共查询到20条相似文献,搜索用时 217 毫秒
1.
Rouhollah Alizadeh James Joseph Beaudoin Laila Raki 《Journal of the American Ceramic Society》2007,90(2):670-672
Helium gas is used as a nanostructural probe to investigate the structural changes in C–S–H (I) due to the removal of interlayer water. Changes in the 002 basal spacing are correlated with helium inflow characteristics. Similarities to helium inflow experiments conducted on hydrated Portland cement and C3 S pastes are discussed. Conclusions are drawn with respect to the viability of considering C–S–H (I) as a physical model for the drying of Portland cement and C3 S pastes. 相似文献
2.
Christiane Rößler Jochen Stark Frank Steiniger Willem Tichelaar 《Journal of the American Ceramic Society》2006,89(2):627-632
Using electron diffraction, we demonstrate that the fibrous calcium–silicate–hydrates (C–S–H) of tricalciumsilicate (C3 S) hydration possess a crystalline structure. The crystalline nature was revealed by limiting the electron dose, which is common in electron microscopy of biomacromolecules. Compared with room temperature, the fading of the electron diffraction patterns at −175°C occurs at an electron dose that is about one order of magnitude higher. A combination of low-dose and cryo-protection methods offers the possibility to investigate the structures of water-containing cement phases by high-resolution electron microscopy in a close-to-native state. 相似文献
3.
Linghong Zhang Lionel J. J. Catalan Raymond J. Balec rew C. Larsen Hassan Haji Esmaeili Stephen D. Kinrade 《Journal of the American Ceramic Society》2010,93(1):279-287
The effects of aliphatic sugar alcohols (e.g., threitol, xylitol, sorbitol) on the hydration of tricalcium silicate (C3 S) and ordinary portland cement (OPC) were investigated and compared with those of sucrose, a well-established cement set retarder. Only sugar alcohols which contain threo diol functionality retarded the setting of C3 S and OPC, their efficacy increasing with the number of threo hydroxy pairs and, to a smaller extent, with the overall population of hydroxy groups. None, however, were as effective as sucrose. The initial and final setting times increased exponentially with the concentration of saccharide, although the hydration of OPC was less inhibited than that of C3 S. Saccharides function as "delayed accelerators," that is, cement hydration is first inhibited and then proceeds faster than in saccharide-free cement. This behavior is consistent with the theory that the induction period is controlled by slow formation and/or poisoning of the stable calcium silicate hydrate (CSH) nuclei. The early inhibiting influence of saccharides on CSH precipitation is apparently stronger than on the growth of crystalline calcium hydroxide. Saccharides did not negatively affect the degree of hydration and compressive strength of fully set OPC paste; on the contrary, sorbitol yielded modest increases. 相似文献
4.
Andrew C. Jupe Angus P. Wilkinson Karen Luke Gary P. Funkhouser 《Journal of the American Ceramic Society》2007,90(8):2595-2602
Class A and H oil well cements are compared at 25° and 50°C with 0%, 1%, 2%, and 4% CaCl2 . Up to 4% CaCl2 accelerated Class A thickening, but 4% led to slower thickening than 2% for Class H. C3 S hydration in the two cements responded differently to CaCl2 . CaCl2 always accelerated aluminate hydration. For Class A, CaCl2 accelerated early Ca(OH)2 precipitation, but sometimes reduced the amount at longer times. This may be coupled to C–S–H gel composition changes. For Class H, Ca(OH)2 precipitation changes nonlinearly with CaCl2 concentration. Ettringite to monosulfate conversion and Friedel's salt formation were sometimes seen. 相似文献
5.
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 (C3 A) and tetracalcium aluminoferrite (C4 AF) and from 1 hr to 28 days for β-dicalcium silicate (β-C2 S) and tricalcium silicate (C3 S). 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 C3 A, and of calcium 相似文献
6.
