共查询到20条相似文献,搜索用时 31 毫秒
1.
Isabel F. Sáez del Bosque Manuel Martín‐Pastor Sagrario Martínez‐Ramírez María Teresa Blanco‐Varela 《Journal of the American Ceramic Society》2013,96(3):957-965
This study aimed to monitor the effect of temperature and the addition of nanosilica on the nanostructure of the C–S–H gel forming during tricalcium silicate (C3S) hydration. Two types of paste were prepared from a synthesized T1 C3S. The first consisted of a blend of deionized water and C3S at a water/solid ratio of 0.425. In the second, a 90 wt% C3S + 10 wt% of nanosilica blend was mixed with water at a water/solid ratio of 0.7. The pastes were stored in closed containers at 100% RH and 25°C, 40°C, or 65°C. The hydration reaction was detained after 1, 14, 28, or 62 d with acetone, and then pastes were studied by 29Si magic angle spinning nuclear magnetic resonance (29Si MAS NMR).The main conclusion was that adding nSA expedites C3S hydration at any age or temperature and modifies the structure of the C–S–H gel formed, two types of C–S–H gel appear. At 25°C and 40°C, more orderly, longer chain gels are initially (1 d) obtained as a result of the pozzolanic reaction between nSA and portlandite (CH) (C–S–HII gel formation). Subsequently, ongoing C3S hydration and the concomitant flow of dimers shorten the mean chain length in the gel. 相似文献
2.
Vito Alunno-Rossetti Gerardo Chiocchio Mario Collepardi 《Cement and Concrete Research》1974,4(2):279-288
Pastes of C3S (w/c ratio = 0.5) were steam cured at 25, 40, 60 and 90°C for 1 hour to 30 days. The results obtained have shown that, as the curing temperature rises, the induction period is shortened and the initial rate of hydration of C3S is increased; at longer curings, on the other hand, such hydration rate is considerably lowered. In order to explain the influence of temperature on the hydration reaction a new hypothesis has been proposed, which takes into account the C/S molar ratio as well as the surface properties of the hydrated silicate. 相似文献
3.
Amélie Bazzoni Suhua Ma Qianqian Wang Xiadong Shen Marco Cantoni Karen L. Scrivener 《Journal of the American Ceramic Society》2014,97(11):3684-3693
Impure tricalcium silicate (C3S) in portland cement may contain various foreign ions. These ions can stabilize different polymorphs of C3S at room temperature and may affect its reactivity. In this paper, the effects of magnesium and zinc on the polymorph type, hydration kinetics, and the hydrate morphology of C3S were investigated. The pure C3S has the T1 structure while magnesium and zinc stabilize polymorphs M3 and T2/T3, respectively. The two elements have distinct effects on the hydration kinetics. Zinc increases the maximum heat released. Magnesium increases the hydration peak width. The C–S–H morphology is modified, leading to longer needles in the presence of zinc and thicker needles in the presence of magnesium. Zinc is incorporated into C–S–H, while magnesium is only incorporated slightly, if at all, but rather seems to inhibit nucleation. Implementing experimentally measured parameters for C–S–H nucleation and growth in the μic hydration model captured well the observed changes in hydration kinetics. This supports C–S–H nucleation and growth to be rate controlling in the hydration of C3S. 相似文献
4.
Zhuo Dai Thuan T. Tran Jørgen Skibsted 《Journal of the American Ceramic Society》2014,97(8):2662-2671
The composition and structure of the calcium‐silicate‐hydrate (C–S–H) phases formed by hydration of white portland cement–metakaolin (MK) blends have been investigated using 27Al and 29Si MAS NMR. This includes blends with 0, 5, 10, 15, 20, 25, 30 wt% MK, following their hydration from 1 d to 1 yr. 29Si MAS NMR reveals that the average Al/Si ratio for the C–S–H phases, formed by hydration of the portland cement–MK blends, increases almost linearly with the MK content but is invariant with the hydration time for a given MK content. Correspondingly, the average aluminosilicate chain lengths of the C–S–H increase with increasing MK content, reflecting the formation of a C–S–H with a lower Ca/Si ratio. The increase in Al/Si ratio with increasing MK content is supported by 27Al MAS NMR which also allows detection of strätlingite and fivefold coordinated aluminum, assigned to AlO5 sites in the interlayer of the C–S–H structure. Strätlingite is observed after prolonged hydration for MK substitution levels above 10 wt% MK. This is at a somewhat lower replacement level than expected from thermodynamic considerations which predict the formation of strätlingite for MK contents above 15 wt% after prolonged hydration for the actual portland cement–MK blends. The increase in fivefold coordinated Al with increasing MK content suggests that these sites may contribute to the charge balance of the charge deficit associated with the incorporation of Al3+ ions in the silicate chains of the C–S–H structure. 相似文献
5.
