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1.
Beta C2S was hydrated at room temperature with and without added CaCl2 or C2H5OH by methods previously studied for the hydration of C3S, i.e. paste, bottle, and ball-mill hydration. The amount of reacted β-C2S, the Ca(OH)2 concentration in the liquid phase, the CaO/SiO2 molar ratio, and the specific surface area of the hydrate were investigated. A topochemical reaction occurs between water and β-C2S, resulting in the appearance of solid Ca(OH)2 and a hydrated silicate with a CaO/SiO2 molar ratio of ≃1. As the liquid phase becomes richer in Ca(OH)2, the first hydrate transforms to one with a higher CaO/SiO2 ratio. Addition of CaCl2 increases the reaction rate and the surface area of the hydrate but to a much lesser extent than in the hydration of C3S, whereas C2H6OH strongly depresses the hydration rate of β-C2S, as observed for C3S hydration.  相似文献   

2.
The pore structure ofβ-C2S, C3S, and portland cement pastes was investigated using mercury porosimetry and H2O and N2 adsorption. The β-C2S had more total macro- and mesoporosities than C3S and portland cement pastes of a similar degree of hydration. C3S and portland cement pastes had similar total porosities but differed in the porosity size distribution. In the mesopore range, the various test methods gave different results. These differences are discussed on the basis of the various models proposed for cement paste. It is shown that shrinkage could be correlated with the volume of pores <0.03 μm, but not with total porosity.  相似文献   

3.
The effects of Al3+, B3+, P5+, Fe3+, S6+, and K+ ions on the stability of the β-phase and its hydration rate were studied in reactive dicalcium silicate (C2S, Ca2SiO4) synthesized using the Pechini process. In particular, the dependences of the phase stability and degree of hydration on the calcination temperature (i.e., particle size) and the concentration of the stabilizing ions were investigated. The phase evolution in doped C2S was determined using XRD, and the degree of hydration was estimated by the peak intensity ratio of the hydrates to the nonhydrates in 29Si MAS NMR spectra. The stabilizing ability of the ions varied significantly, and the B3+ ions were quite effective in stabilizing the β-phase over a wide range of doping concentrations. The hydration results indicated that differently stabilized β-C2S hydrated at different rates, and Al3+- and B3+-doped C2S exhibited increased degree of hydration for all doping concentration ranges investigated. The effect of the doping concentration on degree of hydration was strongly dependent on the stabilizing ions.  相似文献   

4.
Calcium aluminosulfate (Ca4Al6O16S or C4A3̄) was prepared by direct synthesis from calcium and aluminum nitrates, and aluminum sulfate. CaAl4O7(CA2) formed as an intermediate at 900°C, and C4A3̄ was the main phase after calcination at 1100°C. The specific surface areas after calcination at 1100° and 1300°C were ∼2.5 and 1 m2/g, respectively. Hydration was investigated using XRD, DSC, SEM, conduction calorimetry, and solid-state 27Al MAS-NMR spectroscopy. Calorimetry showed that the induction period was longer than that of a sample prepared using conventional solid-state sintering, and this was attributed to the formation of amorphous coatings. Crystalline hydration products, principally calcium monoaluminosulfate hydrate and aluminum hydroxide, appeared subsequently. Although the induction period was very long, complete hydration occurred as early as 3 d in the sample calcined at 1100°C and was 91% complete in the sample calcined at 1300°C.  相似文献   

5.
α-C2SH can be synthesized by hydrothermal treatment of lime and silicic acid for 2 h at 200°C. When heated to 390–490°C, α-C2SH dissociates through a two-step process to form an intermediate phase plus some γ-C2S. This appears to be a new dicalcium silicate different from known dicalcium silicates—α, α'L, α'H, β, and γ phase—and is stable until around 900°C. At 920–960°C, all the phases are transformed to the α'L phase. The intermediate phase has high crystallinity and is stable at room temperature. 29 Si MAS NMR measurements indicate the possibility that it contains both protonated and unprotonated monosilicate anions. The intermediate phase that has passed through the α'phase at higher temperature yields β-C2S on cooling. The intermediate phase is highly active, and completed its hydration in 1 day ( w/s = 1.0, 25°C). Among the crystalline calcium silicate hydrates with Ca/Si = 2.0, it is hillebrandite that yields β-C2S at the lowest temperature.  相似文献   

