fe-containing hydrates and their fate during cement hydration: thermodynamic data and experimental ...

8/21/2019 Fe-Containing Hydrates and Their Fate During Cement Hydration: thermodynamic data and experimental study

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Fe-containing hydrates and their fate during cement

hydration: thermodynamic data and experimental

study

THSE NO 5262(2011)PRSENTE le 07 DECEMBRE 2011

LA FACULTE SCIENCES ET TECHNIQUES DE L'INGNIEUR

LABORATOIRE DES MATRIAUX DE CONSTRUCTION

PROGRAMME DOCTORAL EN STRUCTURES

COLE POLYTECHNIQUE FDRALE DE LAUSANNE

POUR L'OBTENTION DU GRADE DE DOCTEUR S SCIENCES

PAR

Belay Zeleke Dilnesa

accepte sur proposition du jury:

Prof. Nava Setter, prsident du jury

Prof. Karen Scrivener, Dr. Barbara Lothenbach, directeur de thse

Dr. Guillaume Renaudin, rapporteur

Dr. Thomas Matschei, rapporteur

Dr. Paul Bowen, rapporteur

Propose en decembre, 2011


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ABSTRACT

Thermodynamic modeling is a versatile tool for predicting the chemical composition

cement during the hydration of cement. The quality of the thermodynamic modeling

depends directly on the quality and completeness of thermodynamic database used. One

of the main limitations of modeling the hydration of cement is the lack of thermodynamic

data for Fe containing hydrates. In addition, the formation of solid solutions between Fe-

and Al-containing hydrates could stabilize mixed solids. However, it is unclear to what

extent such solid solution formation occurs. Also experimentally it is very difficult to

identify Fe-containing hydrates in hydrating cements by standard analytical techniques as

the signals from Fe-containing phases significantly overlap with those from the

corresponding Al-containing phases.

Thus, in this study, potential Fe-containing hydrates like Fe-hemicarbonate (Fe-Hc), Fe-

monocarbonate (Fe-Mc), Fe-monosulphate (Fe-Ms), Fe-Friedels salt (Fe-Fr), Fe-

strtlingite (Fe-St), Fe-katoite (C3FH6) and Fe-siliceous hydrogarnet (Fe-Si-Hg) weresynthesised at 20, 50 and 80 C. The solid phases were characterized by X-ray powder

diffraction (XRD), Thermogravimetric analysis (TGA), scanning electron microscopy

(SEM), vibrational spectroscopy (Raman and Infrared spectroscopy) and Extended X-ray

absorption fine structure spectroscopy (EXAFS). The compositions of the liquid phases

were analyzed using inductively-coupled plasma optical emission spectrometry and mass

spectrometry (ICP-OES and MS). At ambient temperature Fe-Mc, Fe-Ms, Fe-Fr and Fe-

Si-Hg were stable, while Fe-Hc, Fe-katoite and Fe-St were metastable. Fe-Mc, Fe-Ms,

Fe-Fr and Fe-Si-Hg were stable also at 50, but the Fe-AFm phases were unstable at 80

C while Fe-Si-Hg were stable up to above 100 C.


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The measured composition of the liquid phase was used to calculate the solubility

products at 20 and 50 C and to derive the data for standard conditions (25 C, 1 atm).

The solubility products of Fe-Fr was similar to the solubility product of Al-Fr, while the

solubility products of Fe-Mc and Fe-Ms were about 3 log unit lower than that of Al-Mc

and Al-Ms indicating that in Fe-Friedels salt is probably not stable in cements. The very

low solubility product of Fe-Si-Hg (5 to 7 log units lower than that of Al-Si-Hg) implies

that Fe-Si-Hg could be a stable phase in hydrated cements.

Also the mixed Al- and Fe-containing hydrates were synthesized to study the extent of

solid solution formation. Both XRD and thermodynamic modelling of the liquid

compositions indicated that Al- and Fe-monosulphate and Al- and Fe-Friedels formed

solid solutions with a miscibility gap, while Al- and Fe- monocarbonate existed as two

separate hydrates due to their different crystal structure (Al-Mc: monoclinic, Fe-Mc:

rhombohedral). The formation of solid solution between Al and Fe-siliceous hydrogarnet

seemed probable.To understand to what extent the findings from the synthesised hydrates were relevant for

real cements, the speciation of iron was determined in hydrating cement using EXAFS

spectroscopy. Identification of Fe-containing hydrates and quantification of their

contributions was achieved by combining principal component analysis with iterative

target tests, and linear combination. The results show that several Fe species already

contributed to the overall Fe K-edge spectra of cement pastes during the first day of

hydration. While ferrite was the dominant Fe-containing phase in the unhydrated cement,

Fe-hydroxide was detected shortly after starting the hydration process. With time the

formation of stable Al/Fe-siliceous hydrogarnet was observed, while the amounts of Fe-

hydroxide and ferrite clinker slowly decreased. The latter finding agrees with results from


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thermodynamic modeling of the hydration process, which predicts formation of stable

Al/Fe-siliceous hydrogarnet in cement system.

The determination of the solubility products of these hydrates will help to extend the

thermodynamic data base of cement minerals and establish whether and to which extent

Fe-containing hydrates are stable in fresh and in leached cementitious systems. The

results from this study on the Fe speciation in cementitious systems are important for a

better understanding of cement-water interactions with a view to the durability of

cementitious materials.

Keywords: Fe-containing hydrates; solubility product; solid solution; crystal structure;

thermodynamic modeling; thermodynamic data


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ZUSAMMENFASSUNG

Thermodynamische Modellierung ermglicht die Mineral-Zusammensetzung von Zement

whrend der Hydratisierung zu berechnen. Die Qualitt der Modellierung hngt dabei

stark von der Qualitt und der Vollstndigkeit der verwendeten thermodynamischen

Datenbanken ab. Eine wesentliche Einschrnkung bei der Modellierung der

Hydratisierung von Zement ist das Fehlen von thermodynamischen Daten fr die

eisenhaltigen Zementhydrate. Zudem knnte die Bildung von festen Lsungen (solid

solution) von Fe- und Al-haltigen Hydraten gemischte Festphasen stabilisieren. Zurzeit

ist allerdings nicht bekannt, ob und in welchem Ausmass diese festen Lsungen

entstehen. Die Identifikation der eisenhaltigen Hydrate in Zementstein mittels

Standardtechniken ist sehr schwierig, weil die charakteristischen Signale der Fe-haltigen

Phasen oft stark mit denjenigen der Al-haltigen Phasen berlappen.

In dieser Studie wurden potentiell Fe-haltige Hydrate, wie Fe-Hemikarbonat (Fe-Hc), Fe-

Monokarbonat (Fe-Mc), Fe-Monosulfat (Fe-Ms), Fe-Friedels Salz (Fe-Fr), Fe-Strtlingit(Fe-St), Fe-katoite (C3FH6) und Fe-Si-Hydrogranat (Fe-Si-Hg), bei 20, 50 und 80 C

synthetisert. Die Festphasen wurden mittels Rntgenpulverdiffraktometrie (XRD),

Thermo-gravimetrie (TGA), Raserelektronenmikroskopie (SEM), Raman und Infrarot-

Spektroskopie, und synchrotron-basierter Rntgenabsorptionsspektroskopie (EXAFS)

charakterisiert. Die Zusammensetzung der Flssigphase wurde mittels induktiv

gekoppelter Emissions-spektroskopie mit optischer oder massenspektrometrischer

Detektion (ICP-OES oder MS) bestimmt. Die Untersuchungen zeigen, dass bei

Raumtemperatur Fe-Mc, Fe-Ms, Fe-Fr und Fe-Si-Hg stabil sind whrend Fe-Hc, Fe-

katoite und Fe-St metastabil sind. Fe-Mc, Fe-Ms, Fe-Fr und Fe-Si-Hg sind auch bei 50 C


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stabil. Die Fe-AFm Phasen sind nicht stabil bei 80 C whrend Fe-Si-Hg bis 100 C

stabil ist.

Die gemessenen Lsungszusammensetzungen wurden verwendet um die Lslichkeits-

produkte der Festphasen bei 20 C und 50 C und die thermodynamischen Parameter

unter Standardbedingungn (25 C, 1 atm) zu berechnen. Das Lslichkeitsprodukt von Fe-

Fr ist vergleichbar mit demjenigen der entsprechenden Al Phase (Al-Fr) whrend die

Lslichkeits-produkte von Fe-Mc und Fe-Ms etwa 3 Grssenordnungen tiefer liegen als

diejenigen von Al-Mc und Al-Ms. Dies deutet darauf hin, dass Fe-Friedels Salz in

hydratisiertem Zement wahrscheinlich nicht stabil ist whrend Fe-haltige AFm Phasen

sich bilden knnten. Das sehr tiefe Lslickeitsprodukt von Fe-Si-Hg (5-7 logarithmische

Einheiten tiefer als dasjenige von Al-Si-Hg) impliziert, dass Fe-Si-Hg in hydratisiertem

Zement eine stabile Phase ist.