Soft X‐ray Ptychographic Imaging and Morphological Quantification of Calcium Silicate Hydrates (C–S–H)
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Sungchul Bae Rae Taylor David Shapiro Peter Denes John Joseph Rich Celestre Stefano Marchesini Howard Padmore Tolek Tyliszczak Tony Warwick David Kilcoyne Pierre Levitz Paulo J. M Monteiro 《Journal of the American Ceramic Society》2015,98(12):4090-4095
Morphological details of calcium silicate hydrate (C–S–H) stemming from the hydration process of Portland cement (PC) phases are crucial for understanding the PC‐based systems but are still only partially known. Here we introduce the first soft X‐ray ptychographic imaging of tricalcium silicate (C3S) hydration products. The results are compared using both scanning transmission X‐ray and electron transmission microscopy data. The evidence shows that ptychography is a powerful method to visualize the details of outer and inner product C–S–H of fully hydrated C3S, which have fibrillar and an interglobular structure with average void sizes of 20 nm, respectively. The high‐resolution ptychrography image enables us to perform morphological quantification of C–S–H, and, for the first time, to possibly distinguish the contributions of inner and outer product C–S–H to the small angle scattering of cement paste. The results indicate that the outer product C–S–H is mainly responsible for the q?3 regime, whereas the inner product C–S–H transitions to a q?2 regime. Various hypotheses are discussed to explain these regimes. 相似文献
6.
Simulations of tricalcium silicate (C3S) hydration using a kinetic cellular automaton program, HydratiCA, indicate that the net rate depends both on C3S dissolution and on hydration product growth. Neither process can be considered the sole rate-controlling step because the solution remains significantly undersaturated with respect to C3S yet significantly supersaturated with respect to calcium silicate hydrate (C–S–H). The reaction rate peak is attributed to increasing coverage of C3S by C–S–H, which reduces both the dissolution rate and the supersaturation of C–S–H. This supersaturation dependence is included in a generalized boundary nucleation and growth model to describe the kinetics without requiring significant impingement of products on separate cement grains. The latter point explains the observation that paste hydration rates are insensitive to water/cement ratio. The simulations indicate that the product layer on C3S remains permeable; no transition to diffusion control is indicated, even long after the rate peak. 相似文献
7.
8.
In‐Situ XRD Measurement and Quantitative Analysis of Hydrating Cement: Implications for Sulfate Incorporation in C–S–H
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Luca Valentini Maria Chiara Dalconi Marco Favero Gilberto Artioli Giorgio Ferrari 《Journal of the American Ceramic Society》2015,98(4):1259-1264
The study of hydration kinetics by in‐situ X‐ray powder diffraction can provide fundamental details on the time evolution of the phase assemblage in hydrating cement pastes. The main limit of the technique is the lack of quantitative information about the amount of C–S–H and unbound water, which cannot be measured directly by conventional quantitative phase analysis procedures based on X‐ray diffraction, due to their X‐ray amorphous nature. Here, a mass balance algorithm, which can be used to determine the amount of both C–S–H and capillary water, is presented and compared with methods based on standards. This method can also provide information about the stoichiometry of C–S–H formed by the reaction of C3S, hydrated in the presence of gypsum, suggesting the incorporation of 0.3 mol of sulfate per mole of C–S–H precipitated. In addition, the results show a significant increase in the rate of C3S hydration, when gypsum is added to the system. 相似文献
9.
