Journal of Microscopy, Vol. 259, Issue 1 2015, pp. 53–58
doi: 10.1111/jmi.12247
Received 28 October 2014; accepted 18 February 2015
Investigation of C3S hydration by environmental scanning electron microscope Y. SAKALLI & R. TRETTIN Chemistry of Building Materials & Materials, University of Siegen, Siegen, Germany
Key words. Cement chemistry, C-S-H phases, C3 S Hydration, electron microscopy, ESEM, Hydration.
Summary Tricalciumsilicate (C3 S, Alite) is the major component of the Portland cement clinker, The hydration of the Alite is decisive for the properties of the resulting material due to the high content in cement. The mechanism of the hydration of C3 S is very complicated and not yet fully understood. There are some models that describe the hydration of C3 S in various ways. The Environmental Scanning Electron Microscopy (ESEM) working in gaseous atmosphere enables high-resolution dynamic observations of structure of materials, from micrometre to nanometre scale. This provides a new perspective in material research. ESEM significantly allows imaging of specimen in their natural state without the need for special preparation (coating, drying, etc.) that can alter the physical properties. This paper presents the results of our experimental studies of hydration of C3 S using ESEM. The ESEM turned out to be an important extension of the conventional scanning microscopy. The purpose of these investigations is to gain insight of hydration mechanism to determine which hydration products are formed and to analyze if there are any differences in the composition of the hydration products.
Introduction Alite consists of calcium, silicon, oxygen (Ca3 SiO5 = 3CaO SiO2 ) and 3% foreign oxides. The amount of incorporated foreign oxides (MgO, Al2 O3 , TiO2, Fe2 O3 , etc.) depends mostly on the composition of the starting materials, the firing temperature and the cooling process. The foreign oxides influence the properties of the hydrated clinker. The share of foreign oxides incorporated in Alite increases the strength of the cement (Woerman et al., 1963). Figure 1 presents an SEM image of the ground and not hydrated C3 S. The exact mechanism of the hydration of C3 S has not been elucidated, although it has been studied for more than half a Correspondence to: Y. Sakalli, Chemistry of Building Materials & Materials, University of Siegen, 57076 Siegen, Germany. Tel: +492717404757; fax: +49271740 2930; e-mail: [email protected]
C 2015 The Authors C 2015 Royal Microscopical Society Journal of Microscopy
Fig. 1. Unhydrated C3S.
century. However, there are models that were derived based on experimental observations of hydration. Figure 2 explains the model of C3 S hydration according to Jennings and Parrott. Comparatively, it is difficult to study the hydration mechanism of formed Calcium Silicate Hydrate (C–S–H) phases, because they are in amorphous state, therefore, the X-rays diffraction cannot be used for structure determination. The C–S–H phases are the major hydration products and main binding phases in Portland cement. However, the characterization of its atomic structure and the effects of the physical and chemical conditions (e.g., temperature, Ca/Si ratio) of C–S–H formation on the C–S–H structure remain incomplete. For example, it is unclear whether there is a difference between the structure of C-S-H that forms inside and outside of the original output grains. Although some results suggest that there is a difference between ‘inner’ and ‘outer’ product, this has not been confirmed. There is a related question, whether there is a difference between the structure of the early hydration products and structure of late hydration products. Figure 2 illustrates the difference between
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Fig. 2. Schematic representations for two types of hydration phenomena (Jennings & Parrot, 1986).
Fig. 5. C3 S grain after 96 h hydration.
Fig. 3. Schematic diagram of the arrangement of surface layers on a C3S grain during the slow reaction period based on the hydrogen depth profile measured by nuclear resonance reaction analysis (Bullard, et al., 2010).
Fig. 6. C3 S after 24 h hydration.