Im Weiteren wurden gemischte Al- und Fe-haltigen Hydrate synthetisiert um die

Mglichkeit der Bildung von festen Lsungen (solid solution) zu untersuchen. SowohlXRD Messungen an den Festphasen wie auch die thermodynamische Modellierung der

Lsungszusam-mensetzung zeigen, dass Al-/Fe-Monsulfat wie auch Al-/Fe-Friedels Salz

feste Lsungen mit und ohne Mischungslcke bilden whrend die Al-/Fe-Monokarbonate

aufgrund der unterschiedlichen Kristallstrukturen (Al-Mc: monoklinisch, Fe-Mc:

rhomboedrisch) als zwei separate Hydrate existieren. Mglicherweise findet auch die

Bildung einer festen Lsung bei Al-/Fe-Si-Hydrogranat statt.

Die Speziation von Fe wurde mittels EXAFS Spektroskopie in hydratisiertem Zement

bestimmt um festzustellen, ob die Resultate aus den Untersuchungen mit Einzelphasen

auch auf reale Zementsysteme bertragen werden knnen. Durch Faktoranalyse

(principal component analysis, iterative target transformation) und Linearkombination


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konnten die Fe-haltigen Hydrate im Zementstein identifiziert und deren Anteile

quantifiziert werden. Die Resultate zeigen, dass bereits nach einem Tag Hydratisierung

des Zements mehrere Fe Spezies zum EXAFS Spektrum von Zementstein, das an der Fe

K-Kante bestimmt wurde, beitragen. Whrend Ferrit die dominierende Fe Spezies im

unhydratisierten Zement ist, erfolgte bereits kurz nach Beginn des

Hydratisierungsprozesses die Bildung von Fe-Hydroxid. Mit der Zeit wurde die Bildung

von stabilem Al/Fe-Si-Hydrogranat beobachtet, whrend die Anteile von Ferrit und Fe-

Hydroxid langsam abnahmen. Diese Beobachtungen stehen im Einklang mit der

thermodynamischen Modellierung, welche die Bildung von stabilem Al/Fe-Si-

Hydrogranat in Zementstein voraussagt.

Die Bestimmung der Lslichkeitsprodukte der einzelnen Hydratphasen ermglicht es die

bestehende, thermodynamische Datenbasis fr Zementmineralien zu erweitern und eine

quantitative Beurteilung, ob und in welchem Ausmass Fe-haltige Hydrate in frischen und

gealterten Zementsystemen stabil sind, vorzunehmen. Die Resultate aus dieser Studie zurSpeziation von Fe in Zement sind fr ein besseres Verstndnis der Wechselwirkung von

Wasser und Zement wichtig und damit fr die Beurteilung der Dauerhaftigkeit von

zementartigen Materialien von grosser Bedeutung.

Stichworte: Eisenhaltige Hydratphasen, Lslichkeitsprodukt, Feste Lsungen,

Krystallstruktur; thermodynamische Modellierung; thermodynamische Daten


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ACKNOWLEDGEMENT

First I would like to thank Swiss National Foundation (SNF) for financial assistance

during my study. I owe my deepest gratitude to my thesis supervisor and director Dr.

Barbara Lothenbach, EMPA for excellent supervision. The thesis would not have been

possible without the assistance and guidance of her. I will never find words to thank her

for sharing her time. All you have done for me as a supervisor and as a friend are

unforgettable.

I would like to express my sincere acknowledgement to my thesis director Prof. Karen

Scrivener for all the supervision, supports and valuable discussion throughout my thesis.

It has been a great pleasure to be a member of her team and work together with her.

It is with immense gratitude that I acknowledge my co-supervisor Dr. Erich Wieland, PSI

Switzerland for teaching and guiding me during my study in particular on EXAFS

techniques. He has made available his support all the time.

It gives me great pleasure in acknowledging the support and help of Dr. Guillaume

Renaudin and Dr. Adel Mesbah for synchrotron X-ray diffraction and Raman

measurements and data analysis. I would like to thank many people who have helped me

through the completion of this dissertation: Dr. Rainer Daehn for his assistance on XAS,

Dr. Adrian Wichser for ICP measurement, Dr. Gwenn La Saout for Rietveld refinement,

Dr. Mohsen Ben haha and Florian Deschner for assisting me on the SEM measurement,

Dr. Frank Winnefeld for all the valuable discussions. Dr.Gril Mschner preparation for

old samples and Dr. Konstantin Rozov for Fe-hydrotalcite sample.


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I owe to thank all the laboratory technicians at EMPA particularly Luigi Brunetti, Boris

Ingold and Angela Steffen for helping me in the laboratory. I would like to thank all my

members of lab 135. who have given me love and respect thought my study. All the good

times with friends (Wolfi, Walti, Lucy, Flo, Laura) are memorable.

Many thanks to Trindler family for their care during my stay in Switzerland. My

gratitude goes to my Ethiopian friends living in Switzerland who has given me their

encouragement, care and affection during my study.

Most especially I am grateful to my family particularly my mother Tiruwork and my

father Zeleke for giving me all their cares and love throughout my life. Their support and

inspiration as a parent from my childhood up to now is immense. This is for you.

Last but not least this work is not possible without the support, love, care of my wife

Fasika. Thanks to the almighty God for all you have done for me.


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LIST OF TABLES

Table 1 Oxide and the phase composition of the cements used. ...................................... 17

Table 2 The compositions of the synthetic Fe-cement mixes with varying gypsum(CsH2) and calcite (Cc) content. ............................................................................... 18

Table 3 Reference reactions used to estimate unknown heat capacities of cementminerals. .................................................................................................................... 25

Table 4 Dissolution reaction used for thermodynamic calculation. ................................. 29

Table 5 Thermodynamic data at standard conditions (298 K, 1 atm) used for thecalculation of the liquid phase compositions and for computation ofthermodynamic parameters for the synthesized solids. ............................................ 30

Table 6 Multi pattern refinement (from two sample-to-detector distances: 1/ 150 mm,and 2/ 350 mm) and crystal data of Fe-Mc. .............................................................. 43

Table 7 Fractional coordinate of non hydrogen atoms and isotropic displacement ......... 45

Table 8 Selected interatomic distances () in Fe-Mc. ...................................................... 45

Table 9 EXAFS structural parameters of Fe-Mc equilibrated for three years. ................. 48

Table 10 IR vibrations of Ca4[(AlxFe1-x)2(OH)12].CO3

.nH2O. .......................................... 53

Table 11 Measured ion concentrations and calculated solubility products at differentequilibration times. ................................................................................................... 57

Table 12 Compositions of Al/Fe-monocarbonate after synthesis at 20 C equilibratedfor 3 years at supersaturated and undersaturated condition. ..................................... 58

Table 13 Thermodynamic parameters of carbonate containing AFm phases atstandard conditions (25C, 1 atm). ........................................................................... 61

Table 14 Quantitative phases analyses from Rietveld refinement. ................................... 71

Table 15 Refined structural parameters of Fe-monosulfate (standard deviation in

parentheses). .............................................................................................................. 71

Table 16 Refined interatomic distances in Fe-monosulfate (standard deviation isgiven in parentheses). ................................................................................................ 74

Table 17 Measured ion concentrations and calculated solubility products at differentequilibration times. ................................................................................................... 81

Table 18 Thermodynamic parameters of Fe-monosulfate at standard conditions(25C, 1 atm). ............................................................................................................ 83


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Table 19 Compositions of Al/Fe-monosulfate after synthesis at 20C equilibrated for680 days in supersaturated condition. ....................................................................... 85

Table 20 Solubility products of all the solids formed during the synthesis of Al/Fe-monosulfate solid solution series at 20 C equilibrated for 680 days undersupersaturated condition. .......................................................................................... 87

Table 21 Refined structural parameters of 3CaO.Fe2O3.CaCl2.10H2O (standarddeviation is given in parentheses). ............................................................................ 97

Table 22 Measured ion concentrations and calculated solubility products at 20 C andsampled after different equilibration times synthesized from FeCl3.6H2O andCaO in 0.1M K OH. ................................................................................................ 102

Table 23 Measured ion concentrations and calculated solubility products at 20 and50C and sampled after different equilibration times synthesized from C2F,

CaCl2.2H2O and CaO in distilled water and in 0.1 M KOH. .................................. 102

Table 24 Thermodynamic parameters of Friedels salt at standard conditions (25 C, 1atm). ........................................................................................................................ 104

Table 25 Compositions of Al/Fe-Friedels salt synthesized at 20C and equilibratedfor 270 days under supersaturated condition. ......................................................... 105

Table 26 Measured ion concentrations at different equilibration times in 0.1 M KOH . 114

Table 27 Thermodynamic parameters at standard conditions determined in this study(25C, 1 atm). .......................................................................................................... 116

Table 28 Measured concentration of mixed C3AH6-C3FH6systems equilibrated forthree years ............................................................................................................... 121

Table 29 Measured ion concentrations in the solution of solids synthesized at 110Cand re dissolved and equilibrated for 4 months at 20 C and 50 C. ...................... 126

