction of silanes with cement ... 26
II.4.1.1. Surface protection ... 28
II.4.1.2. Silanes as integral water repellents in cementitious materials ... 30
II.4.1.3. Influence of bulk hydrophobic treatment on the functional properties of mortars ... 31
II.4.2. Microencapsulation as a method for the delayed release ... 33
II.4.2.1. Silica dissolution in cement paste ... 34
CHAPTER - III: METHODS AND RAW MATERIALS CHARACTERIZATION ... 35
MATERIALS ... 36
III.1.1. CEM I and CEM III ... 36
III.1.2. Presentation of the admixtures used as integral water repellents ... 37
MIXING PROPORTIONS ... 38
III.2.1. Mixing procedure and curing conditions for cement pastes ... 39
III.2.2. Mixing procedure of mortars and curing conditions ... 40
CHARACTERIZATION METHODS ... 40
III.3.1. Characterization of the cement paste and admixtures ... 40
III.3.1.1. Phase analysis - X-ray diffraction (XRD/Rietveld analysis) ... 40
III.3.1.2. X-ray Fluorescence (XRF) ... 41
III.3.1.3. Microstructure investigation – Scanning Electron Microscopy (SEM) and Environmental Scanning electron microscopy (ESEM) ... 41
III.3.1.4. Mercury intrusion porosimetry (MIP) ... 42
III.3.1.5. Differential-Scanning Calorimetry with Thermo-Gravimetric Analysis (DSC-TGA) ... 42
III.3.1.6. Isothermal conduction calorimetry (TAM-Air) ... 43
III.3.1.7. Setting time... 43
III.3.1.8. Fourier transformation infrared spectroscopy (FTIR) ... 43
III.3.1.9. Laser granulometry – (Mastersizer) ... 44
III.3.1.10. Electrical resistivity of the liquid ... 44
III.3.1.11. Inductive coupled plasma-optical emission spectrometry (ICP-OES) ... 45
III.3.1.12. Surface tension ... 45
III.3.1.12.1. Pendant drop method ... 45
III.3.1.12.2. Dip ring method (Du Noüy) ... 45
III.3.2. Characterization of mortars ... 45
III.3.2.1. Penetration resistance test ASTM C403 ... 45
III.3.2.2. Evolution of mechanical properties ... 46
III.3.2.2.1. Ultrasonic Pulse Velocity (UPV) ... 46
III.3.2.2.2. Standard compression test on cubes (10 cm side) ... 48
III.3.2.3. Electrical conductivity [152] (ConSensor) ... 48
III.3.2.4. Autogenous deformation (AutoShrink) ... 49
III.4.1. Cement ... 52
III.4.2. FTIR ... 53
III.4.3. ESEM of the microcapsules ... 55
III.4.4. Particle size distribution of the microcapsules ... 56
III.4.5. Thermal analysis of the admixtures (DSC-TGA)... 57
CHAPTER - IV: FUNDAMENTAL STUDY ON THE MICROCAPSULES STABILITY IN ALKALINE SOLUTION ... 59
INTRODUCTION ... 60
RESULTS ... 61
IV.2.1. FTIR of additives in alkaline solution ... 61
IV.2.2. Influence on the surface tension ... 62
IV.2.2.1. Filtrated suspension ... 62
IV.2.2.2. Non-filtrated suspension ... 63
IV.2.2.3. Dip ring method (Du Noüy) ... 64
IV.2.3. Electrical conductivity... 65
IV.2.3.1. Kinetics of the shell dissolution in calcium hydroxide ... 68
IV.2.4. Influence of cations (Ca2+, Na+) on the shell reaction mechanism ... 70
IV.2.4.1. Microcapsules in lime solution ... 71
IV.2.4.2. Microcapsules in NaOH ... 72
IV.2.5. XRF and XRD of the flocs after 24h in lime solution ... 73
IV.2.5.1. FTIR analysis of the reaction products of microcapsules in NaOH ... 74
IV.2.5.2. FTIR of the flocs from limeM vs. resin from sodM ... 75
IV.2.6. What is the influence of Ca2+ cation on the resin release at high pH? ... 76
IV.2.6.1. Low temperature DSC of flocculated microcapsules in lime solution ... 77
A MODEL OF THE SHELL DISSOLUTION AND THE MECHANISM OF THE RESIN RELEASE ... 79
SUMMARY ... 82
CHAPTER - V: CEMENT HYDRATION IN PRESENCE OF SILANES. INFLUENCE ON THE MICROSTRUCTURE DEVELOPMENT ... 85
INTRODUCTION ... 86
EARLY AGE CEMENT HYDRATION ... 86
V.2.1. Cohesion of cement ... 87
V.2.1.1. Rheology ... 87
V.2.2. Setting time ... 91
V.2.3. Hydration kinetics ... 93
V.2.4. Pore solution composition followed by the ICP-OES ... 96
V.2.5. Cement hydration at very early age (first hour) followed by ESEM ... 101
V.3.1. Thermal analysis of cement pastes (DSC-TGA) ... 108
V.3.2. Portlandite content from TGA measurements ... 112
V.3.2.1. Porosity and pore sizes distribution ... 113
V.3.2.2. Phase composition – XRD ... 115
V.3.2.3. SEM-EDX observation on cement pastes ... 119
V.3.2.4. FTIR of cement pastes ... 125
SUMMARY ... 128
CHAPTER - VI: INFLUENCE OF BULK HYDROPHOBIC TREATMENT ON THERMO-CHEMO-MECHANICAL PROPERTIES OF MORTARS ... 131
INTRODUCTION ... 132
METHODOLOGY ... 132
VI.2.1. Equivalent age ... 136
RESULTS ... 137
VI.3.1. Hydration kinetics ... 137
VI.3.2. Influence of the admixtures on the setting time... 139
VI.3.3. Influence of the bulk hydrophobic treatment on the evolution of early age mechanical properties of mortars ... 140
VI.3.3.1. Compressive strength evolution by ConSensor ... 140
VI.3.4. Continuous monitoring of the early age hardening of mortars with integral water repellents 143 VI.3.4.1. Evolution of dynamic E- modulus (Edyn) and Poisson’s ratio (νdyn) ... 144
VI.3.4.2. Autogenous deformation ... 145
VI.3.4.3. Coefficient of thermal expansion (CTE) ... 149
SUMMARY ... 150
CHAPTER - VII: GENERAL CONCLUSIONS AND PERSPECTIVES ... 153
GENERAL CONCLUSIONS ... 154
PERSPECTIVES ... 159
ANNEX 1. EFFECTIVENESS OF THE MICROCAPSULES AS AN INTEGRAL WATER REPELLENT ... 161
ANNEX 2. HYDROPHOBICITY OF CEMENT PASTES CURED FOR 1 DAY ... 161
ANNEX 3 PARTICLE SIZES DISTRIBUTION OF ANHYDROUS CEMENT ... 163
ANNEX 4 CRYSTALLOGRAPHIC STRUCTURE OF HYDRATED CEMENT ... 164
ANNEX 5 RIETVELD ANALYSES REFINEMENT WITH PARAMETERS ... 165
List of Tables
:
Table III-1 Admixtures used as water repellents ... 38
Table III-2 Samples abbreviation and composition ... 40
Table III-3 Chemical characteristics of anhydrous cements ... 52
Table III-4 Chemical composition of anhydrous cements - quantitative elementary analysis by XRF ... 52
Table III-5 Mineralogical composition of the anhydrous cements (XRD- Rietveld analysis) ... 53
Table IV-1 Surface tension of the liquid after centrifugation of the suspension of microcapsules in saturated lime solution (T=20 °C), measured by the pendant drop method ... 63
Table IV-2 Surface tension of a suspension of microcapsules in alkaline solution (T=20 °C) (pendant drop) ... 64
Table IV-3 Surface tension of the suspension of the microcapsules and emulsion in saturated lime solution (T=20 °C) measured by Dip ring method (Ref. ethanol, water, neat resin) ... 65
Table IV-4 Concentration of Ca2+and Si in suspension of lime and microcapsules at
time zero and 24h after mixing (T=20 °C) ... 68
Table IV-5 Qualitative observation of the influence of cations on the microcapsules dissolution mechanism ... 71
