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1.
José Ivan Escalante-Garcia John H. Sharp 《Journal of the American Ceramic Society》1999,82(11):3237-3241
Variation in the composition of C-S-H gel, the main hydration product of portland cement, cured at various temperatures, was studied using scanning electron microscopy with energy dispersive X-ray spectroscopy. Samples of two cement pastes were cured isothermally under water at 10°, 30°, and 60°C for one year. For the inner-product C-S-H gel of both cement pastes, increased curing temperature decreased the Ca/Si and Al/Ca ratios, but increased the S/Ca ratio. The Al/S and (Al + Fe)/S ratios decreased with increased curing temperature. Sulfur, probably in the form of sulfate ions, could be sorbed by the C-S-H gel at higher temperatures. 相似文献
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The formation of afwillite in tricalcium silicate pastes initiated by ding with crystals was studied to determine the effects on development of tensile strength. Afwillite forms in pastes only when fresh surfaces of both tricalcium silicate and afwillite seed are exposed by initial grinding. Higher early strengths reflect increased rates of hydration in seeded pastes, but strengths at later ages are lower than those of untreated pastes. At all ages tensile strength is lower at a given degree of hydration in seeded pastes than in unseeded ones; this behavior is considered to result from changes in pore-size distribution which occur as afwillite forms. Afwillite initially forms concomitantly with calcium silicate hydrate gel but later arises from conversion of the gel. 相似文献
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Proposed Structure for Calcium Silicate Hydrate Gel 总被引:8,自引:0,他引:8
HARRY F.W. TAYLOR 《Journal of the American Ceramic Society》1986,69(6):464-467
Calcium silicate hydrate gel is a very poorly crystalline material that is the main product of reaction of portland cement with water. Evidence is presented for a disordered layer structure, in which most of the layers are structurally imperfect ones of jennite (Ca9 Si6 O32 H22 ), and others are similarly related to 1.4-nm tobermorite (Ca5 Si6 O26 H18 ), both structures being modified by omission of many of their silicate tetrahedra. The evidence comprises conditions of formation, silicate anion type, Ca/Si ratio, H2 O/Ca ratios and densities for various drying conditions, thermogravimetric curve, X-ray powder and selected-area electron diffraction patterns, and results of analytical electron microfcopy. 相似文献
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Effect of Lime on Hydration of Pastes Containing Gypsum and Calcium Aluminates or Calcium Sulfoaluminate 总被引:1,自引:0,他引:1
P. K. MEHTA 《Journal of the American Ceramic Society》1973,56(6):315-319
Chemical reactions responsible for ettringite formation in the commercial expansive cements are reviewed. X-ray diffraction analyses of the hydrated expansive compounds showed that in the presence of Ca(OH)2 and CaSO4 the tricalcium aluminate hydrated very slowly and the monocalcium aluminate quickly, whereas the calcium sulfoaluminate hydrated at a uniform rate during the early hydration period. Scanning micrographs are presented which show that ettringite formed in the presence of Ca(OH)2 is colloidal. It is proposed that colloidal ettringite can adsorb large quantities of water, thereby causing slump loss in fresh concrete and expansion in hardened concrete. 相似文献
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Yoshihiko Okada Hideki Ishida Takeshi Mitsuda 《Journal of the American Ceramic Society》1994,77(3):765-768