Fig. 4. C3 S grain after 96 h hydration.
these two reaction scenarios. Either two different product types are (‘inner’ and ‘outer’ products) formed, which are separated by a boundary and by the original surface of the anhydrous particle (Fig. 2A) are defined or the three different product types (‘inner’, ‘middle’ and ‘outer’ products; Fig. 2B). The middle product is a transitional product and after some days will be consumed and transformed into outer product (Jennings & Parrot, 1986). The second model of C3 S hydration is based on nuclear resonance reaction analysis measurements of hydrogen depth profiles. Based on ideas from the glass corrosion literature, the C 2015 The Authors C 2015 Royal Microscopical Society, 259, 53–58 Journal of Microscopy
INVESTIGATION OF C3 S HYDRATION BY ENVIRONMENTAL SCANNING ELECTRON MICROSCOPE
55
Fig. 7. C3S + nanosilicate after 24 h hydration.
Fig. 9. C3S + nanosilicate after 48 h hydration.
Fig. 8. C3S after 48 h hydration.
Fig. 10. C3S after 96 h hydration.
overall hydrogen depth profile measured by nuclear resonance reaction analysis has been interpreted as a set of layers with differing degrees of calcium/hydrogen exchange as shown in Figure 3 (Bullard, et al., 2010).
The loss on ignition of the reactants was determined and the reactants were weighed in stoichiometric amounts. The mixture was heated at 1450°C in a Pt/Rh crucible in a muffle furnace. The free lime content, CaO not bounded to C3 S, was determined according to Frank (1941) and was less than 0.5%. The phase composition was investigated by X-ray powder diffractometry. C3 S was preserved under argon atmosphere and was grounded with a ball mill to obtain an average particle diameter d50 of 15 ± 2 µm. The measurement was carried out by means of static light scattering with a laser granulometer while the sample was dispersed in isopropanol.
Experimental procedure Synthesis of C3 S Triclinic Tricalciumsilicate (C3 S) was synthesized from CaCO3 and SiO2 : 3C aCO 3 + SiO 2 → C 3 S + 3CO 2 C 2015 The Authors C 2015 Royal Microscopical Society, 259, 53–58 Journal of Microscopy
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Results and discussion
Fig. 11. C3S + nanosilicate after 96 h hydration.
Sample preparation Two tablets were pressed from the synthesized C3 S powder with the XRF sample preparation equipment. The tablets were heated at 1450°C for 3 h in the high-temperature furnace. This approach has two advantages. Firstly, the growth of C3 S grains occurred which helped in better examination. Secondly, the sample preparation for Environmental Scanning Electron Microscopy (ESEM) investigations was simplified. One tablet was hydrated in pure water, other tablet in a suspension of water and nanosilicate. The samples of two tablets were taken after 24, 48 and 96 h and investigated with the SEM in ESEM Mode, with gaseous secondary electron detector and under water vapor atmosphere with 632 Pa (4.74 Torr) sample chamber pressure.
Figure 5 shows two types of C-S-H phases after 96 h of hydration period (see also Fig. 4 for an overview). The green line indicates the size of the original C3 S particle. The C3 S grain was broken down during sample preparation to study the cross-sectional view of the grain. The results of investigations have shown that the hydration process has been completed as described by Jennings and Parrott. Two types of C-S-H phases were formed during the hydration of C3 S. These phases differ in their density and are referred as ‘inner’ product and ‘outer’ product. The inner product is formed within the dimensions of the original C3 S particle and has a higher density as compared to the outer product. The outer product grows inside the pores of C3 S particles and mostly has needle-like structures of lower density. In the next step, it was examined how the hydration proceeds and if the nanosilicate has any influence on the progress of hydration and on the growth of the C-S-H phases. Figures 6–11 show the images that were recorded after 24, 48 and 96 h hydrated samples with and without nanosilicate. The results indicate that the nanosilicate has a minimal effect on the hydration process and on the growth of the C-S-H phases. When the images are considered, it should be noted that the positive response of the samples with silicate is greater than the samples without silicate. The reaction bridle and the C-S-H phases of the samples with silicate are also grown as without silicate. In last step of this work, it was examined if there were any differences between the composition of the formed C-S-H phases (‘Inner’ and ‘Outer’ products). In this context, chemical elemental analysis by EDX on the samples was performed. Figures 12–15 present the results of EDX analysis. Although the ESEM is equipped with latest EDX analysis system, however, elemental analysis results are not precise enough to make accurate statements about the composition of the formed C–S–H phases. During the measurements, the probability of deviations is up to 10%. Possibly it is because of
Fig. 12. EDX – selected area analyses of C3S after 96 h hydration. C 2015 The Authors C 2015 Royal Microscopical Society, 259, 53–58 Journal of Microscopy
INVESTIGATION OF C3 S HYDRATION BY ENVIRONMENTAL SCANNING ELECTRON MICROSCOPE
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Fig. 13. EDX – selected area analyses of C3S + nanosilicate after 96 h hydration.