Table IV-6 Composition of the flocs obtained by XRF ... 73
Table V-2 Portlandite content in hydrated cement paste from the DSC-TGA measurement ... 113
Table V-3 Total open porosity of cement pastes after 1 and 7 days ... 114
Table V-4 Crystalline phases proportions (%) obtained by Rietveld analysis on XRD diffractograms (pastes after 1 day)... 117
Table V-5 Crystalline phases proportions (%) obtained by Rietveld analysis on XRD diffractograms (pastes after 7 days) ... 117
Table V-6 Assignment of observed peaks for cured cement pastes (1 and 7 days) ... 128
Table VI-1 Geometry of the sample according to the testing method... 136
Table VI-2 Initial (IST) and final (FST) setting time of mortars by ASTM C403 . 139
Table VI-3 Average CTE of mortars under sealed conditions ... 150
List of figures
Figure I-1 Water droplets on the surface of hydrophobic mortar (left), and on a
cross-section (right)-integral water repellency. ... 4
Figure I-2 Research methodology. ... 7
Figure II-1 Cement production [20]. ... 10
Figure II-2 Cement classification. ... 12
Figure II-3 Hexagonal portlandite plates (left) and needle-like crystals of ettringite (right). ... 15
Figure II-4 Hydration kinetics of BFS cement [33]. ... 17
Figure II-5 Formation of hydration products with respect to hydration time [49, 50]. ... 19
Figure II-6 Schematic representation of electrical forces developed when a surface of a charged particle reacts in an aqueous solution (reproduced from [54]). ... 20
Figure II-7 Thixotropic behaviour and hysteresis loop. ... 21
Figure II-8 Effect of the hydrophobic treatment of the capillary pore (reproduced from [75]). ... 25
Figure II-9 Reaction mechanism between octyle-triethoxy silane and cement. .... 26
Figure II-10 Silane hydrolysis in basic and acid environments [78]. ... 27
Figure II-11 Post treatment water repellent vs. integral water repellent. ... 28
Figure II-12 Representation of the 3 types of surface hydrophobic treatment of cementitious materials: a) surface impregnation [with Si-material], b) surface sealing [organic film] and c) coating (reproduced from [86]). ... 29
plane. In an amorphous silica model the Si-O-Si bond angle may vary, but the Si-O distances are constant; each oxygen ion is linked to not more than two cations; the coordination number of oxygen ions about the control cation is 4 or less (reproduced from [130]). ... 34
Figure III-1 Formulas of octyltriethoxysilane and silicone resin. ... 37
Figure III-2 Schematic representation of a microcapsule dispersed in water: silicone resin is encapsulated in SiO2 shell. ... 38
Figure III-3 Setup for the electrical resistivity measurements at 4 points: yellow cables induce current of 50 mA at, 108 Hz, red cables connected to the electrodes for measuring the voltage. ... 44
Figure III-4 Penetration needle for setting time test ASTM C403. ... 46
Figure III-5 FreshCon-Ultrasonic device for elastic Young modulus evolution: left) Pulse generator (PIEZOMECHANIK HVP 1000-50) with computer and moulds with sensors for p and s waves, Right) Plexiglas/rubber mould with central sensors. ... 47
Figure III-6 ConSensor device for the continuous monitoring of mortar electrical conductivity. ... 49
Figure III-7 Correlation between the compressive strength and electrical conductivity of mortar reproduced from [153]. ... 49
Figure III-8 AutoShrink device for the measurements of autogenous deformation of mortars... 50
Figure III-9 Temperature cycle variation for CTE test on mortars. ... 51
Figure III-10 FTIR spectra with characteristic molecule bands vibrations of the emulsion, microcapsules and pure silicone resin (resin peak above correspond to the Si-O-C2H5). ... 54
Figure III-12 Particle size distribution of the microcapsules in volume % (up) and number % (bottom). ... 56
Figure III-13 DSC-TG thermograms of the silicone resin, emulsion and the microcapsules (TGA – dashed curve). ... 57
Figure IV-1 Methodology of the study on the resin delivery. ... 60
Figure IV-2 FTIR spectra of the C-H band vibrations related to the alkane molecules. ... 61
Figure IV-3 Droplet of alkaline solution with microcapsules. ... 64
Figure IV-4 Electrical resistivity of the suspension of microcapsules and calcium hydroxide saturated solution (T=20 °C). ... 67
Figure IV-5 Composition of the filtrated solution of the microcapsules in calcium hydroxide (T=20 °C) at different starting pH. After 240 minutes, the pH of both solutions was ≈10.5. ... 70
Figure IV-6 Aspect of the lime solution with the microcapsules in presence of cations after 24 h (T=20 °C): 1) limeM, 2) limeMCa2+, 3). limeMNa+. ... 71
Figure IV-7 Aspect of the 1M NaOH solution with the microcapsules in presence of cations after 24 h (T=20 °C): 4) SodM, 5) SodMCa2+, 6)SodMNa+. ... 72
Figure IV-8 XRD diffractogram of the flocs from limeM solution (after 24h of reaction). ... 73
Figure IV-9 Comparison of the FTIR spectra of the neat silicon resin (red) and the released resin from the dissolved microcapsules (blue). ... 75
Figure IV-10 FTIR spectra of the flocs from calcium hydroxide solution and of the resin from sodium hydroxide. ... 76
Figure IV-12 DSC thermograms of the flocs from the calcium hydroxide solution,
compared with the microcapsules and the neat resin. ... 78
Figure IV-13 Shematic representation of the stage I of the microcapsules dissolution by OH- in presence of Ca2+. Activation of the surface –OH groups of SiO2 shell. ... 80
Figure IV-14 Shematic representation of the stage II of the microcapsules dissolution by OH- in presence of Ca2+. Formation of the insoluble C-S-H layer at the surface of the shell is a result of Ca2+ incorporation on the shell active sites. ... 81
Figure V-1 Rheometer with rotational bob system. ... 88
Figure V-2 Flow behaviour of OPC cement pastes at various shear rates. ... 89
Figure V-3 Representation of cement particles flocculation upon mixing. ... 89
Figure V-4 Flow behaviour of BFS cement pastes at different shear rates. ... 90
Figure V-5 Setting time of different cement pastes with different admixtures, obtained with a Vicat-test. ... 92
Figure V-6 Hydration kinetics of cement pastes followed by the Isothermal conduction calorimetry. The results are normalized on the mass of cement. ... 94
Figure V-7 Total heat evolution for the cement pastes during 3 days. ... 96
Figure V-8. Sodium concentration in the interstitial solution... 98