Hydrothermal treatment of lime–silica mixtures under saturated steam pressures below 200°C usually gives C-S-H as an initial product, which reacts further to give crystalline calcium silicate hydrates. In this paper, C-S-H was hydro–thermally prepared using CaO and silicic acid at Ca/Si ratios of 0.3 to 2.0 and 120° to 180°C for 2 h. The C-S-H was examined mainly using 29 Si NMR by the magic angle spinning gate proton decoupling and cross polarization magic angle spinning methods. XRD for all of the C-S-H showed bands at 0.304, 0.280, 0.183, and 0.166 nm. NMR results showed that all of the C-S-H contained single chains of silicate anion, which became progressively longer as the Ca/Si ratio decreased, i.e., as the system became richer in silica. This was independent of the preparation temperature. The 0.8 ratio preparations at 180°C contained small amounts of double-chain structure of 1.1-nm tobermorite. The reaction processing in the lime- silicic acid mixtures is also discussed. 相似文献
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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
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水热合成水化硅酸钙(C-S-H)的制备与表征 总被引:1,自引:0,他引:1
本论文以高纯氧化钙与白炭黑为原料,通过水热法合成了水化硅酸钙(C-S-H).采用XRD、SEM对分别选取温度为100℃、120℃、150℃、180℃水热反应6h的水化硅酸钙样品,与150℃分别反应2h、6h、10 h的样品做了物相变化与显微结构的分析,结果表明在低于120℃时产物为结晶度较低的凝胶,随着温度的升高,水化硅酸钙凝胶的结晶度逐渐提高,在150℃和180℃时,生成结晶度较高的托勃莫来石和硬硅钙石;反应时间从6h延长到10h只提高了晶体的结晶度,而没有改变晶体结构.这一结果对改善蒸压制品的蒸压制度具有重要的指导意义. 相似文献
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ARNON BENTUR R. L. BERGER J. H. KUNG N. B. MILESTONE J. F. YOUNG 《Journal of the American Ceramic Society》1979,62(7-8):362-366
The chemical and physical properties of C3 S pastes cured at 4°, 25°, and 65°C were investigated. The 65°C paste had lower H2 O surface area and larger capillary pore volume than the 25°C paste. The structure of the gel in the 4°C paste changes markedly with increased hydration. These changes were reflected in an increase in H2 O surface area, decrease in C/S ratio, and decrease in the diameter of the mesopores. The degree of silicate polymerization increased with time and temperature of curing. In addition, the 4°C paste had a significant amount of monomer in the gel, which polymerizes with time. 相似文献
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Calcium silicate hydrate (C-S-H) can be viewed as a solid solution, 0.833Ca(OH)2 .SiO2 .0.917H2 O-xCa(OH)2 , at equilibrium at 30°C. On this basis, the change in Gibbsfree energy (ΔGr ) in the solid-solution reaction was calculated from solubility duta for C-S-H in water. The change in ΔGr with real ratio decreased notably for the higher calcium contents (CaO/Si02 1.7; ×0.867). Thermochemical values for C-S-H (CaO/SiO2 =1.7) were estimated to be ΔH°=-2890 kJ/mol, ΔG°=-2630 kJ/mol, and S°=200 J1/mol.K at 298 K . 相似文献
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以氢氧化钙和正硅酸四乙酯为原料,采用共沉淀法制备出了一系列的水化硅酸钙(CSH),通过X射线衍射(XRD)、扫描电子显微镜(SEM)等探讨了不同的酒精添加量和有机溶剂添加对CSH的物相和形貌的影响。结果表明;随着酒精添加量的增加CSH的分散性逐渐变好,采用丙三醇作为有机溶剂可以得到分散较好CSH微球。对CSH进行了布洛芬(IBU)载药研究,利用热重-差热分析、Brunauer-Emmett-Teller法和红外光谱表征(FT-IR)合对其在不同载药时间的CSH载药量、比表面积、孔容和表面基团等进行了分析。发现在12 h后载药量达到116.78%,有望成为较好的药物载体材料。 相似文献
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The kinetics of paste, bottle, and ball-mill hydration of 3CaO SiO2 and the effects of additions of electrolytes and alcohols were studied. Paste and bottle hydrations proceed through periods of induction, acceleration, and decay. If 3CaO SiO2 is hydrated in an excess of H2 O, as in bottle hydration, the reaction rate is lower than that for paste hydration. The ball-mill hydration rate is much the highest and is controlled by the removal of the hydrate layer coating the 3CaO SiO2 particles. Electrolytes always accelerate and alcohols retard the reaction rate. Experimental results are discussed with reference to modern theories of the 3CaO SiO2 hydration mechanism. 相似文献