6.
The green emitting Ca2SiO4:Eu2+ (C2S:Eu) phosphors were synthesized by the polymeric precursor process (Pechini-type), and the effects of calcination temperature and europium (Eu) doping concentration on the luminescent properties were investigated. The crystalline β-C2S was obtained in the calcination temperature of 1100°–1400°C, and Eu was reduced into Eu2+ by annealing in 5% H2/N2 atmosphere. The obtained C2S:Eu2+ phosphors exhibited a strong emission at 504 nm under the excitation of λexc=350 nm. The highest photoluminescence (PL) intensity was observed in the C2S:Eu2+ phosphors either calcined at 1300°C or doped with 3 mol% Eu. The obtained PL properties were discussed in terms of crystal structure, particle size and shape, surface roughness, and effect of concentration quenching.  相似文献   

7.
The effect of curing temperature (40°, 60°, 80°C) on the hydration behavior of β-dicalcium silicate (β-C2S) was investigated. The β-C2S was obtained by decomposition of hillebrandite, Ca2(SiO3)(OH)2, at 600°C, has a specific surface area of about 7 m2/g, and is in the form of fibrous crystals. The dependence of the hydration reaction on temperature continues until the reaction is completed. The hydration is completed in 1 day at 80°C and in 14 days at 14°C. The hydration mechanism is different above and below 60°C, but at a given temperature, the reaction mechanism and the silicate anion structures of C-S-H do not change significantly from the initial to the late stages of the reaction. High curing temperature and long curing times after completion of reaction promote silicate polymerization. The Ca/Si ratio of C-S-H shows high values, being almost 2.0 above 60°C and 1.95 below 40°C.  相似文献   

8.
Hydrated calcium silicates containing Al3+] or Fe3+] were prepared by autoclaving C3S and β-C2S in the presence of C3A or C2F at 190°C. Al3+] and Fe3+] diffuse into the crystal lattice of α-C2SH and C3SH1.5. Solid solutions containing Al3+] and Fe3+] were placed in contact at 25°C with sources of sulfates, either in aqueous stirred suspensions or as pastes. Al3+] and Fe3+] remain stable in the solid solution, inhibiting the formation of ettringite. This absence of ettringite can explain the resistance of autoclaved cement pastes and concretes to sulfate attack.  相似文献   

9.
β-dicalcium silicate synthesized by thermal dissociation of hydrothermally prepared hillebrandite (Ca2(SiO3)(OH)2) exhibits extremely high hydration activity. Characterization of the hydrates obtained and investigation of the hydration mechanism was carried out with the aid of trimethylsilylation analysis, 29Si magic angle spinning nuclear magnetic resonance, transmission electron microscopy selected area electron diffraction, and XRD. The silicate anion structure of C-S-H consisted mainly of a dimer and a single-chain polymer. Polymerization advances with increasing curing temperature and curing time. The C-S-H has an oriented fibrous structure and exhibits a 0.73-nm dreierketten in the longitudinal direction. On heating, the C-S-H dissociates to form β-C2S. The temperature at which βC2S begins to form decreases with increasing chain length of the C-S-H or as the Ca/Si ratio becomes higher. The high activity of β-C2S is due to its large specific surface area and the fact that the hydration is chemical-reaction-rate-controlled until its completion. As a result, the hydration progresses in situ and C-S-H with a high Ca/Si ratio is formed.  相似文献   

10.
The chemical and physical properties of C3S, β-C2S, a C3S/C2S blend, and portland cement pastes cured at 25°C were investigated. The H2O specific surface areas of the calcium silicate samples follow a common linear relation when plotted against a CIS ratio. The β-C2S had higher capillary porosity and N2 surface area, resulting from increased mesopore volume at the expense of micropores. All calcium silicate pastes had similar polysilicate content vs time curves, indicating an aging process which is not sensitive to the starting composition of the hydrating calcium silicate. The polysilicate content of portland cement was much lower than that of the corresponding calcium silicate pastes. Strength-capillary porosity relations for the various systems are discussed.  相似文献   