very high excitation of the electron beam. However, it could be still detected through the analysis that there are differences in the composition of the individual phases (‘Inner’ und ‘Outer’ product). In Future, for further investigations of the composition of phases, more refined techniques like TEM can be used and their results will be published. Conclusions
Fig. 14. EDX – line profile analyses of C3S after 24 h hydration.
Fig. 15. EDX – element profile plot firm Figure 4. C 2015 The Authors C 2015 Royal Microscopical Society, 259, 53–58 Journal of Microscopy
These investigations have shown that the formed products of the C3 S hydration using ESEM can very well be characterized. For normal SEM investigations, sample surface must be made conductive using sputtering technique because the samples should be examined in high vacuum mode. The applied conductive surface prevents the charging of the sample. The conductive layer reveals important information such as the details of the different C–S–H phases or the details of the interfacial transition zone. For high vacuum mode investigations,
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well dried samples should be used. Drying process is responsible for many changes such as occurrence of artefacts, and structure of aqueous C–S–H phases can be changed or partially destroyed. The samples can be examined using ESEM in an aqueous atmosphere without pretreatment and without drying. Therefore, different reaction zones and different rehydration products were identified. These results show that the differences between unreacted C3 S, ‘Inner’ and ‘Outer’ product and the different phases are clearly differentiated. Microstructure of the C–S–H phases can also be explored. A slight difference has been found in the growth of C–S–H phases of the specimen with and without silicate. The C–S–H phases of sample with silicate have shown better growth than the specimen without silicate. But unfortunately, the EDX analysis of ESEM depends on many reasons of functioning (great suggestion area and great depth of information area). It is not precise enough to determine if there is a difference in the composition of the C–S–H phases. In conclusion, it can be stated that very reliable and new information can be obtained from the results of these investigations, which facilitate the understanding of some processes of the hydration process of C3 S and describe the nano-/microstructure of the formed C–S–H phases. Future work In the next step of investigations, a series of new samples with the same approach will be produced and then the TEMLamellas will be prepared from these samples using focused ion beam and this sample will be investigated with TEM and latest ChemiSTEM element analysis technology. These studies are designed to deliver the missing information of the composition of the C–S–H phases. As a result of these investigations, details of the nanostructure of the C–S–H phases can be explained. References Brown, P.W., Franz, E., Frohndhoff, G. & Taylor, H.F. (1984) Analyses of the aqueous phase during early C3S hydration. Cement Concrete Res. 14, 257–262. Bullard, J.W., Jennings, H.M., Livingston, et al. (2010) Mechanism of cement hydration. Cement Concrete Res. 41, 1208–1223.