Table 30 Refined structure parameters of Fe siliceous hydrogarnet (standardsdeviation are indicated in parentheses). .................................................................. 133

Table 31 Measured ion concentrations of solids synthesized at 110 C (re dissolved

and equilibrated for 4 months at 20 C and 50 C) and at 20 C(equilibrated for 3years under oversaturated condition). ..................................................................... 134

Table 32 Measured ion concentration of Ca3(AlxFe1-x)2(SiO4)(OH)8equilibrated forfour months from dissolution (undersaturation) experiment. ................................. 140

Table 33 Summary of the results obtained in chapter 3 and comparison with their Al-analogues. ................................................................................................................ 146

Table 34 Relative weights of Fe-containing phases in hydrated OPC at 20 C and 50C obtained from LC fitting. ................................................................................... 165


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Table 35 Relative weights of Fe-containing phases in HS hydrated at 20 C and 50 Cobtained from LC fitting. ........................................................................................ 166


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LIST OF FIGURES

Fig. 1 Calculated volume changes during the hydration of OPC. ...................................... 5

Fig. 2 Calculated (lines) and measured (dots) composition of the liquid phase ofordinary Portland cement during hydration [6]. ......................................................... 5

Fig. 3 A sample of edges and the corresponding electronic transitions [25]. ..................... 8

Fig. 4 Sample XAS Spectrum of FeO with XANES and EXAFS region [26]. .................. 9

Fig. 5 Time-dependent XRD pattern of Fe-Hc (and Fe-Mc) synthesized at 20 C; C2F:2CaOFe2O3, Fe-Mc: Fe-monocarbonate, Fe-Hc: Fe-hemicarbonate. ...................... 38

Fig. 6 TGA and DTG curves of Fe-Hc formation at 20 C for different equilibrationtimes. CH: Portlandite, C: carbonates. ...................................................................... 38

Fig. 7 Time-dependent XRD pattern of Fe-Mc formed at 20 C. * unidentified ............. 40

Fig. 8. TGA and DTG curves of Fe-Mc formation at 20 C for different equilibrationtimes. CH: Portlandite, C: carbonates. ...................................................................... 41

Fig. 9 Comparison of XRD pattern of Fe-Mc equilibrated for one year at 20, 50 and80 C. CH: portlandite, C: carbonate, Fe2O3: hematite. ............................................ 42

Fig. 10 Rietveld plot from powder pattern recorded with a sample-to-detector distanceof 150 mm (red crosses are experimental data, black line is calculated pattern,

blue line is the difference pattern, green sticks are Bragg peaks positions for Fe-Mc and calcite). ......................................................................................................... 44

Fig. 11a. Projection of the Fe-Mc structure along b axis (the interlayer part of thestructure is ordered for clarity; i.e. the statistical distribution between onecarbonate and two water molecule has been alternatively ordered). b. 3Dcohesion in Fe-Mc structure (representation of the main hydrogen bonds). ............ 46

Fig. 12. Fe K-edge EXAFS data of Fe-Mc: Experimental (solid line) and theoretical(dots) Fourier transform (modulus) obtained from k3-weighted, normalized,background-subtracted spectrum (inset). .................................................................. 47

Fig. 13 a) Raman spectra on Fe-Mc in the frequencies range 200 cm -1 1800 cm-1b)Raman spectra on Fe-Mc in the frequencies range 2800 cm-1 4000 cm-1. ............. 49

Fig. 14 SEM micrographs of Fe-Mc. ................................................................................ 50

Fig. 15 Thermal analysis (DTG and TGA) of Ca3(AlxFe1-x)2O3.CaCO3.nH2O. ............... 51

Fig. 16 IR spectra of Al-Mc and Fe-Mc. .......................................................................... 52


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Fig. 17 XRD pattern of the Al/Fe-Mc after 3 years hydration time at 20 C * peak dueto additional water in Mc. ......................................................................................... 54

Fig. 18 Layer thickness for Al-Mc and Fe-Mc after refinement by Le Bail fitting andRietveld analysis. C4FcH12: Fe-Mc, C4AcH11: Al-Mc. ............................................. 55

Fig. 19 Values of a-parameters for Al-Mc and Fe-Mc. .................................................... 55

Fig. 20. Calculated solubility products of Fe-Mc and Fe-Hc from the solubilityexperiments. Squares: experimental solubility product of Fe-Hc, Triangles:experimental solubility product of Fe-Mc. ............................................................... 60

Fig. 21 Measured (symbols) and calculated (lines) concentrations in the liquid phasesof the synthesized monocarbonate at different Al/Al+Fe ratios. .............................. 62

Fig. 22 Changes in the total volume of phases of a hydrated model mixture consisting

of Al2O3, Fe2O3and a fixed SO3/(Al,Fe)2O3ratio of 1 as a function of the calcitecontent (CO2/(Al,Fe)2O3ratio) at 20 C at constant amount of solids: (Al2O3+Fe2O3+ CaSO4+ CaO + CaCO3). ............................................................................ 63

Fig. 23 XRD pattern of C4FsH12 formed at 20 C after different equilibration times. ..... 68

Fig. 24 TGA and DTG curves of C4FsH12 formation at 20C after differentequilibration times. ................................................................................................... 69

Fig. 25 XRD pattern of C4FsH12 equilibrated for 360 days at 20, 50 and 80 C. ............. 70

Fig. 26. Rietveld plot for Fe-monosulfate samples (synthesized at 20 C: top, and at

50 C: bottom) with = 1.5418. ............................................................................ 72

Fig. 27 Details of the Rietveld plot from the sample Fe-Ms-50 C. ................................. 73

Fig. 28 Spectral range 100 cm-1 1500 cm-1of Raman spectra from sample Fe-Ms-20C (comparison with Al-monosulfate spectra [79]). ................................................. 75

Fig. 29 Spectral range 2800 cm-1 4000 cm-1of Raman spectra from sample Fe-Ms-50 C (comparison with Al-monosulfate spectra [79]). ............................................ 76

Fig. 30 Thermal analysis (TGA and DTG) of Al and Fe-monosulfate after 680 days. .... 77

Fig. 31 XRD pattern of the C4AsH12-C4FsH12series after 680 days equilibration at20 C. Al-monosulfate (2= 19.89), Fe-monosulfate (2= 19.99) and *Al-ettringite. # Al-monocarbonate (2= 23.50). .......................................................... 78

Fig. 32 Layer thickness observed for the C4(A,F)sH12solid solution in this study andreported in literature [12, 87, 88]. ............................................................................. 79

Fig. 33 Values of a-parameters for the C4(A,F)sH12solid solution series determined inthis study and reported in literature [12, 87, 88]. ...................................................... 79


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Fig. 34 Calculated solubility products of Fe-monosulfate from the solubilityexperiments. symbols: experimental data. ................................................................ 84

Fig. 35 Lippmann diagram illustrating the total solubility products of Al/Fe-monosulfate solid solution series: total experimentally determined solubilityproduct (symbols), modeled total solubility products assuming ideal solidsolution (dashed lines), modeled total solubility products assuming a non-idealsolid solution with a miscibility gap (a0= 1.26 and a1= 1.57) (solid lines) andsolubility products assuming no solid solution (dotted lines). X-axis: Al/(Al +Fe) ratios in the solid and Al/(Al + Fe) ratios in the liquid. ...................................... 89

Fig. 36 Measured (points) and calculated (lines) concentrations in the liquid phases ofthe synthesized monosulfate with different Al/(Al+Fe) mole ratio, assuming acontinuous solid solution with a miscibility gap. ...................................................... 90

Fig. 37 XRD pattern of 3CaO.Fe2O3.CaCl2

.10H2O (Fe-Fr)synthesized at 20 C and

sampled after different equilibration times from FeCl3.6H2O and CaO in 0.1 MKOH. ......................................................................................................................... 93

Fig. 38 Comparison of the XRD patterns of Fe-Friedels salts equilibrated for threeyears at different pH values: synthesized a). FeCl3.6H2O and CaO in 0.1M KOH(pH = 11.94), b). C2F, CaCl2.2H2O and CaO in distilled water (pH = 12.39) andc). C2F, CaCl2.2H2O, and CaO in 0.1 M KOH (pH = 12.84), CH-portlandite. ........ 94

Fig. 39 TGA-DTG curves of Fe-Friedels salt synthesized at 20 C and sampled afterdifferent equilibration times from FeCl3.6H2O and CaO in 0.1M KOH. ................. 95

Fig. 40 Rietveld plot for Fe-Friedels salt recorded at = 0.697751 and at asample-to-detector distance of 150 mm. ................................................................... 96

Fig. 41 Thermal analysis (TGA and DTG) of Al and Fe-Friedels salt synthesizedfrom FeCl3.6H2O and CaO in 0.1 M KOH and equilibrated for 270 days. .............. 98

Fig. 42 Raman spectra recorded for Fe-Friedels salt crystal. .......................................... 99

Fig. 43 Values of a-parameters for the Al/Fe-Friedel salt solid solution determined inthis study compared to the findings by Kuzel et al. [88], Goetz Neunhoeffer et al.[100], Rapin et al. [99] and Rousselot et al. [96]. ................................................... 100