Figure V-9 Potassium concentration in the interstitial solution. ... 98
Figure V-10 Concentration of Si in the interstitial solution ... 99
Figure V-11 Ca2+ concentration in the interstitial solution. ... 100
Figure V-13 ESEM images of the referent C1 cement at different hydration times. The development of the initial hydrates (C-S-H gel on the grain surface) is observed. 102
Figure V-14 ESEM images of C3 paste. Low hydration level is observed, with absence of dense ettringite. ... 102
Figure V-15 ESEM image of the BFS paste with the silane emulsion E. Retarding effect on the hydration is correlated with the increased and intensified formation of ettringite at early age. ... 103
Figure V-16 Microcapsules entrapped by the C-S-H network. Clear debris is seen. ... 104
Figure V-17 ESEM images of OPC pastes at 1 hour of hydration. ... 106
Figure V-18 ESEM images on BFS paste after 1h of hydration. Clear outline of the microcapsules is observed in C3M. Densely packed, short ettringite needles are favoured by silanes from emulsion (C3E), while long ettringite is observed in neat paste (C3). . 107
Figure V-19 DSC-TGA thermograms of cement pastes (OPC) with admixtures at 1 day. ... 108
Figure V-20 DSC-TGA thermogram of cement pastes (BFC) with admixtures after 1 day of curing. ... 110
Figure V-21 DSC-TGA thermograms of a) C1 and b) C3 pastes after 7 days. ... 111
Figure V-22 Pore size distribution forOPC and BFS cement pastes at 1 and 7 days of curing. ... 114
Figure V-23 XRD diffractograms of the OPC pastes after 1 day of curing: C1-blue, C1E- green and C1M-red. ... 116
Figure V-24 XRD diffractograms of the BFS pastes after 1 day of curing: C3-blue, C3E- green and C3M-red. ... 116
Figure V-26 SEM images of cement paste after 1 day: Left) Perpendicular growth of small portlandite in C3 paste, right) Precipitation of large portlandite crystals in spherical pore observed in C3E. ... 120
Figure V-27 CHS gel in cement matrix after 1 day: Unhydrated C3S in C-S-H with
isolated spherical pores in C1M. ... 122
Figure V-28 Wide range of sizes for the spherical pores (marked in ellipse) distributed in the C-S-H matrix of C1M (1d). The pores remained at the place of the dissolved microcapsule. ... 122
Figure V-29 SEM image of C1M after 1day. Spherical pores identified in the dense C-S-H gel. The size of the pores is given. ... 123
Figure V-30 SEM imagse of cement paste with the microcapsules after 7 days of curing. Left) Closed pores in C1M are indicated, Right) Pore sizes in C3M correspond to the sizes of the microcapsules... 124
Figure V-31 SEM image of cement pastes after 28 days: Left) Crystallization of portlandite in closed pore in C1E, Right) Spherical pores in C1M as a result of dissolved microcapsules. ... 124
Figure V-32 FTIR spectra of OPC (a) and BFS (b) cement pastes after 1 day of curing. ... 126
Figure V-33 FTIR spectra of OPC (a) and BFS (b) cement pastes at 7 days of curing. ... 127
Figure VI-1 Evolution of hydration and mechanical properties of mortars corresponding to OPC mortars. ... 133
Figure VI-2 Methodology of the study on the evolution of the mechanical properties with integral water repellents. ... 134
Figure VI-4 Cumulative heat of hydration of mortars with OPC and BFS cements. ... 138
Figure VI-5 Penetration resistance of mortars measured by ASTM C403. ... 139
Figure VI-6 Compressive strength of the mortar cubes measured by standard compression test for given curing time in hours. ... 140
Figure VI-7 Conductivity of mortar samples measured by ConSensor, a) mortars with OPC cement; b) mortars with BFS cement. Initial and final setting times (from ASTM C403) are presented as vertical dashed lines. ... 141
Figure VI-8 Compressive strength evolution recorded with ConSensor test device: Conductivity curve is calibrated with the results of the compressive strength on cube (markers) for each corresponding curing time. ... 142
Figure VI-9 Evolution of p-and s-waves velocities. ... 143
Figure VI-10 Early age evolution of Poisson ratio (νdyn) and dynamic E-modulus
(Edyn) of OPC (a) and BFS (b) mortars. ... 144
Figure VI-11 Autogenous deformation of OPC and BFS mortars with admixtures. Vertical and horizontal lines represent the time when the maximum shrinkage is reached. ... 146
Figure VI-12 CTE evolution of OPC (a) and BFS (b) mortars followed by AutoShrink device. ... 149
Figure VII-1 Capillary water absorption measured by NBN 480-5 standard method. ... 161
Figure VII-2 Aspect of the “attraction forces” between the water droplet and cement pastes after 1 day of curing. ... 162
Figure VII-3 Particle size distribution of anhydrous cements. ... 163
Abstract
For the last 10 years, silicone-based admixtures have been successfully used for bulk waterproofing treatment of cementitious materials. However, a reduction in mechanical properties of treated materials is rather observed and becomes a major problem for the in-situ application. A new concept of a knowledge-based integral water repellent has been designed in such a way that the negative effect on mechanical properties is significantly reduced. The technology comprises the delayed release of the hydrophobic agent (silicone resin) which is achieved by encapsulation of the resin in SiO2 shell. A
multidisciplinary research was conducted in order to propose a model of the delayed release and the silica shell reaction mechanism in cement paste. Therefore, a study on the microcapsules reaction in calcium hydroxide solution was conducted by means of FTIR, DSC-TGA, surface tension measurements and chemical analysis by ICP-OES. It was shown that microcapsules flocculate in presence of Ca2+, what appears to be the main factor that
contribute to the delayed release of the resin.
The influence of the microcapsules on Ordinary Portland (OPC) and Blast furnace slag (BFS) cement hydration process was compared with the emulsion of silane monomer and silicone resin. It was shown that the emulsion delays the setting and influences the early age hydration by prolonging the dormant period and decreasing the hydration heat. Cement microstructure and hydration products development was observed by SEM/ESEM. Quantitative analysis of hydration products was assessed by Rietveld analysis of XRD diffractograms. Emulsion induced a significant delay in the cement paste setting by changing the amount and morphology of ettringite and portlandite at very early age. Differently, microcapsules didn’t show any effect on these properties.