Chen, J.J., Thomasb, J.J., Taylorc, H.F. & Jennings, H.M. (2004) Solubility and structure of calcium silicate hydrate. Cement Concrete Res. 34, 1499–1519. De la Torre, A., Bruque, S., Campo, J. & Aranda, M. (2002) The superstructure of C3S from synchrotron and neutron powder diffraction and its role in quantitative phase analyses. Cement Concrete Res, 32, 1347–1356. Frank, B. (1941) Bestimmung von Calciumoxid und Calciumhydroxid neben wasserfreiem und wasserhaltigem Calciumsilicat. Zeitschrift f¨ur anorganische und allgemeine Chemie. 247, 180–184. Hewlett, P. (2004) Lea’s Chemistry of Cement and Concrete. Elsevier Science, Oxford, UK. Jennings, H.M. (2000) A model for the microstructure of calcium silicate hydrate in cement paste. Cement Concrete Res. 30, 101–116. Jennings, H.M. & Parrot, L.J. (1986) Microstructural analysis of hydrated alite paste. J. Mater. Sci. 21, 4053–4059. Meredith, P. & Donald, A.M. (1995) Pre-induction and induction hydration of tricalcium silicate: an environmental scanning electron microscopy study. J. Mater. Sci. 30, 1921–1930. Neubauer, C.M. & Jennings, H.M. (1996) The role of the environmental scanning electron microscope in the investigation of cement-based materials. Scanning. 18, 515–521. Richardson, I. (2000) The nature of hydration products in hardened cement pastes. Cement Concrete Comp. 2, 97–113. Richardson, I. & Groves, G. (1993) Microstructure and microanalysis of hardened ordinary Portland cement pastes. J. Mater. Sci. 28, 265– 277. Soler, J.M. (1988–2007) Thermodynamic Description of the Solubility of C-S-H Gels in Hydrated Portland Cement “Literature Review.” Institut de Ci`encies de la Terra “Jaume Almera” (CSIC). FI-27160 Olkiluoto, Finland. Stokes, D.J. (2003) Recent advances in electron imaging, image interpretation and applications: environmental scanning electron microscopy. Phil. Trans. R. Soc. Lond. A. 361, 2771–2787. Taylor, H. (1997) Cement Chemistry. American Society of Civil Engineers Cement Chemistry, 2nd edn. T. Telford, London. Trettin, R. & Wieker, W. (1986) Zur Hydratation von Trikalziumsilikat I. Ursachen der Induktionsperiode. Silikattechnik, 37, 75–78. Woerman, E., Hahn, I. & Eysel, W. (1963) Chemische und strukturelle Untersuchungen der Mischkristallbildung von Tricalciumsilikat. ZKG Int., 59, 70–80. Young, J. & Tong, H. (1977) Microstructure and strength development of beta-dicalcium silicate pastes with and without admixtures. Cement Concrete Res. 7, 627–636.
C 2015 The Authors C 2015 Royal Microscopical Society, 259, 53–58 Journal of Microscopy
doi: 10.1111/jmi.12247
Received 28 October 2014; accepted 18 February 2015
Investigation of C3S hydration by environmental scanning electron microscope Y. SAKALLI & R. TRETTIN Chemistry of Building Materials & Materials, University of Siegen, Siegen, Germany
Key words. Cement chemistry, C-S-H phases, C3 S Hydration, electron microscopy, ESEM, Hydration.
Summary Tricalciumsilicate (C3 S, Alite) is the major component of the Portland cement clinker, The hydration of the Alite is decisive for the properties of the resulting material due to the high content in cement. The mechanism of the hydration of C3 S is very complicated and not yet fully understood. There are some models that describe the hydration of C3 S in various ways. The Environmental Scanning Electron Microscopy (ESEM) working in gaseous atmosphere enables high-resolution dynamic observations of structure of materials, from micrometre to nanometre scale. This provides a new perspective in material research. ESEM significantly allows imaging of specimen in their natural state without the need for special preparation (coating, drying, etc.) that can alter the physical properties. This paper presents the results of our experimental studies of hydration of C3 S using ESEM. The ESEM turned out to be an important extension of the conventional scanning microscopy. The purpose of these investigations is to gain insight of hydration mechanism to determine which hydration products are formed and to analyze if there are any differences in the composition of the hydration products.
Introduction Alite consists of calcium, silicon, oxygen (Ca3 SiO5 = 3CaO SiO2 ) and 3% foreign oxides. The amount of incorporated foreign oxides (MgO, Al2 O3 , TiO2, Fe2 O3 , etc.) depends mostly on the composition of the starting materials, the firing temperature and the cooling process. The foreign oxides influence the properties of the hydrated clinker. The share of foreign oxides incorporated in Alite increases the strength of the cement (Woerman et al., 1963). Figure 1 presents an SEM image of the ground and not hydrated C3 S. The exact mechanism of the hydration of C3 S has not been elucidated, although it has been studied for more than half a Correspondence to: Y. Sakalli, Chemistry of Building Materials & Materials, University of Siegen, 57076 Siegen, Germany. Tel: +492717404757; fax: +49271740 2930; e-mail: [email protected]
C 2015 The Authors C 2015 Royal Microscopical Society Journal of Microscopy
Fig. 1. Unhydrated C3S.