The in situ early-age hydration and pozzolanic reaction in cements blended with natural zeolites were investigated by time-resolved synchrotron X-ray powder diffraction with Rietveld quantitative phase analysis. Chabazite and Na-, K-, and Ca-exchanged clinoptilolite materials were mixed with Portland cement in a 3:7 weight ratio and hydrated in situ at 40 °C.The evolution of phase contents showed that the addition of natural zeolites accelerates the onset of C3S hydration and precipitation of CH and AFt. Kinetic analysis of the consumption of C3S indicates that the enveloping C–S–H layer is thinner and/or less dense in the presence of alkali-exchanged clinoptilolite pozzolans. The zeolite pozzolanic activity is interpreted to depend on the zeolite exchangeable cation content and on the crystallinity. The addition of natural zeolites alters the structural evolution of the C–S–H product. Longer silicate chains and a lower C/S ratio are deduced from the evolution of the C–S–H b-cell parameter. 相似文献
10.
The hydration of tricalcium silicate (C3S) was studied by secondary neutrals mass spectrometry (SNMS), a method that enables determination of the Ca/Si ratio of the formed calcium silicate hydrate (C-S-H) phase with an extremely low information depth. It was found that the magnitude of this parameter within the hydrate layer formed at the surface of the nonhydrated C3S is not constant and increases with increasing distance from the liquid-solid interface. It was also found that, at a constant distance from the surface, the Ca/Si ratio declines with hydration time. The kinetics of the hydration process is characterized by a very fast initial reaction, followed by a dormant period and a subsequent period of renewed hydration. The rate of hydration becomes distinctly accelerated by elevated temperature and retarded by the presence of sucrose, while NaCl affects the initial hydration kinetics only to a small degree. 相似文献
11.
Jonathan Lapeyre Hongyan Ma Aditya Kumar 《Journal of the American Ceramic Society》2019,102(10):5976-5988
The focus of this study is to elucidate the role of particle size distribution (PSD) of metakaolin (MK) on hydration kinetics of tricalcium silicate (C3S–T1) pastes. Investigations were carried out utilizing both physical experiments and phase boundary nucleation and growth (pBNG) simulations. [C3S + MK] pastes, prepared using 8%mass or 30%mass MK, were investigated. Three different PSDs of MK were used: fine MK, with particulate sizes <20 µm; intermediate MK, with particulate sizes between 20 and 32 µm; and coarse MK, with particulate sizes >32 µm. Results show that the correlation between specific surface area (SSA) of MK's particulates and the consequent alteration in hydration behavior of C3S in first 72 hours is nonlinear and nonmonotonic. At low replacement of C3S (ie, at 8% mass), fine MK, and, to some extent, coarse MK act as fillers, and facilitate additional nucleation and growth of calcium silicate hydrate (C–S–H). When C3S replacement increases to 30% mass, the filler effects of both fine and coarse MK are reversed, leading to suppression of C–S–H nucleation and growth. Such reversal of filler effect is also observed in the case of intermediate MK; but unlike the other PSDs, the intermediate MK shows reversal at both low and high replacement levels. This is due to the ability of intermediate MK to dissolve rapidly—with faster kinetics compared to both coarse and fine MK—which results in faster release of aluminate [Al(OH)4−] ions in the solution. The aluminate ions adsorb onto C3S and MK particulates and suppress C3S hydration by blocking C3S dissolution sites and C–S–H nucleation sites on the substrates’ surfaces and suppressing the post-nucleation growth of C–S–H. Overall, the results suggest that grinding-based enhancement in SSA of MK particulates does not necessarily enhance early-age hydration of C3S. 相似文献
12.
Jörg Nehring Daniel Jansen Jürgen Neubauer Friedlinde Goetz-Neunhoeffer 《Journal of the American Ceramic Society》2019,102(6):3152-3162
C3S and CA are the main phases of OPC and Fe-rich CAC, respectively. The objective of this research was to investigate the influence of CA on C3S hydration, representing an under sulfated OPC-rich binder, and to shed light on the underlying hydration mechanisms. To this end, C3S was blended with 1-30 wt-% CA and the pastes (w/c 0.5) were investigated by heat flow calorimetry, in situ X-ray diffraction and analysis of the pore solution chemistry. CA additions ≥5 wt-% reveal a separation into three distinct heat flow maxima, whereas additions ≤3 wt-% just retard the start of the main reaction. The silicate reaction (dissolution of C3S and precipitation of C–S–H with or without CH) can be retarded for 4 to ≥22 hours in comparison to pure C3S depending on the admixed CA content. The start of the silicate reaction seems to be related to a decrease in Al- and increase in Ca-concentration in the pore solution. However, it can be shown in this study that C3S is able to dissolve even at high Al concentrations in the pore solution. 相似文献
13.