Sang-Koo Kwon Seong-Hyeon Hong Doh-Yeon Kim Nong M. Hwang 《Journal of the American Ceramic Society》2000,83(5):1247-1252
Microstructural evolution during the heat treatment of cement clinker was investigated. Two model specimens, which consisted of faceted tricalcium silicate (C3 S) and spherical dicalcium silicate (C2 S) grains dispersed in a liquid matrix, were prepared with 5 wt% of large seed particles. The seed particles of faceted C3 S grains grew extensively, whereas those of the spherical C2 S grains grew rather slowly, relative to the matrix grains. As a consequence, C3 S grains exhibited a bimodal size distribution that was typical of exaggerated grain growth, whereas C2 S grains retained a uniform and normal size distribution. These results suggest that the growth of faceted C3 S grains was controlled by the interface atomic attachment, such as two-dimensional nucleation, and that of spherical C2 S grains was controlled by diffusion through the liquid matrix. The dependence of growth mechanisms on grain morphology has been explained in terms of the atomistic structure of the solid/liquid interface. 相似文献
7.
The Pore Structure of Hydrated Cementitious Compounds of Different Chemical Composition 总被引:1,自引:0,他引:1
ARNON BENTUR 《Journal of the American Ceramic Society》1980,63(7-8):381-386
The pore structure ofβ-C2 S, C3 S, and portland cement pastes was investigated using mercury porosimetry and H2 O and N2 adsorption. The β-C2 S had more total macro- and mesoporosities than C3 S and portland cement pastes of a similar degree of hydration. C3 S 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
8.
Young-Min Kim Seong-Hyeon Hong Hwan Kim 《Journal of the American Ceramic Society》2002,85(8):1941-1946
A chlorine-bearing alinite cement was synthesized using reagent-grade chemicals, and the phase evolution and hydration behavior of the alinite clinker were examined. The effects of the MgO content on alinite formation and hydration also were investigated. Alinite began to appear at 1000°C from β-C2 S, C11 A7 CaCl2 , and unreacted raw materials, and an almost single-phase alinite was obtained at 1300°C. The alinite phase also was produced without MgO addition. However, CaO, β-C2 S, and C11 A7 CaCl2 phases were present. Alinite cements hydrated rapidly after a short incubation period, and the hydration products were C-S-H gels, Ca(OH)2 , and a Fridel's saltlike phase. The local environmental changes of silicon and aluminum during the formation and hydration of alinite were determined using magic-angle-spinning nuclear magnetic resonance spectroscopy. The Cl− -ion exsolution from the alinite paste during hydration was measured using ion chromatography. 相似文献
9.
Sabine Thomas Karin Meise-Gresch Werner Müller-Warmuth Ivan Odler 《Journal of the American Ceramic Society》1993,76(8):1998-2004
10.
Marie-Noëlle de Noirfontaine Sandrine Tusseau-Nenez Marcel Signes-Frehel Gilles Gasecki Caroline Girod-Labianca 《Journal of the American Ceramic Society》2009,92(10):2337-2344
Alite is the major compound of anhydrous Portland cement: it is composed of tricalcium silicate Ca3 SiO5 (C3 S) 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 Ca3 P2 O8 ) as alternative fuels in cement plants raises the question about the effect of phosphorus on C3 S and its consequences on reactivity with water. This paper deals with a systematic study of C3 S triclinic T1 polymorph doped with P2 O5 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 –Ca2 SiO4 polymorph, noted α'H –C2 S(P). As phosphorus content increases, C3 S is more and more decomposed into free lime and α'H –C2 S(P). The α'H phase was detected from 0.1 wt% P2 O5 and located at the interfaces of C3 S grains. Two identification keys are proposed in order to highlight the α'H –C2 S(P) phase: the XRD angular window at 2θCu =32.8°–33.2° and a smooth aspect on SEM micrographs. 相似文献
11.