Fig. 44 Experimental determined solubility products of Fe-Friedels salt as a functionof pH. ...................................................................................................................... 103

Fig. 45 Calculated solubility products of Fe-Friedels salt from the solubilityexperiments compared with the solubility product Al-Friedels salt calculatedfrom measured concentrations reported in literature [54, 94, 101-103]. ................ 104

Fig. 46 Measured (points) and calculated (lines) concentrations in the liquid phases ofthe synthesized Friedels salt at different Al/(Al+ Fe) ratio, assuming ideal solidsolution. ................................................................................................................... 106


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Fig. 47 Nomenclature of minerals of the hydrogarnet group. ......................................... 110

Fig. 48 Time-dependent XRD pattern of C3AH6synthesized at 20 C, * C4AcH11. ...... 112

Fig. 49 Thermal analysis (TGA and DTG) of C3AH6and C3FH6synthesized at 20 Cand sampled after different equilibration times. ..................................................... 113

Fig. 50 Solubility products of C3AH6calculated from the solubility experimentscarried out in this study and from different published data [7, 111, 112, 114-116]. ........................................................................................................................ 115

Fig. 51 Time-dependent XRD pattern of C3FH6synthesized at 20 C and the samplesynthesized at 110 C and equilibrated for 5 days. ................................................. 118

Fig. 52 XRD pattern of mixed Al and Fe hydrogarnets after 3 years equilibration. ...... 120

Fig. 53 Calculated solids in the CaO-Al2O3-Fe2O3-H2O system in 0.1 M KOH usingthe solubility products as given in Table 28. .......................................................... 122

Fig. 54 The XRD pattern of Al containing Si-hydrogarnet synthesized at 20 C and110 C. * Al-Si-hydrogarnet with two different compositions (see inlet); oC3AH6; - KNO3present as impurity; +CaF2added as an internal standard. ........... 123

Fig. 55 Thermal analysis (TGA and DTG) of Al-and Fe-Si hydrogarnet synthesized at20 C and 110 C. The circle region indicates the water loss of hydrogarnetswith different compositions. ................................................................................... 124

Fig. 56 Estimation of the silica content for synthesized Al-containing hydrogarnet;

PDF: Powder Diffraction File. ICSD: Inorganic Crystal Structure Database. Thecomposition of the synthesized solid solution series was estimated from the unitcell size as indicated by the line. ............................................................................. 125

Fig. 57 Comparison of published solubility products of Al-Si-hydrogarnet calculatedin this study from the data reported in [7, 110, 112, 117], C3AH6 (dashed line),C3AS0.41H5.18 (solid line), C3AS0.84H4.32 (dotted line).............................................. 128

Fig. 58 Solubility products as a function of Si content between C3AH6and C3AS3endmembers at 25 C. ................................................................................................... 129

Fig. 59 Time-dependent XRD pattern of C3FSH4 synthesized at 20 C from C2F, * thesolid synthesized at 110 C. R: rutile. ..................................................................... 130

Fig. 60 Rietveld plot for Fe-Si-Hydrogarnet sample with = 0.697751 and asample-to-detector distance of 150 mm (top) and 400 mm (bottom). .................... 132

Fig. 61 Zoom of the Rietveld plot from pattern recorded for a sample-to-detectordistance of 400 mm showing the two hydrogarnet phases (systematic shoulders,right side, for hydrogarnet diffraction peaks). ........................................................ 133


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Fig. 62 Calculated solubility products of Fe-Si-hydrogarnetsfrom the solubilityexperiments. (lines show calculated values, full symbols show the measuredvalues from undersaturation and empty symbols from oversaturation). ................. 135

Fig. 63 XRD pattern of the solid solution series of Ca3Fe2(SiO4)3-y(OH)4y, + CH. Thedotted lines indicate the peak shifts. *Main reflections of the hydroandradite endmembers. Note that Xsi= y = 3 ............................................................................... 136

Fig. 64 Solubility products as a function of Si content in between C3FH6and C3FS3end members at 25 C. The dotted line connects the solubility products of C3FH6and C3FS3................................................................................................................ 138

Fig. 65 XRD pattern of the solid solution series of Ca3(AlxFe1-x)2(SiO4)(OH)8synthesized at 110 C. ............................................................................................. 139

Fig. 66 Lippmann diagram illustrating the total solubility products of Al/Fe-siliceous

hydrogarnet solid solution series Ca3(AlxFe1-x)2(SiO4)0.9(OH)8.4at a) 20 C b) 50C: .experimentally determined total solubility products (filled symbols),modeled total solubility products assuming ideal solid solution (dashed lines). Inaddition also the solubility product of C3AS0.84H4.32 and C3FS0.95H4.1derivedfrom the experimental data (empty symbols) and the solubility productsassuming no solid solution (dotted lines) are given. X-axis: Al/(Al + Fe) ratio inthe solid or liquid phases, respectively. .................................................................. 143

Fig. 67 XRD patterns of OPC (+) and HS (*) cements hydrated at 20 C. .................... 149

Fig. 68 TGA-DTG curves of OPC (+) and HS (*) cements hydrated at 20 C. ............. 150

Fig. 69 XRD patterns of OPC (+) and HS (*) cement hydrated for 1 year at 50 C:The XRD peak at 2~ 11.30 is between the monosulfate and monocarbonatepeaks. ...................................................................................................................... 151

Fig. 70 TGA-DTG curves of OPC (+) and HS (*) cement hydrated for 1 year at 50 C 152

Fig. 71 XRD patterns of OPC (+) and HS (*) hydrated at 20 C after selectivedissolution using SAM. Note that the samples suffered from carbonation duringSAM extraction. ...................................................................................................... 153

Fig. 72 TGA-DTG curves of OPC (+) and HS (*) hydrated at 20 C after selective

dissolution with SAM. ............................................................................................ 154

Fig. 73 XRD patterns of OPC (+) and HS (*) hydrated at 50 C for 150 days afterselective dissolution with SAM. ............................................................................. 154

Fig. 74 SEM/EDX of hydrated OPC for 2 years at (a) 20 C and (b) 50 C afterselective dissolution with SAM. ............................................................................. 156

Fig. 75 Atomic ratio of hydrated OPC for 2 years at (a) 20 C and (b) 50 C afterselective dissolution with SAM. ............................................................................. 157


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ix

Fig. 76 Fe K-edge XANES spectra of Fe-containing hydrates. The broken linesindicate the position of related spectral features. .................................................... 159

Fig. 77 k3-weigthed experimental bulk-EXAFS spectra of Fe-containing phases usedas reference compounds. The broken lines indicate the position of relatedspectral features. ..................................................................................................... 160

Fig. 78 EXAFS spectra of hydrated OPC at 20 C and at different ages (line:experimental data; dots: modelled data). The broken lines outline selectedspectral features. ..................................................................................................... 161

Fig. 79 EXAFS spectra of hydrated OPC at 50 C and at different ages (line:experimental data; dots: modeled data). The broken lines outline selectedspectral features. ..................................................................................................... 162

Fig. 80 EXAFS spectra of hydrated HS at 20 C and at different ages (line:

experimental data; dots: modeled data). The broken lines outline selectedspectral features. ..................................................................................................... 163

Fig. 81 EXAFS spectra of hydrated HS at 50 C and at different ages (line:experimental data; dots: modeled data). The broken lines outline selectedspectral features. ..................................................................................................... 163

Fig. 82 Volume changes of hydrated phases at different hydration ages duringhydration of OPC at room temperature. .................................................................. 168

Fig. 83 Heat flow of the hydration of C2F and synthetic Fe-cement in the presence ofdifferent amounts of gypsum. ................................................................................. 172

Fig. 84 XRD (above) and TGA-DTG (below) analysis of C2F and synthetic Fe-cement after 3 days of hydration in the presence of different amounts of gypsum*Fe-OH-AFm +unidentified. .................................................................................. 173

Fig. 85 XRD (above) and TGA-DTG (below) analysis of C2F and synthetic Fe-cement after 3 months of hydration in the presence of different amounts ofgypsum *Fe-AFm hydroxyl. ................................................................................... 175

Fig. 86 Calculated phase diagram of thermodynamic stable hydrate assemblages ofsynthetic Fe-cement with different amounts of gypsum. ........................................ 176

Fig. 87 Conduction calorimeter curve of the hydration of synthetic Fe-cement withdifferent amounts of gypsum and calcite. ............................................................... 177

Fig. 88 XRD (above) and TGA-DTG (below) analysis of synthetic Fe-cement after 3months of hydration with different amounts of gypsum and calcite ...................... 179

Fig. 89 Calculated phase diagram of thermodynamic stable hydrate assemblages ofFe-synthetic cement with different amounts of gypsum and calcite. ...................... 180


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TABLE OF CONTENTS

i

Table of Contents

Abstract................................................................................................................................ i

Zusammenfassung.............................................................................................................. iv

Acknowledgement............................................................................................................. vii

ListofTables........................................................................................................................ i

ListofFigures...................................................................................................................... iv

1 INTRODUCTION........................................................................................................... 1

1.1 OrdinaryPortlandcement(OPC)............................................................................ 1

1.2 Cementhydrationandthermodynamicmodeling.................................................1

1.3 Thefateofironoxidesduringthehydrationofcements.......................................6

1.4 Characterizationofcementitioussystem............................................................... 7

1.4.1 Standardanalyticaltechniques....................................................................... 7

1.4.2 Xrayabsorptionspectroscopy(XAS)..............................................................7

1.5 Objectiveofthisstudy.......................................................................................... 10

1.6 Outlineofthethesis.............................................................................................. 11

2 MATERIALSANDMETHODS...................................................................................... 12

2.1. SynthesisofFecontainingphases.................................................................... 12

2.1.1. FehemicarbonateandFe/Almonocarbonate.............................................12

2.1.2. Femonosulfate............................................................................................. 13

2.1.3. FeFriedelsSalt............................................................................................. 14


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ii

2.1.4. Festrtlingite................................................................................................ 14

2.1.5. Synthesisofhydrogarnets............................................................................ 14

2.1.5.1.