A model for an ideal solid solution, developed by Nourtier‐Mazauric et al. [Oil & Gas Sci. Tech. Rev. IFP, 60 [2] (2005) 401], is applied to calcium–silicate–hydrate (C–S–H). Fitting the model to solubility data reported in the literature for C–S–H yields reasonable values for the compositions of the end‐members of the solid solution and for their equilibrium constants. This model will be useful in models of hydration kinetics of tricalcium silicate because it is easier to implement than other solid solution models, it clearly identifies the driving force for growth of the most favorable C–S–H composition, and it still allows the model to accurately capture variations in C–S–H composition as the aqueous solution changes significantly at early hydration times. 相似文献
14.
Sungchul Bae Rae Taylor Daniel Hernández‐Cruz Seyoon Yoon David Kilcoyne Paulo J.M Monteiro 《Journal of the American Ceramic Society》2015,98(9):2914-2920
Calcium silicate hydrates (C‐S‐H), the primary binding phase in concrete, is the most prominent physiochemical factor controlling the mechanical and chemical properties in the production of concrete. This paper reports the local‐binding structure and morphological details of C‐S‐H as determined by high‐resolution X‐ray spectromicroscopy. Hydrated tricalcium silicate (C3S) was used to determine the properties and role of the outer products (Op) of C3S. C‐S‐H with different molar ratios of Ca/Si, were synthesized (Syn‐CSH) to quantitatively evaluate the effect of silicate polymerization on Ca L and Si K edge of C‐S‐H. Near edge X‐ray absorption fine structure (NEXAFS) spectroscopy of Syn‐CSH showed no variation in peak positions and energy separation for CaLIII, II edge for the Ca/Si ratios investigated. Compared to Syn‐CSH, C3S, when hydrated for 17 d, had a similar local structure around Ca. Si K edge NEXAFS analysis on Syn‐CSH showed a tendency for the peak positions of both the Si K edge and the peak induced by multiple scattering to shift to higher energy levels. The results also indicated that the distance between the two peaks increased with a decrease of the Ca/Si ratio in Syn‐CSH. Silicate polymerization influenced the multiple scattering of distant shell atoms more than the binding energy of the core atoms. Op of C3S had a uniform and higher degree of silicate polymerization compared to the core area. The results imply that Op reduces the hydration process of C3S into the core area thereby playing a key role on the properties of concrete upon formation. 相似文献
15.
Krassimir Garbev Günter Beuchle Uwe Schweike Daniela Merz Olga Dregert Peter Stemmermann 《Journal of the American Ceramic Society》2014,97(7):2298-2307
New cementitious materials based on calcium hydrosilicate hydrates were recently developed as potential substitutes for ordinary portland cement, but with a reduced CO2 footprint. The materials are produced by hydrothermal processing of SiO2 and Ca(OH)2, giving rise to calcium silicate hydrates, followed by mechanical activation of the latter via cogrinding with various siliceous materials. Thus, the chemical composition in terms of C/S ratio could be adjusted over a broad range (1–3). In this study the synthesis of a previously unknown cementitious material produced via the combination of mechanical activation in a laboratory mill and thermal treatment of a mixture of quartz and hydrothermally synthesized calcium silicate hydrates: α‐Ca2[HSiO4](OH) (α‐C2SH) and Ca6[Si2O7](OH)6 (jaffeite) are reported. It forms independently of the type of mill used (eccentric vibrating mill, vibration grinding mill) after thermal treatment of the ground materials at 360°C–420°C. The new material is X‐ray amorphous and possesses a CaO/SiO2 ratio of 2. A characteristic feature in regards to the silicate anionic structure is the increased silicate polymerization (up to 27% Si2O7 dimers) as revealed by the trimethylsilylation method. Infrared (IR) spectra show a very broad absorption band centered at about 935 cm?1. Another characteristic feature is the presence of ~2.5 wt% H2O as shown by thermogravimetry (TG) coupled with IR spectroscopy. As this water is bound mostly as hydroxyl to Ca, we refer to this new cementitious material as calcium‐oxide–hydroxide–silicate (C–CH–S). Calorimetric measurements point to a very high hydraulic reactivity which is beyond that for typical C2S materials. The influence of the type of grinding on the thermal behavior of α‐C2SH upon its transformation into water‐free Ca2SiO4 modifications is discussed. 相似文献
16.