Moreover, it was showed that the microcapsules slightly influence autogenous deformation by increasing the shrinkage of mortars.
Microencapsulation of the silicone resin proved to be a promising solution for the bulk hydrophobic treatment of cementitious materials with no-influence on cement hydration.
Keywords: cement, hydration, bulk hydrophobic treatment, microencapsulation, silicone resin, structural properties.
Résumé
Au cours de ces dix dernières années, les additifs à base de silicone ont été utilisés avec succès afin d’améliorer l’imperméabilité à cœur des matériaux cimentaires. Cependant, la réduction significative des propriétés mécaniques des matériaux traités constitue le problème majeur pour cette application in-situ. Un nouveau concept a alors vu le jour. Celui-ci est entièrement basé sur des matériaux hydrofuges permettant de conserver de bonnes propriétés mécaniques. Le principe de cette technologie repose sur la libération tardive d’un agent hydrophobe (résine en silicone) grâce à l’encapsulation de cet agent dans une enveloppe de SiO2. Une étude multidisciplinaire a été menée pour proposer un
modèle simulant la libération retardée de l’agent hydrophobe ainsi que les mécanismes de réaction de l’enveloppe de silice dans une pâte de ciment. Plus spécifiquement, une étude sur la réaction de microcapsules dans une solution d’hydroxyde de calcium a été conduite au moyen de FTIR, DSC-TGA, mesures de tension de surface et par ICP-OES. Il a été démontré que les microcapsules floculent en présence de Ca2+, ce qui semble être le
principal facteur responsable de la libération progressive de la résine.
de la pâte cimentaire en changeant la quantité et la morphologie de l’ettringite et de la portlandite dès le tout début de la réaction. Par ailleurs, la présence des microcapsules ne montre aucune influence sur ces propriétés.
Un travail expérimental sur des mortiers a été réalisé de sorte à appliquer ce concept de libération tardive en tant que solution contre la dégradation des propriétés mécaniques. L’influence du nouvel additif sur les paramètres tels que le durcissement, le changement de volume, le module de Young dynamique et la résistance à la compression ont été analysés. De plus, des techniques expérimentales innovantes (AutoShrink, Ultrasonic Pulse Velocity and ConSensor) ont été couplées aux techniques d’essais plus traditionnelles (test de résistance à la pénétration et résistance à la compression sur des cubes). Les microcapsules ont réduit, avec succès, l’impact négatif des silanes sur la résistance à la compression ainsi que sur le module de Young dynamique. De plus, il a été démontré que les microcapsules influencent faiblement la déformation endogène en réduisant le retrait des mortiers.
La micro-encapsulation de résine de silicone a ainsi démontré qu’elle constitue une solution prometteuse pour le traitement hydrofuge à cœur des matériaux cimentaires sans pour autant avoir une influence sur l’hydratation du ciment.
Table of acronyms and abbreviations
OPC, Ordinary Portland Cement SEM/ESEM, Scanning electron microscopy/ Environmental Scanning electron microscopy
BFS, blast-furnace slag cement MIP, mercury intrusion porosimetry
C3A, tricalcium aluminate DSC-TGA, Differential-Scanning Calorimetry with
Thermo-Gravimetric Analysis
C3S, tricalcium silicate, Alite FTIR, Fourrier transformation infrared
spectroscopy
C2S, dicalcium silicate, Belite ICP-OES , Inductive coupled plasma-optical
emission spectrometry C4AF, calcium-tetra alumoferrite UPV, Ultrasonic Pulse Velocity
CS̄H2, gypsum Edyn [GPa], dynamic Young’s modulus
C-S-H, calcium silico hydrate Vs [m/s], shear wave velocity
C-A-S-H, calcium aluminate silicate hydrate Vp [m/s], compressional- wave velocity
AFt, Ettringite ρ [g/cm3], density
AFm, calcium aluminate monosulphate νdyn [-], Poisson’s ratio
CH, Portlandite CTE [µm/m/°C], coefficient of thermal expansion W/C, water to cement ratio R , Universal gas constant (R=8.314 J/mol/K) C/S, cement to sand ratio Ea [J/mol], apparent activation energy RH [%], relative humidity q [W/g], Heat flow
Θ [°], angle Q [J/g], Cumulative heat
Publication list
Within the scope of this thesis following papers have been published:
N. Milenković, J-P. Lecomte, S. Staquet, M-P. Delplancke : “Cement paste setting and early age hydration in presence of encapsulated and emulsified siloxane”, 2nd International
RILEM/COST Conference on Early Age Cracking and Serviceability in Cement-based Materials and Structures - EAC2 12–14 September 2017, ULB-VUB, Brussels, Belgium N. Milenković, J-P. Lecomte, B. Delsaute, M-P. Delplancke, S. Staquet: “Influence of silanes on the setting time and early age hardening of bulk hydrophobic mortars”, 2nd International
RILEM/COST Conference on Early Age Cracking and Serviceability in Cement-based Materials and Structures - EAC2 12–14 September 2017, ULB-VUB, Brussels, Belgium J-P. Lecomte, V. Fromond, M-J. Sarrazin, N. Milenković, C. Pierre: “Use of silicone resin emulsions as integral water repellent for mortar and fibre-reinforced cement boards (FRC)”, International inorganic-bonded Fiber Composites Conference, Fuzhou, China, 2016. N. Milenković, J-P. Lecomte, M-J. Sarrazin, C. Pierre, M-P. Delplancke: “New silicone resin-based integral water repellent for cementitious construction material” WEBINAR organized in the frame of the « European coating show reloaded », 2016.
N. Milenkovic, J-P. Lecomte, C. Pierre, M-P. Delplancke: “Getting under the skin- Examining silane-based integral water repellent and its impact on cement hydration”, Technical paper, European Coatings Journal, March 2015: p.102-105.
N. Milenković, S. Staquet, J-P. Lecomte, C. Pierre, M-P. Delplancke: "Non-ionic silane emulsion as integral water repellent – impact on cement hydration process" HYDROPHOBE VII, Proceedings of "7th International Conference on Water Repellent Treatment and Protective Surface Technology for Building Materials", Lisbon, Portugal, 2014.
N. Milenković, J. Carette, J-P. Lecomte, M-P. Delplancke, S. Staquet: "Continuous Monitoring of the Setting and Early Age Hardening of Mortars with Novel Integral Water Repellent". Proceedings of International Symposium on Environmentally Friendly Concrete - ECO-Crete, Reykjavik, Iceland, 2014: p.337-344.
Oral presentations:
International RILEM/COST Conference on Early Age Cracking and Serviceability in Cement-based Materials and Structures - EAC2, 12–14 September 2017, ULB-VUB, Brussels, Belgium
HYDROPHOBE VII, 7th International Conference on Water Repellent Treatment and Protective Surface Technology for Building Materials", 11-12 September 2014, Lisbon, Portugal.