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为考察矿渣对水泥水化进程的影响,系统研究了在不同的养护龄期、水胶比、矿渣掺量条件下,水泥-矿渣复合浆体的矿渣反应程度、非蒸发水含量、Ca(OH)2含量、孔隙率和力学性能.根据实验结果,研究了复合浆体中矿渣反应程度和非蒸发水含量的变化规律,探讨了矿渣的掺入对Ca(OH)2含量的影响,提出了水化反应进程中水泥与矿渣对Ca(OH)2的供求模式,分析了矿渣与水泥的叠加与互补效应,确定了矿渣的最佳掺量范围和最大掺量范围.上述结果可为矿渣在水泥基材料中合理有效地利用提供一定的科学依据. 相似文献
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J. A. CARD K. MOHAN H. F. W. TAYLOR G. CLIFF 《Journal of the American Ceramic Society》1980,63(5-6):336-337
One hundred sixty-one particles of C-S-H from C3 S pastes aged 1 to 180 days were analyzed. For pastes made from two C3 S samples, the mean Ca:Si ratios were 1.52 and 1.61, respectively. The overall range of Ca:Si ratios was 1.21 to 1.96; most of the variation is considered to represent real differences in composition between individual particles. No significant correlations with curing time, degree of reaction, or morphological type of C-S-H were found. 相似文献
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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
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Kinetics of the Hydration of Tricalcium Silicate 总被引:3,自引:0,他引:3
The hydration of tricalcium silicate was followed at a water/C3 S ratio of 0.7 between 5° and 50°C by determining free lime and combined water. Free lime was estimated by the o -cresol method, whereas combined water was calculated from the amount of free water remaining in the paste as determined by extraction with methyl ethyl ketone. The ratio of free lime to combined water was constant throughout the hydration; this ratio indicated that CSH(II) may be represented as 1.68CaO · SiO2 · 2.58H2 O. When maximum supersaturation of the solution with Ca2+] is attained, the induction period terminates and the reaction proceeds rapidly, probably as the result of propagative surface nucleation-growth of CSH(II). Kinetic equations were derived for these reactions. When the surface of C3 S is entirely covered by CSH(II), the reaction becomes slow and is controlled by diffusion of water. Constants involved in the kinetic equations are evaluated and discussed. 相似文献
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Structure of Calcium Silicate Hydrates Formed in Alkaline-Activated Slag: Influence of the Type of Alkaline Activator 总被引:1,自引:0,他引:1
Ana Fernández-Jiménez Francisca Puertas Isabel Sobrados Jesús Sanz 《Journal of the American Ceramic Society》2003,86(8):1389-1394
The influence of the alkaline activator (NaOH, waterglass, or Na2 CO3 ) on the structure of the hydrated calcium silicate formed in alkali-activated slag (AAS) cement pastes has been investigated by FTIR, 29 Si and 27 Al magic-angle scattering nuclear magnetic resonance, and TEM/EDX techniques. In all cases, the main product formed after 7 d of activation, with activators giving an Na2 O concentration of 4%, is a semicrystalline calcium silicate hydrate with a dreierkette-type anion. In these structures, linear finite chains of silicate tetrahedra ( Q 2 units) are linked to central Ca-O layers, and tetrahedral aluminum occupies bridging positions in the chains. The main chain length and the amount of aluminum incorporated in the tetrahedral chains depend on the activator used. The detection of Q 3 silicon entities in alkaline-activated slags is discussed in relation to the possible formation of cross-linked structures that may be responsible for increased flexural and compressive strengths in AAS mortars. 相似文献
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本文研究了蒸汽养护条件下,甲酸钙/纳米C-S-H(NC)复合对粉煤灰-水泥体系早期抗压强度的影响,并结合XRD、DSC-TG、MIP、SEM及FTIR等手段分析了其影响机理。结果表明:蒸汽养护条件下掺入甲酸钙能显著提高粉煤灰-水泥体系的早期抗压强度,且掺量为1.5%(质量分数)时效果最佳;甲酸钙能促进水泥和粉煤灰水化,提高水化产物的生成速率,降低粉煤灰-水泥体系的孔隙率和总孔容;在掺入甲酸钙的基础上掺入NC可进一步提高体系抗压强度,且随着NC掺量的增加而提高;NC能促进水化产物生成,提升水化程度,细化孔结构,提高体系致密度。 相似文献