Silicafree

hydrogarnets:

Ca3(AlxFe1x)2(OH)12

.......................................

14

2.1.5.2. Siliceoushydrogarnets:Ca3(AlxFe1x)2(SiO4)(OH)8.................................15

2.1.6. Hydratedcementsamples............................................................................ 16

2.1.7. SynthesisofsyntheticFecement................................................................. 17

2.2. Analyticalmethods........................................................................................... 18

2.2.1. PowderXraydiffraction............................................................................... 18

2.2.2. Synchrotronpowderdiffraction................................................................... 19

2.2.3. Thermogravimetricanalysis.......................................................................... 19

2.2.4. Vibrationalspectroscopy(RamanandInfraredspectroscopy)....................20

2.2.5. Scanningelectronmicroscopy(SEM)...........................................................20

2.2.6. Liquidphaseanalysis.................................................................................... 20

2.2.7. Selectivedissolution..................................................................................... 21

2.2.8. SynchrotronbasedXrayabsorptionspectroscopy(XAS)............................22

2.2.8.1. Datacollectionandreduction............................................................... 22

2.2.8.2. Dataanalysisandfitting........................................................................ 23

2.2.9. Calorimetry................................................................................................... 24

2.3. Thermodynamicmodeling................................................................................ 24

2.3.1. EstimationofheatcapacityofFecontainingphases...................................25

2.3.2. Determinationofsolubilityproducts............................................................25

2.3.3. Thermodynamicsofsolidsolutions..............................................................31

2.3.4. Thermodynamicmodelingofcementhydration..........................................34


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iii

3. SYNTHETICFECONTAININGHYDRATES................................................................... 35

3.1. IroncontainingcarbonateAFmphases............................................................35

3.1.1.

Introduction..................................................................................................

35

3.1.2. Fehemicarbonate......................................................................................... 37

3.1.3. Femonocarbonate....................................................................................... 40

3.1.3.1. Kineticsofformation............................................................................ 40

3.1.3.2. Effectoftemperature........................................................................... 42

3.1.3.3.

Structureof

Fe

Mc

................................................................................

43

3.1.3.4. ComparisonofpureFe andAlMc.......................................................50

3.1.4. MixedCaO.(AlxFe1x)2O3.CaCO3.nH2Osystems..............................................53

3.1.5. Solubility........................................................................................................ 55

3.1.5.1. Determinationofsolubilityproductsat20Cand50C......................56

3.1.5.2. Estimationofthesolubilityproductunderstandardconditions.........59

3.1.5.3. ModelingofmixedCaO(AlxFe1x)2O3CaCO3nH2Osystems.................61

3.1.6. ModelingofC3AC2FCaCO3CaSO4H2Osystemincementhydration.........62

3.1.7. Conclusions................................................................................................... 64

3.2. Fecontainingmonosulfate............................................................................... 67

3.2.1. Introduction.................................................................................................. 67

3.2.2. Kineticsofformation.................................................................................... 67

3.2.3. Effectsoftemperature.................................................................................. 69

3.2.4. StructureofC4FsH12...................................................................................... 70

3.2.5. ComparisonofC4AsH12withC4FsH12............................................................74

3.2.6. SolidsolutionbetweenAlandFemonosulfate(C4(A,F)sH12)......................77


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iv

3.2.7. SolubilityofAl/Femonosulfate.................................................................... 80

3.2.7.1. Determinationofsolubilityproductsat20,50and80C....................80

3.2.7.2.

Determinationof

solubility

products

under

standard

condition

.........

82

3.2.7.3. Determinationofsolubilityproductofthesolidsolutionandmodeling

oftheliquidphase................................................................................................ 84

3.2.8. Conclusions................................................................................................... 91

3.3. FeFriedelssalt(3CaO.Fe2O3

.CaCl2

.10H2O).......................................................92

3.3.1. Introductions................................................................................................. 92

3.3.2. Kineticsofformation.................................................................................... 92

3.3.3. StructureofFeFriedelssalt......................................................................... 95

3.3.4. ComparisonofAlFriedelssaltandFeFriedels..........................................97

3.3.5. SolidsolutionbetweenAlandFeFriedelssalt(3CaO(AlxFe1x)2CaCl2.10H2O..

....................................................................................................................... 99

3.3.6. Solubility...................................................................................................... 100

3.3.6.1. SolubilityofFeFriedelssalt............................................................... 100

3.3.6.2. Determinationofthesolubilityproductsofthesolidsolutionand

modelingoftheliquidphase.............................................................................. 105

3.3.7. Conclusions................................................................................................. 106

3.4. Festrtlingite.................................................................................................. 108

3.5. Hydrogarnets.................................................................................................. 109

3.5.1. Introduction................................................................................................ 109

3.5.2. AlKatoite,C3AH6......................................................................................... 111

3.5.3. FeKatoite,C3FH6......................................................................................... 117


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3.5.4. Solidsolutionbetweenaluminumandironkatoite,C3(A,F)H6..................119

3.5.5. Aluminumsiliceoushydrogarnet,C3ASH4...................................................122

3.5.6.

Ironsiliceous

hydrogarnet,

C3FSH4

.............................................................

129

3.5.7. SolidsolutionbetweenCa3Fe2(OH)12andCa3Fe2O6(SiO2)3(hydroandradite,

Ca3Fe2(SiO4)3y(OH)4y).............................................................................................. 136

3.5.8. Solidsolutionbetweenaluminumandironsiliceoushydrogarnet,C3(A,F)SH4

..................................................................................................................... 138

3.5.9. Conclusions................................................................................................. 143

3.6. Summary......................................................................................................... 145

4. FECONTAININGHYDRATESINHYDRATEDCEMENT..............................................147

4.1. IdentificationofFecontaininghydratesinhydratedcement........................147

4.1.1. Introduction................................................................................................ 147

4.1.2. Characterizationofhydratedcementusingstandardanalyticaltechniques...

..................................................................................................................... 149

4.1.3. Spectroscopicinvestigation........................................................................ 158

4.1.3.1. XANESandEXAFSspectraofFecontainingreferencecompounds...158

4.1.3.2. IdentificationofFecontaininghydrates............................................160

4.1.4. Thermodynamicmodeling.......................................................................... 167

4.1.5. Conclusions................................................................................................. 169

4.2. SyntheticFecement....................................................................................... 171

4.2.1. Introduction................................................................................................ 171

4.2.2. EffectsofgypsumontheofhydrationofsyntheticFecement.................172

4.2.3. EffectsofcalciteontheofhydrationofsyntheticFecement...................177


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4.2.4. Conclusions................................................................................................. 180

5. GENERALCONCLUSIONANDOUTLOOK................................................................. 182

5.1.

Generalconclusion

.........................................................................................

182

5.2. Outlook........................................................................................................... 186

ABBREVATIONS............................................................................................................... 188

APPENDIX........................................................................................................................ 191

AppendixA:Additionalfittedstructuralparameters.................................................191

AppendixB:Additionalfigures................................................................................... 192

REFERENCES.................................................................................................................... 197


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CHAPTER 1 INTRODUCTION

1

1 INTRODUCTION

In this chapter a general overview about the hydration of Portland cements, different

characterization techniques, thermodynamic modeling and the reaction of ferrite phases isgiven. Moreover, the objective of the study is briefly explained.

1.1 Ordinary Portland cement (OPC)

The raw materials for Portland cement production are a mixture of limestone and clay

minerals containing calcium oxide, silicon oxide, aluminum oxide, ferric oxide, and

magnesium oxide. The raw materials are ground together in a raw mill and then heated in

a cement kiln at a temperature between 1400-1500 C which produces nodules of clinker.

The clinker is mixed with a few percent of gypsum and finely ground to make cement.