General introduction
The general context of this study is the protection of construction cement-based materials (mortar, concrete) against water penetration. Cement is one of the most important materials used in the building and construction industry, beside wood and steel, due to its good functional characteristics and ease of application. However, many natural phenomena (rain, corrosive agents, extreme temperature variations, etc.) influence its performance over time [1]. One of the most detrimental effects on the structural properties of cementitious materials comes from water that is absorbed by the porous cementitious matrix. Absorbed water can freeze in the cementitious pore system, increase its volume and induce internal cracks. Consequently, it influences functional properties of cement and its products. Thus, protection of cementitious materials by post- or integral water-repellent treatment with hydrophobic agents appears to be a logical solution towards prevention of the functional problems. Among others, silanes are commonly used as hydrophobic agents in cementitious materials due to their good hydrophobic properties and compatibility with silica containing substrates.
Durability of the concrete structures in the framework of eco-efficiency had been evaluated and published by P. Mora [2]. According to him by increasing concrete durability from 50 to 500 years its environmental impact would be reduced by a factor of 10. Yu et al. [3] have discussed the economical aspect of the repair of concrete structures damaged by corrosion. The “Law of Fives” states that $1 spent on design and construction is equivalent to $5 spent as damage initiates and before it propagates, $25 once deterioration has begun to propagate, and $125 after extensive damage has occurred. Evidently, it is expected from the use of integral water repellent in cementitious materials to have positive influence on the economic and environmental issues.
The interest of the bulk hydrophobic treatment of cement-based materials, from the commercial point of view, is very high. Several companies provide additives for bulk treatment of cement based materials in the form of powder or emulsion. However, the lack of scientific data on the influence of those materials on specific steps of cement hydration raises the following question: what is the influence of these additives on the
This PhD thesis is done as a part of the NISHYCEM project that is carried out by a consortium between Université Libre de Bruxelles (ULB) and industrial partners from Belgium (Dow Corning, Prefer, Technichem, CRIC-OCCN), and is supported by the Walloon Region and GreenWin. The NISHYCEM project aims to develop a ready-to-use admixture for bulk hydrophobic treatment of cementitious materials. A new technology of bulk hydrophobic treatment of cement based materials was developed in order to reduce the negative effect that integral water repellents have on the mechanical properties.
Motivation for the research
The focus of this study is on the use of silicone-based hydrophobic agent for cementitious materials. In the past 40 years, silanes were successfully used as a hydrophobic material in the construction as surface protection. They are proven to attach to the cement hydration products with their non-hydrophobic part (-Si-O- group), positioning their hydrophobic tail (alkyl, phenyl) towards the pore walls. In such a way, the water is successfully repelled and its potential negative effects on the aesthetic and functional properties are decreased. The post-treatment of building materials by silane and siloxane water repellent is a proven protection method against water penetration [4-8]. For instance, silanes are the most beneficial in terms of water protection of concrete if applied after 28 days of concrete curing [9]. However, in many cases, this technique is not used due to the extra labor costs and complicated in-situ preparation of the substrate for post treatment application. Furthermore, it is influenced by climatic weathering [10].
Integral water repellent technology started to be used in the last 10 years in order to make the whole structure hydrophobic [5, 11-14]. Bulk hydrophobic treatment of cementitious materials may to be more attractive than surface treatments, which requires additional work for in-situ preparation. With bulk waterproofing, disadvantages of surface treatment, such as extra-work or impact of weathering, could be overcome.
Figure I-1 Water droplets on the surface of hydrophobic mortar (left), and on a cross-section (right)-integral water repellency.
If the surface is mechanically damaged (cracks, for example), bulk waterproofing is evidently an advantage as it retains its hydrophobic nature, while the treated surface would lose its property. Surface treatment is obtained thanks to the polymerization of the silane on the substrate. If the substrate is not well prepared for the treatment (clean surface, right humidity and influence of the weather conditions) it can lead to the unsuccessful reaction between the silane and cement. Also, the right thickness of the silane layer is sometimes hard to reach.. All aforementioned negative effects can be successfully avoided with bulk waterproofing of cement based materials.
Aim of the research
The fundamental understanding of the phenomena of bulk waterproofing of cementitious materials and understanding of the mode of action of a new delivery system is the objective of this thesis.
The present thesis has the purpose to contribute to the understanding of the influence of silane and silicone resin based integral water repellents on cement hydration. A new
“delivery system”, which refers to the way the active material (silane, silicone resin) is
formulated to enable its effective application, was developed such as to release the active material at a later stage of the cement hydration. A core-shell silica based
microencapsulation technology is used as a novel delivery system for the active agent.
Dow Corning internal studies have also demonstrated that higher molecular weight species obtained by hydrolysis and condensation of silanes (silicone resin) have higher efficiency as hydrophobic admixture and are expected to have lower impact on mechanical properties of cement matrixes. A new concept of a knowledge-based integral water repellent is tested in this work: novel silicon based ready-to-use admixture for hydrophobic treatment in bulk that keeps all functional properties of cementitious materials.
The use of silanes and siloxanes as hydrophobic agents for the post-treatment of cementitious materials is in the current scientific focus. However, the bulk water proofing of cement-based materials, as relatively new research field, raises many questions which need to be answered and also gives numerous possibilities for further research.
Methodology
The influence of delayed release integral water repellent (microcapsules) on cement hydration is compared to the benchmark silane emulsion. The study was conducted in several stages, as it is shown on Figure I-2.
Microcapsules
Lack of scientific data in the field of the use of the microencapsulation technology in building materials inspired a work on the study of the microcapsules dissolution in the artificial interstitial solution that is used to mimic the pore solution in cement. It is known that the kinetics of amorphous silica dissolution depends on the pH, temperature etc. However, the main focus was put on the type of cations in the alkaline solution and its influence on the microcapsule reaction with it. In order to assess this particular phenomenon, we observed the microcapsules dissolution in sodium and calcium hydroxide solutions. An influence on the surface tension of the suspension was observed. Moreover, the conditions necessary for the resin release are assessed.
Figure I-2 Research methodology.
Cement paste
An influence of the admixtures on the early age hydration of cement paste was studied. The microstructure development during hydration of OPC and BFS cements pastes with initial water to cement ratio of 0.5 was assessed. Cement pastes hydration degree and products were characterized by DSC-TGA and the XRD. Quantification of hydration products was done by applying Rietveld analysis on XRD diffractograms. Influence of the admixtures on size and morphology of hydration products was observed by SEM microscopy. Total open porosity and pore sizes distribution were analyzed by MIP. Stability of the additives in mature pastes were verified by FTIR.
products during early age hydration. This mainly comprises the first days of hydration, when the most important hydration reactions (formation of C-S-H, ettringite and portlandite) and physical changes (setting, porosity development) take place. Cement slurry flow behavior was investigated with rotational viscometer with two co-axial cylinders. Setting time was determined by automated Vicat needle test. Cement hydration kinetics during first 3 days was followed by Isothermal Conduction Calorimetry (ICC). During this period all important hydration steps are clearly seen (low reaction period has started). Furthermore, the stability of the additives in cement pore solution was observed, as well as its influence on the cement constituents and hydration products. Composition of cement paste pore solution was analyzed by ICP-OES. An influence of the admixtures on hydration products morphology during at very early age (first hour) is observed by ESEM during first hour of hydration.
