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Speciation of iron(III) in hydrated cements 5. GENERAL CONCLUSION AND OUTLOOK Standard analytical techniques (XRD, TGA, SEM) shows C-S-H, CH, AFt and AFm phases formation during hydration. With selective dissolution using SAM the presence of Al- and Fe-containing siliceous hydrogarnet was confirmed in the hydrated cements. EXAFS spectroscopy further shows that during the first few hours of hydration Fe(OH)3 formed. At later ages, Fe-containing siliceous hydrogarnet was identified as the main Fe- containing hydrate. Thermodynamic modeling of the hydration predicts that iron should be bound in siliceous hydrogarnet, possibly as a solid solution together with aluminum: Ca3(AlxFe1-x)2(SiO4)3-y(OH)4y. These modeling results are in agreement with the experimental observations. The investigations have been complemented with a study on the hydration of synthetic, aluminum free cements. In the presence of sulfate, Fe-ettringite was found to be stable besides C-S-H and CH. Possibly Fe-siliceous hydrogarnets were also present, but they could not be clearly identified standard analytical techniques. The same hydrate assemblage (Fe-ettringite, C-S-H and CH) was observed for the calcite free and calcite containing synthetic Fe-cements. The experimental findings are supported by the modeling results. In Portland cements, however, the formation of Fe-ettringite is not expected as the more stable Al-ettringite preferentially forms. The presence of aluminum in the investigated Portland cements leads to the formation of stable Al-ettringite and Al- containing AFm phases while all Fe is released during ferrite dissolution present as Fe- siliceous hydrogarnet in the long term. In general, the solubility products of Fe-containing hydrates determined in this study will help in the future to establish whether and to what extent Fe-containing hydrates are stable in blended cementitious systems, and allow further considerations on the durability 185
5. GENERAL CONCLUSION AND OUTLOOK of cementitious materials and assessments related to the safe disposal of radioactive and hazardous wastes. A significant part of the aluminum in hydrated Portland cement might be incorporated in C-S-H. Recent experimental data indicates that up to 50% of aluminum present in a blended PC-slag system was incorporated in the C-A-S-H phase [140]. The incorporation in Portland cement is somewhat lower as the incorporation of aluminium in C-S-H decreases with increasing Ca/Si ratio of the C-S-H [141]. This poses the question whether C-S-H might also incorporate significant amounts of iron. NMR results, however, indicate that the uptake of iron in C-S-H is much lower than the uptake of aluminum. The presence of Fe 3+ within the structure of the solids distorts the NMR signal and leads to strong dipolar coupling between the spin of the element investigated and the spins of the two unpaired electrons from Fe 3+ [142]. Montheilet et al. [143] calculated on the basis of the distortion of H-NMR measurements that 2.5×10 15 Fe were present per m 2 of C-S-H in a white cement, which corresponds to 1 Fe per 25’000 Si 2 . In a grey cement, the H-NMR measurements indicate that 2-3 times more Fe are bound in the C-S-H [144], so that in a grey cement there might be 1 Fe per 10’000 Si, which corresponds to 0.1 mg Fe2O3 per 1 g SiO2 and thus is a negligible quantity. 5.2. Outlook The research presented in this thesis also reveals that in different areas more detailed studies should be carried out to address the following topics: Solid solutions in the interlayer structure of Fe-Friedel’s salt and of mixed hydrogarnets (Ca3(AlxFe1-x)2(SiO4)3-y(OH)4y). 2 Surface area of C-S-H: 125 m 2 /cm 3 , Molar volume of C-S-H :78 cm 3 /mol: 2.5×10 15 Fe/m 2 × 125 m 2 /cm 3 ×78 cm 3 /mol /(6×10 23 parts per mol) = 0.000041 Fe/Si = 1 Fe/25’000 Si 186
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Fe-containing hydrates and their fa
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The measured composition of the liq
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ZUSAMMENFASSUNG Thermodynamische Mo
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konnten die Fe-haltigen Hydrate im
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I owe to thank all the laboratory t
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Table 19 Compositions of Al/Fe-mono
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LIST OF FIGURES Fig. 1 Calculated v
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Fig. 34 Calculated solubility produ
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Fig. 62 Calculated solubility produ
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Table of Contents TABLE OF CONTENTS
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TABLE OF CONTENTS 3. SYNTHETIC FE
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TABLE OF CONTENTS 3.5.4. Solid solu
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1 INTRODUCTION CHAPTER 1 INTRODUCTI
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CHAPTER 1 INTRODUCTION be formed. T
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cm 3 /100 g cement 85 80 75 70 65 6
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CHAPTER 1 INTRODUCTION 1.4 Characte
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CHAPTER 1 INTRODUCTION Fig. 4 Sampl
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CHAPTER 1 INTRODUCTION Identificat
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CHAPTER 2 MATERIALS AND METHODS han
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3CaOAl2O3 + 6H2O → 3CaOAl2O36H2O
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CHAPTER 2 MATERIALS AND METHODS Tab
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CHAPTER 2 MATERIALS AND METHODS 2.2
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CHAPTER 2 MATERIALS AND METHODS fil
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CHAPTER 2 MATERIALS AND METHODS at
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CHAPTER 2 MATERIALS AND METHODS the
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CHAPTER 2 MATERIALS AND METHODS 0 t
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CHAPTER 2 MATERIALS AND METHODS Tab
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CHAPTER 2 MATERIALS AND METHODS 2.3
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CHAPTER 2 MATERIALS AND METHODS The
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CHAPTER 3 SYNTHETIC FE-CONTAINING H
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a). b). CHAPTER 3 SYNTHETIC FE-CONT
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o layer thickness (A) 8.0 7.8 7.6 C
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Phase log KSo CHAPTER 3 SYNTHETIC F
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volume [cm 3 ] 700 600 500 400 300
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Intensity [arb. units] Fe-Fr CHAPTE
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Page 160 and 161: CHAPTER 3 SYNTHETIC FE-CONTAINING H
Page 172 and 173: CHAPTER 4 FE-CONTAINING HYDRATES IN
Page 182 and 183: (Al+Fe)/Ca (Al+Fe)/Ca 0.8 0.6 0.4 0
Page 188 and 189: k 3 (k) CHAPTER 4 FE-CONTAINING HYD
Page 200 and 201: differentiated relative weight Weig
Page 202 and 203: Early reaction CHAPTER 4 FE-CONTAIN
Page 204 and 205: weight loss in % differentiated rel
Page 208 and 209: 5. GENERAL CONCLUSION AND OUTLOOK a
Page 212 and 213: 5. GENERAL CONCLUSION AND OUTLOOK
Page 214 and 215: Techniques XRD X-ray diffraction TG
Page 216 and 217: APPENDIX APPENDIX Appendix A: Addit
Page 218 and 219: Intensity (arb. Units) P Fe 2O 3 R
Page 220 and 221: APPENDIX Appendix B7 XRD patterns o
Page 222 and 223: REFERENCES REFRENCES [1] H.F.W. Tay
Page 224 and 225: REFRENCES [29] M. Vespa, R. Dähn,
Page 226 and 227: REFRENCES [54] M. Balonis, B. Lothe
Page 228 and 229: REFRENCES [81] H.F.W. Taylor, Cryst
Page 230 and 231: REFRENCES [107] K. Kyritsis, N. Mel
Page 232 and 233: REFRENCES [134] M. Wilke, F. Farges
Page 235 and 236: CURRCULUM VITAE Curriculum Vitae Na
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