The clinker contains four major phases, called alite (Ca3SiO5 or C3S), belite (C2S or

Ca2SiO4), aluminate (C3A or Ca3Al2O3) and ferrite (C2(A,F)). The formulas given are

idealized, as all clinker phases contain in addition a number of minor elements [1]. Ferrite

designates a solid solution series with the formula Ca2(AlxFe1-x)2O5with 0 x < 0.7. It

crystallizes in the orthorhombic crystal system, the unit-cell dimensions vary with the

Al2O3/Fe2O3ratio. In ferrite as present in cement clinker, a part of Fe3+can be replaced

by Mg2+ in combination with Si4+ or Ti4+ resulting in the typical clinker ferrite

composition of approximately Ca2AlFe0.6Mg0.2Si0.15Ti0.05O5.

1.2 Cement hydration and thermodynamic modeling

Alite and belite constitute over 80 wt.% of most Portland cements. Alite is the most

important phase for strength development during the first month, while C2S reacts much

slowly and contributes rather to the long-term strength of the cement. Both the silicate


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2

phases react with water as shown below to form calcium hydroxide and calcium-silicate

hydrate (C-S-H) with Ca/Si ratio of 1.5 to 1.9:

C3S + 5.3H2O C1.7SH4+ 1.3CHC2S + 4.3H2O C1.7SH4+ 0.3CH

Tricalcium aluminate (Ca3Al2O3) constitutes 5-10% of most Portland cement clinkers. In

the absence of any additives, C3A reacts with water to form two intermediate hexagonal

phases, C2AH8and C4AH13. The structure of C2AH8is not precisely known, but C4AH13

has a layered structure based on the calcium hydroxide structure. All of the aluminum in

C4AH13is octahedral. C2AH8and C4AH13are metastable phases that transform with time

into the thermodynamically more stable cubic phase C3AH6.

2C3A + 21H2O C2AH8+ C4AH132C3AH6+ 9H2O

In the presence of gypsum, anhydrite or bassanite, C3A reacts slowly and forms Al-

ettringite, which can convert to Al-monosulfate after the depletion of calcium sulfates

and further Al-ettringite.

C3A + 3CsH2+ 26H2O C6As3H32

2C3A + C6As3H32+ 4H2O 3C4AsH12

In the presence of carbonate, C3A forms Al-hemicarbonate or Al-monocarbonate,

depending of the availability of calcite [2].

C3A + 0.5Cc + 0.5CH + 11.5H2O C4Ac0.5H12

C3A + Cc + 11H2O C4AcH11

The reaction of ferrite (C2(A,F)) is similar to the reactions of C3A though the presence of

Fe makes it more complicated. The Al from C2(A,F) can form as discussed above Al-

containing OH-AFm phases (C2AH8and C4AH13) or Al-katoite (C3AH6). In the presence

of gypsum or carbonate, monosulfate, hemicarbonate, monocarbonate and ettringite can


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3

be formed. The fate of Fe is unclear. If we assume partial substitution of Al by Fe, a solid

solution can be formed as in

C2(A,F) + 2CH + 19H2O C2(A,F)H8+ C4(A,F)H132C3(A,F)H6+ 9H2OIn the presence of gypsum,

C2(A,F) + 6CsH2+ 2CH + 50H2O 2C6(A,F)s3H32

C2(A,F) + C6(A,F)s3H32+ 2CH + 2H2O 3C4(A,F)sH12

In the presence of calcite,

C2(A,F) + Cc + 11H2O C4(A,F)cH11

The hydration of cement is far more complex than the sum of the hydration reactions of

the individual minerals. The major constituents of OPC are alite, belite, aluminate and

ferrite and in addition a number of other minerals such as calcium sulfates (gypsum,

hemihydrate and/or anhydrite), calcite, calcium oxide, magnesium oxide, Na- and K-

sulfates are usually present. In contact with water, the easily soluble solids in the cement,

such as gypsum, alkali sulfate and calcium oxide, react until equilibrium with the pore

solution is reached or they are dissolved completely. The clinker phases hydrate slowly

and release continuously Ca, Si, Al, Fe and OH- to solution, which then precipitate as

calcium silicate hydrates (C-S-H), ettringite or as other hydrate phases. The balance

between dissolution rates of the clinker phases and precipitation rates of the secondary

phases determines the amount of Ca, Al, Fe, Si, and OH- released and the rate of

formation of C-S-H, ettringite and the other hydrates.

Thermodynamic modeling of the interactions between solid and liquid phase in cements

using geochemical speciation codes helps to provide a basis for the interpretation of the

hydration process [3, 4]. Furthermore, it allows the composition of the hydrate


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4

assemblages to be predicted under different conditions (e.g., initial clinker composition,

water-to-cement (w/c) ratios, etc.) and for longer time scales.

Hydration models have been developed in the past years to quantify the composition of

the solid phases and liquid phases in cementitious systems during hydration [3-6]. For

OPC systems, thermodynamic modeling in combination with calculated hydration rates

correctly predicts the depletion of gypsum within the first day of hydration (Fig. 1). In

this phase a strong decrease of the sulfate concentration in the pore solution is observed

as ettringite continues to precipitate (Fig. 2). The depletion of aqueous sulfate during the

first day is compensated by the release of OH-to fulfill conditions of electroneutrality in

solution, which gives rise to a significant increase in pH. This increase in pH decreases

the Ca concentration constrained by the portlandite solubility (Fig. 2). After the first day

the precipitation of ettringite (6Ca(OH)2(AlxFe1-x)2(SO4)326H2O(s)) ends as gypsum is

exhausted. Subsequently, calcium monocarbonate (3CaO(AlxFe1-

x)2O3CaCO311H2O(s))and hydrotalcite (Mg4Al2(OH)143H2O) start forming. Calcite is

slowly consumed due to the formation of monocarbonate. After hydration time of one

month and longer, the solid paste is mainly composed of C-S-H, portlandite, ettringite

and monocarbonate. With the exception of ettringite, the amount of hydration products

continues to slowly increase with time.


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5

0.01 0.1 1 10 100 1000

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

calcitehydrotalcite

ettringite

monocarbonate

portlandite

C-S-H

gypsum

C4AF

C3A

C2S

C3S

pore solution

cm

3/100gcement

hydration time [days]

Fig. 1 Calculated volume changes during the hydration of OPC.

0

100

200

300

400

500

600

0.01 0.1 1 10 100 1000 10000time [hours]

[mM]

K OH-

Na SO4

Ca Si

CaSO 4,Ca(OH) 2C-S-H, ettringite,

brucite

C-S-H, Ca(OH) 2,

ettringite,

monocarbonate,

hydrotalcite

K

SO4

Ca

Na

OH-

Si

Fig. 2 Calculated (lines) and measured (dots) composition of the liquid phase of ordinary Portland

cement during hydration [6].

Application of thermodynamic models requires that the thermodynamic data of the

hydrates formed in OPC are known. In the past years a set of thermodynamic data for

selected hydrates have been critically reviewed [6]. Additionally, the solubility of


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6

numerous hydrates particularly Al-containing phases have been investigated

experimentally between 5 to 85 C, which served as a basis to extend the cement database

[3, 7]. However, there is a lack of thermodynamic data on Fe-hydrates that limitsthermodynamic modeling to predict the fate of Fe-during cement hydration.

1.3 The fate of iron oxides during the hydration of cements

Ferrite C2(A,F) (Ca4(Fex-1Alx)4O10) is an important clinker phase in Portland cements

(5-15%). The rate at which it reacts with water appears to be somewhat variable perhaps

due to differences in composition or other characteristics, but it reacts fast initially and

much more slowly at later ages [8, 9].

In pure system, i.e. in the presence of Ca, Al, Fe, and sulfate or carbonate only, Fe-

containing ettringite, monosulfate and monocarbonate were found to precipitate and to

form solid solutions with their Al-containing analogues [10-17]. Further, the formation of

an amorphous iron hydroxide phase was reported [16-20]. In the complex cement matrix,

however, the situation appears to be unclear due to the presence of silica. It was

suggested that Fe-containing siliceous hydrogarnets might form in cementitious systems

[21-23]. Harchand et al. [24] found that no Fe(OH)3 was present in hydrated cements

based on Mssbauer spectroscopy but they could not gain any further information from

the spectra concerning the kind of Fe-containing hydrates formed. Whether and to what

extent Al/Fe-ettringite, Al/Fe-monosulfates, Al/Fe-monocarbonate, amorphous Fe(OH)3

or Al/Fe (siliceous) hydrogarnets, respectively, might form in Portland cement is poorly

understood.


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7

1.4 Characterization of cementitious system

1.4.1 Standard analytical techniques

Commonly used analytical techniques to characterize cementitious system include XRD,TGA, microscopic techniques (SEM and TEM) and vibrational spectroscopies (IR and

Raman). X-ray diffraction (XRD) is a key technique for characterizing the crystalline

phase composition of materials. Moreover, it allows phase identification and provides

information about crystal structure. However, it does not give sufficient information

about poorly crystalline and amorphous phases. Thermogravimetric analysis (TGA) helps

to characterize and identify phases from complex cement matrix based on the weight loss

over a specific temperature range. The limitation of TGA is due to the difficulty of

distinguishing different phases within the complex cement matrix which have the weight

loss at the same temperature. Scanning electron microscopy (SEM) is used to study the

microstructure of cement and cementitious materials and in combination with EDX

(energy dispersive X-ray spectroscopy) to characterize the chemical composition of the

different phases and their spatial distribution. The above standard analytical techniques

cannot provide a clear identification of Fe-containing hydrates in hydrated cement as

signals from Fe-containing phases overlap with its Al-analogues.