century. However, there are models that were derived based on experimental observations of hydration. Figure 2 explains the model of C3 S hydration according to Jennings and Parrott. Comparatively, it is difficult to study the hydration mechanism of formed Calcium Silicate Hydrate (C–S–H) phases, because they are in amorphous state, therefore, the X-rays diffraction cannot be used for structure determination. The C–S–H phases are the major hydration products and main binding phases in Portland cement. However, the characterization of its atomic structure and the effects of the physical and chemical conditions (e.g., temperature, Ca/Si ratio) of C–S–H formation on the C–S–H structure remain incomplete. For example, it is unclear whether there is a difference between the structure of C-S-H that forms inside and outside of the original output grains. Although some results suggest that there is a difference between ‘inner’ and ‘outer’ product, this has not been confirmed. There is a related question, whether there is a difference between the structure of the early hydration products and structure of late hydration products. Figure 2 illustrates the difference between
54
Y. SAKALLI & R. TRETTIN
Fig. 2. Schematic representations for two types of hydration phenomena (Jennings & Parrot, 1986).
Fig. 5. C3 S grain after 96 h hydration.
Fig. 3. Schematic diagram of the arrangement of surface layers on a C3S grain during the slow reaction period based on the hydrogen depth profile measured by nuclear resonance reaction analysis (Bullard, et al., 2010).
Fig. 6. C3 S after 24 h hydration.
Fig. 4. C3 S grain after 96 h hydration.
these two reaction scenarios. Either two different product types are (‘inner’ and ‘outer’ products) formed, which are separated by a boundary and by the original surface of the anhydrous particle (Fig. 2A) are defined or the three different product types (‘inner’, ‘middle’ and ‘outer’ products; Fig. 2B). The middle product is a transitional product and after some days will be consumed and transformed into outer product (Jennings & Parrot, 1986). The second model of C3 S hydration is based on nuclear resonance reaction analysis measurements of hydrogen depth profiles. Based on ideas from the glass corrosion literature, the C 2015 The Authors C 2015 Royal Microscopical Society, 259, 53–58 Journal of Microscopy
INVESTIGATION OF C3 S HYDRATION BY ENVIRONMENTAL SCANNING ELECTRON MICROSCOPE
55
Fig. 7. C3S + nanosilicate after 24 h hydration.
Fig. 9. C3S + nanosilicate after 48 h hydration.
Fig. 8. C3S after 48 h hydration.
Fig. 10. C3S after 96 h hydration.
overall hydrogen depth profile measured by nuclear resonance reaction analysis has been interpreted as a set of layers with differing degrees of calcium/hydrogen exchange as shown in Figure 3 (Bullard, et al., 2010).
The loss on ignition of the reactants was determined and the reactants were weighed in stoichiometric amounts. The mixture was heated at 1450°C in a Pt/Rh crucible in a muffle furnace. The free lime content, CaO not bounded to C3 S, was determined according to Frank (1941) and was less than 0.5%. The phase composition was investigated by X-ray powder diffractometry. C3 S was preserved under argon atmosphere and was grounded with a ball mill to obtain an average particle diameter d50 of 15 ± 2 µm. The measurement was carried out by means of static light scattering with a laser granulometer while the sample was dispersed in isopropanol.
Experimental procedure Synthesis of C3 S Triclinic Tricalciumsilicate (C3 S) was synthesized from CaCO3 and SiO2 : 3C aCO 3 + SiO 2 → C 3 S + 3CO 2 C 2015 The Authors C 2015 Royal Microscopical Society, 259, 53–58 Journal of Microscopy
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Y. SAKALLI & R. TRETTIN
Results and discussion
Fig. 11. C3S + nanosilicate after 96 h hydration.