Mortar
The exact time when the microcapsules release the resin is not a matter of one but several factors: microcapsule sizes distribution, pH and composition of the interstitial solution etc. A model of the active agent delayed release in cement matrix is aimed to be proposed and discussed in terms of its effect on mortars functional properties.
Cement
Cement is one of the most spread-out materials in building industry. Ordinary Portland cement (OPC) is made of milled cement clinker in which up to 5 wt. % of gypsum (CS̄H) or anhydrite is added as a set regulator. Cement clinker is a product of thermally treated raw materials (limestone, marl and clay) in a rotary kiln at 1450 °C. After firing, rapid cooling of the sintered mass is induced, resulting in a formation of a clinker rock. As a product of such treatment, cement clinker consists of several calcium silicate and aluminate phases which hydrate in contact with water, giving a high strength material.
Cement production process is presented in Figure II-1. It consists of 3 main phases:
1. excavation and preparation of raw materials, 2. grinding and firing of raw materials,
3. cooling, fine milling and packing.
Figure II-1 Cement production [20].
transported to the preheating tower, where it is being heated up to 700 °C, where the organic materials are burned and the transformation of limestone into lime takes place in a process of calcination. Pre-calcined raw mix enters the rotary kiln, where is being sintered at 1450 °C. High temperature induces chemical reactions and physical melting of the raw mix that changes raw mix into clinker. The next step in the production process is rapid cooling of the melted mix. This process is used to create clinker mineral phases [21] which define chemical properties of cement.
Cement clinker rock is mixed with gypsum (up to 5 wt.%) and further milled to powder in a ball mill. After the milling process, the obtained powder is stored in a storage silos. Such prepared material is called cement.
Cement is used as binder for the preparation of mortars and concrete [22]. Due to its hydraulic properties, cement hydrates in the presence of water. A series of reactions of hydration takes place which results in a formation of different calcium silico hydrates (C-S-H) and other hydration products.
II.1.1. Classification of cement
Figure I-2 Cement classification.
Cement paste and mortar
Cement paste is described as a dense suspension of cement particles in water [22]. Upon mixing with water, such a system is in the slurry state. Due to the fact that the cement is a hydraulic material, it reacts in water in a series of hydration reactions that lead to the stiffening of the suspension, formation of the porous solid skeleton and rise in the mechanical properties.
II.2.1. Cement hydration
In the literature, cement hydration is defined as a synthesis of all the changes that occur when anhydrous cement is mixed with water [22]. Cement hydration is a process where anhydrous cement reacts in contact with water through a series of exothermic hydration reactions. These reactions are accompanied by heat release and formation of hydration products that lead to the solidification.
Anhydrous cement consists of 4 main mineral phases, which hydrate in presence of water and gypsum.
C3S - tricalcium silicate (3CaO.SiO2)
This mineral phase is also known as alite. Alite is the most important cement phase constituent of Portland cement. Usually, 50 – 70 wt.% of cement clinker are C3S phase,
modified in composition and crystalline structure by ionic substitutions [22]. Hahn [23] reported that Ca2+ in C3S can be partially replaced by Mg2+, while Al3+ or Fe3+ cations can
replace both Ca2+ and Si4+ in certain extent. Taylor [22] described the alite polymorphs as
monoclinic (M1, M2, M3), triclinic (T1, T2, T3) and rhombohedral (R) form. Most common crystalline structures in cement are monoclinic polymorphs M1 to M3 [24], although other polymorphs can be present. However, the debate on the C3S polymorphs present in
cement is in scientific focus since the ’80s [25] as these polymorphs are difficult to distinguish by the XRD at low temperatures, due to very similar XRD patterns.
C3S is the most important phase for controlling the setting and early age hardening of
cement paste. In presence of water C3S reacts relatively quickly (over 12 to24h). C3S
reacts with water according to the following equation (Eq.1):
2C3S + 6H → C3S2H3 + 3CH ΔrH=-517 J/g (1)
The reaction between C3S and water is exothermal. Upon the contact with water, C3S
grains start to hydrate and produce C-S-H and portlandite. The dissolution of C3S grains
results in a release of Ca2+, OH- and SiO42- into the solution, which is partially transformed
into C-S-H on the surface on the C3S grain [22]. These reactions occur repeatedly until the
C2S – dicalcium silicate (2CaO.SiO2)
C2S is also known as Belite. Belite is a calcium silicate, present in about 15-30 wt.% in
Ordinary Portland cement. Its monoclinic crystal is often modified by ionic substitutions and its mostly under the β-polymorph form [26]. Belite from clinker usually contains 4-6 wt.% of oxides that can partially substitute CaO or SiO2. Main substituents are Al2O3 [27]
(Al3+ in tetrahedral sites) and Fe2O3. Moreover, in cements with high sulphate content, S6+
coupled with 2Al3+has a tendency to substitute 3Si4+ in the crystal [28]. Clinker high in
SO3 content is mostly prone to have high concentration of S6+ in C2S.
Belite reacts with water similarly to C3S. However, this reaction is the slowest one among
those of the main cement phases. The main hydration products during this exothermal reaction are C-S-H and portlandite (Eq.2):
2C2S+4H→C3S2H3 +CH ΔrH=-262 J/g (2)
C3A – calcium aluminate (3CaO.Al2O3)
Typical content of calcium aluminate in cement is around 6 wt. %. Pure calcium aluminate does not have polymorphic modification. However, two Na+ C3A can replace Ca2+ in C3A,
thus changing its crystalline system. Depending on the amount of the Na+ substituent, C3A
crystal system may vary from cubic (0-2.4 wt.% NaO), orthorhombic (3.7-4.6 wt.% NaO) to monoclinic (4.7-5.6 wt.% of NaO) [29]. Usually, in commercial clinkers, a mixture of C3A orthorhombic and cubic forms is mostly present.
In contact with water C3A hydrates very quickly, in the first 15 min. In presence of
gypsum, large number of water molecules reacts with C3A forming ettringite (Eq.3). This
reaction is highly exothermal (ΔrH=-1672 J/g). After all gypsum has been dissolved and
consumed, ettringite further reacts with remaining C3A and 4 molecules of water to
produce calcium aluminate monosulphate (AFm)(Eq.4):
C3A+3CS̄H2+26H→C6AS̄3H32 (Ettringite, AFt) ΔrH=-1672 J/g (3)
Figure I-3 Hexagonal portlandite plates (left) and needle-like crystals of ettringite (right).
Hydration kinetics of C3A is dependent on the concentration of gypsum: low amount of
gypsum will result in a faster hydration of the aluminate, and vice versa. This is due to the fact that SO42- is attaching to the aluminate grain, preventing water to rapidly hydrate the
grain. Furthermore, with higher gypsum content, more ettringite is produced, minimizing the conditions for the formation of AFm from AFt phase. These reactions are the main reactions that prevent the “false set” of cement paste that can have a negative impact on the development of cement paste’s mechanical properties at early age.