R. F. Abreu J. Schneider M. A. Cincotto 《Journal of the American Ceramic Society》2005,88(6):1514-1520
The structure, surface fractal dimension, and global hydration kinetics of silica particles obtained from rice husk ashes (RHAs) were studied with 29 Si-NMR spectroscopy and spin–lattice relaxation techniques. Silica particles presented an amorphous fraction higher than 93%, with traces of silica-organic bonding and crystal-like domains. Fe-impurities are located preferentially on the surface of the particles. From the effect of these paramagnetic ions on the spin–lattice relaxation of Q3 and Q4 silicate groups, the surface of the particles was characterized as being effectively two-dimensional ( D =1.9±0.1). The hydration kinetics of the particles during the reaction with lime and water was monitored from 8 to 706 days. The process can be described by a power law, with the characteristic exponent higher than those measured for other cements. Also, Johnson–Mehl–Avrami expressions reproduce equally well the experimental data, with parameters compatible with growth habits and morphology known for C–S–H. Two types of Q2 tetrahedra were identified in C–S–H, which can be attributed to the bridging and nonbridging silicate groups predicted by the "dreier-kette" structural model of C–S–H. 相似文献
12.
A New Approach to Modeling the Nucleation and Growth Kinetics of Tricalcium Silicate Hydration 总被引:2,自引:0,他引:2
Jeffrey J. Thomas 《Journal of the American Ceramic Society》2007,90(10):3282-3288
The hydration kinetics of tricalcium silicate (C3 S), the main constituent of portland cement, were analyzed with a mathematical "boundary nucleation" model in which nucleation of the hydration product occurs only on internal boundaries corresponding to the C3 S particle surfaces. This model more closely approximates the C3 S hydration process than does the widely used Avrami nucleation and growth model. In particular, the boundary model accounts for the important effect of the C3 S powder surface area on the hydration kinetics. Both models were applied to isothermal calorimetry data from hydrating C3 S pastes in the temperature range of 10°–40°C. The boundary nucleation model provides a better fit to the early hydration rate peak than does the Avrami model, despite having one less varying parameter. The nucleation rate (per unit area) and the linear growth rate of the hydration product were calculated from the fitted values of the rate constants and the independently measured powder surface area. The growth rate follows a simple Arrhenius temperature dependence with a constant activation energy of 31.2 kJ/mol, while the activation energy associated with the nucleation rate increases with increasing temperature. The start of the nucleation and growth process coincides with the time of initial mixing, indicating that the initial slow reaction period known as the "induction period" is not a separate chemical process as has often been hypothesized. 相似文献
13.
Early Hydration of Tricalcium Silicate 总被引:1,自引:0,他引:1
M. E. TADROS JAN SKALNY R. S. KALYONCU 《Journal of the American Ceramic Society》1976,59(7-8):344-347
The hydration of tricalcium silicate (C3 S) in the preacceleration stages was studied. The C3 S particles carry a positive charge during the early stages of hydration. Following a rapid hydrolysis of C3 S, calcium ions adsorbed on the Si-rich surface of C3 S particles, greatly reducing their further dissolution, thus initiating the induction period. The [Ca2+ ] and [OH- ] continue to increase at lower rates and, because Ca(OH)2 crystal growth is inhibited by silicate ions, become supersaturated with respect to Ca(OH)2 . When the supersaturation reaches a value of ∼1.5 to 2.0 times the saturation concentration, nuclei are formed, and rapid growth of Ca(OH)2 and C-S-H is initiated. These products act as sinks for the ions in solution, thus enhancing the further dissolution of C3 S. 相似文献
14.
Beta C2 S was hydrated at room temperature with and without added CaCl2 or C2 H5 OH by methods previously studied for the hydration of C3 S, i.e. paste, bottle, and ball-mill hydration. The amount of reacted β-C2 S, 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-C2 S, 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 C3 S, whereas C2 H6 OH strongly depresses the hydration rate of β-C2 S, as observed for C3 S hydration. 相似文献
15.