Sample preparation Two tablets were pressed from the synthesized C3 S powder with the XRF sample preparation equipment. The tablets were heated at 1450°C for 3 h in the high-temperature furnace. This approach has two advantages. Firstly, the growth of C3 S grains occurred which helped in better examination. Secondly, the sample preparation for Environmental Scanning Electron Microscopy (ESEM) investigations was simplified. One tablet was hydrated in pure water, other tablet in a suspension of water and nanosilicate. The samples of two tablets were taken after 24, 48 and 96 h and investigated with the SEM in ESEM Mode, with gaseous secondary electron detector and under water vapor atmosphere with 632 Pa (4.74 Torr) sample chamber pressure.
Figure 5 shows two types of C-S-H phases after 96 h of hydration period (see also Fig. 4 for an overview). The green line indicates the size of the original C3 S particle. The C3 S grain was broken down during sample preparation to study the cross-sectional view of the grain. The results of investigations have shown that the hydration process has been completed as described by Jennings and Parrott. Two types of C-S-H phases were formed during the hydration of C3 S. These phases differ in their density and are referred as ‘inner’ product and ‘outer’ product. The inner product is formed within the dimensions of the original C3 S particle and has a higher density as compared to the outer product. The outer product grows inside the pores of C3 S particles and mostly has needle-like structures of lower density. In the next step, it was examined how the hydration proceeds and if the nanosilicate has any influence on the progress of hydration and on the growth of the C-S-H phases. Figures 6–11 show the images that were recorded after 24, 48 and 96 h hydrated samples with and without nanosilicate. The results indicate that the nanosilicate has a minimal effect on the hydration process and on the growth of the C-S-H phases. When the images are considered, it should be noted that the positive response of the samples with silicate is greater than the samples without silicate. The reaction bridle and the C-S-H phases of the samples with silicate are also grown as without silicate. In last step of this work, it was examined if there were any differences between the composition of the formed C-S-H phases (‘Inner’ and ‘Outer’ products). In this context, chemical elemental analysis by EDX on the samples was performed. Figures 12–15 present the results of EDX analysis. Although the ESEM is equipped with latest EDX analysis system, however, elemental analysis results are not precise enough to make accurate statements about the composition of the formed C–S–H phases. During the measurements, the probability of deviations is up to 10%. Possibly it is because of
Fig. 12. EDX – selected area analyses of C3S after 96 h hydration. C 2015 The Authors C 2015 Royal Microscopical Society, 259, 53–58 Journal of Microscopy
INVESTIGATION OF C3 S HYDRATION BY ENVIRONMENTAL SCANNING ELECTRON MICROSCOPE
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Fig. 13. EDX – selected area analyses of C3S + nanosilicate after 96 h hydration.
very high excitation of the electron beam. However, it could be still detected through the analysis that there are differences in the composition of the individual phases (‘Inner’ und ‘Outer’ product). In Future, for further investigations of the composition of phases, more refined techniques like TEM can be used and their results will be published. Conclusions
Fig. 14. EDX – line profile analyses of C3S after 24 h hydration.
Fig. 15. EDX – element profile plot firm Figure 4. C 2015 The Authors C 2015 Royal Microscopical Society, 259, 53–58 Journal of Microscopy
These investigations have shown that the formed products of the C3 S hydration using ESEM can very well be characterized. For normal SEM investigations, sample surface must be made conductive using sputtering technique because the samples should be examined in high vacuum mode. The applied conductive surface prevents the charging of the sample. The conductive layer reveals important information such as the details of the different C–S–H phases or the details of the interfacial transition zone. For high vacuum mode investigations,
58
Y. SAKALLI & R. TRETTIN
well dried samples should be used. Drying process is responsible for many changes such as occurrence of artefacts, and structure of aqueous C–S–H phases can be changed or partially destroyed. The samples can be examined using ESEM in an aqueous atmosphere without pretreatment and without drying. Therefore, different reaction zones and different rehydration products were identified. These results show that the differences between unreacted C3 S, ‘Inner’ and ‘Outer’ product and the different phases are clearly differentiated. Microstructure of the C–S–H phases can also be explored. A slight difference has been found in the growth of C–S–H phases of the specimen with and without silicate. The C–S–H phases of sample with silicate have shown better growth than the specimen without silicate. But unfortunately, the EDX analysis of ESEM depends on many reasons of functioning (great suggestion area and great depth of information area). It is not precise enough to determine if there is a difference in the composition of the C–S–H phases. In conclusion, it can be stated that very reliable and new information can be obtained from the results of these investigations, which facilitate the understanding of some processes of the hydration process of C3 S and describe the nano-/microstructure of the formed C–S–H phases. Future work In the next step of investigations, a series of new samples with the same approach will be produced and then the TEMLamellas will be prepared from these samples using focused ion beam and this sample will be investigated with TEM and latest ChemiSTEM element analysis technology. These studies are designed to deliver the missing information of the composition of the C–S–H phases. As a result of these investigations, details of the nanostructure of the C–S–H phases can be explained. References Brown, P.W., Franz, E., Frohndhoff, G. & Taylor, H.F. (1984) Analyses of the aqueous phase during early C3S hydration. Cement Concrete Res. 14, 257–262. Bullard, J.W., Jennings, H.M., Livingston, et al. (2010) Mechanism of cement hydration. Cement Concrete Res. 41, 1208–1223.