C4AF – calcium alumoferrite (4CaO.Al2O3.Fe2O3)
Scientists have investigated that C4AF hydrates in presence of water and gives the same
hydration products like C3A, under comparable conditions [30]. In presence of gypsum
and water, it hydrates to alumoferrite hydroxide ((A,F)H3, ferrite gel), AFt (Eq.5) and AFm
phase (Eq.6) [31]:
C4AF+ 3CS̄H2+ 29H→ C6(A,F)S̄3H32 + (A,F)H3 ΔrH=-418 J/g (5)
C4AF+ C6(A,F)S̄3H32 + 7H→ 3C4(A,F)S̄H12 + (A,F)H3 (6)
Under comparable conditions, the kinetics of these reactions is slightly lower compared to C3A. Its hydration kinetics is strongly dependent on Fe3+/Al3+ratio, due to the higher
Relative reactivity of cement phases is given in the following order: C3A>C3S>C2S≈C4AF.
However, as these minerals are prone to substitution of their metal ions by Na+, K+, Al3+,
Fe3+ and other, their absolute reaction rate can vary and depends of the nature of the
cationic species that were involved into the ionic substitution.
II.2.2. Cement hydration
Cement hydration is a coupled process of several chemical processes that occur at different rate. Hydration kinetics is determined by the nature of these processes and is influenced by the chemical composition of cement, water to cement (W/C) ratio, temperature and of the type of additives. These processes involve several reaction categories [22, 32-34].
Dissolution of calcium silicates and aluminates in presence of water considers the detachment of molecules of and ions from the surface of the solid cement compounds. The liberation of ions (Ca2+, Na+, K+, SO42-, SiO44+, OH-) into the pore solution raises the pH
of the system above 12,5 and enriches the liquid with highly mobile cations that further react to form hydration products [22, 35].
Diffusion is a transport of the cations and anions through the pore solution of cement paste away from the surface of the dissolving cement compounds [22, 36, 37]. During this process, dissolved ions in the solution diffuse along the adsorption layer on the surface of C3S, C2S, C3A and C4AF, where formation of the C-S-H is the most dominant reaction
[22]. As a result of the diffusion process, nucleation [38] of hydration products initiates precipitation and growth of solids in a series of reactions due to high concentration of dissolved ions [39]. Due to high mobility of dissolved ions, complexation and adsorption of different ions during cement hydration occur on the solid surfaces of cement compound or from the solution [40]. Accumulated ions can on the surface of hydrated phase induce further growth of precipitates.
Abovementioned reactions during cement hydration occur during long period, with different rates, taking into consideration the maturity of the hydrated cement paste. The rates of hydration reactions are mostly related to the hydration of C3A (and its reaction
with gypsum) and C3S at very early age (over 48 hours). These reactions can be explained
Hydration kinetics of blast furnace slag cement is presented in Figure I-4.
Figure I-4 Hydration kinetics of BFS cement [33].
Based on the hydration curve, cement hydration is described with 5 hydration stages, depending of the chemical processes that take place:
Stage I – Initial hydration
Initial reaction between cement and water involves dissolution and hydration of C3A and
C3S phases. When the water is added, gypsum firstly dissolves in an aqueous phase. At
the same time, cement minerals start to hydrolyse and dissolve, raising the Ca2+ and OH
-ions concentrat-ions in the solution. Raise in pH of the solution is a consequence of the dissolution of silicates and aluminates. The wetting of these phases provide a diffusion layer on the surface of the cement grain, that further enables an exchange of ions through the layer and formation of hydration products. The first hydration product at the surface of cement grains are amorphous aluminate and silicate gel [22, 41-43], that further grows. Beside this, reaction of gypsum with C3A in alkaline solution will produce
The metastable barrier hypothesis proposes that the decrease in the hydration reactions is caused by the continuous formation of a metastable layer of C-S-H on the cement grain, that passivates the surface by preventing water molecules to react with silicates and aluminates [44].
Stage II – Dormant phase (low hydration reactions)
After the initial very intense hydration of cement minerals, the reaction rate start to decrease. The dormant phase is the second hydration step that is described as a phase with low hydration reactions. The onset for the transition between the induction and the dormant stage is proposed with the slow dissolution hypothesis [33]. It takes into account the nucleation of the C-S-H and the supersaturation conditions of the solution as the controlling mechanisms for this transition. More specifically, a “superficially hydroxylated layer” [45] is forming on the surface of C3S and acts as a barrier that leads
to the decrease in the hydration rate. The dissolution rate of C3S decreases very rapidly
with an increase in concentration of Ca(OH)2. The supersaturation conditions in the
alkaline solution induce very fast nucleation and C-S-H on the surface of C3S. This is
followed by the very slow growth of C-S-H due to its low surface area at the very beginning of the reaction [33].
Stage III – Acceleration phase
The onset for the acceleration phase is a fast nucleation and growth of hydration products, mainly C-S-H and Ca(OH)2 (portlandite). The metastable layer of C-S-H on
hydrating cement minerals breaks as the osmotic pressure between the layer and the cement grain exceeds its critical value (due to oversaturation of the solution behind the layer). Nucleation and growth of the C-S-H and precipitation of portlandite that takes place as the concentration of Ca2+ is oversaturated in the pore solution. Growth of C-S-H
is rate-controlled by hydration of C3S and precipitation of portlandite [46]. The maximum
Stage IV – Deceleration phase
Deceleration phase takes place after the maximum of the hydration peak. It is related to the decrease in the rate of cement hydration and slow crystallization of hydration products, especially of C-S-H. Furthermore, the lack of SO42-, which is usually fully
dissolved and consumed by ettringite formation, increases the dissolution rate of remaining C3A [22]. As a result, ettringite further reacts with the remaining C3A to
produce AFm.
The second hydration peak maximum (Figure I-4, peak B) is related to the hydration of the blast furnace slag. Slag hydration releases less heat than cement, thus appearing as a separate peak or as a shoulder to the main hydration curve. Normally, slag doesn’t have hydraulic properties. However, in presence of Ca(OH)2, which acts as a main donor of OH-
ions, BFS reacts with cement silicates to form C-S-H during pozzolanic reaction [47]. BFS activation takes place when the pH of the aqueous phase is higher than 11.5 [48].
During deceleration phase, the development of the mechanical characteristics (strength, elastic properties etc.) takes place and continues until the material is fully hydrated.
Stage V – Curing
A period of slow hydration reactions takes place for a long time (for years) if additional water is available. This period is characterized by low diffusion rates.
II.2.3. Cement particles interaction during early age hydration – cohesion
II.2.3.1. Electric double-layer forces
Interaction between two hydrating cement particles is dependent on the electrical double layer forces (Figure I-6). These forces occur when the surface of two particles in aqueous media exhibit an electric charge. These electrical forces can be attractive or repulsive. When two cement particles are suspended in aqueous solution, if the repulsive forces between the particles dominate, the system will have good flowing properties [51]. This is the case during first hours of cement hydration, before the setting. At this time, cement particles are attracting Ca2+ and OH- ions, which are forming the first electric layer on
their surface. The first electric layer attracts other Ca2+ and OH- ions from the solution,
which thickens the layer around the particle [52]. As the ionic layer becomes thicker, the electro‐ static force of the particles declines [53]. This mainly occurs due to the formation of the C-S-H on the surface of hydrating particles increasing the distance from the surface of the charged particle.