11.
The carbonation-reaction kinetics of beta-dicalcium silicate (2CaO·SiO2 or β-C2S) and tricalcium silicate (3CaO. SiO2 or C3S) powders were determined as a function of material parameters and reaction conditions and an equation was developed which predicted the degree of reaction. The effect of relative humidity, partial pressure of CO2, surface area, reaction temperature, and reaction time on the degree of reaction was determined. Carbonation followed a decreasing-volume, diffusion-controlled kinetic model. The activation energies for carbonation of β-C2S and C3S were 16.9 and 9.8 kcal/mol, respectively. Aragonite was the principal carbonate formed during the reaction and the rate of carbonate formation was coincident with depletion of the calcium silicates; C-S-H gel formation was minimal.  相似文献   

12.
The effect on β-C2S of two stabilizing agents, calcium sulfate and alumina, has been investigated using high-resolution 29Si solid state NMR spectroscopy. Syntheses were achieved via the gel route, wet or dry processes. Room-temperature NMR spectra characteristics were analyzed as a function of the sintering temperature. The incorporation of Al3+ and S6+ ions, which finds expression in a noticeable line broadening, is shown to be effective above 1200°C. The 29Si chemical shift is unchanged upon doping, suggesting a mean SiO4 tetrahedra geometry identical to that in pure β-C2S. General trends on the structure adopted by C2S upon Al3+ and S6+ doping are also discussed.  相似文献   

13.
The adsorption of calcium lignosulfonate and salicylic acid was studied on the hydration products of the four principal components of portland cement. To investigate the adsorption as a function of development of hydration product, the determinations were made after varying hydration times. The times allowed were from 5 min to 24 hr for tricalcium aluminate (C3A) and tetracalcium aluminoferrite (C4AF) and from 1 hr to 28 days for β-dicalcium silicate (β-C2S) and tricalcium silicate (C3S). Samples were characterized with respect to surface area and poresize distribution. The effect of gypsum on the adsorption was also investigated. The results indicate that the amounts of salicylic acid and calcium lignosulfonate adsorbed on the hydration products of C3A, and of calcium  相似文献   

14.
A mixture of CaO and silicic acid prepared with a Ca/Si ratio of 2.0 was hydrothermally synthesized at 80° to 200°C, and the thermal decomposition behavior of the products (C-S-H with Ca(OH)2) was analyzed using XRD, 29Si MAS NMR, and the trimethylsililation method (TMS). It was found that the main silicate anion structure of C-S-H was a mixture of a dimer and a single-chain polymer (larger than Si5O16) and that polymerization advanced with an increase of the synthesizing temperature. On heating, the products decomposed to form β-C2S. It was found that the decomposition was gradual and that the-higher the temperature of hydrothermal synthesis, the lower was the temperature of the decomposition into β-C2S. Although the decomposition proceeded to form a monomer (β-C2S) from the polymer and dimer, this dimer was resistant to heat and did not decompose unless heated to above 400°C.  相似文献   

15.
The binary compounds Ca3Al2O6 (C3A), Ca12Al14O33 (C12A7), CaAl2O4 (CA), CaAl4O7 (CA2), and CaAl12O19 (CA6) in the CaO-Al2O3 system have been synthesized as high-compound-purity ceramic powders by using the self-propagating combustion synthesis (SPCS) method. Materials characterization of the above-mentioned phases was performed via powder X-ray diffractometry (XRD), Fourier transform infrared spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The structural characterization of the C12A7 phase has been performed via Rietveld analysis on the powdered XRD samples. It has hereby been shown that, by using this synthesis procedure, it should be possible to manufacture high-purity ceramic powders of CA, CA2, and C12A7 at 850°C, C3A at 1050°C, and CA6 at 1200°C in a dry-air atmosphere.  相似文献   

16.
A pseudobinary phase equilibrium diagram has been established for the P2O5-bearing Ca2SiO4-CaFe4O7 system to confirm the occurrence of remelting reaction in α-Ca2SiO4 solid solutions (C2S(ss)). The reaction started at 1290°C immediately after the α-to-α'H transition and finished at 1145°C. The reaction products were made up of about 1 wt% of liquid and 99 wt% of solid α'H-C2S(ss). The liquid exsolved at 1290°C was rich in Fe2O3, consisting of about 30 wt% of Ca2SiO4 and 70 wt% of CaFe4O7. The liquid coexisting with α-C2S(ss) precipitated new α'-phase crystals in association with the remelting reaction.  相似文献   