This paper presents the results of a C3S paste characterization study. The objective was to determine the parameters needed to model the process of degradation. The experimental study focused on determining the portlandite content and the ionic diffusion coefficients of C3S paste. The molar C/S ratio of C–S–H in hydrated C3S pastes was also investigated. The portlandite content was determined with an experimental method based on an electron microprobe analysis.This method leads to a portlandite mass content of 24.4 ± 2.3%. The diffusion coefficient of each ionic species was determined by inverse analysis of diffusion test data performed on hydrated C3S samples using a multiionic transport model. 相似文献
17.
Under deep oil-well conditions of elevated temperature and pressure, crystalline calcium silicate hydrates are formed during Portland cement hydration. The use of silica rich mineral additives leads to the formation of crystalline hydrates with better mechanical properties than those formed without the additive. The effects of silica flour, silica fume (amorphous silica), and a natural zeolite mixture on the hydration of Class H cement slurries at 180 °C under externally applied pressures of 7 and 52 MPa are examined in real time using in-situ synchrotron X-ray diffraction. For some compositions examined, but not all, pressure was found to have a large effect on the kinetics of crystalline hydrate formation. The use of silica fume delayed both C3S hydration and the formation of crystalline silicate hydrates compared to what was seen with other silica sources. 相似文献
18.
Andrew C. Jupe Angus P. Wilkinson Gary P. Funkhouser 《Cement and Concrete Research》2012,42(8):1083-1087
The hydration of tricalcium silicate (C3S) is accelerated by pressure. However, the extent to which temperature and/or cement additives modify this effect is largely unknown. Time-resolved synchrotron powder diffraction has been used to study cement hydration as a function of pressure at different temperatures in the absence of additives, and at selected temperatures in the presence of retarding agents. The magnitudes of the apparent activation volumes for C3S hydration increased with the addition of the retarders sucrose, maltodextrin, aminotri(methylenephosphonic acid) and an AMPS copolymer. Pressure was found to retard the formation of Jaffeite relative to the degree of C3S hydration in high temperature experiments. For one cement slurry studied without additives, the apparent activation volume for C3S hydration remained close to ~ ? 28 cm3 mol? 1 over the range 25 to 60 °C. For another slurry, there were possible signs of a decrease in magnitude at the lowest temperature examined. 相似文献
19.
The hydration of a tricalcium silicate paste at ambient temperature and at 200 °C under high pressure (up to 1000 bar) has been studied. Two high pressure cells have been used, one allows in-situ electrical conductivity measurements during hydration under high pressure. The hydration products were characterized by thermal analysis, X-ray diffraction and 29Si NMR measurements. The pressure has a large kinetic effect on the hydration of a C3S paste at room temperature. The pressure was seen to affect drastically the hydration of a C3S paste at 200 °C and this study evidences the competition between the different high temperature phases during the hydration. 相似文献
20.
Andrew C. Jupe Angus P. Wilkinson Gary P. Funkhouser 《Cement and Concrete Research》2012,42(8):1166-1173
A sample cell for the simultaneous measurement of synchrotron X-ray powder diffraction and ultrasound shear-wave reflection data from cement slurries is described. White cement slurries at 25 and 50 °C with 0–3% bwoc CaCl2 were studied to illustrate the potential of the apparatus. The decrease in reflected S-wave amplitude, in dB, showed a linear correlation with C3S hydration. CaCl2 retarded the development of G′ and G″ relative to the extent of C3S hydration. At short times, there was a correlation between the time evolution of both G′ and G″, and the amount of precipitated CH seen by diffraction, which was almost independent of CaCl2 concentration and temperature. CaCl2 addition resulted in a decrease in the amount of CH visible to X-rays, relative the degree of C3S hydration. This may indicate a change in C–S–H gel C:S ratio or the presence of nanoscale CH that could not be seen by diffraction. 相似文献