1.4.2 X-ray absorption spectroscopy (XAS)

X-ray absorption spectroscopy (XAS) is a technique used to obtain structural information

of a compound. It is element specific and accounts for the localgeometric and electronic

structures. A synchrotron light source is used as the X-ray photon source. The energy is

tuned to an energy at which the incident photon can excite a core electron of the

absorbing atom to a continuum state. The electron is now considered a photoelectron and


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8

propagated as a spherical wave. The energy of this photoelectron is equal to the energy of

the absorbed photon minus the binding energy of the electron to the atom. The energy at

which these photoelectrons are absorbed is related to the edges seen in XAS, K, L and Mwhich correspond to the particular electronic transitions (Fig. 3).

Fig. 3 A sample of edges and the corresponding electronic transitions [25].

The number of X-ray photons that are transmitted through a sample (I t) is equal to the

number of X-ray photons shone on the sample (I0) multiplied by a decreasing exponential

factor that depends on the absorption coefficient () of the type of atoms in the sample

and the thickness of the samplex.

It= I0e x

There are two main regions of the XAS spectrum providing structural information:

XANES and EXAFS (Fig. 4).


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9

Fig. 4 Sample XAS Spectrum of FeO with XANES and EXAFS region [26].

The X-ray absorption near edge structure, XANES, is the part of the spectrum that gives

qualitative data based on modeling and simulation. XANES is used to give information

about the average oxidation state and coordination environment. By taking unknown

spectra and fitting a linear combination of known reference spectra, one can get an

estimate of the contribution of each reference to the unknown spectra.

Extended X-ray absorption fine structure, EXAFS, is the part of spectrum that gives

quantitative data on the local structure around the absorber atom. From EXAFS mainly

information on the type of neighboring atoms, their distance from absorber atom (bond

length), the number of neighboring atoms (coordination numbers) and ordering effects(Debye-Waller factor) can be extracted. As described above, the photoelectron can be

thought of as a wave centered at an atom. The wave vector of the photoelectron is related

to the difference in binding energy of the electron, E0, and the energy of the photon, E, as

shown below:


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10

, k=2/

When this wave interacts with other atoms, there is either a destructive or constructive

interference. The phase and amplitude of interference that occurs is related to the type

and location of the incident atom. Therefore, analysis of EXAFS data allows structural

information about the type of atom and its coordination environment to be determined.

XANES and EXAFS techniques allow dilute samples to be examined (concentration of

the X-ray absorber down to a few tens of ppm). Most importantly, XAS can be used to

study amorphous solids, surface adsorbed complexes, or species in solution in addition to

crystalline materials. There is growing interest in the application of this technique for

quantification of species in a complex mixture [27].

Synchrotron-based X-ray absorption spectroscopy (XAS) can be used as a

complementary technique to gain molecular-level information from cementitious systems

[28-30]. Furthermore, advanced high resolution synchrotron-based X-ray micro-probe

allows to obtain spatially resolved information on the speciation of the X-ray absorber of

interest in compact matrices, such as cementitious materials [28, 30].

1.5 Objective of this study

As discussed above, the fate of iron during cement hydration is poorly known. Moreover,

experimentally determined thermodynamic solubility products and other thermodynamic

parameters are lacking for Fe-hydrates. The general objectives of this study are the

following:

Synthesis and characterization of Fe-hydrates and investigation of their solid

solution formation with the Al-analogous. Experimental determination of

solubility products and other thermodynamic parameters of Fe-hydrates.


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11

Identification of Fe-hydrates in hydrated Portland cements using XAS technique.

Thermodynamic modelling of Portland cement hydration including the newly

determined thermodynamic data for iron phases and compare them to the

experimental data in Portland cements and in synthetic Al-free cements.

1.6 Outline of the thesis

The thesis contains five chapters:

Chapter 1:contains the introduction and the objective of the thesis.

Chapter 2: presents the materials and methods used to study Fe-containing hydrates

possibly present in cementitious system. It explains the procedures followed to synthesize

pure Fe-containing phases and their solid solutions with Al. In the course of this chapter

the analytical techniques used to characterize both the solid and the liquid phases are

presented. Furthermore, the application of thermodynamics in the framework of thisstudy is explained.

Chapter 3: briefly presents the results obtained on formation of Fe-containing phases,

their crystal structure, and formation of solid solution with their Al-analogues and

determination of thermodynamic data.

Chapter 4: describes identification of hydrated phases in cements particularly Fe-

containing hydrates using EXAFS. It also presents thermodynamic modeling of Portland

cement and hydration study of Al-free Fe-synthetic cement.

Chapter 5: presents the general conclusions of the study and the outlook for future

investigations.


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CHAPTER 2 MATERIALS AND METHODS

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2 MATERIALS AND METHODS

2.1. Synthesis of Fe-containing phases

C3A and C2F clinkers were used as starting materials for the synthesis. C3A and C2F were

prepared by mixing appropriate amounts of CaCO3with Al2O3 and Fe2O3 powders and

burning at 1400 C and 1350 C respectively for 24 hours. The powders were ground to

63 m. XRD analysis indicated that no other solids than C3A or C2F were present. CaO

was synthesized by burning CaCO3 at 1000 C.

2.1.1. Fe-hemicarbonate and Fe/Al-monocarbonate

Pure Fe-Mc and Fe-Hc were synthesized by the addition of appropriate amounts of C2F,

CaCO3, and CaO to 0.1 M KOH solution (50 ml) at liquid/solid ratio ~ 20. The

stoichiometry of the reaction is given by:

2CaO.Fe2O3+ CaCO3+ CaO + 12H2O 3CaO.Fe2O3

.CaCO3.12H2O

2CaO.Fe2O3+ 0.5CaCO3+ 1.5CaO + 10H2O 3CaO.Fe2O3.Ca(CO3)0.5.10H2O

0.1 M KOH solution was used to simulate the high pH present in the pore solution of

Portland cement. Al/Fe-monocarbonates were synthesized by precipitation from

supersaturated solutions. Appropriate amounts of C3A, C2F, CaCO3, and CaO were added

to 0.1 M KOH solution (pH = 13.0). The mole fraction of Al varied from x = 0 to 1. The

overall stoichometric reaction is given by:

xC3A + (1-x)C2F + CaCO3+ (1-x)CaO + nH2O 3CaO(AlxFe1-x)2O3CaCO3nH2O.

The samples were stored in closed PE-bottles at different temperatures (20, 50 and 80 C)

and sampled up to three years. After equilibration the solid and liquid phases were

separated by vacuum filtration through 0.45m nylon filters. All sample preparation and


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handling were done in a glove box filled with N2-atmosphere to minimize CO2

contamination.

The mixes used in the undersaturation experiments correspond to those prepared for the

oversaturation experiments. After an equilibration time of 3 years, an additional amount

of 0.1 M KOH solution was added to duplicate the volume of the solution (resulting in

undersaturation) and equilibrated for further 15 months. Note that, all the 3 years old

samples prepared during the previous PhD project [31].

2.1.2. Fe-monosulfate

Pure Fe-monosulfate was synthesized by the addition of appropriate amounts of C 2F,

CaSO42H2O and CaO to 50 ml of 0.4 M KOH solution (pH = 13.6) at liquid/solid ratio ~

20. The overall stoichometric reaction is given by:

2CaOFe2O3+ CaSO42H2O + CaO + 10H2O 3CaOFe2O3CaSO412H2O

0.4 M KOH solution was used to mimic the high pH conditions in the pore solution of

Portland cement in which monosulfate is formed. At lower KOH concentrations the

formation of Fe-ettringite instead of Fe-monosulfate is favored [15]. Mixed Al/Fe-

monosulfate was synthesized by precipitation from supersaturated solutions. Again

appropriate amounts of C3A, C2F, CaSO4 2H2O, and CaO were added to 0.4 M KOH

solution (pH = 13.6). The mole fraction of Al varied from x = 0 to 1. The overall

stoichiometric reaction is given by:

xC3A +(1-x)C2F +CaSO42H2O + (1-x)CaO +10H2O3CaO(AlxFe1x)2O3CaSO412H2O

Sample handling was as described in section 2.1.1.


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2.1.3. Fe-Friedels Salt

Pure Fe-Friedels salt was synthesized in three different ways:

a. By the addition of appropriate amounts of C2F, CaCl2.

2H2O, and CaO to

distilled water (50 ml) at liquid/solid ratio ~ 20 according to:

2CaOFe2O3+ CaCl22H2O + CaO + 8H2O 3CaOFe2O3.CaCl210H2O

b. By mixing appropriate amounts of C2F, CaCl22H2O, and CaO in 0.1 M KOH

solution (50 ml) at liquid/solid ratio ~ 20 according to the above reaction.

c. By the addition of appropriate amounts of AlCl36H2O, FeCl36H2O, and CaO

in 50 ml of 0.1 M KOH at a liquid/solid ratio ~ 20 to obtain

4CaO(AlxFe1-x)2O3Cl210 H2O.