17.
Alite is the major compound of anhydrous Portland cement: it is composed of tricalcium silicate Ca3SiO5 (C3S) modified in composition and crystal structure by ionic substitutions. Alite is also the main hydraulic phase of cement and the most important for subsequent strength development. Using raw meals (rich in Ca3P2O8) as alternative fuels in cement plants raises the question about the effect of phosphorus on C3S and its consequences on reactivity with water. This paper deals with a systematic study of C3S triclinic T1 polymorph doped with P2O5 in the range 0–0.9 wt%. All the samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and electron-microprobe analysis. The appearance of a phase rich in phosphorus is shown. It displays a structure derivative of the α'H–Ca2SiO4 polymorph, noted α'H–C2S(P). As phosphorus content increases, C3S is more and more decomposed into free lime and α'H–C2S(P). The α'H phase was detected from 0.1 wt% P2O5 and located at the interfaces of C3S grains. Two identification keys are proposed in order to highlight the α'H–C2S(P) phase: the XRD angular window at 2θCu=32.8°–33.2° and a smooth aspect on SEM micrographs.  相似文献   

18.
A series of strontium-bearing dicalcium silicate (Ca2Si04 solid solutions (C2S( ss )), (SrχCa1-χ)2SiO4 with 0.02 ≤χ≤ 0.10, was prepared and examined by powder X-ray diffrac-tometry. These crystals, heated in the stable-temperature region of the α phase and then quenched in water, were composed of the β phase, with χ≤ 0.08, and the α'L and β phases, with χ= 0.10. With increasing x, the unit-cell axes of the β phase expanded and the β angle became small with eventual increase in the unit-cell volume. The Rietveld analysis of the β-C2S( ss ) with χ= 0.08 showed that the Sr2+ ions preferentially occupied the seven-coordinated site rather than the eight-coordinated site. This site preference, which was originally established in the parent α-phase structure, seemed to cause the systematic change in the cell dimensions.  相似文献   

19.
The hydration of β-C2S prepared from hillebrandite [Ca2(SiO3)(OH)2] and having specific surface areas of 6.8, 5.5, and 3.1 m2/g was investigated. Different specific areas were obtained by varying the dissociation temperature of hillebrandite. In addition, the hydration of β-C2S synthesized from high-temperature solid-state reaction was also studied as a comparison. The specific surface area exerts a strong influence on the hydration rate, which increases as the surface area increases. The degree of influence changes with the reaction, becoming greater as hydration progresses. There is initially a linear relationship between specific area and the time required to complete a specific reaction. The specific surface area also affects the reaction mechanism. In the case of specific areas of 5.5 m2/g or less, the reaction changes from a chemical reaction to a diffusion-controlled one, and the degree of reaction comes almost to a halt at 80% to 85%. The Ca/Si ratios of hydrate and the silicate anion structures were also investigated in this study.  相似文献   

20.
29Si magic-angle spinning nuclear magnetic resonance (MASNMR) was used to study the room-temperature hydration of C3S, ß-C2S, and reactive ß-C2S mixed with different amounts of silica fume (SF) that had been hydrated up to nine months and longer. The overall CaO:SiO2 molar ratios of the mixes were 0.12, 0.20, 0.35, 0.50, and 0.80. NMR spectroscopy was used to quantify the remaining starting materials and the resulting hydration products of different species. A broad peak assigned to Q3, appearing in both the fourier transform (FT) and the cross-polarization (CP) modes, increased in intensity with increased SF content and with age. This Q3 species was attributed to two sources: (1) the surface hydroxylation of SF and (2) the cross-linking of dreierketten (chains of silicate tetrahedra arranged in a repeating three-unit conformation) in the calcium silicate hydrate (C-S-H) structure. A Q4 species also appeared in the CP spectra of samples with large SF additions after extended hydration and was attributed to cross-polarization by adjacent hydroxylated Q3 species at the surface of amorphous SiO2.  相似文献   

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