The rate of paste hydration of 3Ca O·SiO2 (C3 S) and the effects of additions of CaCl2 , CdI2 , and CrCl3 , were studied by differential thermal analysis and thermogravimetry. X-ray analyses were used to identify the synthesized C3 S. The salts CaCl2 , CdI2 , and CrCl3 , accelerated the hydration of C3 S. The degree of hydration was estimated by the amount of Ca(OH)2 , formed, as determined by TG. 相似文献
16.
SEISHI GOTO MASAKI DAIMON GIRO HOSAKA RENICHI KONDO 《Journal of the American Ceramic Society》1976,59(7-8):281-284
Hardened C3 S paste cured for 1 year at 20°C was examined to confirm the composition and the morphology of hydrated tricalcium silicate. A new technique was used in which the samples for scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) were etched in 1% HNO3 -alcohol or in glycerol-alcohol (4:6 by volume). After the surface was etched in 1% HNO3 -alcohol, SEM clearly showed the difference in texture in the outer and inner C-S-H products. The existence of a zonal texture within the inner C-S-H products was shown, in addition to the unreacted core; particles 0.1 to 0.2 μm in diameter were observed. After free CH extraction with glycerol-alcohol, two new types of C-S-H grains could be identified. One type has a smooth surface, which seems to be produced from C3 S grains trapped within the growing CH crystals in the early stage of hydration, the C/S mol ratio for these being >3. The other type is covered with many acicular outer C-S-H gel hydration products and has a C/S mol ratio >3. 相似文献
17.
H. M. JENNINGS B. J. DALGLEISH P. L. PRATT 《Journal of the American Ceramic Society》1981,64(10):567-572
This study of C3 S hydrates used a high-voltage electron microscope equipped with a gas reaction cell that allows the specimen to be kept moist, and high-resolution scanning and scanning transmission microscopes. Mechanical thinning and ion-beam thinning coupled with fractography allowed this study of microstructural development with time, enabling both the morphologies and the spatial relations of the morphologies to be observed. The combination of several microscopic techniques allowed the hydration products of C3 S to be classified and compared with those of Diamond for portland cement hydrates. 相似文献
18.
Effect of Carbonation on Alkali-Activated Slag Paste 总被引:2,自引:0,他引:2
Carbonation on waterglass- and NaOH-activated slag pastes was analyzed and compared with carbonation in Portland cement pastes to determine possible differences. Thermogravimetry-differential thermal analysis (TG/DTA), Fourier-transform infrared spectrometry, and nuclear magnetic resonance were used to determine the effects on the main reaction products. According to the TG/DTA results, carbonate precipitation following carbonation is much more intense in Portland cement pastes than in alkali-activated slag pastes. This may be attributed to the fact that in Portland cement paste both the portlandite and the C–S–H gel can be carbonated, whereas in alkali-activated slag pastes, only the C–S–H gel is carbonated directly. In both systems, carbonation leads to the formation of CaCO3 , Si-rich C–S–H gel, silica gel, and alumina. The carbonation of waterglass-activated slag pastes is not altered by the presence of either of the organic additives used in the study. 相似文献
19.
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 (C2 S, Ca2 SiO4 ) 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 C2 S was determined using XRD, and the degree of hydration was estimated by the peak intensity ratio of the hydrates to the nonhydrates in 29 Si 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-C2 S hydrated at different rates, and Al3+ - and B3+ -doped C2 S 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
20.
R. L. BERGER ARNON BENTUR N. B. MILESTONE J. H. KUNG 《Journal of the American Ceramic Society》1979,62(7-8):358-362
The chemical and physical properties of C3 S, β-C2 S, a C3 S/C2 S blend, and portland cement pastes cured at 25°C were investigated. The H2 O specific surface areas of the calcium silicate samples follow a common linear relation when plotted against a CIS ratio. The β-C2 S 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