2.1.4. Fe-strtlingite

Different methods were also used to obtain Fe-strtlingite (C2FSH8). The first method

was mixing appropriate amounts of Fe(OH)3, Na2SiO35H2O and CaO in 0.1 M KOH.

The second method was by mixing 2FeCl36H2O, Na2SiO35H2O, and 2Ca(NO3)24H2O

in 0.1 M KOH. The samples were equilibrated at 7, 28 and 200 days at 20, 50 and 80 C.

2.1.5. Synthesis of hydrogarnets

2.1.5.1. Silica free hydrogarnets: Ca3(AlxFe1-x)2(OH)12

C3AH6and C3FH6were synthesized by mixing appropriate amounts of C3A or C2F and

CaO in 50 ml 0.1 M KOH to obtain a liquid/solid ratio of ~ 20. The suspensions were

equilibrated at 20, 50 and 80 C up to three years. The stoichiometry of the reactions is

given by:


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3CaOAl2O3+ 6H2O 3CaOAl2O36H2O

2CaOFe2O3+ CaO + 6H2O 3CaOFe2O36H2O

The samples were stored in closed PE-bottles and sampled after different reaction times.


2.1.5.2. Siliceous hydrogarnets: Ca3(AlxFe1-x)2(SiO4)(OH)8

a) Synthesis at ambient temperature (supersaturation experiments)

In a first attempt, C3ASH4 and C3FSH4 were synthesized by mixing stoichiometric

amounts of C3A or C2F with CaO and Na2SiO35H2O at 20 C in 50 ml 0.1 M KOH at

liquid/solid ratio of ~ 20. The samples were stored in closed PE-bottles at different

temperatures (20, 50 and 80 C) and sampled up to three years under supersaturated

conditions. Sample handling was as described in section 2.1.1.

b) Hydrothermal synthesis (undersaturation experiments)

Due the slow reaction of the C2F clinkers and the poor crystallinity of the products

formed at 20 C, mixed Ca3(AlxFe1-x)2(SiO4)(OH)8 solids were also prepared

hydrothermally at 110 C. Stoichiometric amounts of AlCl36H2O, FeCl36H2O,

Na2SiO35H2O and Ca(NO3)24H2O were mixed with 200 ml of 1 M KOH at a

liquid/solid ratio of ~ 25 to obtain 3CaO(AlxFe1-x)2O3SiO24H2O. A pH of approximately

13.5 (measured at 20 C) was observed after mixing. The mixes were stored for 5 days in

closed teflon vessels at approximately 110 C. The same procedure was used to prepare

Fe-hydrogarnets Ca3Fe2(SiO4)3-y(OH)4y containing different quantities of silica and

hydroxide.


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After aging for 5 days at 110 C, the solid and liquid phases were separated by vacuum

filtration through 0.45m nylon filters. The residues were dried in N2-filled desiccators

over saturated CaCl2 solutions for 1 week. The dried solids were re-dissolved in 0.1 M

KOH at liquid/solid-ratio of ~ 20 in HDPE bottles and equilibrated at 20 C and 50 C for

4 months (undersaturation experiments).

2.1.6. Hydrated cement samples

To study the fate of iron in hydrated cements, hydration experiment were carried out

using an ordinary Portland cement (OPC), CEM I 32.5 R and a sulfate resistant cement

HS (CEM I 42.5 N). The chemical composition of the cements used for this study is

listed in Table 1. The cement pastes were prepared at a water/cement (w/c) ratio of 0.425

and hydrated at 20 and 50 C. The latter temperature was chosen since the composition of

the hydration assemblage is expected to change around 48 C [3, 32]. The cements were

hydrated for 4, 8, 16 hours, 1, 28, 150 days, 1 and 3 years at 20 and 50 C.The hydration of the cements was stopped using isopropanol. The sample were dried in

an oven at 40 C for 1 hour. The sample was ground by hand for XRD, EXAFS and TGA

analysis.


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Table 1 Oxide and the phase composition of the cements used.

OPC HS OPC HSCEM I 32.5 R CEM I42.5 N CEM I 32.5 R CEM I42.5 N

a

Chemical analysis (g/100g) (g/100g)b

Phase composition (g/100g) (g/100g)SiO2 20.34 17.55 C3S 53.5 60.0

Al2O3 5.17 4.58 C2S 18.0 5.1

Fe2O3 3.09 7.2 C3A 8.5 0.0CaO 63.38 60.34 C2(A,F) 9.4 21.9MgO 2.53 1.98 CaSO4 2.5 2.7K2O 0.91 1.02

cK2SO4 1.5 1.5

Na2O 0.2 0.33cNa2SO4 0.2 0.2

SO3 2.41 2.67dK2O 0.1 0.2

CO2 0.12 0.73dNa2O 0.1 0.2

TiO2 0.32 0.53 CaO(free) 1.2 -

Mn2O3 0.06 0.07 CaCO3 0.8 -P2O5 0.25 0.34dMgO 2.5 2.0

Cl 0.03 0.073 dSO3 0.2 0.3Loss of ignition 1.01 3.24

aXRF data corrected for ignition loss.bCalculated from the chemical analysis.cEstimated based on the alkali content and on the alkali distribution given in Taylor (1987).dPresent as solid solution in the major clinker phases

2.1.7. Synthesis of synthetic Fe-cement

In addition, the hydration products of Al-free synthetic cements were investigated. The

clinker composition of the synthetic Fe-cement consisted of 78.5% C3S, 19.3% C2F,

0.5% Na2SO4and 1.7 % K2SO4. The alkalis were added to mimic real Portland cement.

No Al-phases were present to allow the identification of Fe-containing hydrates.

The synthetic cements were hydrated in the presence and the absence of calcite and

gypsum with a liquid/solid ratio of 1. Different quantities of gypsum and calcite were

added while the ratio of C3S to C2F was kept constant (Table 2). The phase assemblage

was investigated after 3 days and 3 months. The results from the studies were compared

to those from studies on the synthesized phases [10-14, 19] and the studies in OPC

systems [21-23, 33-35].


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Table 2 The compositions of the synthetic Fe-cement mixes with varying gypsum (CsH2) and

calcite (Cc) content.

Sample ID C3S C2F Na2SO4 K2SO4 CsH2 Ccg/100g g/100g g/100g g/100g g/100g g/100g

Gyp-0% 78.5 19.3 0.5 1.7 0.0Gyp-6% 73.7 18.1 0.5 1.7 6.0Gyp-26% 57.6 14.2 0.5 1.7 26.0

Cc1 70.7 19.3 0.5 1.7 7.8Cc 2 66.3 18.1 0.5 1.7 6 7.4Cc 3 56.2 15.4 0.5 1.7 20 6.2

C2F-pure 97.8 0.5 1.7

C2F-Gyp 65.2 0.5 1.7 32.6

C2F-Gyp-Cc 58.6 0.5 1.7 32.6 6.6

C2F-Cc 88 0.5 1.7 9.8

2.2. Analytical methods

2.2.1. Powder X-ray diffraction

X-ray powder diffraction (XRD) measurements were carried out using CuKradiation on

a PANalytical XPert Pro MPD diffractometer in a -2 configuration with an angular

scan 5-75 2 and an XCelerator detector. To study the effect of relative humidity, a

climatic chamber (Anton Paar) specially designed for the X- ray diffractometer in a -

configuration was used. The sample was placed in a sample tray of the climatic chamber

of the X-ray diffractometer where both temperature and relative humidity can be

controlled. The diffractograms of the synthesized pure phases and identification of new

phases in cement paste were verified using the PDF database of the International Centre

for Diffraction Data (ICDD). CaF2was mixed to the powder samples as internal standard

to determine the unit cell parameters for some Fe-containing phases.


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2.2.2. Synchrotron powder diffraction

Synchrotron powder diffraction data were collected at the Swiss-Norwegian Beam Line

(SNBL) at the European Synchrotron Radiation Facility (ESRF), Grenoble, France. The

powder material was introduced into glass capillaries (0.5 mm diameter). Data collection

was performed at 295 K at a wavelength of = 0.72085 using a MAR345 image plate

detector with the highest resolution (3450 x 3450 pixels with a pixel size of 100 m). The

calculated absorption coefficient mR (m= powder packing factor, = linear absorption

coefficient, R = radius of the capillary) was estimated at 0.65. Three sample-to-detector

distances were used (150, 250 and 350 mm) in order to combine the advantages of high

resolution and extended 2 range. The detector parameters and the wavelength were

calibrated with NIST LaB6. The exposure time was 60s with a rotation of the capillary by

60. The two-dimensional data were integrated with the Fit2D program which produced

the correct intensity in relative scale [36]. This 2D detector was used in order to perfectly

define the background, to observe very weak diffraction peaks, and to improve

fe-containing hydrates and their fate during cement hydration: thermodynamic data and experimental ...

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