Figure I-6 Schematic representation of electrical forces developed when a surface of a charged particle reacts in an aqueous solution (reproduced from [54]).
II.2.3.2. Rheology of cement paste
However, with certain shear applied to the slurry cement particles start to move and the suspension begin to flow. The property of a material to start to flow under certain shear stress is called thixotropy (Figure I-7).
Figure I-7 Thixotropic behaviour and hysteresis loop.
Thixotropic behaviour (Eq.7) of cement paste is usually described by the Bingham model [55]:
𝜏 = 𝜏0+ 𝜇𝛾𝑛 (7)
Where τ is shear stress, τo is a yield stress, µ is the plastic viscosity, γn the shear rate.
Thixotropic behaviour of cement paste is directly related to cement or cement-polymer-cement interaction. Upon mixing with water, cement slurry is considered as a colloidal dispersion of particles in alkaline medium [56]. Particles are being linked by C-S-H, which transforms the “colloidal dispersion” into “coagulated cement particles” [57]. The term “coagulation” describes cement particles that comes into contact for some time. As they are interconnecting by the first C-S-H and ettringite, some force is required to separate them.
II.2.4. Setting and hardening
hydration products, leading to the initial and final setting (loss of plasticity). This results in the development of a porous skeleton during the setting and hardening.
Pore system in cement paste is a product of particle interconnection during cement hydration. Its development strongly depends on the hydration degree and the morphology of the hydration products [58]. Long AFt needles, for example, extends the distance from two cement particles thus increasing porosity. Higher W/C ratio generally increases the total porosity of cement paste [59].
Chemistry of silanes and siloxanes. Interaction with cement
II.3.1. Silanes and siloxanesSilanes are molecules based on 1 silicon atom with the general formula (SiRn).
A silane that contains at least one carbon-silicon bond (≡Si- CH3) is known as an
organosilane. [60, 61]. The bond between Si and C atom is characterized as very stable, very non-polar. Presence of the methyl group in the molecule, leads to the molecule with low surface tension.
Silanes reactivity depends on the nature of the hydrolysable group that is linked to the silicon atom: chlorosilanes, silazanes, alkoxysilanes and acyloxysilanes [62]. Among others, alkoxy silanes, and especially alkyl-alkoxy silanes are commonly used as hydrophobic agents for cementitious materials due to their ability to react with the silica containing substrates at the room temperature [62].
The general formula of alkyl alkoxy silanes is given with the following formula:
RnSiX(4-n)
Rn is an alkyl chain, non-hydrolysable hydrocarbon that can be alkyl, aromatic,
II.3.2. Silicone resins
Highly branched siloxanes obtained by hydrolysis and condensation of silane are called “silicone resins” [63]. These materials can be defined as highly-branched of cross-linked “polymers” in which silicon atom is directly bonded to the carbon atom (alkyl, phenyl group), with at least one oxygen atom connected to the silicon atom. Silicones are often described as hybrids between organic and inorganic compounds, more specifically between organic polymers and silicates. The organic nature of the silicone comes from the Si-C bond, while they are given an inorganic character due to the Si-O-Si bond, also present in silicates. This particular characteristics lead silicones to be used in the construction industry, especially for the treatment of inorganic materials. The structure of silicone resin is schematically represented as follows:
, where R represents the alkyl chain. In general, resins can contain mono- (M), di- (D), tri- (T) and quaternary- (Q) functional units. M, D, T, Q units differ by the number of oxygen atoms connected to the Si atom. A silicone resin needs to contain a majority of T or Q units.
Silicone resins are highly branched. This is due to the fact that monomers (silane) can easily interlink between each other with their reactive groups. Silicone resins are made with a majority of tri- and tetra- functional silanes which leads to the formation of a network of high-molecular weight and highly branched species.
Silicones have a high permeability to oxygen and water vapour, although the liquid water is not capable of wetting a silicone surface due to its hydrophobic properties. Thus, they prove to be a successful candidate for the hydrophobic treatment of cementitious materials. Moreover, silicones show an outstanding weathering resistance with their low reactivity towards the polluted air and water and high UV resistance.
II.3.3. Silane admixture
Silanes can be introduced as integral water-repellents in cementitious materials (mortar, concrete) in the form of neat additive [64-68], emulsion or powder [69, 70]. Silicones and its derivate are insoluble in water, thus making an oil-in-water emulsion a very suitable delivery system.
Silane emulsion is a heterogeneous system consisting of immiscible silane dispersed as a droplet in other immiscible system. Its stability, however, may be poor if the silane droplet is not properly stabilized (silane hydrolyse in water) [71-73]. As the silane droplets are very small, the interfacial area is very large comparing to the droplet volume. The reactivity of the silane makes emulsion instable. To prevent this, an emulsifier (surfactant) is used. Surfactants have the ability to accumulate at the oil/water interface, creating the energy barrier against flocculation and droplet coalescence [71]. If properly formulated, silane can be homogeneously dispersed in the delivery substrate and form stable oil-in-water dispersion.
Hydrophobic treatment of cementitious materials
Hydrophobicity is defined as a property of a surface to repel water. The origin of the word is in Greek language, where hydro means water and phobicity means lack of affinity. Scientific community accepted definition of hydrophobicity as the following: a surface is hydrophobic when its static water contact angle θ is over 90°, otherwise it is hydrophilic (θ<90°) [74].
𝛥𝑃 =2𝛾𝑐𝑜𝑠𝜃
𝑟 (8)
Figure I-8 Effect of the hydrophobic treatment of the capillary pore (reproduced from [75]).
The contact angle between water and untreated cement is very small (θ <90°) due to the molecular attraction between the cement and water molecule. Water easily spreads on the surface and is sucked by the interconnected pores. The weakening of the interaction force between water and the cement surface, results in an increase of the contact angle (θ >90°). Water-repellent effect is achieved by hydrophobic treatment of the material [76].
mN/m) [77]. The surface tension of triethoxy silane varies from 22.15 mN/m at 10 °C to 20.80 mN/m at 25 °C) [77].
II.4.1. Reaction of silanes with cement
Silanes react with cement in a series of processes of hydrolysis and condensation. Detailed description of the silane, siloxane and silicone resin bonding to the inorganics can be found in [78].
Hydrolysis and condensation of silanes can be described by three main reactions:
≡Si-OR + H2O ⇄ ≡Si-OH + ROH (1)
≡Si-OH + ≡Si-OH ⇄ ≡Si-O-Si≡ + H2O (2)
≡Si-OR + ≡Si-OH ⇄ ≡Si-O-Si≡ + ROH (3)
Mechanism of n-octyltriethoxysilane reaction with the silica containing substrate is given in Figure I-9.
Figure I-9 Reaction mechanism between octyle-triethoxy silane and cement.