Chen, J.J., Thomasb, J.J., Taylorc, H.F. & Jennings, H.M. (2004) Solubility and structure of calcium silicate hydrate. Cement Concrete Res. 34, 1499–1519. De la Torre, A., Bruque, S., Campo, J. & Aranda, M. (2002) The superstructure of C3S from synchrotron and neutron powder diffraction and its role in quantitative phase analyses. Cement Concrete Res, 32, 1347–1356. Frank, B. (1941) Bestimmung von Calciumoxid und Calciumhydroxid neben wasserfreiem und wasserhaltigem Calciumsilicat. Zeitschrift f¨ur anorganische und allgemeine Chemie. 247, 180–184. Hewlett, P. (2004) Lea’s Chemistry of Cement and Concrete. Elsevier Science, Oxford, UK. Jennings, H.M. (2000) A model for the microstructure of calcium silicate hydrate in cement paste. Cement Concrete Res. 30, 101–116. Jennings, H.M. & Parrot, L.J. (1986) Microstructural analysis of hydrated alite paste. J. Mater. Sci. 21, 4053–4059. Meredith, P. & Donald, A.M. (1995) Pre-induction and induction hydration of tricalcium silicate: an environmental scanning electron microscopy study. J. Mater. Sci. 30, 1921–1930. Neubauer, C.M. & Jennings, H.M. (1996) The role of the environmental scanning electron microscope in the investigation of cement-based materials. Scanning. 18, 515–521. Richardson, I. (2000) The nature of hydration products in hardened cement pastes. Cement Concrete Comp. 2, 97–113. Richardson, I. & Groves, G. (1993) Microstructure and microanalysis of hardened ordinary Portland cement pastes. J. Mater. Sci. 28, 265– 277. Soler, J.M. (1988–2007) Thermodynamic Description of the Solubility of C-S-H Gels in Hydrated Portland Cement “Literature Review.” Institut de Ci`encies de la Terra “Jaume Almera” (CSIC). FI-27160 Olkiluoto, Finland. Stokes, D.J. (2003) Recent advances in electron imaging, image interpretation and applications: environmental scanning electron microscopy. Phil. Trans. R. Soc. Lond. A. 361, 2771–2787. Taylor, H. (1997) Cement Chemistry. American Society of Civil Engineers Cement Chemistry, 2nd edn. T. Telford, London. Trettin, R. & Wieker, W. (1986) Zur Hydratation von Trikalziumsilikat I. Ursachen der Induktionsperiode. Silikattechnik, 37, 75–78. Woerman, E., Hahn, I. & Eysel, W. (1963) Chemische und strukturelle Untersuchungen der Mischkristallbildung von Tricalciumsilikat. ZKG Int., 59, 70–80. Young, J. & Tong, H. (1977) Microstructure and strength development of beta-dicalcium silicate pastes with and without admixtures. Cement Concrete Res. 7, 627–636.
C 2015 The Authors C 2015 Royal Microscopical Society, 259, 53–58 Journal of Microscopy
